Overview
The scanning electrochemical microscope (SECM) was introduced in 19891
as an instrument that could examine chemistry at high
resolution near interfaces. By detecting reactions that occur at a small electrode (the tip) as it is scanned in close proximity to a
surface, the SECM can be employed to obtain chemical reactivity images of surfaces and quantitative measurements of reaction
rates. Numerous studies with the SECM have now been reported from a number of laboratories all over the world, and the instrument
has been used for a wide range of applications, including studies of corrosion, biological systems (e.g., enzymes, skin, leaves),
membranes, and liquid/liquid interfaces.2,3 Trapping and electrochemical detection of single molecules with the SECM has also been
reported.
The CHI920D Scanning Electrochemical Microscope consists of a digital function generator, a bipotentiostat, high resolution data
acquisition circuitry, a three dimensional nanopositioner, and a sample and cell holder. Diagrams for the SECM and cell/sample holder
are shown below. The three dimensional nanopositioner has a spatial resolution down to nanometers but it allows a maximum traveling
distance of 50 millimeters. The potential control range of the bipotentiostat is ± 10 V and the current range is ± 250 mA. The instrument
is capable of measuring current down to sub-picoamperes.
In addition to SECM imaging, other modes of operation are available for scanning probe applications: Probe Scan Curve, Probe
Approach Curve, Surface Interrogation SECM, and Surface Patterned Conditioning. Probe Scan Curve mode allows the probe to move
in the X, Y, or Z direction while the probe and substrate potentials are controlled and currents are measured. The probe can be stopped
when the current reaches a specified level. This is particularly useful for searching for an object on the surface and determining
approach curves. Probe Approach Curve mode allows the probe to approach the surface of the substrate. It is also very useful for
distinguishing the surface process using PID control. The step size is automatically adjusted to allow fast surface approach, without
letting the probe touch the surface. Surface Patterned Conditioning allows the user to edit a pattern for surface conditioning by
controlling the tip at two different potentials and durations. Constant height, constant current, potentiometric, and impedance modes
are available for SECM imaging and probe scan curve.
The 920D can do everything the 760E can do, and more. The 920D is designed for scanning electrochemical microscopy, but many
conventional electrochemical techniques have also been integrated for convenience, such as CV, LSV, CA, CC, DPV, NPV, SWV, ACV,
SHACV, FTACV, i-t, DPA, DDPA, TPA, SSF, STEP, IMP, IMPE, IMPT, and CP. When the instrument is used as a bipotentiostat, the
second channel can be controlled at an independent constant potential, to scan or step at the same potential as the first channel, or to
scan with a constant potential difference with the first channel. The second channel works with CV, LSV, CA, DPV, NPV, DNPV, SWV,
and i-t.
The 920D SECM is the latest upgrade to the 900 series SECM. The 920D uses a stepper motor positioner in conjunction with a
closed-loop 3-dimensional piezo positioner. The stepper motor positioner has a resolution of 8 nanometers with 50 mm travel distance.
Closed-loop piezo control allows improved linearity and reduced hysteresis of the piezo devices. Improvements include very stable and
accurate potential and current control, and dual-channel data acquisition at high speed (1 MHz with 16-bit resolution).
1. A. J. Bard, F.-R. F. Fan, J. Kwak, and O. Lev, Anal. Chem. 61, 132 (1989); U.S. Patent No. 5,202,004 (April 13, 1993).
2. A. J. Bard, F.-R. Fan, M. V. Mirkin, in Electroanalytical Chemistry, A. J . Bard, Ed., Marcel Dekker, New York, 1994, Vol. 18, pp 243-373.
3. A. J. Bard and M. V. Mirkin, Eds. Scanning Electrochemical Microscopy, Marcel Dekker, New York, 2001.

Specifications

 

Model 920D Series Specifications – for older models (920C, etc.),

 

 

Nanopositioner

X, Y, Z resolution: 1.6 nm with Piezo positioner, closed loop control, 8 nm with stepper motor positioner X, Y, Z total distance: 50 mm

Potentiostat / Bipotentiostat Zero resistance ammeter

2- or 3- or 4-electrode configuration

Floating (isolated from earth) or earth ground

Maximum potential: ±10 V for both channels Maximum current: ±250 mA continuous (sum of two current channels), ±350 mA peak

Compliance Voltage: ±13 V

Potentiostat rise time: < 1 μs, 0.8 μs typical

Applied potential ranges (volts): ±0.01, ±0.05, ±0.1,

±0.65, ±3.276, ±6.553, ±10

Applied potential resolution: 0.0015% of potential range

Applied potential accuracy: ±1 mV, ±0.01% of scale

Applied potential noise: < 10 μV rms

Measured current range: ±10 pA to ±0.25 A in 12 ranges Measured current resolution: 0.0015% of current range, minimum 0.3 fA

Current measurement accuracy: 0.2% if current range

>=1e-6 A/V, 1% otherwise

Input bias current: < 20 pA

Galvanostat

Galvanostat applied current range: 3 nA – 250 mA Applied current accuracy: 20 pA ±0.2% if > 3e-7A, ±1% otherwise

Applied current resolution: 0.03% of applied current range

Measured potential range (volts): ±0.025, ±0.1, ±0.25,

±1, ±2.5, ±10

Measured potential resolution: 0.0015% of measured range

Electrometer

Reference electrode input impedance: 1×10¹² ohm

Reference electrode input bandwidth: 10 MHz

Reference electrode input bias current: <= 10 pA @

25°C

Waveform Generation and Data Acquisition Fast waveform update: 10 MHz @ 16-bit

Fast data acquisition: dual channel 16-bit ADC,

1,000,000 samples/sec simultaneously External signal recording channel at maximum 1 MHz sampling rate

Other Features

Automatic and manual iR compensation Current measurement bias: full range with 16-bit resolution, 0.003% accuracy Potential measurement bias: ±10 V with 16-bit resolution, 0.003% accuracy External potential input

Potential and current analog output

Programmable potential filter cutoff: 1.5 MHz, 150 KHz,

15 KHz, 1.5 KHz, 150 Hz, 15 Hz, 1.5 Hz, 0.15 Hz

Programmable signal filter cutoff: 1.5 MHz, 150 KHz, 15

KHz, 1.5 KHz, 150 Hz, 15 Hz, 1.5 Hz, 0.15 Hz RDE control output: 0-10 V (corresponding to 0-10000 rpm), 16-bit, 0.003% accuracy

Digital input/output lines programmable through macro

command

Flash memory for quick software update

Serial port or USB selectable for data communication

Cell control: purge, stir, knock

Maximum data length: 256K-16384K selectable

Real Time Absolute and Relative Distance Display

Real Time Probe and Substrate Current Display

Dual-channel measurements for CV, LSV, CA, DPV,

NPV, SWV, i-t

CV simulation and fitting program, user-defined mechanisms

Impedance simulation and fitting program

Scanning Probe Techniques

SECM Imaging (SECM): constant height, constant current, potentiometric and impedance modes Probe Approach Curves (PAC)

Probe Scan Curve (PSC): constant height, constant

current, potentiometric, impedance, and constant impedance modes

Surface Patterned Conditioning (SPC)

Surface Interrogation SECM (SISECM)

Z Probe Constant Current Control

Sweep Techniques Cyclic

Voltammetry (CV)

Linear Sweep Voltammetry

Tafel Plot (TAFEL)

Step and Pulse Techniques Staircase Voltammetry (SCV)

Chronoamperometry (CA)

Chronocoulometry (CC)

Differential Pulse Voltammetry (DPV)

Normal Pulse Voltammetry (NPV)

Differential Normal Pulse Voltammetry (DNPV)

Square Wave Voltammetry

AC Techniques

AC Voltammetry (ACV)

Second Harmonic AC Voltammetry (SHACV)

Fourier Transform AC Voltammetry (FTACV)

AC Impedance (IMP)

Impedance versus Potential (IMPE)

Impedance versus Time (IMPT)

Galvanostatic Techniques Chronopotentiometry (CP)

Chronopotentiometry with Current Ramp (CPCR)

Multi-Current Steps

Other Techniques Amperometric i-t Curve (i-t)

Differential Pulse Amperometry (DPA)

Double Differential Pulse Amperometry (DDPA)

Triple Pulse Amperometry (TPA)

Integrated Pulse Amperometric Detection (IPAD)

Bulk Electrolysis with Coulometry (BE)

Hydrodynamic Modulation Voltammetry (HMV)

Sweep-Step Functions (SSF)

Multi-Potential Steps (STEP)

Electrochemical Noise Measurement (ECN)

Open Circuit Potential – Time (OCPT)

Various Stripping Voltammetry

Potentiometry

Experimental Parameters

CV and LSV scan rate: 0.000001 to 10,000 V/s, two channels simultaneously

Potential increment during scan: 0.1 mV @ 1,000 V/s

CA and CC pulse width: 0.0001 to 1000 sec

CA minimum sample interval: 1 μs, both channels

CC minimum sample interval: 1 μs

True integrator for CC

DPV and NPV pulse width: 0.001 to 10 sec SWV frequency: 1 Hz to 100 kHz i-t sample interval: minimum 1 μs, both channels

ACV frequency: 0.1 Hz to 10 kHz

SHACV frequency: 0.1 Hz to 5 kHz FTACV frequency: 0.1 Hz to 50 Hz, simultaneously acquire 1st, 2nd, 3rd, 4th, 5th, and 6th harmonics ACV

data

IMP frequency: 0.00001 Hz to 1 MHz IMP amplitude: 0.00001 V to 0.7 V rms

2D and 3D Graphics:

Interactive visualization of SECM surfaces

Color mapping

Laplacian smoothing

Stereoscopic 3D anaglyph imaging

High compatibility: Windows 98 and up, 256 colors

(VGA) and up, no special video card or display required

 

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