Structural origin of surface transformations in arsenic sulfide thin films upon UV-irradiation

Abstract

Photostructural transformations within AsxS100-x (x = 30, 33, 35, 40) thin films upon exposure to LED light of different wavelengths, in both air and argon environments have been studied by high resolution XPS, Raman spectroscopy and LEIS methods. These complementary results show that light of energies close to the band gap does not modify chemical composition of the surface, but induces simple photopolymerization reactions. Superbandgap UV light, however, significantly increases S/As ratio on the surface due to formation of S-rich layer under both environmental conditions. It is proposed that photovaporization of both oxide and non-oxide cage-like molecules is responsible for the observed effect.

Ternary CdS1–xSexnanocrystals formed in Cd‐doped As–Se–S films due to photoenhanced diffusion during micro‐Raman measurement

“…The lineshape and spectral position of Cd peak in the initial spectrum (before the first sputtering step), distinctly different from the bulk, are due to cadmium oxide and hydroxide on the film surface, which are removed together with other surface contamination. High‐resolution XPS spectra of amorphous As–Se–S [ 12,13 ] as well as related binary As–Se [ 34–36 ] and As–S [ 37,38 ] systems were thoroughly studied; therefore, we focus here primarily on the features related to Cd doping. High‐resolution XPS spectra consecutively measured from the same surface area of a Cd‐doped As 2 (Se 0.5 S 0.5 ) 3 film after 1,000 eV Ar + ion sputtering (the duration of each sputtering session was 30 s) enabled us to trace the variation of As, S, Se, and Cd concentrations as functions of the sputtering duration.…”

Raman evidence for the oxidation of amorphous As2(SexS1–x)3 film surfaces under visible light

“…The mechanism of the photoinduced formation of As 2 O 3 crystallites on an arsenic chalcogenide film surface is related to a thermal effect of illumination when most of the light is absorbed within the top layer of the film resulting in the material heating [17][18][19]21]. For As 2 S 3 this effect is revealed under UV irradiation when most of the UV light is absorbed within the top 0.05 μm layer of the film and the material is heated up to 740 °C [17].…”

“…Photochemical reactions may occur on the surface of amorphous chalcogenide samples due to the interaction with oxygen from the ambient air (photooxidation) which is facilitated by illumination with ultraviolet (UV) light, strongly absorbed within the surface layer [16,17]. For As 2 S 3 films, in particular, this was shown to result in photooxidation of the surface which was confirmed by x-ray diffraction (XRD) [16,17], energy-dispersive x-ray spectroscopy (EDX) [16,17], and x-ray photoelectron spectroscopy (XPS) [18]. In our earlier study [19], we presented direct evidence for the oxidation of amorphous As 2 S 3 surface under UV laser irradiation based on Raman spectroscopy results.…”