Controlling Morphology and Excitonic Disorder in Monolayer WSe 2 Grown by Salt-Assisted CVD Methods.

Chemical synthesis is a compelling alternative to top-down fabrication for controlling the size, shape, and composition of two-dimensional (2D) crystals. Precision tuning of the 2D crystal structure has broad implications for the discovery of new phenomena and the reliable implementation of these materials in optoelectronic, photovoltaic, and quantum devices. However, precise and predictable manipulation of the edge structure in 2D crystals through gas-phase synthesis is still a formidable challenge. Here, we demonstrate a salt-assisted low-pressure chemical vapor deposition method that enables tuning W metal flux during growth of 2D WSe 2 monolayers and, thereby, direct control of their edge structure and optical properties. The degree of structural disorder in 2D WSe 2 is a direct function of the W metal flux, which is controlled by adjusting the mass ratio of WO 3 to NaCl. This edge disorder then couples to excitonic disorder, which manifests as broadened and spatially varying emission profiles. Our work links synthetic parameters with analyses of material morphology and optical properties to provide a unified understanding of intrinsic limits and opportunities in synthetic 2D materials.