Effect of the microscopic electronic states of the tip on the scanning tunneling microscopy image

Abstract

Based on the first-principles electronic state theory of the sample/tip system, the tunneling conductances for Si(100) and Si(111) surfaces with the W tip are calculated numerically with a cluster model approach. The tunnel current derived from the tunnel Hamiltonian formalism is expressed by the linear combination of atomic orbital scheme with the norm-conserving pseudopotentials, which makes numerical simulation for STM image feasible from the data of electronic states of the separated tip and sample system. The W8 cluster is studied as a model of the (111) protrusion of the W tip. Four active orbitals in an energy range of 1.3 eV which predominantly contribute to the tunneling conductance are found. All of them mainly comprise the dzz and pz orbitals of the tip having a large amplitude at the apex atom with the lobe directed towards the surface.