Scanning Electrochemical Microscopy

Abstract Scanning electrochemical microscopy (SECM) is one of a number of scanning probe microscopy (SPM) techniques that arose out of the development of the scanning tunneling and atomic force microscopes. Scanning probe microscopes operate by scanning, or “rastering,” a small probe tip over the surface to be imaged. The SECM tip is electrochemically active, and imaging occurs in an electrolyte solution. In most cases, the SECM tip is an ultramicroelectrode (UME), and the tip signal is a Faradaic current from electrolysis of solution species. Some SECM experiments use an ion‐selective electrode (ISE) as a tip. In this case, the tip signal is usually a voltage proportional to the logarithm of the ion activity in solution. The use of an electrochemically active tip allows an extremely versatile set of experiments, with chemical sensitivity to processes occurring at a substrate surface as an essential aspect. A requirement of SPM techniques is that the signal from the tip must be perturbed in some reproducible fashion by the presence of the surface. One of the two methods used in SECM to provide this signal change is known as the “feedback” mode. Feedback can provide topographic images of either electronically insulating or conducting surfaces. A unique advantage of SECM is the ability to design experiments in which the mediator interacts with the substrate surface to provide chemical and electrochemical activity maps at micrometer and submicrometer resolution.