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

Abstract

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.

Coherent Light Photo-modification, Mass Transport Effect, and Surface Relief Formation in AsxS100-x Nanolayers: Absorption Edge, XPS, and Raman Spectroscopy Combined with Profilometry Study

“…in crystalline As 2 S 3 and is a main component for both stoichiometric, As 40 S 60 , and As-rich As–S glasses and films. The component 2 (and 2’) can be assigned to S-rich S–SAs s.u., and it is in a good agreement with our earlier investigations and theoretical estimations [19]. The As 3d core level spectra of As 40 S 60 nanolayers (both as-deposited and illuminated by green laser light) are fitted using three components: arsenic bonded to three sulfur atoms As–S 3 (1, 1’), arsenic bonded to two sulfur, and one arsenic atoms As–S 2 As (2, 2’) and finally, arsenic bonded to one sulfur and two arsenic atoms As–SAs 2 (3, 3’).…”

“…The As 3d core level spectra of As 40 S 60 nanolayers (both as-deposited and illuminated by green laser light) are fitted using three components: arsenic bonded to three sulfur atoms As–S 3 (1, 1’), arsenic bonded to two sulfur, and one arsenic atoms As–S 2 As (2, 2’) and finally, arsenic bonded to one sulfur and two arsenic atoms As–SAs 2 (3, 3’). These assignments are based on our previous study [19] and are in excellent agreement with the published data [16, 24]. It should be noted that for the best fit of the As 3d core level spectra of As 45 S 55 nanolayers, the fourth component is needed.…”

“…2, Table 2). This is in accordance with the results of our in situ under-bandgap laser light illumination of As 2 S 3 nanolayers [19]. The decreasing of concentration of homopolar As–As bonds in the structure of As 40 S 60 and As 50 S 50 films under laser illumination correlates well with the partial disappearance of the S–S bonds and creation of new As–S bonds.…”

“…This phenomenon was observed in our previous investigations [19] and was explained by the processes of the structural ordering under the laser light illumination. In addition, the decreasing of components with homopolar As–As bonds in the structure of As 40 S 60 and As 50 S 50 nanolayers under the near-bandgap laser light illumination was observed (Fig.…”

“…few topmost layers) of the materials at short-range order scale and to determine the structural units which form the investigated material. This method was successfully used to characterize the top surface nanolayer structure of the amorphous materials [19–21]. The results of XPS investigation of As x S 100- x ( x  = 40, 45, 50) thin film surface nanolayers are summarized in Fig.…”