Role of Covalent Tip-Surface Interactions in Noncontact Atomic Force Microscopy on Reactive Surfaces

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Abstract
Total-energy pseudopotential calculations are used to study the imaging process in non-contact atomic force microscopy on Si(111) surfaces. The atomic resolution seen in some parts of the experimental images is attributed to the onset of covalent bonding between a localized dangling bond on the atom at the apex of the tip and the dangling bonds on the adatoms in the surface. This interaction dominates the force gradients, which drive the frequency changes used to create the experimental images, and provides a mechanism for atomic resolution imaging on reactive surfaces.