Low-Temperature Synthesis of <i>n</i>‑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 <i>n</i>-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