A method for the large-area synthesis of WSe₂ monolayers is described. WO₃ and Se powders are placed in a ceramic boat in a furnace, with the Se powder at a lower temperature (270°C). Sapphire substrates are placed downstream, where WO₃ and Se vapors are brought by an Ar/H₂ gas. The center heating zone is heated to 925°C, with the sapphire substrates at ~750–850°C. After 15 minutes, the furnace cools naturally. The morphology of WSe₂ varies with substrate temperature. At 850°C, WSe₂ forms triangular shapes with low nucleation density, while at 750°C, it forms a continuous, polycrystalline film. Raman spectra show characteristic peaks for monolayer and bilayer WSe₂. Photoluminescence (PL) spectra indicate strong emission at ~760 nm for monolayer WSe₂, with lower intensity for bilayer. TEM images show periodic atomic arrangements and hexagonal lattice structures. The study confirms that hydrogen plays an important role in the reaction. The synthesis method produces highly crystalline, large-area WSe₂ monolayers in a hot-wall CVD chamber. The results demonstrate that WSe₂ monolayers can be grown at 850°C as triangle-shaped, single-crystalline flakes, while lower temperatures produce continuous, polycrystalline films. The experimental section details characterization techniques used, including AFM, Raman spectroscopy, PL spectroscopy, TEM, XPS, and electrical measurements. The study provides a reliable method for the synthesis of high-quality WSe₂ monolayers.A method for the large-area synthesis of WSe₂ monolayers is described. WO₃ and Se powders are placed in a ceramic boat in a furnace, with the Se powder at a lower temperature (270°C). Sapphire substrates are placed downstream, where WO₃ and Se vapors are brought by an Ar/H₂ gas. The center heating zone is heated to 925°C, with the sapphire substrates at ~750–850°C. After 15 minutes, the furnace cools naturally. The morphology of WSe₂ varies with substrate temperature. At 850°C, WSe₂ forms triangular shapes with low nucleation density, while at 750°C, it forms a continuous, polycrystalline film. Raman spectra show characteristic peaks for monolayer and bilayer WSe₂. Photoluminescence (PL) spectra indicate strong emission at ~760 nm for monolayer WSe₂, with lower intensity for bilayer. TEM images show periodic atomic arrangements and hexagonal lattice structures. The study confirms that hydrogen plays an important role in the reaction. The synthesis method produces highly crystalline, large-area WSe₂ monolayers in a hot-wall CVD chamber. The results demonstrate that WSe₂ monolayers can be grown at 850°C as triangle-shaped, single-crystalline flakes, while lower temperatures produce continuous, polycrystalline films. The experimental section details characterization techniques used, including AFM, Raman spectroscopy, PL spectroscopy, TEM, XPS, and electrical measurements. The study provides a reliable method for the synthesis of high-quality WSe₂ monolayers.