Structural and Optical Properties of Tungsten Disulfide Nanoscale Films Grown by Sulfurization from W and WO 3 .

Tungsten disulfide (WS 2 ) was prepared from W metal and WO 3 by ion beam sputtering and sulfurization in a different number of layers, including monolayer, bilayer, six-layer, and nine-layer. To obtain better crystallinity, the nine-layer of WS 2 was also prepared from W metal and sulfurized in a furnace at different temperatures (800, 850, 900, and 950 °C). X-ray diffraction revealed that WS 2 has a 2-H crystal structure and the crystallinity improved with increasing sulfurization temperature, while the crystallinity of WS 2 sulfurized from WO 3 (WS 2 -WO 3 ) is better than that sulfurized from W-metal (WS 2 -W). Raman spectra show that the full-width at half maximum (FWHM) of WS 2 -WO 3 is narrower than that of WS 2 -W. We demonstrate that high-quality monocrystalline WS 2 thin films can be prepared at wafer scale by sulfurization of WO 3 . The photoluminescence of the WS 2 monolayer is strongly enhanced and centered at 1.98 eV. The transmittance of the WS 2 monolayer exceeds 80%, and the measured band gap is 1.9 eV, as shown by ultraviolet-visible-infrared spectroscopy.