Corrosion by Scanning Probe Microscopy

In addition, a bipotentiostat is used to control the tip potential with respect to the surface and independent of control of the surface potential with respect to the reference electrode. The tip potential E, is given by E, = Eg + E , where Eg is the bias potential that generates the tnnneling current between tip and surface, and E (a vital variable not typical of other applications of STM and AFM) is the potential of the surface relative to the reference electrode. 

Although oxides are generally considered to be insulators, it is sometimes possible to monitor the surface of an oxide film by STM. Basically two mechanisms that explain the imaging of oxide surfaces by in situ STM are considered  

The oxide film may be very thin, involving only a few monolayers, so that electron tunneling through the film may occur. 

Surfaces of transition metals that have been passivated by electrochemical oxidation or by the action of chemical oxidizing agents have been extensively investigated by in situ STM/AFM these investigations 

Most of the early corrosion studies by in situ methods were directed toward elucidation of the mechanism of pitting corrosion, the nature of the transition from the potential region for passivation to the pitting 

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