Large-Area synthesis of WSe₂ from WO₃ by selenium-oxygen ion exchange

Few-layer tungsten diselenide (WSe₂) is attractive as a next-generation electronic material as it exhibits modest carrier mobilities and energy band gap in the visible spectra, making it appealing for photovoltaic and low-powered electronic applications. Here we demonstrate the scalable synthesis of large-Area, few-layer WSe₂ via replacement of oxygen in hexagonally stabilized tungsten oxide films using dimethyl selenium. Cross-sectional transmission electron microscopy reveals successful control of the final WSe₂ film thickness through control of initial tungsten oxide thickness, as well as development of layered films with grain sizes up to several hundred nanometers. Raman spectroscopy and atomic force microscopy confirms high crystal uniformity of the converted WSe₂, and time domain thermo-reflectance provide evidence that near record low thermal conductivity is achievable in ultrathin WSe₂ using this method.