Tunable Wetting Property in Growth Mode-Controlled WS₂ Thin Films

Area of Science:

• Materials Science
• Surface Science
• Nanotechnology

Background:

• Tungsten disulfide (WS₂) is a transition metal dichalcogenide with potential applications in electronics and sensors.
• Understanding the surface properties of WS₂ films is crucial for optimizing device performance.
• Wetting behavior is influenced by film thickness, substrate material, and surface morphology.

Purpose of the Study:

• To investigate the thickness-dependent wetting properties of WS₂ films on Al₂O₃ and SiO₂/Si substrates.
• To correlate wetting behavior with film characteristics such as thickness and surface roughness.
• To assess the stability of these wetting properties under ambient conditions.

Main Methods:

• Fabrication of WS₂ films with gradient thickness via annealing of WO₃ precursors in a sulfur atmosphere at 800°C.
• Characterization of WS₂ film thickness using Raman spectroscopy.
• Measurement of water contact angles on WS₂ films.
• Analysis of WS₂ film surface morphology using Transmission Electron Microscopy (TEM).

Main Results:

• Raman spectroscopy revealed step-like thickness variations in WS₂ films over centimeter-scale substrates.
• A significant, thickness-dependent change in water contact angle was observed, varying with the substrate (Al₂O₃ vs. SiO₂/Si).
• TEM analysis indicated that differences in WS₂ surface roughness were responsible for the observed variations in wetting properties.

Conclusions:

• The wetting behavior of WS₂ films is strongly dependent on film thickness and the underlying substrate.
• Surface roughness plays a key role in determining the contrasting wetting properties between different WS₂/substrate interfaces.
• The observed thickness-dependent wetting properties of WS₂ films are stable in air for at least two weeks.