Mechanistic insights into diffusion-controlled 2D WSe2 growth via chemical vapor deposition in confined spaces

Two-dimensional transition metal dichalcogenides (TMDs) have garnered significant attention for their potential in electronic and optoelectronic devices. While chemical vapor deposition (CVD) is a primary technique for producing large-area monolayer TMDs, the use of metal oxide precursors with high melting points presents various synthetic limitations. As an alternative, metal salt-based precursors have emerged due to their water solubility and low melting points. However, challenges remain in obtaining high-quality TMDs from these liquid precursors to, largely due to a limited understanding of the precursor diffusion process. Here, we present a systematic study on spin-coated precursor-based CVD growth of WSe2 in confined spaces, demonstrating a significant enhancement in the uniformity of domain size and number density through regulated precursor diffusion achieved by substrate covering. Furthermore, we show that microscopic precursor diffusion, both within and beyond the flake edges, influences edge morphologies and local optical emission properties. These findings provide valuable insights into the fabrication of large-area TMD monolayers, which hold promise for electronic and optoelectronic applications.