Photo-induced birefringence and surface ripples structures in As-S-Ag chalcogenide thin-films

Abstract

Photo-induced phenomena are investigated in new metastable Agx(As20S80)100-x chalcogenide thin-films prepared by the co-evaporation technique. Under irradiation using an Ar laser at 488 nm, periodic ripples structures formation are observed inside of the irradiated spot. With an increasing irradiation time or power density, a characteristic evolution of ripples is observed from a random structure to a series of generally aligned peaks-and-valleys periodic structures until a complete break-up of the film (laser dewetting). The scanning electron microscopy (SEM) of irradiated areas shows periodic ripples are aligned perpendicularly to the electric field vector of the incident light. Moreover, photo-induced birefringence (PIB) is observed during ripples formation. The kinetics of structural changes during the irradiation of the films is analysed using Raman spectroscopy. The molecular rearrangement from sulphur-cis toward sulphur-trans through irradiation is proposed to explain the experimentally observed PIB.