Superconducting AgMo6S8 thin films prepared by reactive sputtering

Preferentially oriented thin films of the Chevrel-phase superconductor AgMo6S8 were prepared by reactive sputtering. Ag and Mo were simultaneously sputtered from separate guns onto sapphire substrates held at about 8500C with H2S gas injected near the substrate. The films have superconducting critical temperatures up to 9.2 K and narrow-phase transitions. The reactive sputtering process chosen for the preparation of our films makes it possible to change the superconducting properties and the microstructure of the samples in a systematic way by changing individual preparation parameters and to study which of the preparation conditions are the most crucial for the formation of the Chevrel phase. We find that the superconducting transition temperature of the Chevrel phase is very sensitive to both substrate temperature and to the flow of H2S but insensitive to the background pressure in the chamber before deposition. The microstructure can be changed by controlling the H2S pressure. X-ray measurements show that the films are preferentially oriented with the rhombohedral 001 planes parallel to the surface of the substrate