Low-energy excitation in As2S3 glass studied by inelastic X-ray scattering

The low-energy excitation of As2S3 glass was measured for the first time by high-resolution inelastic X-ray scattering to obtain an additional insight into the Boson peak. The experiments were performed at room temperature at Q = 1.5–63.6 nm−1 and ω = −40–50 meV. Besides an acoustic-like collective mode in the low-Q region, the low-energy excitation was clearly observed above 20 nm−1 around 3 meV, whose intensity increases with increasing Q and exhibits a maximum at 39 nm−1 in coincidence with the third peak of the structural factor S(Q). The observations suggest that the low-energy excitation of As2S3 glass at Q > 20 nm−1 may originate from localized vibrational soft modes associated with the dynamical correlation of S atoms with the nearest-neighboring As atoms.