Structural model of homogeneous As-S glasses derived from Raman spectroscopy and high-resolution XPS

The structure of homogeneous bulk AsxS100-x (25 x 42) glasses, prepared by the conventional rocking-melting-quenching method, was investigated using high-resolution X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. It is shown that the main building blocks of their glass networks are regular AsS3/2 pyramids and sulfur chains. In the S-rich domain, the existence of quasi-tetrahedral (QT) S = As(S1/2)3 units is deduced from XPS data, but with a concentration not exceeding 3-5% of total atomic sites. Therefore, QT units do not appear as primary building blocks of the glass backbone in these materials, and an optimally-constrained network may not be an appropriate description for glasses when x 40. It is shown that, in contrast to Se-based glasses, the 'chain-crossing' model is only partially applicable to sulfide glasses.