Changing the composition of Ag–As–S amorphous films using photo-induced solid state reaction

The technique of step-by-step optically-induced solid state reaction of Ag into As33S67 amorphous films, which has allowed the design of films with known silver concentrations, is reported. The host, As33S67 films, were photo-doped by consecutive dissolution of a 10 nm layer of silver, which resulted in a single layer film of optical quality as measured by optical transmissivity. The silver concentration of the samples ranged between 1 and 41 at.%. Such Ag containing films cannot be prepared directly by vacuum evaporation from AgAsS glasses due to the phase separation during evaporation process. We analyzed the affect of the silver doping in the host material on optical, thermal properties, and its structure by means of optical spectroscopy, temperature-modulated differential scanning calorimetry, and Raman spectroscopy, respectively. Optically-induced silver dissolution led to a formation of the solid solutions in above mentioned concentration range, connected with a decrease of –S–S– bonds due to their solid state reaction with migrating silver ions. The films with a silver content close to 25 at.% had the structure of stoichiometric AgAsS2. There is evidence of As–As bond formation in photo-doped materials with a silver content >40 at.%. Results of all analytical techniques we used have helped to understand the processes taking place during silver photo-dissolution.