The scanning Kelvin microscope with voltage modulation: a new principle to image discrete surface potentials†

The historical development of a scanning microscope based upon the Kelvin probe is given. The aim of this instrument is the imaging of the spatial distribution of the contact potential difference between the miniaturised probe and the surface of a sample. This was possible on the micrometer scale only after finding the means to measure and control the distance between the probe and the surface. Furthemore, the contact potential difference was measured directly by compensating the contact potential difference as proposed by Lord Kelvin. © 1997 John Wiley & Sons Ltd.