Raman evidence for surface oxidation of amorphous As2S3 thin films under ultraviolet irradiation

Amorphous As2S3 films with surface roughness near 0.5 nm were prepared by thermal evaporation. Raman measurements performed under ultraviolet (UV) laser excitation (325 nm) revealed a series of sharp intense peaks appearing at laser power density P-exc above 150 kW/cm(2). No such effects were observed at Raman measurements under visible (514.7 or 632.8 nm) light excitation, even for much higher P-exc values. The new Raman peaks are identified as arsenolite (As2O3) features. UV light-assisted oxidation of the As2S3 surface is discussed.