1ST-PRINCIPLE SIMULATION OF SCANNING TUNNELING MICROSCOPY SPECTROSCOPY WITH CLUSTER-MODELS OF W, PT, TIC, AND IMPURITY ADSORBED TIPS

Tunneling current and conductance in scanning tunneling microscopy/spectroscopy (STM/STS) are calculated for various kind of tips using first-principle local density approximation (LDA) method with the tunneling-Hamiltonian formalism. As models of tip, tungsten cluster, platinum cluster, carbon adsorbed tungsten cluster, and titanium carbide cluster are used. Graphite surface is used for the simulation. STM image and qualitative feature of STS spectrum mainly depend on the arrangement of atoms at the tip apex and not so much affected by the atomic compositions of the tip because the most of tunneling current comes from a single or a few atom at the tip apex.