Structure of Se-rich As-Se glasses by high-resolution x-ray photoelectron spectroscopy

To establish the validity of various proposed structural models, we have investigated the structure of the binary AsₓSe_100-x chalcogenide glass family (x40) by high-resolution x-ray photoelectron spectroscopy. From the composition dependence of the valence band, the contributions to the density of states from the $4p$ lone pair electrons of Se and the $4p$ bonding states and $4s$ electrons of Se and As are identified in the top part of the band. The analysis of Se $3d$ and As $3d$ core-level spectra supports the so-called chain crossing model for the atomic structure of Se-rich AsₓSe_100-x bulk glasses. The results also indicate small deviations (~3--8%) from this model, especially for glass compositions with short Se chains (25<x40). For example, the presence of As-As homopolar defect bonds in the stoichiometric As₄₀Se₆₀ and of Se-Se-Se fragments in a glass with composition $x=30$ is established.