On the origin of the Boson peak in the Raman scattering spectrum of As2S3 glass

The origin of the low energy vibrations, which give rise to the Boson peak of glasses, is still poorly understood. This paper presents a Raman study of H-doped and O-doped vitreous As2S3, with particular emphasis on the frequency region below 100 cm−1. We found that while doping with hydrogen up to 1660 ppm does not affect the Raman spectrum of As2S3 glass, similar doping with oxygen results in an increase of the intensity of the Boson peak. Doping with oxygen also results in an increase in intensity of the 310 cm−1 peak, due to asymmetric vibrations of the glass network. A comparative study of the Raman spectra of glassy and crystalline As2S3 indicates a matching of the broad glassy Boson peak with the narrow crystalline peak at 26 cm−1. We suggest that asymmetric optical vibrations of the AsS3 pyramids with respect to each other may be related to the Boson peak. While the 310 cm−1 peak is due to vibrations of the pyramids involving intramolecular (covalent) primary bonds, the Boson peak is suggested to originate, in part, on a translatory vibration involving intermolecular (van der Waals) secondary bonds between the sulfur atoms and their surroundings.