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 µm 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

Specifications, Techniques, and Applications

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SECM book by A. Bard

Download CHI900 demo software             CHI900 Brochure (old brochure but contains some useful application notes and references)