Structure and optical properties of molybdenum disulphide (MoS2) thin film deposited by the dip technique

Molybdenum dichalcogenides appear to be very promising semiconductor materials for various applications such as solar cells [1, 2], rechargeable batteries [3] and solid lubricants for metallic and ceramic surfaces in environments where hydrocarbon or other fluid-based lubricants are unsuitable, such as in high vacuum or high temperature applications [4, 5]. They have also been widely used in space-technology where their low co-efficient of friction in vacuum is of particular value [6]. These applications arise from the optical, electrochemical and mechanical properties of these compounds. They exhibit a layer-type structure in which monolayers of Mo are sandwiched between monolayers of sulphur, which are held together by relatively weak van der Waals forces. These materials have band gaps (1.78 eV) well-matched to the solar spectrum [7]. A number of methods exist for the production of MoS2 thin films, including sputtering [8–10], electrochemical deposition [7, 11], and pulsed laser deposition [12–15]. In this communication, preliminary results on structural and optical properties of MoS2 thin films produced by a dip-coating [16, 17] technique are reported. In the film deposition process the substrate was first immersed and then withdrawn vertically from the freshly prepared methanolic solution of ammonium molybdate and ammonium thiocyanate at a controlled speed of about 1.33 mm/s with the help of a pulley and geared motor. The substrate with the liquid layer adhering to it was then transferred to a high temperature furnace under atmospheric conditions for heat treatment. The chemicals reacted on the substrate and form the desired solid film according to the following reaction.