Copper sulphide films prepared by reactive evaporation, when heated in
air at 500K, oxidized to Cu2O after a series of intermediate chemical
transitions. Golden yellow coloured Cu2O films showed a large absorpt
ion before the fundamental absorption edge. The optical band gap was f
ound to be (2.29+/-0.02)eV. When these Cu2O films were further heated
they got converted to CuO and the optical band gap was found to be (2.
17+/-0.02)eV.