Study of the local electrical properties of metal surfaces using an AFM with a conducting probe

The performances of coating materials for electrical contact elements are more and more often investigated through various means. We report here a new method we have developed for a few years in our lab, which consists in performing localized resistance measurements over a surface by means of an atomic force microscope (AFM) with a conducting probe. This technique enables us to simultaneously obtain a cartography of the surface roughness and of the local conductance within a given microscopic area of a sample with nanometer scale resolution. Although the elaboration of suitable probes remains an open problem, some convincing images of metal surfaces have already been obtained, revealing occasionally surprising features. It can be observed for instance that the local resistance values can vary by several orders of magnitude between two adjacent grains. Calculations performed from the measurements allow one to clarify the mechanical nature of the tip/surface nanocontact and hence to determine the most probable transport process according to the range of resistance considered