Energy resolved STM mapping of C₆₀ on metal surfaces: A theoretical study

We present a detailed theoretical study of scanning tunneling imaging and spectroscopy of \Csixty on silver and gold surfaces, motivated by the recent experiments and discussion by X. Lu et al. [PRL \textbf{90}, 096802 (2003) and PRB \textbf{70}, 115418 (2004)]. The surface/sample/tip system is described within a self--consistent DFT based tight--binding model. The topographic and conductance images are computed at constant current from a full self--consistent transport theory based on nonequilibrium Green's functions and compared with those simulated from the local density of states. The molecular orbitals of \Csixty are clearly identified in the energy resolved maps, in close correspondence with the experimental results. We show how the tip structure and orientation can affect the images. In particular, we consider the effects of truncated tips on the energy resolved maps.