Confined acoustic modes and spectral determination of network connectivity: Raman signatures of nanometric structure in g-GexSe1−x

Low-temperature Raman scattering results are presented on three glass compositions of GexSe1−x (15, 20, and 27 At. Ge%), and conciled with their reported structural data. The acoustic range is marked by the absence of Boson peak, and features discrete modes corresponding to nanometric dynamic aggregates. First sharp diffraction peak (FSDP) in structure factor S(k), due to Ge-Ge correlations brought about by shared Ge[Se1/2]4 tetrahedra medium-range structures, signifies 3D networking of Se-chains. A measure of volume-fraction of these entities determined from the FSDP area, and their number density ρMRS∝(k3Area)FSDP is found to relate directly to the network connectivity, defined from optical Raman spectra in terms of the degree of cross-linking of Se-chains.