Structural transformations on the As<sub>X</sub>S<sub>100-X</sub>: X-ray photoelectron and electron microscopy investigations

Abstract

Background: The research of chalcogenide glassy (ChG) materials formed a ge-neral understanding of electronic phenomena in disordered structures. The numerous investigations of their fundamental physical and chemical properties have been already studied. Unique structural, electronic and optical properties determined their various applications. Photosensitivity is the main feature of chalcogenide glasses for fabrication phase-change memory, tailoring direct waveguides and grating patterning. Materials and methods: Amorphous As x S 100-x (x = 40, 45, 50) were prepared by thermal vacuum evaporation from appropriate bulk glass powders onto silicon wafers. The surface chemical composition and structure of material were investigated by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) on as-deposited ChG thin film samples and samples being illuminated by near bandgap laser (l = 532 nm, photon energy ~ 2.4 eV, p = 25 mW), under ambient conditions. Results: All spectra of S 2p electron core level were fitted by two components: S-As 2 and S-SAs s.u. The As 3d core level spectra of As 40 S 60 and As 50 S 50 nanolayers contains As-S 3 , As-S 2 As and As-SAs 2 s.u. As 45 S 55 structure is characterized by the presence of the fourth, As-As 3 component apart from previous mentioned three. Near-bandgap laser light illumination of As x S 100-x (x = 40, 45, 50) samples causes decreasing of the contribution of components with the homopolar S-S bonds in all samples, decreasing of components with homopolar As-As bonds in the structure of As 40 S 60 and As 50 S 50 nanolayers and increasing of concentration of components with As-As bonds in As 45 S 55 films. Conclusion: The local and molecular structure of the surface layers of As x S 100-x thin films (x = 40, 45, 50) and their structural transformations induced by coherent laser irradiation with energy close to band gap energy, with using XPS and SEM were investigated. An essential difference between the surface stoichiometry and the composition of the appropriate glasses has been found. Established that this behavior caused by peculiarities of the molecular component of the gas phase during deposition. This indicates that the type of molecules in a pair plays a decisive role in forming composition of the film. Laser irradiation reduces the concentration of homopolar S-S bonds in the structure of all As x S 100-x nanolayers (x = 40, 45, 50). However a decreasing of the As-As homopolar bond concentration induced by laser light was observed only on samples of As 40 S 60 and As 50 S 50 films. During illumination significant contribution of As-S 2 As and As-SAs 2 s.u. and the appiarence of As-enriched As-As 3 s.u. was seen in the case of As 45 S 55 thin film sample. SEM photos of the surface of the films confirm the ordering of the structure of the films during processing. Keywords: X-ray photoelectron spectroscopy, amorphous film, laser irradiation, scanning electron microscopy, structural units.