High-quality synthesis of Sulfur-based TMDs via Molecular Beam Epitaxy*

Sulfur is one of the most frequently used chalcogens when synthesizing transition metal dichalcogenide (TMD) films or bulks. Due to the high partial vapor pressure, however, elemental sulfur is known to be difficult to control under an ultra-high vacuum environment. With FeS₂ solid-state source, we can gain control of sulfur flux and successfully grow S-based TMDs including MoS₂ and WS₂. Preliminary ex-situ characterizations with XPS, AFM, and Raman are done to ensure the quality of the film after each growth. Furthermore, by combining MBE growth with in-situ scanning tunneling microscopy/spectroscopy (STM/S) and Angle-Resolved Photoemission Spectroscopy (ARPES) we confirm the characteristic band structures of the WS₂ and MoS₂ films on different substrates and observed a significant reduction of intrinsic impurities compared to chemical vapor deposition (CVD) grown samples. MBE growth of sulfides introduces a high-quality, scalable platform with effective defect controls for device applications.