EFFICIENT METHOD FOR THE SIMULATION OF STM IMAGES - I - GENERALIZED GREEN-FUNCTION FORMALISM

We present a theoretical formalism specially suited for the simulation of scanning tunneling microscopy (STM) images. The method allows for a realistic description of the STM system, taking fully into account i ts three-dimensional nature. Bias effects may also be considered since the theory is not restricted to the low-bias limit. The starting poin t is the previously applied Landauer-Buttiker formula, which expresses the current at the STM junction as a sum of transmission coefficients linking eigenstates at each electrode. The transmission coefficients are directly obtained from the scattering matrix which is, in our appr oach evaluated through Green-function techniques; in particular, we em ploy the surface Green-function matching (SGFM) method to find the Gre en function at the interface, and explicitly derive simple expressions for the current. Additionally, the formalism goes beyond the elastic- scattering limit by considering inelastic effects via an optical poten tial. We also present a method to analyze the current in terms of cont ributions arising from individual atomic orbital interactions and thei r interference with other interactions. To this end, the SGFM method i s replaced by a first-order expansion of the interface Green function. [S0163-1829(47)04648-1].