Vibrational and conductive microscopic investigation of thermal dewetting in Ag-As-S chalcogenide thin films

Highlights: • During thermal dewetting silver migrates with the retracting edges. • Silver atoms bonds stronger to the chalcogenide matrix as the temperature increases. • The electrical conductivity of chalcogenide structures decays during dewetting. Chalcogenide thin films hold a great promise for integrated photonics and sensor applications, however their patterning by traditional photolithography can be troublesome. Recently, our group demonstrated that thermal dewetting may be combined with photolithography to obtain 3D microstructures of chalcogenide glasses and low-loss resonators. Nevertheless, mass transport during the dewetting may lead to compositional and structural modifications changing the optical and electrical properties of the film. Here, we investigate the thin film structure and composition at different dewetting stages using Raman Spectroscopy and Energy Dispersive Spectroscopy. The topography and local electrical conductivity are measured by Conductive Atomic Force Microscopy. The correlation of the structural changes and the local electrical conductivity shows the formation of a silver-rich domain during the dewetting close to a phase separation, where the dewetted area presents only residual silver. Surprisingly, the conductivity of the dewetted motifs decays with the treating temperature and no further increment in silver concentration is observed. The study of the structural, as well as the electrical behaviour of thin films during thermal dewetting, is crucial for choosing an appropriate composition and its use in integrated photonics.