4. Near-field probes

Scanning probe microscopes, developed since the 1980s, have in common the use of an extremely fine tip brought close to a surface, whose position is scanned along the surface to obtain a two-dimensional mapping of a specific property related to the tip-surface interaction (figure 9 , ). This property may be a tunnel current between an electrically polarized tip and a conductive surface (in the case of STM), or a force between the tip and the surface (in the case of AFM). These techniques have recently made it possible to obtain direct spatial images of the phenomena at play at atomic...