Role of Quenchingin the Growth of WSe₂ Monolayer Nanostructures with Salt-AssistedChemical 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.