Holomb R. Photon energy-dependent vibrational spectroscopy of As(Ge)xS100-x glasses combined with first-principles calculations of As(Ge)nSm clusters

The thesis is dedicated to spectroscopical study of nanostructure formation processes in glassy arsenic and germanium sulphides and their influence on optical properties of glasses. The peculiarities of absorption edge of g-AsxS100-x and technologically modified g-GeS2(Tx,Vy) glasses were explained by results of first-principles calculations of electronic structure of As(Ge)nSm clusters. The polymorph transformations of realgar molecules during excitation of the micro-Raman spectra of g-AsxS100-x (х?40) glasses by lasers with photon energy (Eex) larger than 1.96 eV were detected. In the spectra of sulphur-rich g-AsxS100-x excited with Eex=2.41 eV the transformations of S8 rings to chain-like sulfur Sn were observed. The nanoclusters based on SGe3/3 s. u. were detected in the structure of g-GeS2 and defined as structurally different component from the basic structure of the glass. The resonance effects in the micro-Raman spectra of g-GeS2 were found to be related to the presence of edge-shared GeS4 bi-tetrahedra in the glassy matrix. The dependence of "Boson" peak (BP) characteristics in the low-frequency Raman spectra of glasses on concentration (с-AsxS100-x) and synthesis condition (с-GeS2) was investigated. The low frequency vibration modes of chain-like clusters with length of ~1 nm. calculated ab initio indicate the possibility for collective torsion vibrations to contribute in spectral region of BP in the Raman spectra of ChGS.