Role of Quenching in the Growth of WSe₂ Monolayer Nanostructures with Salt-Assisted Chemical Vapor Deposition

While monolayers of WSe2, an intrinsic p-type two-dimensional semiconductor, have been widely studied for their optical and electrical properties, large-scale synthesis of WSe2 monolayers via chemical vapor deposition (CVD) can be challenging due to the high temperatures required to generate sufficient W vapor phase from oxide precursors. Utilizing a mixture of NaCl and tungsten oxide as a source enables lower growth temperatures in atmospheric pressure CVD to 825 °C–850 °C. However, the increased W vapor pressure can disrupt the balance between W and Se supplies during the slow cooling process, causing uncontrolled overgrowth at the edges of the WSe2 flakes. This issue is effectively addressed by employing thermal quenching immediately following growth, resulting in monolayer WSe2 flake nanostructures with uniform morphology and optical properties. The synthesized WSe2 monolayers exhibit characteristic p-type semiconducting behaviors with a positive photoresponse.