Abstract
We demonstrate chemical vapor deposition of large monolayer tungsten disulfide (WS2) (>200 μm). Photoluminescence and Raman spectroscopy provide insight into the structural and strain heterogeneity of the flakes. We observe exciton quenching at grain boundaries that originate from the nucleation site at the center of the WS2 flakes. Temperature variable transport measurements of top-gated WS2 transistors show an apparent metal-to-insulator transition. Variable range and thermally activated hopping mechanisms can explain the carrier transport in the insulating phase at low and intermediate temperatures. The devices exhibit room-temperature field-effect electron mobility as high as 48 cm2/V.s. The mobility increases with decreasing temperature and begins to saturate at below 100 °K, possibly due to Coulomb scattering or defects.