Gas-phase substitution synthesis of Cu1.8S and Cu2S superlattice nanowires from CdS nanowires

Single-crystalline wurtzite CdS nanowires underwent gas-phase substitution to form unique superlattice cubic Cu1.8S (digenite) and hexagonal Cu2S (chalcocite) structures, using thermal evaporation of CuCl2 at 500∼600 °C. The Cu1.8S nanowires consisted of superlattices along the 〈111〉 direction, with controlled growth direction ([110], [211], [100], [111]) and superlattice periods of 1.6 and 1.9 nm. As the temperature decreased, the growth direction evolved from [100] to the higher surface-energy [110] or [211] directions, with longer superlattice periods. The Cu2S nanowires also exhibited a superlattice along the [0001] growth direction, with a periodicity of 2.7 nm and could be irreversibly converted into superlattice Cu1.8S by electron-beam irradiation.