Flux synthesis and point defect repair of ultrapure Transition-Metal Dichalcogenides

Two-dimensional transition metal dichalcogenides (2D-TMDs) have garnered significant attention due to their unique structural, electronic, and optical properties. These properties make them highly suitable for a range of applications, including optoelectronics, next-generation electronics, and emerging quantum technologies. However, the inherent presence of point defects in these materials can significantly alter device performance.

In this work, we present an improved flux growth method for bulk TMD crystals that yields large crystals with low defect densities when compared to other crystal synthesis techniques for TMDs. Our approach integrates a post-growth annealing step conducted in a chalcogen-rich environment, designed to repair the isovalent and charged defects that naturally form during these crystal growth process.

Using techniques such as conductive atomic force microscopy (c-AFM), we achieve high-resolution imaging of these defects at the nanoscale, enabling a direct counting of defect concentrations in both monolayer and bulk exfoliated TMD samples. Specifically, we demonstrate an order-of-magnitude reduction in both the isovalent and charged defect densities. In WSe₂ we find a final isovalent defect density of 10¹⁰ /cm²and charged defect density of 10⁹ /cm².