Tunable Wetting Property in Growth Mode-Controlled WS₂ Thin Films

We report on a thickness-dependent wetting property of WS₂/Al₂O₃ and WS₂/SiO₂/Si structures. We prepared WS₂ films with gradient thickness by annealing thickness-controlled WO₃ films at 800 °C in sulfur atmosphere. Raman spectroscopy measurements showed step-like variation in the thickness of WS₂ over substrates several centimeters in dimension. On fresh surfaces, we observed a significant change in the water contact angle depending on film thickness and substrate. Transmission electron microscopy analysis showed that differences in the surface roughness of WS₂ films can account for the contrasting wetting properties between WS₂/Al₂O₃ and WS₂/SiO₂/Si. The thickness dependence of water contact angle persisted for longer than 2 weeks, which demonstrates the stability of these wetting properties when exposed to air contamination.