Two-Dimensional High-Quality Monolayered Triangular WS2 Flakes for Field-Effect Transistors.

Large-area uniform of single-crystal tungsten disulfide (WS2) is important for advanced optoelectronics based on two-dimensional (2D) atomic crystals. However, difficulties in controlling the interrelated growth parameters restrict its development in devices. Herein, we present the synthesis of triangular monolayered WS2 flakes with good uniformity and single crystal by adjusting the introduction time of sulfur precursor and the distances between the sources and substrates to control the nucleation density. Investigation of the morphology and structure by transmission electron microscopy and Raman spectroscopy indicates that a series of triangular (side length of 233 μm) monolayered WS2 flakes shows high-quality structure and homogenous crystallinity. Field-effect transistors based on the fabricated triangular monolayered WS2 with single crystal demonstrate environmentally stable charge transport with a field-effect mobility of 50.5 cm2/V s and current modulation Ion/ Ioff of ∼107. The results of this study pave the way for the application of monolayered WS2 in a multitude of 2D-material-based devices.