CONTRAST MECHANISM IN NONCONTACT AFM ON REACTIVE SURFACES

Total-energy pseudopotential calculations are used to study the imagin g process in non-contact atomic force microscopy on Si(111) surfaces. The atomic resolution seen in the experiments is attributed to the ons et of covalent bonding between a localised dangling bond on the atom a t the apex of the tip and the dangling bonds on the adatoms in the sur face. This interaction dominates the force gradients, which drive the frequency changes used to create the experimental images. Force vs. ti p displacement curves provide information about the optimum operation range and show the importance of the relaxation of the tip apex and su rface atoms in the understanding of the damping images. (C) 1998 Elsev ier Science B.V.