ELECTROCHEMICAL QUARTZ CRYSTAL NANOBALANCE

Transcription

1 T E C H N I C A L M A N U A L ELECTROCHEMICAL QUARTZ CRYSTAL NANOBALANCE SYSTEM EQCN-900/F ELCHEMA P.O. Box 5067 Potsdam, New York Tel.: (315) FAX: (315)

2 TABLE OF CONTENTS 1. INTRODUCTION SPECIFICATIONS CONTROLS Front Panel Back Panel Faraday Cage: Side Panel Faraday Cage: Internal Panel OPERATING INSTRUCTIONS Inspection Precautions Faraday Cage Grounding Thermal Sensitivity INSTALLATION Initial Set-up Power ON Checks Connections to a Potentiostat and Electrochemical Cell Testing Experiment with Real Cell ON Quartz Crystal Immittance Measurements Other Utilities (Optional) CRYSTAL-CELL ASSEMBLY Mounting Quartz Crystals Assembling Piezocells in ROTACELL holder Disassembling Piezocells from ROTACELL holder Final Checks ELECTRICAL CIRCUITS SERVICING NOTES WARRANTY, SHIPPING DAMAGE, GENERAL... 40

3 1. INTRODUCTION 1. INTRODUCTION The Model EQCN-900F Electrochemical Quartz Crystal Nanobalance is a measurement system for monitoring extremely small variation in the mass of a metal working electrode. The system allows one also to record the quartz crystal immittance (QCI) characteristics using an external frequency sweep generator. The amplitude of the a.c. current flowing through the crystal and the a.c. voltage accross the crystal are provided for QCI measurements. The EQCN-900F System consists of a Model EQCN-900F Nanobalance Instrument, Model EQCN-900F-2 Faraday Cage, and Model EQCN Remote Probe Unit. The material of the working electrode is gold, unless otherwise ordered. The working electrode is in the form of a thin film, and is placed on one side of a quartz single crystal wafer which is sealed to the side opening in an electrochemical cell. The AT-cut quartz crystal oscillates in the shear mode at nominal 10 MHz frequency. Any change in the mass rigidly attached to the working electrode results in the change of the quartz crystal oscillation frequency. The frequency of the working quartz crystal is compared to the frequency of the standard reference quartz crystal. The frequency measurements are differential, i.e. the frequency of the reference crystal is subtracted from the frequency of the working crystal. The obtained frequency difference is then measured by a precision frequency counter and displayed on the front panel. The frequency difference is converted to a voltage signal, calibrated in Sauerbrey mass units (referred to as the effective mass) and output to an analog recorder, or analog-to-digital converter. Typical processes leading to the frequency change which corresponds to the effective mass change at the working electrode are listed below: adsorption/desorption metal/alloy plating surface oxidation corrosion and corrosion protection etching heterogeneous polymerization ion ingress to (or egress from) ion exchange films oxidation/reduction of conductive polymer films intercalation coadsorption and competitive adsorption moisture accumulation (from gaseous phase) etc. 2

4 1. INTRODUCTION With the Model EQCN-900F you can monitor time transients of the effective electrode mass in an electrochemical or non-electrochemical cell, filled with liquid or gas. You can also perform voltammetric experiments of any type, and monitor potential or current dependence of the effective electrode mass. The resolution of the EQCN-900F is 0.1 Hz which corresponds approximately to 0.1 ng of the effective mass change. The short-term stability is mostly dependent on the state of the working electrode surface and purity of the solution. Usually, it is better than 5 Hz. The exceptional linearity of mass measurements extends up to 100 _g. The use of AT-cut quartz crystals reduces temperature coefficient to the minimum. Under normal circumstances, the effect of temperature can be neglected in the range near the room temperature. If a very high sensitivity or wide temperature range are required, it is recommended to use a thermostatted cell and Model EQCN-900-3B Remote Probe Unit with thermostatted reference oscillator, or Model EQCN Remote Probe Unit with external reference quartz crystal. To perform electrochemical measurements, a potentiostat may be required. We offer a line of potentiostats specially designed to work with oscillating quartz crystal electrodes. The Model PS-205B is a general purpose potentiostat/galvanostat with potential control from -8 to +8 V, rise time of 500 ns, and 0.05% accuracy. The Model PS-305 is a precision potentiostat/galvanostat, and Models PS-505 and PS-605 offer exceptionally low noise and high precision, as well as an extended potential range control (-10 to +10 V). For computer controlled measurements, we recommend a Data Logger and Control System DAQ-616SC with 16-bit VOLTSCAN Real-Time Data Acquisition and Control. It includes powerful data processing and graphing capabilities designed specially for electrochemical applications using different voltammetric techniques. 3

5 2. SPECIFICATIONS 2. SPECIFICATIONS Measurement Functions (1) EQCN: Electrochemical Quartz Crystal Nanobalance, (2) QCI: Quartz Crystal Immittance measurements, (3) F/V-C: Frequency-to-Voltage Converter Oscillators Working Oscillator WO (EQCN):... - internal oscillator for external QC (ca. 10 MHz); Reference Oscillator RO (EQCN):... - internal (f = MHz), or - external (9.9 < f < 10.1 MHz), TTL/CMOS compatible; Frequency Scanning Generator FSG (QCI):... - external (9.8 < f < 10.2 MHz), TTL/CMOS compatible; Measurement Ranges Frequency Difference (digital)... Frequency Shift (analog)... Frequency Shift Linearity... Mass Change... Mass Change Linearity... Extended Linearity... Mass Change Sign... Overload Indicator... 0 to 500,000 Hz to khz, to khz, to khz, to Hz 0.02 % of reading % FS to _g, to _g, to _g, to ng 0.02 % of reading % FS 10 % over nominal range + for f WO < f RO - for f WO > f RO (_m > 0, mass increase) ca. 3 % over nominal range Resolution Frequency Difference:... Mass Change: Hz (analog) 0.1 ng (analog) 4

6 2. SPECIFICATIONS Measurement speed Mass change:... Frequency shift:... IQC, VQC, φ: µs per point (max) with Filter OFF 30 µs per point (max) with Filter OFF 20 ms per point Sensitivity Quartz Crystal a.c. Current Amplitude: Quartz Crystal a.c. Voltage Amplitude:... Phase Detector Output (_, PD-OUT):... Calibration: IQC, _:... VQC, m, f:... Voltage to Mass Change Ratio:... Voltage to Frequency Shift Ratio: ma/v, 5 ma/v, 2 ma/v, 1mA/V, 0.5 ma/v, 0.2 ma/v, 0.1 ma/v 200 mv (constant) 45 deg/v (i.e. -90 deg -2 V, +90 deg +2 V) software hardware 10 V per nominal range (Mass mode) 10 V per nominal range (Frequency mode) RANGE MASS CHANGE FREQUENCY SHIFT (_g or khz) V/_g V/kHz V/_g V/kHz V/_g V/kHz mv/ng mv/hz Mass and Frequency Shift: Extended linearity:... Offsets: coarse:... fine:... Calibration: % over nominal range 0 to 90 _g or 90 khz (approx.) 0 to 900 ng or 900 Hz (approx.) hardware Recorder Outputs Analog Output Voltage Ranges: Mass Change (V-OUT):... Frequency Shift (V-OUT): to +10 V (MASS output mode) -10 to +10 V (FREQUENCY output mode) (note: DAQ-616 accepts 10 V inputs) Quartz Crystal a.c. Current (IQC-OUT): to +3 V (1 V/dB) Quartz Crystal a.c. Voltage (VQC-OUT):... 0 to +200 mv (constant) Phase Shift (φ, PD-OUT): to +3 V Offsets: Mass Change:... 0 or variable (0 to ca. 900 ng) 5

7 2. SPECIFICATIONS Frequency Shift:... Quartz Crystal a.c. Current (i QC -OUT):... Quartz Crystal a.c. Voltage (V QC -OUT):... Phase Shift (PD-OUT):... Calibration: IQC, _:... VQC, _m, _f:... 0 or variable (0 to ca. 900 Hz) software 0 V software software hardware Operating Parameters Working QC Resonator Frequency:... Reference Crystal Frequency: MHz band MHz (internal), 9.9 to 10.1 MHz (external, TTL/CMOS) 110/220 V, Hz Power Supply:... Dimensions: Instrument H x 14.5W x 15D, inch Faraday Cage... 14H x 12W x 11D, inch Typical Measurement System Components Model EQCN-900F Model EQCN-900F-2 Model EQCN Model EQCN-906 Model DAQ-616SC Model PS-605E Model RTC-100 Electrochemical Quartz Crystal Nanobalance Instrument Faraday Cage Remote Probe Unit (mounted on back of Faraday Cage) Frequency Scanning Generator Data Logger and Control Processor System Potentiostat/Galvanostat Rotacell Cell System Other Options Model EQCN-900-3B Model RTC-100/T Model THERM-3 Model TSR-100 Model STIR-2 Model FG-806 Model FC-299 Model PS-205B Electrodes Remote Probe Unit with thermostatted reference oscillator option (mounted on back of Faraday Cage) ROTACELL Cell System with Thermostat Temperature Controller Temperature Probe (solid state, teflon coated) Stirrer External Frequency Reference ( MHz) Frequency Meter/Calibrator/Generator (0.1 Hz to 60 khz) General Purpose Potentiostat/Galvanostat Wide selection of quartz crystal working electrodes with Ag, Au, Al, Cr, Cu, Fe, Ni, Pt, and Zn coatings 6

8 7 3. CONTROLS

9 3. CONTROLS 3. CONTROLS The front and back view of the Instrument are presented in Figures 1 and 2, respectively. The side panel of the Remote Probe Unit is depicted in Figure 3 and the inside panel of the Faraday Cage is shown in Figure 4. Read this Chapter carefully since it provides you with a full and systematic description of the functionality and limitations of all features and facilities available in the instrument. For exemplary schematics of connections and experimental measurement set-up, refer to Chapter FRONT PANEL Controls for the front panel are described in the following order: Switches Adjustable Potentiometers Panel Meters Diode Indicators Other Controls Switches 1. QCI Toggle switch controlling power supplies to the QCI subsystem. To perform QCI measurements, set the QCI switch ON and allow 15 minutes to warm up and stabilize the temperature. Then, set the MODE switch (see: below) to the QCI measurements. When doing EQCN measurements, it is recommended to set the QCI switch OFF to achieve a better temperature stability. 2. MODE Toggle switch with two positions: EQCN - for Electrochemical Quartz Crystal Nanobalance measurements. In the EQCN mode, the frequency displayed on the FREQUENCY (_F) panel meter corresponds to the difference between the frequency of the EQCN working oscillator and the reference oscillator (either the one sealed inside the Remote Probe Unit or an external reference oscillator). QCI - for Quartz Crystal Immittance measurements 8

10 3. CONTROLS ELCHEMAF Figure 1. Front panel view of the Model EQCN-900F Electrochemical Quartz Crystal Nanobalance with immittance measurement unit (QCI). 9

11 3. CONTROLS In the QCI mode, the external scanning generator output connected to the Faraday Cage F-SCAN input is enabled and the working oscillator WO used for EQCN measurements is disabled. 3. ATTENUATION Rotary switch for selection of the a.c. current range for a.c. current flowing through the quartz crystal under test in QCI measurements. The range selection has no effect on the EQCN oscillator. The ATTENUATION from 10 to 0.1 can be selected. This is an initial attenuation and it is automatically adjusted during measurements. For our standard laboratory crystals (QC-10-xx series) in air, the initial attenuation of 10 should be used. The same crystals in solution present much higher resistance at the resonance so that a higher gain is necessary, for instance you can use the ATTENUATION of 0.2. The frequency scanning should not be too fast, as this can generate an excessive noise on the IQC output. The frequency scan time of 60 seconds is recommended (it is set by QCI software and the Data Logger on the FSCAN page). If necessary, you can additionally use an external filter, e.g. ELCHEMA 3-Channel Tunable Filter, Model FLT-03, or perform digital smoothing using Data/Smooth utility in QCI POLARITY Two position toggle switch to select the sign of the voltage signal representing the mass change. The importance of the sign change can be realized by considering the following relationships. When the working crystal frequency is lower than the reference crystal frequency, the mass increase is manifested by the increase in the measured frequency difference. In this situation, the '+' sign should be selected to have the recorder output voltage V-OUT increasing with the electrode mass increase. When the working crystal frequency is higher than the reference crystal frequency, the mass increase is manifested by the decrease in the measured frequency difference. In this situation, the '-' sign should be selected to have the recorder output voltage V-OUT increasing with the electrode mass increasing. 5. OFFSET Toggle switch to turn the offset for MASS or FREQUENCY in EQCN measurements ON or OFF. 6. FUNCTION OUTPUT FUNCTION toggle switch with two positions: MASS - for conversion of frequency difference signal _f ac (which is an a.c. signal) to the apparent mass change signal V _m (which is an analog dc voltage signal). The V _m voltage is scaled in mass units (10 V per nominal mass RANGE). The V _m signal is displayed on the Mass/Frequency METER and is also available at the V- OUT BNC socket on the back panel of the instrument when the MASS output mode is selected. The V _m signal can be used to monitor apparent mass changes during experiments when the EQCN mode and MASS output mode are used. The output voltage range at the V-OUT BNC output is 10 V. FREQUENCY - for conversion of frequency difference signal _f ac (an a.c. signal) to the analog dc voltage V _f proportional to the frequency of the _f ac signal. The V _f voltage is displayed on the Mass/Frequency METER in V-OUT mode and is also available at the V-OUT BNC socket on the back panel of the instrument 10

12 3. CONTROLS when the FREQUENCY output mode is selected. The V _f signal is scaled to have a sensitivity of 10 V per nominal frequency shift RANGE and can be used to monitor the frequency shift related to apparent mass changes and/or changes in viscoelastic properties of a solution and an electrode film during experiments when the EQCN mode and FREQUENCY output mode are used. The output voltage range at the V-OUT BNC output is 10 V. 7. V-OUT RANGE RANGE selector for the F/V-Convertor. This is a four position rotary switch for the range selection, from 100 to 0.1 _g, or 100 to 0.1 khz FS, depending on the output FUNCTION switch setting, MASS or FREQUENCY, respectively. The range selected is indicated by a lighting diode. For each range, the extended linearity from -110% to +110% of the range value can be utilized. Adjustable Potentiometers 8-9. OFFSET Two multiturn precision low-noise potentiometers marked COARSE and FINE for precision offset of the amplified mass signals. An exact zero offset can be obtained by setting the OFFSET toggle switch OFF. When the OFFSET toggle switch is ON, the zero offset can be obtained by turning both potentiometers clockwise until a resistance is felt (with the POLARITY switch in '+' position). Set a zero mass on the 100 _g first, then increase the sensitivity by switching to the 10 _g range and readjust the FINE offset knob position. Apply the same procedure on more sensitive mass ranges, if necessary. In the EQCN measurements, usually the offset is not set to zero (that is: _m = 0 on the Mass METER, with the crystal disconnected) but rather the offset is adjusted (to whatever value) to have a zero mass reading on the Mass METER with the crystal connected to the internal EQCN oscillator. This allows the experimenter to increase the mass sensitivity to the level otherwise impossible to attain. Usually, the mass is adjusted (offset) to zero just before recording the experimental masspotential curve, or a mass-time transient. This is because in the EQCN technique we do not measure the absolute mass of the electrode but rather the mass change during the experiment. It is therefore convenient to start the experiment from a zero mass reading. Panel Meters 10. _F FREQUENCY DPM Digital Panel Meter displaying, in Hz, the frequency difference between the frequency of the working quartz crystal and the frequency of a reference oscillator 11

13 3. CONTROLS (either the internal reference oscillator or an external TTL/CMOS reference oscillator). 11. METER Digital Panel Meter displaying the mass change or frequency shift depending on the output FUNCTION setting. When the FUNCTION toggle switch is set to MASS, the apparent mass change of the QC electrode is displayed and this switch is set to FREQUENCY, the frequency shift of the QC electrode is displayed. Usually, the mass reading is adjusted (using OFFSET knobs) to zero just before recording the experimental mass-potential curve, or a mass-time transient. This is because in the EQCN technique we do not measure the absolute mass of the electrode but rather the mass change during the experiment. Similar concerns the frequency shift See also how the POLARITY switch affects the mass readings. The DPM displays values in the range from to and includes decimal point dependent on the range selected. The extended linearity is 10 % over the nominal range. The overload diode is activated when the measured values exceed the range by ca. 3 %. Diode Indicators 12. OVERLOAD Red LED activated when the measured mass change (frequency shift) exceeds the actual V-OUT RANGE by ca. 3 %. 13. ATTENUATION INDICATORS Green LED's indicating the i QC sensitivity selection. 14. FILTER INDICATORS Green LED's indicating the FILTER selection. When all of the indicators are off, the filter is disconnected. The time constant of the filter increases from left to right (10 ms to 1000 ms). 15. MASS RANGE INDICATORS Green LED's indicating the MASS RANGE selection. Other Controls 16. FILTER The FILTER selector switch which controls a filter damping the noise on the output voltage at the recorder V-OUT BNC socket on the back panel of the Instrument. Use a setting which works best for the particular experiment you are doing. Make sure that the damping acts only on the high frequency noise and not on the (slower) signal. Usually, the first or second setting, from the top, is appropriate. The filter time 12

14 3. CONTROLS constants increase, from top to bottom, in the following order: 10, 40, 80, 200, 1000 ms. When all FILTER indicators are off, the filter is disconnected. 17. POWER Main power switch. The switch is illuminated when the POWER is ON. 13

15 3. CONTROLS 3.2. BACK PANEL 1. _F-IN BNC socket for connection to the socket marked _F-OUT on the side panel of the Faraday Cage. This connection is necessary in the EQCN mode. Optionally, it may also be utilized to perform a precision F-to-V conversion, e.g. to convert frequency of an external source, up to 100 khz, to a DC voltage proportional to the input frequency. The DC voltage is output to V-OUT and is also displayed on the METER DPM. The input signal should have an amplitude 0.1 to 2.5 V (i.e V p-p ) and the FUNCTION toggle switch should be in FREQUENCY position. 2. V-OUT BNC output socket providing voltage signals corresponding to: (a) relative apparent mass change of rigidly attached film to the EQCN working quartz crystal (for the FUNCTION switch in the MASS position); (b) frequency shift corresponding to the mass change or any change in visoelastic or other properties of the solution or films on the quartz crystal (for the FUNCTION switch in the FREQUENCY position). 3. IQC BNC output socket providing a rough analog voltage signal representing the current flowing through the quartz crystal under test in the QCI measurements. This output signal is offset and calibrated by the Data Logger under QCI 2.0 software and converted to the admittance modulus Y, conductance G, susceptance B, log Y, etc. utilizing VQC and PD functions. 4. VQC BNC output socket providing an analog voltage signal equal to the amplitude of the a.c. voltage across the quartz crystal under test in QCI measurements. This signal is constant (100 to 300 mv, typically: 200 mv). 5. PD, φ BNC output socket providing output from digital Phase Detector. The analog voltage signal is from -2 to +2 V for phase shift of +90 o to -90 o (±3.5 V max), i.e. the sign is reversed. After offset and calibration by the Data Logger, the φ signal has the sensitivity of 45 deg/v and zero offset (-2 V corresponding to -90 deg and +2 V corresponding to +90 deg). At frequencies lower than the resonance frequency, the phase shift is positive (the current is leading the voltage). At the resonance, the phase shift passes through zero and becomes negative (the current is lagging the voltage). At the anti-resonance, the phase shift again passes through zero and becomes positive. The phase detector output may have a higher uncertainty when the QC current has a very low value, e.g. near the anti-resonance. 6. I/O Standard female DB-25 socket for input/output communication. It should be connected to the corresponding male DB-25 connector on the side panel of the Faraday Cage. 7. SPLY 8-pin audio-type connector with DC supplies for the Remote Probe Unit. This socket should be connected to the corresponding socket on the side panel of the Faraday Cage. 14

16 15 3. CONTROLS

17 3. CONTROLS 8. GND Black or brown isolated Banana socket connected to the analog ground of the instrument circuitry. The analog ground is floating, i.e. it is not connected directly to the instrument CHASSIS or to the power line ground wire. You can connect externally the GND socket to the instrument CHASSIS or analog ground of other instruments, if necessary. 9. CHASSIS Banana socket shorted to the instrument chassis. The instrument chassis is connected internally to the power line ground wire (a.c. ground). You can use this socket for reference purposes or to provide grounding for other instruments, if necessary. 10. POWER socket HP type socket for A.C. power inlet. It will accept 110 V or 220 V, 50 to 60 Hz. If the 110/220 V switch is not set properly for your power supply voltage, remove the power cord from the instrument and change the position of the 110/220 V selector to the appropriate position. Use power cords supplied with the instrument. American, British, and European power cords are available /220 V switch Power line voltage selector. The switch is set to 110 V when shipped within the USA and Japan, and 220 V, elsewhere. Check the position of this switch before you connect power to the instrument. WARNING: Make sure the power in the instrument is OFF and power cord removed from the instrument before you change the position of the 110/200 V switch. 12. FUSE Power fuse. Use 250 V, 2 A slow melting fuse if replacement is necessary. WARNING: Make sure the power in the instrument is OFF, and the power cord is disconnected from the instrument before you replace the fuse. 16

18 3. CONTROLS 3.3. Faraday Cage: Side Panel (Remote Probe Unit) The following controls and connectors are located on the side panel of the Remote Probe Unit which is factory mounted on the back of the Faraday Cage. 1. RE BNC socket for connection to the Reference Electrode input in your potentiostat. Make sure that the shield of this cable is connected to the a.c. ground. 2. CE BNC socket for connection to the Counter Electrode output in your potentiostat. Make sure that the shield of this cable is grounded to the a.c. ground. 3. WE BNC socket for connection to the Working Electrode input in your potentiostat. Make sure that the shield of this cable is connected to the a.c. ground. For best noise reduction, the working electrode should be at the ground potential (either virtual ground or shorted to GND). 4. F-SCAN IN BNC input socket for connection to a Frequency Scanning Generator, e.g. ELCHEMA FG-906S providing a TTL/CMOS compatible squarewave with frequency scanned in the range from ca. 9.5 to 10.1 MHz. This connection is necessary only in the QCI mode. The TTL/CMOS compatibility means that the signal amplitude is 5 V and voltage levels are 0 and +5 V. The generator must be able to provide 50 ma current without any change in the voltage amplitude. The rise time and fall time should be on the order of 5 ns or shorter. The generator should have an exceptional frequency stability (DDS with oven stabilized oscillator is a must). 5. EXT.REF. IN BNC input socket for connection to a stable frequency source, e.g. ELCHEMA FG-806 providing a TTL/CMOS compatible square wave with frequency set in the range from ca. 9.9 to 10.1 MHz. This connection is only necessary if you want to use an external reference frequency instead of the internal frequency reference. The external frequency standard is to be utilized in the EQCN measurement mode. The TTL/CMOS compatibility means that the signal amplitude is 5 V and voltage levels are 0 and +5 V. The generator must be able to provide 50 ma current without any change in the voltage amplitude. The rise time and fall time should be on the order of 5 ns or shorter. The generator should have exceptionally good frequency stability (for FG-806 it is ppm, or 10-7 %). 6. _F-OUT BNC output socket providing a frequency difference signal _F which is a.c. sine signal with voltage amplitude of 200 mv and frequency equal to the difference between the working oscillator frequency F WO and the reference oscillator frequency F RO. The _F- OUT should be connected to the _F-IN BNC input on the back panel of the Nanobalance Instrument EQCN-900F. 17

19 3. CONTROLS RE CE WE F-SCAN IN Float. GND INT. EXT. REF. F-REF 9 5 EXT. IN 10 OSC. INT. EXT. F-OUT 7 ΔF-out 6 SPLY 11 I/O 12 Figure 3. View of side panel of the Faraday Cage. 18

20 3. CONTROLS 7. F-OUT BNC output socket providing a high frequency signal f WO, f RO, or f EXT.REF selected by the F-OUT three-position toggle switch. The signal is TTL/CMOS compatible (0 to +5 V, ca. 10 MHz) and can be viewed on an external oscilloscope or its frequency measured using an external high frequency counter. 8. FLOAT/GND toggle Toggle switch to select a floating or grounded EQCN working oscillator. When EQCN is used with potentiostat, the working electrode should be maintained on the ground potential by the potentiostat and the FLOAT/GND toggle should be set to FLOATING. When the potentiostat is not used, the FLOAT/GND toggle can be set to GND. The Faraday Cage chassis may also be connected to the a.c. GND if necessary. 9. F-REF toggle Toggle switch to select either an Internal Reference Oscillator (INT) or an External Reference Oscillator (EXT) as the frequency reference for _f measurements. 10. F-OUT toggle Three-position toggle switch to select frequency for output at the BNC output socket marked F-OUT. The selected frequency can be: a Working Oscillator (OSC.) frequency, an Internal Reference (REF.) frequency, or an External Reference (EXT.) frequency. 11. I/O Standard male DB-25 socket for input/output communication. It should be connected to the corresponding female DB-25 connector on the back panel of the Nanobalance Instrument. 12. SPLY 8-pin audio-type connector for DC supplies for the Remote Probe Unit. This socket should be connected to the corresponding socket on the back panel of the Nanobalance Instrument. 19

21 3. CONTROLS 3.4. Faraday Cage: Internal Panel 1. REF REFERENCE ELECTRODE yellow pin tip banana jack for connection to the reference electrode (e.g., saturated calomel electrode, SCE, or a double-junction silver/silver chloride electrode, Ag/AgCl) for experiments involving a potentiostat. Use as short a wire as possible. 2. CE COUNTER ELECTRODE red pin tip banana jack for connection to the counter electrode (auxiliary electrode) in the electrochemical cell for experiments involving a potentiostat. Use a short wire for the connection. 3. AIR (EQCN) White pin tip banana socket for connection to the electrode exposed to air in the EQCN cell assembly. Use this socket for EQCN measurements only. The MODE switch on the front panel of the Nanobalance Instrument must be set to EQCN. 4. SLN (EQCN) Blue pin tip banana socket for connection to the EQCN electrode immersed in the solution. This is a connection to your working electrode deposited on the quartz crystal. Use this socket for EQCN measurements only. The MODE switch on the front panel of the Nanobalance Instrument must be set to EQCN. 5. AIR (QCI) White pin tip banana socket for connection to the quartz crystal electrode exposed to air. Use this socket for QCI measurements only. The MODE switch on the front panel of the Nanobalance Instrument must be set to QCI. This socket is not connected to the AIR (EQCN) white jack (3). 6. SLN (QCI) Blue pin tip banana socket for connection to the quartz crystal electrode immersed in the solution. This is a connection to your working electrode (the sensor) deposited on the quartz crystal. Use this socket for QCI measurements only. The MODE switch on the front panel of the Nanobalance Instrument must be set to QCI. This socket is not connected to the working electrode input of the potentiostat. It is also not connected to the LIQUID (EQCN) blue jack (6). Note that the QC inputs (5) and (6) are optically isolated from the frequency scanning generator (F-SCAN IN) input on the side panel of the Faraday Cage (Remote Probe Unit) and have no galvanic connection to it. 20

22 3. CONTROLS 1 2 REF CE 3 EQCN 4 AIR SOLN QCI 5 AIR SOLN 6 Figure 4. View of the inside panel of the Faraday Cage. 21

23 4. OPERATING INSTRUCTIONS 4. OPERATING INSTRUCTIONS 4.1. INSPECTION After the instrument is unpacked, the instrument should be carefully inspected for damage received in transit. If any shipping damage is found, follow the procedure outlined in the "Claim for Damage in Shipment" section at the end of this Manual PRECAUTIONS Care should be taken when making any connections to the instrument. Use the guidelines for maximum voltage at the inputs. There should be no signal applied to the inputs when the instrument is turned off. The outputs should not be loaded. They can only be connected to high input impedance devices such as plotters or oscilloscopes. Use minimal force when putting on, or taking off, the BNC connections, otherwise they might become loose. Push the BNC forward when making a connection or a disconnection in order to relieve the rotational tension on the BNC socket. Observe the color codes when connecting the power to the probe unit. Operate the instrument in a cool and well ventilated environment. Contact us in the event that any of our components do not operate properly. Our components are marked with seals. DO NOT try to open and fix anything yourself, otherwise your warranty agreement will be nullified. 22

24 4. OPERATING INSTRUCTIONS 4.3. FARADAY CAGE The Faraday cage tips over easily. It is also possible for someone to accidently brush against it and break, or spill the contents of the cell inside. Hence, it is recommended to secure the Faraday cage if necessary GROUNDING AND INTERFERENCES It is very important to properly ground the Nanobalance system. The circuitry operates at a high frequency of 10 MHz and is very susceptible to electromagnetic radiation and interference present in the surroundings. Since the working oscillator can not be enclosed in a case due the nature of measurements, the use of a Faraday cage is necessary. Usually, the door of the Faraday cage does not need to be completely closed. (Do not lock the door unless you see an improvement in shielding efficiency and temperature stability of the crystal frequency.). If you find that in your application leaving the door of the Faraday cage wide open does not result in any external influences on the frequency reading, you may leave them open. Normally, Faraday cage does not need to be grounded with additional wires. You can connect the Faraday cage chassis to the AC ground or water pipe using a thick grounding cable, if necessary. Make this connection only if you see an improvement in shielding or reduction in noise. Avoid creating ground loops! The Nanobalance Instrument (EQCN-900F) is connected to the AC ground through the HP type 3-conductor power cable. With a short banana-to-banana cable, you may connect the chassis of your potentiostat to the chassis of the Nanobalance Instrument EQCN-900F using the CHASSIS banana socket (metal hex nut) on the back panel of the EQCN-900F. You can also use this socket for reference purposes or to connect to other instruments which need to be grounded. The analog ground of the EQCN-900F is provided on the back panel (black banana socket marked GND) for reference purposes. Normally, do not connect anything to this socket. However, you can short it to the AC ground (CHASSIS) or to the analog ground of the potentiostat if necessary. Remove all unnecessary cables from the instrument before doing measurements. (Cables which are not connected on the other end may act as antennas and should also be removed. Note that some measurement instruments, e.g. oscilloscopes, have often the cable guard shorted to the AC ground. Making a connection to such an instrument is equivalent to shorting the analog ground of Nanobalance Instrument to the AC ground.). Since the oscillating circuit is connected to the electrochemical cell through the working electrode, changes in position of wires connected to the Reference and Counter Electrodes with respect to ground planes may result in some frequency change due to the change in parasitic capacitance. Make sure that all electrodes are firmly attached to the cell top and the connecting wires are short and do not bounce during measurements. The connections between the working quartz crystal and the Remote Probe Unit (blue and white tip banana jacks) should be as short as possible and the inter-wire capacitance should be kept constant during measurements. 23

25 4. OPERATING INSTRUCTIONS In the piezogravimetric technique, we do not measure the absolute mass of the working electrode but rather the mass change that occurs during the experiment. At the beginning of the experiment, you set the initial mass to zero (or any other value you wish) using the mass OFFSET potentiometers located on the front panel of the instrument. Due to the high sensitivity of measurements (compare it with a regular balance), it is essential that you maintain all the system parameters (including parasitic capacitances of connecting wires and cables) constant. Only then the frequency change observed during the experiment will correspond to the change in values of parameters of the equivalent circuit of the quartz crystal assembly (especially the inductance change proportional to the change in mass rigidly attached to the working electrode). With electrochemical cells, a significant frequency change (observed as a drift) may occur even at constant potential due to surface changes, adsorption, poisoning, etc. Use only high purity chemicals. Please keep in mind that the gold substrate may undergo slow dissolution at higher potentials which may lead to the apparent mass decrease (absolute frequency increase). Very often mass changes may result as a consequence of the surface oxide formation. Sudden metal dissolution may result in oversaturation and deposition of salts on the electrode surface. Deposits on the surface may be sometimes difficult to remove and may block the surface and change the electrode activity. If you are not familiar with electrochemistry at solid electrodes, consult general textbooks and monographies (e.g., A. J. Bard and L. R. Faulkner, Electrochemical Methods, J. Wiley and Sons, New York, 1980). WARNING: Do not attach ground wires to a gas or heating pipe THERMAL SENSITIVITY As with any electronic equipment, this instrument should be warmed up in order to achieve the greatest accuracy. Under normal circumstances, the frequency difference readout on the front panel of the instrument should be stable to 1-2 Hz after 15 minute warmup and the mass change readout should stabilize in 30 minutes. In order to reduce the heat generation, it is recommended to set the QCI section OFF when precision EQCN measurements are made. 24

26 5. INSTALLATION 5. INSTALLATION The operating instructions have been made short and simple but make sure they are followed in this exact order. Bold letters indicate connections and controls on the EQCN- 900F system only. For the sake of clarity, the Model EQCN-900F is often referred to in the text as the Nanobalance Instrument or the Instrument. The other two system components are: Model EQCN-900F-2 Faraday Cage and the Model EQCN Remote Probe Unit which is factory mounted on the back of the Faraday Cage Initial set-up (1) Unpacking. Carefully remove all paper and tape used in shipping. Place instrument on a convenient bench. Check the items against the packing list. (2) The Faraday Cage (EQCN-900F-2) should be placed on the bench on the left side of the Nanobalance Instrument (EQCN-900F) to have the connections as short as possible. The Remote Probe Unit, Model EQCN-900-3, has been mounted on the back of the Faraday Cage in the factory. (3) This instrument has been set for either 110 or 220 V a.c., Hz, power supply. If necessary, you can change this setting by changing the position of the supply voltage selector 110/220 located on the back panel of the instrument. If you have to make the change, make sure the power in the instrument, AC, and in all other devices is off, and nothing is connected to the instrument or the Faraday Cage. With the power cord disconnected from the instrument, set the power supply voltage switch to the appropriate position, 110 or 220 V. Connect the power cord back to the instrument. (4) Connect the 8-conductor cable with 8-pin audio-type connectors to the sockets marked SPLY on the back of the instrument and to the corresponding socket on the side panel of the Faraday Cage. (5) Connect the multiconductor cable with standard DB-25 connectors to the sockets marked I/O on the back panel of the instrument and to the corresponding socket on the side panel of the Faraday Cage. 25

27 5. INSTALLATION (6) Connect the BNC socket labeled _F-IN on the back panel of the Instrument to the corresponding BNC socket on the side panel of the Faraday Cage marked _F-OUT using the coaxial cable provided. (7) Connect the V-OUT BNC socket on the back panel of the Instrument to the input of the recorder or, if you use an ELCHEMA data acquisition system, to the M input BNC cable of the Break-Up Box DAQ-617. (8) Put the QCI toggle switch to the OFF position. Put the MODE switch to the EQCN position (for Quartz Crystal Nanobalance measurements). (9) Put the RANGE selector to 100 _g position (least sensitive). (10) Put the ATTENUATION switch to '1 (ma/v)'. (11) Put the mass change POLARITY (+/-) switch to the + (plus) position. (12) Zero the recorder. (13) Set the range on the recorder to 10 V. 26

28 27 5. INSTALLATION

29 28 5. INSTALLATION

30 5. INSTALLATION 5.2. Power ON checks (1) Turn the power switch ON. (2) Set the MODE switch to EQCN. (3) Set the output FUNCTION to MASS. (4) Set the METER mode to V-OUT. (5) Set the OFFSET toggle switch OFF. (6) Set the FILTER selector to the first (top) position. (7) Connect pin tip plugs from the Crystal-Cell assembly (ROTACELL, Model RTC- 100) to the white and blue pin tip jacks CRYSTAL, inside the Faraday Cage, in the EQCN section. These jacks are labeled AIR and SLN (SOLUTION), respectively. Insert an EQCN cell with quartz crystal in the ROTACELL (For Crystal-Cell assembly instructions refer to Chapter 5.) (8) At this point, the frequency meter should give you some frequency difference reading. Typical values are from 500 Hz to 90 khz. If the reading is 0, the contacts to the working crystal may not be good or crystal cannot oscillate due to a strong damping (thick film deposited on the crystal, broken crystal, etc.). (9) Note the voltage at the output. The recorder output voltage V-OUT is 10 V per nominal mass range (FS). (10) Set the OFFSET toggle switch ON. Use the COARSE and FINE OFFSET knobs to set the mass reading on the panel METER to zero. You can now change the MASS RANGE to more sensitive one. Again, use the COARSE and FINE OFFSET knobs to set the MASS reading on the MASS panel meter to zero. (11) Repeat the operations (10) until the MASS RANGE with desired sensitivity is selected. (12) In the following testing, observe the rules: - Start experiments with MASS change set to zero (or close to zero). - Before disconnecting Working Crystal change the mass RANGE to 100 _g. 29

31 5. INSTALLATION 5.3. Connections to a potentiostat and electrochemical cell The EQCN-900/PS-705 system does not require any external connections between the potentiostat and the balance for EQCN measurements so you can skip procedures (1)-(3). When connecting potentiostats from other vendors, make sure that the shields of cables to WE, CE, and REF electrodes can be safely grounded. The WE electrode should be maintained at the ground potential by the potentiostat. The best performance is achieved with PS-205A/B, PS-305 and PS-605E potentiostats which are specially tuned to work best with EQCN systems. First, make the following onnections: (1) Connect the working electrode output in potentiostat to the WE BNC input on the side panel of the Faraday Cage. (2) Connect the reference electrode input in potentiostat to the REF BNC output on the side panel of the Faraday Cage. (3) Connect the counter (auxiliary) electrode output in potentiostat to the CE BNC input on the side panel of the Faraday Cage. Connect the electrodes as follows: (4) First, make sure, that the potentiostat CELL switch is set to OFF (or to a DUMMY CELL) position. (5) Connect the Counter Electrode to the red pin tip jack CE inside the Faraday Cage. (6) Connect the Reference Electrode to the yellow pin tip jack REF inside the Faraday Cage. (7) Make sure that the working crystal is connected to the white and blue pin tip banana jacks marked CRYSTAL, Air and Sln, respectively, inside the Faraday Cage, in the EQCN section. (For Crystal-Cell assembly instructions refer to Chapter 5.) (8) You are now ready to start your experiment. Refer to the next section to learn the details of the experimental procedure illustrated with an example of the deposition and stripping of copper. 30

32 5. INSTALLATION 5.4. Testing experiment with real cell ON (1) You are now ready to use the instrument for measurement purposes. If you want to perform a simple checking experiment, you can use, for example, a 5 mm copper(ii) solution in 0.1 M H 2 SO 4. Program your waveform generator for sweep from 500 mv vs. SCE to 0 mv. (2) Check if the Reference Electrode is connected and placed in the solution. (3) Check if the Counter Electrode is connected and placed in the solution. (4) Set the current range on your potentiostat to 1 ma FS (full scale). (5) Turn the CELL switch on your potentiostat to the ON (or: EXTERNAL CELL) position. (6) Initiate the potential scan. Using the OFFSET knobs, appropriately position the mass response curve on the recorder chart, or monitor plot. (7) Change carefully the cathodic potential limit to more negative value until copper deposition just begins to take place. On the voltammogram, you should be able to observe an increase in cathodic current due to copper deposition, and an increase of the anodic peak due to the copper stripping. On the mass-potential curve which can be recorded simultaneously with the current-potential curve, you should observe a mass histeresis with mass increase in the potential region where copper is being deposited, and a mass decrease which is fastest in the region of the stripping current peak. If mass changes in the opposite direction, change the POLARITY switch (+/-) setting. (When the working crystal frequency is lower than the reference crystal frequency, the mass increase is manifested by the increase in the measured frequency difference. When the working crystal frequency is higher than the reference crystal frequency, the mass increase is manifested by the decrease in the measured frequency difference.) Do not deposit too much copper. During the anodic stripping process, very often a high concentration of the dissolved metal builds up in the vicinity of the electrode surface, and it may result in the formation of metal oxides on the electrode surface (the oxides may be sometimes difficult to remove). Depending on your experiment and the range of your frequency measurement you may wish to increase the sensitivity of measurements by changing the RANGE selector or by increasing the sensitivity of the recorder, e.g., to 500 mv. (Be careful with whatever changes you make in instrument settings and connections because the instrument is capable of outputing 15V at the RECORDER V-OUT). If you want to change the RANGE selector to more sensitive range, first offset the mass reading to zero (or close to zero) with COARSE and FINE offset potentiometers. The 31

33 5. INSTALLATION offset potentiometers will allow you to do measurements at high sensitivity on large signals Quartz Crystal Immittance Measurements To follow the changes in quartz crystal motional characteristics, the quartz crystal under test is typically subjected to oscillations controlled by an independent oscillator (eg. a function generator) able to scan the frequency around the resonance frequency of the crystal. To avoid interferences with the high speed potentiostat circuitry and high precision EQCN circuitry, in the EQCN-900F an external function generator is used for the quartz crystal excitation purpose (eg. an ELCHEMA Model EQCN-906). The input of the frequency scanning generator F-SCAN IN is optically isolated from the EQCN-900F circuits to reduce noise caused by digital part of the external generator. An example of the QCI measurement procedures is presented below. (1) Turn ON the EQCN-900F system. (2) Set the external generator for the following output waveform and scanning characteristics: Function: Amplitude: Offset: Start Frequency: Stop Frequency: Sweep Time: square wave 5 V p-p 0 V MHz MHz 60 s This should supply a square wave of 0 to +5 V, with frequency scanned between MHz to MHz which should cover the frequency range of our laboratory crystals. The frequency scan should be completed in _ scan = 60 s. WARNING: Check the output waveform of the external generator using an oscilloscope to make sure that it does not exceed the input voltage limit of the EQCN-900F, which is 5 V. (Although the EQCN-900F is protected, avoid supplying any signals to the EQCN-900F when the power to the instrument is OFF). (3) Connect the BNC socket marked F-SCAN IN on the side panel of the Faraday Cage to the output of the frequency scanning generator, e.g. Model EQCN-906. (4) Insert the QC Holder, Model CB-AC-1, to the white and blue pin tip banana jacks marked CRYSTAL, AIR and SLN, respectively, inside the Faraday Cage, in the QCI section. If you do not have the QC Holder, use two short 32

34 5. INSTALLATION cables with pin-tip bananas on one side and aligator clips on the other side to connect a test quartz crystal. (6) With the right hand, press both aligators of the QC Holder open and insert a quartz crystal to be tested, such that each contact pin of the crystal makes an electrical contact with the metal body of one of the aligators. Release the aligator clamps. (Note that the plastic insulator on the outside of the aligator clips does not make an electric contact.). (7) Connect the VQC output BNC socket on the back panel of the Nanobalance Instrument to the corresponding socket on the Data Logger back panel.. (8) Connect the IQC output BNC socket on the back panel of the Nanobalance Instrument to the corresponding socket on the Data Logger back panel.. (9) Connect the φ (Phase Detector) output BNC socket on the back panel of the Nanobalance Instrument to the corresponding socket on the Data Logger back panel.. (10) Turn the QCI toggle switch ON. Wait 15 minutes to warm up the QCI section an the temperatures to stabilize. Set the MODE switch to the QCI position. (11) Set the ATTENUATION switch to the position 10 (10 ma/v). (11) Put the mass change POLARITY (+/-) switch to the + (plus) position. (12) In QCI program in Data Logger, set the variables on the VARIABLES page of the Tabbed Notebook as follows: x: f frequency MHz y: Y Y modulus ms z fi phase shift deg (13) In QCI program, set the plot scale on the SCALE page of the Tabbed Notebook as follows: variable units/v min max f Y fi (14) Turn the external Waveform Generator ON. (15) Initiate the frequency sweep by clicking on the PRE-SCAN button on FSCAN page of the Tabbed Notebook in QCI program in Data Logger, followed by clicking on the RUN button located on the Run Panel which appears on the right-side of the screen. (16) Observe the shape of the curve recorded. There should be a peak close to the resonance frequency of the quartz crystal. After the scan is finished, click on the ANALYZE button on the cool bar and check the characteristics of the admittance curve recorded. Then try the SIMULATE and/or EVALUATE 33

35 5. INSTALLATION buttons for further data processing. Consult the QCI manual for standard procedures and sample graphs obtained for QC in air and in solution. (17) Set now a narrower frequency scan, but still covering both the admittance maximum and minimum. This usually results in an improvement in the evaluation of the equivalent circuit elements. Please note that the evaluation is basically not a strict fitting, so if you want to scan only over a small portion of the immittance spectrum, use values of passive elements estimated in a wider scan. You can still do simulation by entering values of these parameters. (18) To perform measurements with EQCN cells, remove the QC fixture and connect the white and blue wires from the ROTACELL assembly to the white and blue pin tip banana jacks in the QCI section inside the Faraday Cage. (For Crystal-Cell assembly instructions refer to Chapter 5.). Follow the procedures (10)-(17) above, with exception of the initial IQC Attenuation, which should be set at 0.5 mv/v. (18) Shut-off procedure: (i) - Set the QCI toggle switch to OFF. Set the MODE toggle switch to EQCN. (ii) - Set the CELL off, CONTROL off, and then also PROGRAM off on your potentiostat. (iii) - Turn OFF the EQCN-900F, potentiostat, generator, recorder, computer, and other instruments, if any Other utilities (Optional) (1) The frequency difference may be viewed and measured externally by connecting a measuring device to the _F-OUT BNC output located on the side panel of the Faraday Cage. This output provides a sinusoidal wave, 0.4 V p-p. (When connected to the _ F-IN input on the back panel of the Nanobalance Instrument, frequency of this signal is displayed on the _F FREQUENCY panel meter). (2) The absolute frequency of the working oscillator WO and the reference oscillator RO may be viewed and measured externally by connecting a measuring device to the F-OUT BNC output located on the side panel of the Remote Probe Unit attached to the Faraday Cage. This output provides a high frequency wave (ca. 10 MHz), approximately 0 to 5 V. Use only short concentric cables (2-3 feet) to connect the F-OUT BNC socket to the measuring device (an oscilloscope or frequency meter). The WO and RO are selected with the toggle switch F-OUT located above the F-OUT BNC socket. 34