CHI900B CH Instruments Scanning Electrochemical Microscope

The CH Instruments CHI900B Scanning Electrochemical Microscope was introduced in 19891 as an instrument that could examine chemistry at high resolution near interfaces. It is based on reactions that occur at a small electrode (the tip) as it is scanned in close proximity to a surface. SECM can be employed to obtain chemical reactivity images of surfaces and also in 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. 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 sample and cell holder. The diagrams of 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 ± 10V and the current range is ± 10mA. The instrument is capable of measuring current down to 1 pA.

In addition to SECM imaging, three other modes of operation are provided 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 duration. The Probe Scan Curve mode allows the probe to move in X, Y, or Z direction while the probe and substrate potentials are controlled and currents are measured. The probe can be stopped when 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. The PID control is used in this case. It automatically adjusts the step size to allow fast surface approach yet without 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 used as bipotentiostat, the 2nd channel can be controlled at a independent constant potential, to scan or step at the same potential as the first channel, and to scan with a constant potential difference with the first channel. The 2nd channel works with CV, LSV, CA, DPV, NPV, SWV, and i-t.

The CHI900B SECM is an upgrade from the CHI900 SECM. We changed Inchworm motors to the 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 with travel 80 um with a resolution of 1.6 nm.

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

The other improvements for the CHI900B over the CHI900 include faster data acquisition (25K Hz versus 500Hz), but still maintain the same quality for slow measurements. The iR compensation and a galvanostat are added. A hardware current re-zero circuitry is also added. The low-pass filter will have lower cutoff frequencies. Other improvements will be flash memory and Serial/USB communication.