Conversion of CuS thin films to structured nanosheet CuyS (1 < y ≦ 2) by vacuum annealing

In this study, large-area and uniform thickness novel nano-sheet structured CuS thin films on ITO glass have been prepared by the one-step electrodeposition method from a dimethyl sulfoxide solution. Thin films of completely preserved nano-sheet like morphology of CuyS (y = 1.75, 1.8, 1.95, and 2.0) are grown by vacuum annealing CuS thin films at 500 °C for different lengths of time. The 500 °C sample heated for 10 hours was nearly converted to single phase of Cu2S with y ∼ 2. The optical direct band gaps of nano-sheet CuyS thin films annealed at 500 °C of 2, 6, and 10 hours in vacuum were found to be 1.94, 1.68, and 1.44 eV, respectively.