Synthesis of Large-Area WS(2) monolayers with Exceptional Photoluminescence

Monolayer WS(2) offers great promise for use in optical devices due to its direct bandgap and high photoluminescence intensity. While fundamental investigations can be performed on exfoliated material, large-area and high quality materials are essential for implementation of technological applications. In this work, we synthesize monolayer WS(2) under various controlled conditions and characterize the films using photoluminescence, Raman and x-ray photoelectron spectroscopies. We demonstrate that the introduction of hydrogen to the argon carrier gas dramatically improves the optical quality and increases the growth area of WS(2), resulting in films exhibiting mm(2) coverage. The addition of hydrogen more effectively reduces the WO(3) precursor and protects against oxidative etching of the synthesized monolayers. The stoichiometric WS(2) monolayers synthesized using Ar + H(2) carrier gas exhibit superior optical characteristics, with photoluminescence emission full width half maximum (FWHM) values below 40 meV and emission intensities nearly an order of magnitude higher than films synthesized in a pure Ar environment.