Composition and local atomic environment in As2Se3 films and their changes under the coherent radiation


Background. Amorphous chalcogenides is a class of non-crystalline materials obtained by combination of chalcogen (S, Se or Te) elements with other chemical elements demonstrating a large IR transparency and unique electronic and optical properties. Photosensitivety and laser induced processes taking place at the surface of chalcogenide nanolayers increases the functionality of such media and extends their applications to the field of modern nanooptics and nanophotonics.
Materials and methods. Amorphous As2Se3 nanolayers were synthesized by thermal evaporation in a vacuum from target As2Se3 glasses. Near order structure of the surface nanolayers of the thin amorphous films a-As2Se3 under ambient conditions and its changes under the influence of near bandgap laser illumination, are investigated by X-ray photoelectron spectroscopy, Raman- and surface enhanced Raman spectroscopy.
Results. It was established that the structure of the film contains structural units with As-As and Se-Se homopolar bonds apart from the stoichiometric ones. X-ray photoelectron spectroscopy indicate that thelaser illumination increases Se-Se bonds and decreases As-As bonds due to the breaking of the As-Se bonds, formation Se-Se and As-O bonds and evaporation the most volatile As-O s.u. Such surface transformations are confirmed by surface enhanced Raman spectroscopy: the additional Se-rich nanoclusters formation at the surface of irradiated As-Se nanolayers is revealed by the increasing in intensity of the peak at 232 cm-1. The appearance of 251 cm-1 Raman mode in the spectra of irradiated film is interpreted as vibrations of As2Se3 based nanoclusters.
Conclusion. The composition and local structural changes at the surface of As2S3 nanolayers under near bandgap laser illumination were studied by X-ray photoelectron-, Raman-, and surface-enhanced Raman spectroscopy. Results show that the composition of surface of amorphous As-Se film is slightly enriched by chalcogen in comparison with composition of target As2Se3 glass. The results of photoelectron spectroscopy show that the near bandgap laser irradiations destroy the 2As-As-Se s.u. and, simultaneously, lead to formation of additional Se-Se-As і As-3Se s.u. at the surface of irradiated films. In contrast with the amorphous As2Se3 films, the surface-enhanced Raman spectroscopy of irradiated ones reveal the increasing of intensities of 232 and 251 cm-1 Raman bands characteristics for vibrations found in nanoclusters based on amorphous Se and crystalline As2S3 fragments, respectively

Keywords: X-ray photoelectron spectroscopy, Raman spectroscopy, amorphous film, laser irradiation, structural units