Electrochemical Scanning Probe Microscopy

Scanning probe microscopy (SPM) encompasses a broad suite of closely related techniques for imaging surfaces. In SPM, a probe with an ultrafine tip is brought very close to the surface under study. Depending on the nature of the tip and the particular mode being used, interactions between the surface and the tip lead to measurable changes in the system. The tip is itself mounted on a sensitive cantilever; forces that act on the tip deflect the cantilever, and/or alter its resonant frequency. By measuring that signal, SPM can analyze physical, electrical, magnetic and other properties of the surface at the atomic scale. Finally, these measurements can be built up into an image of the sample as the tip is scanned across the surface.

There are dozens of individual techniques in SPM, and more continue to develop and find applications. One of these techniques is electrochemical SPM (ECSPM), in which SPM imaging is carried out in an electrochemical cell. The SPM probe is submerged in the electrolytic liquid of the cell. Typically, the sample acts as one electrode in the electrochemical reaction, while the SPM tip itself is the other active electrode. Through the use of a reference electrode and the control electronics, the SPM system provides control over the electrochemical conditions of the cell with a potentiostat or galvanostat to ensure constant potential or constant current. The ECSPM can then simultaneously measure electrochemical data and imaging data.

Applications for ECSPM typically include analyses of materials and processes that involve electrochemistry to some degree. Electroplating of metals is one such application, where ECSPM can be used to physically measure the effect of different conditions in the deposition process. Corrosion, which is essentially an unwanted electrochemical reaction, is another process that can be studied using ECSPM. The use of SPM allows researchers to study the process at the atomic scale in steel and other materials and components subject to corrosion. Another established application for ECSPM is the analysis of batteries and battery materials. This extends into more modern applications involving hydrogen fuel cells, which again are essentially electrochemical in nature. There are also life science applications involving biological membranes, ionic transport and similar phenomena.

Relatively few vendors are involved in ECSPM. Veeco, which is the leader in general SPM for lab and process use, offers several different options for ECSPM. Agilent, which entered the SPM market with its acquisition of Molecular Imaging (see IBO 11/31/05), is also strong in ECSPM. A handful of smaller vendors also offer ECSPM; among them are Nanonics, Sensolytics and Heka. Most instruments are general SPMs that have been configured with an electrochemical cell and other accessories, but Heka’s ElProScan instrument, which debuted late in 2006, is designed specifically for ECSPM. Due to limited applications, the total market for ECSPM was less than $5 million in 2007.

ECSPM at a Glance:

Leading Suppliers

• Veeco Instruments

• Agilent Technologies

• Nanonics

Largest Markets

• Metals

• Electronics

• Fuel Cells

Instrument Cost

• $75,000–$200,000

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