PROPAGATOR THEORY OF SCANNING-TUNNELING-MICROSCOPY

We develop a quantum mechanical scattering theory for electrons which tunnel out of (or into) the tip of a scanning tunneling microscope. Th e method is based on propagators (or Green functions) for quasistation ary scattering with the tip being an electron source (or sink). The re sults for the tunneling current generalize the Tersoff-Hamann approach of scanning tunneling microscopy. In contrast to previous calculation s the present theory relates the tunneling current to the potential di stribution of the sample. Expressions for the corrugation are availabl e through a simple perturbation expansion scheme. Analytical model cal culations are presented and compared with existing results.