First-principles study of the atomic-scale structure of clean silicon tips in dynamic force microscopy

Abstract

In the present work we report on our ab initio pseudopotential calculations based on density functional theory to investigate the atomic-scale behavior of clean silicon tips in noncontact atomic force microscopy (AFM). The AFM tip structures are modeled by silicon clusters with [111] and [001] termination. The structural changes induced by their reciprocal interaction are investigated by calculating the short-range chemical forces during a vertical approach and retraction of one silicon tip on top of another tip. For a specific tip geometry with [111] termination, the theoretical force curves exhibit an hysteretic behavior only at the first approach and retraction cycle. The absence of this effect at the second scan is due to sharpening of the initially blunt tip via short-range chemical forces. A specific finger print of the [001]-oriented tip is an energy dissipation induced by a breaking and formation process of a chemical bond between two silicon atoms under its apex atom.