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

By Morrish, Rachel; Haak, Trevor & Wolden, Colin A.
Published in Chemistry of Materials NULL 2014

Abstract

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.

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