Quantum theory of scanning tunneling microscopy and spectroscopy and its application to surface electronic processes

Abstract A theoretical simulation of STM/STS has been performed for various surface systems, based on the first-principles local density functional (LDA) calculation. Cluster models made of 10–20 atoms are utilized for the tip, and slab models with several atomic layers are adopted for the sample surface. The tunnel current is almost concentrated on a single apex atom, if the other atoms on the top of the tip are not located on the same level. In such a case the STM image is normal, with atomic resolution. However, if the apex of the tip is formed by more than one atom, abnormal images tend to be formed. We verify this feature by numerical results for graphite, Si(100), and Si (111)/Ag surfaces, and discuss the light emission from STM, based on realistic calculations of the electronic states of the tip/sample systems.