Effect of deposition variables on the properties of molybdenum sulfide films prepared by the activated reactive evaporation technique

Abstract

Summary Non-crystalline molybdenum sulfides (MoS x , 2 ≤ x ≤ 3) are excellent cathode materials for the secondary lithium batteries. Molybdenum sulfide films were therefore synthesized by the activated reactive evaporation (ARE) technique which involved evaporating molybdenum using an electron beam source in an H 2 S plasma. The composition of the films showed wide variation depending on the deposition variables such as deposition rate, anode current, working pressure and gas flow rate. Deposition rate was the most dominant factor controlling the composition of the films where desorption of sulfur from the films was a limiting step. Sulfur adsorption was enhanced due to reaction of condensing molybdenum and sulfur atoms to form molybdenum sulfide. However, after reaching saturation ( i.e. no more sulfur atoms are available to form MoS x ) molybdenum atoms were embedded as excess atoms, leading films to be called sulfur deficient films in a chemical composition sense. The second dominant factor controlling the film composition was ARE anode current. Sulfur content in the film increased at low anode currents where thermodynamically reactive HS was produced (as opposed to sulfur and hydrogen at high anode current) hence enhancing the formation of molybdenum sulfide.