Low-Temperature Synthesis of n-Type WS₂ Thin Films via H₂S Plasma Sulfurization of WO₃

Thin tungsten disulfide (WS2) films were prepared on SnO2:F (FTO)-coated glass substrates by H2S plasma sulfurization of sputtered WO3. The reactive environment provided by the plasma enabled the complete transformation of a 75 nm oxide film to stoichiometric WS2 within 1 h at 500 °C. An apparent activation energy of 63.6 ± 1.9 kJ/mol was calculated for the plasma conversion process, which is less than half the barrier reported for the reaction of WO3 with H2S. The conversion followed Deal–Grove behavior, with the growing WS2 overlayer hindering diffusion to and from the reactive interface. The calibrated light absorption and relative intensity of the second-order Raman 2LA(M) peak were identified as two additional methods for progressively monitoring the thickness of the WS2 layer. The semiconducting WS2 layers exhibited n-type behavior with an indirect band gap at 1.4 eV and an absorption coefficient of ∼5 × 104 cm–1. Preliminary electrochemical measurements showed that the presence of WS2 reduced the overpotential required for the hydrogen evolution reaction by 360 mV relative to FTO while displaying good stability.