PC5271 wiki - User contributions [en]

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2024-04-27T04:09:25Z

E0309214: /* Quartz Crystal MicroBalance (QCM) */

'''Welcome to the wiki page for the course PC5271: Physics of Sensors!'''

This is the repository where projects are documented. Creation of new accounts have now been blocked,and editing/creating pages is enabled. If you need an account, please contact Christian.

Deadline for editing reports is Saturday, 27 April, 23:59SGT - Make sure your description is ready by then so we can start assessing it :)

==Projects==
===[[Project 1 (Example)]]===
Keep a very brief description of a project or even a suggestion here, and perhaps the names of the team members, or who to contact if there is interest to join. Once the project has stabilized, keep stuff in the project page linked by the headline.

===[[Simple Optical Heart Rate Monitor]]===
This project demonstrates the principles of photoplethysmography (PPG) through the construction of a simple device to measure heart rate. The project involves using an pulse sensor to detect variations in light absorption caused by changes in blood volume during each heartbeat.

===[[Gas sensor]]===
This project aims to use high and low detection methods of tin dioxide (SnO2) sensor to detect carbon monoxide or other combustible gases.

===[[Optical Sensor for Noise Flickering]]===
Group Members: Eric Cheung; Lee An Min, Amanda; Loh Jia Ying Whitney

This project aims to use a simple voltage divider made up with resistors and LDR to measure visual noise tags.

===[[Real time temperature alarm ]]===

This project aims to build a system using Python and Raspberry Pi to measure and display temperature in real-time using temperature sensors, and to issue an alarm when the temperature exceeds the set threshold

===[[Impedance Spectroscopy for Detecting Phase Transitions in KBr]]===

This project aims to use Impedance spectroscopy as a sensor to detect phase transition in Potassium Bromide (KBr).

===[[Sensor for locating sound sources]]===
A microphone array is used to capture sound signals, and the direction of the sound source is determined by analyzing the time difference of sound signals received by different microphones.

===[[Optical Sensor for UV Radiation]]===
This project aims to design a photodiode-based optical sensor to detect UV radiation levels.

===[[High Sensitive Position Sensor based on PDH technique]]===

Group Members: Angela Anna Baiju, Chenyue Gu

This project uses PDH locking technique to align a cavity to its resonance and read out the error signal to analyse the position change and other noises present in the system.

===[[Photodiodes as Single Photon Detectors]]===
Group Members: Abas Syahbana, Lu Xinghaou

In this project, we will use several LEDs as Single Photon Avalanche Detectors (SPADs). We will use a light bulb as the light source and grating to vary the wavelength of the light source. Thus, by knowing which light source is working for the LEDs to detect photons, we can determine band gaps of each LEDs.

===[[Temperature Sensor]]===
This project aims to construct a portable non-contact thermometer to detect the component temperature after the circuit board is energized, thereby preventing burns from direct contact.

===[[Quartz Crystal MicroBalance (QCM)]]===
This project aims to create a quartz crystal microbalance that can measure small masses (on the order of micrograms and below) for a start. The bigger goal would be to create one that can detect the thicknesses of thin films.

==Resources==
===Recorded sessions===
===Devices and material===
Apart form the stuff in the teaching lab, we have a resources you may want to consider for your project:
*...
===Books and links===
===Software===
* Various Python extensions. [https://www.python.org Python] is a very powerful free programming language that runs on just about any computer platform. It is open source and completely free.
* [https://www.gnuplot.info Gnuplot]: A free and very mature data display tool that works on just about any platform used that produces excellent publication-grade eps and pdf figures. Can be also used in scripts. Open source and completely free.
* Matlab: Very common, good toolset also for formal mathematics, good graphics. Expensive. We may have a site license, but I am not sure how painful it is for us to get a license for this course. Ask if interested.
* Mathematica: More common among theroetical physicists, very good in formal maths, now with better numerics. Graphs are ok but can be a pain to make looking good. As with Matlab, we do have a campus license. Ask if interested.

===Data sheets===
A number of components might be useful for several groups. Some common data sheets are here:
* Generic Silicon pin Photodiode type [[Media:Bpw34.pdf|BPW34]]
* Digital microphone [https://www.knowles.com/docs/default-source/default-document-library/sph0655lm4h-1_cornell_ii_datasheet9e1e1c731dff6ddbb37cff0000940c19.pdf SPH0655LM4H-1]; a small adapter board exists (see [[Soldering small parts]])
* Thermistor type [[Media:Thermistor B57861S.pdf|B57861S]] (R0=10kΩ, B=3988Kelvin). Search for [https://en.wikipedia.org/wiki/Steinhart-Hart_equation Steinhart-Hart equation]. See [[Thermistor]] page here as well.
* Resistor color codes are explained [https://en.wikipedia.org/wiki/Electronic_color_code here]

==Some wiki reference materials==
* [https://www.mediawiki.org/wiki/Special:MyLanguage/Manual:FAQ MediaWiki FAQ]
* [[Writing mathematical expressions]]
* [[Uploading images and files]]

Quartz Crystal MicroBalance (QCM)

2024-04-23T04:42:17Z

E0309214:

==Abstract==

This project aims to construct a circuit that mimics a quartz crystal microbalance. This can be done via a combination of resistors, capacitors, and a quartz crystal. Testing of the QCM can be done by measuring the fundamental frequency of the quartz crystal oscillator, followed by adding a test mass such as the ink of a permanent marker on the oscillator to determine the frequency change. The original intention of building this QCM is to investigate if it is possible to measure the mass of thin films ex-situ. However, due to experimental and time constraints, we shall focus on building a circuit that can detect mass changes on the order of micrograms.
----
==Team members==
Tan Jhoon Yong
----
==Idea==
Quartz crystal microbalance (QCM) is widely used to measure mass changes to substances involved in physical and chemical processes. In my field of research, we often have to find out the thicknesses of thin films as part of the process of characterizing the samples. There are a few methods that are usually employed in my research to measure thin films' thicknesses such as observing the reflection high-energy electron diffraction (RHEED) oscillations during pulsed-laser deposition (PLD), atomic force microscopy (AFM), X-ray diffraction (XRD) (if the sample is ordered), and fitting of data from spectroscopic ellipsometry (SE). These techniques usually expend a significant amount of time but provide an accurate value to the thickness measurements. Creating a QCM that can work ex-situ will assist my research, and also serves as a reference point and hastens the process of fitting models in SE analysis.
----
Many of the developments and features that exist in today’s commercial QCM instruments were pioneered in laboratories with custom-built instruments to meet specific research needs, such as the use of internal reference crystals to separate the effects of a liquid environment from those of a film sample.
----
==Working Principle==
[[File:AT and BT cut.png|340px|thumb|right|Figure 1: Orientation of AT- and BT- cut crystals]]The working principle behind the QCM is based on the piezoelectric effect. The piezoelectric effect is the generation of electric charges by a crystalline material upon subjecting it to stress.<ref>Meissner A (1927) € Uber piezoelectrische Krystalle bei Hochfrequenz. Z Tech Phys 8:74</ref> An oscillating electric field applied across the device induces an acoustic wave that propagates through the crystal and meets minimum impedance when the device's thickness is a half-integer multiple of the wavelength of the acoustic wave.<ref>O’Sullivan, C. K., & Guilbault, G. G. (1999). Commercial quartz crystal microbalances – theory and applications. Biosensors and Bioelectronics, 14(8), 663–670.</ref> It is a shear mode device in which the acoustic wave propagates in a direction perpendicular to the crystal surface.<ref>Ebersole, R., Miller, J., Moran, J., & Ward, M. (1990). PZ quartz sensors for use in clinical analysis. J. Am. Chem. Soc, 112, 3239.</ref> Therefore, crystals cut in specific crystal axes have to be used to utilize the shear mode. A resonant oscillation in the crystal is achieved by putting the crystal in an oscillation circuit where the electrical and mechanical oscillations are close to the fundamental frequency of the crystal. Changes to the mass of the crystal would result in a proportional change in its natural frequency according to the Sauerbrey equation<ref>Sauerbrey, G. (1959). Verwendung von Schwingquarzen zur Wägung dünner Schichten und zur Mikrowägung. Zeitschrift für Physik, 155(2), 206–222.</ref>

<math>

\Delta m = \frac{C}{n} \Delta f

</math>

 
where <math>\Delta f</math> is the change in resonance frequency, <math>C</math> is the specific sensitivity of the crystal, <math>\Delta m</math> is the mass adsorbed on the active area, and <math>n</math> is the harmonic number. <math>C</math> describes how much material per unit area is required to change the resonant frequency of the crystal by 1Hz. A smaller <math>C</math> value gives a higher mass sensitivity. This value depends on the fundamental resonant frequency of the crystal, and it is defined as 
 
<math>

C = \frac{t_q \rho_q}{f_0}

</math>
 
where <math>t_q</math> is the thickness of the quartz, <math>\rho_q</math> is the density of the quartz plate, and f0 is the fundamental resonant frequency of quartz. With these, we can determine the mass of the deposited material. 
 
Another consideration would be the energy dissipation of the crystal to the surroundings. This is important, especially for viscoelastic films. Viscoelastic films violate the Sauerbrey condition that the bound mass is rigidly attached to the crystal without any slip. Such viscoelastic films dissipate energy via mechanical losses in the flexible mass.
 
----

==Setup==
The typical QCM set-up of piezoelectric quartz crystal microbalance is shown in Figure 2.
The oscillator circuit is connected to the power supply and sample stage mount where the piezoelectric quartz crystal is. We can determine the resonance frequency of the quartz crystal using an oscilloscope, frequency counter, or spectrum analyzer.

To determine the feasibility of this QCM project, we built a simple oscillating circuit as a foundation to test if we can detect the resonance frequency of the quartz crystal. This also serves as a time buffer while waiting for the AT-cut quartz to be delivered. Figures 3 and 4 show the electrical circuit diagram and its implementation on a breadboard respectively.

As the electrical current generated from the oscillation of the quartz crystal is an alternating current due to the piezoelectric effect, we employ the usage of logic gates called inverters to convert DC to AC for readout. Adding a resistor to the circuit allows for the control of the potential difference across the inverter. In this oscillating circuit, we use a 14-pin integrated circuit and measure the resonant frequency of a CMAC CK q5 crystal oscillator.
[[File:Circuit diagram 1st.png|340px|thumb|left|Figure 3: Circuit Diagram]]
[[File:Typical setup.png|340px|thumb|right|Figure 2: Typical Setup for a QCM measurement]]
[[File:1st setup.jpeg|340px|thumb|right|Figure 4: Experimental Setup]]
 
----

==Measurements==
[[File:1st setup waveform.jpeg|340px|thumb|right|Figure 5: Waveform observed with an oscilloscope using the CMAC CK q5 crystal oscillator]]
[[File:10mhz waveform.jpeg|340px|thumb|right|Figure 6: Waveform observed with an oscilloscope using the AT-cut quartz crystal]]
A DC power supply of 5V is given and an oscilloscope is connected to see the signal's waveform. A frequency counter is connected to the electrical circuit and communicated to my computer via the Arduino Integrated Development Environment. The frequency is measured for 10 seconds 10 times to get an average. Eventually, a resonant frequency of 10.000001Mhz is recorded, which is very close to the 10Mhz value that was provided by the manufacturer.

The waveform seen on the oscilloscope is observed to be periodic and looks like a square-wave oscillation. There seem to be additional peaks periodically formed as well, which could likely come from circuit impedance mismatches. Mismatches in impedance between different components or sections of a circuit can cause signal reflections and distortions, leading to additional peaks in the waveform. We would have to adjust the values of the capacitors and resistors.

Then, we replace the 10Mhz crystal oscillator with the AT-cut crystal. Although we managed to obtain the frequency signal generated by the AT-cut crystal, the surface of the crystal is very sensitive such that waving your hands near the oscillator causes the waveform to change. To make the signal more stable, we construct another circuit design similar to the Colpitts oscillator.<ref>US 1624537, Colpitts, Edwin H., "Oscillation generator", published 1 February 1918, issued 12 April 1927</ref> One of the advantages of using this layout is that relatively low phase noise can be achieved, making them suitable for applications requiring stable and low-noise oscillation.
 
----

==Second Set-Up==
The circuit design and the actual circuit are shown in Figures 7 and 8. 2N2222 bipolar junction transistors were used with a combination of capacitors and resistors. The purpose of the transistor is to amplify the voltage across the resonant circuit and stabilize the oscillations through a feedback loop. A DC power supply of 9V is applied across the circuit and an oscilloscope is connected to observe the waveform. Figure 8 shows the waveform, which seems to be a superposition of a square wave and another periodic signal which could be due to the aforementioned circuit impedance mismatches.
[[File:Circuit diagram 2nd.png|340px|thumb|left|Figure 7: Circuit Diagram for 2nd setup]]
[[File:2nd setup.jpeg|340px|thumb|right|Figure 8: 2nd Experimental setup]]
 
We use the Anritsu MS2711D Spectrum Master to look for the resonance frequencies as a cross-reference to the frequency counter measurement. In Figure 9, the resonance frequency of the piezoelectric quartz oscillator and its higher-order harmonics are shown. From the wide scan, we can see that the zeroth-order overtone occurs at approximately 6Mhz, and the higher-order harmonics occur in multiple integers of 6MHz.
[[File:Wide scan.jpeg|340px|thumb|right|Figure 9: Spectral survey scan using the Anritsu MS2711D Spectrum Master]]
[[File:Narrow scan.jpeg|340px|thumb|left|Figure 10: Spectral narrow scan using the Anritsu MS2711D Spectrum Master]]
 
----

==Second Measurement==
The procedure for the frequency counter measurements is the same as that of the 10MHz crystal oscillator. The fundamental resonant frequency is measured to be 5.986804MHz. Using this as the reference resonance frequency, we can now test its effectiveness in mass measurements with the Sauerbrey equation.
[[File:Permanent marker.jpeg|340px|thumb|left|Figure 11: Depiction of how ink was placed on the quartz crystal plate]]
[[File:Ink no signal.jpeg|340px|thumb|right|Figure 12: No spectral signatures from measurement]]
 
[[File:Increase power.jpeg|340px|thumb|right|Figure 13: Increasing DC power supply shows a fundamental mode of resonance]]
Firstly, a permanent marker is used where we dot the center of the quartz crystal shown in Figure 11. [insert permanent marker ink] Initially, there was no signal shown in Figure 12. This is most likely due to the damping of the resonance oscillations due to the added mass, thereby decreasing the voltage gain. However, increasing the DC supply voltage sufficiently allows the fundamental mode to be observed as shown in Figure 13. We repeated the frequency counter measurements and found the new resonance frequency to be 5.984613MHz.

To test the mass limit of this setup, a small Blu Tack weighing 2.1 grams is placed on the center of the oscillator. A new oscillator is used so that the dried ink does not interfere with the measurement. The Spectrum Master did not record any spectral features, which suggests that the oscillation of the crystal is too damped to be detected and that the gain is insufficient. Increasing the DC power supply to 18V is inadequate to produce a spectral feature. For safety purposes, this will be the limit that we shall test.
[[File:Blu tack.jpeg|340px|thumb|left|Figure 14: Depiction of how Blu tack was placed on the quartz crystal plate]]
[[File:Blu tack no signal.jpeg|340px|thumb|right|Figure 15: No spectral signatures from measurement]]
 
Based on the Sauerbrey equation, the decrease in resonance frequency of 2191Hz corresponds to an increase in mass of 969 micrograms. This value is derived by using the following:
* thickness of quartz crystal plate <math> t_q = 1 </math> mm
* density of quartz crystal <math> \rho_q = 2648 </math> kg m-3
* fundamental resonance frequency of quartz crystal plate <math> f_0 = 5.986804 </math> MHz

To understand how accurate this measurement is, let us approximate the volume of ink to be a drop of water and calculate how much a drop of water weighs. We assume that the density of the marker ink is approximately similar to water. A drop of water of 0.1ml is approximately 100 micrograms. This shows that the measurement is about an order of magnitude higher than the approximation.

This huge error arises because of the assumptions of using the Sauerbrey equation. The Sauerbrey equation is valid under the following conditions:

*The added mass is small compared to the mass of the crystal
*The added mass is rigidly adsorbed onto the surface of the crystal
*The mass is evenly distributed over the active area of the crystal.

Based on these conditions, the second and third conditions are not fulfilled. In the next section, we discuss what are how these assumptions can be relaxed.
----

==Potential Improvements and Conclusion==
Some better models describe the relationship between frequency change and mass adsorbed where we consider the added mass to be viscoelastic. The Sauerbrey equation fails to describe viscoelastic films on the quartz oscillator as the condition where the added mass is rigidly bound is not adhered to. This model is called the QCM-D, where D refers to the energy dissipation by the film. This technique is prevalent in the fields of lipids, proteins, nanoparticles, etc.<ref>Chen, Q., Xu, S., Liu, Q., Masliyah, J., & Xu, Z. (2016). QCM-D study of nanoparticle interactions. Advances in Colloid and Interface Science, 233, 94–114.</ref> However, this requires the use of liquid media. 

To conclude, we managed to detect the quartz crystal oscillation with a simple circuit design. Changes in resonance frequency due to added mass can also be detected, but the margin of error is too large for it to be usable for research purposes. Future improvements to this experiment can be done by adopting energy dissipation within our considerations.
----
==References==
<references />

Quartz Crystal MicroBalance (QCM)

2024-04-23T04:37:55Z

E0309214: /* References */

==Abstract==

This project aims to construct a circuit that mimics a quartz crystal microbalance. This can be done via a combination of resistors, capacitors, and a quartz crystal. Testing of the QCM can be done by measuring the fundamental frequency of the quartz crystal oscillator, followed by adding a test mass such as the ink of a permanent marker on the oscillator to determine the frequency change. The original intention of building this QCM is to investigate if it is possible to measure the mass of thin films ex-situ. However, due to experimental and time constraints, we shall focus on building a circuit that can detect mass changes on the order of micrograms.
----
==Team members==
Tan Jhoon Yong
----
==Idea==
Quartz crystal microbalance (QCM) is widely used to measure mass changes to substances involved in physical and chemical processes. In my field of research, we often have to find out the thicknesses of thin films as part of the process of characterizing the samples. There are a few methods that are usually employed in my research to measure thin films' thicknesses such as observing the reflection high-energy electron diffraction (RHEED) oscillations during pulsed-laser deposition (PLD), atomic force microscopy (AFM), X-ray diffraction (XRD) (if the sample is ordered), and fitting of data from spectroscopic ellipsometry (SE). These techniques usually expend a significant amount of time but provide an accurate value to the thickness measurements. Creating a QCM that can work ex-situ will assist my research, and also serves as a reference point and hastens the process of fitting models in SE analysis.
----
Many of the developments and features that exist in today’s commercial QCM instruments were pioneered in laboratories with custom-built instruments to meet specific research needs, such as the use of internal reference crystals to separate the effects of a liquid environment from those of a film sample.
----
==Working Principle==
[[File:AT and BT cut.png|340px|thumb|right|Figure 1: Orientation of AT- and BT- cut crystals]]The working principle behind the QCM is based on the piezoelectric effect. The piezoelectric effect is the generation of electric charges by a crystalline material upon subjecting it to stress.[1] An oscillating electric field applied across the device induces an acoustic wave that propagates through the crystal and meets minimum impedance when the device's thickness is a half-integer multiple of the wavelength of the acoustic wave.[2] It is a shear mode device in which the acoustic wave propagates in a direction perpendicular to the crystal surface.[3] Therefore, crystals cut in specific crystal axes have to be used to utilize the shear mode. A resonant oscillation in the crystal is achieved by putting the crystal in an oscillation circuit where the electrical and mechanical oscillations are close to the fundamental frequency of the crystal. Changes to the mass of the crystal would result in a proportional change in its natural frequency according to the Sauerbrey equation[4]

<math>

\Delta m = \frac{C}{n} \Delta f

</math>

 
where <math>\Delta f</math> is the change in resonance frequency, <math>C</math> is the specific sensitivity of the crystal, <math>\Delta m</math> is the mass adsorbed on the active area, and <math>n</math> is the harmonic number. <math>C</math> describes how much material per unit area is required to change the resonant frequency of the crystal by 1Hz. A smaller <math>C</math> value gives a higher mass sensitivity. This value depends on the fundamental resonant frequency of the crystal, and it is defined as 
 
<math>

C = \frac{t_q \rho_q}{f_0}

</math>
 
where <math>t_q</math> is the thickness of the quartz, <math>\rho_q</math> is the density of the quartz plate, and f0 is the fundamental resonant frequency of quartz. With these, we can determine the mass of the deposited material. 
 
Another consideration would be the energy dissipation of the crystal to the surroundings. This is important, especially for viscoelastic films. Viscoelastic films violate the Sauerbrey condition that the bound mass is rigidly attached to the crystal without any slip. Such viscoelastic films dissipate energy via mechanical losses in the flexible mass.
 
----

==Setup==
The typical QCM set-up of piezoelectric quartz crystal microbalance is shown in Figure 2.
The oscillator circuit is connected to the power supply and sample stage mount where the piezoelectric quartz crystal is. We can determine the resonance frequency of the quartz crystal using an oscilloscope, frequency counter, or spectrum analyzer.

To determine the feasibility of this QCM project, we built a simple oscillating circuit as a foundation to test if we can detect the resonance frequency of the quartz crystal. This also serves as a time buffer while waiting for the AT-cut quartz to be delivered. Figures 3 and 4 show the electrical circuit diagram and its implementation on a breadboard respectively.

As the electrical current generated from the oscillation of the quartz crystal is an alternating current due to the piezoelectric effect, we employ the usage of logic gates called inverters to convert DC to AC for readout. Adding a resistor to the circuit allows for the control of the potential difference across the inverter. In this oscillating circuit, we use a 14-pin integrated circuit and measure the resonant frequency of a CMAC CK q5 crystal oscillator.
[[File:Circuit diagram 1st.png|340px|thumb|left|Figure 3: Circuit Diagram]]
[[File:Typical setup.png|340px|thumb|right|Figure 2: Typical Setup for a QCM measurement]]
[[File:1st setup.jpeg|340px|thumb|right|Figure 4: Experimental Setup]]
 
----

==Measurements==
[[File:1st setup waveform.jpeg|340px|thumb|right|Figure 5: Waveform observed with an oscilloscope using the CMAC CK q5 crystal oscillator]]
[[File:10mhz waveform.jpeg|340px|thumb|right|Figure 6: Waveform observed with an oscilloscope using the AT-cut quartz crystal]]
A DC power supply of 5V is given and an oscilloscope is connected to see the signal's waveform. A frequency counter is connected to the electrical circuit and communicated to my computer via the Arduino Integrated Development Environment. The frequency is measured for 10 seconds 10 times to get an average. Eventually, a resonant frequency of 10.000001Mhz is recorded, which is very close to the 10Mhz value that was provided by the manufacturer.

The waveform seen on the oscilloscope is observed to be periodic and looks like a square-wave oscillation. There seem to be additional peaks periodically formed as well, which could likely come from circuit impedance mismatches. Mismatches in impedance between different components or sections of a circuit can cause signal reflections and distortions, leading to additional peaks in the waveform. We would have to adjust the values of the capacitors and resistors.

Then, we replace the 10Mhz crystal oscillator with the AT-cut crystal. Although we managed to obtain the frequency signal generated by the AT-cut crystal, the surface of the crystal is very sensitive such that waving your hands near the oscillator causes the waveform to change. To make the signal more stable, we construct another circuit design similar to the Colpitts oscillator.[5] One of the advantages of using this layout is that relatively low phase noise can be achieved, making them suitable for applications requiring stable and low-noise oscillation.
 
----

==Second Set-Up==
The circuit design and the actual circuit are shown in Figures 7 and 8. 2N2222 bipolar junction transistors were used with a combination of capacitors and resistors. The purpose of the transistor is to amplify the voltage across the resonant circuit and stabilize the oscillations through a feedback loop. A DC power supply of 9V is applied across the circuit and an oscilloscope is connected to observe the waveform. Figure 8 shows the waveform, which seems to be a superposition of a square wave and another periodic signal which could be due to the aforementioned circuit impedance mismatches.
[[File:Circuit diagram 2nd.png|340px|thumb|left|Figure 7: Circuit Diagram for 2nd setup]]
[[File:2nd setup.jpeg|340px|thumb|right|Figure 8: 2nd Experimental setup]]
 
We use the Anritsu MS2711D Spectrum Master to look for the resonance frequencies as a cross-reference to the frequency counter measurement. In Figure 9, the resonance frequency of the piezoelectric quartz oscillator and its higher-order harmonics are shown. From the wide scan, we can see that the zeroth-order overtone occurs at approximately 6Mhz, and the higher-order harmonics occur in multiple integers of 6MHz.
[[File:Wide scan.jpeg|340px|thumb|right|Figure 9: Spectral survey scan using the Anritsu MS2711D Spectrum Master]]
[[File:Narrow scan.jpeg|340px|thumb|left|Figure 10: Spectral narrow scan using the Anritsu MS2711D Spectrum Master]]
 
----

==Second Measurement==
The procedure for the frequency counter measurements is the same as that of the 10MHz crystal oscillator. The fundamental resonant frequency is measured to be 5.986804MHz. Using this as the reference resonance frequency, we can now test its effectiveness in mass measurements with the Sauerbrey equation.
[[File:Permanent marker.jpeg|340px|thumb|left|Figure 11: Depiction of how ink was placed on the quartz crystal plate]]
[[File:Ink no signal.jpeg|340px|thumb|right|Figure 12: No spectral signatures from measurement]]
 
[[File:Increase power.jpeg|340px|thumb|right|Figure 13: Increasing DC power supply shows a fundamental mode of resonance]]
Firstly, a permanent marker is used where we dot the center of the quartz crystal shown in Figure 11. [insert permanent marker ink] Initially, there was no signal shown in Figure 12. This is most likely due to the damping of the resonance oscillations due to the added mass, thereby decreasing the voltage gain. However, increasing the DC supply voltage sufficiently allows the fundamental mode to be observed as shown in Figure 13. We repeated the frequency counter measurements and found the new resonance frequency to be 5.984613MHz.

To test the mass limit of this setup, a small Blu Tack weighing 2.1 grams is placed on the center of the oscillator. A new oscillator is used so that the dried ink does not interfere with the measurement. The Spectrum Master did not record any spectral features, which suggests that the oscillation of the crystal is too damped to be detected and that the gain is insufficient. Increasing the DC power supply to 18V is inadequate to produce a spectral feature. For safety purposes, this will be the limit that we shall test.
[[File:Blu tack.jpeg|340px|thumb|left|Figure 14: Depiction of how Blu tack was placed on the quartz crystal plate]]
[[File:Blu tack no signal.jpeg|340px|thumb|right|Figure 15: No spectral signatures from measurement]]
 
Based on the Sauerbrey equation, the decrease in resonance frequency of 2191Hz corresponds to an increase in mass of 969 micrograms. This value is derived by using the following:
* thickness of quartz crystal plate <math> t_q = 1 </math> mm
* density of quartz crystal <math> \rho_q = 2648 </math> kg m-3
* fundamental resonance frequency of quartz crystal plate <math> f_0 = 5.986804 </math> MHz

To understand how accurate this measurement is, let us approximate the volume of ink to be a drop of water and calculate how much a drop of water weighs. We assume that the density of the marker ink is approximately similar to water. A drop of water of 0.1ml is approximately 100 micrograms. This shows that the measurement is about an order of magnitude higher than the approximation.

This huge error arises because of the assumptions of using the Sauerbrey equation. The Sauerbrey equation is valid under the following conditions:

*The added mass is small compared to the mass of the crystal
*The added mass is rigidly adsorbed onto the surface of the crystal
*The mass is evenly distributed over the active area of the crystal.

Based on these conditions, the second and third conditions are not fulfilled. In the next section, we discuss what are how these assumptions can be relaxed.
----

==Potential Improvements and Conclusion==
Some better models describe the relationship between frequency change and mass adsorbed where we consider the added mass to be viscoelastic. The Sauerbrey equation fails to describe viscoelastic films on the quartz oscillator as the condition where the added mass is rigidly bound is not adhered to. This model is called the QCM-D, where D refers to the energy dissipation by the film. This technique is prevalent in the fields of lipids, proteins, nanoparticles, etc. [6] However, this requires the use of liquid media. 

To conclude, we managed to detect the quartz crystal oscillation with a simple circuit design. Changes in resonance frequency due to added mass can also be detected, but the margin of error is too large for it to be usable for research purposes. Future improvements to this experiment can be done by adopting energy dissipation within our considerations.
----
==References==
# Meissner A (1927) € Uber piezoelectrische Krystalle bei Hochfrequenz. Z Tech Phys 8:74
# O’Sullivan, C. K., & Guilbault, G. G. (1999). Commercial quartz crystal microbalances – theory and applications. Biosensors and Bioelectronics, 14(8), 663–670.
# Ebersole, R., Miller, J., Moran, J., & Ward, M. (1990). PZ quartz sensors for use in clinical analysis. J. Am. Chem. Soc, 112, 3239.
# Sauerbrey, G. (1959). Verwendung von Schwingquarzen zur Wägung dünner Schichten und zur Mikrowägung. Zeitschrift für Physik, 155(2), 206–222.
# US 1624537, Colpitts, Edwin H., "Oscillation generator", published 1 February 1918, issued 12 April 1927
# Chen, Q., Xu, S., Liu, Q., Masliyah, J., & Xu, Z. (2016). QCM-D study of nanoparticle interactions. Advances in Colloid and Interface Science, 233, 94–114.

Quartz Crystal MicroBalance (QCM)

2024-04-23T04:37:20Z

E0309214: /* Second Measurement */

==Abstract==

This project aims to construct a circuit that mimics a quartz crystal microbalance. This can be done via a combination of resistors, capacitors, and a quartz crystal. Testing of the QCM can be done by measuring the fundamental frequency of the quartz crystal oscillator, followed by adding a test mass such as the ink of a permanent marker on the oscillator to determine the frequency change. The original intention of building this QCM is to investigate if it is possible to measure the mass of thin films ex-situ. However, due to experimental and time constraints, we shall focus on building a circuit that can detect mass changes on the order of micrograms.
----
==Team members==
Tan Jhoon Yong
----
==Idea==
Quartz crystal microbalance (QCM) is widely used to measure mass changes to substances involved in physical and chemical processes. In my field of research, we often have to find out the thicknesses of thin films as part of the process of characterizing the samples. There are a few methods that are usually employed in my research to measure thin films' thicknesses such as observing the reflection high-energy electron diffraction (RHEED) oscillations during pulsed-laser deposition (PLD), atomic force microscopy (AFM), X-ray diffraction (XRD) (if the sample is ordered), and fitting of data from spectroscopic ellipsometry (SE). These techniques usually expend a significant amount of time but provide an accurate value to the thickness measurements. Creating a QCM that can work ex-situ will assist my research, and also serves as a reference point and hastens the process of fitting models in SE analysis.
----
Many of the developments and features that exist in today’s commercial QCM instruments were pioneered in laboratories with custom-built instruments to meet specific research needs, such as the use of internal reference crystals to separate the effects of a liquid environment from those of a film sample.
----
==Working Principle==
[[File:AT and BT cut.png|340px|thumb|right|Figure 1: Orientation of AT- and BT- cut crystals]]The working principle behind the QCM is based on the piezoelectric effect. The piezoelectric effect is the generation of electric charges by a crystalline material upon subjecting it to stress.[1] An oscillating electric field applied across the device induces an acoustic wave that propagates through the crystal and meets minimum impedance when the device's thickness is a half-integer multiple of the wavelength of the acoustic wave.[2] It is a shear mode device in which the acoustic wave propagates in a direction perpendicular to the crystal surface.[3] Therefore, crystals cut in specific crystal axes have to be used to utilize the shear mode. A resonant oscillation in the crystal is achieved by putting the crystal in an oscillation circuit where the electrical and mechanical oscillations are close to the fundamental frequency of the crystal. Changes to the mass of the crystal would result in a proportional change in its natural frequency according to the Sauerbrey equation[4]

<math>

\Delta m = \frac{C}{n} \Delta f

</math>

 
where <math>\Delta f</math> is the change in resonance frequency, <math>C</math> is the specific sensitivity of the crystal, <math>\Delta m</math> is the mass adsorbed on the active area, and <math>n</math> is the harmonic number. <math>C</math> describes how much material per unit area is required to change the resonant frequency of the crystal by 1Hz. A smaller <math>C</math> value gives a higher mass sensitivity. This value depends on the fundamental resonant frequency of the crystal, and it is defined as 
 
<math>

C = \frac{t_q \rho_q}{f_0}

</math>
 
where <math>t_q</math> is the thickness of the quartz, <math>\rho_q</math> is the density of the quartz plate, and f0 is the fundamental resonant frequency of quartz. With these, we can determine the mass of the deposited material. 
 
Another consideration would be the energy dissipation of the crystal to the surroundings. This is important, especially for viscoelastic films. Viscoelastic films violate the Sauerbrey condition that the bound mass is rigidly attached to the crystal without any slip. Such viscoelastic films dissipate energy via mechanical losses in the flexible mass.
 
----

==Setup==
The typical QCM set-up of piezoelectric quartz crystal microbalance is shown in Figure 2.
The oscillator circuit is connected to the power supply and sample stage mount where the piezoelectric quartz crystal is. We can determine the resonance frequency of the quartz crystal using an oscilloscope, frequency counter, or spectrum analyzer.

To determine the feasibility of this QCM project, we built a simple oscillating circuit as a foundation to test if we can detect the resonance frequency of the quartz crystal. This also serves as a time buffer while waiting for the AT-cut quartz to be delivered. Figures 3 and 4 show the electrical circuit diagram and its implementation on a breadboard respectively.

As the electrical current generated from the oscillation of the quartz crystal is an alternating current due to the piezoelectric effect, we employ the usage of logic gates called inverters to convert DC to AC for readout. Adding a resistor to the circuit allows for the control of the potential difference across the inverter. In this oscillating circuit, we use a 14-pin integrated circuit and measure the resonant frequency of a CMAC CK q5 crystal oscillator.
[[File:Circuit diagram 1st.png|340px|thumb|left|Figure 3: Circuit Diagram]]
[[File:Typical setup.png|340px|thumb|right|Figure 2: Typical Setup for a QCM measurement]]
[[File:1st setup.jpeg|340px|thumb|right|Figure 4: Experimental Setup]]
 
----

==Measurements==
[[File:1st setup waveform.jpeg|340px|thumb|right|Figure 5: Waveform observed with an oscilloscope using the CMAC CK q5 crystal oscillator]]
[[File:10mhz waveform.jpeg|340px|thumb|right|Figure 6: Waveform observed with an oscilloscope using the AT-cut quartz crystal]]
A DC power supply of 5V is given and an oscilloscope is connected to see the signal's waveform. A frequency counter is connected to the electrical circuit and communicated to my computer via the Arduino Integrated Development Environment. The frequency is measured for 10 seconds 10 times to get an average. Eventually, a resonant frequency of 10.000001Mhz is recorded, which is very close to the 10Mhz value that was provided by the manufacturer.

The waveform seen on the oscilloscope is observed to be periodic and looks like a square-wave oscillation. There seem to be additional peaks periodically formed as well, which could likely come from circuit impedance mismatches. Mismatches in impedance between different components or sections of a circuit can cause signal reflections and distortions, leading to additional peaks in the waveform. We would have to adjust the values of the capacitors and resistors.

Then, we replace the 10Mhz crystal oscillator with the AT-cut crystal. Although we managed to obtain the frequency signal generated by the AT-cut crystal, the surface of the crystal is very sensitive such that waving your hands near the oscillator causes the waveform to change. To make the signal more stable, we construct another circuit design similar to the Colpitts oscillator.[5] One of the advantages of using this layout is that relatively low phase noise can be achieved, making them suitable for applications requiring stable and low-noise oscillation.
 
----

==Second Set-Up==
The circuit design and the actual circuit are shown in Figures 7 and 8. 2N2222 bipolar junction transistors were used with a combination of capacitors and resistors. The purpose of the transistor is to amplify the voltage across the resonant circuit and stabilize the oscillations through a feedback loop. A DC power supply of 9V is applied across the circuit and an oscilloscope is connected to observe the waveform. Figure 8 shows the waveform, which seems to be a superposition of a square wave and another periodic signal which could be due to the aforementioned circuit impedance mismatches.
[[File:Circuit diagram 2nd.png|340px|thumb|left|Figure 7: Circuit Diagram for 2nd setup]]
[[File:2nd setup.jpeg|340px|thumb|right|Figure 8: 2nd Experimental setup]]
 
We use the Anritsu MS2711D Spectrum Master to look for the resonance frequencies as a cross-reference to the frequency counter measurement. In Figure 9, the resonance frequency of the piezoelectric quartz oscillator and its higher-order harmonics are shown. From the wide scan, we can see that the zeroth-order overtone occurs at approximately 6Mhz, and the higher-order harmonics occur in multiple integers of 6MHz.
[[File:Wide scan.jpeg|340px|thumb|right|Figure 9: Spectral survey scan using the Anritsu MS2711D Spectrum Master]]
[[File:Narrow scan.jpeg|340px|thumb|left|Figure 10: Spectral narrow scan using the Anritsu MS2711D Spectrum Master]]
 
----

==Second Measurement==
The procedure for the frequency counter measurements is the same as that of the 10MHz crystal oscillator. The fundamental resonant frequency is measured to be 5.986804MHz. Using this as the reference resonance frequency, we can now test its effectiveness in mass measurements with the Sauerbrey equation.
[[File:Permanent marker.jpeg|340px|thumb|left|Figure 11: Depiction of how ink was placed on the quartz crystal plate]]
[[File:Ink no signal.jpeg|340px|thumb|right|Figure 12: No spectral signatures from measurement]]
 
[[File:Increase power.jpeg|340px|thumb|right|Figure 13: Increasing DC power supply shows a fundamental mode of resonance]]
Firstly, a permanent marker is used where we dot the center of the quartz crystal shown in Figure 11. [insert permanent marker ink] Initially, there was no signal shown in Figure 12. This is most likely due to the damping of the resonance oscillations due to the added mass, thereby decreasing the voltage gain. However, increasing the DC supply voltage sufficiently allows the fundamental mode to be observed as shown in Figure 13. We repeated the frequency counter measurements and found the new resonance frequency to be 5.984613MHz.

To test the mass limit of this setup, a small Blu Tack weighing 2.1 grams is placed on the center of the oscillator. A new oscillator is used so that the dried ink does not interfere with the measurement. The Spectrum Master did not record any spectral features, which suggests that the oscillation of the crystal is too damped to be detected and that the gain is insufficient. Increasing the DC power supply to 18V is inadequate to produce a spectral feature. For safety purposes, this will be the limit that we shall test.
[[File:Blu tack.jpeg|340px|thumb|left|Figure 14: Depiction of how Blu tack was placed on the quartz crystal plate]]
[[File:Blu tack no signal.jpeg|340px|thumb|right|Figure 15: No spectral signatures from measurement]]
 
Based on the Sauerbrey equation, the decrease in resonance frequency of 2191Hz corresponds to an increase in mass of 969 micrograms. This value is derived by using the following:
* thickness of quartz crystal plate <math> t_q = 1 </math> mm
* density of quartz crystal <math> \rho_q = 2648 </math> kg m-3
* fundamental resonance frequency of quartz crystal plate <math> f_0 = 5.986804 </math> MHz

To understand how accurate this measurement is, let us approximate the volume of ink to be a drop of water and calculate how much a drop of water weighs. We assume that the density of the marker ink is approximately similar to water. A drop of water of 0.1ml is approximately 100 micrograms. This shows that the measurement is about an order of magnitude higher than the approximation.

This huge error arises because of the assumptions of using the Sauerbrey equation. The Sauerbrey equation is valid under the following conditions:

*The added mass is small compared to the mass of the crystal
*The added mass is rigidly adsorbed onto the surface of the crystal
*The mass is evenly distributed over the active area of the crystal.

Based on these conditions, the second and third conditions are not fulfilled. In the next section, we discuss what are how these assumptions can be relaxed.
----

==Potential Improvements and Conclusion==
Some better models describe the relationship between frequency change and mass adsorbed where we consider the added mass to be viscoelastic. The Sauerbrey equation fails to describe viscoelastic films on the quartz oscillator as the condition where the added mass is rigidly bound is not adhered to. This model is called the QCM-D, where D refers to the energy dissipation by the film. This technique is prevalent in the fields of lipids, proteins, nanoparticles, etc. [6] However, this requires the use of liquid media. 

To conclude, we managed to detect the quartz crystal oscillation with a simple circuit design. Changes in resonance frequency due to added mass can also be detected, but the margin of error is too large for it to be usable for research purposes. Future improvements to this experiment can be done by adopting energy dissipation within our considerations.
----
==References==
# Meissner A (1927) € Uber piezoelectrische Krystalle bei Hochfrequenz. Z Tech Phys 8:74
# O’Sullivan, C. K., & Guilbault, G. G. (1999). Commercial quartz crystal microbalances – theory and applications. Biosensors and Bioelectronics, 14(8), 663–670.
# Ebersole, R., Miller, J., Moran, J., & Ward, M. (1990). PZ quartz sensors for use in clinical analysis. J. Am. Chem. Soc, 112, 3239.
# Sauerbrey, G. (1959). Verwendung von Schwingquarzen zur Wägung dünner Schichten und zur Mikrowägung. Zeitschrift für Physik, 155(2), 206–222.
# US 1624537, Colpitts, Edwin H., "Oscillation generator", published 1 February 1918, issued 12 April 1927

Quartz Crystal MicroBalance (QCM)

2024-04-23T04:33:52Z

E0309214: /* Second Set-Up */

==Abstract==

This project aims to construct a circuit that mimics a quartz crystal microbalance. This can be done via a combination of resistors, capacitors, and a quartz crystal. Testing of the QCM can be done by measuring the fundamental frequency of the quartz crystal oscillator, followed by adding a test mass such as the ink of a permanent marker on the oscillator to determine the frequency change. The original intention of building this QCM is to investigate if it is possible to measure the mass of thin films ex-situ. However, due to experimental and time constraints, we shall focus on building a circuit that can detect mass changes on the order of micrograms.
----
==Team members==
Tan Jhoon Yong
----
==Idea==
Quartz crystal microbalance (QCM) is widely used to measure mass changes to substances involved in physical and chemical processes. In my field of research, we often have to find out the thicknesses of thin films as part of the process of characterizing the samples. There are a few methods that are usually employed in my research to measure thin films' thicknesses such as observing the reflection high-energy electron diffraction (RHEED) oscillations during pulsed-laser deposition (PLD), atomic force microscopy (AFM), X-ray diffraction (XRD) (if the sample is ordered), and fitting of data from spectroscopic ellipsometry (SE). These techniques usually expend a significant amount of time but provide an accurate value to the thickness measurements. Creating a QCM that can work ex-situ will assist my research, and also serves as a reference point and hastens the process of fitting models in SE analysis.
----
Many of the developments and features that exist in today’s commercial QCM instruments were pioneered in laboratories with custom-built instruments to meet specific research needs, such as the use of internal reference crystals to separate the effects of a liquid environment from those of a film sample.
----
==Working Principle==
[[File:AT and BT cut.png|340px|thumb|right|Figure 1: Orientation of AT- and BT- cut crystals]]The working principle behind the QCM is based on the piezoelectric effect. The piezoelectric effect is the generation of electric charges by a crystalline material upon subjecting it to stress.[1] An oscillating electric field applied across the device induces an acoustic wave that propagates through the crystal and meets minimum impedance when the device's thickness is a half-integer multiple of the wavelength of the acoustic wave.[2] It is a shear mode device in which the acoustic wave propagates in a direction perpendicular to the crystal surface.[3] Therefore, crystals cut in specific crystal axes have to be used to utilize the shear mode. A resonant oscillation in the crystal is achieved by putting the crystal in an oscillation circuit where the electrical and mechanical oscillations are close to the fundamental frequency of the crystal. Changes to the mass of the crystal would result in a proportional change in its natural frequency according to the Sauerbrey equation[4]

<math>

\Delta m = \frac{C}{n} \Delta f

</math>

 
where <math>\Delta f</math> is the change in resonance frequency, <math>C</math> is the specific sensitivity of the crystal, <math>\Delta m</math> is the mass adsorbed on the active area, and <math>n</math> is the harmonic number. <math>C</math> describes how much material per unit area is required to change the resonant frequency of the crystal by 1Hz. A smaller <math>C</math> value gives a higher mass sensitivity. This value depends on the fundamental resonant frequency of the crystal, and it is defined as 
 
<math>

C = \frac{t_q \rho_q}{f_0}

</math>
 
where <math>t_q</math> is the thickness of the quartz, <math>\rho_q</math> is the density of the quartz plate, and f0 is the fundamental resonant frequency of quartz. With these, we can determine the mass of the deposited material. 
 
Another consideration would be the energy dissipation of the crystal to the surroundings. This is important, especially for viscoelastic films. Viscoelastic films violate the Sauerbrey condition that the bound mass is rigidly attached to the crystal without any slip. Such viscoelastic films dissipate energy via mechanical losses in the flexible mass.
 
----

==Setup==
The typical QCM set-up of piezoelectric quartz crystal microbalance is shown in Figure 2.
The oscillator circuit is connected to the power supply and sample stage mount where the piezoelectric quartz crystal is. We can determine the resonance frequency of the quartz crystal using an oscilloscope, frequency counter, or spectrum analyzer.

To determine the feasibility of this QCM project, we built a simple oscillating circuit as a foundation to test if we can detect the resonance frequency of the quartz crystal. This also serves as a time buffer while waiting for the AT-cut quartz to be delivered. Figures 3 and 4 show the electrical circuit diagram and its implementation on a breadboard respectively.

As the electrical current generated from the oscillation of the quartz crystal is an alternating current due to the piezoelectric effect, we employ the usage of logic gates called inverters to convert DC to AC for readout. Adding a resistor to the circuit allows for the control of the potential difference across the inverter. In this oscillating circuit, we use a 14-pin integrated circuit and measure the resonant frequency of a CMAC CK q5 crystal oscillator.
[[File:Circuit diagram 1st.png|340px|thumb|left|Figure 3: Circuit Diagram]]
[[File:Typical setup.png|340px|thumb|right|Figure 2: Typical Setup for a QCM measurement]]
[[File:1st setup.jpeg|340px|thumb|right|Figure 4: Experimental Setup]]
 
----

==Measurements==
[[File:1st setup waveform.jpeg|340px|thumb|right|Figure 5: Waveform observed with an oscilloscope using the CMAC CK q5 crystal oscillator]]
[[File:10mhz waveform.jpeg|340px|thumb|right|Figure 6: Waveform observed with an oscilloscope using the AT-cut quartz crystal]]
A DC power supply of 5V is given and an oscilloscope is connected to see the signal's waveform. A frequency counter is connected to the electrical circuit and communicated to my computer via the Arduino Integrated Development Environment. The frequency is measured for 10 seconds 10 times to get an average. Eventually, a resonant frequency of 10.000001Mhz is recorded, which is very close to the 10Mhz value that was provided by the manufacturer.

The waveform seen on the oscilloscope is observed to be periodic and looks like a square-wave oscillation. There seem to be additional peaks periodically formed as well, which could likely come from circuit impedance mismatches. Mismatches in impedance between different components or sections of a circuit can cause signal reflections and distortions, leading to additional peaks in the waveform. We would have to adjust the values of the capacitors and resistors.

Then, we replace the 10Mhz crystal oscillator with the AT-cut crystal. Although we managed to obtain the frequency signal generated by the AT-cut crystal, the surface of the crystal is very sensitive such that waving your hands near the oscillator causes the waveform to change. To make the signal more stable, we construct another circuit design similar to the Colpitts oscillator.[5] One of the advantages of using this layout is that relatively low phase noise can be achieved, making them suitable for applications requiring stable and low-noise oscillation.
 
----

==Second Set-Up==
The circuit design and the actual circuit are shown in Figures 7 and 8. 2N2222 bipolar junction transistors were used with a combination of capacitors and resistors. The purpose of the transistor is to amplify the voltage across the resonant circuit and stabilize the oscillations through a feedback loop. A DC power supply of 9V is applied across the circuit and an oscilloscope is connected to observe the waveform. Figure 8 shows the waveform, which seems to be a superposition of a square wave and another periodic signal which could be due to the aforementioned circuit impedance mismatches.
[[File:Circuit diagram 2nd.png|340px|thumb|left|Figure 7: Circuit Diagram for 2nd setup]]
[[File:2nd setup.jpeg|340px|thumb|right|Figure 8: 2nd Experimental setup]]
 
We use the Anritsu MS2711D Spectrum Master to look for the resonance frequencies as a cross-reference to the frequency counter measurement. In Figure 9, the resonance frequency of the piezoelectric quartz oscillator and its higher-order harmonics are shown. From the wide scan, we can see that the zeroth-order overtone occurs at approximately 6Mhz, and the higher-order harmonics occur in multiple integers of 6MHz.
[[File:Wide scan.jpeg|340px|thumb|right|Figure 9: Spectral survey scan using the Anritsu MS2711D Spectrum Master]]
[[File:Narrow scan.jpeg|340px|thumb|left|Figure 10: Spectral narrow scan using the Anritsu MS2711D Spectrum Master]]
 
----

==Second Measurement==
The procedure for the frequency counter measurements is the same as that of the 10MHz crystal oscillator. The fundamental resonant frequency is measured to be 5.986804MHz. Using this as the reference resonance frequency, we can now test its effectiveness in mass measurements with the Sauerbrey equation.
[[File:Permanent marker.jpeg|340px|thumb|left|Depiction of how ink was placed on the quartz crystal plate]]
[[File:Ink no signal.jpeg|340px|thumb|right|No spectral signatures from measurement]]
 
[[File:Increase power.jpeg|340px|thumb|right|Increasing DC power supply shows a fundamental mode of resonance]]
Firstly, a permanent marker is used where we dot the center of the quartz crystal shown in Figure (). [insert permanent marker ink] Initially, there was no signal shown in Figure (). [Explain why] However, increasing the DC supply voltage sufficiently allows the fundamental mode to be observed as shown in Figure (). We repeated the frequency counter measurements and found the new resonance frequency to be 5.984613MHz.

To test the mass limit of this setup, a small Blu Tack weighing 2.1 grams is placed on the center of the oscillator. A new oscillator is used so that the dried ink does not interfere with the measurement. The Spectrum Master did not record any spectral features, which suggests that the oscillation of the crystal is too damped to be detected and that the gain is insufficient. Increasing the DC power supply to 18V is inadequate to produce a spectral feature. For safety purposes, this will be the limit that we shall test.
[[File:Blu tack.jpeg|340px|thumb|left|Depiction of how Blu tack was placed on the quartz crystal plate]]
[[File:Blu tack no signal.jpeg|340px|thumb|right|No spectral signatures from measurement]]
 
Based on the Sauerbrey equation, the decrease in resonance frequency of 2191Hz corresponds to an increase in mass of 969 micrograms. This value is derived by using the following:
* thickness of quartz crystal plate <math> t_q = 1 </math> mm
* density of quartz crystal <math> \rho_q = 2648 </math> kg m-3
* fundamental resonance frequency of quartz crystal plate <math> f_0 = 5.986804 </math> MHz

To understand how accurate this measurement is, let us approximate the volume of ink to be a drop of water and calculate how much a drop of water weighs. We assume that the density of the marker ink is approximately similar to water. A drop of water of 0.1ml is approximately 100 micrograms. This shows that the measurement is about an order of magnitude higher than the approximation.

This huge error arises because of the assumptions of using the Sauerbrey equation. The Sauerbrey equation is valid under the following conditions:

*The added mass is small compared to the mass of the crystal
*The added mass is rigidly adsorbed onto the surface of the crystal
*The mass is evenly distributed over the active area of the crystal.

Based on these conditions, the second and third conditions are not fulfilled.
----

==Potential Improvements and Conclusion==
Some better models describe the relationship between frequency change and mass adsorbed where we consider the added mass to be viscoelastic. The Sauerbrey equation fails to describe viscoelastic films on the quartz oscillator as the condition where the added mass is rigidly bound is not adhered to. This model is called the QCM-D, where D refers to the energy dissipation by the film. This technique is prevalent in the fields of lipids, proteins, nanoparticles, etc. [6] However, this requires the use of liquid media. 

To conclude, we managed to detect the quartz crystal oscillation with a simple circuit design. Changes in resonance frequency due to added mass can also be detected, but the margin of error is too large for it to be usable for research purposes. Future improvements to this experiment can be done by adopting energy dissipation within our considerations.
----
==References==
# Meissner A (1927) € Uber piezoelectrische Krystalle bei Hochfrequenz. Z Tech Phys 8:74
# O’Sullivan, C. K., & Guilbault, G. G. (1999). Commercial quartz crystal microbalances – theory and applications. Biosensors and Bioelectronics, 14(8), 663–670.
# Ebersole, R., Miller, J., Moran, J., & Ward, M. (1990). PZ quartz sensors for use in clinical analysis. J. Am. Chem. Soc, 112, 3239.
# Sauerbrey, G. (1959). Verwendung von Schwingquarzen zur Wägung dünner Schichten und zur Mikrowägung. Zeitschrift für Physik, 155(2), 206–222.
# US 1624537, Colpitts, Edwin H., "Oscillation generator", published 1 February 1918, issued 12 April 1927

Quartz Crystal MicroBalance (QCM)

2024-04-23T04:31:56Z

E0309214: /* Measurements */

==Abstract==

This project aims to construct a circuit that mimics a quartz crystal microbalance. This can be done via a combination of resistors, capacitors, and a quartz crystal. Testing of the QCM can be done by measuring the fundamental frequency of the quartz crystal oscillator, followed by adding a test mass such as the ink of a permanent marker on the oscillator to determine the frequency change. The original intention of building this QCM is to investigate if it is possible to measure the mass of thin films ex-situ. However, due to experimental and time constraints, we shall focus on building a circuit that can detect mass changes on the order of micrograms.
----
==Team members==
Tan Jhoon Yong
----
==Idea==
Quartz crystal microbalance (QCM) is widely used to measure mass changes to substances involved in physical and chemical processes. In my field of research, we often have to find out the thicknesses of thin films as part of the process of characterizing the samples. There are a few methods that are usually employed in my research to measure thin films' thicknesses such as observing the reflection high-energy electron diffraction (RHEED) oscillations during pulsed-laser deposition (PLD), atomic force microscopy (AFM), X-ray diffraction (XRD) (if the sample is ordered), and fitting of data from spectroscopic ellipsometry (SE). These techniques usually expend a significant amount of time but provide an accurate value to the thickness measurements. Creating a QCM that can work ex-situ will assist my research, and also serves as a reference point and hastens the process of fitting models in SE analysis.
----
Many of the developments and features that exist in today’s commercial QCM instruments were pioneered in laboratories with custom-built instruments to meet specific research needs, such as the use of internal reference crystals to separate the effects of a liquid environment from those of a film sample.
----
==Working Principle==
[[File:AT and BT cut.png|340px|thumb|right|Figure 1: Orientation of AT- and BT- cut crystals]]The working principle behind the QCM is based on the piezoelectric effect. The piezoelectric effect is the generation of electric charges by a crystalline material upon subjecting it to stress.[1] An oscillating electric field applied across the device induces an acoustic wave that propagates through the crystal and meets minimum impedance when the device's thickness is a half-integer multiple of the wavelength of the acoustic wave.[2] It is a shear mode device in which the acoustic wave propagates in a direction perpendicular to the crystal surface.[3] Therefore, crystals cut in specific crystal axes have to be used to utilize the shear mode. A resonant oscillation in the crystal is achieved by putting the crystal in an oscillation circuit where the electrical and mechanical oscillations are close to the fundamental frequency of the crystal. Changes to the mass of the crystal would result in a proportional change in its natural frequency according to the Sauerbrey equation[4]

<math>

\Delta m = \frac{C}{n} \Delta f

</math>

 
where <math>\Delta f</math> is the change in resonance frequency, <math>C</math> is the specific sensitivity of the crystal, <math>\Delta m</math> is the mass adsorbed on the active area, and <math>n</math> is the harmonic number. <math>C</math> describes how much material per unit area is required to change the resonant frequency of the crystal by 1Hz. A smaller <math>C</math> value gives a higher mass sensitivity. This value depends on the fundamental resonant frequency of the crystal, and it is defined as 
 
<math>

C = \frac{t_q \rho_q}{f_0}

</math>
 
where <math>t_q</math> is the thickness of the quartz, <math>\rho_q</math> is the density of the quartz plate, and f0 is the fundamental resonant frequency of quartz. With these, we can determine the mass of the deposited material. 
 
Another consideration would be the energy dissipation of the crystal to the surroundings. This is important, especially for viscoelastic films. Viscoelastic films violate the Sauerbrey condition that the bound mass is rigidly attached to the crystal without any slip. Such viscoelastic films dissipate energy via mechanical losses in the flexible mass.
 
----

==Setup==
The typical QCM set-up of piezoelectric quartz crystal microbalance is shown in Figure 2.
The oscillator circuit is connected to the power supply and sample stage mount where the piezoelectric quartz crystal is. We can determine the resonance frequency of the quartz crystal using an oscilloscope, frequency counter, or spectrum analyzer.

To determine the feasibility of this QCM project, we built a simple oscillating circuit as a foundation to test if we can detect the resonance frequency of the quartz crystal. This also serves as a time buffer while waiting for the AT-cut quartz to be delivered. Figures 3 and 4 show the electrical circuit diagram and its implementation on a breadboard respectively.

As the electrical current generated from the oscillation of the quartz crystal is an alternating current due to the piezoelectric effect, we employ the usage of logic gates called inverters to convert DC to AC for readout. Adding a resistor to the circuit allows for the control of the potential difference across the inverter. In this oscillating circuit, we use a 14-pin integrated circuit and measure the resonant frequency of a CMAC CK q5 crystal oscillator.
[[File:Circuit diagram 1st.png|340px|thumb|left|Figure 3: Circuit Diagram]]
[[File:Typical setup.png|340px|thumb|right|Figure 2: Typical Setup for a QCM measurement]]
[[File:1st setup.jpeg|340px|thumb|right|Figure 4: Experimental Setup]]
 
----

==Measurements==
[[File:1st setup waveform.jpeg|340px|thumb|right|Figure 5: Waveform observed with an oscilloscope using the CMAC CK q5 crystal oscillator]]
[[File:10mhz waveform.jpeg|340px|thumb|right|Figure 6: Waveform observed with an oscilloscope using the AT-cut quartz crystal]]
A DC power supply of 5V is given and an oscilloscope is connected to see the signal's waveform. A frequency counter is connected to the electrical circuit and communicated to my computer via the Arduino Integrated Development Environment. The frequency is measured for 10 seconds 10 times to get an average. Eventually, a resonant frequency of 10.000001Mhz is recorded, which is very close to the 10Mhz value that was provided by the manufacturer.

The waveform seen on the oscilloscope is observed to be periodic and looks like a square-wave oscillation. There seem to be additional peaks periodically formed as well, which could likely come from circuit impedance mismatches. Mismatches in impedance between different components or sections of a circuit can cause signal reflections and distortions, leading to additional peaks in the waveform. We would have to adjust the values of the capacitors and resistors.

Then, we replace the 10Mhz crystal oscillator with the AT-cut crystal. Although we managed to obtain the frequency signal generated by the AT-cut crystal, the surface of the crystal is very sensitive such that waving your hands near the oscillator causes the waveform to change. To make the signal more stable, we construct another circuit design similar to the Colpitts oscillator.[5] One of the advantages of using this layout is that relatively low phase noise can be achieved, making them suitable for applications requiring stable and low-noise oscillation.
 
----

==Second Set-Up==
The circuit design and the actual circuit are shown in Figure (). 2N2222 bipolar junction transistors were used with a combination of capacitors and resistors. The purpose of the transistor is to amplify the voltage across the resonant circuit and stabilize the oscillations through a feedback loop. A DC power supply of 9V is applied across the circuit and an oscilloscope is connected to observe the waveform. Figure () shows the waveform, which seems to be a superposition of a square wave and another periodic signal which could be due to the aforementioned circuit impedance mismatches.
[[File:Circuit diagram 2nd.png|340px|thumb|right|Circuit Diagram for 2nd setup]]
[[File:2nd setup.jpeg|340px|thumb|left|2nd Experimental setup]]
 
We use the Anritsu MS2711D Spectrum Master to look for the resonance frequencies as a cross-reference to the frequency counter measurement. In Figure (), the resonance frequency of the piezoelectric quartz oscillator and its higher-order harmonics are shown. [insert resonance frequency narrow, wide scan of frequency] From the wide scan, we can see that the zeroth-order overtone occurs at approximately 6Mhz, and the higher-order harmonics occur in multiple integers of 6MHz.
[[File:Wide scan.jpeg|340px|thumb|right|Spectral survey scan using the Anritsu MS2711D Spectrum Master]]
[[File:Narrow scan.jpeg|340px|thumb|left|Spectral narrow scan using the Anritsu MS2711D Spectrum Master]]
 
----
==Second Measurement==
The procedure for the frequency counter measurements is the same as that of the 10MHz crystal oscillator. The fundamental resonant frequency is measured to be 5.986804MHz. Using this as the reference resonance frequency, we can now test its effectiveness in mass measurements with the Sauerbrey equation.
[[File:Permanent marker.jpeg|340px|thumb|left|Depiction of how ink was placed on the quartz crystal plate]]
[[File:Ink no signal.jpeg|340px|thumb|right|No spectral signatures from measurement]]
 
[[File:Increase power.jpeg|340px|thumb|right|Increasing DC power supply shows a fundamental mode of resonance]]
Firstly, a permanent marker is used where we dot the center of the quartz crystal shown in Figure (). [insert permanent marker ink] Initially, there was no signal shown in Figure (). [Explain why] However, increasing the DC supply voltage sufficiently allows the fundamental mode to be observed as shown in Figure (). We repeated the frequency counter measurements and found the new resonance frequency to be 5.984613MHz.

To test the mass limit of this setup, a small Blu Tack weighing 2.1 grams is placed on the center of the oscillator. A new oscillator is used so that the dried ink does not interfere with the measurement. The Spectrum Master did not record any spectral features, which suggests that the oscillation of the crystal is too damped to be detected and that the gain is insufficient. Increasing the DC power supply to 18V is inadequate to produce a spectral feature. For safety purposes, this will be the limit that we shall test.
[[File:Blu tack.jpeg|340px|thumb|left|Depiction of how Blu tack was placed on the quartz crystal plate]]
[[File:Blu tack no signal.jpeg|340px|thumb|right|No spectral signatures from measurement]]
 
Based on the Sauerbrey equation, the decrease in resonance frequency of 2191Hz corresponds to an increase in mass of 969 micrograms. This value is derived by using the following:
* thickness of quartz crystal plate <math> t_q = 1 </math> mm
* density of quartz crystal <math> \rho_q = 2648 </math> kg m-3
* fundamental resonance frequency of quartz crystal plate <math> f_0 = 5.986804 </math> MHz

To understand how accurate this measurement is, let us approximate the volume of ink to be a drop of water and calculate how much a drop of water weighs. We assume that the density of the marker ink is approximately similar to water. A drop of water of 0.1ml is approximately 100 micrograms. This shows that the measurement is about an order of magnitude higher than the approximation.

This huge error arises because of the assumptions of using the Sauerbrey equation. The Sauerbrey equation is valid under the following conditions:

*The added mass is small compared to the mass of the crystal
*The added mass is rigidly adsorbed onto the surface of the crystal
*The mass is evenly distributed over the active area of the crystal.

Based on these conditions, the second and third conditions are not fulfilled.
----

==Potential Improvements and Conclusion==
Some better models describe the relationship between frequency change and mass adsorbed where we consider the added mass to be viscoelastic. The Sauerbrey equation fails to describe viscoelastic films on the quartz oscillator as the condition where the added mass is rigidly bound is not adhered to. This model is called the QCM-D, where D refers to the energy dissipation by the film. This technique is prevalent in the fields of lipids, proteins, nanoparticles, etc. [6] However, this requires the use of liquid media. 

To conclude, we managed to detect the quartz crystal oscillation with a simple circuit design. Changes in resonance frequency due to added mass can also be detected, but the margin of error is too large for it to be usable for research purposes. Future improvements to this experiment can be done by adopting energy dissipation within our considerations.
----
==References==
# Meissner A (1927) € Uber piezoelectrische Krystalle bei Hochfrequenz. Z Tech Phys 8:74
# O’Sullivan, C. K., & Guilbault, G. G. (1999). Commercial quartz crystal microbalances – theory and applications. Biosensors and Bioelectronics, 14(8), 663–670.
# Ebersole, R., Miller, J., Moran, J., & Ward, M. (1990). PZ quartz sensors for use in clinical analysis. J. Am. Chem. Soc, 112, 3239.
# Sauerbrey, G. (1959). Verwendung von Schwingquarzen zur Wägung dünner Schichten und zur Mikrowägung. Zeitschrift für Physik, 155(2), 206–222.
# US 1624537, Colpitts, Edwin H., "Oscillation generator", published 1 February 1918, issued 12 April 1927

Quartz Crystal MicroBalance (QCM)

2024-04-23T04:31:17Z

E0309214: /* Setup */

==Abstract==

This project aims to construct a circuit that mimics a quartz crystal microbalance. This can be done via a combination of resistors, capacitors, and a quartz crystal. Testing of the QCM can be done by measuring the fundamental frequency of the quartz crystal oscillator, followed by adding a test mass such as the ink of a permanent marker on the oscillator to determine the frequency change. The original intention of building this QCM is to investigate if it is possible to measure the mass of thin films ex-situ. However, due to experimental and time constraints, we shall focus on building a circuit that can detect mass changes on the order of micrograms.
----
==Team members==
Tan Jhoon Yong
----
==Idea==
Quartz crystal microbalance (QCM) is widely used to measure mass changes to substances involved in physical and chemical processes. In my field of research, we often have to find out the thicknesses of thin films as part of the process of characterizing the samples. There are a few methods that are usually employed in my research to measure thin films' thicknesses such as observing the reflection high-energy electron diffraction (RHEED) oscillations during pulsed-laser deposition (PLD), atomic force microscopy (AFM), X-ray diffraction (XRD) (if the sample is ordered), and fitting of data from spectroscopic ellipsometry (SE). These techniques usually expend a significant amount of time but provide an accurate value to the thickness measurements. Creating a QCM that can work ex-situ will assist my research, and also serves as a reference point and hastens the process of fitting models in SE analysis.
----
Many of the developments and features that exist in today’s commercial QCM instruments were pioneered in laboratories with custom-built instruments to meet specific research needs, such as the use of internal reference crystals to separate the effects of a liquid environment from those of a film sample.
----
==Working Principle==
[[File:AT and BT cut.png|340px|thumb|right|Figure 1: Orientation of AT- and BT- cut crystals]]The working principle behind the QCM is based on the piezoelectric effect. The piezoelectric effect is the generation of electric charges by a crystalline material upon subjecting it to stress.[1] An oscillating electric field applied across the device induces an acoustic wave that propagates through the crystal and meets minimum impedance when the device's thickness is a half-integer multiple of the wavelength of the acoustic wave.[2] It is a shear mode device in which the acoustic wave propagates in a direction perpendicular to the crystal surface.[3] Therefore, crystals cut in specific crystal axes have to be used to utilize the shear mode. A resonant oscillation in the crystal is achieved by putting the crystal in an oscillation circuit where the electrical and mechanical oscillations are close to the fundamental frequency of the crystal. Changes to the mass of the crystal would result in a proportional change in its natural frequency according to the Sauerbrey equation[4]

<math>

\Delta m = \frac{C}{n} \Delta f

</math>

 
where <math>\Delta f</math> is the change in resonance frequency, <math>C</math> is the specific sensitivity of the crystal, <math>\Delta m</math> is the mass adsorbed on the active area, and <math>n</math> is the harmonic number. <math>C</math> describes how much material per unit area is required to change the resonant frequency of the crystal by 1Hz. A smaller <math>C</math> value gives a higher mass sensitivity. This value depends on the fundamental resonant frequency of the crystal, and it is defined as 
 
<math>

C = \frac{t_q \rho_q}{f_0}

</math>
 
where <math>t_q</math> is the thickness of the quartz, <math>\rho_q</math> is the density of the quartz plate, and f0 is the fundamental resonant frequency of quartz. With these, we can determine the mass of the deposited material. 
 
Another consideration would be the energy dissipation of the crystal to the surroundings. This is important, especially for viscoelastic films. Viscoelastic films violate the Sauerbrey condition that the bound mass is rigidly attached to the crystal without any slip. Such viscoelastic films dissipate energy via mechanical losses in the flexible mass.
 
----

==Setup==
The typical QCM set-up of piezoelectric quartz crystal microbalance is shown in Figure 2.
The oscillator circuit is connected to the power supply and sample stage mount where the piezoelectric quartz crystal is. We can determine the resonance frequency of the quartz crystal using an oscilloscope, frequency counter, or spectrum analyzer.

To determine the feasibility of this QCM project, we built a simple oscillating circuit as a foundation to test if we can detect the resonance frequency of the quartz crystal. This also serves as a time buffer while waiting for the AT-cut quartz to be delivered. Figures 3 and 4 show the electrical circuit diagram and its implementation on a breadboard respectively.

As the electrical current generated from the oscillation of the quartz crystal is an alternating current due to the piezoelectric effect, we employ the usage of logic gates called inverters to convert DC to AC for readout. Adding a resistor to the circuit allows for the control of the potential difference across the inverter. In this oscillating circuit, we use a 14-pin integrated circuit and measure the resonant frequency of a CMAC CK q5 crystal oscillator.
[[File:Circuit diagram 1st.png|340px|thumb|left|Figure 3: Circuit Diagram]]
[[File:Typical setup.png|340px|thumb|right|Figure 2: Typical Setup for a QCM measurement]]
[[File:1st setup.jpeg|340px|thumb|right|Figure 4: Experimental Setup]]
 
----

==Measurements==
[[File:1st setup waveform.jpeg|340px|thumb|right|Waveform observed with an oscilloscope using the CMAC CK q5 crystal oscillator]]
[[File:10mhz waveform.jpeg|340px|thumb|right|Waveform observed with an oscilloscope using the AT-cut quartz crystal]]
A DC power supply of 5V is given and an oscilloscope is connected to see the signal's waveform. A frequency counter is connected to the electrical circuit and communicated to my computer via the Arduino Integrated Development Environment. The frequency is measured for 10 seconds 10 times to get an average. Eventually, a resonant frequency of 10.000001Mhz is recorded, which is very close to the 10Mhz value that was provided by the manufacturer.

The waveform seen on the oscilloscope is observed to be periodic and looks like a square-wave oscillation. There seem to be additional peaks periodically formed as well, which could likely come from circuit impedance mismatches. Mismatches in impedance between different components or sections of a circuit can cause signal reflections and distortions, leading to additional peaks in the waveform. We would have to adjust the values of the capacitors and resistors.

Then, we replace the 10Mhz crystal oscillator with the AT-cut crystal. Although we managed to obtain the frequency signal generated by the AT-cut crystal, the surface of the crystal is very sensitive such that waving your hands near the oscillator causes the waveform to change. To make the signal more stable, we construct another circuit design similar to the Colpitts oscillator.[5] One of the advantages of using this layout is that relatively low phase noise can be achieved, making them suitable for applications requiring stable and low-noise oscillation.
 
----
==Second Set-Up==
The circuit design and the actual circuit are shown in Figure (). 2N2222 bipolar junction transistors were used with a combination of capacitors and resistors. The purpose of the transistor is to amplify the voltage across the resonant circuit and stabilize the oscillations through a feedback loop. A DC power supply of 9V is applied across the circuit and an oscilloscope is connected to observe the waveform. Figure () shows the waveform, which seems to be a superposition of a square wave and another periodic signal which could be due to the aforementioned circuit impedance mismatches.
[[File:Circuit diagram 2nd.png|340px|thumb|right|Circuit Diagram for 2nd setup]]
[[File:2nd setup.jpeg|340px|thumb|left|2nd Experimental setup]]
 
We use the Anritsu MS2711D Spectrum Master to look for the resonance frequencies as a cross-reference to the frequency counter measurement. In Figure (), the resonance frequency of the piezoelectric quartz oscillator and its higher-order harmonics are shown. [insert resonance frequency narrow, wide scan of frequency] From the wide scan, we can see that the zeroth-order overtone occurs at approximately 6Mhz, and the higher-order harmonics occur in multiple integers of 6MHz.
[[File:Wide scan.jpeg|340px|thumb|right|Spectral survey scan using the Anritsu MS2711D Spectrum Master]]
[[File:Narrow scan.jpeg|340px|thumb|left|Spectral narrow scan using the Anritsu MS2711D Spectrum Master]]
 
----
==Second Measurement==
The procedure for the frequency counter measurements is the same as that of the 10MHz crystal oscillator. The fundamental resonant frequency is measured to be 5.986804MHz. Using this as the reference resonance frequency, we can now test its effectiveness in mass measurements with the Sauerbrey equation.
[[File:Permanent marker.jpeg|340px|thumb|left|Depiction of how ink was placed on the quartz crystal plate]]
[[File:Ink no signal.jpeg|340px|thumb|right|No spectral signatures from measurement]]
 
[[File:Increase power.jpeg|340px|thumb|right|Increasing DC power supply shows a fundamental mode of resonance]]
Firstly, a permanent marker is used where we dot the center of the quartz crystal shown in Figure (). [insert permanent marker ink] Initially, there was no signal shown in Figure (). [Explain why] However, increasing the DC supply voltage sufficiently allows the fundamental mode to be observed as shown in Figure (). We repeated the frequency counter measurements and found the new resonance frequency to be 5.984613MHz.

To test the mass limit of this setup, a small Blu Tack weighing 2.1 grams is placed on the center of the oscillator. A new oscillator is used so that the dried ink does not interfere with the measurement. The Spectrum Master did not record any spectral features, which suggests that the oscillation of the crystal is too damped to be detected and that the gain is insufficient. Increasing the DC power supply to 18V is inadequate to produce a spectral feature. For safety purposes, this will be the limit that we shall test.
[[File:Blu tack.jpeg|340px|thumb|left|Depiction of how Blu tack was placed on the quartz crystal plate]]
[[File:Blu tack no signal.jpeg|340px|thumb|right|No spectral signatures from measurement]]
 
Based on the Sauerbrey equation, the decrease in resonance frequency of 2191Hz corresponds to an increase in mass of 969 micrograms. This value is derived by using the following:
* thickness of quartz crystal plate <math> t_q = 1 </math> mm
* density of quartz crystal <math> \rho_q = 2648 </math> kg m-3
* fundamental resonance frequency of quartz crystal plate <math> f_0 = 5.986804 </math> MHz

To understand how accurate this measurement is, let us approximate the volume of ink to be a drop of water and calculate how much a drop of water weighs. We assume that the density of the marker ink is approximately similar to water. A drop of water of 0.1ml is approximately 100 micrograms. This shows that the measurement is about an order of magnitude higher than the approximation.

This huge error arises because of the assumptions of using the Sauerbrey equation. The Sauerbrey equation is valid under the following conditions:

*The added mass is small compared to the mass of the crystal
*The added mass is rigidly adsorbed onto the surface of the crystal
*The mass is evenly distributed over the active area of the crystal.

Based on these conditions, the second and third conditions are not fulfilled.
----

==Potential Improvements and Conclusion==
Some better models describe the relationship between frequency change and mass adsorbed where we consider the added mass to be viscoelastic. The Sauerbrey equation fails to describe viscoelastic films on the quartz oscillator as the condition where the added mass is rigidly bound is not adhered to. This model is called the QCM-D, where D refers to the energy dissipation by the film. This technique is prevalent in the fields of lipids, proteins, nanoparticles, etc. [6] However, this requires the use of liquid media. 

To conclude, we managed to detect the quartz crystal oscillation with a simple circuit design. Changes in resonance frequency due to added mass can also be detected, but the margin of error is too large for it to be usable for research purposes. Future improvements to this experiment can be done by adopting energy dissipation within our considerations.
----
==References==
# Meissner A (1927) € Uber piezoelectrische Krystalle bei Hochfrequenz. Z Tech Phys 8:74
# O’Sullivan, C. K., & Guilbault, G. G. (1999). Commercial quartz crystal microbalances – theory and applications. Biosensors and Bioelectronics, 14(8), 663–670.
# Ebersole, R., Miller, J., Moran, J., & Ward, M. (1990). PZ quartz sensors for use in clinical analysis. J. Am. Chem. Soc, 112, 3239.
# Sauerbrey, G. (1959). Verwendung von Schwingquarzen zur Wägung dünner Schichten und zur Mikrowägung. Zeitschrift für Physik, 155(2), 206–222.
# US 1624537, Colpitts, Edwin H., "Oscillation generator", published 1 February 1918, issued 12 April 1927

Quartz Crystal MicroBalance (QCM)

2024-04-23T04:30:17Z

E0309214: /* Working Principle */

==Abstract==

This project aims to construct a circuit that mimics a quartz crystal microbalance. This can be done via a combination of resistors, capacitors, and a quartz crystal. Testing of the QCM can be done by measuring the fundamental frequency of the quartz crystal oscillator, followed by adding a test mass such as the ink of a permanent marker on the oscillator to determine the frequency change. The original intention of building this QCM is to investigate if it is possible to measure the mass of thin films ex-situ. However, due to experimental and time constraints, we shall focus on building a circuit that can detect mass changes on the order of micrograms.
----
==Team members==
Tan Jhoon Yong
----
==Idea==
Quartz crystal microbalance (QCM) is widely used to measure mass changes to substances involved in physical and chemical processes. In my field of research, we often have to find out the thicknesses of thin films as part of the process of characterizing the samples. There are a few methods that are usually employed in my research to measure thin films' thicknesses such as observing the reflection high-energy electron diffraction (RHEED) oscillations during pulsed-laser deposition (PLD), atomic force microscopy (AFM), X-ray diffraction (XRD) (if the sample is ordered), and fitting of data from spectroscopic ellipsometry (SE). These techniques usually expend a significant amount of time but provide an accurate value to the thickness measurements. Creating a QCM that can work ex-situ will assist my research, and also serves as a reference point and hastens the process of fitting models in SE analysis.
----
Many of the developments and features that exist in today’s commercial QCM instruments were pioneered in laboratories with custom-built instruments to meet specific research needs, such as the use of internal reference crystals to separate the effects of a liquid environment from those of a film sample.
----
==Working Principle==
[[File:AT and BT cut.png|340px|thumb|right|Figure 1: Orientation of AT- and BT- cut crystals]]The working principle behind the QCM is based on the piezoelectric effect. The piezoelectric effect is the generation of electric charges by a crystalline material upon subjecting it to stress.[1] An oscillating electric field applied across the device induces an acoustic wave that propagates through the crystal and meets minimum impedance when the device's thickness is a half-integer multiple of the wavelength of the acoustic wave.[2] It is a shear mode device in which the acoustic wave propagates in a direction perpendicular to the crystal surface.[3] Therefore, crystals cut in specific crystal axes have to be used to utilize the shear mode. A resonant oscillation in the crystal is achieved by putting the crystal in an oscillation circuit where the electrical and mechanical oscillations are close to the fundamental frequency of the crystal. Changes to the mass of the crystal would result in a proportional change in its natural frequency according to the Sauerbrey equation[4]

<math>

\Delta m = \frac{C}{n} \Delta f

</math>

 
where <math>\Delta f</math> is the change in resonance frequency, <math>C</math> is the specific sensitivity of the crystal, <math>\Delta m</math> is the mass adsorbed on the active area, and <math>n</math> is the harmonic number. <math>C</math> describes how much material per unit area is required to change the resonant frequency of the crystal by 1Hz. A smaller <math>C</math> value gives a higher mass sensitivity. This value depends on the fundamental resonant frequency of the crystal, and it is defined as 
 
<math>

C = \frac{t_q \rho_q}{f_0}

</math>
 
where <math>t_q</math> is the thickness of the quartz, <math>\rho_q</math> is the density of the quartz plate, and f0 is the fundamental resonant frequency of quartz. With these, we can determine the mass of the deposited material. 
 
Another consideration would be the energy dissipation of the crystal to the surroundings. This is important, especially for viscoelastic films. Viscoelastic films violate the Sauerbrey condition that the bound mass is rigidly attached to the crystal without any slip. Such viscoelastic films dissipate energy via mechanical losses in the flexible mass.
 
----

==Setup==
The typical QCM set-up of piezoelectric quartz crystal microbalance is shown in Figure ().
The oscillator circuit is connected to the power supply and sample stage mount where the piezoelectric quartz crystal is. We can determine the resonance frequency of the quartz crystal using an oscilloscope, frequency counter, or spectrum analyzer.

To determine the feasibility of this QCM project, we built a simple oscillating circuit as a foundation to test if we can detect the resonance frequency of the quartz crystal. This also serves as a time buffer while waiting for the AT-cut quartz to be delivered. Figures () and () show the electrical circuit diagram and its implementation on a breadboard.

As the electrical current generated from the oscillation of the quartz crystal is an alternating current due to the piezoelectric effect, we employ the usage of logic gates called inverters to convert DC to AC for readout. Adding a resistor to the circuit allows for the control of the potential difference across the inverter. In this oscillating circuit, we use a 14-pin integrated circuit and measure the resonant frequency of a CMAC CK q5 crystal oscillator.
[[File:Circuit diagram 1st.png|340px|thumb|left|Circuit Diagram]]
[[File:Typical setup.png|340px|thumb|right|Typical Setup for a QCM measurement]]
[[File:1st setup.jpeg|340px|thumb|right|Experimental Setup]]
 
----
==Measurements==
[[File:1st setup waveform.jpeg|340px|thumb|right|Waveform observed with an oscilloscope using the CMAC CK q5 crystal oscillator]]
[[File:10mhz waveform.jpeg|340px|thumb|right|Waveform observed with an oscilloscope using the AT-cut quartz crystal]]
A DC power supply of 5V is given and an oscilloscope is connected to see the signal's waveform. A frequency counter is connected to the electrical circuit and communicated to my computer via the Arduino Integrated Development Environment. The frequency is measured for 10 seconds 10 times to get an average. Eventually, a resonant frequency of 10.000001Mhz is recorded, which is very close to the 10Mhz value that was provided by the manufacturer.

The waveform seen on the oscilloscope is observed to be periodic and looks like a square-wave oscillation. There seem to be additional peaks periodically formed as well, which could likely come from circuit impedance mismatches. Mismatches in impedance between different components or sections of a circuit can cause signal reflections and distortions, leading to additional peaks in the waveform. We would have to adjust the values of the capacitors and resistors.

Then, we replace the 10Mhz crystal oscillator with the AT-cut crystal. Although we managed to obtain the frequency signal generated by the AT-cut crystal, the surface of the crystal is very sensitive such that waving your hands near the oscillator causes the waveform to change. To make the signal more stable, we construct another circuit design similar to the Colpitts oscillator.[5] One of the advantages of using this layout is that relatively low phase noise can be achieved, making them suitable for applications requiring stable and low-noise oscillation.
 
----
==Second Set-Up==
The circuit design and the actual circuit are shown in Figure (). 2N2222 bipolar junction transistors were used with a combination of capacitors and resistors. The purpose of the transistor is to amplify the voltage across the resonant circuit and stabilize the oscillations through a feedback loop. A DC power supply of 9V is applied across the circuit and an oscilloscope is connected to observe the waveform. Figure () shows the waveform, which seems to be a superposition of a square wave and another periodic signal which could be due to the aforementioned circuit impedance mismatches.
[[File:Circuit diagram 2nd.png|340px|thumb|right|Circuit Diagram for 2nd setup]]
[[File:2nd setup.jpeg|340px|thumb|left|2nd Experimental setup]]
 
We use the Anritsu MS2711D Spectrum Master to look for the resonance frequencies as a cross-reference to the frequency counter measurement. In Figure (), the resonance frequency of the piezoelectric quartz oscillator and its higher-order harmonics are shown. [insert resonance frequency narrow, wide scan of frequency] From the wide scan, we can see that the zeroth-order overtone occurs at approximately 6Mhz, and the higher-order harmonics occur in multiple integers of 6MHz.
[[File:Wide scan.jpeg|340px|thumb|right|Spectral survey scan using the Anritsu MS2711D Spectrum Master]]
[[File:Narrow scan.jpeg|340px|thumb|left|Spectral narrow scan using the Anritsu MS2711D Spectrum Master]]
 
----
==Second Measurement==
The procedure for the frequency counter measurements is the same as that of the 10MHz crystal oscillator. The fundamental resonant frequency is measured to be 5.986804MHz. Using this as the reference resonance frequency, we can now test its effectiveness in mass measurements with the Sauerbrey equation.
[[File:Permanent marker.jpeg|340px|thumb|left|Depiction of how ink was placed on the quartz crystal plate]]
[[File:Ink no signal.jpeg|340px|thumb|right|No spectral signatures from measurement]]
 
[[File:Increase power.jpeg|340px|thumb|right|Increasing DC power supply shows a fundamental mode of resonance]]
Firstly, a permanent marker is used where we dot the center of the quartz crystal shown in Figure (). [insert permanent marker ink] Initially, there was no signal shown in Figure (). [Explain why] However, increasing the DC supply voltage sufficiently allows the fundamental mode to be observed as shown in Figure (). We repeated the frequency counter measurements and found the new resonance frequency to be 5.984613MHz.

To test the mass limit of this setup, a small Blu Tack weighing 2.1 grams is placed on the center of the oscillator. A new oscillator is used so that the dried ink does not interfere with the measurement. The Spectrum Master did not record any spectral features, which suggests that the oscillation of the crystal is too damped to be detected and that the gain is insufficient. Increasing the DC power supply to 18V is inadequate to produce a spectral feature. For safety purposes, this will be the limit that we shall test.
[[File:Blu tack.jpeg|340px|thumb|left|Depiction of how Blu tack was placed on the quartz crystal plate]]
[[File:Blu tack no signal.jpeg|340px|thumb|right|No spectral signatures from measurement]]
 
Based on the Sauerbrey equation, the decrease in resonance frequency of 2191Hz corresponds to an increase in mass of 969 micrograms. This value is derived by using the following:
* thickness of quartz crystal plate <math> t_q = 1 </math> mm
* density of quartz crystal <math> \rho_q = 2648 </math> kg m-3
* fundamental resonance frequency of quartz crystal plate <math> f_0 = 5.986804 </math> MHz

To understand how accurate this measurement is, let us approximate the volume of ink to be a drop of water and calculate how much a drop of water weighs. We assume that the density of the marker ink is approximately similar to water. A drop of water of 0.1ml is approximately 100 micrograms. This shows that the measurement is about an order of magnitude higher than the approximation.

This huge error arises because of the assumptions of using the Sauerbrey equation. The Sauerbrey equation is valid under the following conditions:

*The added mass is small compared to the mass of the crystal
*The added mass is rigidly adsorbed onto the surface of the crystal
*The mass is evenly distributed over the active area of the crystal.

Based on these conditions, the second and third conditions are not fulfilled.
----

==Potential Improvements and Conclusion==
Some better models describe the relationship between frequency change and mass adsorbed where we consider the added mass to be viscoelastic. The Sauerbrey equation fails to describe viscoelastic films on the quartz oscillator as the condition where the added mass is rigidly bound is not adhered to. This model is called the QCM-D, where D refers to the energy dissipation by the film. This technique is prevalent in the fields of lipids, proteins, nanoparticles, etc. [6] However, this requires the use of liquid media. 

To conclude, we managed to detect the quartz crystal oscillation with a simple circuit design. Changes in resonance frequency due to added mass can also be detected, but the margin of error is too large for it to be usable for research purposes. Future improvements to this experiment can be done by adopting energy dissipation within our considerations.
----
==References==
# Meissner A (1927) € Uber piezoelectrische Krystalle bei Hochfrequenz. Z Tech Phys 8:74
# O’Sullivan, C. K., & Guilbault, G. G. (1999). Commercial quartz crystal microbalances – theory and applications. Biosensors and Bioelectronics, 14(8), 663–670.
# Ebersole, R., Miller, J., Moran, J., & Ward, M. (1990). PZ quartz sensors for use in clinical analysis. J. Am. Chem. Soc, 112, 3239.
# Sauerbrey, G. (1959). Verwendung von Schwingquarzen zur Wägung dünner Schichten und zur Mikrowägung. Zeitschrift für Physik, 155(2), 206–222.
# US 1624537, Colpitts, Edwin H., "Oscillation generator", published 1 February 1918, issued 12 April 1927

Quartz Crystal MicroBalance (QCM)

2024-04-23T04:28:51Z

E0309214: /* Second Measurement */

==Abstract==

This project aims to construct a circuit that mimics a quartz crystal microbalance. This can be done via a combination of resistors, capacitors, and a quartz crystal. Testing of the QCM can be done by measuring the fundamental frequency of the quartz crystal oscillator, followed by adding a test mass such as the ink of a permanent marker on the oscillator to determine the frequency change. The original intention of building this QCM is to investigate if it is possible to measure the mass of thin films ex-situ. However, due to experimental and time constraints, we shall focus on building a circuit that can detect mass changes on the order of micrograms.
----
==Team members==
Tan Jhoon Yong
----
==Idea==
Quartz crystal microbalance (QCM) is widely used to measure mass changes to substances involved in physical and chemical processes. In my field of research, we often have to find out the thicknesses of thin films as part of the process of characterizing the samples. There are a few methods that are usually employed in my research to measure thin films' thicknesses such as observing the reflection high-energy electron diffraction (RHEED) oscillations during pulsed-laser deposition (PLD), atomic force microscopy (AFM), X-ray diffraction (XRD) (if the sample is ordered), and fitting of data from spectroscopic ellipsometry (SE). These techniques usually expend a significant amount of time but provide an accurate value to the thickness measurements. Creating a QCM that can work ex-situ will assist my research, and also serves as a reference point and hastens the process of fitting models in SE analysis.
----
Many of the developments and features that exist in today’s commercial QCM instruments were pioneered in laboratories with custom-built instruments to meet specific research needs, such as the use of internal reference crystals to separate the effects of a liquid environment from those of a film sample.
----
==Working Principle==
[[File:AT and BT cut.png|340px|thumb|right|Orientation of AT- and BT- cut crystals]]The working principle behind the QCM is based on the piezoelectric effect. The piezoelectric effect is the generation of electric charges by a crystalline material upon subjecting it to stress.[1] An oscillating electric field applied across the device induces an acoustic wave that propagates through the crystal and meets minimum impedance when the device's thickness is a half-integer multiple of the wavelength of the acoustic wave.[2] It is a shear mode device in which the acoustic wave propagates in a direction perpendicular to the crystal surface.[3] Therefore, crystals cut in specific crystal axes have to be used to utilize the shear mode. A resonant oscillation in the crystal is achieved by putting the crystal in an oscillation circuit where the electrical and mechanical oscillations are close to the fundamental frequency of the crystal. Changes to the mass of the crystal would result in a proportional change in its natural frequency according to the Sauerbrey equation[4]

<math>

\Delta m = \frac{C}{n} \Delta f

</math>

 
where <math>\Delta f</math> is the change in resonance frequency, <math>C</math> is the specific sensitivity of the crystal, <math>\Delta m</math> is the mass adsorbed on the active area, and <math>n</math> is the harmonic number. <math>C</math> describes how much material per unit area is required to change the resonant frequency of the crystal by 1Hz. A smaller <math>C</math> value gives a higher mass sensitivity. This value depends on the fundamental resonant frequency of the crystal, and it is defined as 
 
<math>

C = \frac{t_q \rho_q}{f_0}

</math>
 
where <math>t_q</math> is the thickness of the quartz, <math>\rho_q</math> is the density of the quartz plate, and f0 is the fundamental resonant frequency of quartz. With these, we can determine the mass of the deposited material. 
 
Another consideration would be the energy dissipation of the crystal to the surroundings. This is important, especially for viscoelastic films. Viscoelastic films violate the Sauerbrey condition that the bound mass is rigidly attached to the crystal without any slip. Such viscoelastic films dissipate energy via mechanical losses in the flexible mass.
 
----
==Setup==
The typical QCM set-up of piezoelectric quartz crystal microbalance is shown in Figure ().
The oscillator circuit is connected to the power supply and sample stage mount where the piezoelectric quartz crystal is. We can determine the resonance frequency of the quartz crystal using an oscilloscope, frequency counter, or spectrum analyzer.

To determine the feasibility of this QCM project, we built a simple oscillating circuit as a foundation to test if we can detect the resonance frequency of the quartz crystal. This also serves as a time buffer while waiting for the AT-cut quartz to be delivered. Figures () and () show the electrical circuit diagram and its implementation on a breadboard.

As the electrical current generated from the oscillation of the quartz crystal is an alternating current due to the piezoelectric effect, we employ the usage of logic gates called inverters to convert DC to AC for readout. Adding a resistor to the circuit allows for the control of the potential difference across the inverter. In this oscillating circuit, we use a 14-pin integrated circuit and measure the resonant frequency of a CMAC CK q5 crystal oscillator.
[[File:Circuit diagram 1st.png|340px|thumb|left|Circuit Diagram]]
[[File:Typical setup.png|340px|thumb|right|Typical Setup for a QCM measurement]]
[[File:1st setup.jpeg|340px|thumb|right|Experimental Setup]]
 
----
==Measurements==
[[File:1st setup waveform.jpeg|340px|thumb|right|Waveform observed with an oscilloscope using the CMAC CK q5 crystal oscillator]]
[[File:10mhz waveform.jpeg|340px|thumb|right|Waveform observed with an oscilloscope using the AT-cut quartz crystal]]
A DC power supply of 5V is given and an oscilloscope is connected to see the signal's waveform. A frequency counter is connected to the electrical circuit and communicated to my computer via the Arduino Integrated Development Environment. The frequency is measured for 10 seconds 10 times to get an average. Eventually, a resonant frequency of 10.000001Mhz is recorded, which is very close to the 10Mhz value that was provided by the manufacturer.

The waveform seen on the oscilloscope is observed to be periodic and looks like a square-wave oscillation. There seem to be additional peaks periodically formed as well, which could likely come from circuit impedance mismatches. Mismatches in impedance between different components or sections of a circuit can cause signal reflections and distortions, leading to additional peaks in the waveform. We would have to adjust the values of the capacitors and resistors.

Then, we replace the 10Mhz crystal oscillator with the AT-cut crystal. Although we managed to obtain the frequency signal generated by the AT-cut crystal, the surface of the crystal is very sensitive such that waving your hands near the oscillator causes the waveform to change. To make the signal more stable, we construct another circuit design similar to the Colpitts oscillator.[5] One of the advantages of using this layout is that relatively low phase noise can be achieved, making them suitable for applications requiring stable and low-noise oscillation.
 
----
==Second Set-Up==
The circuit design and the actual circuit are shown in Figure (). 2N2222 bipolar junction transistors were used with a combination of capacitors and resistors. The purpose of the transistor is to amplify the voltage across the resonant circuit and stabilize the oscillations through a feedback loop. A DC power supply of 9V is applied across the circuit and an oscilloscope is connected to observe the waveform. Figure () shows the waveform, which seems to be a superposition of a square wave and another periodic signal which could be due to the aforementioned circuit impedance mismatches.
[[File:Circuit diagram 2nd.png|340px|thumb|right|Circuit Diagram for 2nd setup]]
[[File:2nd setup.jpeg|340px|thumb|left|2nd Experimental setup]]
 
We use the Anritsu MS2711D Spectrum Master to look for the resonance frequencies as a cross-reference to the frequency counter measurement. In Figure (), the resonance frequency of the piezoelectric quartz oscillator and its higher-order harmonics are shown. [insert resonance frequency narrow, wide scan of frequency] From the wide scan, we can see that the zeroth-order overtone occurs at approximately 6Mhz, and the higher-order harmonics occur in multiple integers of 6MHz.
[[File:Wide scan.jpeg|340px|thumb|right|Spectral survey scan using the Anritsu MS2711D Spectrum Master]]
[[File:Narrow scan.jpeg|340px|thumb|left|Spectral narrow scan using the Anritsu MS2711D Spectrum Master]]
 
----
==Second Measurement==
The procedure for the frequency counter measurements is the same as that of the 10MHz crystal oscillator. The fundamental resonant frequency is measured to be 5.986804MHz. Using this as the reference resonance frequency, we can now test its effectiveness in mass measurements with the Sauerbrey equation.
[[File:Permanent marker.jpeg|340px|thumb|left|Depiction of how ink was placed on the quartz crystal plate]]
[[File:Ink no signal.jpeg|340px|thumb|right|No spectral signatures from measurement]]
 
[[File:Increase power.jpeg|340px|thumb|right|Increasing DC power supply shows a fundamental mode of resonance]]
Firstly, a permanent marker is used where we dot the center of the quartz crystal shown in Figure (). [insert permanent marker ink] Initially, there was no signal shown in Figure (). [Explain why] However, increasing the DC supply voltage sufficiently allows the fundamental mode to be observed as shown in Figure (). We repeated the frequency counter measurements and found the new resonance frequency to be 5.984613MHz.

To test the mass limit of this setup, a small Blu Tack weighing 2.1 grams is placed on the center of the oscillator. A new oscillator is used so that the dried ink does not interfere with the measurement. The Spectrum Master did not record any spectral features, which suggests that the oscillation of the crystal is too damped to be detected and that the gain is insufficient. Increasing the DC power supply to 18V is inadequate to produce a spectral feature. For safety purposes, this will be the limit that we shall test.
[[File:Blu tack.jpeg|340px|thumb|left|Depiction of how Blu tack was placed on the quartz crystal plate]]
[[File:Blu tack no signal.jpeg|340px|thumb|right|No spectral signatures from measurement]]
 
Based on the Sauerbrey equation, the decrease in resonance frequency of 2191Hz corresponds to an increase in mass of 969 micrograms. This value is derived by using the following:
* thickness of quartz crystal plate <math> t_q = 1 </math> mm
* density of quartz crystal <math> \rho_q = 2648 </math> kg m-3
* fundamental resonance frequency of quartz crystal plate <math> f_0 = 5.986804 </math> MHz

To understand how accurate this measurement is, let us approximate the volume of ink to be a drop of water and calculate how much a drop of water weighs. We assume that the density of the marker ink is approximately similar to water. A drop of water of 0.1ml is approximately 100 micrograms. This shows that the measurement is about an order of magnitude higher than the approximation.

This huge error arises because of the assumptions of using the Sauerbrey equation. The Sauerbrey equation is valid under the following conditions:

*The added mass is small compared to the mass of the crystal
*The added mass is rigidly adsorbed onto the surface of the crystal
*The mass is evenly distributed over the active area of the crystal.

Based on these conditions, the second and third conditions are not fulfilled.
----

==Potential Improvements and Conclusion==
Some better models describe the relationship between frequency change and mass adsorbed where we consider the added mass to be viscoelastic. The Sauerbrey equation fails to describe viscoelastic films on the quartz oscillator as the condition where the added mass is rigidly bound is not adhered to. This model is called the QCM-D, where D refers to the energy dissipation by the film. This technique is prevalent in the fields of lipids, proteins, nanoparticles, etc. [6] However, this requires the use of liquid media. 

To conclude, we managed to detect the quartz crystal oscillation with a simple circuit design. Changes in resonance frequency due to added mass can also be detected, but the margin of error is too large for it to be usable for research purposes. Future improvements to this experiment can be done by adopting energy dissipation within our considerations.
----
==References==
# Meissner A (1927) € Uber piezoelectrische Krystalle bei Hochfrequenz. Z Tech Phys 8:74
# O’Sullivan, C. K., & Guilbault, G. G. (1999). Commercial quartz crystal microbalances – theory and applications. Biosensors and Bioelectronics, 14(8), 663–670.
# Ebersole, R., Miller, J., Moran, J., & Ward, M. (1990). PZ quartz sensors for use in clinical analysis. J. Am. Chem. Soc, 112, 3239.
# Sauerbrey, G. (1959). Verwendung von Schwingquarzen zur Wägung dünner Schichten und zur Mikrowägung. Zeitschrift für Physik, 155(2), 206–222.
# US 1624537, Colpitts, Edwin H., "Oscillation generator", published 1 February 1918, issued 12 April 1927

Quartz Crystal MicroBalance (QCM)

2024-04-23T04:20:31Z

E0309214:

==Abstract==

This project aims to construct a circuit that mimics a quartz crystal microbalance. This can be done via a combination of resistors, capacitors, and a quartz crystal. Testing of the QCM can be done by measuring the fundamental frequency of the quartz crystal oscillator, followed by adding a test mass such as the ink of a permanent marker on the oscillator to determine the frequency change. The original intention of building this QCM is to investigate if it is possible to measure the mass of thin films ex-situ. However, due to experimental and time constraints, we shall focus on building a circuit that can detect mass changes on the order of micrograms.
----
==Team members==
Tan Jhoon Yong
----
==Idea==
Quartz crystal microbalance (QCM) is widely used to measure mass changes to substances involved in physical and chemical processes. In my field of research, we often have to find out the thicknesses of thin films as part of the process of characterizing the samples. There are a few methods that are usually employed in my research to measure thin films' thicknesses such as observing the reflection high-energy electron diffraction (RHEED) oscillations during pulsed-laser deposition (PLD), atomic force microscopy (AFM), X-ray diffraction (XRD) (if the sample is ordered), and fitting of data from spectroscopic ellipsometry (SE). These techniques usually expend a significant amount of time but provide an accurate value to the thickness measurements. Creating a QCM that can work ex-situ will assist my research, and also serves as a reference point and hastens the process of fitting models in SE analysis.
----
Many of the developments and features that exist in today’s commercial QCM instruments were pioneered in laboratories with custom-built instruments to meet specific research needs, such as the use of internal reference crystals to separate the effects of a liquid environment from those of a film sample.
----
==Working Principle==
[[File:AT and BT cut.png|340px|thumb|right|Orientation of AT- and BT- cut crystals]]The working principle behind the QCM is based on the piezoelectric effect. The piezoelectric effect is the generation of electric charges by a crystalline material upon subjecting it to stress.[1] An oscillating electric field applied across the device induces an acoustic wave that propagates through the crystal and meets minimum impedance when the device's thickness is a half-integer multiple of the wavelength of the acoustic wave.[2] It is a shear mode device in which the acoustic wave propagates in a direction perpendicular to the crystal surface.[3] Therefore, crystals cut in specific crystal axes have to be used to utilize the shear mode. A resonant oscillation in the crystal is achieved by putting the crystal in an oscillation circuit where the electrical and mechanical oscillations are close to the fundamental frequency of the crystal. Changes to the mass of the crystal would result in a proportional change in its natural frequency according to the Sauerbrey equation[4]

<math>

\Delta m = \frac{C}{n} \Delta f

</math>

 
where <math>\Delta f</math> is the change in resonance frequency, <math>C</math> is the specific sensitivity of the crystal, <math>\Delta m</math> is the mass adsorbed on the active area, and <math>n</math> is the harmonic number. <math>C</math> describes how much material per unit area is required to change the resonant frequency of the crystal by 1Hz. A smaller <math>C</math> value gives a higher mass sensitivity. This value depends on the fundamental resonant frequency of the crystal, and it is defined as 
 
<math>

C = \frac{t_q \rho_q}{f_0}

</math>
 
where <math>t_q</math> is the thickness of the quartz, <math>\rho_q</math> is the density of the quartz plate, and f0 is the fundamental resonant frequency of quartz. With these, we can determine the mass of the deposited material. 
 
Another consideration would be the energy dissipation of the crystal to the surroundings. This is important, especially for viscoelastic films. Viscoelastic films violate the Sauerbrey condition that the bound mass is rigidly attached to the crystal without any slip. Such viscoelastic films dissipate energy via mechanical losses in the flexible mass.
 
----
==Setup==
The typical QCM set-up of piezoelectric quartz crystal microbalance is shown in Figure ().
The oscillator circuit is connected to the power supply and sample stage mount where the piezoelectric quartz crystal is. We can determine the resonance frequency of the quartz crystal using an oscilloscope, frequency counter, or spectrum analyzer.

To determine the feasibility of this QCM project, we built a simple oscillating circuit as a foundation to test if we can detect the resonance frequency of the quartz crystal. This also serves as a time buffer while waiting for the AT-cut quartz to be delivered. Figures () and () show the electrical circuit diagram and its implementation on a breadboard.

As the electrical current generated from the oscillation of the quartz crystal is an alternating current due to the piezoelectric effect, we employ the usage of logic gates called inverters to convert DC to AC for readout. Adding a resistor to the circuit allows for the control of the potential difference across the inverter. In this oscillating circuit, we use a 14-pin integrated circuit and measure the resonant frequency of a CMAC CK q5 crystal oscillator.
[[File:Circuit diagram 1st.png|340px|thumb|left|Circuit Diagram]]
[[File:Typical setup.png|340px|thumb|right|Typical Setup for a QCM measurement]]
[[File:1st setup.jpeg|340px|thumb|right|Experimental Setup]]
 
----
==Measurements==
[[File:1st setup waveform.jpeg|340px|thumb|right|Waveform observed with an oscilloscope using the CMAC CK q5 crystal oscillator]]
[[File:10mhz waveform.jpeg|340px|thumb|right|Waveform observed with an oscilloscope using the AT-cut quartz crystal]]
A DC power supply of 5V is given and an oscilloscope is connected to see the signal's waveform. A frequency counter is connected to the electrical circuit and communicated to my computer via the Arduino Integrated Development Environment. The frequency is measured for 10 seconds 10 times to get an average. Eventually, a resonant frequency of 10.000001Mhz is recorded, which is very close to the 10Mhz value that was provided by the manufacturer.

The waveform seen on the oscilloscope is observed to be periodic and looks like a square-wave oscillation. There seem to be additional peaks periodically formed as well, which could likely come from circuit impedance mismatches. Mismatches in impedance between different components or sections of a circuit can cause signal reflections and distortions, leading to additional peaks in the waveform. We would have to adjust the values of the capacitors and resistors.

Then, we replace the 10Mhz crystal oscillator with the AT-cut crystal. Although we managed to obtain the frequency signal generated by the AT-cut crystal, the surface of the crystal is very sensitive such that waving your hands near the oscillator causes the waveform to change. To make the signal more stable, we construct another circuit design similar to the Colpitts oscillator.[5] One of the advantages of using this layout is that relatively low phase noise can be achieved, making them suitable for applications requiring stable and low-noise oscillation.
 
----
==Second Set-Up==
The circuit design and the actual circuit are shown in Figure (). 2N2222 bipolar junction transistors were used with a combination of capacitors and resistors. The purpose of the transistor is to amplify the voltage across the resonant circuit and stabilize the oscillations through a feedback loop. A DC power supply of 9V is applied across the circuit and an oscilloscope is connected to observe the waveform. Figure () shows the waveform, which seems to be a superposition of a square wave and another periodic signal which could be due to the aforementioned circuit impedance mismatches.
[[File:Circuit diagram 2nd.png|340px|thumb|right|Circuit Diagram for 2nd setup]]
[[File:2nd setup.jpeg|340px|thumb|left|2nd Experimental setup]]
 
We use the Anritsu MS2711D Spectrum Master to look for the resonance frequencies as a cross-reference to the frequency counter measurement. In Figure (), the resonance frequency of the piezoelectric quartz oscillator and its higher-order harmonics are shown. [insert resonance frequency narrow, wide scan of frequency] From the wide scan, we can see that the zeroth-order overtone occurs at approximately 6Mhz, and the higher-order harmonics occur in multiple integers of 6MHz.
[[File:Wide scan.jpeg|340px|thumb|right|Spectral survey scan using the Anritsu MS2711D Spectrum Master]]
[[File:Narrow scan.jpeg|340px|thumb|left|Spectral narrow scan using the Anritsu MS2711D Spectrum Master]]
 
----
==Second Measurement==
The procedure for the frequency counter measurements is the same as that of the 10MHz crystal oscillator. The fundamental resonant frequency is measured to be 5.986804MHz. Using this as the reference resonance frequency, we can now test its effectiveness in mass measurements with the Sauerbrey equation. 

Firstly, a permanent marker is used where we dot the center of the quartz crystal shown in Figure (). [insert permanent marker ink] Initially, there was no signal shown in Figure (). [Explain why, insert no spectral signature for ink]However, increasing the DC supply voltage sufficiently allows the fundamental mode to be observed as shown in Figure (). [insert increase dc power supply] We repeated the frequency counter measurements and found the new resonance frequency to be 5.984613MHz.

To test the mass limit of this setup, a small Blu Tack weighing 2.1 grams is placed on the center of the oscillator. A new oscillator is used so that the dried ink does not interfere with the measurement. The Spectrum Master did not record any spectral features, which suggests that the oscillation of the crystal is too damped to be detected and that the gain is insufficient. [insert no spectral signature for blu tack] Increasing the DC power supply to 18V is inadequate to produce a spectral feature. For safety purposes, this will be the limit that we shall test.

Based on the Sauerbrey equation, the decrease in resonance frequency of 2191Hz corresponds to an increase in mass of 969 micrograms. This value is derived by using the following:
* thickness of quartz crystal plate <math> t_q = 1 </math> mm
* density of quartz crystal <math> \rho_q = 2648 </math> kg m-3
* fundamental resonance frequency of quartz crystal plate <math> f_0 = 5.986804 </math> MHz

To understand how accurate this measurement is, let us approximate the volume of ink to be a drop of water and calculate how much a drop of water weighs. We assume that the density of the marker ink is approximately similar to water. A drop of water of 0.1ml is approximately 100 micrograms. This shows that the measurement is about an order of magnitude higher than the approximation.

This huge error arises because of the assumptions of using the Sauerbrey equation. The Sauerbrey equation is valid under the following conditions:

*The added mass is small compared to the mass of the crystal
*The added mass is rigidly adsorbed onto the surface of the crystal
*The mass is evenly distributed over the active area of the crystal.

Based on these conditions, the second and third conditions are not fulfilled.
----
==Potential Improvements and Conclusion==
Some better models describe the relationship between frequency change and mass adsorbed where we consider the added mass to be viscoelastic. The Sauerbrey equation fails to describe viscoelastic films on the quartz oscillator as the condition where the added mass is rigidly bound is not adhered to. This model is called the QCM-D, where D refers to the energy dissipation by the film. This technique is prevalent in the fields of lipids, proteins, nanoparticles, etc. [6] However, this requires the use of liquid media. 

To conclude, we managed to detect the quartz crystal oscillation with a simple circuit design. Changes in resonance frequency due to added mass can also be detected, but the margin of error is too large for it to be usable for research purposes. Future improvements to this experiment can be done by adopting energy dissipation within our considerations.
----
==References==
# Meissner A (1927) € Uber piezoelectrische Krystalle bei Hochfrequenz. Z Tech Phys 8:74
# O’Sullivan, C. K., & Guilbault, G. G. (1999). Commercial quartz crystal microbalances – theory and applications. Biosensors and Bioelectronics, 14(8), 663–670.
# Ebersole, R., Miller, J., Moran, J., & Ward, M. (1990). PZ quartz sensors for use in clinical analysis. J. Am. Chem. Soc, 112, 3239.
# Sauerbrey, G. (1959). Verwendung von Schwingquarzen zur Wägung dünner Schichten und zur Mikrowägung. Zeitschrift für Physik, 155(2), 206–222.
# US 1624537, Colpitts, Edwin H., "Oscillation generator", published 1 February 1918, issued 12 April 1927

Quartz Crystal MicroBalance (QCM)

2024-04-23T04:05:03Z

E0309214:

==Abstract==

This project aims to construct a circuit that mimics a quartz crystal microbalance. This can be done via a combination of resistors, capacitors, and a quartz crystal. Testing of the QCM can be done by measuring the fundamental frequency of the quartz crystal oscillator, followed by adding a test mass such as the ink of a permanent marker on the oscillator to determine the frequency change. The original intention of building this QCM is to investigate if it is possible to measure the mass of thin films ex-situ. However, due to experimental and time constraints, we shall focus on building a circuit that can detect mass changes on the order of micrograms.
----
==Team members==
Tan Jhoon Yong
----
==Idea==
Quartz crystal microbalance (QCM) is widely used to measure mass changes to substances involved in physical and chemical processes. In my field of research, we often have to find out the thicknesses of thin films as part of the process of characterizing the samples. There are a few methods that are usually employed in my research to measure thin films' thicknesses such as observing the reflection high-energy electron diffraction (RHEED) oscillations during pulsed-laser deposition (PLD), atomic force microscopy (AFM), X-ray diffraction (XRD) (if the sample is ordered), and fitting of data from spectroscopic ellipsometry (SE). These techniques usually expend a significant amount of time but provide an accurate value to the thickness measurements. Creating a QCM that can work ex-situ will assist my research, and also serves as a reference point and hastens the process of fitting models in SE analysis.
----
Many of the developments and features that exist in today’s commercial QCM instruments were pioneered in laboratories with custom-built instruments to meet specific research needs, such as the use of internal reference crystals to separate the effects of a liquid environment from those of a film sample.
----
==Working Principle==
[[File:AT and BT cut.png|340px|thumb|right|Orientation of AT- and BT- cut crystals]]The working principle behind the QCM is based on the piezoelectric effect. The piezoelectric effect is the generation of electric charges by a crystalline material upon subjecting it to stress.[1] An oscillating electric field applied across the device induces an acoustic wave that propagates through the crystal and meets minimum impedance when the device's thickness is a half-integer multiple of the wavelength of the acoustic wave.[2] It is a shear mode device in which the acoustic wave propagates in a direction perpendicular to the crystal surface.[3] Therefore, crystals cut in specific crystal axes have to be used to utilize the shear mode. A resonant oscillation in the crystal is achieved by putting the crystal in an oscillation circuit where the electrical and mechanical oscillations are close to the fundamental frequency of the crystal. Changes to the mass of the crystal would result in a proportional change in its natural frequency according to the Sauerbrey equation[4]

<math>

\Delta m = \frac{C}{n} \Delta f

</math>

 
where <math>\Delta f</math> is the change in resonance frequency, <math>C</math> is the specific sensitivity of the crystal, <math>\Delta m</math> is the mass adsorbed on the active area, and <math>n</math> is the harmonic number. <math>C</math> describes how much material per unit area is required to change the resonant frequency of the crystal by 1Hz. A smaller <math>C</math> value gives a higher mass sensitivity. This value depends on the fundamental resonant frequency of the crystal, and it is defined as 
 
<math>

C = \frac{t_q \rho_q}{f_0}

</math>
 
where <math>t_q</math> is the thickness of the quartz, <math>\rho_q</math> is the density of the quartz plate, and f0 is the fundamental resonant frequency of quartz. With these, we can determine the mass of the deposited material. 
 
Another consideration would be the energy dissipation of the crystal to the surroundings. This is important, especially for viscoelastic films. Viscoelastic films violate the Sauerbrey condition that the bound mass is rigidly attached to the crystal without any slip. Such viscoelastic films dissipate energy via mechanical losses in the flexible mass.
 
----
==Setup==
The typical QCM set-up of piezoelectric quartz crystal microbalance is shown in Figure ().
The oscillator circuit is connected to the power supply and sample stage mount where the piezoelectric quartz crystal is. We can determine the resonance frequency of the quartz crystal using an oscilloscope, frequency counter, or spectrum analyzer.

To determine the feasibility of this QCM project, we built a simple oscillating circuit as a foundation to test if we can detect the resonance frequency of the quartz crystal. This also serves as a time buffer while waiting for the AT-cut quartz to be delivered. Figures () and () show the electrical circuit diagram and its implementation on a breadboard.

As the electrical current generated from the oscillation of the quartz crystal is an alternating current due to the piezoelectric effect, we employ the usage of logic gates called inverters to convert DC to AC for readout. Adding a resistor to the circuit allows for the control of the potential difference across the inverter. In this oscillating circuit, we use a 14-pin integrated circuit and measure the resonant frequency of a CMAC CK q5 crystal oscillator.
[[File:Circuit diagram 1st.png|340px|thumb|left|Circuit Diagram]]
[[File:Typical setup.png|340px|thumb|right|Typical Setup for a QCM measurement]]
[[File:1st setup.jpeg|340px|thumb|right|Experimental Setup]]
 
----
==Measurements==
[[File:1st setup waveform.jpeg|340px|thumb|right|Waveform observed with an oscilloscope using the CMAC CK q5 crystal oscillator]]
[[File:10mhz waveform.jpeg|340px|thumb|right|Waveform observed with an oscilloscope using the AT-cut quartz crystal]]
A DC power supply of 5V is given and an oscilloscope is connected to see the signal's waveform. A frequency counter is connected to the electrical circuit and communicated to my computer via the Arduino Integrated Development Environment. The frequency is measured for 10 seconds 10 times to get an average. Eventually, a resonant frequency of 10.000001Mhz is recorded, which is very close to the 10Mhz value that was provided by the manufacturer.

The waveform seen on the oscilloscope is observed to be periodic and looks like a square-wave oscillation. There seem to be additional peaks periodically formed as well, which could likely come from circuit impedance mismatches. Mismatches in impedance between different components or sections of a circuit can cause signal reflections and distortions, leading to additional peaks in the waveform. We would have to adjust the values of the capacitors and resistors.

Then, we replace the 10Mhz crystal oscillator with the AT-cut crystal. Although we managed to obtain the frequency signal generated by the AT-cut crystal, the surface of the crystal is very sensitive such that waving your hands near the oscillator causes the waveform to change. To make the signal more stable, we construct another circuit design similar to the Colpitts oscillator.[5] One of the advantages of using this layout is that relatively low phase noise can be achieved, making them suitable for applications requiring stable and low-noise oscillation.
 
----
==Second Set-Up==
[[File:Circuit diagram 2nd.png|340px|thumb|right|Circuit Diagram for 2nd setup]]
[[File:2nd setup.jpeg|340px|thumb|right|2nd Experimental setup]]
The circuit design and the actual circuit are shown in Figure (). 2N2222 bipolar junction transistors were used with a combination of capacitors and resistors. The purpose of the transistor is to amplify the voltage across the resonant circuit and stabilize the oscillations through a feedback loop.

A DC power supply of 9V is applied across the circuit and an oscilloscope is connected to observe the waveform. Figure () shows the waveform, which seems to be a superposition of square wave and another periodic signal which could be due to the aforementioned circuit impedance mismatches.

We use the Anritsu MS2711D Spectrum Master to look for the resonance frequencies as a cross-reference to the frequency counter measurement. In Figure (), the resonance frequency of the piezoelectric quartz oscillator and its higher-order harmonics are shown. [insert resonance frequency narrow, wide scan of frequency] From the wide scan, we can see that the zeroth-order overtone occurs at around approximately 6Mhz, and the higher-order harmonics occur in multiple integers of 6MHz.
[[File:Wide scan.jpeg|340px|thumb|left|Spectral survey scan using the Anritsu MS2711D Spectrum Master]]
[[File:Narrow scan.jpeg|340px|thumb|right|Spectral narrow scan using the Anritsu MS2711D Spectrum Master]]
 
----
==Second Measurement==
The procedure for the frequency counter measurements is the same as that of the 10MHz crystal oscillator. The fundamental resonant frequency is measured to be 5.986804MHz. Using this as the reference resonance frequency, we can now test its effectiveness in mass measurements with the Sauerbrey equation. 

Firstly, a permanent marker is used where we dot the center of the quartz crystal shown in Figure (). [insert permanent marker ink] Initially, there was no signal shown in Figure (). [Explain why, insert no spectral signature for ink]However, increasing the DC supply voltage sufficiently allows the fundamental mode to be observed as shown in Figure (). [insert increase dc power supply] We repeated the frequency counter measurements and found the new resonance frequency to be 5.984613MHz.

To test the mass limit of this setup, a small Blu Tack weighing 2.1 grams is placed on the center of the oscillator. A new oscillator is used so that the dried ink does not interfere with the measurement. The Spectrum Master did not record any spectral features, which suggests that the oscillation of the crystal is too damped to be detected and that the gain is insufficient. [insert no spectral signature for blu tack] Increasing the DC power supply to 18V is inadequate to produce a spectral feature. For safety purposes, this will be the limit that we shall test.

Based on the Sauerbrey equation, the decrease in resonance frequency of 2191Hz corresponds to an increase in mass of 969 micrograms. This value is derived by using the following:
* thickness of quartz crystal plate <math> t_q = 1 </math> mm
* density of quartz crystal <math> \rho_q = 2648 </math> kg m-3
* fundamental resonance frequency of quartz crystal plate <math> f_0 = 5.986804 </math> MHz

To understand how accurate this measurement is, let us approximate the volume of ink to be a drop of water and calculate how much a drop of water weighs. We assume that the density of the marker ink is approximately similar to water. A drop of water of 0.1ml is approximately 100 micrograms. This shows that the measurement is about an order of magnitude higher than the approximation.

This huge error arises because of the assumptions of using the Sauerbrey equation. The Sauerbrey equation is valid under the following conditions:

*The added mass is small compared to the mass of the crystal
*The added mass is rigidly adsorbed onto the surface of the crystal
*The mass is evenly distributed over the active area of the crystal.

Based on these conditions, the second and third conditions are not fulfilled.
----
==Potential Improvements and Conclusion==
Some better models describe the relationship between frequency change and mass adsorbed where we consider the added mass to be viscoelastic. The Sauerbrey equation fails to describe viscoelastic films on the quartz oscillator as the condition where the added mass is rigidly bound is not adhered to. This model is called the QCM-D, where D refers to the energy dissipation by the film. This technique is prevalent in the fields of lipids, proteins, nanoparticles, etc. [6] However, this requires the use of liquid media. 

To conclude, we managed to detect the quartz crystal oscillation with a simple circuit design. Changes in resonance frequency due to added mass can also be detected, but the margin of error is too large for it to be usable for research purposes. Future improvements to this experiment can be done by adopting energy dissipation within our considerations.
----
==References==
# Meissner A (1927) € Uber piezoelectrische Krystalle bei Hochfrequenz. Z Tech Phys 8:74
# O’Sullivan, C. K., & Guilbault, G. G. (1999). Commercial quartz crystal microbalances – theory and applications. Biosensors and Bioelectronics, 14(8), 663–670.
# Ebersole, R., Miller, J., Moran, J., & Ward, M. (1990). PZ quartz sensors for use in clinical analysis. J. Am. Chem. Soc, 112, 3239.
# Sauerbrey, G. (1959). Verwendung von Schwingquarzen zur Wägung dünner Schichten und zur Mikrowägung. Zeitschrift für Physik, 155(2), 206–222.
# US 1624537, Colpitts, Edwin H., "Oscillation generator", published 1 February 1918, issued 12 April 1927

File:10mhz waveform.jpeg

2024-04-23T03:57:53Z

E0309214:

Quartz Crystal MicroBalance (QCM)

2024-04-23T03:44:20Z

E0309214:

==Abstract==

This project aims to construct a circuit that mimics a quartz crystal microbalance. This can be done via a combination of resistors, capacitors, and a quartz crystal. Testing of the QCM can be done by measuring the fundamental frequency of the quartz crystal oscillator, followed by adding a test mass such as the ink of a permanent marker on the oscillator to determine the frequency change. The original intention of building this QCM is to investigate if it is possible to measure the mass of thin films ex-situ. However, due to experimental and time constraints, we shall focus on building a circuit that can detect mass changes on the order of micrograms.
----
==Team members==
Tan Jhoon Yong
----
==Idea==
Quartz crystal microbalance (QCM) is widely used to measure mass changes to substances involved in physical and chemical processes. In my field of research, we often have to find out the thicknesses of thin films as part of the process of characterizing the samples. There are a few methods that are usually employed in my research to measure thin films' thicknesses such as observing the reflection high-energy electron diffraction (RHEED) oscillations during pulsed-laser deposition (PLD), atomic force microscopy (AFM), X-ray diffraction (XRD) (if the sample is ordered), and fitting of data from spectroscopic ellipsometry (SE). These techniques usually expend a significant amount of time but provide an accurate value to the thickness measurements. Creating a QCM that can work ex-situ will assist my research, and also serves as a reference point and hastens the process of fitting models in SE analysis.
----
Many of the developments and features that exist in today’s commercial QCM instruments were pioneered in laboratories with custom-built instruments to meet specific research needs, such as the use of internal reference crystals to separate the effects of a liquid environment from those of a film sample.
----
==Working Principle==
The working principle behind the QCM is based on the piezoelectric effect. The piezoelectric effect is the generation of electric charges by a crystalline material upon subjecting it to stress.[1] An oscillating electric field applied across the device induces an acoustic wave that propagates through the crystal and meets minimum impedance when the device's thickness is a half-integer multiple of the wavelength of the acoustic wave.[2] It is a shear mode device in which the acoustic wave propagates in a direction perpendicular to the crystal surface.[3] Therefore, crystals cut in specific crystal axes have to be used to utilize the shear mode.

A resonant oscillation in the crystal is achieved by putting the crystal in an oscillation circuit where the electrical and mechanical oscillations are close to the fundamental frequency of the crystal. Changes to the mass of the crystal would result in a proportional change in its natural frequency according to the Sauerbrey equation[4] 
 
<math>

\Delta m = \frac{C}{n} \Delta f

</math>

 
where <math>\Delta f</math> is the change in resonance frequency, <math>C</math> is the specific sensitivity of the crystal, <math>\Delta m</math> is the mass adsorbed on the active area, and <math>n</math> is the harmonic number. <math>C</math> describes how much material per unit area is required to change the resonant frequency of the crystal by 1Hz. A smaller <math>C</math> value gives a higher mass sensitivity. This value depends on the fundamental resonant frequency of the crystal, and it is defined as 
 
<math>

C = \frac{t_q \rho_q}{f_0}

</math>
 
where <math>t_q</math> is the thickness of the quartz, <math>\rho_q</math> is the density of the quartz plate, and f0 is the fundamental resonant frequency of quartz. With these, we can determine the mass of the deposited material. 
 
Another consideration would be the energy dissipation of the crystal to the surroundings. This is important, especially for viscoelastic films. Viscoelastic films violate the Sauerbrey condition that the bound mass is rigidly attached to the crystal without any slip. Such viscoelastic films dissipate energy via mechanical losses in the flexible mass.
[[File:AT and BT cut.png|200px|thumb|left|Orientation of AT- and BT- cut crystals]]
 
----
==Setup==
The typical QCM set-up of piezoelectric quartz crystal microbalance is shown in Figure ().
[[File:Typical setup.png|center|500px|thumb|Typical Setup for a QCM measurement]]
 
The oscillator circuit is connected to the power supply and sample stage mount where the piezoelectric quartz crystal is. We can determine the resonance frequency of the quartz crystal using an oscilloscope, frequency counter, or spectrum analyzer. To determine the feasibility of this QCM project, we built a simple oscillating circuit as a foundation to test if we can detect the resonance frequency of the quartz crystal. This also serves as a time buffer while waiting for the AT-cut quartz to be delivered. Figures () and () shows the electrical circuit diagram and its implementation on a breadboard. As the electrical current generated from the oscillation of the quartz crystal is an alternating current due to the piezoelectric effect, we employ the usage of logic gates called inverters to convert DC to AC for readout. Adding a resistor to the circuit allows for the control of the potential difference across the inverter. In this oscillating circuit, we use a 14-pin integrated circuit and measure the resonant frequency of a CMAC CK q5 crystal oscillator.
[[File:Circuit diagram 1st.png|340px|thumb|left|Circuit Diagram]][[File:1st setup.jpeg|340px|thumb|right|Experimental Setup]]
----
==Measurements==
A DC power supply of 5V is given and an oscilloscope is connected to see the signal's waveform. A frequency counter is connected to the electrical circuit and communicated to my computer via the Arduino Integrated Development Environment. The frequency is measured for 10 seconds 10 times to get an average. Eventually, a resonant frequency of 10.000001Mhz is recorded, which is very close to the 10Mhz value that was provided by the manufacturer. The waveform seen on the oscilloscope is observed to be periodic and looks like a square-wave oscillation. [picture is waveform of first set up with 10Mhz] There seem to be additional peaks periodically formed as well, which could likely come from circuit impedance mismatches. Mismatches in impedance between different components or sections of a circuit can cause signal reflections and distortions, leading to additional peaks in the waveform. We would have to adjust the values of the capacitors and resistors.
 
Then, we replace the 10Mhz crystal oscillator with the AT-cut crystal. [picture is waveform of first set up] Although we managed to obtain the frequency signal generated by the AT-cut crystal, the surface of the crystal is very sensitive such that waving your hands near the oscillator causes the waveform to change. To make the signal more stable, we construct another circuit design similar to the Colpitts oscillator.[5] One of the advantages of using this layout is that relatively low phase noise can be achieved, making them suitable for applications requiring stable and low-noise oscillation.
----
==Second Set-Up==
The circuit design and the actual circuit is shown in Figure (). 2N2222 bipolar junction transistors were used with a combination of capacitors and resistors. The purpose of the transistor is to amplify the voltage across the resonant circuit and stabilise the oscillations through a feedback loop. 
A DC power supply of 9V is applied across the circuit and an oscilloscope is connected to observe the waveform. Figure () shows the waveform, which seems to be a superposition of square wave and another periodic signal which could be due to the aforementioned circuit impedance mismatches. [insert second set up] We use the Anritsu MS2711D Spectrum Master to look for the resonance frequencies as a cross-reference to the frequency counter measurement. In Figure (), the resonance frequency of the piezoelectric quartz oscillator and its higher-order harmonics are shown. [insert resonance frequency narrow, wide scan of frequency] From the wide scan, we can see that the zeroth-order overtone occurs at around approximately 6Mhz, and the higher-order harmonics occur in multiple integers of 6MHz.
----
==Second Measurement==
The procedure for the frequency counter measurements is the same as that of the 10MHz crystal oscillator. The fundamental resonant frequency is measured to be 5.986804MHz. Using this as the reference resonance frequency, we can now test its effectiveness in mass measurements with the Sauerbrey equation. 

Firstly, a permanent marker is used where we dot the center of the quartz crystal shown in Figure (). [insert permanent marker ink] Initially, there was no signal shown in Figure (). [Explain why, insert no spectral signature for ink]However, increasing the DC supply voltage sufficiently allows the fundamental mode to be observed as shown in Figure (). [insert increase dc power supply] We repeated the frequency counter measurements and found the new resonance frequency to be 5.984613MHz.

To test the mass limit of this setup, a small Blu Tack weighing 2.1 grams is placed on the center of the oscillator. A new oscillator is used so that the dried ink does not interfere with the measurement. The Spectrum Master did not record any spectral features, which suggests that the oscillation of the crystal is too damped to be detected and that the gain is insufficient. [insert no spectral signature for blu tack] Increasing the DC power supply to 18V is inadequate to produce a spectral feature. For safety purposes, this will be the limit that we shall test.

Based on the Sauerbrey equation, the decrease in resonance frequency of 2191Hz corresponds to an increase in mass of 969 micrograms. This value is derived by using the following:
* thickness of quartz crystal plate <math> t_q = 1 </math> mm
* density of quartz crystal <math> \rho_q = 2648 </math> kg m-3
* fundamental resonance frequency of quartz crystal plate <math> f_0 = 5.986804 </math> MHz

To understand how accurate this measurement is, let us approximate the volume of ink to be a drop of water and calculate how much a drop of water weighs. We assume that the density of the marker ink is approximately similar to water. A drop of water of 0.1ml is approximately 100 micrograms. This shows that the measurement is about an order of magnitude higher than the approximation.

This huge error arises because of the assumptions of using the Sauerbrey equation. The Sauerbrey equation is valid under the following conditions:

*The added mass is small compared to the mass of the crystal
*The added mass is rigidly adsorbed onto the surface of the crystal
*The mass is evenly distributed over the active area of the crystal.

Based on these conditions, the second and third conditions are not fulfilled.
----
==Potential Improvements and Conclusion==
Some better models describe the relationship between frequency change and mass adsorbed where we consider the added mass to be viscoelastic. The Sauerbrey equation fails to describe viscoelastic films on the quartz oscillator as the condition where the added mass is rigidly bound is not adhered to. This model is called the QCM-D, where D refers to the energy dissipation by the film. This technique is prevalent in the fields of lipids, proteins, nanoparticles, etc. [6] However, this requires the use of liquid media. 

To conclude, we managed to detect the quartz crystal oscillation with a simple circuit design. Changes in resonance frequency due to added mass can also be detected, but the margin of error is too large for it to be usable for research purposes. Future improvements to this experiment can be done by adopting energy dissipation within our considerations.
----
==References==
# Meissner A (1927) € Uber piezoelectrische Krystalle bei Hochfrequenz. Z Tech Phys 8:74
# O’Sullivan, C. K., & Guilbault, G. G. (1999). Commercial quartz crystal microbalances – theory and applications. Biosensors and Bioelectronics, 14(8), 663–670.
# Ebersole, R., Miller, J., Moran, J., & Ward, M. (1990). PZ quartz sensors for use in clinical analysis. J. Am. Chem. Soc, 112, 3239.
# Sauerbrey, G. (1959). Verwendung von Schwingquarzen zur Wägung dünner Schichten und zur Mikrowägung. Zeitschrift für Physik, 155(2), 206–222.
# US 1624537, Colpitts, Edwin H., "Oscillation generator", published 1 February 1918, issued 12 April 1927

Quartz Crystal MicroBalance (QCM)

2024-04-23T03:39:33Z

E0309214: /* Setup */

==Abstract==

This project aims to construct a circuit that mimics a quartz crystal microbalance. This can be done via a combination of resistors, capacitors, and a quartz crystal. Testing of the QCM can be done by measuring the fundamental frequency of the quartz crystal oscillator, followed by adding a test mass such as the ink of a permanent marker on the oscillator to determine the frequency change. The original intention of building this QCM is to investigate if it is possible to measure the mass of thin films ex-situ. However, due to experimental and time constraints, we shall focus on building a circuit that can detect mass changes on the order of micrograms.

==Team members==
Tan Jhoon Yong
==Idea==
Quartz crystal microbalance (QCM) is widely used to measure mass changes to substances involved in physical and chemical processes. In my field of research, we often have to find out the thicknesses of thin films as part of the process of characterizing the samples. There are a few methods that are usually employed in my research to measure thin films' thicknesses such as observing the reflection high-energy electron diffraction (RHEED) oscillations during pulsed-laser deposition (PLD), atomic force microscopy (AFM), X-ray diffraction (XRD) (if the sample is ordered), and fitting of data from spectroscopic ellipsometry (SE). These techniques usually expend a significant amount of time but provide an accurate value to the thickness measurements. Creating a QCM that can work ex-situ will assist my research, and also serves as a reference point and hastens the process of fitting models in SE analysis.

Many of the developments and features that exist in today’s commercial QCM instruments were pioneered in laboratories with custom-built instruments to meet specific research needs, such as the use of internal reference crystals to separate the effects of a liquid environment from those of a film sample.

==Working Principle==
The working principle behind the QCM is based on the piezoelectric effect. The piezoelectric effect is the generation of electric charges by a crystalline material upon subjecting it to stress.[1] An oscillating electric field applied across the device induces an acoustic wave that propagates through the crystal and meets minimum impedance when the device's thickness is a half-integer multiple of the wavelength of the acoustic wave.[2] It is a shear mode device in which the acoustic wave propagates in a direction perpendicular to the crystal surface.[3] Therefore, crystals cut in specific crystal axes have to be used to utilize the shear mode.

A resonant oscillation in the crystal is achieved by putting the crystal in an oscillation circuit where the electrical and mechanical oscillations are close to the fundamental frequency of the crystal. Changes to the mass of the crystal would result in a proportional change in its natural frequency according to the Sauerbrey equation[4] 
 
<math>

\Delta m = \frac{C}{n} \Delta f

</math>

 
where <math>\Delta f</math> is the change in resonance frequency, <math>C</math> is the specific sensitivity of the crystal, <math>\Delta m</math> is the mass adsorbed on the active area, and <math>n</math> is the harmonic number. <math>C</math> describes how much material per unit area is required to change the resonant frequency of the crystal by 1Hz. A smaller <math>C</math> value gives a higher mass sensitivity. This value depends on the fundamental resonant frequency of the crystal, and it is defined as 
 
<math>

C = \frac{t_q \rho_q}{f_0}

</math>
 
where <math>t_q</math> is the thickness of the quartz, <math>\rho_q</math> is the density of the quartz plate, and f0 is the fundamental resonant frequency of quartz. With these, we can determine the mass of the deposited material. 
 
Another consideration would be the energy dissipation of the crystal to the surroundings. This is important, especially for viscoelastic films. Viscoelastic films violate the Sauerbrey condition that the bound mass is rigidly attached to the crystal without any slip. Such viscoelastic films dissipate energy via mechanical losses in the flexible mass.
[[File:AT and BT cut.png|200px|thumb|left|Orientation of AT- and BT- cut crystals]]
 
==Setup==
The typical QCM set-up of piezoelectric quartz crystal microbalance is shown in Figure ().
[[File:Typical setup.png|center|500px|thumb|Typical Setup for a QCM measurement]]
 
The oscillator circuit is connected to the power supply and sample stage mount where the piezoelectric quartz crystal is. We can determine the resonance frequency of the quartz crystal using an oscilloscope, frequency counter, or spectrum analyzer. To determine the feasibility of this QCM project, we built a simple oscillating circuit as a foundation to test if we can detect the resonance frequency of the quartz crystal. This also serves as a time buffer while waiting for the AT-cut quartz to be delivered. Figures () and () shows the electrical circuit diagram and its implementation on a breadboard. As the electrical current generated from the oscillation of the quartz crystal is an alternating current due to the piezoelectric effect, we employ the usage of logic gates called inverters to convert DC to AC for readout. Adding a resistor to the circuit allows for the control of the potential difference across the inverter. In this oscillating circuit, we use a 14-pin integrated circuit and measure the resonant frequency of a CMAC CK q5 crystal oscillator.
[[File:Circuit diagram 1st.png|340px|thumb|left|Circuit Diagram]][[File:1st setup.jpeg|340px|thumb|right|Experimental Setup]]

==Measurements==
A DC power supply of 5V is given and an oscilloscope is connected to see the signal's waveform. A frequency counter is connected to the electrical circuit and communicated to my computer via the Arduino Integrated Development Environment. The frequency is measured for 10 seconds 10 times to get an average. Eventually, a resonant frequency of 10.000001Mhz is recorded, which is very close to the 10Mhz value that was provided by the manufacturer. The waveform seen on the oscilloscope is observed to be periodic and looks like a square-wave oscillation. [picture is waveform of first set up with 10Mhz] There seem to be additional peaks periodically formed as well, which could likely come from circuit impedance mismatches. Mismatches in impedance between different components or sections of a circuit can cause signal reflections and distortions, leading to additional peaks in the waveform. We would have to adjust the values of the capacitors and resistors.
 
Then, we replace the 10Mhz crystal oscillator with the AT-cut crystal. [picture is waveform of first set up] Although we managed to obtain the frequency signal generated by the AT-cut crystal, the surface of the crystal is very sensitive such that waving your hands near the oscillator causes the waveform to change. To make the signal more stable, we construct another circuit design similar to the Colpitts oscillator.[5] One of the advantages of using this layout is that relatively low phase noise can be achieved, making them suitable for applications requiring stable and low-noise oscillation.

==Second Set-Up==
The circuit design and the actual circuit is shown in Figure (). 2N2222 bipolar junction transistors were used with a combination of capacitors and resistors. The purpose of the transistor is to amplify the voltage across the resonant circuit and stabilise the oscillations through a feedback loop. 
A DC power supply of 9V is applied across the circuit and an oscilloscope is connected to observe the waveform. Figure () shows the waveform, which seems to be a superposition of square wave and another periodic signal which could be due to the aforementioned circuit impedance mismatches. [insert second set up] We use the Anritsu MS2711D Spectrum Master to look for the resonance frequencies as a cross-reference to the frequency counter measurement. In Figure (), the resonance frequency of the piezoelectric quartz oscillator and its higher-order harmonics are shown. [insert resonance frequency narrow, wide scan of frequency] From the wide scan, we can see that the zeroth-order overtone occurs at around approximately 6Mhz, and the higher-order harmonics occur in multiple integers of 6MHz.

==Second Measurement==
The procedure for the frequency counter measurements is the same as that of the 10MHz crystal oscillator. The fundamental resonant frequency is measured to be 5.986804MHz. Using this as the reference resonance frequency, we can now test its effectiveness in mass measurements with the Sauerbrey equation. 

Firstly, a permanent marker is used where we dot the center of the quartz crystal shown in Figure (). [insert permanent marker ink] Initially, there was no signal shown in Figure (). [Explain why, insert no spectral signature for ink]However, increasing the DC supply voltage sufficiently allows the fundamental mode to be observed as shown in Figure (). [insert increase dc power supply] We repeated the frequency counter measurements and found the new resonance frequency to be 5.984613MHz.

To test the mass limit of this setup, a small Blu Tack weighing 2.1 grams is placed on the center of the oscillator. A new oscillator is used so that the dried ink does not interfere with the measurement. The Spectrum Master did not record any spectral features, which suggests that the oscillation of the crystal is too damped to be detected and that the gain is insufficient. [insert no spectral signature for blu tack] Increasing the DC power supply to 18V is inadequate to produce a spectral feature. For safety purposes, this will be the limit that we shall test.

Based on the Sauerbrey equation, the decrease in resonance frequency of 2191Hz corresponds to an increase in mass of 969 micrograms. This value is derived by using the following:
* thickness of quartz crystal plate <math> t_q = 1 </math> mm
* density of quartz crystal <math> \rho_q = 2648 </math> kg m-3
* fundamental resonance frequency of quartz crystal plate <math> f_0 = 5.986804 </math> MHz

To understand how accurate this measurement is, let us approximate the volume of ink to be a drop of water and calculate how much a drop of water weighs. We assume that the density of the marker ink is approximately similar to water. A drop of water of 0.1ml is approximately 100 micrograms. This shows that the measurement is about an order of magnitude higher than the approximation.

This huge error arises because of the assumptions of using the Sauerbrey equation. The Sauerbrey equation is valid under the following conditions:

*The added mass is small compared to the mass of the crystal
*The added mass is rigidly adsorbed onto the surface of the crystal
*The mass is evenly distributed over the active area of the crystal.

Based on these conditions, the second and third conditions are not fulfilled.

==Potential Improvements and Conclusion==
Some better models describe the relationship between frequency change and mass adsorbed where we consider the added mass to be viscoelastic. The Sauerbrey equation fails to describe viscoelastic films on the quartz oscillator as the condition where the added mass is rigidly bound is not adhered to. This model is called the QCM-D, where D refers to the energy dissipation by the film. This technique is prevalent in the fields of lipids, proteins, nanoparticles, etc. [6] However, this requires the use of liquid media. 

To conclude, we managed to detect the quartz crystal oscillation with a simple circuit design. Changes in resonance frequency due to added mass can also be detected, but the margin of error is too large for it to be usable for research purposes. Future improvements to this experiment can be done by adopting energy dissipation within our considerations.

==References==
# Meissner A (1927) € Uber piezoelectrische Krystalle bei Hochfrequenz. Z Tech Phys 8:74
# O’Sullivan, C. K., & Guilbault, G. G. (1999). Commercial quartz crystal microbalances – theory and applications. Biosensors and Bioelectronics, 14(8), 663–670.
# Ebersole, R., Miller, J., Moran, J., & Ward, M. (1990). PZ quartz sensors for use in clinical analysis. J. Am. Chem. Soc, 112, 3239.
# Sauerbrey, G. (1959). Verwendung von Schwingquarzen zur Wägung dünner Schichten und zur Mikrowägung. Zeitschrift für Physik, 155(2), 206–222.
# US 1624537, Colpitts, Edwin H., "Oscillation generator", published 1 February 1918, issued 12 April 1927

File:Blu tack no signal.jpeg

2024-04-23T03:24:52Z

E0309214:

File:Ink no signal.jpeg

2024-04-23T03:24:35Z

E0309214:

File:Increase power.jpeg

2024-04-23T03:24:06Z

E0309214:

File:Blu tack.jpeg

2024-04-23T03:23:45Z

E0309214:

File:Permanent marker.jpeg

2024-04-23T03:23:13Z

E0309214:

File:Narrow scan.jpeg

2024-04-23T03:22:37Z

E0309214:

File:Wide scan.jpeg

2024-04-23T03:22:20Z

E0309214:

File:1st setup waveform.jpeg

2024-04-23T03:21:19Z

E0309214:

File:Typical setup.png

2024-04-23T03:19:31Z

E0309214:

File:2nd setup.jpeg

2024-04-23T03:19:04Z

E0309214:

File:1st setup.jpeg

2024-04-23T03:18:40Z

E0309214:

File:Circuit diagram 2nd.png

2024-04-23T03:18:08Z

E0309214:

File:Circuit diagram 1st.png

2024-04-23T03:17:32Z

E0309214:

Quartz Crystal MicroBalance (QCM)

2024-04-23T03:15:22Z

E0309214: /* Potential Improvements and Conclusion */

==Abstract==

This project aims to construct a circuit that mimics a quartz crystal microbalance. This can be done via a combination of resistors, capacitors, and a quartz crystal. Testing of the QCM can be done by measuring the fundamental frequency of the quartz crystal oscillator, followed by adding a test mass such as the ink of a permanent marker on the oscillator to determine the frequency change. The original intention of building this QCM is to investigate if it is possible to measure the mass of thin films ex-situ. However, due to experimental and time constraints, we shall focus on building a circuit that can detect mass changes on the order of micrograms.

==Team members==
Tan Jhoon Yong
==Idea==
Quartz crystal microbalance (QCM) is widely used to measure mass changes to substances involved in physical and chemical processes. In my field of research, we often have to find out the thicknesses of thin films as part of the process of characterizing the samples. There are a few methods that are usually employed in my research to measure thin films' thicknesses such as observing the reflection high-energy electron diffraction (RHEED) oscillations during pulsed-laser deposition (PLD), atomic force microscopy (AFM), X-ray diffraction (XRD) (if the sample is ordered), and fitting of data from spectroscopic ellipsometry (SE). These techniques usually expend a significant amount of time but provide an accurate value to the thickness measurements. Creating a QCM that can work ex-situ will assist my research, and also serves as a reference point and hastens the process of fitting models in SE analysis.

Many of the developments and features that exist in today’s commercial QCM instruments were pioneered in laboratories with custom-built instruments to meet specific research needs, such as the use of internal reference crystals to separate the effects of a liquid environment from those of a film sample.

==Working Principle==
The working principle behind the QCM is based on the piezoelectric effect. The piezoelectric effect is the generation of electric charges by a crystalline material upon subjecting it to stress.[1] An oscillating electric field applied across the device induces an acoustic wave that propagates through the crystal and meets minimum impedance when the device's thickness is a half-integer multiple of the wavelength of the acoustic wave.[2] It is a shear mode device in which the acoustic wave propagates in a direction perpendicular to the crystal surface.[3] Therefore, crystals cut in specific crystal axes have to be used to utilize the shear mode.

A resonant oscillation in the crystal is achieved by putting the crystal in an oscillation circuit where the electrical and mechanical oscillations are close to the fundamental frequency of the crystal. Changes to the mass of the crystal would result in a proportional change in its natural frequency according to the Sauerbrey equation[4] 
 
<math>

\Delta m = \frac{C}{n} \Delta f

</math>

 
where <math>\Delta f</math> is the change in resonance frequency, <math>C</math> is the specific sensitivity of the crystal, <math>\Delta m</math> is the mass adsorbed on the active area, and <math>n</math> is the harmonic number. <math>C</math> describes how much material per unit area is required to change the resonant frequency of the crystal by 1Hz. A smaller <math>C</math> value gives a higher mass sensitivity. This value depends on the fundamental resonant frequency of the crystal, and it is defined as 
 
<math>

C = \frac{t_q \rho_q}{f_0}

</math>
 
where <math>t_q</math> is the thickness of the quartz, <math>\rho_q</math> is the density of the quartz plate, and f0 is the fundamental resonant frequency of quartz. With these, we can determine the mass of the deposited material. 
 
Another consideration would be the energy dissipation of the crystal to the surroundings. This is important, especially for viscoelastic films. Viscoelastic films violate the Sauerbrey condition that the bound mass is rigidly attached to the crystal without any slip. Such viscoelastic films dissipate energy via mechanical losses in the flexible mass.
[[File:AT and BT cut.png|200px|thumb|left|Orientation of AT- and BT- cut crystals]]
 
==Setup==
The typical QCM set-up of piezoelectric quartz crystal microbalance is shown in Figure (). The oscillator circuit is connected to the power supply and sample stage mount where the piezoelectric quartz crystal is. We can determine the resonance frequency of the quartz crystal using an oscilloscope, frequency counter, or spectrum analyzer. To determine the feasibility of this QCM project, we built a simple oscillating circuit as a foundation to test if we can detect the resonance frequency of the quartz crystal. This also serves as a time buffer while waiting for the AT-cut quartz to be delivered. Figure () shows the electrical circuit diagram and its implementation on a breadboard. As the electrical current generated from the oscillation of the quartz crystal is an alternating current due to the piezoelectric effect, we employ the usage of logic gates called inverters to convert DC to AC for readout. Adding a resistor to the circuit allows for the control of the potential difference across the inverter. In this oscillating circuit, we use a 14-pin integrated circuit and measure the resonant frequency of a CMAC CK q5 crystal oscillator.

==Measurements==
A DC power supply of 5V is given and an oscilloscope is connected to see the signal's waveform. A frequency counter is connected to the electrical circuit and communicated to my computer via the Arduino Integrated Development Environment. The frequency is measured for 10 seconds 10 times to get an average. Eventually, a resonant frequency of 10.000001Mhz is recorded, which is very close to the 10Mhz value that was provided by the manufacturer. The waveform seen on the oscilloscope is observed to be periodic and looks like a square-wave oscillation. [picture is waveform of first set up with 10Mhz] There seem to be additional peaks periodically formed as well, which could likely come from circuit impedance mismatches. Mismatches in impedance between different components or sections of a circuit can cause signal reflections and distortions, leading to additional peaks in the waveform. We would have to adjust the values of the capacitors and resistors.
 
Then, we replace the 10Mhz crystal oscillator with the AT-cut crystal. [picture is waveform of first set up] Although we managed to obtain the frequency signal generated by the AT-cut crystal, the surface of the crystal is very sensitive such that waving your hands near the oscillator causes the waveform to change. To make the signal more stable, we construct another circuit design similar to the Colpitts oscillator.[5] One of the advantages of using this layout is that relatively low phase noise can be achieved, making them suitable for applications requiring stable and low-noise oscillation.

==Second Set-Up==
The circuit design and the actual circuit is shown in Figure (). 2N2222 bipolar junction transistors were used with a combination of capacitors and resistors. The purpose of the transistor is to amplify the voltage across the resonant circuit and stabilise the oscillations through a feedback loop. 
A DC power supply of 9V is applied across the circuit and an oscilloscope is connected to observe the waveform. Figure () shows the waveform, which seems to be a superposition of square wave and another periodic signal which could be due to the aforementioned circuit impedance mismatches. [insert second set up] We use the Anritsu MS2711D Spectrum Master to look for the resonance frequencies as a cross-reference to the frequency counter measurement. In Figure (), the resonance frequency of the piezoelectric quartz oscillator and its higher-order harmonics are shown. [insert resonance frequency narrow, wide scan of frequency] From the wide scan, we can see that the zeroth-order overtone occurs at around approximately 6Mhz, and the higher-order harmonics occur in multiple integers of 6MHz.

==Second Measurement==
The procedure for the frequency counter measurements is the same as that of the 10MHz crystal oscillator. The fundamental resonant frequency is measured to be 5.986804MHz. Using this as the reference resonance frequency, we can now test its effectiveness in mass measurements with the Sauerbrey equation. 

Firstly, a permanent marker is used where we dot the center of the quartz crystal shown in Figure (). [insert permanent marker ink] Initially, there was no signal shown in Figure (). [Explain why, insert no spectral signature for ink]However, increasing the DC supply voltage sufficiently allows the fundamental mode to be observed as shown in Figure (). [insert increase dc power supply] We repeated the frequency counter measurements and found the new resonance frequency to be 5.984613MHz.

To test the mass limit of this setup, a small Blu Tack weighing 2.1 grams is placed on the center of the oscillator. A new oscillator is used so that the dried ink does not interfere with the measurement. The Spectrum Master did not record any spectral features, which suggests that the oscillation of the crystal is too damped to be detected and that the gain is insufficient. [insert no spectral signature for blu tack] Increasing the DC power supply to 18V is inadequate to produce a spectral feature. For safety purposes, this will be the limit that we shall test.

Based on the Sauerbrey equation, the decrease in resonance frequency of 2191Hz corresponds to an increase in mass of 969 micrograms. This value is derived by using the following:
* thickness of quartz crystal plate <math> t_q = 1 </math> mm
* density of quartz crystal <math> \rho_q = 2648 </math> kg m-3
* fundamental resonance frequency of quartz crystal plate <math> f_0 = 5.986804 </math> MHz

To understand how accurate this measurement is, let us approximate the volume of ink to be a drop of water and calculate how much a drop of water weighs. We assume that the density of the marker ink is approximately similar to water. A drop of water of 0.1ml is approximately 100 micrograms. This shows that the measurement is about an order of magnitude higher than the approximation.

This huge error arises because of the assumptions of using the Sauerbrey equation. The Sauerbrey equation is valid under the following conditions:

*The added mass is small compared to the mass of the crystal
*The added mass is rigidly adsorbed onto the surface of the crystal
*The mass is evenly distributed over the active area of the crystal.

Based on these conditions, the second and third conditions are not fulfilled.

==Potential Improvements and Conclusion==
Some better models describe the relationship between frequency change and mass adsorbed where we consider the added mass to be viscoelastic. The Sauerbrey equation fails to describe viscoelastic films on the quartz oscillator as the condition where the added mass is rigidly bound is not adhered to. This model is called the QCM-D, where D refers to the energy dissipation by the film. This technique is prevalent in the fields of lipids, proteins, nanoparticles, etc. [6] However, this requires the use of liquid media. 

To conclude, we managed to detect the quartz crystal oscillation with a simple circuit design. Changes in resonance frequency due to added mass can also be detected, but the margin of error is too large for it to be usable for research purposes. Future improvements to this experiment can be done by adopting energy dissipation within our considerations.

==References==
# Meissner A (1927) € Uber piezoelectrische Krystalle bei Hochfrequenz. Z Tech Phys 8:74
# O’Sullivan, C. K., & Guilbault, G. G. (1999). Commercial quartz crystal microbalances – theory and applications. Biosensors and Bioelectronics, 14(8), 663–670.
# Ebersole, R., Miller, J., Moran, J., & Ward, M. (1990). PZ quartz sensors for use in clinical analysis. J. Am. Chem. Soc, 112, 3239.
# Sauerbrey, G. (1959). Verwendung von Schwingquarzen zur Wägung dünner Schichten und zur Mikrowägung. Zeitschrift für Physik, 155(2), 206–222.
# US 1624537, Colpitts, Edwin H., "Oscillation generator", published 1 February 1918, issued 12 April 1927

Quartz Crystal MicroBalance (QCM)

2024-04-23T03:10:09Z

E0309214:

==Abstract==

This project aims to construct a circuit that mimics a quartz crystal microbalance. This can be done via a combination of resistors, capacitors, and a quartz crystal. Testing of the QCM can be done by measuring the fundamental frequency of the quartz crystal oscillator, followed by adding a test mass such as the ink of a permanent marker on the oscillator to determine the frequency change. The original intention of building this QCM is to investigate if it is possible to measure the mass of thin films ex-situ. However, due to experimental and time constraints, we shall focus on building a circuit that can detect mass changes on the order of micrograms.

==Team members==
Tan Jhoon Yong
==Idea==
Quartz crystal microbalance (QCM) is widely used to measure mass changes to substances involved in physical and chemical processes. In my field of research, we often have to find out the thicknesses of thin films as part of the process of characterizing the samples. There are a few methods that are usually employed in my research to measure thin films' thicknesses such as observing the reflection high-energy electron diffraction (RHEED) oscillations during pulsed-laser deposition (PLD), atomic force microscopy (AFM), X-ray diffraction (XRD) (if the sample is ordered), and fitting of data from spectroscopic ellipsometry (SE). These techniques usually expend a significant amount of time but provide an accurate value to the thickness measurements. Creating a QCM that can work ex-situ will assist my research, and also serves as a reference point and hastens the process of fitting models in SE analysis.

Many of the developments and features that exist in today’s commercial QCM instruments were pioneered in laboratories with custom-built instruments to meet specific research needs, such as the use of internal reference crystals to separate the effects of a liquid environment from those of a film sample.

==Working Principle==
The working principle behind the QCM is based on the piezoelectric effect. The piezoelectric effect is the generation of electric charges by a crystalline material upon subjecting it to stress.[1] An oscillating electric field applied across the device induces an acoustic wave that propagates through the crystal and meets minimum impedance when the device's thickness is a half-integer multiple of the wavelength of the acoustic wave.[2] It is a shear mode device in which the acoustic wave propagates in a direction perpendicular to the crystal surface.[3] Therefore, crystals cut in specific crystal axes have to be used to utilize the shear mode.

A resonant oscillation in the crystal is achieved by putting the crystal in an oscillation circuit where the electrical and mechanical oscillations are close to the fundamental frequency of the crystal. Changes to the mass of the crystal would result in a proportional change in its natural frequency according to the Sauerbrey equation[4] 
 
<math>

\Delta m = \frac{C}{n} \Delta f

</math>

 
where <math>\Delta f</math> is the change in resonance frequency, <math>C</math> is the specific sensitivity of the crystal, <math>\Delta m</math> is the mass adsorbed on the active area, and <math>n</math> is the harmonic number. <math>C</math> describes how much material per unit area is required to change the resonant frequency of the crystal by 1Hz. A smaller <math>C</math> value gives a higher mass sensitivity. This value depends on the fundamental resonant frequency of the crystal, and it is defined as 
 
<math>

C = \frac{t_q \rho_q}{f_0}

</math>
 
where <math>t_q</math> is the thickness of the quartz, <math>\rho_q</math> is the density of the quartz plate, and f0 is the fundamental resonant frequency of quartz. With these, we can determine the mass of the deposited material. 
 
Another consideration would be the energy dissipation of the crystal to the surroundings. This is important, especially for viscoelastic films. Viscoelastic films violate the Sauerbrey condition that the bound mass is rigidly attached to the crystal without any slip. Such viscoelastic films dissipate energy via mechanical losses in the flexible mass.
[[File:AT and BT cut.png|200px|thumb|left|Orientation of AT- and BT- cut crystals]]
 
==Setup==
The typical QCM set-up of piezoelectric quartz crystal microbalance is shown in Figure (). The oscillator circuit is connected to the power supply and sample stage mount where the piezoelectric quartz crystal is. We can determine the resonance frequency of the quartz crystal using an oscilloscope, frequency counter, or spectrum analyzer. To determine the feasibility of this QCM project, we built a simple oscillating circuit as a foundation to test if we can detect the resonance frequency of the quartz crystal. This also serves as a time buffer while waiting for the AT-cut quartz to be delivered. Figure () shows the electrical circuit diagram and its implementation on a breadboard. As the electrical current generated from the oscillation of the quartz crystal is an alternating current due to the piezoelectric effect, we employ the usage of logic gates called inverters to convert DC to AC for readout. Adding a resistor to the circuit allows for the control of the potential difference across the inverter. In this oscillating circuit, we use a 14-pin integrated circuit and measure the resonant frequency of a CMAC CK q5 crystal oscillator.

==Measurements==
A DC power supply of 5V is given and an oscilloscope is connected to see the signal's waveform. A frequency counter is connected to the electrical circuit and communicated to my computer via the Arduino Integrated Development Environment. The frequency is measured for 10 seconds 10 times to get an average. Eventually, a resonant frequency of 10.000001Mhz is recorded, which is very close to the 10Mhz value that was provided by the manufacturer. The waveform seen on the oscilloscope is observed to be periodic and looks like a square-wave oscillation. [picture is waveform of first set up with 10Mhz] There seem to be additional peaks periodically formed as well, which could likely come from circuit impedance mismatches. Mismatches in impedance between different components or sections of a circuit can cause signal reflections and distortions, leading to additional peaks in the waveform. We would have to adjust the values of the capacitors and resistors.
 
Then, we replace the 10Mhz crystal oscillator with the AT-cut crystal. [picture is waveform of first set up] Although we managed to obtain the frequency signal generated by the AT-cut crystal, the surface of the crystal is very sensitive such that waving your hands near the oscillator causes the waveform to change. To make the signal more stable, we construct another circuit design similar to the Colpitts oscillator.[5] One of the advantages of using this layout is that relatively low phase noise can be achieved, making them suitable for applications requiring stable and low-noise oscillation.

==Second Set-Up==
The circuit design and the actual circuit is shown in Figure (). 2N2222 bipolar junction transistors were used with a combination of capacitors and resistors. The purpose of the transistor is to amplify the voltage across the resonant circuit and stabilise the oscillations through a feedback loop. 
A DC power supply of 9V is applied across the circuit and an oscilloscope is connected to observe the waveform. Figure () shows the waveform, which seems to be a superposition of square wave and another periodic signal which could be due to the aforementioned circuit impedance mismatches. [insert second set up] We use the Anritsu MS2711D Spectrum Master to look for the resonance frequencies as a cross-reference to the frequency counter measurement. In Figure (), the resonance frequency of the piezoelectric quartz oscillator and its higher-order harmonics are shown. [insert resonance frequency narrow, wide scan of frequency] From the wide scan, we can see that the zeroth-order overtone occurs at around approximately 6Mhz, and the higher-order harmonics occur in multiple integers of 6MHz.

==Second Measurement==
The procedure for the frequency counter measurements is the same as that of the 10MHz crystal oscillator. The fundamental resonant frequency is measured to be 5.986804MHz. Using this as the reference resonance frequency, we can now test its effectiveness in mass measurements with the Sauerbrey equation. 

Firstly, a permanent marker is used where we dot the center of the quartz crystal shown in Figure (). [insert permanent marker ink] Initially, there was no signal shown in Figure (). [Explain why, insert no spectral signature for ink]However, increasing the DC supply voltage sufficiently allows the fundamental mode to be observed as shown in Figure (). [insert increase dc power supply] We repeated the frequency counter measurements and found the new resonance frequency to be 5.984613MHz.

To test the mass limit of this setup, a small Blu Tack weighing 2.1 grams is placed on the center of the oscillator. A new oscillator is used so that the dried ink does not interfere with the measurement. The Spectrum Master did not record any spectral features, which suggests that the oscillation of the crystal is too damped to be detected and that the gain is insufficient. [insert no spectral signature for blu tack] Increasing the DC power supply to 18V is inadequate to produce a spectral feature. For safety purposes, this will be the limit that we shall test.

Based on the Sauerbrey equation, the decrease in resonance frequency of 2191Hz corresponds to an increase in mass of 969 micrograms. This value is derived by using the following:
* thickness of quartz crystal plate <math> t_q = 1 </math> mm
* density of quartz crystal <math> \rho_q = 2648 </math> kg m-3
* fundamental resonance frequency of quartz crystal plate <math> f_0 = 5.986804 </math> MHz

To understand how accurate this measurement is, let us approximate the volume of ink to be a drop of water and calculate how much a drop of water weighs. We assume that the density of the marker ink is approximately similar to water. A drop of water of 0.1ml is approximately 100 micrograms. This shows that the measurement is about an order of magnitude higher than the approximation.

This huge error arises because of the assumptions of using the Sauerbrey equation. The Sauerbrey equation is valid under the following conditions:

*The added mass is small compared to the mass of the crystal
*The added mass is rigidly adsorbed onto the surface of the crystal
*The mass is evenly distributed over the active area of the crystal.

Based on these conditions, the second and third conditions are not fulfilled.

==Potential Improvements and Conclusion==

==References==
# Meissner A (1927) € Uber piezoelectrische Krystalle bei Hochfrequenz. Z Tech Phys 8:74
# O’Sullivan, C. K., & Guilbault, G. G. (1999). Commercial quartz crystal microbalances – theory and applications. Biosensors and Bioelectronics, 14(8), 663–670.
# Ebersole, R., Miller, J., Moran, J., & Ward, M. (1990). PZ quartz sensors for use in clinical analysis. J. Am. Chem. Soc, 112, 3239.
# Sauerbrey, G. (1959). Verwendung von Schwingquarzen zur Wägung dünner Schichten und zur Mikrowägung. Zeitschrift für Physik, 155(2), 206–222.
# US 1624537, Colpitts, Edwin H., "Oscillation generator", published 1 February 1918, issued 12 April 1927

Quartz Crystal MicroBalance (QCM)

2024-04-23T03:09:04Z

E0309214: /* Second Measurement */

==Abstract==

This project aims to construct a circuit that mimics a quartz crystal microbalance. This can be done via a combination of resistors, capacitors, and a quartz crystal. Testing of the QCM can be done by measuring the fundamental frequency of the quartz crystal oscillator, followed by adding a test mass such as the ink of a permanent marker on the oscillator to determine the frequency change. The original intention of building this QCM is to investigate if it is possible to measure the mass of thin films ex-situ. However, due to experimental and time constraints, we shall focus on building a circuit that can detect mass changes on the order of micrograms.

==Team members==
Tan Jhoon Yong
==Idea==
Quartz crystal microbalance (QCM) is widely used to measure mass changes to substances involved in physical and chemical processes. In my field of research, we often have to find out the thicknesses of thin films as part of the process of characterizing the samples. There are a few methods that are usually employed in my research to measure thin films' thicknesses such as observing the reflection high-energy electron diffraction (RHEED) oscillations during pulsed-laser deposition (PLD), atomic force microscopy (AFM), X-ray diffraction (XRD) (if the sample is ordered), and fitting of data from spectroscopic ellipsometry (SE). These techniques usually expend a significant amount of time but provide an accurate value to the thickness measurements. Creating a QCM that can work ex-situ will assist my research, and also serves as a reference point and hastens the process of fitting models in SE analysis.

Many of the developments and features that exist in today’s commercial QCM instruments were pioneered in laboratories with custom-built instruments to meet specific research needs, such as the use of internal reference crystals to separate the effects of a liquid environment from those of a film sample.

==Working Principle==
The working principle behind the QCM is based on the piezoelectric effect. The piezoelectric effect is the generation of electric charges by a crystalline material upon subjecting it to stress.[1] An oscillating electric field applied across the device induces an acoustic wave that propagates through the crystal and meets minimum impedance when the device's thickness is a half-integer multiple of the wavelength of the acoustic wave.[2] It is a shear mode device in which the acoustic wave propagates in a direction perpendicular to the crystal surface.[3] Therefore, crystals cut in specific crystal axes have to be used to utilize the shear mode.

A resonant oscillation in the crystal is achieved by putting the crystal in an oscillation circuit where the electrical and mechanical oscillations are close to the fundamental frequency of the crystal. Changes to the mass of the crystal would result in a proportional change in its natural frequency according to the Sauerbrey equation[4] 
 
<math>

\Delta m = \frac{C}{n} \Delta f

</math>

 
where <math>\Delta f</math> is the change in resonance frequency, <math>C</math> is the specific sensitivity of the crystal, <math>\Delta m</math> is the mass adsorbed on the active area, and <math>n</math> is the harmonic number. <math>C</math> describes how much material per unit area is required to change the resonant frequency of the crystal by 1Hz. A smaller <math>C</math> value gives a higher mass sensitivity. This value depends on the fundamental resonant frequency of the crystal, and it is defined as 
 
<math>

C = \frac{t_q \rho_q}{f_0}

</math>
 
where <math>t_q</math> is the thickness of the quartz, <math>\rho_q</math> is the density of the quartz plate, and f0 is the fundamental resonant frequency of quartz. With these, we can determine the mass of the deposited material. 
 
Another consideration would be the energy dissipation of the crystal to the surroundings. This is important, especially for viscoelastic films. Viscoelastic films violate the Sauerbrey condition that the bound mass is rigidly attached to the crystal without any slip. Such viscoelastic films dissipate energy via mechanical losses in the flexible mass.
[[File:AT and BT cut.png|200px|thumb|left|Orientation of AT- and BT- cut crystals]]
 
==Setup==
The typical QCM set-up of piezoelectric quartz crystal microbalance is shown in Figure (). The oscillator circuit is connected to the power supply and sample stage mount where the piezoelectric quartz crystal is. We can determine the resonance frequency of the quartz crystal using an oscilloscope, frequency counter, or spectrum analyzer. To determine the feasibility of this QCM project, we built a simple oscillating circuit as a foundation to test if we can detect the resonance frequency of the quartz crystal. This also serves as a time buffer while waiting for the AT-cut quartz to be delivered. Figure () shows the electrical circuit diagram and its implementation on a breadboard. As the electrical current generated from the oscillation of the quartz crystal is an alternating current due to the piezoelectric effect, we employ the usage of logic gates called inverters to convert DC to AC for readout. Adding a resistor to the circuit allows for the control of the potential difference across the inverter. In this oscillating circuit, we use a 14-pin integrated circuit and measure the resonant frequency of a CMAC CK q5 crystal oscillator.

==Measurements==
A DC power supply of 5V is given and an oscilloscope is connected to see the signal's waveform. A frequency counter is connected to the electrical circuit and communicated to my computer via the Arduino Integrated Development Environment. The frequency is measured for 10 seconds 10 times to get an average. Eventually, a resonant frequency of 10.000001Mhz is recorded, which is very close to the 10Mhz value that was provided by the manufacturer. The waveform seen on the oscilloscope is observed to be periodic and looks like a square-wave oscillation. [picture is waveform of first set up with 10Mhz] There seem to be additional peaks periodically formed as well, which could likely come from circuit impedance mismatches. Mismatches in impedance between different components or sections of a circuit can cause signal reflections and distortions, leading to additional peaks in the waveform. We would have to adjust the values of the capacitors and resistors.
 
Then, we replace the 10Mhz crystal oscillator with the AT-cut crystal. [picture is waveform of first set up] Although we managed to obtain the frequency signal generated by the AT-cut crystal, the surface of the crystal is very sensitive such that waving your hands near the oscillator causes the waveform to change. To make the signal more stable, we construct another circuit design similar to the Colpitts oscillator.[5] One of the advantages of using this layout is that relatively low phase noise can be achieved, making them suitable for applications requiring stable and low-noise oscillation.

==Second Set-Up==
The circuit design and the actual circuit is shown in Figure (). 2N2222 bipolar junction transistors were used with a combination of capacitors and resistors. The purpose of the transistor is to amplify the voltage across the resonant circuit and stabilise the oscillations through a feedback loop. 
A DC power supply of 9V is applied across the circuit and an oscilloscope is connected to observe the waveform. Figure () shows the waveform, which seems to be a superposition of square wave and another periodic signal which could be due to the aforementioned circuit impedance mismatches. [insert second set up] We use the Anritsu MS2711D Spectrum Master to look for the resonance frequencies as a cross-reference to the frequency counter measurement. In Figure (), the resonance frequency of the piezoelectric quartz oscillator and its higher-order harmonics are shown. [insert resonance frequency narrow, wide scan of frequency] From the wide scan, we can see that the zeroth-order overtone occurs at around approximately 6Mhz, and the higher-order harmonics occur in multiple integers of 6MHz.

==Second Measurement==
The procedure for the frequency counter measurements is the same as that of the 10MHz crystal oscillator. The fundamental resonant frequency is measured to be 5.986804MHz. Using this as the reference resonance frequency, we can now test its effectiveness in mass measurements with the Sauerbrey equation. 

Firstly, a permanent marker is used where we dot the center of the quartz crystal shown in Figure (). [insert permanent marker ink] Initially, there was no signal shown in Figure (). [Explain why, insert no spectral signature for ink]However, increasing the DC supply voltage sufficiently allows the fundamental mode to be observed as shown in Figure (). [insert increase dc power supply] We repeated the frequency counter measurements and found the new resonance frequency to be 5.984613MHz.

To test the mass limit of this setup, a small Blu Tack weighing 2.1 grams is placed on the center of the oscillator. A new oscillator is used so that the dried ink does not interfere with the measurement. The Spectrum Master did not record any spectral features, which suggests that the oscillation of the crystal is too damped to be detected and that the gain is insufficient. [insert no spectral signature for blu tack] Increasing the DC power supply to 18V is inadequate to produce a spectral feature. For safety purposes, this will be the limit that we shall test.

Based on the Sauerbrey equation, the decrease in resonance frequency of 2191Hz corresponds to an increase in mass of 969 micrograms. This value is derived by using the following:
* thickness of quartz crystal plate <math> t_q = 1 </math> mm
* density of quartz crystal <math> \rho_q = 2648 </math> kg m-3
* fundamental resonance frequency of quartz crystal plate <math> f_0 = 5.986804 </math> MHz

To understand how accurate this measurement is, let us approximate the volume of ink to be a drop of water and calculate how much a drop of water weighs. We assume that the density of the marker ink is approximately similar to water. A drop of water of 0.1ml is approximately 100 micrograms. This shows that the measurement is about an order of magnitude higher than the approximation.

This huge error arises because of the assumptions of using the Sauerbrey equation. The Sauerbrey equation is valid under the following conditions:

*The added mass is small compared to the mass of the crystal
*The added mass is rigidly adsorbed onto the surface of the crystal
*The mass is evenly distributed over the active area of the crystal.

Based on these conditions, the second and third conditions are not fulfilled.

==References==
# Meissner A (1927) € Uber piezoelectrische Krystalle bei Hochfrequenz. Z Tech Phys 8:74
# O’Sullivan, C. K., & Guilbault, G. G. (1999). Commercial quartz crystal microbalances – theory and applications. Biosensors and Bioelectronics, 14(8), 663–670.
# Ebersole, R., Miller, J., Moran, J., & Ward, M. (1990). PZ quartz sensors for use in clinical analysis. J. Am. Chem. Soc, 112, 3239.
# Sauerbrey, G. (1959). Verwendung von Schwingquarzen zur Wägung dünner Schichten und zur Mikrowägung. Zeitschrift für Physik, 155(2), 206–222.
# US 1624537, Colpitts, Edwin H., "Oscillation generator", published 1 February 1918, issued 12 April 1927

Quartz Crystal MicroBalance (QCM)

2024-04-23T03:00:25Z

E0309214: /* Second Measurement */

==Abstract==

This project aims to construct a circuit that mimics a quartz crystal microbalance. This can be done via a combination of resistors, capacitors, and a quartz crystal. Testing of the QCM can be done by measuring the fundamental frequency of the quartz crystal oscillator, followed by adding a test mass such as the ink of a permanent marker on the oscillator to determine the frequency change. The original intention of building this QCM is to investigate if it is possible to measure the mass of thin films ex-situ. However, due to experimental and time constraints, we shall focus on building a circuit that can detect mass changes on the order of micrograms.

==Team members==
Tan Jhoon Yong
==Idea==
Quartz crystal microbalance (QCM) is widely used to measure mass changes to substances involved in physical and chemical processes. In my field of research, we often have to find out the thicknesses of thin films as part of the process of characterizing the samples. There are a few methods that are usually employed in my research to measure thin films' thicknesses such as observing the reflection high-energy electron diffraction (RHEED) oscillations during pulsed-laser deposition (PLD), atomic force microscopy (AFM), X-ray diffraction (XRD) (if the sample is ordered), and fitting of data from spectroscopic ellipsometry (SE). These techniques usually expend a significant amount of time but provide an accurate value to the thickness measurements. Creating a QCM that can work ex-situ will assist my research, and also serves as a reference point and hastens the process of fitting models in SE analysis.

Many of the developments and features that exist in today’s commercial QCM instruments were pioneered in laboratories with custom-built instruments to meet specific research needs, such as the use of internal reference crystals to separate the effects of a liquid environment from those of a film sample.

==Working Principle==
The working principle behind the QCM is based on the piezoelectric effect. The piezoelectric effect is the generation of electric charges by a crystalline material upon subjecting it to stress.[1] An oscillating electric field applied across the device induces an acoustic wave that propagates through the crystal and meets minimum impedance when the device's thickness is a half-integer multiple of the wavelength of the acoustic wave.[2] It is a shear mode device in which the acoustic wave propagates in a direction perpendicular to the crystal surface.[3] Therefore, crystals cut in specific crystal axes have to be used to utilize the shear mode.

A resonant oscillation in the crystal is achieved by putting the crystal in an oscillation circuit where the electrical and mechanical oscillations are close to the fundamental frequency of the crystal. Changes to the mass of the crystal would result in a proportional change in its natural frequency according to the Sauerbrey equation[4] 
 
<math>

\Delta m = \frac{C}{n} \Delta f

</math>

 
where <math>\Delta f</math> is the change in resonance frequency, <math>C</math> is the specific sensitivity of the crystal, <math>\Delta m</math> is the mass adsorbed on the active area, and <math>n</math> is the harmonic number. <math>C</math> describes how much material per unit area is required to change the resonant frequency of the crystal by 1Hz. A smaller <math>C</math> value gives a higher mass sensitivity. This value depends on the fundamental resonant frequency of the crystal, and it is defined as 
 
<math>

C = \frac{t_q \rho_q}{f_0}

</math>
 
where <math>t_q</math> is the thickness of the quartz, <math>\rho_q</math> is the density of the quartz plate, and f0 is the fundamental resonant frequency of quartz. With these, we can determine the mass of the deposited material. 
 
Another consideration would be the energy dissipation of the crystal to the surroundings. This is important, especially for viscoelastic films. Viscoelastic films violate the Sauerbrey condition that the bound mass is rigidly attached to the crystal without any slip. Such viscoelastic films dissipate energy via mechanical losses in the flexible mass.
[[File:AT and BT cut.png|200px|thumb|left|Orientation of AT- and BT- cut crystals]]
 
==Setup==
The typical QCM set-up of piezoelectric quartz crystal microbalance is shown in Figure (). The oscillator circuit is connected to the power supply and sample stage mount where the piezoelectric quartz crystal is. We can determine the resonance frequency of the quartz crystal using an oscilloscope, frequency counter, or spectrum analyzer. To determine the feasibility of this QCM project, we built a simple oscillating circuit as a foundation to test if we can detect the resonance frequency of the quartz crystal. This also serves as a time buffer while waiting for the AT-cut quartz to be delivered. Figure () shows the electrical circuit diagram and its implementation on a breadboard. As the electrical current generated from the oscillation of the quartz crystal is an alternating current due to the piezoelectric effect, we employ the usage of logic gates called inverters to convert DC to AC for readout. Adding a resistor to the circuit allows for the control of the potential difference across the inverter. In this oscillating circuit, we use a 14-pin integrated circuit and measure the resonant frequency of a CMAC CK q5 crystal oscillator.

==Measurements==
A DC power supply of 5V is given and an oscilloscope is connected to see the signal's waveform. A frequency counter is connected to the electrical circuit and communicated to my computer via the Arduino Integrated Development Environment. The frequency is measured for 10 seconds 10 times to get an average. Eventually, a resonant frequency of 10.000001Mhz is recorded, which is very close to the 10Mhz value that was provided by the manufacturer. The waveform seen on the oscilloscope is observed to be periodic and looks like a square-wave oscillation. [picture is waveform of first set up with 10Mhz] There seem to be additional peaks periodically formed as well, which could likely come from circuit impedance mismatches. Mismatches in impedance between different components or sections of a circuit can cause signal reflections and distortions, leading to additional peaks in the waveform. We would have to adjust the values of the capacitors and resistors.
 
Then, we replace the 10Mhz crystal oscillator with the AT-cut crystal. [picture is waveform of first set up] Although we managed to obtain the frequency signal generated by the AT-cut crystal, the surface of the crystal is very sensitive such that waving your hands near the oscillator causes the waveform to change. To make the signal more stable, we construct another circuit design similar to the Colpitts oscillator.[5] One of the advantages of using this layout is that relatively low phase noise can be achieved, making them suitable for applications requiring stable and low-noise oscillation.

==Second Set-Up==
The circuit design and the actual circuit is shown in Figure (). 2N2222 bipolar junction transistors were used with a combination of capacitors and resistors. The purpose of the transistor is to amplify the voltage across the resonant circuit and stabilise the oscillations through a feedback loop. 
A DC power supply of 9V is applied across the circuit and an oscilloscope is connected to observe the waveform. Figure () shows the waveform, which seems to be a superposition of square wave and another periodic signal which could be due to the aforementioned circuit impedance mismatches. [insert second set up] We use the Anritsu MS2711D Spectrum Master to look for the resonance frequencies as a cross-reference to the frequency counter measurement. In Figure (), the resonance frequency of the piezoelectric quartz oscillator and its higher-order harmonics are shown. [insert resonance frequency narrow, wide scan of frequency] From the wide scan, we can see that the zeroth-order overtone occurs at around approximately 6Mhz, and the higher-order harmonics occur in multiple integers of 6MHz.

==Second Measurement==
The procedure for the frequency counter measurements is the same as that of the 10MHz crystal oscillator. The fundamental resonant frequency is measured to be 5.986804MHz. Using this as the reference resonance frequency, we can now test its effectiveness in mass measurements with the Sauerbrey equation. 

Firstly, a permanent marker is used where we dot the center of the quartz crystal shown in Figure (). [insert permanent marker ink] Initially, there was no signal shown in Figure (). [Explain why, insert no spectral signature for ink]However, increasing the DC supply voltage sufficiently allows the fundamental mode to be observed as shown in Figure (). [insert increase dc power supply] We repeated the frequency counter measurements and found the new resonance frequency to be 5.984613MHz.

To test the mass limit of this setup, a small Blu Tack weighing 2.1 grams is placed on the center of the oscillator. A new oscillator is used so that the dried ink does not interfere with the measurement. The Spectrum Master did not record any spectral features, which suggests that the oscillation of the crystal is too damped to be detected and that the gain is insufficient. [insert no spectral signature for blu tack] Increasing the DC power supply to 18V is inadequate to produce a spectral feature. For safety purposes, this will be the limit that we shall test.

Based on the Sauerbrey equation, the decrease in resonance frequency of 2191Hz corresponds to an increase in mass of 969 micrograms. To understand how accurate this measurement is, let us approximate the volume of ink to be a drop of water and calculate how much a drop of water weighs. We assume that the density of the marker ink is approximately similar to water. A drop of water of 0.1ml is approximately 100 micrograms. This shows that measurement is about an order of magnitude higher than the approximation.

This huge error arises because of the assumptions of using the Sauerbrey equation. The Sauerbrey equation is valid under the following conditions:

*The added mass is small compared to the mass of the crystal
*The added mass is rigidly adsorbed onto the surface of the crystal
*The mass is evenly distributed over the active area of the crystal.

Based on these conditions, the second and third conditions are not fulfilled.

==References==
# Meissner A (1927) € Uber piezoelectrische Krystalle bei Hochfrequenz. Z Tech Phys 8:74
# O’Sullivan, C. K., & Guilbault, G. G. (1999). Commercial quartz crystal microbalances – theory and applications. Biosensors and Bioelectronics, 14(8), 663–670.
# Ebersole, R., Miller, J., Moran, J., & Ward, M. (1990). PZ quartz sensors for use in clinical analysis. J. Am. Chem. Soc, 112, 3239.
# Sauerbrey, G. (1959). Verwendung von Schwingquarzen zur Wägung dünner Schichten und zur Mikrowägung. Zeitschrift für Physik, 155(2), 206–222.
# US 1624537, Colpitts, Edwin H., "Oscillation generator", published 1 February 1918, issued 12 April 1927

Quartz Crystal MicroBalance (QCM)

2024-04-23T02:43:35Z

E0309214:

==Abstract==

This project aims to construct a circuit that mimics a quartz crystal microbalance. This can be done via a combination of resistors, capacitors, and a quartz crystal. Testing of the QCM can be done by measuring the fundamental frequency of the quartz crystal oscillator, followed by adding a test mass such as the ink of a permanent marker on the oscillator to determine the frequency change. The original intention of building this QCM is to investigate if it is possible to measure the mass of thin films ex-situ. However, due to experimental and time constraints, we shall focus on building a circuit that can detect mass changes on the order of micrograms.

==Team members==
Tan Jhoon Yong
==Idea==
Quartz crystal microbalance (QCM) is widely used to measure mass changes to substances involved in physical and chemical processes. In my field of research, we often have to find out the thicknesses of thin films as part of the process of characterizing the samples. There are a few methods that are usually employed in my research to measure thin films' thicknesses such as observing the reflection high-energy electron diffraction (RHEED) oscillations during pulsed-laser deposition (PLD), atomic force microscopy (AFM), X-ray diffraction (XRD) (if the sample is ordered), and fitting of data from spectroscopic ellipsometry (SE). These techniques usually expend a significant amount of time but provide an accurate value to the thickness measurements. Creating a QCM that can work ex-situ will assist my research, and also serves as a reference point and hastens the process of fitting models in SE analysis.

Many of the developments and features that exist in today’s commercial QCM instruments were pioneered in laboratories with custom-built instruments to meet specific research needs, such as the use of internal reference crystals to separate the effects of a liquid environment from those of a film sample.

==Working Principle==
The working principle behind the QCM is based on the piezoelectric effect. The piezoelectric effect is the generation of electric charges by a crystalline material upon subjecting it to stress.[1] An oscillating electric field applied across the device induces an acoustic wave that propagates through the crystal and meets minimum impedance when the device's thickness is a half-integer multiple of the wavelength of the acoustic wave.[2] It is a shear mode device in which the acoustic wave propagates in a direction perpendicular to the crystal surface.[3] Therefore, crystals cut in specific crystal axes have to be used to utilize the shear mode.

A resonant oscillation in the crystal is achieved by putting the crystal in an oscillation circuit where the electrical and mechanical oscillations are close to the fundamental frequency of the crystal. Changes to the mass of the crystal would result in a proportional change in its natural frequency according to the Sauerbrey equation[4] 
 
<math>

\Delta m = \frac{C}{n} \Delta f

</math>

 
where <math>\Delta f</math> is the change in resonance frequency, <math>C</math> is the specific sensitivity of the crystal, <math>\Delta m</math> is the mass adsorbed on the active area, and <math>n</math> is the harmonic number. <math>C</math> describes how much material per unit area is required to change the resonant frequency of the crystal by 1Hz. A smaller <math>C</math> value gives a higher mass sensitivity. This value depends on the fundamental resonant frequency of the crystal, and it is defined as 
 
<math>

C = \frac{t_q \rho_q}{f_0}

</math>
 
where <math>t_q</math> is the thickness of the quartz, <math>\rho_q</math> is the density of the quartz plate, and f0 is the fundamental resonant frequency of quartz. With these, we can determine the mass of the deposited material. 
 
Another consideration would be the energy dissipation of the crystal to the surroundings. This is important, especially for viscoelastic films. Viscoelastic films violate the Sauerbrey condition that the bound mass is rigidly attached to the crystal without any slip. Such viscoelastic films dissipate energy via mechanical losses in the flexible mass.
[[File:AT and BT cut.png|200px|thumb|left|Orientation of AT- and BT- cut crystals]]
 
==Setup==
The typical QCM set-up of piezoelectric quartz crystal microbalance is shown in Figure (). The oscillator circuit is connected to the power supply and sample stage mount where the piezoelectric quartz crystal is. We can determine the resonance frequency of the quartz crystal using an oscilloscope, frequency counter, or spectrum analyzer. To determine the feasibility of this QCM project, we built a simple oscillating circuit as a foundation to test if we can detect the resonance frequency of the quartz crystal. This also serves as a time buffer while waiting for the AT-cut quartz to be delivered. Figure () shows the electrical circuit diagram and its implementation on a breadboard. As the electrical current generated from the oscillation of the quartz crystal is an alternating current due to the piezoelectric effect, we employ the usage of logic gates called inverters to convert DC to AC for readout. Adding a resistor to the circuit allows for the control of the potential difference across the inverter. In this oscillating circuit, we use a 14-pin integrated circuit and measure the resonant frequency of a CMAC CK q5 crystal oscillator.

==Measurements==
A DC power supply of 5V is given and an oscilloscope is connected to see the signal's waveform. A frequency counter is connected to the electrical circuit and communicated to my computer via the Arduino Integrated Development Environment. The frequency is measured for 10 seconds 10 times to get an average. Eventually, a resonant frequency of 10.000001Mhz is recorded, which is very close to the 10Mhz value that was provided by the manufacturer. The waveform seen on the oscilloscope is observed to be periodic and looks like a square-wave oscillation. [picture is waveform of first set up with 10Mhz] There seem to be additional peaks periodically formed as well, which could likely come from circuit impedance mismatches. Mismatches in impedance between different components or sections of a circuit can cause signal reflections and distortions, leading to additional peaks in the waveform. We would have to adjust the values of the capacitors and resistors.
 
Then, we replace the 10Mhz crystal oscillator with the AT-cut crystal. [picture is waveform of first set up] Although we managed to obtain the frequency signal generated by the AT-cut crystal, the surface of the crystal is very sensitive such that waving your hands near the oscillator causes the waveform to change. To make the signal more stable, we construct another circuit design similar to the Colpitts oscillator.[5] One of the advantages of using this layout is that relatively low phase noise can be achieved, making them suitable for applications requiring stable and low-noise oscillation.

==Second Set-Up==
The circuit design and the actual circuit is shown in Figure (). 2N2222 bipolar junction transistors were used with a combination of capacitors and resistors. The purpose of the transistor is to amplify the voltage across the resonant circuit and stabilise the oscillations through a feedback loop. 
A DC power supply of 9V is applied across the circuit and an oscilloscope is connected to observe the waveform. Figure () shows the waveform, which seems to be a superposition of square wave and another periodic signal which could be due to the aforementioned circuit impedance mismatches. [insert second set up] We use the Anritsu MS2711D Spectrum Master to look for the resonance frequencies as a cross-reference to the frequency counter measurement. In Figure (), the resonance frequency of the piezoelectric quartz oscillator and its higher-order harmonics are shown. [insert resonance frequency narrow, wide scan of frequency] From the wide scan, we can see that the zeroth-order overtone occurs at around approximately 6Mhz, and the higher-order harmonics occur in multiple integers of 6MHz.

==Second Measurement==
The procedure for the frequency counter measurements is the same as that of the 10MHz crystal oscillator. The fundamental resonant frequency is measured to be 5.986804MHz. Using this as the reference resonance frequency, we can now test its effectiveness in mass measurements with the Sauerbrey equation. 

Firstly, a permanent marker is used where we dot the center of the quartz crystal shown in Figure (). [insert permanent marker ink] There was no signal initially as shown in Figure (). [Explain why, insert no spectral signature for ink]However, increasing the DC supply voltage sufficiently allows the fundamental mode to be observed as shown in Figure (). [insert increase dc power supply] We repeated the frequency counter measurements and found the new resonance frequency to be 5.984613MHz. Based on the Sauerbrey equation, the decrease in resonance frequency of 2191Hz corresponds to an increase in mass of 969 micrograms. To get a sense of how accurate this measurement is, let us calculate how much a drop of water weighs. We assume that the density of the marker ink is approximately similar to water. A drop of water of 0.1ml is approximately 0.1 grams. [cite] This shows that measurement is about an order of magnitude higher than the approximation. This huge error arises because of the assumptions of using the Sauerbrey equation. The Sauerbrey equation is valid under the following conditions:
==References==
# Meissner A (1927) € Uber piezoelectrische Krystalle bei Hochfrequenz. Z Tech Phys 8:74
# O’Sullivan, C. K., & Guilbault, G. G. (1999). Commercial quartz crystal microbalances – theory and applications. Biosensors and Bioelectronics, 14(8), 663–670.
# Ebersole, R., Miller, J., Moran, J., & Ward, M. (1990). PZ quartz sensors for use in clinical analysis. J. Am. Chem. Soc, 112, 3239.
# Sauerbrey, G. (1959). Verwendung von Schwingquarzen zur Wägung dünner Schichten und zur Mikrowägung. Zeitschrift für Physik, 155(2), 206–222.
# US 1624537, Colpitts, Edwin H., "Oscillation generator", published 1 February 1918, issued 12 April 1927

Quartz Crystal MicroBalance (QCM)

2024-04-23T02:23:13Z

E0309214: /* Working Principle */

Quartz Crystal MicroBalance (QCM)

2024-04-19T09:16:01Z

E0309214: /* Setup */

Quartz Crystal MicroBalance (QCM)

2024-04-19T08:15:19Z

E0309214: /* Setup */

Quartz Crystal MicroBalance (QCM)

2024-04-18T09:14:58Z

E0309214: /* Idea */

Quartz Crystal MicroBalance (QCM)

2024-04-18T09:10:50Z

E0309214: /* Idea */

Quartz Crystal MicroBalance (QCM)

2024-04-18T09:02:44Z

E0309214: /* Abstract */

Quartz Crystal MicroBalance (QCM)

2024-03-26T03:27:41Z

E0309214:

==Abstract==
This project aims to measure the thickness of thin films using a quartz crystal microbalance(QCM). The thin films of interest are grown using magnetron sputtering at the eMagic Lab. In particular, Au will be deposited on a 10mm x 10mm x 0.5mm MgO(001) substrate. Thickness measurements are important in characterizing the sample, and it is helpful to get an estimate of the thickness which serves as a reference when fitting data from spectroscopic ellipsometry(SE). We can corroborate the measurements with atomic force microscopy(AFM) and SE data.

==Team members==
Tan Jhoon Yong
==Idea==
Measurements of the thickness of thin films are essential to get a preliminary idea of the thin-film interference effects. Getting a more accurate measurement of the thickness allows us to probe the optical properties of thin films better with SE data fitting.
==Sample Preparation==
7 samples of varying thicknesses of Au are deposited on a 10mm x 10mm x 0.5mm MgO(001) substrate using magnetron sputtering in an Ar-filled chamber. Insitu thickness measurement results are as follows: 20.6nm, 12.4nm, 8.3nm, 4.2nm, 2.1nm, 1.0nm.
==Working Principle==
The working principle behind the QCM is based on the piezoelectric effect. The piezoelectric effect is the generation of electric charges by a crystalline material upon subjecting it to stress.[1] An oscillating electric field applied across the device induces an acoustic wave that propagates through the crystal and meets minimum impedance when the device's thickness is a half-integer multiple of the wavelength of the acoustic wave.[2] It is a shear mode device in which the acoustic wave propagates in a direction perpendicular to the crystal surface.[3] Therefore, crystals cut in specific crystal axes have to be used to utilize the shear mode.
[[File:AT and BT cut.png|200px|thumb|left|Orientation of AT- and BT- cut crystals]]
A resonant oscillation in the crystal is achieved by putting the crystal in an oscillation circuit where the electrical and mechanical oscillations are close to the fundamental frequency of the crystal. Changes to the mass of the crystal would result in a proportional change in its natural frequency according to the Sauerbrey equation[4] 
 
Δf = -CΔm/A 
 
where Δf is the change in resonance frequency, C is the specific sensitivity of the crystal, Δm is the change in mass, and A is the active area of the crystal. C describes how much material per unit area is required to change the resonant frequency of the crystal by 1Hz. A smaller C value gives a higher mass sensitivity. This value depends on the fundamental resonant frequency of the crystal, and it is defined as 
 
C = vqρq/2f0² 
where vq is the shear wave velocity in quartz, ρq is the density of the quartz plate, and f0 is the fundamental resonant frequency of quartz. With these, we can determine the mass of the deposited material. 
 
Another consideration would be the energy dissipation of the crystal to the surroundings. This is important, especially for viscoelastic films. Viscoelastic films violate the Sauerbrey condition that the bound mass is rigidly attached to the crystal without any slip. Such viscoelastic films dissipate energy via mechanical losses in the flexible mass.
==Setup==
....
==Measurements==
....
==References==
# Meissner A (1927) € Uber piezoelectrische Krystalle bei Hochfrequenz. Z Tech Phys 8:74
# O’Sullivan, C. K., & Guilbault, G. G. (1999). Commercial quartz crystal microbalances – theory and applications. Biosensors and Bioelectronics, 14(8), 663–670.
# Ebersole, R., Miller, J., Moran, J., & Ward, M. (1990). PZ quartz sensors for use in clinical analysis. J. Am. Chem. Soc, 112, 3239.
# Sauerbrey, G. (1959). Verwendung von Schwingquarzen zur Wägung dünner Schichten und zur Mikrowägung. Zeitschrift für Physik, 155(2), 206–222.

Quartz Crystal MicroBalance (QCM)

2024-03-26T01:42:05Z

E0309214:

==Abstract==
This project aims to measure the thickness of thin films using a quartz crystal microbalance(QCM). The thin films of interest are grown using magnetron sputtering at the eMagic Lab. In particular, Au will be deposited on a 10mm x 10mm x 0.5mm MgO(001) substrate. Thickness measurements are important in characterizing the sample, and it is helpful to get an estimate of the thickness which serves as a reference when fitting data from spectroscopic ellipsometry(SE). We can corroborate the measurements with atomic force microscopy(AFM) and SE data.

==Team members==
Tan Jhoon Yong
==Idea==
Measurements of the thickness of thin films are essential to get a preliminary idea of the thin-film interference effects. Getting a more accurate measurement of the thickness allows us to probe the optical properties of thin films better with SE data fitting.
==Sample Preparation==
7 samples of varying thicknesses of Au are deposited on a 10mm x 10mm x 0.5mm MgO(001) substrate using magnetron sputtering in an Ar-filled chamber. Insitu thickness measurement results are as follows: 20.6nm, 12.4nm, 8.3nm, 4.2nm, 2.1nm, 1.0nm.
==Working Principle==
The working principle behind the QCM is based on the piezoelectric effect. The piezoelectric effect is the generation of electric charges by a crystalline material upon subjecting it to stress.[1] An oscillating electric field applied across the device induces an acoustic wave that propagates through the crystal and meets minimum impedance when the device's thickness is a half-integer multiple of the wavelength of the acoustic wave.[2] It is a shear mode device in which the acoustic wave propagates in a direction perpendicular to the crystal surface.[3] Therefore, crystals cut in specific crystal axes have to be used to utilize the shear mode.
[[File:AT and BT cut.png|200px|thumb|left|Orientation of AT- and BT- cut crystals]]
A resonant oscillation in the crystal is achieved by putting the crystal in an oscillation circuit where the electrical and mechanical oscillations are close to the fundamental frequency of the crystal. Changes to the mass of the crystal would result in a proportional change in its natural frequency according to the Sauerbrey equation[4] 
 
Δf = -CΔm/A 
 
where Δf is the change in resonance frequency, C is the specific sensitivity of the crystal, Δm is the change in mass, and A is the active area of the crystal. C describes how much material per unit area is required to change the resonant frequency of the crystal by 1Hz. A smaller C value gives a higher mass sensitivity. This value depends on the fundamental resonant frequency of the crystal, and it is defined as 
 
C = v0ρ0/2f0² 
Therefore, we can determine the mass of the deposited material. For the scope of this project, energy dissipation is assumed to be negligible,
==Setup==
....
==Measurements==
....
==References==
# Meissner A (1927) € Uber piezoelectrische Krystalle bei Hochfrequenz. Z Tech Phys 8:74
# O’Sullivan, C. K., & Guilbault, G. G. (1999). Commercial quartz crystal microbalances – theory and applications. Biosensors and Bioelectronics, 14(8), 663–670.
# Ebersole, R., Miller, J., Moran, J., & Ward, M. (1990). PZ quartz sensors for use in clinical analysis. J. Am. Chem. Soc, 112, 3239.
# Sauerbrey, G. (1959). Verwendung von Schwingquarzen zur Wägung dünner Schichten und zur Mikrowägung. Zeitschrift für Physik, 155(2), 206–222.

Quartz Crystal MicroBalance (QCM)

2024-03-26T01:25:21Z

E0309214:

==Abstract==
This project aims to measure the thickness of thin films using a quartz crystal microbalance(QCM). The thin films of interest are grown using magnetron sputtering at the eMagic Lab. In particular, Au will be deposited on a 10mm x 10mm x 0.5mm MgO(001) substrate. Thickness measurements are important in characterizing the sample, and it is helpful to get an estimate of the thickness which serves as a reference when fitting data from spectroscopic ellipsometry(SE). We can corroborate the measurements with atomic force microscopy(AFM) and SE data.

==Team members==
Tan Jhoon Yong
==Idea==
Measurements of the thickness of thin films are essential to get a preliminary idea of the thin-film interference effects. Getting a more accurate measurement of the thickness allows us to probe the optical properties of thin films better with SE data fitting.
==Sample Preparation==
7 samples of varying thicknesses of Au are deposited on a 10mm x 10mm x 0.5mm MgO(001) substrate using magnetron sputtering in an Ar-filled chamber. Insitu thickness measurement results are as follows: 20.6nm, 12.4nm, 8.3nm, 4.2nm, 2.1nm, 1.0nm.
==Working Principle==
The working principle behind the QCM is based on the piezoelectric effect. The piezoelectric effect is the generation of electric charges by a crystalline material upon subjecting it to stress.[1] An oscillating electric field applied across the device induces an acoustic wave that propagates through the crystal and meets minimum impedance when the device's thickness is a half-integer multiple of the wavelength of the acoustic wave.[2] It is a shear mode device in which the acoustic wave propagates in a direction perpendicular to the crystal surface.[3] Therefore, crystals cut in specific crystal axes have to be used to utilize the shear mode.
[[File:AT and BT cut.png|200px|thumb|left|Orientation of AT- and BT- cut crystals]]
A resonant oscillation in the crystal is achieved by putting the crystal in an oscillation circuit where the electrical and mechanical oscillations are close to the fundamental frequency of the crystal. Changes to the mass of the crystal would result in a proportional change in its natural frequency according to the Sauerbrey equation 
&Delta:f = -C&Delta:m/A 
where &Delta:f is the change in resonance frequency, C is the specific sensitivity of the crystal, &Delta:m is the change in mass, and A is the active area of the crystal.
==Setup==
....
==Measurements==
....
==References==
# Meissner A (1927) € Uber piezoelectrische Krystalle bei Hochfrequenz. Z Tech Phys 8:74
# O’Sullivan, C. K., & Guilbault, G. G. (1999). Commercial quartz crystal microbalances – theory and applications. Biosensors and Bioelectronics, 14(8), 663–670.
# Ebersole, R., Miller, J., Moran, J., & Ward, M. (1990). PZ quartz sensors for use in clinical analysis. J. Am. Chem. Soc, 112, 3239.
# Sauerbrey, G. (1959). Verwendung von Schwingquarzen zur Wägung dünner Schichten und zur Mikrowägung. Zeitschrift für Physik, 155(2), 206–222.

Quartz Crystal MicroBalance (QCM)

2024-03-26T00:53:44Z

E0309214:

File:AT and BT cut.png

2024-03-19T01:46:09Z

E0309214:

Quartz Crystal MicroBalance (QCM)

2024-03-19T01:37:59Z

E0309214:

Main Page

2024-03-07T07:24:54Z

E0309214:

'''Welcome to the wiki page for the course PC5271: Physics of Sensors!'''

This is the repository where projects are documented. Creation of new accounts have now been blocked,and editing/creating pages is enabled. If you need an account, please contact Christian.

==Projects==
===[[Project 1 (Example)]]===
Keep a very brief description of a project or even a suggestion here, and perhaps the names of the team members, or who to contact if there is interest to join. Once the project has stabilized, keep stuff in the project page linked by the headline.

===[[Simple Optical Heart Rate Monitor]]===
This project demonstrates the principles of photoplethysmography (PPG) through the construction of a simple device to measure heart rate. The project involves using an LED and photodiode to detect variations in light absorption caused by changes in blood volume during each heartbeat.

===[[Gas sensor]]===
This project aims to use high and low detection methods of tin dioxide (SnO2) sensor to detect carbon monoxide or other combustible gases.

===[[Optical Sensor for Noise Flickering]]===
Group Members: Eric Cheung; Lee An Min, Amanda; Loh Jia Ying Whitney

This project aims to use a simple voltage divider made up with resistors and LDR to measure visual noise tags.

===[[Real time temperature alarm ]]===

This project aims to build a system using Python and Raspberry Pi to measure and display temperature in real-time using temperature sensors, and to issue an alarm when the temperature exceeds the set threshold

===[[Impedance spectroscopy of KBr]]===

This project aims to study the electrical properties of Potassium Bromide (KBr) using impedance spectroscopy.

===[[Sensor that recognizes specific sounds and steers toward the source]]===
A microphone array is used to capture sound signals, and the direction of the sound source is determined by analyzing the time difference of sound signals received by different microphones.

===[[Optical Sensor for UV Radiation]]===
This project aims to design a photodiode-based optical sensor to detect UV radiation levels.

===[[High Sensitive Position Sensor based on PDH technique]]===

Group Members: Angela Anna Baiju, Chenyue Gu, Joel K Jose

This project uses PDH locking technique to align a cavity to its resonance and read out the error signal to analyse the position change and other noises present in the system.

===[[Photodiodes as Single Photon Detectors]]===
Group Members: Abas Syahbana, Lu Xinghaou

In this project, we will use several LEDs as Single Photon Avalanche Detectors (SPADs). We will use a light bulb as the light source and grating to vary the wavelength of the light source. Thus, by knowing which light source is working for the LEDs to detect photons, we can determine band gaps of each LEDs.

===[[Temperature Sensor]]===
This project aims to construct a portable non-contact thermometer to detect the component temperature after the circuit board is energized, thereby preventing burns from direct contact.

===[[Quartz Crystal MicroBalance (QCM)]]===
This project aims to measure the thicknesses of gold thin films on a MgO(001) substrate using a QCM.

==Resources==
===Recorded sessions===
===Devices and material===
Apart form the stuff in the teaching lab, we have a resources you may want to consider for your project:
*...
===Books and links===
===Software===
* Various Python extensions. [https://www.python.org Python] is a very powerful free programming language that runs on just about any computer platform. It is open source and completely free.
* [https://www.gnuplot.info Gnuplot]: A free and very mature data display tool that works on just about any platform used that produces excellent publication-grade eps and pdf figures. Can be also used in scripts. Open source and completely free.
* Matlab: Very common, good toolset also for formal mathematics, good graphics. Expensive. We may have a site license, but I am not sure how painful it is for us to get a license for this course. Ask if interested.
* Mathematica: More common among theroetical physicists, very good in formal maths, now with better numerics. Graphs are ok but can be a pain to make looking good. As with Matlab, we do have a campus license. Ask if interested.

===Data sheets===
A number of components might be useful for several groups. Some common data sheets are here:
* Generic Silicon pin Photodiode type [[Media:Bpw34.pdf|BPW34]]
* Digital microphone [https://www.knowles.com/docs/default-source/default-document-library/sph0655lm4h-1_cornell_ii_datasheet9e1e1c731dff6ddbb37cff0000940c19.pdf SPH0655LM4H-1]; a small adapter board exists (see [[Soldering small parts]])

==Some wiki reference materials==
* [https://www.mediawiki.org/wiki/Special:MyLanguage/Manual:FAQ MediaWiki FAQ]
* [[Writing mathematical expressions]]
* [[Uploading images and files]]

Main Page

2024-03-07T07:24:21Z

E0309214:

'''Welcome to the wiki page for the course PC5271: Physics of Sensors!'''

This is the repository where projects are documented. Creation of new accounts have now been blocked,and editing/creating pages is enabled. If you need an account, please contact Christian.

==Projects==
===[[Project 1 (Example)]]===
Keep a very brief description of a project or even a suggestion here, and perhaps the names of the team members, or who to contact if there is interest to join. Once the project has stabilized, keep stuff in the project page linked by the headline.

===[[Simple Optical Heart Rate Monitor]]===
This project demonstrates the principles of photoplethysmography (PPG) through the construction of a simple device to measure heart rate. The project involves using an LED and photodiode to detect variations in light absorption caused by changes in blood volume during each heartbeat.

===[[Gas sensor]]===
This project aims to use high and low detection methods of tin dioxide (SnO2) sensor to detect carbon monoxide or other combustible gases.

===[[Optical Sensor for Noise Flickering]]===
Group Members: Eric Cheung; Lee An Min, Amanda; Loh Jia Ying Whitney

This project aims to use a simple voltage divider made up with resistors and LDR to measure visual noise tags.

===[[Real time temperature alarm ]]===

This project aims to build a system using Python and Raspberry Pi to measure and display temperature in real-time using temperature sensors, and to issue an alarm when the temperature exceeds the set threshold

===[[Impedance spectroscopy of KBr]]===

This project aims to study the electrical properties of Potassium Bromide (KBr) using impedance spectroscopy.

===[[Sensor that recognizes specific sounds and steers toward the source]]===
A microphone array is used to capture sound signals, and the direction of the sound source is determined by analyzing the time difference of sound signals received by different microphones.

===[[Optical Sensor for UV Radiation]]===
This project aims to design a photodiode-based optical sensor to detect UV radiation levels.

===[[High Sensitive Position Sensor based on PDH technique]]===

Group Members: Angela Anna Baiju, Chenyue Gu, Joel K Jose

This project uses PDH locking technique to align a cavity to its resonance and read out the error signal to analyse the position change and other noises present in the system.

===[[Photodiodes as Single Photon Detectors]]===
Group Members: Abas Syahbana, Lu Xinghaou

In this project, we will use several LEDs as Single Photon Avalanche Detectors (SPADs). We will use a light bulb as the light source and grating to vary the wavelength of the light source. Thus, by knowing which light source is working for the LEDs to detect photons, we can determine band gaps of each LEDs.

===[[Temperature Sensor]]===
This project aims to construct a portable non-contact thermometer to detect the component temperature after the circuit board is energized, thereby preventing burns from direct contact.

===[[Quartz Crystal Microbalance (QCM)]]===
This project aims to measure the thicknesses of gold thin films on a MgO(001) substrate using a QCM.

==Resources==
===Recorded sessions===
===Devices and material===
Apart form the stuff in the teaching lab, we have a resources you may want to consider for your project:
*...
===Books and links===
===Software===
* Various Python extensions. [https://www.python.org Python] is a very powerful free programming language that runs on just about any computer platform. It is open source and completely free.
* [https://www.gnuplot.info Gnuplot]: A free and very mature data display tool that works on just about any platform used that produces excellent publication-grade eps and pdf figures. Can be also used in scripts. Open source and completely free.
* Matlab: Very common, good toolset also for formal mathematics, good graphics. Expensive. We may have a site license, but I am not sure how painful it is for us to get a license for this course. Ask if interested.
* Mathematica: More common among theroetical physicists, very good in formal maths, now with better numerics. Graphs are ok but can be a pain to make looking good. As with Matlab, we do have a campus license. Ask if interested.

===Data sheets===
A number of components might be useful for several groups. Some common data sheets are here:
* Generic Silicon pin Photodiode type [[Media:Bpw34.pdf|BPW34]]
* Digital microphone [https://www.knowles.com/docs/default-source/default-document-library/sph0655lm4h-1_cornell_ii_datasheet9e1e1c731dff6ddbb37cff0000940c19.pdf SPH0655LM4H-1]; a small adapter board exists (see [[Soldering small parts]])

==Some wiki reference materials==
* [https://www.mediawiki.org/wiki/Special:MyLanguage/Manual:FAQ MediaWiki FAQ]
* [[Writing mathematical expressions]]
* [[Uploading images and files]]

Main Page

2024-03-07T07:23:55Z

E0309214:

'''Welcome to the wiki page for the course PC5271: Physics of Sensors!'''

This is the repository where projects are documented. Creation of new accounts have now been blocked,and editing/creating pages is enabled. If you need an account, please contact Christian.

==Projects==
===[[Project 1 (Example)]]===
Keep a very brief description of a project or even a suggestion here, and perhaps the names of the team members, or who to contact if there is interest to join. Once the project has stabilized, keep stuff in the project page linked by the headline.

===[[Simple Optical Heart Rate Monitor]]===
This project demonstrates the principles of photoplethysmography (PPG) through the construction of a simple device to measure heart rate. The project involves using an LED and photodiode to detect variations in light absorption caused by changes in blood volume during each heartbeat.

===[[Gas sensor]]===
This project aims to use high and low detection methods of tin dioxide (SnO2) sensor to detect carbon monoxide or other combustible gases.

===[[Optical Sensor for Noise Flickering]]===
Group Members: Eric Cheung; Lee An Min, Amanda; Loh Jia Ying Whitney

This project aims to use a simple voltage divider made up with resistors and LDR to measure visual noise tags.

===[[Real time temperature alarm ]]===

This project aims to build a system using Python and Raspberry Pi to measure and display temperature in real-time using temperature sensors, and to issue an alarm when the temperature exceeds the set threshold

===[[Impedance spectroscopy of KBr]]===

This project aims to study the electrical properties of Potassium Bromide (KBr) using impedance spectroscopy.

===[[Sensor that recognizes specific sounds and steers toward the source]]===
A microphone array is used to capture sound signals, and the direction of the sound source is determined by analyzing the time difference of sound signals received by different microphones.

===[[Optical Sensor for UV Radiation]]===
This project aims to design a photodiode-based optical sensor to detect UV radiation levels.

===[[High Sensitive Position Sensor based on PDH technique]]===

Group Members: Angela Anna Baiju, Chenyue Gu, Joel K Jose

This project uses PDH locking technique to align a cavity to its resonance and read out the error signal to analyse the position change and other noises present in the system.

===[[Photodiodes as Single Photon Detectors]]===
Group Members: Abas Syahbana, Lu Xinghaou

In this project, we will use several LEDs as Single Photon Avalanche Detectors (SPADs). We will use a light bulb as the light source and grating to vary the wavelength of the light source. Thus, by knowing which light source is working for the LEDs to detect photons, we can determine band gaps of each LEDs.

===[[Temperature Sensor]]===
This project aims to construct a portable non-contact thermometer to detect the component temperature after the circuit board is energized, thereby preventing burns from direct contact.

===[[Quartz Crystal Microbalance(QCM)]]===
This project aims to measure the thicknesses of gold thin films on a MgO(001) substrate using a QCM.

==Resources==
===Recorded sessions===
===Devices and material===
Apart form the stuff in the teaching lab, we have a resources you may want to consider for your project:
*...
===Books and links===
===Software===
* Various Python extensions. [https://www.python.org Python] is a very powerful free programming language that runs on just about any computer platform. It is open source and completely free.
* [https://www.gnuplot.info Gnuplot]: A free and very mature data display tool that works on just about any platform used that produces excellent publication-grade eps and pdf figures. Can be also used in scripts. Open source and completely free.
* Matlab: Very common, good toolset also for formal mathematics, good graphics. Expensive. We may have a site license, but I am not sure how painful it is for us to get a license for this course. Ask if interested.
* Mathematica: More common among theroetical physicists, very good in formal maths, now with better numerics. Graphs are ok but can be a pain to make looking good. As with Matlab, we do have a campus license. Ask if interested.

===Data sheets===
A number of components might be useful for several groups. Some common data sheets are here:
* Generic Silicon pin Photodiode type [[Media:Bpw34.pdf|BPW34]]
* Digital microphone [https://www.knowles.com/docs/default-source/default-document-library/sph0655lm4h-1_cornell_ii_datasheet9e1e1c731dff6ddbb37cff0000940c19.pdf SPH0655LM4H-1]; a small adapter board exists (see [[Soldering small parts]])

==Some wiki reference materials==
* [https://www.mediawiki.org/wiki/Special:MyLanguage/Manual:FAQ MediaWiki FAQ]
* [[Writing mathematical expressions]]
* [[Uploading images and files]]

Main Page

2024-03-07T07:22:55Z

E0309214:

'''Welcome to the wiki page for the course PC5271: Physics of Sensors!'''

This is the repository where projects are documented. Creation of new accounts have now been blocked,and editing/creating pages is enabled. If you need an account, please contact Christian.

==Projects==
===[[Project 1 (Example)]]===
Keep a very brief description of a project or even a suggestion here, and perhaps the names of the team members, or who to contact if there is interest to join. Once the project has stabilized, keep stuff in the project page linked by the headline.

===[[Simple Optical Heart Rate Monitor]]===
This project demonstrates the principles of photoplethysmography (PPG) through the construction of a simple device to measure heart rate. The project involves using an LED and photodiode to detect variations in light absorption caused by changes in blood volume during each heartbeat.

===[[Gas sensor]]===
This project aims to use high and low detection methods of tin dioxide (SnO2) sensor to detect carbon monoxide or other combustible gases.

===[[Optical Sensor for Noise Flickering]]===
Group Members: Eric Cheung; Lee An Min, Amanda; Loh Jia Ying Whitney

This project aims to use a simple voltage divider made up with resistors and LDR to measure visual noise tags.

===[[Real time temperature alarm ]]===

This project aims to build a system using Python and Raspberry Pi to measure and display temperature in real-time using temperature sensors, and to issue an alarm when the temperature exceeds the set threshold

===[[Impedance spectroscopy of KBr]]===

This project aims to study the electrical properties of Potassium Bromide (KBr) using impedance spectroscopy.

===[[Sensor that recognizes specific sounds and steers toward the source]]===
A microphone array is used to capture sound signals, and the direction of the sound source is determined by analyzing the time difference of sound signals received by different microphones.

===[[Optical Sensor for UV Radiation]]===
This project aims to design a photodiode-based optical sensor to detect UV radiation levels.

===[[High Sensitive Position Sensor based on PDH technique]]===

Group Members: Angela Anna Baiju, Chenyue Gu, Joel K Jose

This project uses PDH locking technique to align a cavity to its resonance and read out the error signal to analyse the position change and other noises present in the system.

===[[Photodiodes as Single Photon Detectors]]===
Group Members: Abas Syahbana, Lu Xinghaou

In this project, we will use several LEDs as Single Photon Avalanche Detectors (SPADs). We will use a light bulb as the light source and grating to vary the wavelength of the light source. Thus, by knowing which light source is working for the LEDs to detect photons, we can determine band gaps of each LEDs.

===[[Temperature Sensor]]===
This project aims to construct a portable non-contact thermometer to detect the component temperature after the circuit board is energized, thereby preventing burns from direct contact.

===[[Thickness Measurements of Thin Films using Quartz Crystal Microbalance(QCM)]]===
This project aims to measure the thicknesses of gold thin films on a MgO(001) substrate using a QCM.

==Resources==
===Recorded sessions===
===Devices and material===
Apart form the stuff in the teaching lab, we have a resources you may want to consider for your project:
*...
===Books and links===
===Software===
* Various Python extensions. [https://www.python.org Python] is a very powerful free programming language that runs on just about any computer platform. It is open source and completely free.
* [https://www.gnuplot.info Gnuplot]: A free and very mature data display tool that works on just about any platform used that produces excellent publication-grade eps and pdf figures. Can be also used in scripts. Open source and completely free.
* Matlab: Very common, good toolset also for formal mathematics, good graphics. Expensive. We may have a site license, but I am not sure how painful it is for us to get a license for this course. Ask if interested.
* Mathematica: More common among theroetical physicists, very good in formal maths, now with better numerics. Graphs are ok but can be a pain to make looking good. As with Matlab, we do have a campus license. Ask if interested.

===Data sheets===
A number of components might be useful for several groups. Some common data sheets are here:
* Generic Silicon pin Photodiode type [[Media:Bpw34.pdf|BPW34]]
* Digital microphone [https://www.knowles.com/docs/default-source/default-document-library/sph0655lm4h-1_cornell_ii_datasheet9e1e1c731dff6ddbb37cff0000940c19.pdf SPH0655LM4H-1]; a small adapter board exists (see [[Soldering small parts]])

==Some wiki reference materials==
* [https://www.mediawiki.org/wiki/Special:MyLanguage/Manual:FAQ MediaWiki FAQ]
* [[Writing mathematical expressions]]
* [[Uploading images and files]]

Quartz Crystal MicroBalance (QCM)

2024-03-07T03:41:37Z

E0309214: Created page with "==Abstract== This project aims to measure the thickness of thin films using a quartz crystal microbalance(QCM). The thin films of interest are grown using magnetron sputtering at the eMagic Lab. In particular, Au will be deposited on a 10mm x 10mm x 0.5mm MgO(001) substrate. Thickness measurements are important in characterizing the sample, and it is helpful to get an estimate of the thickness which serves as a reference when fitting data from spectroscopic ellipsometry(..."