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QCM100 Manual - Stanford Research Systems

1. The self assembly of alkanethiol monolayers onto gold has been studied extensively due to the potential application of these interfaces to 1 chemical and biological sensing 2 nano and micro device manufacturing and 3 surface modification A significant amount of work has been dedicated to understanding the steady state properties of SAMs once they have formed However more recently it has become clear that alkanethiol SAMs are highly dynamic structures and a lot of renewed effort has been dedicated to the understanding of the mechanism of monolayer formation OCM100 Quartz Crystal Microbalance ASRS ASRS Theory Operation and Calibration 2 31 The QCM100 system provides a unique opportunity to monitor in situ and in real time the rate of adsorption of alkanethiols onto gold the change i e decrease in frequency resulting from the adsorption of alkanethiol molecules onto the gold electrode of a QCM crystal allows direct measurement of the rate of formation of SAMs Tip Silanes are another common material used in SAMs Silanization has also been studied with QCMs using crystals with electrodes custom coated with thin layers of Si 111 Several examples of direct measurement of adsorption kinetics of alkanethiolate SAMs on QCM crystals from both gas and liquid phase are included in the references list at the end of this chapter Self Assembled Monolayer Frequency
2. Electrode Materials Gold electrodes 100 1000 nm thick are the most commonly used in QCM applications because of the ease with which gold is evaporated However other metals such as Pt Cu Al and Ni have also been used A thin 2 20 nm adhesion layer of either Cr Ti or Si is often deposited directly on the quartz to aid in the adhesion of the metal electrode Chromium is recommended for polished blank surfaces and also for crystals operated in a harsh environment However Cr can be a problem in some electrochemical applications spurious electrochemical responses can sometimes result if diffusion of the adhesion material to the electrode surface occurs In that case Titanium is recommended as a substitute adhesive layer If Ti is still a problem Palladium can be utilized as a barrier metal between the Cr or Ti and the primary metallization consult Stanford Research Systems for availability of alternative electrode materials A zinc layer sandwiched between the adhesion layer and the electrode pad on the front or deposition side of the crystal has a relatively low bulk modulus and has been shown to absorb stress imposed by the deposited materials The buffer layer prolongs useful crystal life particularly when depositing dielectric materials The crystal should have a modest surface roughness as keying in structure The buffer layer can be a zinc layer of 600 nm QCM100 Quartz Crystal Microbalance 3 6 Sensor Crystals and Holders
3. The flow cell is made of chemically resistant Kynar and includes two inlet and outlet ports with 0 040 ID thru hole and fitted with barbed hose adapters for 0 062 ID tubing Simply slide your tube over the barbed stems to create a reliable low pressure connection to a syringe siphon system or peristaltic pump Consult Chapter 3 for additional tips on the operation of Iquid flow cells Tip For flowing QCM setups requiring connection to a flow injection or sequential injection analysis system it is common practice to interface the capillary tubing to the flow cell using a short section of 1 16 ID PHARMED tubing for example part 1557 from www upchurch com Eliminating gas bubbles trapped inside the crystal chamber is essential for accurate measurements Please consult the Bubbles and Liquid Flow Cells section in Chapter 3 for some useful bubble elimination tricks Operation Two modes of operation are common for QCM flow cells Batch Mode The crystal is exposed to a sequence of sample solvent batches through a series of load rinse exchanges Syringes and the siphon principle are commonly used to manually inject new solutions into the crystal chamber OCM100 Quartz Crystal Microbalance ASRS ASRS Getting Started 1 13 Flow Mode A constant flow of solution solvent runs over the crystal in an open or closed flow configuration In open flow systems the Syphon principle is recommended to implement the lowes
4. possibly even shaky It might even be difficult to obtain a stable baseline Spurious signals might become evident in electrochemical QCM experiments As the sensor crystal is coated the series resonance resistance increases indicating a loss of crystal Q When this occurs the circuit may occasionally resonate at one of the anharmonic frequencies The oscillation may switch to an anharmonic mode or it may alternate between the fundamental and anharmonic frequencies a condition known as mode hopping This is a potentially dangerous scenario since it might lead to early termination of a deposition or film growth process Notice that there is no outward evidence of mode hopping except for a discontinuity in the film thickness Also even though the film thickness changes dramatically the mass sensitivity and rate of growth change by only a few percent Some experiments can cause irreversible changes on the crystal surface For example the use of silver depositions on gold electrodes for calibration of electrochemical QCMs is not always recommended because silver is hard to remove reversibly from gold electrodes Copper or lead are often recommended instead Crystals exposed to etching solutions i e Piranha solution usually need to be replaced after two to three experiments Film stress can be particularly damaging Stress can bend the crystal and induce a frequency change not related to mass It can cause the electrode to tear from the
5. sandwiched between a titanium or chromium adhesion layer of 10 to 16 nm and a gold silver or aluminum outer electrode layer of about 200 nm For applications requiring transparent electrodes tin doped indium oxide ITO electrodes are recommended ITO is routinely used to make transparent conductive coatings which are applied in a wide variety of applications Transparent electrodes are often used in cell adhesion studies when visualization of the sample cells is required during the experiments ITO coated QCM crystals can be special ordered directly from Stanford Research Systems or through your local SRS representative In principle any type of material that can be deposited onto the surface of the underlying metal electrode can be used on the sensor crystals The only limitation on the use of such materials is that their deposition must be carried out in such a way that the temperature of the quartz crystal does not exceed 573 C above which quartz looses its piezoelectric activity Quartz blanks are available directly from Stanford Research Systems contact the factory or your local representative for details Strict attention to cleanliness is required while performing a custom electrode deposition It is important to keep in mind that mass changes at the QCM active electrode surface influence the frequency because these electrodes are part of the composite resonator composed of 1 the quartz crystal 2 its metal electrodes 3 a
6. 3 it holds four crystals is made entirely of Teflon and it is specifically designed for immersion into a 100mL beaker Figure 3 Crystal Cleaning Basket SRS Part O100CCB The entire basket is made out of Teflon and is shown here holding its maximum load of 4 crystals not included OCM100 Quartz Crystal Microbalance ASRS Sensor Crystals and Holders 3 21 Tips for Operation in Liquids ASRS To minimize measurement errors in liquid phase QCM experiments the sample fluids should be prepared carefully Changes in temperature flow rates properties of the solvent as well as air bubbles will affect the sensor signal For reproducible measurements keep the following tips in mind Check for Chemical Compatibility Before starting an experiment check for chemical compatibility between sample solutions solvents holder flow cell orings and crystals For example avoid contact between Viton orings and DMSO solvent If necessary consider replacing incompatible components with alternative materials Check the POGO contacts regularly It is good practice to check the POGO contacts regularly for signs of corrosion and wear Replace the pins with new ones if necessary see Head Cleaning above Degas the sample liquid Whenever possible sample liquids should be degassed to avoid the growth of air bubbles on the surface of immersed crystals Presoak the crystal in the sample liquid To minimize long term i e hours lo
7. 1 OCM100 Quartz Crystal Microbalance 5 2 D5 D6 J1 J2 13 L1 L2 P1 P2 PCI Q1 R1 R2 R3 R4 R5 R6 R7 R8 R9 R10 R11 R12 R 13 R 14 R15 R 16 R17 R18 R19 R20 R21 R22 R23 R24 R25 R 26 R 27 R 28 R 29 R 30 R31 R 32 OCM100 Quartz Crystal Microbalance Parts List 3 00011 303 3 00011 303 1 00505 100 1 00003 120 1 00003 120 6 00236 631 6 00236 631 4 00370 441 4 00019 443 7 01422 701 3 00580 360 4 01213 462 4 01280 462 4 01471 461 4 01503 461 4 01503 461 4 01503 461 4 01503 461 4 01503 461 4 01503 461 4 01575 461 4 01338 462 4 01455 461 4 01447 461 4 01447 461 4 01455 461 4 01455 461 4 01146 462 4 01209 462 4 01242 462 4 01088 462 4 01088 462 4 01227 462 4 01213 462 4 01338 462 4 01338 462 4 01213 462 4 01191 462 4 01455 461 4 01447 461 4 01447 461 4 01117 462 4 01117 462 RED RED RJ45 MODULAR BNC BNC FR47 FR47 500 20K QCM100 MMBT3906LT1 10 0K 49 9K 470 10K 10K 10K 10K 10K 10K 10M 200K 100 47 47 100 100 2 00K 9 09K 20 0K 499 499 14 0K 10 0K 200K 200K 10 0K 5 90K 100 47 47 1 00K 1 00K LED T1 Package LED T1 Package Connector Misc Connector BNC Connector BNC Ferrite bead SMT Ferrite bead SMT Pot Multi Turn Trim 3 8 Square Top Ad Pot 10 Turn Panel Printed Circuit Board Integrated Circuit Surface Mount Pkg Thin Film 1 50 ppm MELF Resistor Thin Film 1 50 ppm MELF Resistor Thick Film 5 200 ppm Chip
8. 1998 6337 6340 Spangler B D and Tyler B Capture Agents for a Quartz Crystal Microbalance Continuous Flow Biosensor Functionalized Self assembled Monolayers on Gold Anal Chim Acta 399 1999 51 62 Note Professor Spangler is also CEO of SensoPath Technologies a company specialized in the development of materials for the design and fabrication of SAMs on gold surfaces www sensoPath com D S Karpovich and G J Blanchard Direct Measurement of the Adsorption Kinetics of Alkanethiolate Self Assembled Monolayers on a Microcrystalline Gold Surface Langmuir 10 1994 3315 C R Suri et al Biosensors and Bioelectronics 9 1994 325 S Yamaguchi et al Adsorption Immobilization and Hybridization of DNA Studies by the use of QC Oscillators Anal Chem 65 1993 1925 OCM100 Quartz Crystal Microbalance ASRS Theory Operation and Calibration 2 39 P E Hockberger et al Cellular engineering control of cell substrate interactions in Nanofabrication and Biosystems H C Hoch L W Jelinski and H G Craighead Eds Cambridge University press 1996 276 299 D S Karpovich and G J Blanchard Direct Measurement of the Adsorption Kinetics of Alkanethiolate Self Assembled Monolayers on a Microcrystalline Gold Surface Langmuir 10 1994 3315 H M Schessler et al Quantitating the Balance between Enthalpic and Entropic Forces in Alkanethiol Gold Monolayer Self Assembly J Am
9. 7 01413 720 9 00267 917 47 4 02K 1 00K 1 000K 1 000K 220 49 9 47 100K 100K 47 49 9 4 99K 4 99K 10 374 100 100 ADTI 6T ADTI 6T AD8367ARU DS8921AM OPA337UA AD8009 3 8 4 40X1 4PF 4 40X3 16PP PCB POST RED 4 24 BLK BNC BUSHING 3 8X5 8 032THK MALE BNC 4979 EQCM EQCM GENERIC OCM100 Quartz Crystal Microbalance Thick Film 5 200 ppm Chip Resistor Thin Film 1 50 ppm MELF Resistor Thin Film 1 50 ppm MELF Resistor Resistor Metal Film 1 8W 0 1 25ppm Resistor Metal Film 1 8W 0 1 25ppm Thick Film 5 200 ppm Chip Resistor Thin Film 1 50 ppm MELF Resistor Thick Film 5 200 ppm Chip Resistor Thick Film 5 200 ppm Chip Resistor Thick Film 5 200 ppm Chip Resistor Thick Film 5 200 ppm Chip Resistor Thin Film 1 50 ppm MELF Resistor Thin Film 1 50 ppm MELF Resistor Thin Film 1 50 ppm MELF Resistor Thick Film 5 200 ppm Chip Resistor Thin Film 1 50 ppm MELF Resistor Thin Film 1 50 ppm MELF Resistor Thin Film 1 50 ppm MELF Resistor Transformer Transformer Integrated Circuit Thru hole Pkg Integrated Circuit Surface Mount Pkg Integrated Circuit Surface Mount Pkg Integrated Circuit Surface Mount Pkg Lugs Screw Black All Types Screw Panhead Phillips Binding Post Wire 24 UL1007 Strip 1 4x1 4 Tin Insulators Washer nylon Connector BNC Fabricated Part Fabricated Part Product Labels ASRS
10. Capacitance Cancellation 2 7 Frequency Measurement 2 8 Resistance Measurement 2 11 Gas Phase Measurements 2 16 Liquid Contact Measurements 2 18 Immersion Test 2 21 Electrochemical Quartz Crystal Microbalance 2 22 Chemical and Biological Sensors 2 28 Self Assembled Monolayers 2 30 Dissipation Technique 2 33 References 2 34 Chapter 3 Sensor Crystals and Holders Introduction 3 3 Sensor Crystals 3 3 Principle of Operation 3 4 Crystal Handling 3 11 Surface Modifications 3 15 Crystal Holder 3 18 SRS QCM100 Quartz Crystal Microbalance iv Contents Crystal Cleaning Basket Tips for Operation in Liquids Tips for Operation in Gases Bubbles and Liquid Flow Cells References Chapter 4 QCM Circuit Description Introduction QCM25 Circuit Description QCM100 Circuit Description Schematic Diagrams Chapter 5 Parts List QCM100 QCM25 3 20 3 21 3 23 3 24 3 27 4 3 4 5 4 9 5 1 5 5 OCM100 Quartz Crystal Microbalance ASRS Overview v Front Panel Overview ASRS STANFORD RESEARCH SYSTEMS MODEL QCM100 QUARTZ CRYSTAL MICROBALANCE ANALOG CONTROLLER Power Crystal Probe Frequency Conductance Co Compensation Output Output SET DIAL TO NULL Co osc A ADJUST cu HOLD RJ45 Cat 5 Straight 0 10V Rs 1 KQ Figure 1 Front Panel of OCM100 Analog Controller Power Switch w green PWR LED The QCM100 Analog Controller is turned on by flipping the power switch A green PWR LED lights up to indicate th
11. Chem Soc 118 1996 9645 D S Karpovich and G J Blanchard Vapor adsorption onto metal and modified interfaces Evidence for adsorbate penetration of an alkanethiol Monolayer on Gold Langmuir 13 1997 4031 D S Karpovich and G J Blanchard An Undergraduate Laboratory Experiment for he Direct Measurement of Monolayer Formation Kinetics J Chem Education 72 1995 466 J Justin Gooding and D Brynn Hibbert The application of alkanethiol self assembled monolayers to enzyme electrodes TrAC Trends in Analytical Chemistry 18 8 1999 525 Zhao Yang Wu et al QCM Immunosensor for Schistsoma Japonicum Infected Rabit Serum Analytical Sciences 19 2003 437 Yung Chuan Liu Chih Ming Wang and Kuang Pin Hsiung Comparison of Different Protein Immobilization Methods on Quartz Crystal Microbalance Surface in Flow Injection Immunoassay Analytical Biochemistry 299 2001 130 135 S Yamaguchi et al Adsorption Immobilization and Hybridization of DNA Studies by the use of QC Oscillators Anal Chem 65 1993 1925 F Caruso et al QCM Study of DNA Immobilization and Hybridization for Nucleic Acid Sensor Development Anal Chem 69 1997 2043 Ito K et al Quantitative analysis for solid phase hybridization reaction and binding reaction of DNA binder to hybrids using a QCM Anal Chim Acta 32 1996 29 35 Caruso F et al In situ measurement of DNA immobilization and hy
12. Figure 1 shows a standard 1 inch diameter gold coated sensor crystal When mounted on a Crystal Holder it is the Liquid Surface that will be in contact with the sample gas or liquid during the measurements The counter electrode and electrical contacts for the electrodes are on the Contact Surface of the crystal in the leak poof crystal chamber The most appropriate cleaning method depends on the sample system the interaction of the sample with the crystal surface and the properties of the Sensor Crystal itself Note Before starting a surface cleaning ensure that the crystal material will not be damaged by the chemicals Perform a practice test on a discarded crystal whenever possible Avoid basic high pH cleaners since they will etch all exposed quartz surfaces Tip A Crystal Cleaning Basket SRS Part O100CCB described at the end of this chapter is available directly from Stanford Research Systems This accessory makes cleaning and OCM100 Quartz Crystal Microbalance 3 12 Sensor Crystals and Holders surface modification treatment of the standard 1 QCM crystals very safe and easy The cleaning basket holds four crystals is made entirely of Teflon and it is specifically designed for immersion into a 100mL beaker Several cleaning procedures are described below which can be used as guidelines to develop your own Proper crystal handling practices must be used throughout any cleaning process General Purpose For gener
13. NY 1979 Pages 235 253 ASRS OCM100 Quartz Crystal Microbalance 3 30 Sensor Crystals and Holders A Krozer and Michael Rodahl X ray Photoemission spectroscopy study of UV ozone oxidation of Au under ultrahigh vacuum conditions J Vac Sci Technol A 15 3 1997 1704 38 Advincula R Park M Yang J Mays J Subphase Adsorption of Polyelectrolyte Block Copolymer K Amphiphiles at the Air Water Interface In situ Investigations using the Quartz Crystal Microbalance Technique and the Langmuir Blodgett Trough Polymer Preprints 1999 40 1084 S Ryeol Kim JD Kim MS Park YK Chang and SM Chang The Characteristics of Quartz Crystal Microbalance Coated with Lipid Langmuir Blodgett Films as an olfactory sensing system Sensors and Materials 8 8 1996 513 521 L Prime G M Whitesides Science 252 1991 1164 K Prime G Whitesides A Model System Using Self Assembled Monolayers J Am Chem Soc 1993 v 115 10714 10721 Ramon Colorado Jr Ramon J Villazana and T Randall Lee Self Assembled Monolayers on Gold Generated from Aliphatic Dithiocarboxylic Acids Langmuir 14 1998 6337 6340 Zhao Yang Wu et al QCM Immunosensor for Schistsoma Japonicum Infected Rabit Serum Analytical Sciences 19 2003 437 a Spangler B D and Tyler B Capture Agents for a Quartz Crystal Microbalance Continuous Flow Biosensor 41 S 42 C Functionalized Self assembled Monolayers
14. OCM100 Quartz Crystal Microbalance 4 1 Chapter 4 QCM Circuit Description The Quartz Crystal Microbalance consists of two circuits the QCM25 Crystal Oscillator located in a small enclosure that attaches directly to the crystal holder and the QCM100 Analog Controller The QCM25 attaches to the QCM100 via a Cat 5 cable wired straight through to RJ 45 connectors This section describes the circuitry of both the QCM25 and the QCM100 In This Chapter Introduction 4 3 QCM25 Circuit Description 4 3 QCM100 Circuit Description 4 5 Capacitive Nulling By The QCM100 4 5 ASRS OCM100 Quartz Crystal Microbalance 4 2 Circuit Description QCM100 Quartz Crystal Microbalance Circuit Description 4 3 Introduction The Quartz Crystal Microbalance consists of two circuits the QCM25 Crystal Oscillator located in a small enclosure that attaches directly to the crystal holder and the QCM100 Analog Controller The QCM25 attaches to the QCM100 via a Cat 5 cable wired straight through to RJ 45 connectors This cable can be up to 25 feet in length The QCM25 consists of transformer isolated and gain controlled RF amplifiers which maintain the 5 MHz oscillation of the crystal in the holder The QCM25 is powered from the QCM100 which also provides the varactor bias to the QCM25 to null the effect of the crystal s static and holder capacitance allowing the crystal to run at the series resonance frequency The 5 MHz signal from the QCM25 is sent di
15. Open Flow Systems whenever possible If necessary use Flow Injection Analysis FIA compatible pumps and high quality injection ports to flow sample and carriers over the OCM100 Quartz Crystal Microbalance ASRS Sensor Crystals and Holders 3 23 crystal Syringe based injection analysis systems often produce cleaner baselines because of the absence of noise transients induced by peristaltic pumps Persitaltic pumps are suitable for flow measurements in closed systems but they always add noise to the signal A capillary tube located between the chamber outlet and the pump is often recommended to reduce noise caused by pressure fluctuations induced by the pump Pulse dampening modules located between the pump and the crystal are often used in Flow Injection Analysis setups although noise reduction is not always as good as expected In order to avoid excessive stress to the crystal and leaks over the oring selas flowrates should not exceed 5mL min under any circumstances External temperature i e heating loop stabilization of the liquid samples is recommended for flow rates above 0 2 mL min Do not tighten the crystal retainer during experiments Tightening of the crystal retainer will exert additional stress on the crystal and change its frequency of oscillation Tighten the retainer at the beginning of an experiment and do not touch it again until all measurements are finished Orings often swell when coming in contact with liquids and
16. The line input should be between 90 and 264 VAC 47 to 63 Hz allowing worldwide operation from line power The 15 VDC from the switching power supply is re regulated to 12 VDC and 5 VDC by linear regulators The 12 VDC power supply is used for analog circuits in the QCM100 and the 5 VDC supply is used to power the 5 MHz TTL output buffer in the QCM100 and to power the QCM25 oscillator via the Cat 5 cable The differential RS 485 5 MHz signal from the QCM25 is terminated into R12 100 Q and converted to a single ended TTL signal by U5 a DS8921A RS 485 transceiver The 5 MHz TTL signal drives all eight inputs of U6 a 74HC541 octal buffer The outputs of the octal buffer are combined via R15 amp R16 each 100 Q which drive the output BNC via the balun T1 The output has a 50 output impedance and the balun ensures that the shield current returns to the source which reduces the opportunity for the 5 MHz spreading everywhere The differential AGC signal is ac terminated by R29 R30 and C16 17 and is applied to the differential amplifier U9A creating a single ended voltage with a gain of 1x The gain of 1X is with respect to the AGC voltage in the QCM25 One needs to be aware that the QCM25 has a source resistance of 2x1 KQ for the differential AGC signal to compute the gain correctly U9B functions as a comparator which turns the OSC LED on when the AGC voltage exceeds about 0 8 VDC or Veong gt 2 0 which corresponds to crystal wit
17. cycles of the frequency output over a one second interval can not provide resolution better than 1 5x10 and so a more elaborate counter architecture is required A reciprocal interpolating counter can provide a much better frequency resolution than 1 cycle per gate interval Virtually all frequency counters can measure the frequency of the 2 4 V square wave in 50 Q provided by the QCM100 Frequency Output OCM100 Quartz Crystal Microbalance SRS ASRS Theory Operation and Calibration 2 9 Counters are available with RS 232 and or IEEE 488 interfaces to facilitate computer data acquisition The speed of the interface is not very critical as typically only one reading is taken each second Counters are relatively simple to set up and read via their computer interfaces Software drivers for National Instruments LabView products or other data acquisition programs are often available Frequency counters used at SRS for QCM measurements are listed below Manufacturer Model Digits Second Stanford Research Systems SR620 10 Agilent 53131 10 Agilent 53132 12 Errors In The Measurement Of Frequency The QCM25 Crystal Oscillator will oscillate at the frequency such that the phase shift around the entire loop is 360 Referring to Figure 5 important sources of phase shift within the network include 1 180 from the inverting amplifier A 2 180 37 p Hz deviation from 5 MHz from the low pass filter 3 0 0 20
18. in the Sauerbrey equation which relates the mass change per unit area at the QCM electrode surface to the observed change in oscillation frequency of the crystal Af Ci Am eqn 1 where Af the observed frequency change in Hz Am the change in mass per unit area in g cm C the sensitivity factor for the crystal 56 6 Hz yg cm for a 5 MHz AT cut quartz crystal at room temperature The Sauerbrey equation relies on a linear sensitivity factor C which is a fundamental property of the QCM crystal Thus in theory the QCM mass sensor does not require calibration However it must be kept in mind that the Sauerbrey equation is only strictly applicable to uniform rigid thin film deposits Vacuum and gas phase thin film depositions which fail to fulfill any of these conditions actually exhibit more complicated frequency mass correlations and often require some calibration to yield accurate results For many years QCMs were just regarded as gas phase mass detectors however recently their application has been extended since scientists realized that they can be operated in contact with liquids and viscoelastic deposits In this case both frequency and series resonance resistance of the quartz oscillator are important to completely characterize the material in contact with the crystal electrode The development of QCM systems for use in fluids opened a new world of applications including electrochemistry and micro rhe
19. match method The accuracy of the mass load and film thickness calculation is often limited by how well the Z Factor and density of the material are known Density and Z Factor values are typically very close to bulk values The bulk density and shear modulus values for common film materials can be found in many material reference handbooks The Lu and Lewis equation is generally considered to be a good match to the experimental results for frequency changes up to 40 relative to the unloaded crystal Keep also in mind that the Z match equation strictly applies to rigid deposits Films which behave viscoelastically such as some organic polymer films with large thickness or viscosity will exhibit significant deviations from both equations 1 and 5 Crystal failures are also often seen before a 40 shift in frequency is reached Common problems are 1 shorts in the crystal electrodes due to excessive buildup 2 mode hopping to other anharmonic resonant frequencies due to the buildup of composite resonant modes 3 deviations from theory due to fringing electrode fields developed between the electrodes and the film 4 unexpected shifts in fundamental frequency due to stress build up on the crystal surface 5 splitting of source material resulting in non uniform films etc QCM100 Quartz Crystal Microbalance 2 18 Theory Operation and Calibration Liquid Contact Measurements Until fairly recently it was believed that exc
20. model for the thickness shear mode resonator with a viscoelastic film near film resonance Anal Chem 72 2000 141 1 Consult ref 17 7 Celia Henry Measuring the masses Quartz Crystal Microbalances Anal Chem News and Features October 1 1996 p 626A 7 Daniel A Buttry and Michael Ward Measurement of Interfacial Processes at Electrode Surfaces with the Electrochemical Quartz Crystal Microbalance Chem Rev 92 6 1992 1355 7 Graeme Andrew Snook Investigation of Solid State Reactions by Electrochemical and Quartz Crystal Microbalance Measurements Ph D Thesis 2000 Department of Chemistry Monash University Clayton 3168 Melbourne Australia and Division of Minerals CSIRO Clayton South 3169 Melbourne Australia under the supervision of Professor Alan Maxwell Bond Monash and Professor Stephen Fletcher CSIRO Available for download from http www bond chem monash edu au theses Note the use of Lead acetate is proposed as a better alternative to Cu and Ag deposition 3 Scott Grimshaw Quartz Crystal Thin Film Monitoring Forges Ahead Photonics Spectra April 2003 p 82 4 John R Vig and Arthur Ballato Ultrasonic Instruments and Devices Academic Press 1999 Chapter 7 Frequency Control Devices Note this is probably the most thorough paper on the properties of QCM quartz crystal resonators gt Ballato A and Vig J R Static and dynamic frequency temperature behavior of s
21. quartz and in the worst case it can even cause the quartz itself to fracture ca Temperature effects The intrinsic dependence of the resonant frequency of a quartz crystal on temperature is well known and generally quite small In fact the AT cut quartz crystals commonly used in QCM experiments owe their popularity to their near zero temperature coefficient OCM100 Quartz Crystal Microbalance ASRS Sensor Crystals and Holders 3 9 at room temperature As a result the intrinsic temperature dependence of the QCM sensor crystals is negligible at or around room temperature 1 3 Hz C and is generally ignored for monolayer adsorption desorption processes in the gas phase A thermal effect less often discussed in connection with quartz crystal oscillators is based on the fact that dynamic changes in temperature around a crystal unit can produce thermal gradients which induce frequency transients dependent on the rate of temperature change around the sensor The static frequency vs temperature characteristic is modified by this thermal transient effect resulting from the thermal gradient induced stresses Proper thermal compensation requires consideration of both static and dynamic i e rate of change frequency temperature behavior of the QCM crystals Larger changes in frequency with temperature should be expected when QCM crystals are immersed in liquids This is due to the coupling of the shear mode oscillation with the temperatur
22. time Detection of Organic Compounds in Liquid Environments Using Polymer coated Thickness Shear Mode Quartz Resonators Anal Chem 72 2000 4888 12 G Sauerbrey Z Phys 155 1959 206 13 Daniel Buttry Applications of the QCM to Electrochemistry in A Series of Advances in Electroanalytical Chemistry edited by Allen Bard Marcel Dekker 1991 p 23 33 ASRS OCM100 Quartz Crystal Microbalance 3 28 Sensor Crystals and Holders 14 C Gabrielli et al Calibration of the Electrochemical Quartz Crystal Microbalance J Electrochem Soc 139 9 1991 2657 15 D R Denison Linearity of Heavily Loaded Quartz Crystal Microbalance J Vac Sci Technol 10 1973 126 K H Behrndt Long Term Operation of Crystal Oscillators in Thin Film Deposition J Vac Sci Technol 8 5 1971 622 Chih shun Lu Mass determination with piezoelectric quartz crystal resonators J Vac Sci Technol 12 1 1975 578 16 Ward M D and Delawski E J Radial Mass Sensitivity of the Quartz Crystal Microbalance in Liquid Media Anal Chem 63 1991 886 R W Cernosek et al Analysis of the radial dependence of mass sensitivity for Modified electrode quartz crystal resonators Anal Chem 50 1998 237 17 S J Martin R J Huber et al Resonator Oscillator Response to Liquid Loading Anal Chem 69 1997 2050 18 S Martin H Bandey R Cernozek A R Hillman and M J Brown Equivalent circuit
23. to 10 625 VDC log scale Impedance 1 KQ Connector BNC Capacitance Cancellation Range 10 to 40 pF 20 pF nominal Achievable Cancellation 0 01 pF Quartz Crystals Frequency 5 MHz AT cut plano plano Diameter 1 inch Electrodes Chromium gold polished unpolished Crystal Holder Material Kynar O ring Viton Connector BNC OCM100 Quartz Crystal Microbalance SRS 1 1 Chapter 1 Getting Started This chapter provides instructions for 1 unpacking 2 checking and 3 connecting the QCM100 Analog Controller to its accessories and to your experiment Quick Start instructions are also provided to perform QCM measurements In This Chapter Unpacking 1 3 Before You Open the Box 1 3 Checklist 1 3 Standard Equipment Supplies 1 3 Optional Equipment 1 3 Quick Start Instructions 1 4 Crystal Installation 1 6 Flow Cell 1 11 ASRS OCM100 Quartz Crystal Microbalance 1 2 Getting Started QCM100 Quartz Crystal Microbalance Getting Started 1 3 Unpacking ASRS Before You Open the Box Read the entire Safety and Preparation for Use section of this manual before starting any installation procedure Read and follow all installation and operation instructions in this manual to ensure that the performance of this instrument is not compromised Checklist Open the box es and inspect all components of the QCM100 System Report any damage to Stanford Research Systems immediately Compare the contents of the shippi
24. 060 512 1 OU C25 5 00299 568 IU C26 5 00375 552 100P C27 5 00299 568 1U C28 5 00299 568 IU D1 3 00010 303 GREEN D2 3 00010 303 GREEN D3 3 00011 303 RED D4 3 00011 303 RED ASRS DESCRIPTION Parts List Cap Tantalum SMT all case sizes Cap Tantalum SMT all case sizes Cap Tantalum SMT all case sizes Cap Ceramic 50V SMT 1206 10 X7R Capacitor Chip SMT1206 50V 5 NPO Capacitor Chip SMT1206 50V 5 NPO Cap Ceramic 50V SMT 1206 Cap Ceramic 50V SMT 1206 Cap Ceramic 50V SMT 1206 Cap Ceramic 50V SMT 1206 Cap Ceramic 50V SMT 1206 10 X7R 10 X7R 10 X7R 10 X7R 10 X7R Cap Stacked Metal Film 50V 5 40 85c Cap Stacked Metal Film 50V 5 40 85c Cap Stacked Metal Film 50V 5 40 85c Cap Stacked Metal Film 50V 5 40 85c Cap Ceramic 50V SMT 1206 4 Cap Ceramic 50V SMT 1206 4 Cap Ceramic 50V SMT 1206 4 Cap Ceramic 50V SMT 1206 4 10 X7R 10 X7R 10 X7R 10 X7R Cap Stacked Metal Film 50V 5 40 85c Cap Stacked Metal Film 50V 5 40 85c Cap Stacked Metal Film 50V 5 40 85c Cap Stacked Metal Film 50V 5 40 85c Cap Stacked Metal Film 50V 5 40 85c Cap Ceramic 50V SMT 1206 4 10 X7R Capacitor Chip SMT1206 50V 5 NPO Cap Ceramic 50V SMT 1206 4 Cap Ceramic 50V SMT 1206 4 LED T1 Package LED T1 Package LED T1 Package LED T1 Package 10 X7R 10 X7R 5
25. 21A RS 485 transceiver The 5 MHz TTL signal is converted by U2 into a differential RS 485 signal which drives one pair of the Cat 5 cable connected to the QCM100 This pair is terminated into 100 and converted to TTL in the QCM100 The front face of the crystal is connected to the shield of the BNC connector which is connected to the binding post connector on the QCM2S The back face of the crystal is connected to the front face via the RF transformers and so both faces of the crystal are at the same dc potential Both faces are electrically isolated at de from all circuits in the QCM25 and the QCM100 allowing the user to make unburdened measurements of de currents on and off the front face of the crystal as might occur in electrochemistry measurements The QCM25 chassis ground is ac coupled to the circuit ground via the series combination of C9 0 1 uF and RS 47 Q The front face of the crystal and so the bias point binding post are ac coupled to the circuit ground via the series combination of C10 1000 pF and R6 47 Q OCM100 Quartz Crystal Microbalance ASRS Circuit Description 4 5 QCM100 Circuit Description ASRS The QCM100 Analog Controller is used with the QCM25 Oscillator to provide power varactor bias and conversion of the differential 5 MHz and AGC signals from the QCM25 into single ended signals available to the user on the QCM100 front panel BNCs The QCM100 is powered by a universal input 15 VDC 1A power supply
26. 5 MHz polished crystal OCM100 Quartz Crystal Microbalance ASRS Theory Operation and Calibration 2 21 Immersion Test ASRS A comparison against the theoretical predictions of equations 6 and 7 is usually a good starting point when testing a new experimental liquid QCM100 setup Two common checkup procedures are described Water Immersion For a gold coated 5 MHz polished crystal and assuming that the electrode capacitance has been properly cancelled a decrease in frequency of 715 Hz and an increase in series resonance resistance of 380 Q is expected when switching from air to complete immersion in water at 20 C Glycerol H 0 Immersion Figure 7 shows resistance and frequency change values expected for a polished 5 MHz crystal immersed in a series of viscous glycerol water solutions at 20 C Operation at increasing glycerol concentrations is an excellent test of a QCM experimental setup and should provide predictable results up to more than 88 glycerol In both procedures an agreement between measured and expected values within 25 is generally considered acceptable for glycerol concentrations up to 70 Frequency shifts are much larger at least a factor of two and unpredictable for unpolished crystals so they are not recommended for system checkup QCM100 Quartz Crystal Microbalance 2 22 Theory Operation and Calibration Electrochemical Quartz Crystal Microbalance In most electrochemical experiment
27. 6 port injection valve Typical flow rates were 50 uL min temperature stability was 0 1 C at 27 C and the buffer solution was PBS pH7 5 Antigen mouse gamma globulin was first introduced into the cell Step 1 resulting in a 35Hz frequency step caused by the non specific metal protein binding interactions between the protein and the bare gold surface i e physical adsorption The QCM100 Quartz Crystal Microbalance 2 30 Theory Operation and Calibration remaining non specific binding sites were then blocked with excess ovalbumin Step 2 resulting in the second and smaller frequency step Finally Step 3 antibody goat anti mouse IgG was flowed over the immobilized protein layer and the specific interaction between antigen and antibody proteins resulted in the final 40Hz frequency step The real advantage of the QCM technology in this application is that it is label free the sample flowed over the immobilized surface layer does not need to be modified or labeled in any way Thus it is much more physiologically relevant because labeling something with a fluorescent probe i e ELISA often changes its properties The ability to see changes in the QCM signal after every individual step provides an additional advantage over standard immunoassays such as ELISA where no user feedback is available until the entire process is completed TIP Using a QCM biosensor you cannot only tell whether something binds to a given protein immobiliz
28. 62 4 01191 462 4 01660 462 4 01660 462 4 01215 462 4 01191 462 4 01479 461 4 01242 462 4 01242 462 4 01660 462 4 01338 462 4 01527 461 4 01213 462 4 01213 462 4 01471 461 4 01338 462 4 01184 462 4 01213 462 4 01213 462 4 01660 462 4 01660 462 4 01213 462 4 01191 462 4 01519 461 4 01479 461 4 01527 461 4 01479 461 4 01431 461 4 01431 461 4 01479 461 4 01527 461 4 01479 461 4 01479 461 4 01479 461 2 00025 217 6 00622 610 1 0K 100K 1 0K 1 0K 1 0K SPDT ADT1 6T Parts List Thin Film 1 50 ppm MELF Resistor Thin Film 1 50 ppm MELF Resistor Thick Film 5 200 ppm Chip Resistor Thin Film 1 50 ppm MELF Resistor Thick Film 5 200 ppm Chip Resistor Thin Film 1 50 ppm MELF Resistor Thin Film 1 50 ppm MELF Resistor Thin Film 1 50 ppm MELF Resistor Thin Film 1 50 ppm MELF Resistor Thin Film 1 50 ppm MELF Resistor Thin Film 1 50 ppm MELF Resistor Thin Film 1 50 ppm MELF Resistor Thin Film 1 50 ppm MELF Resistor Thick Film 5 200 ppm Chip Resistor Thin Film 1 50 ppm MELF Resistor Thin Film 1 50 ppm MELF Resistor Thin Film 1 50 ppm MELF Resistor Thin Film 1 50 ppm MELF Resistor Thick Film 5 200 ppm Chip Resistor Thin Film 1 50 ppm MELF Resistor Thin Film 1 50 ppm MELF Resistor Thick Film 5 200 ppm Chip Resistor Thin Film 1 50 ppm MELF Resistor Thin Film 1 50 ppm MELF Resistor Thin Film 1 50 ppm MELF Resistor Thin Film 1 50
29. 6250BCSA AD822 LMC6082IM LMC6082IM OPA277UA LM13700M LMC6082IM 6 LOCK 2 520194 2 6 32X3 8PP 4 40X1 4PP 3ED8 6 32X1 4PP 4 40X3 8PF GROMMET DG532 3 RED 3 BLACK 6 32 X 3 16 5 1 2 18 2 26 WHITE BINDING POST 0 250 6 32X1 4 PF UC SPST ON NONE OF 15V 15W 1A QCM100 QCM100 QCM100 QCM100 QCM100 Quartz Crystal Microbalance Voltage Reg TO 220 TAB Package Voltage Reg TO 220 TAB Package Integrated Circuit Surface Mount Pkg Integrated Circuit Surface Mount Pkg Integrated Circuit Surface Mount Pkg Integrated Circuit Surface Mount Pkg Integrated Circuit Surface Mount Pkg Integrated Circuit Surface Mount Pkg Integrated Circuit Surface Mount Pkg Integrated Circuit Surface Mount Pkg Integrated Circuit Surface Mount Pkg Integrated Circuit Surface Mount Pkg Integrated Circuit Surface Mount Pkg Integrated Circuit Surface Mount Pkg Integrated Circuit Surface Mount Pkg Integrated Circuit Surface Mount Pkg Crystal Dial Hardware Misc Lugs Nut Kep Washer lock Termination Screw Panhead Phillips Screw Panhead Phillips Power Entry Hardware Screw Panhead Phillips Screw Black All Types Grommet Wire 18 UL1007 Stripped 3 8x3 8 No Tin Wire 18 UL1007 Stripped 3 8x3 8 No Tin Screw Black All Types Wire 18 UL1007 Stripped 3 8x3 8 No Tin Wire 26 UL1061 Hardware Misc Lugs Screw Flathead Phillips Switch Rocker Power Supply Fabricated Part Fa
30. Alkanethiol Adsorption to Gold oes Resistance 2 341 0 340 5 2 340 N T E 4 339 5 D oO gt S 5 6 339 8 9 L ir 8 338 5 10 338 12 337 5 150 170 190 210 230 250 270 290 310 Time seconds Figure 14 Raw QCM Af vs time and Resistance vs time data for adsorption of 510 M 16 mercaptohexadecanoic acid from ethanol to bare gold Figure 14 is a graphical representation of the chemical adsorption kinetics of 16 mercaptohexadecanoic acid on to bare gold measured in real time with a QCM100 quartz crystal microbalance In this simple experiment a polished Au Cr crystal mounted on a standard holder was immersed in 200 mL of ethanol housed inside a temperature stabilized 500mL beaker The reaction was triggered by rapidly injecting ImL of 10 M solution of 16 mercaptohexadecanoic acid providing a diluted 510 M solution of alkanethiol to react with the bare gold A short transient in the frequency and resistance indicates the point of insertion of the thiol and is due to a slight temperature difference between the solvent and the sample solution The fast drop in frequency following the injection is due to the fast formation of thiol gold bonds followed by a slower annealing process The absence of a sharp positive step in the resistance verifies that the fast frequency drop is not due to a change in the viscosity of the solution The results are in excellent agreement with the observations of Blanch
31. C used as the varactor reference voltage The front panel 10 turn potentiometer P2 divides the reference voltage which is amplified and buffered by U8A The output of U8A is 1 05x the varactor hold voltage The resistive divider R20 R23 provides 1 00x and 0 95x the varactor hold voltage When in the HOLD mode the multiplexer sends the 1 00x tap to the varactor via the output filter buffer U8B When in the ADJUST mode the multiplexer switches between the 1 05x and 0 95x taps at 75 Hz This 75 Hz offset square wave is filtered by the output filter buffer to produce an offset and 90 phase shifted sine wave to modulate the varactor voltage OCM100 Quartz Crystal Microbalance ASRS Circuit Description 4 7 The AGC voltage from the differential amplifier U9A is filtered and 90 phase shifted by the two pole Butterworth filter U10B The AC component of this signal is amplified by 100x by U11 an OPA277 low offset voltage operational amplifier The output of U11 is further amplified by a voltage controlled gain amplifier consisting of U12 an LM13700 dual operational transconductance amplifier and U13B The gain of the voltage controlled amplifier U12 is controlled by the AGC voltage The gain increases exponentially with the AGC voltage varying between 1x and 100x as the AGC voltage goes from 0 VDC to 10 VDC As mentioned previously there is little modulation of the AGC voltage when the crystal losses are low i e when the AGC voltage is h
32. Hz OCM100 Quartz Crystal Microbalance SRS ASRS Sensor Crystals and Holders 3 5 The large diameter of the crystal 1 inch and the relatively much smaller oscillation area assures good separation between the active electrode pads and the mounting structure of the holder and minimizes the coupling of other resonant modes to the thickness shear oscillation Surface Finish Electrode surface roughness can cause large apparent mass loadings due to the liquid that is trapped within pores at the crystal surface As a general rule optically polished crystals 50 A average surface roughness are required to obtain good agreement between theory and experiment during liquid immersion experiments The QCM100 1 inch sensor crystals are available in two finishes unpolished 3 um average surface roughness typical or polished optically clear 50 A average surface roughness typical Rough surfaces are popular because they are less expensive and provide enhanced surface area However they suffer from a quantitatively unpredictable dependence of the oscillation frequency in a liquid due to trapping of fluid in the pores and pits on the surface Tip For liquid phase applications optically polished crystals are required if crystal to crystal reproducibility is to be expected A water Immersion Test refer to Chapter 2 usually provides a quick and easy way to test the quality of a crystal finish for liquid QCM applications
33. Operation and Service Manual QCM100 Quartz Crystal Microbalance Analog Controller QCM25 Crystal Oscillator 1 S RS Stanford Research Systems Operation and Service Manual QCM100 Quartz Crystal Microbalance Analog Controller QCM25 Crystal Oscillator 1 S RS Stanford Research Systems Revision 1 2 03 01 04 Certification Stanford Research Systems certifies that this product met its published specifications at the time of shipment Warranty This Stanford Research Systems product is warranted against defects in materials and workmanship for a period of one 1 year from the date of shipment Service For warranty service or repair this product must be returned to a Stanford Research Systems authorized service facility Contact Stanford Research Systems or an authorized representative before returning this product for repair Information in this document is subject to change without notice Copyright Stanford Research Systems Inc 2002 All rights reserved Stanford Research Systems Inc 1290 C Reamwood Avenue Sunnyvale California 94089 www thinkSRS com Printed in U S A OCM100 Quartz Crystal Microbalance ASRS Safety and Preparation For Use i Safety and Preparation for Use Line Voltage The QCM100 Analog Controller operates from a 90 132 or 175 264 V AC power source having a line frequency between 47 and 63 Hz Power consumption is 20 VA total Power Entry Module A power entry module labele
34. Resistor Thick Film 5 200 ppm Chip Resistor Thick Film 5 200 ppm Chip Resistor Thick Film 5 200 ppm Chip Resistor Thick Film 5 200 ppm Chip Resistor Thick Film 5 200 ppm Chip Resistor Thick Film 5 200 ppm Chip Resistor Thick Film 5 200 ppm Chip Resistor Thin Film 1 50 ppm MELF Resistor Thick Film 5 200 ppm Chip Resistor Thick Film 5 200 ppm Chip Resistor Thick Film 5 200 ppm Chip Resistor Thick Film 5 200 ppm Chip Resistor Thick Film 5 200 ppm Chip Resistor Thin Film 1 50 ppm MELF Resistor Thin Film 1 50 ppm MELF Resistor Thin Film 1 50 ppm MELF Resistor Thin Film 1 50 ppm MELF Resistor Thin Film 1 50 ppm MELF Resistor Thin Film 1 50 ppm MELF Resistor Thin Film 1 50 ppm MELF Resistor Thin Film 1 50 ppm MELF Resistor Thin Film 1 50 ppm MELF Resistor Thin Film 1 50 ppm MELF Resistor Thin Film 1 50 ppm MELF Resistor Thick Film 5 200 ppm Chip Resistor Thick Film 5 200 ppm Chip Resistor Thick Film 5 200 ppm Chip Resistor Thin Film 1 50 ppm MELF Resistor Thin Film 1 50 ppm MELF Resistor ASRS R 33 R 34 R35 R 36 R 37 R 38 R 39 R40 R41 R42 R 43 R 44 R 50 R51 R52 R 53 R 54 R55 R 56 R57 R58 R59 R 60 R61 R 62 R 63 R 64 R65 R 66 R 67 R 68 R 69 R 70 R71 R72 R73 R74 R75 R 76 R 77 R 78 Tl ASRS 4 01146 462 4 01146 462 4 01527 461 4 01199 462 4 01479 461 4 01338 462 4 01338 462 4 01213 4
35. Stanford Research Systems in a variety of electrode materials Table l Standard 1 inch QCM Sensor Crystals SRS Part Frequency Material Diam Finish Maxtek Part Qty 10 ea MHz inch O100RX1 5 0 Chrome Gold 1 0 Polished 149211 1 O100RX2 5 0 Indium Tin Oxide 1 0 Transparent N A O100RX3 5 0 Titanium Gold 1 0 Polished 149238 1 O100RX4 5 0 Titanium Platinum 1 0 Polished 149240 1 ASRS OCM100 Quartz Crystal Microbalance 3 4 Sensor Crystals and Holders Principle of Operation AT cut quartz crystals are most commonly used as QCM sensors because of their superior mechanical and piezoelectric properties and because they can be cut to give nearly zero temperature coefficients at room temperature Due to the piezoelectric properties and crystalline orientation of AT cut quartz the application of a voltage between the sensor crystal electrodes results in the production of internal mechanical stress An oscillating electric field of the proper frequency applied across the disk induces a pure shear mode oscillation that propagates through the crystal The designation of the oscillation as a pure shear mode indicates that the motion of the disk surface is perfectly parallel to the disk s face For shear mode oscillation there are several frequencies that correspond to resonant conditions For all resonant modes displacement maxima occur at the crystal faces making the device sensitive to surfac
36. Technol 10 1 1973 126 Klaus H Behrndt Long Term Operation of Crystal Oscillators in Thin Film Deposition J Vac Sci technol 8 5 1971 622 10 C Lu and O Lewis Investigation of film thickness determination by oscillating quartz resonators with large mass load J Appl Phys 43 1972 4385 Chih shun Lu Mass determination with piezoelectric quartz crystal resonators J Vac Sci Technol 12 1 1975 578 1 D R Denison Linearity of Heavily Loaded Quartz Crystal Microbalance J Vac Sci Technol 10 1973 126 K H Behrndt Long Term Operation of Crystal Oscillators in Thin Film Deposition J Vac Sci Technol 8 5 1971 622 1 T Nomura and M Okuhara Anal Chim Acta 142 1982 281 13 A P M Glassford Response of a Quartz Crystal Microbalance to a liquid Deposit J Vac Sci Technol 15 6 1978 1836 1 K Keiji Kanazawa and Joseph Gordon II Frequency of a Quartz Microbalance in Contact with Liquid Anal Chem 57 1985 1770 OCM100 Quartz Crystal Microbalance ASRS Theory Operation and Calibration 2 35 K Keiji Kanazawa and Joseph G Gordon II Analytica Chimica Acta 175 1985 99 105 1 Stephen J Martin James J Spates Kurt O Wesendorf Thomas Schnneider and Robert J Huber Resonator Oscillator Response to Liquid Loading Anal Chem 69 1997 2050 16 Stephen Martin Victoria Edwards Granstaff and Gregory C Frye Characterization of a Quartz Cr
37. action washing and even changes in pH 2 swelling of the polymer films in aqueous solution can lead to reduced sensitivity and reproducibility of the immunosensor OCM100 Quartz Crystal Microbalance ASRS Sensor Crystals and Holders 3 17 Electroless Deposition Pre treatment QCMs are used to measure 1 plating rates and thicknesses in both electrolytic and electroless baths 2 plating efficiencies in electrolytic baths and 3 etching rates in chemical etching processes It is important to assure that the Sensor Crystal is properly preconditioned during the electroless deposition of metals Plating initiation must be complete and the crystal must be in close proximity to the action taking place in the rest of the tank Preplating is recommended if adhesion problems are observed with untreated crystals Pre treatment with catalyst may be prescribed in some cases It is recommended not to expose the entire Crystal Holder to catalysis during pre treatment to avoid excessive metallization of the holder during deposition ASRS OCM100 Quartz Crystal Microbalance 3 18 Sensor Crystals and Holders Crystal Holder Description The standard Crystal Holder bundled with the QCM100 system is specifically designed to provide users with a rugged compact and easy to use sensor crystal housing for QCM experiments in air or liquids Figure 2 The Crystal Holder with a 1 inch sensor crystal mounted Its main features include rugged de
38. ailable to QCM100 users and describes the most popular theoretical models used to interpret the results The procedure for capacitance compensation is also described in detail In This Chapter Background The QCM Oscillator Capacitance Cancellation Frequency Measurement Frequency Counter Selection Criteria Errors In The Measurement Of Frequency Resistance Measurement Resistance Calculation Errors In The Measurement Of Rm Noise In The Measurement Of Rm Calibration of Rm Gas Phase Measurements Sauerbrey Equation Z match Method Liquid Contact Measurements Immersion Test Water Immersion Glycerol H20 Immersion Electrochemical Quartz Crystal Microbalance Electrochemical Apparatus Calibration Polymer Modified Electrodes Chemical and Biological Sensors Self Assembled Monolayers Dissipation Technique References ASRS 2 3 2 4 2 7 2 8 2 8 2 9 2 11 2 11 2 14 2 14 2 15 2 16 2 16 2 17 2 18 2 21 2 21 2 21 2 22 2 22 2 25 2 26 2 28 2 30 2 33 2 34 OCM100 Quartz Crystal Microbalance 2 2 Theory Operation and Calibration QCM100 Quartz Crystal Microbalance Theory Operation and Calibration 2 3 Background Sauerbrey was the first to recognize the potential usefulness of the Quartz Crystal Microbalance QCM technology and demonstrate the extremely sensitive nature of these piezoelectric devices towards mass changes at the surface of QCM electrodes The results of his work are embodied
39. ain control circuit generates a voltage to maintain the oscillation amplitude at a fixed level of 1 V The attenuator is controlled by this voltage between 0 and 1 Vdc providing an attenuation of 50 dB volt so that A 10 2 The AGC voltage is amplified by 5x in the QCM25 Crystal Oscillator and by 2 5 x in the QCM100 Analog Controller before being output via the Conductance BNC on the front panel of the QCM100 Hence referenced to the voltage Ve at the QCM100 Conductance output BNC Aa 10 A fixed gain amplifier with gain A 45 dB 20 log 250 200 46 94 dB or 222 X This inverting amplifier has a bandwidth of 500 MHz and so introduces very little extraneous phase shift A source resistance Rs of 100 Q This source resistance consists of two series 50 Q resistors one of which is inside the amplifier A1 This source impedance is reduced by a factor of 4 x to 25 Q by the 2 1 transformer which follows An isolation transformer with a 2 1 turns ratio hence an attenuation of A 0 5 This transformer allows galvanic isolation of the crystal from the oscillator circuit which is important in electrochemistry applications In addition to reducing the source impedance by 4 x the transformer also increases the load impedance seen at the input of the transformer by 4 x so that when Rm 0 Q the load will be 200 Q Rm the motional resistance of the crystal at series resonance Rm can vary from about 10 40 Q for a dry cr
40. al Inspect the sensor crystal at this time and clean it if necessary OCM100 Quartz Crystal Microbalance 1 8 Getting Started 6 Hold the crystal Contact Surface down above the Crystal Holder s head and point the wrap around electrode towards the reference pin at end of probe See Figure 6 below Figure 6 QCM Crystal in Crystal Holder cavity with wrap around electrode pointing towards reference pin 7 Turn the crystal 90 clockwise before laying it centered onto the head oring Turning the crystal as instructed assures a fresh contact surface develops between the crystal electrodes and the POGO pins The crystal should end up as shown in Figure 7 below Figure 7 Crystal in place with correct electrode orientation OCM100 Quartz Crystal Microbalance SRS Getting Started 1 9 8 Place the retainer ring or Flow Cell over the crystal with its notch mating with the reference pin as shown in Figure 8 below Figure 8 Retainer ring in place 9 Attach the retainer cover and thread the first quarter turn Inspect the retainer ring to make sure the alignment notch remained mated with the reference pin Fig 9 Retainer cover in place 10 Tighten the retainer cover the rest of the way finger tight is OK ASRS OCM100 Quartz Crystal Microbalance 1 10 Getting Started 11 Connect the Crystal Holder to the QCM25 Crystal Oscillator as shown in Figure 10 Figure 10 The OCM Probe consisting of a Crys
41. al purpose applications such as electrochemistry liquid and viscoelastic film studies it is usually sufficient to sonicate the crystals in a solution of non basic detergent in deionized water Immediately rinse liberally with deionized water and dry in a gentle flow of nitrogen gas Hydrocarbon contaminants UV ozone treatment CO snow cleaning and plasma cleaning are some low cost and very efficient methods used for cleaning hydrocarbon impurities adsorbed from the ambient air Neither method affects the quartz gold surfaces They are both often applied to components used in high vacuum environments Biomaterials lipids proteins and similar biomolecules Step 1 Treat the crystal in a UV ozone or plasma cleaning chamber for 10 minutes Step 2 Immerse the crystal into a 1 1 5 solution of hydrogen peroxide 30 ammonia 25 and deionized water heated to a temperature of about 75 C for 5 minutes Step 3 Immediately rinse with deionized water and dry with nitrogen gas Step 4 Treat the crystal again with UV ozone for 10 minutes immediately before measurement this removes any remaining surface contaminants Lipid vesicles Step 1 Treat the crystal in a UV ozone or plasma cleaning chamber for 10 minutes Step 2 Immerse the crystal into water with 2 of sodium dodecyl sulfate SDS at room temperature for 30 minutes Step 3 Immediately rinse with deionized water and blow dry with nitrogen gas Step 4 Treat
42. ant frequency but also in damping of the resonant oscillation the viscous loss is manifested as an increase in series resonance resistance R of the QCM resonator Thus R serves as an excellent independent measure of viscous loading by the medium liquid or soft film at the crystal s surface Af and AR measurements are both routinely used as independent indicators of mass loading and viscosity at the crystal liquid interface of the QCM resonator during chemical and electrochemical depositions in solution In a separate study a Butterworth Van Dyke equivalent circuit model Figure 1 was applied to derive a linear relationship between the change in series resonance resistance AR of the quartz oscillator and pv nr under liquid loading AR n 5 Ly n 2 s PL NL Pa Ha eqn 7 Where AR change in series resonance resistance in Q OCM100 Quartz Crystal Microbalance ASRS ASRS Theory Operation and Calibration 2 19 n number of sides in contact with liquid s angular frequency at series resonance 2rfs Ly inductance for the unperturbed dry resonator usually in mH The QCM100 System was specifically designed for operation under heavy viscous loading The standard Crystal Holder supports operation in gas and liquid environments and provides single electrode exposure to liquids i e n 1 in eqn 7 as required for compatibility with electrochemical QCM measurements The Crystal Oscillat
43. ard s group OCM100 Quartz Crystal Microbalance 2 32 Theory Operation and Calibration corresponding to the adsorption desorption kinetics of thiols from hexane and under very similar experimental conditions Besides good mechanical and chemical properties an additional advantage of SAMs is that they make it possible to tailor probe surfaces at the molecular level for the immobilization of specific biomolecules such as proteins or DNA Several studies have reported significant improvement in detection limits when SAM immobilization is used to design immunosensor QCM probes OCM100 Quartz Crystal Microbalance ASRS ASRS Theory Operation and Calibration 2 33 Dissipation Technique An alternative method for studying the properties of the loaded QCM Sensor called the Dissipation Technique has been used in gaseous as well as in liquid environments In this case the crystal is driven at its resonant frequency by an oscillator that can be intermittently disconnected causing the crystal oscillation amplitude to decay exponentially From the recorded decay curve the absolute Q factor inversely proportional to R and the frequency of the oscillator are simultaneously obtained Independent studies have shown that as long as the effect of the parasitic capacitance Co is properly cancelled i e as easily accomplished with the QCM100 the results provided by the Dissipation Technique should be in good agreement with t
44. asurement in liquids and soft films is also affected by temperature mostly through the temperature coefficient of the viscosity For example a 4 Q C change in resistance is to be expected in water around room temperature Noise In The Measurement Of Rm Ve varies logarithmically with Rm over most of the range of interest There is an important advantage in this the fractional resolution of the resistance is nearly independent of the resistance and so allows detailed and low noise measurement of the viscous losses To estimate the noise in resistance measurements we can take the derivative of the equation for the motional resistance units are Ohms and Ohms Volt Rm 10 000 10 75 OCM100 Quartz Crystal Microbalance ASRS Theory Operation and Calibration 2 15 dRm dV 10 000 10 In 10 1 5 2 000 In 10 10 4605 10 0 4605 Rm 75 Noise on the V signal AVg is typically 50 uV with one second averaging Rm for a 5 MHz crystal in water is about 375 Q The fractional noise in the resistance measurement is then ARm Rm AV dRm dV Rm AV 0 4605 Rm 75 Rm 28 ppm This low noise floor for fractional resistance measurements allows very small changes in dissipation losses to be measured This is also the reason why a high precision voltmeter i e with at least six digits of resolution is recommended for these measurements Calibration of Rm Re
45. ayers ASRS 3 3 3 3 3 4 3 4 3 4 3 5 3 5 3 7 3 8 3 8 3 11 3 11 3 12 3 12 3 12 3 12 3 13 Polystyrene removal 3 13 Crystal rinsing 3 14 Surface Modifications 3 15 Sputtering or evaporation 3 15 Spin coating 3 15 Langmuir Blodgett films 3 16 Self assembled monolayers SAM 3 16 Electroless Deposition Pre treatment 3 17 Crystal Holder 3 18 Description 3 18 Head Cleaning 3 19 Crystal Cleaning Basket 3 20 Tips for Operation in Liquids 3 21 Tips for Operation in Gases 3 23 Bubbles and Liquid Flow Cells 3 24 References 3 27 OCM100 Quartz Crystal Microbalance 3 2 Sensor Crystals and Holders OCM100 Quartz Crystal Microbalance Sensor Crystals and Holders 3 3 Introduction The standard sensor crystal used by the QCM100 System consists of a thin disk of 5 MHz AT cut o quartz with circular electrodes patterned on both sides Figure 1 Standard 1 inch QCM sensor crystal The crystal on the left shows the contact surface while the one on the right shows the liquid surface Standard sensor crystals are 1 inch in diameter and are available with a variety of electrode materials Stanford Research Systems also provides a rugged and easy to operate Crystal Holder compatible with both gas and liquid QCM experiments Crystal Holders must be electrically connected to a Crystal Oscillator Model QCM25 for operation with a QCM100 Analog Controller Sensor Crystals QCM Sensor Crystals are available directly from
46. bodies antigens and DNA on the surface of quartz crystal electrodes SAMs can be deposited on gold or silver electrodes by fhiolization Since sulfur donor atoms strongly coordinate on metal substrates Au Ag Pt etc sulfur containing molecules such as disulfides R SS R sulfides R S R and thiols can form various functionalized SAMs with highly organized and compact construction Besides good mechanical and chemical properties an additional advantage of SAMs is that they make it possible to tailor electrode surfaces at the molecular level for the immobilization of specific biomolecules such as proteins or DNA Tip Thiolization agents specifically designed for SAM immobilization of proteins and DNA on metallic surfaces have recently become commercially available Consult the factory for up to date recommendations A silane layer silanization is another common material used for SAMs However since the coating can react irreversibly with the quartz material the QCM crystal cannot be used repeatedly in this application SAMs vs Polymer films Most conventional methods used for the development of QCM immunosensors have relied heavily on polymeric coatings deposited on the electrodes and capable of forming hydrophobic or covalent bonds with antibodies Polymeric films suffer of several disadvantages 1 polymer films attach to the electrode surface through weak hydrophobic bonds which can be easily broken by mechanical inter
47. bricated Part Fabricated Part Lexan Overlay ASRS Parts List 5 5 Z O0 9 00267 917 GENERIC Product Labels QCM25 Parts List REF SRS PART VALUE DESCRIPTION CI 5 00318 569 2 2U T35 Cap Tantalum SMT all case sizes C2 5 00299 568 AU C3 5 00299 568 AU C4 5 00299 568 AU C5 5 00299 568 AU C6 5 00298 568 OIU C7 5 00299 568 AU C8 5 00299 568 AU C9 5 00299 568 AU C10 5 00387 552 1000P C11 5 00299 568 AU C12 5 00387 552 1000P C13 5 00387 552 1000P C14 5 00299 568 AU C15 5 00299 568 AU C16 5 00299 568 AU C17 5 00299 568 AU C18 5 00299 568 AU C19 5 00364 552 12P C20 5 00372 552 56P C21 5 00372 552 56P Cap Ceramic 50V SMT 1206 10 X7R Cap Ceramic 50V SMT 1206 10 X7R Cap Ceramic 50V SMT 1206 10 X7R Cap Ceramic 50V SMT 1206 10 X7R Cap Ceramic 50V SMT 1206 10 X7R Cap Ceramic 50V SMT 1206 10 X7R Cap Ceramic 50V SMT 1206 10 X7R Cap Ceramic 50V SMT 1206 10 X7R Capacitor Chip SMT1206 50V 5 NPO Cap Ceramic 50V SMT 1206 10 X7R Capacitor Chip SMT1206 50V 5 NPO Capacitor Chip SMT1206 50V 5 NPO Cap Ceramic 50V SMT 1206 10 X7R Cap Ceramic 50V SMT 1206 10 X7R Cap Ceramic 50V SMT 1206 10 X7R Cap Ceramic 50V SMT 1206 10 X7R Cap Ceramic 50V SMT 1206 10 X7R Capacitor Chip SMT1206 50V 5 NPO Capacitor Chip SMT1206 50V 5 NPO Capacitor Chip SMT1206 50V 5 NPO C22 5 00380 552 270P Capacito
48. bridization using a 27Mhz QCM Colloids Surf B Biointerfaces 10 1998 199 204 Yung Chuan Liu Chih Ming Wang and Kuang Pin Hsiung Comparison of Different Protein Immobilization Methods on Quartz Crystal Microbalance Surface in Flow Injection Immunoassay Analytical Biochemistry 299 2001 130 135 Michael Rodahl Fredrik Hook Anatol Krozer Peter Brzezinski and Bengt Kasemo QCM setup for frequency and Q factor measurements in gaseous and liquid environments Rev Sci Instrum 66 7 1995 3924 S J Geelhood C W Frank and K Kanazawa Transient QCM Behaviors Compared J of the Electrochemical Society 149 1 2002 H33 ASRS OCM100 Quartz Crystal Microbalance 2 40 Theory Operation and Calibration OCM100 Quartz Crystal Microbalance Chapter 3 3 1 Sensor Crystals and Holders This chapter describes the basic features and functionality of the QCM Sensor Crystals and Holder including recommended practices for 1 cleaning 2 handling 3 surface modification 4 probe mounting 5 electrical connection and 6 general maintenance In This Chapter Introduction Sensor Crystals Principle of Operation Frequency Geometry Surface Finish Electrode Materials Mass Sensitivity Maximum Loads Useful Life Temperature effects Crystal Handling Cleaning General Purpose Hydrocarbon contaminants Biomaterials lipids proteins and similar biomolecules Lipid vesicles Self assembled Monol
49. cally achieved with temperature controlled baths and jacketed cells Tight temperature control is necessary for QCM measurements involving protein adsorption protein protein interaction immunosensor development self asembled monolayers Langmuir films and DNA hybridization studies Temperature stabilization better than 0 05 C is generally required to eliminate temperature related transients and drifts in lengthy measurements This level of temperature control is particularly important if small series resonance resistance changes need to be detected and measured Each individual QCM user must determine the effect of temperature on the experiments being performed and either control the temperature accordingly or measure the temperature and compensate for it The table below summarizes some of the most relevant static temperature coefficients for 5MHz QCM crystals around room temperature Tip QCM100 Quartz Crystal Microbalance 3 10 Sensor Crystals and Holders Whenever practical the use of flow cells is recommend for both gas and liquid studies to minimize temperature transient effects Temperature stabilization better than 0 05 C is generally required to eliminate temperature related transients and drifts in lengthy measurements The table below compiles some very important temperature coefficients Temperature coefficient in air 1 3 Hz C Temperature coefficient in water 8Hz C 40 C OCM100 Quartz Crystal Microbalanc
50. can determine Rm Ri Av 1 OCM100 Quartz Crystal Microbalance ASRS Theory Operation and Calibration 2 7 Capacitance Cancellation The QCM100 System incorporates a method of nulling C capacitance insuring that the frequency and resistance values measured correspond to the true series resonant parameters of the quartz oscillator The front panel of the QCM100 Analog Controller includes 1 a ten turn DIAL to control the bias voltage required by the varactor Cy and 2 a switch to set the controller into the Adjust Mode for nulling Co There are two ways to operate the QCM100 Analog Controller to null Co 1 The unit to unit variations in Co are small enough and the reproducibly of Cy is good enough 2 pF that most users can just set the varactor bias to a fixed value and forget about the whole issue Set the ten turn dial to 8 0 which will provide 9 0 volts of reverse bias to the varactor making C about 18 pF This method is recommended for dry applications where Rm is low This is not recommended for sticky applications such as solutions of glycerol where Rm can be very high Null C with the conductance lock in peak detection circuit In the Adjust Mode the unit will modulate the varactor bias with a 75 Hz sine wave and indicate if the Co compensation is High Low or Nulled Start with the ten turn dial set to 8 0 the LED should indicate that the crystal is oscillating and switch to Adjust Mode Reduce
51. ck Panel Overview ASRS SRS QCM100 WARNING NO USER SERVICEABLE PARTS INSIDE REFER SERVICE TO QUALIFIED TECHNICIAN SEE OPERATION MANUAL FOR SAFETY NOTICE Overview vii A C POWER CHASSIS GROUND 90 132 or 175 264 VAC 47 63 Hz 20 VA TOTAL Figure 2 Back Panel of OCM100 Analog Controller Power Entry Module The Power Entry Module is used to connect the QCM100 Analog Controller to a power source through the power cord provided with the instrument The center pin is connected to the QCM100 chassis so that the entire box can be grounded The source voltage requirements are 90 132 or 175 264 VAC 47 63 Hz 20 VA TOTAL Connect the QCM100 to a properly grounded outlet Consult an electrician if necessary Chassis Ground Use this grounding lug to connect the QCM100 chassis directly to facility ground QCM100 Quartz Crystal Microbalance viii Overview QCM25 Crystal Oscillator Overview QCM Controller Crystal Face Biss Power ASRS QCM25 Crystal Oscillator 5 MHz Crystal nn Figure 3 QCM25 Crystal Controller top view QCM Controller Connector The QCM Controller connector is a RJ 45 connector used to electrically connect the QCM25 Crystal Oscillator to the QCM100 Analog Controller Crystal Probe connector A 3 foot long Cat 5 Straight Through cable is used to electrically connect the two boxes A cable up to 25 feet in length may be used A green Power LED
52. crobalance 2 24 Theory Operation and Calibration EQCM Frequency Measurement 100 3000 Reduction o Cu II 2e gt Cu s 2000 aood 1000 o 200 Massogram lt wo 1000 g 300 yot E e oltammogram L 2000 E 2 400 i o 3000 re 4 500 J L 4000 600 5000 Oxidation 700 nl e 6000 0 7 0 5 0 3 0 1 0 1 0 3 0 5 Volts vs Ag AgCI Figure 9 Cyclic voltammogram and massogram data for Cu deposition on a Au electrode The frequency potential diagram shows a frequency decrease in perfect sync with the deposition of Cu metal reduction on the crystal s surface The mass sensing capabilities of the QCM100 are complemented by its ability to simultaneously detect subtle changes in the viscous loading of the QCM crystal during redox processes Figure 10 is a graphical representation of the changes in series resonance resistance that take place at the QCM sensor i e working electrode during a cyclic voltammetric scan of a 50mM solution of K Fe CN in 1M Na SO4 50mV sec scan rate As the potential of the electrode becomes less positive Fe CN is depleted and replaced by a layer of Fe CN adjacent to the sensor crystal Since solutions of Fe CN are more viscous than Fe CN the resistance readings increase at more negative voltages as the more viscous reduced product exerts additional loading on the crystal The resistance change corresponding to the convers
53. crystals frequency fluctuations depend not only on the T but also on the rate of change of T Avoid sudden pressure changes such as pressure transients in gas flow systems or flowrate changes in liquid flow injection systems Whenever possible replace peristaltic pumps with Syphon setups or syringe pumps Relax mechanical stress It is often a good practice to tap on the holder flow cell before starting a new set of measurements Gentle tapping helps to dislodge trapped bubbles and relaxes mechanical stresses at the oring seats resulting in reduced drift problems Wait for the signal to stabilize after liquid exchange In flowing setups it is important to keep in mind that detectable signal transients are to be expected after sudden changes in flow rates and after liquid exchanges i e new sample injections Flow transients can last less several seconds and can seriously compromise your long term measurements if bubbles are introduced into the flow stream or large temperature differences between the liquid and the holder are established Use small and constant flow rates During liquid flow experiments flowrates should be kept small and constant to eliminate signal transients due to pressure and temperature fluctuations Recommended flow rates should be below 0 2 mL min to assure minimal transients and flow induced noise in the frequency measurements Rely on gravity the Syphon principle or syringe pumps to flow liquids through a cell in
54. d A C POWER on the back plane of the QCM100 box provides connection to the power source and to a protective ground Power Cord The QCM100 package includes a detachable three wire power cord for connection to the power source and protective ground The exposed metal parts of the box are connected to the power ground to protect against electrical shock Always use an outlet which has a properly connected protective ground Consult with an electrician if necessary Keep all electrical wiring in your experimental setup neatly organized and in good working condition Inspect all HV wires periodically for problems as part of your safety checkups Grounding A chassis grounding lug is available in the back plane of the QCM100 box next to the power entry module Connect a heavy duty ground wire 12A WG or larger from the CHASSIS GROUND lug directly to a facility earth ground to provide additional protection against electrical shock Both front panel BNC shields are connected to the chassis ground and the AC power source ground via the power cord Do not apply any voltage to the shield GFCI Ground Fault Circuit Interrupter GFCI protected outlets are often available in production and laboratory environments particularly in proximity to water sources GFCI s are generally regarded as an important defense against electrocution However the use of GFCI in conjunction with the QCM100 must not be regarded as a substitute for proper groundi
55. d Daniel A Buttry Determination of Ion Populations and Solvent Content as functions of Redox State and pH in Polyaniline J Am Chem Soc 109 1987 3574 3 Michael Ward Investigation of Open Circuit Reactions of Polymer Films Using the QCM Reactions of Polyvinylferrocene Films J Phys Chem 92 1988 2049 Charles K Baker and John R Reynolds A quartz microbalance study of the electrosynthesis of polypyrrole J Electroanal Chem 251 1988 307 3 Stephen Martin Victoria Edwards Granstaff and Gregory C Frye Characterization of a Quartz Crystal Microbalance with Simultaneous Mass and Liquid Loading Anal Chem 63 1991 2272 Ralf Lucklum and Peter Hauptmann The Df DR QCM technique an approach to an advanced sensor signal interpretation Electrochimica Acta 45 2000 3907 R A Etchenique and E L Calvo Gravimetric measurement in redox polymer electrodes with the EQCM beyond the Sauerbrey limit Electrochemistry Communications 1 5 1999 167 OCM100 Quartz Crystal Microbalance ASRS Theory Operation and Calibration 2 37 R A Etchenique and E J Calvo Electrochemical Quartz Crystal Impedance Study of Redox Hydrogen Mediators for Amperometric Enzyme Electrodes Anal Chem 69 1997 4833 3 E J Calvo R Etchenique P N Bartlett K Singhal and Santamaria Quartz Crystal Impedance studies at 10 MHZ of viscoelastic liquids and films Faraday Discuss 107 1997 141 Diethelm J
56. d by a frequency counter and a digital multimeter or A D converter respectively OCM100 Quartz Crystal Microbalance SRS Theory Operation and Calibration 2 23 Potentiostat Digital Multimeter QCM100 Analog Controller Reference Electrode Crystal Holder Frequency Counter Counter Electrode Work Electrode Figure 8 Schematic of EOCM apparatus A PC not shown is often interfaced to the potentiostat frequency counter and DMM and integrates the QCM and electrochemical data into a single software package Note The QCM25 Crystal Oscillator provides transformer isolation of the crystal s front face i e liquid surface electrode This allows direct electrical connection of the quartz crystal face to the working electrode pin of any standard potentiostat galvanostat With the instrument in Figure 8 a typical cyclic voltammetric EQCM experiment would involve the application of the electrochemical waveform to the working electrode and the simultaneous measurement of the current flowing through the electrochemical cell and the oscillation frequency and series resonance resistance of the crystal Figure 9 is an example of a typical voltammogram massogram plot obtained from a 10 mM solution of CuSO in 0 1 M H SO using a 1 inch diameter Au coated quartz crystal mounted in a standard Crystal Holder as the working electrode Note cathodic current is treated as positive ASRS QCM100 Quartz Crystal Mi
57. ders In order to avoid frequency transients due to temperature changes it is best to temperature stabilize the flow cell crystal holder and eliminate temperature differences between the gas samples and the holder Immersion in a temperature stabilized water bath often does the job and allows to set up a preheating loop to equalize the gas temperature with the sensor Keep in mind that changes in frequency are not only related to static changes in temperature around the crystal but also to the rate of change of temperature with time Use small and constant flow rates During flow experiments flowrates should be kept small and constant to eliminate signal transients due to pressure and temperature fluctuations Control humidity if necessary Adjustment of the humidity is often a requirement for accurate gas phase measurements It is generally recommended to adjust control the humidity of the gas before flowing into the measurement chamber common procedure consists of exposing the gas to saturated salt solutions with well known humidity values Bubbles and Liquid Flow Cells Eliminating gas bubbles trapped inside flow cell chambers is essential for accurate long term QCM measurements The highest risk of bubble formation is when liquid enters an empty chamber Bubbles can also form spontaneously if liquids are not previously degassed and the chamber temperature is greater AT gt 2 C than the liquid temperature This section describes
58. e it can flow to form a metastable continuous film or form a droplet on the surface depending on the wettability of the substrate By spinning the substrate the droplet is forced to spread out while the solvent evaporates If deposition conditions such as choice of solvent solution concentration and QCM100 Quartz Crystal Microbalance 3 16 Sensor Crystals and Holders spin speed are chosen carefully a thin film of uniform thickness is deposited on the substrate Polystyrene is a common material spin coated onto QCM sensor crystals Toulene is the solvent of choice UV Ozone treatment can be used to tailor the hydrophobicity of organic polymeric coatings Compact and easy to use laboratory spin coaters compatible with QCM crystals are commercially available Consult the factory for recommendations Langmuir Blodgett films Langmuir Blodgett films LBFs are artificial structures prepared by sequential transfer of monomolecular layers one molecule thick performed on a liquid surface usually H20 onto a solid substrate such as a glass slide or a silicon wafer LBFs are very thin and very well ordered This technology is attractive to researchers because of its ability to produce thin films 1 whose thicknesses can be precisely varied and 2 which can be modified to produce smart sensing devices Self assembled monolayers SAM Self assembled monolayer SAM techniques offer a new strategy for the immoblization of anti
59. e SRS Sensor Crystals and Holders 3 11 Crystal Handling ASRS Note Please read the following instructions about general handling of sensor crystals e Keep the crystals in a clean and dry place When not in use store them in their original box and wrapper e Avoid touching the metal electrodes of the crystal e Rinse only with deionized water or another appropriate residue free solvent before drying the crystal e Always use a flow of dry oil free inert gas e g nitrogen to blow dry the crystal It is better to blow the liquid off the crystal than to let it evaporate on the electrodes e Do not handle the sensor crystal using bare fingers Hold the sensor crystal with tweezers and only from its outer edge i e outside the electrode area to prevent scratches The tweezers should have smooth gripping surfaces and preferably be made out of soft plastic material e Before starting a surface cleaning confirm that the crystal material will not be damaged by the cleaning solutions Perform a test run on a discarded or practice crystal whenever possible Cleaning The surface properties of the sensor crystal determine the interaction of sample material with the surface Therefore the development of proper protocols for surface preparation and cleaning are required to obtain reproducible measurements This section provides the basic information you need to develop a cleaning protocol suitable for your sample surface system
60. e dependent viscosity and density of the fluid The temperature coefficient due to this effect is 8 Hz C and 4Q C for water As a result for experiments in liquid phase in which the frequency is to be monitored at length the temperature must be controlled to at least 0 1 C and preferably better If temperature control is not possible or practical it is always good practice to wait at least 30 minutes before performing any accurate measurements after the crystal comes in contact with a new liquid medium and measure the temperature of the solution around the crystal during the experiments to perform temperature compensation Careful control of the temperature is required in high accuracy measurements to avoid frequency hysteresis effects the dependence of resonator frequency at a specific temperature on its prior temperature history For example it is often observed that the frequency vs Temperature curve obtained going from T1 to T2 will not coincide with the one obtained immediately after going from T2 to T1 The causes of hysteresis and retrace are not well understood the experimental evidence to date is inconclusive The mechanisms that can cause these effects include strain changes changes in the quartz contamination redistribution in the crystal enclosure and apparent hysteresis or retrace due to thermal gradients In electrochemical experiments temperature control is often required to control reaction rates and is typi
61. e detected signal via R68 in order to blur the comparator response Even with this blurring the sensitivity and reproducibility is remarkable the crystal s electrode and holder capacitance can be nulled with a resolution of about 0 01 pF The 75 Hz modulation on the varactor voltage will also modulate the frequency of the 5 MHz signal which is used to detect mass accumulation on the crystal face Most users will want to turn this modulation off while making mass measurements However the effect of this modulation and frequency modulations caused by the line frequency will be virtually eliminated if gate times for the frequency measurement are an integral multiple of 0 2 S so that there are an integral number of modulation cycles during each measurement ASRS OCM100 Quartz Crystal Microbalance 4 8 Circuit Description OCM100 Quartz Crystal Microbalance Chapter 5 QCM Parts List QCM100 Parts List REF SRSPART VALUE C1 5 00318 569 2 2U T35 C2 5 00318 569 2 2U T35 C3 5 00318 569 2 2U T35 C4 5 00299 568 1U C5 5 00372 552 56P C6 5 00363 552 10P C7 5 00299 568 1U C8 5 00299 568 IU C9 5 00299 568 IU C10 5 00299 568 1U C11 5 00299 568 1U C12 5 00052 512 01U C13 5 00052 512 01U C14 5 00056 512 IU C15 5 00056 512 IU C16 5 00299 568 IU C17 5 00299 568 IU C18 5 00299 568 IU C19 5 00299 568 IU C20 5 00052 512 01U C21 5 00052 512 OIU C22 5 00052 512 OIU C23 5 00052 512 01U C24 5 00
62. e filter is adjusted during factory calibration so that the loop oscillates at 5 MHz when the crystal is replaced by a 50 Q resistor The gain of U1 is controlled by the voltage Vc at pin 5 The gain is equal to 45 50xVc dB where Vc is between 0 and 1 Vdc Increasing Vc decreases the amplifier gain The SLD output current on pin 6 will ramp Vc up to decrease the gain if the detected signal at the amplifier output pin 10 is greater than 1 Vpp The SDL output sinks a current to increase the amplifier gain if the detected amplifier output is less than 1 Vpp In this way U1 adjusts the loop gain to maintain the oscillation at constant amplitude R11 and C4 determine the AGC loop characteristics and have been selected to provide a critically damped response The AGC voltage is buffered and amplified by U3 an OPA337 operational amplifier The gain which is about 5x is adjusted during factory calibration to calibrate the slope of the AGC curve The slope and offset of the AGC voltage is adjusted to assure compliance to the Voona VS Rerystal characteristic The amplified AGC voltage and ground reference are sent to the QCM100 via two 1 000 KQ resistors over a twisted pair The signal is received in the QCM100 by a differential amplifier to remove common mode signals The AGC signal is filtered and amplified by 2 5x before being output on the front panel Veona BNC The 5 MHz signal on the primary of T1 is converted to a TTL signal by U2 a DS89
63. e perturbations The perturbations to be considered include surface loading by e a thin film mass layer e a contacting Newtonian fluid e a viscoelastic layer of finite thickness Frequency The nominal frequency of oscillation of all standard QCM Sensor Crystals is 5 MHz fundamental mode The unperturbed crystals will normally be within 1 000 ppm of their nominal frequency Operation at 5 MHz is regarded as optimal for laboratory use since it provides 1 acceptable submonolayer sensitivity 2 robustness 331 um crystal thickness and 3 stable oscillation in most viscous media Geometry Figure 1 shows a top and bottom view of a standard linch diameter QCM Sensor Crystal with what is called a wrap around electrode configuration A conductive metallic pad is used to allow connection to the front electrode liquid surface from the back of the crystal electrical contact surface This is required for mounting of the crystal into its Crystal Holder and for proper operation in conductive liquids The exposed area of the front electrode in contact with the liquid is 71 37 cm however the active electrode oscillation i e displacement area is mostly restricted to the area of overlap between the two circular pad electrodes or 0 40 cm All standard 1 inch QCM sensor crystals are planar with both faces parallel to within 1 um Crystal thickness is 331 um as required for fundamental oscillation at 5 M
64. e presence of electrical power Crystal Probe Connector w green OSC LED The Crystal Probe connector is an RJ 45 connector used to connect the QCM100 Analog Controller to the QCM25 Crystal Oscillator QCM Controller connector A 3 foot long Cat 5 Straight cable is used to electrically connect the two boxes A green OSC LED lights to indicate the presence of an oscillating crystal in the circuit and the Conductance Output is gt 2 V Frequency Output Connector The Frequency Output connector is a BNC connector The frequency signal has TTL square wave levels and a source resistance of 50 Q The BNC shield is electrically connected to chassis ground Conductance Output Connector The Conductance Output connector is a BNC connector The conductance signal Ve is related to the series resonance resistance of the QCM crystal by R 10 000 x 10 75 Q Voltage levels span between 0 and 10 625 VDC and source impedance is 1 KQ The BNC shield is electrically connected to chassis ground QCM100 Quartz Crystal Microbalance Vi Overview C Compensation A switch is available to set the controller into the Adjust Mode for nulling Co A ten turn DIAL controls the bias voltage Varactor bias required by the QCM25 Crystal Oscillator to null Co Four LEDs HIGH NULL LOW provide visual feedback while nulling Co Set the Co Compensation switch back to HOLD after nulling Co OCM100 Quartz Crystal Microbalance SRS Ba
65. ectronic Oscillator with automatic gain control EQCM Applications Sensors and actuators B 32 1996 129 136 Note the same experiment as deccribed in Figure 10 is described in page 134 of this publication The numbers required to calculate the change in viscocity in the Nernst layer were obtained from M D Ward et al Anal Chem 65 1993 3232 77 Wolfgang Stockel and Rolf Schumacher In situ Microweighing at the Junction Metal Electrolyte Ber Bunsenges Phys Chem 91 1987 345 C Gabrielli M Keddam and R Torrei Calibration of the Electrochemical Quartz Crystal Microbalance J Electrochem Soc 139 9 1991 2657 Note A calibration procedure based on the deposition of Ag on Au electrodes is described Graeme Andrew Snook Investigation of Solid State Reactions by Electrochemical and Quartz Crystal Microbalance Measurements Ph D Thesis 2000 Department of Chemistry Monash University Clayton 3168 Melbourne Australia and Division of Minerals CSIRO Clayton South 3169 Melbourne Australia under the supervision of Professor Alan Maxwell Bond Monash and Professor Stephen Fletcher CSIRO Available for download from http www bond chem monash edu au theses Note the use of Lead acetate is proposed as a better alternative to Cu and Ag deposition Bruckenstein S and Shay M Experimental aspects of use of the quartz crystal microbalance in solution Electrochim Acta 30 1985 1295 Duke Orata an
66. ed on the crystal but you can also tell how tightly it binds this is very useful additional information QCM Systems are applied routinely by biologists immunologists and biochemists to obtain information about processes such as 1 protein adsorption desorption 2 cell adhesion 3 Protein protein interaction 4 Degradation of polymers 5 biofouling and biofilm formation 6 drug analysis 7 self assembled monolayers and 8 DNA biosensors For more detailed information please consult the references listed at the end of this chapter Self Assembled Monolayers A self assembled monolayer SAM is defined as a two dimensional film one molecule thick covalently assembled at an interface The classical example of a SAM is the reaction of alkanethiols with a gold surface Since sulfur donor atoms strongly coordinate on metal substrates Au Ag Pt etc sulfur containing molecules such as disulfides R SS R sulfides R S R and thiols RSH can form various functionalized SAMs with highly organized and compact construction For example when a clean gold surface is immersed in an alkanethiol solution the following self assembly chemisorption reaction takes place Au RSH Au SR 1 2 HT This reaction self terminates at one monolayer when all accessible gold sites are consumed The Langmuir adsorption model has been applied successfully to model the adsorption desorption kinetics of these processeses
67. el consists of two arms The motional arm has three series components modified by the mass and viscous loading of the crystal 1 Rm resistor corresponds to the dissipation of the oscillation energy from mounting structures and from the medium in contact with the crystal i e losses induced by a viscous solution 2 Cm capacitor corresponds to the stored energy in the oscillation and is related to the elasticity of the quartz and the surrounding medium 3 Lm inductor corresponds to the inertial component of the oscillation which is related to the mass displaced during the vibration Typical values for a 1 diameter 5 MHz crystal used in the QCM100 System are Cm 33 fF Lm 30 mH and Rm 10 for a dry crystal Rm 400 for a crystal with one face in water or Rm 3500 for a crystal with one face in 88 glycerol The motional arm is shunted by the parasitic capacitance Co which represents the sum of the static capacitances of the crystal s electrodes holder and connector capacitance In the QCM100 System C is about 20 pF a value which has been kept small by placing the electronics directly on the Crystal Holder thereby eliminating any cable capacitance In a QCM application the motional inductance Lm is increased when mass is added to the crystal electrode the frequency shift of the series resonance is a sensitive indicator of the added mass Films of less than 1 ng cm can easily be resolved by t
68. ence Aa A An Ao Ap 1 Rearranging and substituting the equation for An 1 An R 4 Rm R R Aa A1 At Ao Ar Solving for Rm Rm Ri Aa Ar At Ao Ap RL Rs 4 From the characteristics of the voltage variable attenuator described above Aa 10 where Vs is the voltage at the Conductance output BNC on the QCM100 A is adjusted during factory calibration so that the product of the gains A At A2 Ar 200 So we have Rm 10 000 10 75 Where Rm is the motional series resonance resistance in Q and Veis the conductance voltage output in V The motional resistance of the crystal at series resonance Rm can be computed from the above equation Figure 6 below graphs Rm vs Vc QCM100 Quartz Crystal Microbalance 2 14 Theory Operation and Calibration Motional Resistance vs Conductance Voltage Rm 10 000 x 104 Vc 5 75 Ohms 10000 1000 100 Motional Resistance Ohms 0 1 2 3 4 5 6 7 8 9 10 11 Conductance Voltage Volts Figure 6 Motional series resonance resistance vs conductance voltage Errors In The Measurement Of Rm Errors in the measurement of Rm will be less than 3 Q 3 of Rm for Rm lt 2 KO and are dominated by the departure of the voltage controlled attenuator from its nominal voltage gain characteristic Keep in mind that the resistance me
69. erature controllers are recommended instead of On Off controllers for temperature stabilization OCM100 Quartz Crystal Microbalance 3 22 Sensor Crystals and Holders To ensure signal stability for flowrates greater than 70 2 mL min use external temperature stabilization as necessary to make sure that the sample liquid is temperature equilibrated prior to flowing into a flow chamber Immersing the flow cell crystal holder in a water bath and running the sample fluid through the same bath i e heating loop prior to entering the QCM chamber is a simple way to assure temperature equalization between the holder and its liquid sample solutions Prepare your solutions carefully To avoid unwanted effects due to changes in the properties of the carrier buffer liquid or solvent solutions should be prepared carefully Whenever possible use purified samples at high concentration and dilute them in the appropriate buffer or solvent just before measurement Use solvents or buffers from the same stock during each measurement series Avoid mechanical vibrations Keep the sensor away from mechanical equipment containing motors or similar vibrating parts Fasten all dangling cables that might transfer vibrations to the crystal holder flow cell Avoid transients Avoid sudden mechanical stresses such as knocking on the crystal holder pulling on cables sudden shifts in the experimental setup etc Avoid sudden temperature changes In AT cut quartz
70. essive viscous loading would prohibit use of the QCM in liquids In fact operation in liquids is indeed possible and the response of the QCM is still extremely sensitive to mass changes at the crystal solution interface For many years QCMs have been used in direct contact with liquids and or viscoelastic films to assess changes in mass and viscoelastic properties during chemical and electrochemical surface processes When the QCM comes in contact with a solution there is a decrease in frequency that is dependent upon the viscosity and the density of the solution A quantitative understanding of the resonator behavior is a prerequisite for proper interpretation of experimental results under total liquid immersion This problem was first treated by Glassford and later by Kanazawa and Gordon Kanazawa s treatment of the influence of the solution properties on the crystal eqn 6 permits the prediction of the change in resonance frequency which accompanies immersion of the crystal into a viscous medium Af fu pL NL T Pa Hall eqn 6 where f frequency of oscillation of unloaded crystal Pq density of quartz 2 648 g cm Ha shear modulus of quartz 2 947 x 10 gem s PL density of the liquid in contact with the electrode NL viscosity of the liquid in contact with the electrode Viscous coupling of the liquid medium to the oscillating crystal surface results not only in a decrease in the series reson
71. f Organic Thin Films on Quartz Resonators Macromol Chem Phys 200 1999 501 E J Calvo et al Quartz Crystal impedance studies at 10 MHz of viscoelastic liquids and films Faraday Discuss 107 1997 141 gt R W Cernosek et al Analysis of the radial dependence of mass sensitivity for modified electrode quartz crystal resonators Anal Chem 50 1998 237 H K Pulker and W Schadler Nuovo Cimento 57B 1968 19 T W Schneider and S J Martin Influence of compressional wave generation on a thickness shear mode resonator response in a fluid Anal Chem 67 1995 3324 H Bahadurand R Parshad Physical Acoustics Vol 16 W P Mason and R N Thurston Eds Academic Press NY 1982 p 37 171 Stephen Martin et al Effect of Surface Roughness on the Response of Thickness Shear Mode Resonators in Liquids Anal Chem 65 1993 2910 Michael Ward and Edward J Delawski Radial Mass Sensitivity of the Quartz Crystal Microbalance in Liquid Media Anal Chem 63 1991 886 8 S J Martin et al Effect of Surface Roughness on the Response of Thickness Shear Mode Resonators in Liquids Anal Chem 65 1993 2910 C K Sullivan and G G Guilbault Commercial Quartz Crystal Microbalances theory and applications Biosensors and Bioelectronics 14 1999 663 670 10 US Patent number 5 233 261 11 See for example Rupa Patel R Zhou K Zinszer F Josse and R Cernozek Real
72. fferentially to the QCM 100 via one twisted pair in the Cat 5 cable allowing measurement of the crystal s series resonant frequency An analog voltage which is proportional to the RF gain in dB required to sustain the crystal s oscillation is also passed to the QCM100 allowing measurement of the crystal s motional resistance QCM25 Circuit Description ASRS The heart of the QCM25 is U1 an AD8367 RF amplifier with 500 MHz bandwidth and up to 45 dB of voltage controlled gain The integrated circuit also has a square law detector SLD and automatic gain control AGC amplifier which measures and controls the amplitude of its output The oscillation of the 5 MHZ crystal is sustained by the gain provided by this integrated circuit The gain required to sustain the oscillation is a measure of the losses in the crystal The RF output of U1 is applied via the transformer T1 to the resistor network formed from the series combination of the 50 Q output resistance of U1 plus R12 49 9 Q plus the crystal s resistance 0 4 kQ and terminated into R17 49 9 Q The attenuation of this network is the smallest at the series resonant frequency of the crystal The AGC amplifier has sufficient gain to maintain the amplitude of the output of U1 at 1 Vpp provided that the crystal s series resistance is less than 4 kQ Dry crystals have about 10 Q of resistance at series resonance while crystals with one face in water have about 400 Q of resistance at se
73. formance when connected to a QCM25 Crystal Oscillator and a QCM100 Analog Controller Head Cleaning It is not uncommon for crystals to break or for oring seals to leak during normal operation If chemical leakage into the crystal cavity is suspected it is very important to act fast and rinse the cavity the POGO contacts and the POGO contact sockets to remove any traces of solution that might lead to damage of the holder Start by removing the crystal from the Crystal Holder and exposing the POGO pins Putting your thumbnail or the flat head of a jeweler screwdriver under the POGO head pull firmly up to remove each contact pin from its socket Rinse the pins and the sockets with deionized water to remove all traces of chemicals Repalce the POGO pins with new ones if necessary Keep in mind that even though the POGO contacts and sockets are gold coated unrinsed chemicals can still lead to corrosion and permanent damage to the holder This is specially true in electrochemical applications where oxidizing acids are often components of the liquid solution in contact with the crystal QCM100 Quartz Crystal Microbalance 3 20 Sensor Crystals and Holders Crystal Cleaning Basket A Crystal Cleaning Basket SRS Part O100CCB is available directly from Stanford Research Systems This accessory makes cleaning and surface modification treatment of the standard 1 QCM crystals very safe and easy The cleaning basket is shown in Figure
74. g Started 1 7 Liquid Surface The liquid surface has the larger electrode pad which connects through a wrap around pad to one of the circuits on the Contact Surface This is the outside i e modified surface in direct contact with the gas or liquid during QCM experiments Figure 5 Liquid surface of OCM crystal In order to insert a new crystal into the holder the following steps must be followed 1 ASRS Place the Crystal Holder s head on a flat surface with its crystal cavity pointing up The crystal cavity contains two spring loaded contacts POGO pins which connect the two Contact Surface circuits of the crystal to the BNC connector on the opposite end of the probe Inspect the head oring to make sure it is free of defects clean and properly seated in its dovetail groove The oring should be free of low spots and show sufficient height above the center ring when viewed from the side with the naked eye Make sure the crystal cavity is clean and dry Dry if necessary Test the travel of the POGO contacts Gently depress the POGO pins a thin wooden applicator does a good job Make sure that they travel freely i e their motion is not restricted They should drop to a level well below the surface of the probe oring by an amount at least equal to the thickness of the crystal When fully extended they should protrude above the surface of the oring by an amount equal or larger than the thickness of the sensor cryst
75. ge in mass per unit area in g cm calculated from Sauerbrey s equation T thickness of the film in cm OCM100 Quartz Crystal Microbalance ASRS ASRS Theory Operation and Calibration 2 17 Z match Method It is generally accepted that when the mass loading from the deposit causes a change in frequency of less than 2 of the frequency of the unloaded crystal Sauerbrey s equation can be used to obtain accurate results in thin film thickness calculations As the thickness of the film increases the Sauerbrey equation must be extended to incorporate the elasticity of the deposit Lu and Lewis gave a simple equation eqn 5 for the calculation of the dependence of Af on Am which is currently applied by most QCM users to calculate rigid thin film thicknesses in gas phase depositions Am Ne Par Z fi tan Z tanfr fu fi fu eqn 5 where Am change in mass per unit area in g cm N Frequency Constant for AT cut quartz crystal 1 668 x 10 Hz Pa density of quartz 2 648 g cm fu frequency of unloaded crystal prior to deposition in Hz f frequency of loaded crystal in Hz Z Z Factor of film material Pa Hq pr wn pr density of film material in g cm Hq shear modulus of quartz 2 947 x 10 g cm s ur shear modulus of film material This analysis of frequency changes including the acoustic impedances of the quartz and film is often called the Z
76. gles and a lab coat n Work in a fume hood The mixture of hydrogen peroxide and sulfuric acid is very exothermic Do not touch the glassware after mixing HOT up to 120 C z Use heat resistant glassware This mixture can get really hot and shutter non thermal graded glass Rinse thoroughly z Keep the etching solution away from organic solvents a Treat with very healthy respect Properly clean and dispose of all chemicals Consider safer alternatives compatible with your application n If not sure how to proceed STOP and seek help from an experienced chemist Prolonged exposure to Piranha solution damages QCM crystals The failure mechanism is believed to involve chemical degradation of the Cr bonding layer located between the quartz and the gold electrode Typically a QCM crystal can be exposed to Piranha solution a maximum of three times before noticeable degradation of performance occurs The first signs of crystal degradation are reduced stability in the frequency baseline Polystyrene removal Step 1 Immerse the crystal into a 1 1 solution of hexane and deionized water and treat it in an ultrasonic bath for 1 minute ASRS OCM100 Quartz Crystal Microbalance 3 14 Sensor Crystals and Holders Step 2 Rinse thoroughly with deionized water and blow dry with nitrogen gas Crystal rinsing Rinse sensor crystals with deonized or distilled water or another appropriate pure liquid In order to prevent recontamina
77. h a resistance of less than 4 kQ The single ended AGC voltage is further amplified and filtered by two low pass Butterworth filters Both filters have two poles The first U10B is set to 80 Hz and the second U10A is set to 8 Hz The Veona BNC output is driven by the second filter via a 1 kQ resistor Together these filters provide a gain of 2 5x for the AGC signal from the QCM25 The gain is adjusted at the factory by setting P1 Capacitive Nulling By The QCM100 The rest of the circuits on the QCM100 schematic are used to determine and set the correct bias for the varactor in the QCM2S As previously discussed a varactor is used in the QCM25 circuit which cancels the current that flows though the crystal s electrode and holder capacitance By canceling this current the capacitances are effectively eliminated from the oscillator circuit allowing the crystal to oscillate at its series resonance frequency The varactor capacitance is controlled by the ten turn potentiometer on the front panel of the QCM100 Cancellation is achieved when the varactor capacitance is equal to the crystal s electrode and holder capacitance Increasing the dial setting increases the reverse bias on the varactor which decreases the varactor capacitance The dial should be set to the position which minimizes the gain required to sustain oscillation it is at this point where the capacitive currents cancel QCM100 Quartz Crystal Microbalance 4 6 Circuit Descr
78. hange in frequency to change in mass for thin rigid deposits whereas the latter relates charge passed in an electrochemical experiment to the number of moles of material electrolyzed Therefore frequency changes can be related to the total charge passed An example would be the electrodeposition of Ag on a Pt electrode QCM crystal The charge Q is an integral measure of the total number of electrons delivered at the interface during the reduction process To the extent that each electron supplied results in the deposition of one atom of Ag there should be a linear relationship between Q and Af as is given by equation 8 Af 10 M C Q n FA eqn 8 where Af frequency change in Hz ASRS OCM100 Quartz Crystal Microbalance 2 26 Theory Operation and Calibration Mw apparent molar mass of the depositing species in grams mole C Sauerbrey s sensitivity factor for the crystal used see eqn 1 Q integrated charge during the reduction in Coulombs A active deposition area of the working liquid contact electrode in cm F Faraday s constant 9 648 x 10 Coulomb mole n number of electrons transferred to induce deposition i e n 1 for Ag deposition The factor of 10 provides for the unit conversion from ug in Csto g in My A plot of Af vs Q will deliver the apparent mass per electron of the deposited species when n is taken into account This is often used to elucidate the mass changes that acco
79. he measurements provided by the QCM100 System OCM100 Quartz Crystal Microbalance 2 34 Theory Operation and Calibration References 1 G Sauerbrey Z Phys 155 1959 206 Daniel Buttry Applications of the QCM to Electrochemistry in A Series of Advances in Electroanalytical Chemistry edited by Allen Bard Marcel Dekker 1991 p 23 33 gt John Henderson Electronic Devices Concepts and Applications Prentice Hall NJ 1991 p 357 For example standard Crystal Holder with a 1 inch 5 MHz crystal connected directly to an SRS QCM25 Crystal Oscillator FC Chagnard P Gilbert N Watkins T Beeler and David W Paul An electronic oscillator with automatic gain control EQCM Applications Sensors and Actuators B 32 1996 129 136 A Arnau T Sogorb and Y Jimenez Circuit for continuous motional series resonant frequency and motional resistance monitoring of quartz crystal resonators by parallel capacitance cancellation Rev Sci Instrum 73 7 2002 2724 For example from the Conductance Output of the QCM100 7 Conductance is the inverse of resistance Conductance 1 Resistance or Resistance 1 Conductance The units of resistance are Ohms Q V A and the units of conductance are Siemens S A V For example Agilent 34401 A with 6 digit resolution or 3458 with eight digits resolution DR Denison Linearity of a Heavily Loaded Quartz Crystal Microbalance J Vac Sci
80. he QCM The motional resistance Rm can also provide important information about a process since soft films and viscous liquids will increase motional losses and increase the value of Rm OCM100 Quartz Crystal Microbalance ASRS ASRS Theory Operation and Calibration 2 5 Co Figure 2 Oscillator Circuit consisting of AGC Amplifier Quartz Resonator and Load Resistor Placing the crystal in an oscillator circuit provides a simple way to measure its motional parameters Figure 2 shows the BVD crystal model driven by an automatic gain control amplifier AGC and terminated into a load resistor RL By returning the voltage on R to the input of the AGC amplifier the circuit will oscillate at a frequency for which the phase shift around the loop is 0 or an integral multiple of 360 provided there is sufficient gain the Barkhausen condition Absent Co it is easy to see that the phase condition is satisfied at the series resonance of Cm and Lm fsr 1 27 LmCm At series resonance the reactance of Cm and Lm cancel leaving only Rm In this case an amplifier gain of Ay Rm RLVRL will provide a loop gain of 1 to sustain oscillation Unfortunately Co cannot be ignored in QCM applications In the circuit shown in Figure 2 C injects a leading current into RL which must be canceled by a lagging current via the motional arm in order to achieve the zero phase condition This requires the circuit run above series resonance
81. he typical characteristics of the frequency signal from the QCM100 Analog Controller for a crystal in water Description Typical Value Frequency 5 0 01 MHz Waveform into 50 Q 2 4 V square wave Stability second to second 0 002 Hz Stability minute to minute 0 10 Hz Temperature coefficient static 8 Hz C Frequency mass coefficient 0 057 Hz ng cm Many of the frequency counter s characteristics are determined by its time base If the time base changes frequency by 10 ppm the reported values will also change by 10 ppm While the accuracy of the counter s time base is not particularly important the stability of the time base is critically important as variations in the time base will be indistinguishable from changes in accumulated mass on the surface of the crystal Often manufacturers will specify accuracy and aging but do not specify short term stability In virtually all counters the short term stability will improve if they are allowed to warm up for an extended period of time To avoid degrading frequency measurements the time base should have a 1 second stability of better than 002 Hz 5 MHz or 4x10 The speed resolution of a counter is also important The accumulated mass can change rapidly in a typical QCM measurement and it is desirable to make frequency measurements with a resolution of 1 10 in a one second interval to not significantly degrade the mass resolution of or add noise to the measurement Simply counting
82. igh The purpose of this gain control is to increase the gain for the AGC modulation when the crystal losses are low so that the apparent sensitivity of the front panel dial is more nearly constant over a wide variety of crystal resistances The gain of U12 is proportional to its bias current In this circuit the lower half of U12 is used as the amplifier channel The top half of U12 together with the Darlington pairs that are normally used as output buffers are used to generate an amplifier bias current which varies exponentially with the AGC voltage The output of the transconductance amplifier pin 12 on U12 is a current This current is converted to a voltage by U13B which is arranged as a transimpedance amplifier U13A inverts the output of U13B and the multiplexer switches between the signal and its inverse at 75 Hz to synchronously detect the modulation on the AGC signal The detected signal is filtered by U3A a two pole Butterworth filter with a low pass set to 0 8 Hz The detected signal will be a positive if the dial setting is too high and will be negative if the dial setting is too low The quad comparators U15 and U16 activate front panel LEDs to indicate to the user how to adjust the dial If the HIGH LED is on the dial should be set lower and if the LOW LED is on the dial should be set higher The NULL LEDs indicate that the dial is set correctly A sawtooth waveform at 16x the modulation frequency is added to th
83. imum sensitivity at the center of the electrode and zero sensitivity at the edges for harmonically driven plane crystals The mass sensitivity distribution has also been shown to become slightly more confined to the electrode region as the mass loading is increased In order to assure reproducibility of results it is very important to assure uniform coverage of the electrodes during measurements There are also situations in which the QCM does not act as a microbalance at all but responds instead to properties such as viscosity and or elasticity of the liquid or film in contact with its surface Maximum Loads QCM sensor crystals can be coated with virtually any material as long as it can be deposited in a sufficiently thin uniform and well attached layer Layer thicknesses typically vary from a few Angstrom to a few micrometers The maximum layer thickness depends on the viscoelastic properties of the coating material As a general rule thicker layers are possible for more rigid coating materials The maximum load on a crystal is limited by two factors 1 total damping or 2 lost sensitivity For highly viscous or solid materials the damping of the crystal increases with increasing layer thickness At a certain thickness usually a couple of micrometers the damping becomes so high that the crystal can no longer be driven i e the measurement fails due to lack of oscillation More elastic materials do not couple completely to the cry
84. ingly and doubly rotated oven controlled quartz resonators Pmt 32nd Ann Symp Freq Conk NTIS Accession No AD A955718 pp 180 188 1978 OCM100 Quartz Crystal Microbalance ASRS Sensor Crystals and Holders 3 29 75 M N Rocklein and S M George Temperature Induced Apparent Mass Changes Observed during QCM Measurements of Atomic Layer Deposition Anal Chem 75 2003 4975 Note This is a dramatic demonstration of thermally induced frequency transients caused by temperature transients in the gas phase 77 Kusters J A and Vig J R Thermal hysteresis in quartz resonators a review Proc 44th Ann Symp Freq Contr IEEE Catalog No 90CH2818 03 pp 165 175 1990 8 J R Vig UV Ozone Cleaning of Surfaces in Treatise on Clean Surface Technology Vol 1 ed by K L Mittal Plenum Press pp 1 26 1987 J R Vig and J W LeBus UV Ozone Cleaning of Surfaces IEEE Trans on Parts Hybrids and Packaging Vol PHP 12 pp 365 370 1976 J R Vig UV Ozone cleaning of surfaces J Vac Sci Technol A3 1985 1027 L Layden and D Wadlow High Velocity carbon dioxide snow for cleaning vacuum system surfaces J Vac Sci Technol A 8 5 1990 3881 Dave Laube Limitations of CO Cleaning for Semiconductor Process Tools Advancing Applications in Contamination Control Feb 2001 p 9 There are many different Plasma Cleaner manufacturers Look for a small system which support
85. ion of Fe CN to Fe CN 6 is 4 Ohms in complete agreement with a 0 9 estimated relative change in pn calculated from previously reported calibration curves 7 OCM100 Quartz Crystal Microbalance ASRS Theory Operation and Calibration 2 25 Series Resonance Resistance EQCM Resistance Measurement Cyclic Voltammogram 7000 440 6000 439 5000 438 AR 4 Ohms 4000 x 437 3000 E 436 2000 ma 435 1000 a s 434 a lt q he 2 E 4 o L pam oO Resistance Ohms ae i 155 432 431 430 0 3 0 2 Volts vs Ag AgCl Figure 10 Changes in series resonance resistance at the QCM sensor during the electrochemical oxidation reduction of Fe CN Fe CN The resistance potential diagram shows a resistance increase in perfect sync with thegeneration of a viscous layer of Fe CN reduction adjacent to the OCM electrode Calibration It has been amply demonstrated in the literature that when experiments involve only relative frequency shifts which are measured in a fixed solution the offset caused by the viscous loading of the liquid has negligible effect on the accuracy of the Sauerbrey equation for the determination of small mass changes in rigid deposits Quantitative interpretation of the EQCM data in those cases is based on the combination of the Sauerbrey equation eqn 1 and Faraday s law The former relates c
86. iption The gain required to sustain oscillation can be inferred from the AGC voltage the higher the AGC voltage the lower the gain required to sustain oscillation This can be done manually by finding the dial setting for which the AGC voltage is at a maximum or by modulating the varactor voltage and detecting the minimum gain setting using synchronous detection The second method is much faster and more accurate and is used by the QCM 100 When the ADJUST HOLD switch on the front panel of the QCM100 is placed in the ADJUST position the varactor voltage will be modulated by 5 around the dial set point The modulation frequency is 75 Hz and the waveform is sinusoidal If the dial is set below the optimum set point then increasing the varactor bias will increase the AGC voltage If the dial is set above the optimum set point then increasing the varactor bias will decrease the AGC voltage If the varactor voltage is modulated then the AGC will also be modulated The AGC modulation will be in phase with the varactor modulation if the dial is below the optimum set point and the AGC modulation will be out of phase with the varactor modulation if the dial is above the optimum set point The AGC modulation will go to zero when the dial is set to the optimum set point The QCM100 uses a synchronous detector i e lock in amplifier to measure the AGC modulation The user need only adjust the dial to null the detected AGC voltage as indicated by fou
87. l as the working electrode surface connect the Work Electrode lead of the potentiostat to the Crystal Face Bias connector of the QCM25 oscillator Consult Chapter 2 for additional details Temperature stabilization is essential in these experiments as well for high accuracy measurements Work Electrode lead connected to Crystal Face Bias connector Potentiostat Digital Multimeter QCM100 Analog Controller Reference Electrode Crystal Holder Frequency Counter Counter Electrode Work Electrode Figure 2 Basic Electrochemical Quartz Crystal Microbalance EQCM setup ASRS OCM100 Quartz Crystal Microbalance 1 6 Getting Started Crystal Installation This section describes the procedure required to replace install the QCM crystal of the Crystal Holder Figure 3 shows the basic components of the Crystal Holder including a standard 1 inch sensor crystal Crystal holder crystal cavity side arm and heed BNC connector OX sensor Er retainer cover liquid side u retainer cover retainer ring retainer ring a a Figure 3 Crystal Holder components contact springs The standard 1 inch diameter sensor crystal has two sides that must be clearly identified before this procedure is started Contact Surface The contact surface has two separate circuits and the smaller electrode pad Fig 4 Contact Surface of QCM crystal OCM100 Quartz Crystal Microbalance ASRS Gettin
88. lights up to indicate the presence of electrical power in the QCM25 box Crystal Face Bias The Crystal Face Bias connector provides a direct electrical connection to the QCM crystal s liquid face electrode i e outer electrode in contact with the solution Use this connector to electrically connect the QCM crystal s liquid face to the Work Electrode lead of a Potentiostat while using the QCM crystal in an electrochemical setup Transformer isolation between the crystal electrodes and the oscillator circuit makes the QCM100 System ideal for electrochemical research and compatible with virtually all potentiostats QCM100 Quartz Crystal Microbalance ASRS ASRS Overview ix 5 MHz Crystal Use this BNC connector to electrically connect the QCM25 Crystal Oscillator to a Crystal Holder or directly to your custom 5MHz QCM crystal holder 1 4 20 MTG Hole Use this threaded hole to mount the QCM25 Crystal Oscillator in your experimental setup using a 1 4 20 threaded fastener Power LED This LED lights up to indicate power is available to the QCM25 electronics This requires connection to a powered QCM100 Analog Controller QCM100 Quartz Crystal Microbalance x Specifications Specifications Frequency Output Frequency 5 MHZ nominal Level TTL square wave Source Impedance 50Q Connector BNC Conductance Output Vc Resistance Calculation R 10 000 x 10 75 Q Resistance Range 0 to 5000 Q Voltage Level 0
89. low i e without surface shear forces While the injected solution flows about the stagnation point any exchange with the surface of the crystal is diffusion limited Thus the rate of adsorption of the sample molecules or particles to the crystal surface is diffusion limited as well The hydrodynamics and deposition of molecules in stagnation point flow conditions have been investigated by Dabros and Van deVen and the user is referred to their publications for details Dabros T van de Ven T G M A direct method for studying particle deposition onto solid surfaces Colloid and Polymer Science 261 1983 694 707 Dabros T and T G M Van de Ven Deposition of latex particles on glass surfaces in an impinging jet Physicochem Hydrodynamics 8 1987 161 172 The stagnation point flow cell was specifically designed for the study of adsorption kinetics of particles micelles and chemical and biological molecules at solid liquid interfaces under well controlled hydrodynamic conditions Examples of surface volume processes that have been studied with the aid of stagnation flow cells include DNA protein interactions protein adsorption cell adhesion biofouling biocompatibility polymer degradation and hydration biofilm formation self assembled monolayers etc Installation The flow cell is used in place of the Crystal Retainer Ring of the Crystal Holder Once installed the cell creates a flow chamber of small volume 0 15 mL
90. mpany redox processes and hence is very useful for characterizing the mechanisms of electron transfer reactions However before any calculations can be performed based on eqn 8 the EQCM must be calibrated in order to properly derive 1 the proportionality constant Cy of the Sauerbrey equation in solution and 2 to account for the effective area of the working electrode This is generally done using a well behaved electrochemical reaction typically electrodeposition of silver copper or lead on a Au or Pt electrode The EQCM calibration method favored by Stanford Research Systems for its QCM100 System is based on the galvanostatic deposition of Ag A 50 mM solution of AgNO in 0 5 M HNO is subjected to a reducing potential and Ag is deposited with a fixed cathodic current density of 50 500 A cm The cathodic current is integrated to obtain the charge as a function of time Excellent linearity is generally observed in Af vs Q plots for depositions within 1 g cm providing a very reliable way to calibrate the proportionality constant of eqn 8 Several calibration procedures are also described in the electrochemistry literature and users are referred to the publications list at the end of this chapter for details Polymer Modified Electrodes The EQCM has been extensively used to study polymer modified electrodes particularly as a gravimetric tool to follow redox processes However for the linear frequency to mass relationshi
91. n M Rodahl and B Kasemo The Piezoelectric Quartz crystal Mass and Dissipation Sensor A means of studying Cell adhesion Langmuir 19 1998 248 Ann Sofie Cans et al Measurement of the Dynamics of Exocytosis and Vesicle Retrieval at Cell Populations Using a QCM Anal Chem 73 2001 5805 C A Keller and B Kasemo Surface Specific Kinetics of Lipid Vesicle Adsorption Measured with a QCM Biophysical Journal 75 1998 1397 Wei W Z et al Selective pharmaceutical analysis technique with sensitive piezoelectric quartz sensors Anal Lett 26 11 1993 2371 Brenda D Spangler and Bonnie J Tyler Capture agents for a QCM continuous flow biosensor functionalized self assembled monolayers on gold Analytica Chimica Acta 399 1999 51 62 See also www sensopath com Y C Liu et al Comparison of Different protein immobilization methods on QCM surface in flow injection immunoassay Anal Biochem 299 2001 130 135 Le Storri S Santoni T Mascini M A piezoelectric biosensor for DNA hybridization detection Anal Lett 31 11 1998 1795 1K L Prime G M Whitesides Science 252 1991 1164 K Prime G Whitesides J Am Chem Soc 1993 v 115 10714 10721 A Model System Using Self Assembled Monolayers Ramon Colorado Jr Ramon J Villazana and T Randall Lee Self Assembled Monolayers on Gold Generated from Aliphatic Dithiocarboxylic Acids Langmuir 14
92. n turn dial to 8 0 Dry Operation Setting 8 Turn the Power switch on and check that the Power LEDs in the QCM100 and QCM25 boxes light up The OSC LED of the QCM100 lights up as soon as oscillation is established in the dry crystal A frequency very close to 5 MHz nominal dry frequency should be displayed by the frequency counter at this time and the Conductance Output voltage should be close to 10 0 VDC 9 The QCM System is ready for mass and viscosity measurements QCM100 Quartz Crystal Microbalance ASRS Getting Started 1 5 10 For operation under liquid immersion record the dry frequency and conductance readings and immerse the entire crystal in the liquid solution of interest For accurate measurements i e at true series resonance perform a Capacitance Cancellation procedure as described in Chapter 2 Consult Chapter 3 for additional tips on QCM operation in liquids 11 For operation with a flow cell see Figure 14 pay special attention when filling the flow chamber for the first time that no air bubbles get trapped in the measurement volume Consult Chapter 3 for some useful tips on QCM operation in liquid flow cells including bubble elimination techniques Temperature stabilization to better than 0 1 C is essential for high accuracy measurements in aqueous solutions due to the high temperature coefficient of viscosity 12 For operation in an electrochemical setup using the liquid face of the QCM crysta
93. ncy reproducibility of 0 008 1 0 04 Hz 0 20 Hz for a wet crystal This error is virtually insignificant QCM100 Quartz Crystal Microbalance 2 10 Theory Operation and Calibration In water the dominant source of frequency drift comes from the temperature dependence of the viscosity of the liquid The series resonant frequency of a 5 MHz AT cut crystal in water will increase by about 8 Hz C The importance of temperature stabilization in liquid experiments is evident from the following table With proper temperature stabilization and or compensation it is possible to perform QCM measurements in water with detection limits well below 0 1Hz rms Summary of sources of frequency error in Water Af 700 Hz Source of Error Typical magnitude of Error for wet crystal Phase shift in low pass filter 0 65 Hz lt 0 1 Reproducibility of Co null lt 0 20 Hz Temperature dependence of 0 8 Hz 0 1 C viscosity static OCM100 Quartz Crystal Microbalance SRS Theory Operation and Calibration 2 11 Resistance Measurement x Ay The QCM100 Analog Controller provides a Conductance Voltage output BNC port that is related to the crystal s motional series resonance resistance Rm 10 000 x 10 75 equation 2 Where Rhis the motional series resonance resistance in Q and Veis the conductance voltage output in V A high precision digital voltmeter with at least 6 digits of resolution and computer interface i
94. ne and PVC are amongst the polymeric materials recommended to protect QCM devices Tip A Crystal Cleaning Basket SRS Part O100CCB described at the end of this chapter is available directly from Stanford Research Systems This accessory makes cleaning and surface modification treatment of the standard 1 QCM crystals very safe and easy The cleaning basket holds four crystals is made entirely of Teflon and it is specifically designed for immersion into a 100mL beaker Several examples of surface modification techniques are described below While not exhaustive they may serve as useful guidelines while developing your own protocols Sputtering or evaporation Thin films i e nm thickness of metals or metal oxides are commonly deposited by sputtering or evaporation To obtain reproducible results careful attention must be paid to cleanliness both in the vacuum chamber and in the preparation of the crystals prior to coating It is generally realized by individual researchers that unless highly specialized coatings are required it is a lot more convenient and cost effective to have a specialized commercial source deposit the electrodes on crystal blanks Spin coating Spin coating is a technique by which very thin polymeric films nm to m thickness are deposited onto a solid substrate To fabricate thin polymer films the polymer material is first dissolved in a volatile solvent If a drop of solution is placed on a substrat
95. ng signal drift it is best to immerse the quartz crystal premounted on its holder in the sample solution several hours before measurements are started Temperature independent frequency drifts as large as 10 Hz and resistance drifts as large 2 ohms are to be expected over a 24hr period even in the purest deionized water bath Long term drifts have many different origins including chemical interaction between the liquid and the electrodes swelling of the orings diffusion of liquid into the quartz changes in coatings etc In flowing systems expose the crystal to the carrier solution for as long as practically possible prior to sample injection Wait for the temperature to stabilize To avoid the generation of air bubbles and reduce temperature related signal changes the sample liquid should be at approximately the same temperature as the sensor holder and the entire experimental setup should be temperature stabilized The generation of air bubbles is facilitated when the temperature of the liquid is lower than that of the holder flow cell Avoid temperature differences greater than 2 C between the sample liquid and the crystal holder Keep in mind that frequency readings are not just affected by the static temperature but also by the rate of change of temperature around the sensor This is very important during the implementation of temperature compensation or stabilization schemes For example PI PID and Fuzzy Logic stabilized temp
96. ng and careful system design GFCI s must also be tested regularly to verify their functionality Always consult an electrician when in doubt Line Fuse The LINE FUSE is internal to the instrument and may not be serviced by the user SRS OCM100 Quartz Crystal Microbalance ii Safety and Preparation For Use Operate Only With Covers In Place To avoid personal injury do not remove the product covers or panels Do not operate the product without all covers and panels in place Liquid Contact With the exception of the Crystal Holder this product is intended for use only in a clean dry laboratory environment Operation in other environments may cause damage to the product and reduce the effectiveness of the safety features To reduce the risk of fire or electrocution do not expose this product to rain or excessive moisture Be careful not to spill liquid of any kind onto or into the product Serviceable Parts The QCM100 Analog Controller does not include any user serviceable parts inside Refer service to a qualified technician OCM100 Quartz Crystal Microbalance ASRS Contents Safety and Preparation For Use i Contents iii Front Panel Overview v Back Panel Overview vii QCM25 Crystal Oscillator Overview viii Specifications x Chapter 1 Getting Started Unpacking 1 3 Quick Start Instructions 1 4 Crystal Installation 1 6 Flow Cell 1 11 Chapter 2 Theory Operation and Calibration Background 2 3 The QCM Oscillator 2 4
97. ng boxes against your original order and the checklist below Report any discrepancies to Stanford Research Systems immediately Standard Equipment Supplies QCM100 Quartz Crystal Microbalance Analog Controller QCM25 Crystal Oscillator Operation and Service Manual Power cord Cat 5 Cable 3 foot long Crystal Holder Three 3 chromium gold QCM crystals Optional Equipment Replacement Crystals SRS Part O100RX1 Replacement ITO Crystals SRS Part O100RX2 Flow Cell SRS Part O100FC Crystal Cleaning Basket SRS Part O100CCB Replacement Crystal Holder O100RH OCM100 Quartz Crystal Microbalance 1 4 Getting Started Quick Start Instructions Figure 1 Basic OCM Setup 1 With the power switch in the Off position connect the QCM100 Analog Controller to a grounded outlet using the power cord 2 Connect the QCM100 Analog Controller to the QCM25 Crystal Oscillator using the Cat 5 cable 3 feet long with RJ 45 end connectors 3 Mount a fresh QCM crystal in the Crystal Holder See separate instructions in the next section 4 Connect the Crystal Holder to the 5 MHz Crystal BNC connector of the QCM25 Crystal Oscillator 5 Connect the frequency output signal of the QCM100 to your frequency counter See Chapter 2 for more information about selecting a frequency counter 6 Connect the Conductance Output to a digital voltmeter or analog to digital converter 7 Set the Co Compensation switch to Hold and the te
98. ny film deposited on the electrodes and 4 any liquid adjacent to the electrode surface which experiences shear forces For this reason when electrodes become delaminated due to poor adhesion of the underlayer or stress caused by the deposit discontinuous changes in frequency occur which render the crystal useless Mass Sensitivity The quartz crystal microbalance is an extremely sensitive sensor capable of measuring mass changes in the nanogram cm range with a wide dynamic range extending into the 100 g cm range Sauerbrey was the first to recognize the potential usefulness of the technology and demonstrate the extremely sensitive nature of these piezoelectric devices towards mass changes at the surface of the QCM electrodes The results of his work are embodied in the Sauerbrey equation which relates the mass change per unit area at the QCM electrode surface to the observed change in oscillation frequency of the crystal Af C Am where Af the observed frequency change in Hz Am the change in mass per unit area in g cm C the sensitivity factor for the crystal 56 6 Hz pg em for a 5 MHz crystal at room temperature The minimum detectable mass change is typically a few ng cm and limited by the noise specifications of the crystal oscillator and the resolution of the frequency counter used to measure frequency shifts For example based on Sauerbrey s equation a minimum OCM100 Quartz Crystal Mic
99. ohannsmann Viscoelastic Analysis of Organic Thin Films on quartz resonators Macromol Chem Phys 200 1999 501 C E Reed K Keiji Kanazawa and J Kaufman Physical description of a viscoelastically loaded AT cut quartz resonator J Appl Phys 68 5 1990 1993 D S Ballantine R M White S J Martin A J Rico E T Zellers G C Frye and H Woltjen Acoustic Wave Sensors Theory Design and Physico Chemical Applications Acad Press London UK 1997 Chapter 5 Chemical and Biological Sensors p 222 G G Guilbault and J Jordan Analytical uses of piezoelectric crystals CRC Reviews 19 p 1 28 W H King Piezoelectric Sorption Detector Anal Chem 36 1964 1735 37 Iddo Ben Dov and Itamar Willmer Piezoelectric Immunosensors for Urine Specimens of Chlamidia trachomatis Employing QCM Microgravimetric Analysis Anal Chem 69 1997 3506 Storri et al Surface modifications for the development of piezoimmunosensors Biosensors and Bioelectronics 13 1998 347 Tajima I et al Monitor of antibodies in human saliva using a piezoelectric QC biosensor Anal Chim Acta 365 1998 147 149 Makoto Muratsugu et al QCM for the detection of microgram quantities of human serum albumin Relationship between the frequency change and the mass of protein adsorbed Anal Chem 65 1993 2933 2937 M Malmsteen J Coll Interf Sci 172 1995 106 No
100. ology More recent developments have focused on tailoring electrode surface chemistry 1 e specialized polymer coatings so that these devices can be applied as discriminating mass detectors for 1 specific gas detection 2 environmental monitoring 3 biosensing and 4 basic surface molecule interaction studies The purpose of this chapter is to provide a brief introduction to the different measurement and calibration techniques available to QCM100 users and to briefly describe the most popular theoretical models used to interpret QCM results A complete coverage of these subjects is obviously beyond the scope of this manual However many articles have been published on the operation and calibration of QCMs in applications ranging from vacuum thin film deposition to electrochemical experiments and QCM users are referred to the publications list at the end of this chapter for more detailed information ASRS OCM100 Quartz Crystal Microbalance 2 4 Theory Operation and Calibration The QCM Oscillator The Butterworth van Dyke BVD electrical model for a quartz crystal resonator is shown in Figure 1 This model is often used to represent the electrical behavior of a crystal resonator near series resonance The model has also been useful in predicting the frequency shifts and losses of an AT cut quartz crystal in QCM applications Co Lm Cm Rm Figure 1 Butterworth van Dyke model of Quartz Crystal Resonator The BVD electrical mod
101. on Gold Anal Chim Acta 399 51 62 1999 Note Professor Spangler is also CEO of SensoPath Technologies a company specialized in the development of materials for the design and fabrication of SAMs on gold surfaces www sensoPath com D S Karpovich and G J Blanchard Direct measurement of the adsorption kinetics of alkanethiolate SAMs on a microcrystalline gold surface Langmuir 10 1994 3315 H M Schessler et al Quantitating the Balance between Enthalpic and Entropic Forces in Alkanethiol Gold Monolayer Self Assembly J Am Chem Soc 118 1996 9645 D S Karpovich and G J Blanchard Vapor adsorption onto metal and modified interfaces Evidence for adsorbate penetration of an alkanethiol Monolayer on Gold Langmuir 13 1997 4031 Yamaguchi et al Adsorption Immobilization and Hybridization of DNA Studies by the use of QC Oscillators Anal Chem 65 1993 1925 F Caruso et al QCM Study of DNA Immobilization and Hybridization for Nucleic Acid Sensor Development Anal Chem 69 1997 2043 R Suri et al Biosensors and Bioelectronics 9 1994 325 S Yamaguchi et al Adsorption Immobilization and Hybridization of DNA Studies by the use of QC Oscillators Anal Chem 65 1993 1925 P E Hockberger et al Cellular engineering control of cell substrate interactions in Nanofabrication and Biosystems H C Hoch L W Jelinski and H G Craighead Eds Cambridge Unive
102. or provides both frequency and resistance change signals and will maintain oscillation up to a series resonance resistance of about 5 kQ it will support crystal operation in highly viscous solutions up to 88 w w glycerol in water Transformer isolation of the oscillator circuit provides compatibility with virtually any potentiostat As an example eqn 6 predicts a decrease in fo of 715 Hz on transfer from vacuum to pure water at 20 C in agreement with the results observed with a QCM100 using 1 inch diameter polished gold coated 5 MHz crystals mounted on a standard Crystal Holder Excellent agreement between the frequency and resistance equations and the experimental results has been proved making the QCM an excellent tool for the evaluation of fluid properties Application examples include in situ monitoring of lubricant and petroleum properties The tight correspondence between theory eqns 6 amp 7 and experiment is clearly illustrated by Figure 7 QCM100 Quartz Crystal Microbalance 2 20 Theory Operation and Calibration gm QCM100 Theory Freq Shift Hz 40 50 60 70 Wt glycerol m QCM100 Theory Resistance Ohms Wt Glycerol Figure 7 Frequency Shift Hz and ResitanceShift Ohms versus glycerol weight percentage in water as predicted by theory and as measured with OCM100 and a
103. p described by eqn 8 to hold true the polymer overlayer must exhibit no changes in rigidity during the electrochemical process Otherwise the viscoelastic changes will also contribute to the frequency change leading to an erroneous interpretation of the mass changes As a consequence it is essential to determine whether or not viscoelastic properties of the polymer film influence the frequency measurement during polymer film experiments OCM100 Quartz Crystal Microbalance ASRS Theory Operation and Calibration 2 27 0 1M Pyrrole in 0 1M HCLO 295 00 300 00 305 00 310 00 315 00 320 00 325 00 330 00 Frequency Shift Hz 335 00 340 00 345 00 350 00 355 00 360 007 1 1 f 1 1 1 i 1 1 1 1 1 1 17 260 00 1 00 0 90 0 80 0 70 0 60 0 50 0 40 0 30 0 20 010 0 00 0 10 0 20 0 30 0 40 Potential vs Agl amp gCl Figure 11 Voltammogram and massogram data for the oxidation of pyrrole to form a polypyrrole film on a gold coated OCM Sensor Crystal Seven cycles of voltammetry between 0 4 and 0 95 V were conducted in this experiment Pyrrole monomer can be oxidized to its radical at 0 65 V As this happens a thin polypyrrole film is formed on the crystal surface resulting in a decrease in the fundamental frequency of oscillation of the crystal The continuous growth of the film is evidenced by the irreversible decrease in frequenc
104. pF Rm 40 Q or 0 81 pF Rm 375 Q from uncompensated C 4 0 0 20 Hz Rm 40 Q or 0 04 Hz Rm 375 Q deviation from series resonance from the crystal in the Rs Rm Rq network If an extraneous phase shift 2 or 3 is present the oscillator will operate away from series resonance allowing the crystal network 4 to cancel the extraneous phase shift The small value of the extraneous phase shifts together with the large do df of the crystal network keeps these frequency errors small The QCM25 Crystal Oscillator is intended to operate only with 5 MHz crystals Typical accuracy of the crystal frequency is 100 ppm or 500 Hz The low pass filter will add an additional phase shift of 37 Hz deviation x 500 Hz 0 0185 when operated 500 Hz from 5 MHz This will cause a dry crystal to run 0 0185 0 20 Hz 0 092 Hz off series resonance or a wet crystal to run 0 0185 0 04 Hz 0 462 Hz off series resonance Since the d df of the low pass filter is 1000x smaller than the db df of a wet crystal the low pass filter does not contribute a significant error to the measurement of the series resonant frequency By modulating the varactor capacitance which nulls Co and using synchronous detection to locate the minimum gain operating point the QCM100 allows the user to reproducibly null C to 0 01 pF The corresponding phase error for a wet crystal is 0 01 pF x 0 81 pF 0 0081 which gives rise to a freque
105. ppm MELF Resistor Thin Film 1 50 ppm MELF Resistor Thin Film 1 50 ppm MELF Resistor Thin Film 1 50 ppm MELF Resistor Thin Film 1 50 ppm MELF Resistor Thick Film 5 200 ppm Chip Resistor Thick Film 5 200 ppm Chip Resistor Thick Film 5 200 ppm Chip Resistor Thick Film 5 200 ppm Chip Resistor Thick Film 5 200 ppm Chip Resistor Thick Film 5 200 ppm Chip Resistor Thick Film 5 200 ppm Chip Resistor Thick Film 5 200 ppm Chip Resistor Thick Film 5 200 ppm Chip Resistor Thick Film 5 200 ppm Chip Resistor Thick Film 5 200 ppm Chip Resistor Switch On None On Toggle Right Angle Transformer 5 3 QCM100 Quartz Crystal Microbalance 5 4 Parts List Ul 3 00346 329 U2 3 00112 329 U3 3 0058 1 360 U4 3 00684 360 U5 3 00375 360 U6 3 00749 360 U7 3 01469 360 U8 3 0058 1 360 U9 3 01445 360 U10 3 01445 360 U11 3 01370 360 U12 3 00372 360 U13 3 01445 360 U14 3 00752 360 U15 3 00728 360 U16 3 00728 360 Yl 6 00958 620 Zo 0 00002 008 Z0 0 00009 000 Zo 0 00025 005 Z0 0 00043 011 Z0 0 00098 042 Zo 0 00141 032 Z0 0 00185 021 Zo 0 00187 021 Z0 0 00197 002 Z0 0 00222 021 Zo 0 00240 026 Z0 0 00252 057 Z0 0 00295 050 Z0 0 00296 050 Zo 0 00297 026 Z0 0 00330 050 Zo 0 00434 054 Z O0 0 00517 000 Zo 0 00901 005 Z0 0 00907 020 Z0 2 00049 211 Zo 6 00965 615 Z0 7 01419 720 Z0 7 01420 720 Z0 7 01421 720 Z0 7 01423 709 7812 7805 AD822 CD4060BCM DS8921AM 74HC541 MAX
106. r Chip SMT1206 50V 5 NPO C23 5 00376 552 120P Capacitor Chip SMT1206 50V 5 NPO C24 5 00384 552 560P Capacitor Chip SMT1206 50V 5 NPO D1 3 00010 303 GREEN LED T1 Package D2 3 00803 360 MMBV609 Integrated Circuit Surface Mount Pkg J1 1 00505 100 RJ45 MODULAR Connector Misc L1 6 00236 631 FR47 Ferrite bead SMT L 2 6 00013 606 2 2UH 5PH Inductor Variable L 3 6 00171 606 4 7UH 5PH Inductor Variable P1 4 00486 441 50 Pot Multi Turn Trim 3 8 Square Top Ad P2 4 00486 441 50 Pot Multi Turn Trim 3 8 Square Top Ad PC1 7 01426 701 QCM25 Printed Circuit Board R1 4 01471 461 470 Thick Film 5 200 ppm Chip Resistor R2 4 01431 461 10 Thick Film 5 200 ppm Chip Resistor R3 4 01431 461 10 Thick Film 5 200 ppm Chip Resistor R5 4 01447 461 47 Thick Film 5 200 ppm Chip Resistor ASRS OCM100 Quartz Crystal Microbalance 5 6 R6 R7 R8 R9 R 10 R11 R12 R13 R14 R15 R16 R17 R18 R19 R 20 R21 R 22 R 23 Tl T2 Ul U2 U3 U4 Zo Z0 Z0 Zo Z0 Z0 Zo Z0 Zo Z0 Z0 Parts List 4 01447 461 4 01175 462 4 01117 462 4 00217 408 4 00217 408 4 01463 461 4 00992 462 4 01447 461 4 01527 461 4 01527 461 4 01447 461 4 00992 462 4 01184 462 4 01184 462 4 01431 461 4 01076 462 4 01021 462 4 01021 462 6 00622 610 6 00622 610 3 00369 340 3 00375 360 3 00686 360 3 00898 360 0 00025 005 0 00150 026 0 00241 021 0 00276 102 0 00277 053 0 00386 003 0 00696 043 1 00388 120 7 01412 720
107. r front panel LEDs If the HIGH LED is on the dial should be moved to a lower setting If the LOW LED is on the dial should be moved to a higher setting Both NULL LEDs will be on when the dial is in the optimum position The reproducibility of this procedure is typically 0 01 pF Nulling the crystal capacitance is only important if the motional loss i e crystal resistance is high The variation of AGC voltage will be very small when the crystal losses are low and so it may not be possible to use this method in low loss situations Dry crystals will oscillate very near their series resonance frequency even when the capacitance has not been nulled Wet crystals or any situation for which the crystal s motional losses are high will require capacitive cancellation in order to oscillate at series resonance or in some cases to oscillate at all The 75 Hz modulation frequency is provided by U4 a CD4060 oscillator with a 14 stage binary divider A 76 8 kHz crystal is used in the oscillator circuit The oscillator frequency is divided by 2 providing a 75 Hz square wave The 75 Hz square wave is level shifted by R9 R10 to produce a square wave between 6 and 12 VDC That square wave is used to switch a dual 1 4 analog multiplexer U14 The analog multiplexer is used to generate the 5 modulated varactor voltage and to synchronously detect a 75 Hz signal on the amplified AGC voltage U7 a MAX6250 provides 5 00 VD
108. rate of 50uL min Due to the non specific adsorption of the protein the frequency of oscillation decreases 9Hz over a period of 5 minutes The sensitivity of the OCM100 for the detection of microgram quantities of proteins is clearly demonstrated by this very straightforward experiment An example of a complex and dynamic biochemical process which has been successfully studied with quartz crystal microbalances is the adsorption of proteins to solid surfaces Figure 12 is the result of a QCM experiment following the adsorption kinetics of bovine OCM100 Quartz Crystal Microbalance ASRS ASRS Theory Operation and Calibration 2 29 serum albumin BSA from an aqueous saline solution on to a polished unmodified gold surface i e physical adsorption The adsorbed mass is small compared to the mass of the quartz crystal evenly distributed and rigidly attached to the gold surface resulting in a frequency decrease of 9Hz proportional to the mass of protein adsorbed on the polished gold electrode The sensitivity of the QCM100 for the detection of microgram quantities of proteins is clearly demonstrated by this very simple experiment Sensitive selective detection of biochemically active compounds can be achieved by employing antigen antibody enzyme substrates and other receptor protein pairs The potential analytical uses of these materials has been reviewed particularly with respect to the development of biochemical sensors QCM st
109. reason for the wide range of application of the technology However the downside of such universal sensitivity is that you always have a great danger of interference For analytical purposes it is imperative to find ways of getting the QCM sensor to respond only to what you are interested in 1 e build specificity into the device This usually involves the addition of a sensitive layer on the surface of the crystal Organic polymers comprise the most common type of coating used with QCM chemical sensors due to their capability to reversibly sorb vapors and liquids In much of the work published on the use of polymer coatings for vapor sensing the acoustic properties of the polymer material have been neglected The relative importance of the mass loading and viscoelastic contributions of the film to the observed QCM response is a subject that has yet to be resolved In no area have the QCM applications seen such dramatic increase in recent years as in the field of biochemical analysis QCM devices are routinely used as biochemical and immunological probes as well as for the investigation and or monitoring of biochemically significant processes BSA Adsorption to Gold 5 Mhz data Frequency Shift Hz A 10 T T T T T T T T 0 200 400 600 800 1000 1200 1400 1600 Time seconds Figure 12 A 10ug ml solution of BSA in 2mM NaCl is flowed over a polished Au Cr QCM crystal in an axial flow cell at a
110. ries resonance At series resonance the crystal impedance is resistive In addition there is about 15 pF of capacitance in parallel with this resistance due to the crystal s electrodes and holder The current which passes through this capacitance is canceled by an equal and opposite current which passes through the varactor diode D2 The QCM100 provides a bias to the varactor diode so that the varactor capacitance is equal to the electrode plus holder capacitance The varactor is driven by the inverted version of the 5 MHz signal from the center tapped secondary of transformer T1 The output from the crystal network is amplified by U4 an AD8009 RF operational amplifier The gain of U4 can be adjusted between 3 5x 5 2x with the potentiometer P2 The pot is adjusted during factory calibration to calibrate the offset on the AGC voltage The slope and offset of the AGC voltage is adjusted to assure compliance to the Voona vs Rerystai Characteristic QCM100 Quartz Crystal Microbalance 4 4 Circuit Description The output of U4 drives a 5 order Bessel low pass filter The filter serves two purposes The first is to attenuate very high frequency signals so that the loop will only oscillate at the crystal s fundamental mode The second is to provide 180 of phase shift at 5 MHz The filter s phase shift together with the 180 of phase shift from the inverting amplifier U1 gives the 360 of phase shift required to sustain oscillation Th
111. robalance ASRS ASRS Sensor Crystals and Holders 3 7 detectable mass specification of 0 18 ng cm should be expected from a QCM system with a 0 01 Hz frequency measurement resolution As a comparison consider that a monolayer of a 20Kda protein 100 coverage adsorbed on a QCM crystal amounts to roughly 10Hz frequency shift or 180 ng cm2 The Sauerbrey equation relies on a sensitivity factor Cs which is a fundamental property of the QCM crystal Thus in theory the QCM mass sensor does not require calibration This ability to calculate the mass sensitivity from first principles is obviously a very attractive feature of these devices However it is very important to notice that the Sauerbrey equation is only strictly applicable to uniform rigid thin film deposits originating from a low pressure i e vacuum gas environment Thick deposits and operation in liquid environments or in contact with viscoelastic films relies on the use of more complex equations relating the frequency shifts to mass loading and often requires calibration of the setup for accurate results Several articles have presented simple ways to calibrate the mass sensitivity of QCMs for electrochemical applications and for vacuum thin film deposition processes and some useful calibration guidelines were also included in Chapter 2 of this manual There is ample evidence supporting a Gaussian mass sensitivity distribution for AT cut crystals with the max
112. rsity press 1996 276 299 OCM100 Quartz Crystal Microbalance ASRS Sensor Crystals and Holders 3 31 Dirk Jope Joachim Sell Howard W Pickering Konrad G Weil Application of a Quartz Crystal Microbalance to the Study of Copper Corrosion in Acid Solution Inhibited by Triazole Iodide Protective Films J Electrochem Soc 142 1995 2170 2173 The CH100 Crystal Holder is also compatible with Maxtek s 1 inch diamter crystals and is also a replacement for its crystal holders model CHC 100 CHT 100 and CHK 100 Operation in liquids requires that the crystal be mounted in a holder such that only the front surface of the crystal is in contact with the fluid while at the same time providing an electrical connection to both electrodes Kynar polyvinilidene fluoride a homopolymer of 1 1 di fluoro ethene is a tough thermoplastic that offers unique properties including high chemical inertness low permeability to gases and liquids resistance to radiation and excellent mechanical strength and toughness For detailed material information consult www atofinachemicals com Erich Uttenhaler et al Ultrasesnitive QCM Sesnors for detection of M13 Phages in liquids Biosensors and Bioelectronics 16 2001 735 743 18 Greenspan L Humidity fixed points of binary saturated aqueous solutions Journal of Research NIST 81A 1977 89 96 ASRS OCM100 Quartz Crystal Microbalance 3 32 Sensor Crystals and Holders
113. s cleaning of wafers for semiconductor industry or optics for IR internal reflectance applications 31 W Kern and D A Puotinen Cleaning solutions based on hydrogen peroxide for use in silicon semiconductor technology RCA Review 31 2 1970 187 3 K Harewood and J S Wolf Anal Biochem 55 1973 573 H M Schessler et al Quantitating the Balance between Enthalpic and Entropic Forces in Alkanethiol Gold Monolayer Self Assembly J Am Chem Soc 118 1996 9645 Y Cohen S Levi S Rubin and I Willner Modified Monolayer electrodes for electrochemical and PZ analysis Novel immunosensor electrodes J ElectroAnal Chem 417 1996 65 Minunni M Guilbault G G and Hock B Quartz Crystal microbalance as a biosensor Anal Lett 28 1995 749 Rupa Patel R Zhou K Zinszer F Josse and R Cernozek Real time Detection of Organic Compounds in Liquid Environments Using Polymer coated Thickness Shear Mode Quartz Resonators Anal Chem 72 2000 4888 R Rella et al Optochemical vapor detection using spin coated thin films of metal substituted phthalocyanine Sensors and Actuators B Chemical 89 2003 86 T G Stange et al STM and AFM Characterization of Polystyrene Spin coated onto Silicon Surfaces Langmuir 8 1992 920 7 J R Vig UV Ozone cleaning of surfaces A review in Surface contamination Genesis Detection and Control K L Mittal Ed Plenum Press
114. s mass changes occur as material is deposited or lost from the working electrode It is of interest to monitor those changes simultaneously with the electrochemical response and the QCM is the standard means of doing so As a gravimetric probe the QCM has been used in many types of electrochemical studies including underpotential deposition of metals corrosion oxide formation dissolution studies adsorption desorption of surfactants and changes in conductive polymer films during redox processes The basic principles and applications of the QCM to electrochemical processes have been extensively reviewed in the electrochemical literature and will only be discussed briefly in this manual Please refer to the publications list at the end of this chapter for more detailed information Electrochemical Apparatus A schematic diagram of the apparatus for electrochemical quartz crystal microbalance EQCM experiments is given in Figure 8 In this example a 1 inch diameter polished QCM crystal is mounted on a Crystal Holder with only one electrode exposed to the conductive solution The Crystal Holder is connected to a QCM25 Crystal Oscillator and the liquid contact electrode is connected to the working electrode lead of the potentiostat through the Crystal Face Bias connector of the QCM25 Crystal Oscillator A QCM100 Analog Controller provides independent frequency and conductance outputs which are read and displaye
115. s recommended for this measurement Resistance Calculation ATTN Le LPF Rs a ir 50dB V X5 X2 5 ASRS Figure 5 QCM Gain Model A gain model of the QCM25 Crystal Oscillator is shown in Figure 5 At series resonance the reactance of the crystal s motional inductance and motional capacitance cancel and so the crystal may be represented by just Rm the motional resistance of the crystal It is also assumed that the static capacitance Co has been nulled as previously described The circuit will oscillate at the frequency for which the net phase shift around the loop is 360 provided there is sufficient gain to overcome the circuit losses Two network elements in the model provide a phase shift The inverting amplifier provides 180 of phase shift The low pass filter is adjusted to provide 180 of phase shift at 5 MHz Hence the circuit will oscillate at the frequency for which the crystal is resistive i e at series resonance The loop gain is the product of the gain or attenuation of each of the network elements If the loop gain is exactly one then the oscillation amplitude will be maintained at a fixed level An AGC circuit controls the loop gain via a voltage controlled variable attenuator OCM100 Quartz Crystal Microbalance 2 12 Theory Operation and Calibration From left to right the circuit consists of the following 1 A voltage controlled variable attenuator with attenuation of Ag An automatic g
116. sahiro Seo Masaki Aomi and Kengo Yoshida A combined Piezoelectric and EQCM study of Underpotential Deposition of Silver on Gold Electrodes Electrochimica Acta 39 8 9 1994 1039 Youngran Lim and Euijin Hwang An Electrochemical QCM study of Oxygen reduction during the Underpotential Deposition of Lead on a Gold Electrode Bull Korean Chem Soc 17 12 1996 1091 EQCM Wall Jet Split Ring Disk Electrode study on Copper dissolution in Chloride Aqueous solution Anal Sciences 16 2000 1049 Michael Benje Matthias Eiermann Udo Pittermann and Konrad G Weil An improved Quartz microbalance Applications to Electrocrystallization and dissolution of Niquel Ber Bunsenges Phys Chem 90 1986 435 Jorg Auge Peter Hauptmann Frank Eichelbaum and Stephen Rosler QCM sensor in liquids Sensors and Actuators B 18 19 1994 518 ASRS OCM100 Quartz Crystal Microbalance 2 36 Theory Operation and Calibration 4 Adrian W Bott Characterization of Films Immobilized on an Electrode Surface Using the EQCM Current Separations 18 3 1999 79 Mark Deakin and Daniel Buttry Electrochemical Applications of the Quartz Crystal Microbalance Anal Chem 61 20 1989 183 Daniel Buttry and Michael Ward Measurement of Interfacial Processes at electrode surfaces with the EQCM Chem Rev 92 6 1992 1355 26 Cheryl Chagnard Patty Gilbert A Neal Watkins Theodore Beeler and David Paul An el
117. sign compatibility with all standard 1 inch diameter QCM sensor crystals compatible with Crystal Oscillator SRS Model QCM25 liquid and gas compatibility leak proof design single electrode exposure to liquids for compatibility with electrochemical QCM measurements chemical resistance Kynar material with Viton O rings broad temperature range 25 C to 110 C easy crystal replacement a simple hand removable retainer cover permits easy crystal replacement without tools standard female BNC connector for easy electrical connection flow cell adapters available SRS Part O100FC and O100AFC Several methods for mounting sensor crystals have been described in the scientific QCM literature The mounting fixture requires serious consideration because of possible influences of stress on the absolute frequency of oscillation and because simple and rapid exchange of crystals is required when the thin film electrodes become damaged or used up For electrochemical applications in solution it must be feasible to expose only one side of the QCM disk to the liquid bath This is necessary to prevent the two QCM electrodes from being capacitively shunted by the solution which can cause cessation of the oscillation The Crystal Holder was specifically designed to address all the above issues OCM100 Quartz Crystal Microbalance ASRS ASRS Sensor Crystals and Holders 3 19 while at the same time providing optimal crystal per
118. sistance measurements for the QCM25 Crystal Oscillator QCM100 are calibrated by replacing the crystal with a precision resistor in parallel with a 18 pF capacitor Two resistor values are used 25 Q and 925 Q The equation for Rm may be inverted to determine the calibration value for Ve Motional resistance Rm in Q and conductance voltage output Vo in volts Rm 10 000 x 10 75 Ve 5 log 10 000 Rm 75 The low pass filter is adjusted so that the QCM25 Crystal Oscillator oscillates at 5 MHz with the 25 Q resistor in place of the crystal The varactor dial is adjusted so that the Crystal Controller oscillates at 5 MHz with the 925 Q resistor in place of the crystal Calibration potentiometers in the QCM25 Crystal Oscillator are adjusted so that P1 pot V 10 000 0 005 Vdc with a calibration resistor of 25 Q and P2 pot V 5 000 0 005 Vdc with a calibration resistor of 925 Q Iterate P1 and P2 adjustments as necessary ASRS OCM100 Quartz Crystal Microbalance 2 16 Theory Operation and Calibration Gas Phase Measurements The first use of QCMs was as mass sensors and thickness monitors in gas phase thin film depositions To this date this continues to be an important area of application for this technology Sauerbrey Equation Sauerbrey s equation eqn 1 is often used to calculate mass loadings and thin film thicknesses in vacuum depositions The basic assumption is that the incremental change in mass from
119. some simple tricks known to effectively prevent and remove bubble trapping in flowing QCM systems and also presents some of the common indicators used to detect the presence of bubbles in liquid flow chambers Eliminating dissolved gases from all sample solutions is the most basic precaution recommended for the minimization of bubble trapping Commercially available online degassing stages and bubble traps are recommended for flow injection analysis setups When filling an empty chamber with a syringe pump for the first time the following procedure generally works very well to displace all trapped bubbles Connect a gt 3mL syringe loaded with the solution you wish to inject into the QCM chamber to the inlet port of the flow cell Connect the outlet port to the body of a 3mL syringe with its plunger removed and mounted vertically to act as a waste collector Push about 1 2mL of solution through the chamber into the waste container Press the syringe back and forth a few times until no more bubbles are seen to evolve into the waste container The number of bubbles will decrease after each back and forth action until no more bubbles are visible Flow reversals are very efficient at displacing bubbles out of the chamber For Syphon systems see Figure 4 a similar method can be employed to remove bubbles from a freshly filled chamber In this case the sample reservoir with the sample solution is connected to the inlet port and a 3 5 mL syringe loaded
120. stal s oscillation With increasing layer thickness the outermost parts of the attached layer will couple weakly and at a certain thickness usually a few micrometers it is lost completely Oscillation is still detected and a frequency is still measured but the equipment can only sense the part of the layer in the vicinity of the crystal OCM100 Quartz Crystal Microbalance 3 8 Sensor Crystals and Holders Useful Life Sensor crystals are often reusable several times However reusing a crystal requires careful handling and cleaning procedures that do not harm the quartz material its electrode pads and its coatings Many practitioners consider their QCM crystals expendable and always discard them at the end of their measurements Traces of consumption and wear can often be detected visually e Edges of the sensor crystal might become cracked and the coating start to show scratches and holes e Inelectrochemistry experiments it is not unusual to observe changes in the adhesion layer of the liquid surface electrode which ultimately result in peeling of the metal pad A common problem is loss of the Cr adhesion layer in Au Cr electrodes Tip these changes are visible from the contact side of the crystal e The liquid surface electrode might become irreversibly discolored or stained from chemical reaction with the analytes buffers or solvent When a crystal is close to being consumed the measurement signal will become noisy
121. stance of the crystal are premeasured by direct immersion of the holder crystal into the same ASRS OCM100 Quartz Crystal Microbalance 3 26 Sensor Crystals and Holders sample solution used in the flow setup Resistance values significantly smaller than the immersion results should prompt the presence of trapped bubbles within the flow chamber Temperature stabilization usually requires immersion of the flow cell into a constant temperature liquid bath In many cases the liquid bath is operated above room temperature If the flowrates are high i e greater than 0 2mL min or the temperature of the bath is far away from the temperature of the sample liquid i e AT gt 2 C external thermal equilibration of the sample fluid is recommended A common trick is to add a temperature equalization loop immersed in the liquid bath between the sample container and the flow cell to provide complete equalization OCM100 Quartz Crystal Microbalance ASRS Sensor Crystals and Holders 3 27 References D S Ballantine et al Acoustic Wave Sensors Theory Design and Physico Chemical Applications Academic Press 1996 C Lu and O Lewis Investigation of film thickness determination by oscillating quartz resonators with large mass load J Appl Phys 43 1972 4385 3 S J Martin R J Huber et al Resonator Oscillator Response to Liquid Loading Anal Chem 69 1997 2050 D Johannsmann Viscoelastic Analysis o
122. t noise flow setup Syringe pumps and 6 port injection valves are commonly used to expose the crystal to a sequence of analytes see Figure 14 Most standard Flow Injection Analysis FIA and Sequential Injection Analysis SIA equipment is compatible with QCM flow cell operation Peristaltic pumps are often applied to closed flow systems but they always add noise to the frequency signal due to pressure transients and coupled vibrations pulse dampening modules are always recommended In all cases the flow rate must be kept under 5mL min to avoid excessive stress on the sensor and to avoid leaks of liquid over the oring 6 port Injection Valve Buffer w pump QCM w Axial Flow Cell QCM100 Figure 14 A Flow Injection Analysis QCM system consisting of syringe pump for buffer solution 6 port injection valve for analyte injection and Axial Flow Cell for QCM Flow Chamber Specifications Flow Volume crystal chamber z0 15 mL Materials Cell Kynar Inlet Outlet Tubes Tefzel Oring Viton OCM100 Quartz Crystal Microbalance 1 14 Getting Started In Out Ports Barbed hose adapters for 1 16 ID tubing w 0 040 ID thru hole Model P 663 from www upchurch com Recommended flow rate lt 0 2 mL min Maximum flow rate 5 mL min OCM100 Quartz Crystal Microbalance SRS Chapter 2 2 1 Theory Operation and Calibration This chapter provides a brief introduction to the measurement techniques and calibration procedures av
123. tal Holder and QCM25 Crystal Oscillator QCM100 Quartz Crystal Microbalance ASRS Getting Started 1 11 Flow Cell The Flow Cell Adapter SRS Part O100FC attaches to the crystal holder to create a small volume Stagnation Point Flow Cell Figure 12 The axial flow cell adapter mounted on a crystal holder Use the Axial Flow Cell Adapter for adsorption desorption studies when 1 well defined flow conditions are needed 2 high sensitivity is required 3 small rinse volume is desirable and 4 flow induced surface shear forces need to be minimized In Flow Out Out Flow Flow Stagnation Quartz Point Crystal Figure 13 Schematic representation of the liquid flow pattern in the Axial Flow Cell A cross sectional view of the Axial Flow Cell including a schematic representation of the stagnation point flow is shown in figure 13 In the axial flow cell the sample flows ASRS QCM100 Quartz Crystal Microbalance 1 12 Getting Started radially from the input port at the center of the cell to the exit channel at the circumference of the cell in a volume of about 150ul The sample solution is perpendicularly injected towards the flat surface of the QCM crystal The stagnation point is located at the center of the crystal electrode overlapping the highest sensitivity area of the flat QCM oscillator The hydrodynamics associated with stagnation point flow are well understood At the stagnation point there is zero hydrodynamic f
124. te the data in these papers is in very good agreement with what was observed at SRS with the QCM100 system and BSA as the test protein A Hengerer C K sslingerl J Decker S Hauckl I Queitsch2 H Wolf and S D bel2 Determination of Phage Antibody Affinities to Antigen by a Microbalance Sensor System BioTechniques 26 956 964 May 1999 7 G G Guibault Analytical uses of immobilized Enzymes Modern Monographs in Analytical Chemistry Vol 2 Marcel Dekker New York 1984 G M Minunni M Mascini G G Guilbault B Hock The Quartz Crystal Microbalance as Biosensor A Status Report on its Future Anal Lett 28 5 1995 749 S Tombelli M Mascini Piezoelectric Quartz Crystal Biosensor Recent Immobilisation Schemes Anal Lett 33 11 2000 pp 2129 2151 ASRS OCM100 Quartz Crystal Microbalance 2 38 Theory Operation and Calibration Kim R Rogers Principles of Affinity Based Biosensors Molecular Biotechnology 14 2000 109 1 A Hengerer et al Determination of Phage Antibody Affinities to Antigen by a Microbalance Sensor System BioTechniques 26 1999 956 Note the affinity results are compared against ELISA and SPR numbers showing excellent agreement Fredrik Hook et al Structural changes in hemoglobin during adsorption to solid surfaces effects of pH ionic strength and ligand binding Proc Natl Acad Sci USA 95 1998 12271 na Fredriksson S Kihlma
125. that can contribute additional drift in the frequency when immersing a crystal holder in a new liquid Dry QCM crystals carefully A common trick used to eliminate residual water from QCM crystals that need to be immersed in dry organic solvents is to rinse the cleaned dried QCM crystals with tetrahydrofurane THF before immersion followed by drying in a flow of dry nitrogen Tips for Operation in Gases To minimize errors in QCM measurements all gas phase experiments i e gas sensor development should be designed carefully Changes in temperature flow rates and gas pressure will adversely affect QCM measurements For reproducible measurements keep the following tips in mind Check for Chemical Compatibility Before starting an experiment check for chemical compatibility between the sample gases holder flow cell orings and crystals If necessary consider replacing components with alternative materials Operate in a flowing gas configuration In order to avoid frequency transients due to sudden air movements around the crystal operate the QCM sensor in a flowing gas configuration Frequency transients as large as 10 Hz can be registered by simply walking past a QCM crystal fully exposed to air Operation within a flow cell also facilitates achieving proper temperature equalization between the crystal and the gas sample Wait for the temperature to stabilize ASRS OCM100 Quartz Crystal Microbalance 3 24 Sensor Crystals and Hol
126. the setting on the dial if the High LED is on increase the setting if the Low LED is on and lock the dial at the middle of the range for which both Null LEDs glow with equal intensity Return the switch to the HOLD Mode setting when done As A General Rule Capacitance cancellation is essential for accurate measurements of liquids and lossy i e soft films Capacitance cancellation should be checked and readjusted every time the environment around the crystal is changed For example when transitioning from air to a liquid phase The cancellation adjustment must be performed with the Crystal Holder and crystal in the actual measurement environment The switch must be in HOLD position during actual QCM measurements OCM100 Quartz Crystal Microbalance ASRS 2 8 Theory Operation and Calibration Frequency Measurement The QCM100 provides a Frequency output port BNC Virtually any commercially available frequency counter can measure the frequency of the 2 4 Vpp square wave into 50 Q provided by the QCM100 Frequency Output Counters are relatively simple to set up and read via their computer interfaces Frequency Counter Selection Criteria The selection criteria for a frequency counter for QCM application include resolution speed time base stability computer interfaces and software drivers Careful selection is required otherwise the frequency counter may degrade the quality of mass measurements The table below lists t
127. the crystal again with UV ozone for 10 minutes immediately before measurement this removes any remaining surface contaminants OCM100 Quartz Crystal Microbalance SRS Sensor Crystals and Holders 3 13 Self assembled Monolayers It is common practice to wash crystals with piranha solution at the end of a QCM immunoassay Piranha solution is also often used to precondition the crystals for a SAM deposition Step 1 Treat the crystal s with piranha solution for three minutes Steps 2 and 3 Repeat treatment 2 more times with fresh piranha solution Step 4 Rinse liberally with deionized water and dry in a gentle flow of nitrogen gas Piranha Solution Piranha solutions are used to remove organic residues from substrates particularly in microfabrication labs The traditional piranha solution is a 3 1 mixture of sulfuric acid and 30 hydrogen peroxide The solution may be mixed before application or prepared on the sample applying the sulfuric acid first followed by the peroxide Warnings Piranha solutions are extremely reactive and may result in explosion or skin burns if not handled with extreme caution n Prepare the smallest possible volume Tip Some QCM users mix the cleaning solution on the crystal surface pippeting the proper ratio of sulfuric acid and hydrogen peroxide directly on the liquid surface electrode of the quartz resonator Do not expose the crystal holder to Piranha solution Wash separately 7 Wear gloves gog
128. the foreign film is treated as though it were really an extension of the thickness of the underlying quartz The foreign film is considered rigid and so thin that it does not experience any shear forces during vibration As a result the sensitivity factor Cr is a fundamental property of the quartz crystal and does not consider any of the properties of the foreign film i e it is only dependent on the acousto elastic properties of quartz Cr 2nf7 Pa La eqn 3 where n number of the harmonic at which the crystal is driven fo the resonant frequency of the fundamental mode of the crystal in Hz Pq density of quartz 2 648 g cm Lg Shear modulus of quartz 2 94710 gem s The dependence of the frequency change on the mass coverage per unit area emphasizes the fact that within certain limits the sensitivity factor is independent of the electrode geometry Thus in theory the QCM mass sensor does not require calibration for this application This ability to calculate mass loading from first principles is obviously a very attractive feature of these devices Film thickness is often the parameter of interest in gas phase thin film depositions If the mass coverage is believed to be uniform the thickness of the film is easily calculated by dividing the mass per unit area provided by Sauerbrey s equation by the material s density Ts Am pr eqn 4 where pr density of film material in g cm Am chan
129. tion follow these two steps 1 Hold the crystal with a pair of tweezers from underneath to prevent transferring contaminants from the tweezers onto the crystal This is generally most critical in biological applications 2 Blow the remaining liquid off the crystal with a gentle flow of nitrogen gas 3 Use a clean lint free cloth to wick off any liquid remaining on the edge of the crystal OCM100 Quartz Crystal Microbalance SRS Sensor Crystals and Holders 3 15 Surface Modifications ASRS The biggest drawback of the QCM sensor is that it is inherently non specific anything that has mass can generate a response from the device The danger of this universal response is that you have a greater chance of experiencing interferences This issue has been addressed in various ways so that the device will only respond to the analyte of interest Those ways usually involve a chemically or biologically sensitive layer i e a coating applied to the surface of the crystal Often the hardest part of the problem is deciding what kind of chemically sensitive material you are going to put on top of the crystal so that it responds specifically to what you are trying to measure In biosensor research the chemical stability of the sensor substrate often limits the quality of the data generated The continuous oxidation of metal electrodes can make it very difficult to reach a drift free signal baseline in aqueous media Polyimide polystyre
130. udies have provided detailed information about the functionalized surfaces developed for a range of biochip and biosensor applications Antigen Antibody Interaction Bare Gold 5 MHz Step 1 Antigen non specific adsorption to bare gold Mouse Gamma Globulin 400 microg mL 10 10 Step 2 Blocking of remaining non specific sites T 20 Ovalbumin I 1 mg mL 30 Ta Y Step 3 Antigen Antibody specific binding f 40 Goat anti mouse IgG 40 microg mL l 50 S 3 60 2 L 70 80 90 100 T T T T T T 1 0 1000 2000 3000 4000 5000 6000 7000 Time s Figure 13 Antigen antibody reaction monitored with a QCM100 system This example shows the immobilization of mouse gamma globulin antigen on a bare gold surface Step 1 and the subsequent binding of an antibody directed against the gamma globulin Step 3 Since the gold surface is not completely covered by antigen in Step 1 a blocking solution of concentrated ovalbumin is used in Step 2 to block all uncovered sites Figure 13 is an example of an application of the QCM100 system as a protein biosensor and a demonstration of the sensitivity of the technology towards protein protein interactions The entire experiment took place on a polished Au Cr QCM crystal housed within an axial flow cell connected to a standard flow injection analysis system consisting of a single syringe pump and a
131. where the net reactance of Cm and Lm is inductive In fact if Rm is large enough it is possible that the motional arm will not be able to contribute enough lagging current to cancel the leading current via Co and the circuit will not oscillate at all Co AGC Amp p RL Cv Figure 3 Oscillator Circuit with Varactor Nulling of Co OCM100 Quartz Crystal Microbalance 2 6 Theory Operation and Calibration A method to cancel C is shown in Figure 3 In this circuit the AGC amplifier drives a transformer with two secondary windings One secondary drives the crystal and load as before while the other secondary inverts the voltage The inverted voltage source injects a current via an adjustable capacitor Cy to cancel the current injected via Co Exact cancellation is achieved when the adjustable capacitor is made equal to Co Jn the SRS QCM25 Crystal Oscillator Cy is a varactor which is made equal to C by finding the bias setting which minimizes the gain required to sustain oscillation mp Lin Cm Rm Figure 4 Oscillator Circuit Model with Cy cancelled by C With Ce canceled the circuit simplifies to that shown in Figure 4 For this circuit the zero phase condition is achieved at series resonance where the reactance of C and Lm cancel At series resonance Rm and RL form a resistive attenuator requiring an AGC gain of Av Rm RVR to sustain oscillation By knowing the AGC gain Ay required to sustain oscillation we
132. with gt 2 mL of the same sample is connected to the output port Pull the syringe plunger up to 1 force liquid into the chamber and 2 eliminate the bubbles formed from the fresh syringe connection Press the syringe back and forth a few times until no more bubbles evolve into the sample reservoir Stop the flow at the inlet and disconnect the syringe when no more bubbles are seen OCM100 Quartz Crystal Microbalance SRS Sensor Crystals and Holders 3 25 It is generally preferable to position the output port above the inlet port in flowing systems Fewer bubbles are generally trapped if the chamber is filled slowly from the bottom up with the output port being the last section of the internal chamber to come in contact with liquid Figure 4 Simple Syphon setup with axial flow cell syringe body sample reservoir and flow clamp The presence or relocation of bubbles on the surface of a crystal is generally detected by paying careful attention to the frequency and resistance readings from the sensor Bubbles displace liquid from the surface of the QCM crystal resulting in increased frequency and reduced resistance readings Tapping gently on a flow cell with a hard object can change the number or location of bubbles if a sharp and opposite sudden shift in frequency and resistance readings is observed the presence of trapped bubbles must be suspected It is sometimes possible to infer the presence of bubbles if the frequency and resi
133. y during the scans A straightforward way to detect changes in film viscoelastic properties of redox films is to simultaneously monitor the series resonance resistance R of the quartz oscillator during the electrochemical experiment Some theoretical models based on the simultaneous measurement of Af and AR have been discussed in the literature for the extension of EQCM gravimetric measurements to non rigid films The viscoelastic analysis of polymeric thin films in EQCM systems is complex because the shear wave exists simultaneously in the quartz crystal the viscoelastic film and the adjacent solution so reflection of the shear wave must be taken into account However solution of this problem would be worthwhile specially if the material properties of the film could be derived This would allow correlation of the electrochemical behavior of the film with its material properties The unique property of the QCM technique is its ability to determine the mass of very thin layers while simultaneously giving information about their viscoelastic properties The ability to measure both mass and structural changes means it is possible to detect phase transitions cross linking and swelling in polymeric thin films ASRS OCM100 Quartz Crystal Microbalance 2 28 Theory Operation and Calibration Chemical and Biological Sensors Anything that has mass can generate a response from a QCM sensor The universal response of the device is the
134. ystal to about 375 Q for a crystal in water to about 5 KQ fora crystal in 90 w w glycerol water solution A second isolation transformer with a turns ratio of 1 1 This transformer allows galvanic isolation of the crystal from the oscillator circuit A load resistance R1 of 50 Q The network of Rs Rm and RL provide a network attenuation An which depends on the crystal s motional resistance An RL RJ4 Rm Ri An RF amplifier with an adjustable gain A2 of about 4 43 x The gain of this amplifier Az is set during calibration to compensate for gain variations of all the other circuit elements A low pass filter This filter is a 5 order Bessel low pass filter with fs 3 7 MHz adjusted so as to provide 180 of phase shift at 5 MHz The phase shift of this filter together with the 180 phase shift of the inverting amplifier A4 provides the 360 of phase shift necessary for oscillation The low pass filter is required to suppress spurious oscillations which would occur due to the high bandwidth of the loop amplifiers The low pass filter attenuates a signal at 5 MHz by about A 7 8 dB or 0 407x OCM100 Quartz Crystal Microbalance ASRS ASRS Theory Operation and Calibration 2 13 The motional resistance of the crystal at series resonance can now be computed The product of the gain or attenuation of all of the elements around the loop is exactly one when the circuit is oscillating at constant amplitude H
135. ystal Microbalance with Simultaneous Mass and Liquid Loading Anal Chem 63 1991 2272 17 Operation in liquids requires that the crystal be mounted in a holder such that only the front surface of the crystal is in contact with the fluid while at the same time providing an electrical connection to both electrodes 18 For pure water at 20 C p 0 9982 g cm and n 1 002107 g cm s 2 H Muramatsu Eiichi Tamiya and Isao Karube Computation of Equivalent Circuit Parameters of Quartz Crystals in Contact with Liquids and Study of Liquid Properties Anal Chem 60 1988 2142 S J Geelhood C W Frank and K Kanazawa Transient Quartz Crystal Microbalance Behaviors Compared Journal of the Electrochemical Society 149 2002 H33 H38 Mengsu Yang and Michael Thompson Multiple Chemical Information from the Thickness Shear Mode Acoustic Wave Sensor in the liquid Phase Anal Chem 65 1993 1158 25 J Martin R W Cernosek and J J Spates Sensing Liquid Properties with Shear mode Resonator Sensors in Proceeds from Transducers Eurosensors IX Stockholm Sweden 1995 7 Mark R Deakin and Owen Melroy Underpotential Metal Deposition on Au monitored in situ with a Quartz Microbalance J Electroanal Chem 239 1988 321 O Melroy K Kanazawa J G Gordon II and D Buttry Direct Determination of the Mass of an Underpotentially Deposited Monolayer of Lead on Gold Langmuir 2 1986 697 Ma

QCM100 Manual - Stanford Research Systems

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