Experimental study of the copper thiosulfate system with respect to thin-film deposition

An experimental study of the copper-thiosulfate system in mild acidic (pH ∼ 5) aqueous solutions, with respect to thin-film formation, was undertaken. Thin films of Cu_xS (1 ≤ x ≤ 2) were deposited by a simple electroless technique on glass or transparent polyester films, at 50 °C. Thin films were deposited from chemical baths in which the ratios of copper to thiosulfate were varied from 1:1 to 1:10. Thin films of different compositions (Cu₂S, Cu_1.8S, Cu_1.4S and CuS) were prepared and then characterized for morphological, optical and electrical properties. The deposited films chemically close to Cu₂S were found to be amorphous, while the CuS films were a mixture of both amorphous and polycrystalline phases. The optical spectra of the Cu₂S films exhibited high transmission both in the visible region of the spectrum (beyond 600 nm) and throughout the near-infrared region (800 to 2500 nm), while CuS films were found to be highly absorptive throughout the near-infrared region, with peaked transmission in the visible region at about 560 nm. The sheet resistances of the films, determined by the standard four-probe measurements, were between 100 and 650 Ω/square.