Kelvin probe force microscopy (KPFM), also known as surface potential microscopy, is a noncontact variant of AFM that was invented in 1991 by Nonnenmacher and coworkers.

Principle

KPFM is a scanning probe method where the potential offset between a probe tip and a surface can be measured using the same principle as a macroscopic Kelvin probe. Using KPFM, images can be recorded that contain information on the local work function or local contact potential difference between tip and sample. The cantilever in the AFM is a reference electrode that forms a capacitor with the surface, over which it is scanned laterally at a constant separation. The cantilever is not piezoelectrically driven at its mechanical resonance frequency as in normal AFM although an alternating current (AC) voltage is applied at this frequency.

SKPFM generates a map of the potential distribution across a sample with a resolution of at least 100 nm. Furthermore, the open circuit potential of various pure metals in solution is linearly related to the Volta potential value measured in air immediately after exposure. SKPFM is a useful tool to assess the practical nobility of a surface. This technique has been successfully applied to the heterogeneous microstructures to provided clear evidence regarding the shape, position, compositional inhomogeneities and local practical nobility of copper-rich intermetallic particles. KPFM, allows us to obtain not only topographic images but also potential images and the work function of surfaces can be observed at atomic or molecular scales. The work function relates to many surface phenomena, including catalytic activity, reconstruction of surfaces, doping and band-bending of semiconductors, charge trapping in dielectric and corrosion. The map of the work function produced by KPFM gives information about the composition and electronic state of the local structures on the surface of a solid.