AsxSe1-x system (0.20≤x≤0.57): EXAFS study of the glass region

The authors have examined the local structure of the AsxSe1-x(0.20≤x≤0.57) system by Extended X-ray Absorption Fine Structure (EXAFS) measurements. The two atoms have been successively excited, with both showing a unique contribution for their radial distribution function. At the arsenic K edge, the one shell fit is consistent with the presence of pyramidal AsSe3 building units, bridged by selenium atoms, as indicated by the data analyzed at the selenium K edge. The evolution of the Debye-Waller factor at the arsenic K edge is discussed as well as the variation of the Se-As distance observed at the selenium edge, both phenomena depending on the arsenic composition. These effects can be explained by the existence of some As-As and Se-Se homopolar bonds in the arsenic- and selenium-rich glasses, respectively. The Fourier transform magnitude from the data collected at 35 K at the arsenic K edge does not show other shells than the first As-Se principal peak. The qualitative interpretation of the XANES part of the absorption spectra is in good agreement with the present structural investigation