Elucidation of PVD MoS2 film formation process and its structure focusing on sub-monolayer region

Sputtering enables uniform and clean deposition over a large area, which is an issue with exfoliation and chemical vapor deposition methods. On the other hand, the process of physical vapor deposition (PVD) film formation has not yet been clarified. We prepared several samples from the sub-monolayer region, and performed Raman spectroscopy, X-ray photon spectroscopy and high-angle annular dark-field scanning transmission electron microscopy. From these results, the internal stresses inherent to PVD films, the bonding states specific to sub-monolayers, and the unique film structure and the grain formation process of PVD films were discussed from the perspective of sub-monolayers. As a conclusion, we found that it is important to suppress the formation of sub-monolayers on the substrate to completely form the first layer.