The effect of tungsten (W) concentration and sulfuration on morphology and optical properties and tuning of the band gap of 2D-MoS2 thin films

摘要

In this study, two dimensions of MoS2:W thin films were deposited by spray pyrolysis on a glass substrate at T = 400 degrees C by changing the concentration of tungsten trioxide as W/Mo = 0.01, 0.05, 0.15, and, 0.2. The annealing process under sulfuration for MoS2:W thin films were studied with a sulfur concentration ratio of S/Mo = 2. The effect of tungsten concentration and annealing on the structural, optical absorbance, and tunning of the band gap of MoS2:W thin films was studied. The XRD results showed that the thin films before sulfuration had an orthorhombic structure and after sulfurization a hexagonal structure. Also, the crystallite size increased as considerably with increasing tungsten (W) concentration up to W/Mo = 0.15. The surface images of thin films by FE-SEM showed that the morphology of crystals changed after annealing and sulfuration. Also, the behavior of optical absorption coefficient (alpha) and extinction coefficient (k) in terms of wavelength in the UV-Vis region has been studied. The energy gap after annealing increases with increasing tungsten concentration. The optical absorption analysis showed that the direct optical gap of the thin films varies in the range Delta E-g = 0.66 before annealing and in the range of Delta E-g = 0.46 after annealing under sulfurization.