Raman Spectroscopic Study of Photostructural and Photochemical Transformations on the Surface of Thermally Evaporated (As1–xBix)2S3 Films

Amorphous (As_1–xBi_x)₂S₃ films with x ≤ 0.18 were prepared by thermal evaporation and studied by Raman spectroscopy. The measured Raman spectra show the evidence for noticeable rearrangement of the amorphous network upon adding Bi to the film composition. A narrow peak near 270 cm⁻¹ is a signature of arsenolite As₂O₃ crystallites formed on the As₂S₃-based film surface due to visible light-induced photo-oxidation, which has been previously reported only under illumination by ultraviolet light. This peak is also revealed in the Raman spectra of the (As_1–xBi_x)₂S₃ films immersed in isopropanol, which means that oxygen that participates in the photo-oxidation reaction does not come from the ambient air but had been absorbed by film at the pre-condensation stage. Non-thermal character of the photoinduced mass transfer in amorphous chalcogenides is confirmed. Photosoftening plays an important role in enhancing the mobility of atoms and enabling the photochemical reactions on the film surface at mild temperatures.