Copper tin sulfide (Cu 4 SnS 4 ) thin films have been prepared by heating a layer of CuS thin film deposited over an SnS thin film, both obtained by chemical bath deposition. Upon heating in a nitrogen atmosphere at 300-340 • C, the CuS layer converts to Cu 8 S 5 , which reacts with the underlying SnS thin film at about 400 • C to form Cu 4 SnS 4 . The optical band gap of Cu 4 SnS 4 has been found to be approximately 1 eV, involving direct forbidden transitions. The films are photosensitive, and the electrical conductivity in the dark is about 1 −1 cm −1 .
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