STM/STS and photoemission study of Ag thin films on Ga/Si(111) ([formula omitted])R30°

Abstract

Silver thin films have been formed by room temperature deposition of Ag on a Ga/Si(111) (3×3)R30° surface. Scanning tunneling microscopy and spectroscopy (STM/STS) have been used to study both the clean Ga/Si(111) (3×3)R30° surface and Ag films with different coverages. For the film formation, Ag first grows into 2D islands on Ga/Si(111) (3×3)R30°. The first layer of the islands forms atomic lines with three-fold symmetry in the 1 × 1 direction of the underlying Si(111) substrate. From a 2 ML coverage, the growth becomes layer-by-layer mode. STS measurements have been performed on Ag films with different coverages in order to investigate their electronic structures. Between 2–4 ML, the STS spectra reveal 2 and 3 peaks below the Fermi level. These peaks move towards the Fermi level with increased film thicknesses and thus share the same behavior as those of quantum well states (QWSs). The energy positions of the peaks have been compared with valence band photoelectron spectra in order to assign them to various parts of the QWSs. In addition, the photoemission results also confirm the existence of QWSs for a 2 ML Ag film on Ga/Si(111) (3×3)R30°.