Sensors and Actuators B: Chemical, vol.381, 2023 (SCI-Expanded)
Obtaining near stoichiometric WS2 films with sputtering is challenging because of high sulfur deficiency during sputtering, which limits the application of these films in different solid-state device applications. In this study, in order to understand the growth pressure effect on the sulfur/tungsten ratio, WS2 films were grown at four different growth pressures, 5, 25, 50, and 100 mTorr, by RF-magnetron sputtering. With increasing growth pressure from 5 to 100 mTorr, it is found that films change from relatively metallic to near stoichiometric WS2 films. The thermal oxidation process of as-deposited WS2 films in the presence of O2 gas was also studied. The study showed that WS2 films were turned into WO3 films without significant change in morphology at a temperature of 400 ℃. The obtained WO3 films were then decorated by Palladium catalysis deposited by RFMS to activate the WO3 films toward H2 gas. The high response of 586-fold at an operating temperature of 200 ℃ for 1000 ppm H2 gas response and recovery times of 360 and 90 s, respectively, has been achieved for the sensor deposited at a growth pressure of 50 mTorr. In addition, a detection limit of 10 ppm was achieved for the sensor.