Synthesis of high quality monolayer WS$_{\mathrm{2}}$ using chemical vapor deposition.

Monolayer tungsten dichalcogenide WS$_{\mathrm{2}}$ have addressed interest from material scientist for new generation of optoelectronics due to thickness dependent optical properties and mechanical flexibility. Continuous monolayers WS$_{\mathrm{2}}$ were synthesized using chemical vapor deposition (CVD) on various substrates, similar to our previous publication. By controlling growth temperature, we could yield high quality monolayer WS$_{\mathrm{2}}$. Optical, atomic force microscopic images and Raman scattering indicate that the film was mostly covered by monolayer WS$_{\mathrm{2}}$ with large grain size about 50 $\mu $m. Strong, direct gap emission at 636 nm with relatively small full width at half maxima and the absence of defect-related transitions in power-dependence photoluminescence (PL) revealed the excellent quality of as-grown film in compared with CVD-grown monolayer MoS$_{\mathrm{2}}$. Moreover, PL intensity and energy mapping at $A$-exciton also shows uniformity and continuity of our films. Our results shows monolayer WS$_{\mathrm{2}}$ could be potentially applied to optoelectronic devices such as light emission diodes/