Direct observation of atomic configuration of a highly oriented MoS2 film/α-Al2O3 (0001) using atomic resolution electron microscopy

We deposited a highly oriented MoS2 film on a 2-in. α-Al2O3 (0001) wafer by metalorganic chemical vapor deposition and determined the atomic configuration of the MoS2/α-Al2O3 (0001) stacking structure by performing atomic resolution electron microscopy observations along two orthogonal zone axis directions, i.e., the 112¯0 and 11¯00 directions of α-Al2O3. The results show that, first, the in-plane positions of Mo atoms coincide with those of the underlying Al and O atoms, and the 112¯0 direction of the monolayer 2H-MoS2 matches that of the α-Al2O3 substrate. Second, the α-Al2O3 surface was a reconstructed Al-I structure. Moreover, we performed the first-principles calculations using the observed in-plane atomic positions of the MoS2/α-Al2O3 structure as a starting configuration and found that the MoS2–Al2O3 distance is larger than the theoretical van der Waals distance. Because no ordered structures were observed between the MoS2 film and the Al2O3 substrate, the experimental and theoretical results strongly suggest that an amorphous interface layer exists between them. Such an amorphous interface layer is likely to weaken the MoS2–Al2O3 interaction that determines the stability of the MoS2/α-Al2O3 (0001) structure. We thus argue that controlling the interface layer is critical for fabricating highly oriented MoS2 films and is vital for improving the performance of field-effect transistors with MoS2 channels.