Dipole tip model investigation of resonance effects in scanning tunneling microscopy

The distribution of the tunneling current in the semiclassical mode of operation of the scanning tunneling microscope is studied using an axially symmetric 3-D tip. The tip is taken as an equipotential of a dipole, thus giving an analytical form for the potential and the field lines between the tip and the surface, with the latter taken to be atomically flat and corresponding to the zero equipotential plane. Field emission resonance calculations are made, allowing conductance and tip-to-surface separation to be determined as functions of bias voltage at constant current. Results are compared with the measurements of Becker, Golovchenko, and Swartzentruber [Phys. Rev. Lett. 55, 987 (1985)]. (C) 1996 American Institute of Physics.