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

Abstract

The structure of homogeneous bulk As _x S_{100− 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 AsS_3/2 pyramids and sulfur chains. In the S-rich domain, the existence of quasi-tetrahedral (QT) S = As(S_1/2)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.

Keywords:

• chalcogenide glass
• Raman spectroscopy
• X-ray photoelectron spectroscopy
• structure
• quasi-tetrahedral unit

Acknowledgements

The authors thank Dr. A.C. Miller (Lehigh University) for help with X-ray photoelectron spectroscopy measurements. R. Golovchak acknowledges support from the US National Science Foundation (NSF Grant No. DMR-0409588 and DMR-0844014), for his Research Exchange visit to Lehigh University through the International Materials Institute for New Functionality in Glass (IMI-NFG).