Seminars Archive

Self-organization and induced processes in chalcogenide nanolayers: experimental and theoretical studies

Abstract
The structure of amorphous thin As₂S₃ and As₂Se₃ nanolayers were investigated by means of photoelectron and Raman spectroscopy including high surface sensitive methods, SRPES and SERS. Results show that the surface of amorphous As₂Se₃ nanolayers is a network with mainly AsSe₃ pyramidal ring and/or chain morphology. Only the small amount of S-S (bridges) and As-As (As₄S₃) was detected. On the contrary, the deeper amorphous As₂S₃ layers contain significant amount of As-As bonds characteristics of realgar-like As₄S₄ molecules. Near bandgap laser irradiation of As₂Se₃ film lead to drastic changes in the structure of both surface and deeper layers and to As-O bonds (oxidation to As₂O₃) formation. There is no sign detected of intensive pararealgar formation at the surface. The relative contribution of the As, Se, C and O atoms in different chemical states to the whole As 3d, Se 3d, C 1s and O 1s signals, its structural origins as well as their relation to the As₄₀Se₆₀ surface and subsurface nanolayers structure before and after laser irradiation is analyzed and discussed in detail. An atomic model of induced structural changes on the surface of As₄₀Se₆₀ nanolayers under ambient conditions and after laser irradiation in air is proposed. The local and medium range structures, electronic and optical properties of binary Ge-S and Ge-Se non-crystalline systems were also investigated by means of photon energy dependent Raman spectroscopy and ab initio DFT calculations.