Valence band x-ray photoelectron spectroscopic studies of phosphorus oxides and phosphates

Abstract

This article reports the results of a continuing study focused on preparing novel surface chemistries on metal surfaces and the study of phosphorus oxygen-containing compounds. In this article we demonstrate the ability of valence band photoelectron spectroscopy to be able to distinguish between three different crystal structures of phosphorus pentoxide, with the differences interpreted using band structure calculations. The spectral differences are highlighted by the use of difference spectra, with the principal features of the difference spectra being reproduced by difference spectra generated from the calculated spectra. Core-level studies are of little use for differentiating between such similar compounds, while valence band photoemission has been found to be particularly effective at identifying subtle differences in surface chemistry. The ability of valence band x-ray photoelectron spectroscopy to distinguish between different phosphate species is exploited to investigate the formation of oxide-free phosphate, phosphite, hypophosphite, and acid phosphate films. These thin (<100 Å) oxide-free films are studied using valence band photoemission and interpreted using both band structure and cluster calculations which show the films to contain different types of phosphate species.