CHI900B/910B Scanning Electrochemical Microscope               <<<Home

 

                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  Trapping and electrochemical detection of single molecules with the SECM has also been reported.

                The CHI900B 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 one nanometer but it allows a maximum traveling distance of several centimeters. The potential control range of the bipotentiostat is 10 V and the current range is 10 mA. The instrument is capable of measuring current down to 1 pA.

                In addition to SECM imaging, three other modes of operation are available for scanning probe applications: Surface Patterned Conditioning, Probe Scan Curve, and Probe Approach Curve. Surface Patterned Conditioning allows user to edit a pattern for surface conditioning by controlling the tip at two different potentials and durations. The 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 in searching for an object on the surface and determining approach curves. The Probe Approach Curve mode allows the probe to approach the surface of the substrate. It is also very useful in distinguishing the surface process, using PID control. The step size is automatically adjusted to allow fast surface approach, without letting the probe touching the surface.

                The CHI900B is designed for scanning electrochemical microscopy, but many conventional electrochemical techniques are also integrated for convenience, such as CV, LSV, CA, CC, DPV, NPV, SWV, i-t, DPA, DDPA, TPA, and CP. When it 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, SWV, and i-t.

                 The CHI900B SECM is an upgrade from the CHI900 SECM. We replaced the old Inchworm motors with a combination of stepper motors and a XYZ piezo block. The stepper motor can travel 25 mm with a resolution of 100 nm. The XYZ piezo block can travel 80 m with a resolution of 1.6 nm.  There is an option for the closed-loop piezo control to improve linearity and reduce hysteresis (model CHI910B).

                With the combination of stepper motor and XYZ piezo block, the 900B can obtain about the same resolution as with the Inchworm motors, but with much better repeatability. There will be no discontinuity problem.

                The other improvements for the CHI900B over the CHI900 include faster data acquisition (25 kHz versus 500 Hz), that maintains the same quality for slow measurements. The iR compensation and a galvanostat have been added, as well as hardware current re-zero circuitry. The low-pass filter will have lower cutoff frequencies. FLASH memory capabilities and Serial/USB communication are currently under development.

 

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.

 

Diagram of Scanning Electrochemical Microscope

 

 

                                    Cell/Sample Holder

 

 

Bipotentiostat (top) and Motor Controller Front View

 Bipotentiostat (top) and Motor Controller Rear View

 

 

Specifications, Techniques, and Applications

 

CHI900B SECM Specifications

 

Nanopositioner:

     X, Y, Z resolution:     1.6 nm

     X, Y, Z total distance:     2.5 cm

     Stepper motor:  2.5 cm travel distance with 0.1 um resolution, open loop

     Piezo XYZ stage:   80-100 um travel distance with 1.6 nm resolution, open loop control with the CHI900B, closed-loop control with the CHI910B

Bipotentiostat:

     Probe Potential:     10 V

     Substrate Potential:     10 V

     Compliance Voltage:     12 V

     3- or 4-electrode configuration

     Reference electrode input impedance:  1e12 ohm

     Current Sensitivity:     10-12 A/V to 10-3 A/V

     Maximum Current:     10 mA

     External signal recording channel

     ADC Resolution:    20-bit @ 1 kHz, 24-bit @ 10 Hz

     Secondary ADC:    25K sampling rate @ 16-bit Galvanostat:

     Current range:    10 mA

Experimental Parameters:

     CV and LSV scan rate:  0.000001 to 25 V/s

     CC and CA pulse width:  0.001 to 1000 sec

     True integrator for CC

     DPV and NPV pulse width:  0.001 to 10 sec

     SWV frequency:  1 to 10 kHz

     Automatic potential and current zeroing

     Automatic and manual iR compensation

     Current low-pass filters, covering 8-decade frequency range, Automatic and manual setting

     RDE control output:  0-10 V (corresponding to 0-10000 rpm)

     Flash memory for quick software update

     Serial port or USB port selectable for data communication

 

Other Features:

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

Cell control: purge, stir, knock

Automatic potential and current zeroing

Current low-pass filters, covering 8-decade frequency range, Automatic and manual setting

RDE control output:  0-10 V (corresponding to 0-10000 rpm)

Flash memory for quick software update

Serial port or USB port selectable for data communication

 

Techniques

 

Scanning Probe Techniques

  SECM Imaging (SECM) : constant height, constant current,   potentiometric modes

  Probe Approach Curves (PAC)

  Probe Scan Curve (PSC) : amperometric, potentiometric and constant current modes

  Surface Patterned Conditioning (SPC)

 

Sweep Techniques

  Cyclic Voltammetry

  Linear Sweep Voltammetry

 

Step and Pulse Techniques

  Staircase Voltammetry (SCV)

  Chronoamperometry (CA)

  Chronocoulometry (CC)

  Differential Pulse Voltammetry (DPV)

  Normal Pulse Voltammetry (NPV)

  Square Wave Voltammetry (SWV)

 

Galvanostatic Techniques

Chronopotentiometry (CP)

Chronopotentiometry with Current Ramp (CPCR)

  Multi-Current Steps (ISTEP)

  Potentiometric Stripping Analysis (PSA)

 

Other Techniques

  Amperometric i-t Curve (i-t)

  Differential Pulse Amperometry (DPA)

  Double Differential Pulse Amperometry (DDPA)

  Triple Pulse Amperometry (TPA)

  Bulk Electrolysis with Coulometry (BE)

  Sweep-Step Functions (SSF)

  Multi-Potential Steps (STEP)

  Various Stripping Voltammetry

  Potentiometry

  Open Circuit Potential Time

 

Applications

  Electrode surface studies

  Corrosion

  Biological samples

  Solid dissolution

  Liquid/liquid interfaces

  Membranes

 

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SECM book by A. Bard

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