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 13676
www.elchema.net
Tel.: (315) 268-1605 FAX: (315) 268-1709
TABLE OF CONTENTS
1. INTRODUCTION ...... 2
2. SPECIFICATIONS ...... 4
3. CONTROLS ...... 7
3.1. Front Panel ...... 7
3.2. Back Panel ...... 13
3.3. Faraday Cage: Side Panel ...... 16
3.4. Faraday Cage: Internal Panel ...... 19
4. OPERATING INSTRUCTIONS ...... 21
4.1. Inspection ...... 21
4.2. Precautions ...... 21
4.3 Faraday Cage ...... 22
4.4. Grounding ...... 22
4.5. Thermal Sensitivity ...... 23
5. INSTALLATION ...... 24
5.1. Initial Set-up ...... 24
5.2. Power ON Checks ...... 26
5.3. Connections to a Potentiostat and Electrochemical Cell ...... 27
5.4. Testing Experiment with Real Cell ON ...... 28
5.5. Quartz Crystal Immittance Measurements ...... 29
5.6. Other Utilities (Optional) ...... 31
6. CRYSTAL-CELL ASSEMBLY ...... 33
6.1. Mounting Quartz Crystals ...... 33
6.2. Assembling Piezocells in ROTACELL holder ...... 33
6.3. Disassembling Piezocells from ROTACELL holder ...... 34
6.4. Final Checks ...... 34
7. ELECTRICAL CIRCUITS ...... 35
8. SERVICING NOTES ...... 39
9. WARRANTY, SHIPPING DAMAGE, GENERAL ...... 40
2
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-900-3 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.
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 μg. 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-900-4 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.
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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 = 10.000 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) ...... 0 to 500,000 Hz
Frequency Shift (analog) ...... -100.0 to +100.0 kHz,
-10.00 to +10.00 kHz,
-1.000 to +1.000 kHz,
-100.0 to +100.0 Hz
Frequency Shift Linearity ...... 0.02 % of reading + 0.05 % FS
Mass Change ...... -100.0 to +100.0 μg,
-10.00 to +10.00 μg,
-1.000 to +1.000 μg,
-100.0 to +100.0 ng
Mass Change Linearity ...... 0.02 % of reading + 0.05 % FS
Extended Linearity ...... 10 % over nominal range
Mass Change Sign ...... + for fWO < fRO
- for fWO > fRO
(Δm > 0, mass increase)
Overload Indicator ...... ca. 3 % over nominal range
Resolution
Frequency Difference: ...... 0.1 Hz (analog)
Mass Change: ...... 0.1 ng (analog)
Measurement speed
Mass change: ...... 30 ms per point (max)
with Filter OFF
Frequency shift: ...... 30 ms per point (max)
with Filter OFF
IQC, VQC, f: ...... 20 ms per point
Sensitivity
Quartz Crystal a.c. Current Amplitude: 10 mA/V, 5 mA/V, 2 mA/V, 1mA/V,
0.5 mA/V, 0.2 mA/V, 0.1 mA/V
Quartz Crystal a.c. Voltage Amplitude: ...... 200 mV (constant)
Phase Detector Output (φ, PD-OUT): ...... 45 deg/V
(i.e. -90 deg Û -2 V,
+90 deg Û +2 V)
Calibration:
IQC, φ: ...... software
VQC, m, f: ...... hardware
Voltage to Mass Change Ratio: ...... 10 V per nominal range (Mass mode)
Voltage to Frequency Shift Ratio: ...... 10 V per nominal range (Frequency mode)
RANGE MASS CHANGE FREQUENCY SHIFT
(μg or kHz)
100.0 0.100 V/μg 0.100 V/kHz
10.00 1.000 V/μg 1.000 V/kHz
1.000 10.00 V/μg 10.00 V/kHz
0.100 100.0 mV/ng 100.0 mV/Hz
Mass and Frequency Shift:
Extended linearity: ...... 10 % over nominal range
Offsets:
coarse: ...... 0 to 90 μg or 90 kHz (approx.)
fine: ...... 0 to 900 ng or 900 Hz (approx.)
Calibration: ...... hardware
Recorder Outputs
Analog Output Voltage Ranges:
Mass Change (V-OUT): ...... -10 to +10 V (MASS output mode)
Frequency Shift (V-OUT): ...... -10 to +10 V (FREQUENCY output mode)
(note: DAQ-616 accepts 10 V inputs)
Quartz Crystal a.c. Current (IQC-OUT): ...... -3 to +3 V (1 V/dB)
Quartz Crystal a.c. Voltage (VQC-OUT): ...... 0 to +200 mV (constant)
Phase Shift (f, PD-OUT): ...... -3 to +3 V
Offsets:
Mass Change: ...... 0 or variable (0 to ca. 900 ng)
Frequency Shift: ...... 0 or variable (0 to ca. 900 Hz)
Quartz Crystal a.c. Current (iQC-OUT): ...... software
Quartz Crystal a.c. Voltage (VQC-OUT): ...... 0 V
Phase Shift (PD-OUT): ...... software
Calibration:
IQC, φ: ...... software
VQC, Δm, Δf: ...... hardware
Operating Parameters
Working QC Resonator Frequency: ...... 10 MHz band
Reference Crystal Frequency: ...... 10.000 MHz (internal),
9.9 to 10.1 MHz (external, TTL/CMOS)
Power Supply: ...... 110/220 V, 50 - 60 Hz
Dimensions: Instrument ...... 4.5H x 14.5W x 15D, inch
Faraday Cage ...... 14H x 12W x 11D, inch
Typical Measurement System Components
Model EQCN-900F Electrochemical Quartz Crystal Nanobalance Instrument
Model EQCN-900F-2 Faraday Cage
Model EQCN-900-3 Remote Probe Unit (mounted on back of Faraday Cage)
Model EQCN-906 Frequency Scanning Generator
Model DAQ-616SC Data Logger and Control Processor System
Model PS-605E Potentiostat/Galvanostat
Model RTC-100 Rotacell Cell System
Other Options
Model EQCN-900-3B Remote Probe Unit with thermostatted reference oscillator option
(mounted on back of Faraday Cage)
Model RTC-100/T ROTACELL Cell System with Thermostat
Model THERM-3 Temperature Controller
Model TSR-100 Temperature Probe (solid state, teflon coated)
Model STIR-2 Stirrer
Model FG-806 External Frequency Reference (9.9-10.2 MHz)
Model FC-299 Frequency Meter/Calibrator/Generator (0.1 Hz to 60 kHz)
Model PS-205B General Purpose Potentiostat/Galvanostat
Electrodes Wide selection of quartz crystal working electrodes with Ag, Au, Al, Cr, Cu, Fe, Ni, Pt, and Zn coatings
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3. CONTROLS
42
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 5.
3.1 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 (ΔF) 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
ELCHEMAF
Figure 1. Front panel view of the Model EQCN-900F Electrochemical Quartz Crystal Nanobalance with immittance measurement unit (QCI).
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 2.0.
4. 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 Δfac (which is an a.c. signal) to the apparent mass change signal VΔm (which is an analog dc voltage signal). The VΔm voltage is scaled in mass units (10 V per nominal mass RANGE). The VΔm 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 VΔm 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 Δfac (an a.c. signal) to the analog dc voltage VΔf proportional to the frequency of the Δfac signal. The VΔf 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 when the FREQUENCY output mode is selected. The VΔf 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.