Determination of effective energy loss functions and x-ray photoelectron spectroscopy source functions for Si 2p photoelectrons from clean Si(111), oxygen-adsorbed Si(111) and SiO2 surfaces

Abstract

Effective energy loss functions for Si 2p photoelectrons were determined for the thermally cleaned Si(111), oxygen-adsorbed Si(111) and SiO2 surfaces by the analysis of the reflection electron energy loss spectroscopy (REELS) spectra using the extended Landau theory. The background subtraction of the Si 2p x-ray photoelectron spectroscopy (XPS) spectra using these effective energy loss functions has enabled the XPS source functions to be derived with considerable effectiveness. This result has indicated that the effective energy loss functions derived for the clean Si(111) surface are significantly affected by the oxygen adsorption and the XPS source functions from the clean and oxygen-adsorbed Si(111) surfaces show a small hump due to the chemical shift by the oxygen adsorption appearing at the tail of the lower kinetic energy side of the Si 2p peak from the oxygen-adsorbed Si surface. On the SiO2 surface, the analysis of the REELS spectrum has yielded the effective energy loss function reflecting the fine structures which were not as clearly observed in the measured REELS spectrum. The Si 2p XPS source function determined for the SiO2 surface at two different measuring geometries showed very good agreement with each other. This study strongly suggests that the present analysis is very informative for the study of the initial oxidation of the silicon surface.