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Scanning Electrochemical Microscopy (SECM)

Photograph of SECM setup.

Figure 1. The basic setup of an SECM can be seen above where UME is ultramicroelectrode, RE is reference electrode, and CE is counter electrode.

The SECM was invented by Allan J. Bard in 1989 where the use of the newly developed ultramicroelectrodes was used in tandem with stepper motors to create a scanning system. The development of the system went on to add a second potentiostat system to the stage of the SECM and subsequent development of the bi-potentiostat. This system can be used in many different modes. Two particular modes of interest are the constant current scanning technique, which can be used to scan the surface of a conductive material, and provide a topographical map of the surface with resolution in the z axis around 100 nm, and the constant voltage scanning technique, which can be used to create a topographical map based on the varying current between the tip and surface of the sample. These techniques can both provide data on how the height of the surface of a material is changing over the entire surface with great detail1.

The SECM has a wide range of use in the material science industry. It can be used for examining the microstructure of a solid or liquid interface, ionic dissolution, electro catalysis, and many other applications. The microscope consists of an ultramicroelectrode that is used as a scanning tip that is brought near the sample to be investigated. The sample itself is set on a stage that also can act as an electrode where different potentials can be applied to the base. These two electrodes are run by a bi-potentiostat that can control independent parameters on each of the electrodes. There is a set of stepper motors as well as piezo motors that can control movement in the x, y, and z directions1. These motors also monitor the location of where the tip of the ultramicroelectrode is in correlation to the stage. You can see the basic setup of an SECM can be seen in Fig. 12.

This instrumentation is used in the corrosion lab to investigate different types of corrosion. The resolution of scanning with the ultrmicroelectrode will be utilized to perform local corrosion analysis on various metal systems. This can be used to map local sites for pitting precursors in steel or local corrosion analysis of different heat zones resulting from weld joints. Corrosion of different interfaces such as grain boundaries and inclusions within the metal can also be examined with great detail.