Unoccupied electronic states of 2D Si on Ag--Si(111)

Abstract

Optimizing substrate characterization to grow 2D Si layers on surfaces is a major issue toward the development of synthesis techniques of the promising silicene. We have used inverse photoemission spectroscopy (IPES) to study the electronic band structure of an ordered 2D Si layer on the -Ag/Si(111) surface (-Ag). Exploiting the large upwards band bending of the -Ag substrate, we could investigate the evolution of the unoccupied surface and interface states in most of the Si band gap. In particular, the k ∥-dispersion of the -Ag free-electron-like S 1 surface state measured by IPES, is reported for the first time. Upon deposition of ∼1 ML Si on -Ag maintained at ∼200 °C, the interface undergoes a metal-insulator transition with the complete disappearance of the S 1 state. The latter is replaced by a higher-lying state U 0 with a minimum at 1.0 eV above E F. The origin of this new state is discussed in terms of various Si 2D structures including silicene.