First-principles investigation of tip-surface interaction on a GaAs(110) surface:: Implications for atomic force and scanning tunneling microscopies

Ab initio pseudopotential total energy techniques are used to investigate the tip-surface interaction in atomic force microscopy on a GaAs(110) surface with a Si tip. Our simulations show significant surface relaxation effects in the near contact region, which lead to a complicated behavior of the total energy and force curves. In particular, the tip-induced displacement of the Ga atoms can exceed 1 Angstrom even in the attractive force region, leading to hysteresis in the energy and force curves. These large tip-induced relaxations of the surface Ga atoms provide a natural explanation to the simultaneous imaging of both anions and cations in recent near-contact scanning tunneling microscopy experiments on this surface. We show that, for tip-surface distances where the surface topography remains unchanged and for a charge neutral Si tip, only the anion sublattice can be resolved in noncontact atomic force microscopy. Close to contact, our simulations prove that, even for atomically sharp tips (1) there is a significant contribution to the total interaction from tip atoms different from the apex atom; (2) large lateral (bonding) forces on the tip apex may develop and change the tip structure well before significant normal repulsive forces appear. [S0163-1829(99)09939-7].