Reactive evaporation of Chevrel phase superconducting compounds

Thin films of Chevrel phase compounds CuMo6S8and HoMo6S8have been formed using a reactive evaporation technique in which the metallic constituents are derived from either electron-gun or resistively heated sources and S vapor is obtained from a molecular beam oven. The constituents are reacted on a sapphire substrate kept at elevated temperatures. Compositional uniformity is insured by controlling the S rate and locking the rates of the other sources to it in a prearranged fashion. The evaporation system used in this work is equipped with a vacuum lock which permits substrates to be changed without reprocessing the system. CuMo6S8films produced using these techniques are relatively pure and well-ordered. HoMo6S8films show a resistance minimum but do not become completely superconducting as prepared, but do so after reactive annealing. These methods have not been used successfully to form PbMo6S8films because of the high volatility and short dwell time of Pb on the substrate surface.