ELECTRON-DIFFRACTION EFFECTS ON SCANNING TUNNELING SPECTROSCOPY

This paper provides further evidence for the relationship between dens ity of states or local density of states (LDOS), and current-voltage ( I-V) curves as obtained from scanning tunneling spectroscopy. a model that takes into account voltage-dependent wave functions is proposed. This model calculates both quantities and compares them. Current-carry ing electrons are considered to come from the bulk of the tip and towa rds the tunneling region. From there, the electrons are diffracted bac k to the tip and forward into the sample. This scattering process is s et within the framework of tight binding by providing boundary conditi ons. The method allows one to solve the steady-state problem, thus per mitting the extraction of information even when the tip-sample distanc e is small (<1 Angstrom). This is particularly important since it can probe regimes beyond the applicability of Bardeen approximation. For a tungsten tip and a silicon sample, the I-V curves closely fellow the LDOS. On the other hand, the conductance-voltage curves present jumps that coincide with the Van Hove singularities of the semiconductor.