Stability of Thin-Film Cu–As₂S₃ and Ag–As₂S₃ Structures

Thin-film Cu–As₂S₃ and Ag–As₂S₃ structures obtained by successively evaporating Cu(Ag) and As₂S₃ in vacuum on glass substrates have been studied. Samples of these structures have been kept in air at room temperature in the dark for 6 months, and transmission spectra have been periodically taken of these samples. The logarithm of inverse transmission coefficient in the transparency domain of As₂S₃ has been used as a measure that is proportional to the thickness of the metal film. It has been found that for Ag–As₂S₃ the thickness of the metal film varies with storage time linearly, whereas for Cu–As₂S₃ this dependence can be described by two different linear sections. From the decrease in metal film thickness, it has been concluded that the Ag–As₂S₃ structure is more stable than Cu–As₂S₃. It has been supposed that silver, unlike copper, does not react with As₂S₃ when the structures are stored in the dark, although it permanently diffuses into As₂S₃ during storage.