Preparation of textured and photoactive 2H-WS2 thin films by sulfurization of WO3

Abstract

Photoactive thin films of tungsten disulfide have been prepared by sulfurization of WO 3 layers. Tungsten trioxide films were deposited on heated quartz and glassy carbon substrates by gaseous reaction of W(CO) 6 with oxygen. Subsequently, the oxide films were treated at 700 °C in a gaseous sulfur atmosphere either in a flowing system or in evacuated and sealed quartz ampoules. The films were investigated by X-ray diffractometry, scanning electron and scanning tunneling microscopy. The photoactivity was measured using time-resolved microwave conductivity. Films consisting of the 2H-WS 2 platelets, highly textured and oriented with their c axis perpendicular to the substrate, were found. In addition, the phase relations in the phase triangle W-O-S were studied by thermochemical equilibrium calculations using the Gibbs free energy minimization technique. The inferred predominance area diagram log P s 2 vs. log p so 2 confirms the high stability of WO 2,9 and WS 2 as observed under related experimental conditions. The effect of the nickel on the orientation of the 2H-WS 2 crystallites obtained after sulfurization of the WO 3 films can be explained by a flux on the basis of the binary Ni-S phase diagram or surfactant mediated growth effect.