Vacuum Preannealing of Precursors in APCVD for Enhanced Quality of Monolayer Transition-Metal Dichalcogenides

Two-dimensional transition-metal dichalcogenides (TMDCs) have garnered significant interest due to their exceptional physical and chemical properties. Among various fabrication techniques, atmospheric pressure chemical vapor deposition (APCVD) is widely used for its ability to produce high-crystallinity films with precise process control. However, in the APCVD process, oxidative impurities such as moisture and oxygen are not effectively removed, as gaseous contaminants are only gradually expelled through diffusion. To mitigate this issue, a vacuum preannealing process was implemented to eliminate moisture adsorbed on the precursor. Fourier-transform infrared (FT-IR) and Raman spectroscopy confirmed the effective removal of physically and chemically adsorbed moisture at 400 °C. The improved quality of the synthesized tungsten diselenide (WSe 2 ) was further validated through Raman and photoluminescence (PL) spectroscopy. Moreover, field-effect transistors (FETs) fabricated with WSe 2 exhibited enhanced electrical performance, achieving a mobility of 27.5 cm 2 /V·s and an on/off ratio of 3 × 10 6 . These findings demonstrate an effective strategy to optimize the APCVD process and enhance the TMDC-based device performance.