In situ investigations of laser and thermally modified As₂S₃ nanolayers: Synchrotron radiation photoelectron spectroscopy and density functional theory calculations

As-deposited, annealed, and in situ As₂S₃ nanolayers, illuminated by blue (405 nm) and red (650 nm) laser light, were studied using synchrotron radiation photoelectron spectroscopy and DFT electronic structure calculations. Changes in composition and local atomic coordination occurring in the irradiated region of As₂S₃ films were monitored by analysis of As 3d and S 2p core levels. These studies show that both the thermal treatment and the red laser illumination of As₂S₃ nanolayers decrease the concentration of homopolar (As-As and S-S) bonds. From the other hand, an increasing concentration of As-rich structural units (s.u.) with a homopolar As-As bond was observed under in situ blue laser illumination of As₂S₃ nanolayers. Molecular orbital energies were calculated for different As- and S-centered s.u. and used for the interpretation of the core levels and valence band spectra. The surface local structure of the As₂S₃ nanolayers and its photoinduced transformation are discussed in detail.