Electronic Structure of the Ultrathin Cs/Si(100)-(2 × 1) and Cs/Si(111)-(7 × 7) Interfaces in the Threshold Energy Region

Abstract

The electronic band structure of the Cs/Si(100)-(2 × 1) and Cs/Si(111)-(7 × 7) interfaces has been studied near the Fermi level at submonolayer coverages. The technique of threshold photoemission spectroscopy with linearly polarized light excitation has been employed. Surface photoemission spectra reveal on Cs-induced band which can be either below the VBM or at the Fermi level, depending on the substrate. Parameters of the Cs band and the change in ionization energy and work function are obtained as a function of Cs coverage. Experimental data provide direct evidence that the Cs/Si(100)-(2 × 1) interface exhibits semiconducting charcter in a great part of the submonolayer range, in contrast to the metallic-like Cs/Si(111)-(7 × 7) interface.