Stability of two orientations of MoS2 on α-Al2O3(0001)

We have studied the morphology of MoS2 on α-Al2O3(0001) using first-principles calculations. We found that the binding energy between MoS2 and the OH-terminated α-Al2O3(0001) surface is weaker than that for the Al-terminated surface. The band gap reduction of MoS2 is also smaller on the OH-terminated surface than on the Al-terminated surface. The strong chemical interaction between MoS2 and α-Al2O3(0001) seems to result in the larger binding energy and the larger band gap reduction on the Al-terminated surface. Despite the different binding characteristics between the OH- and Al-terminated surfaces, the total energy difference between the two orientations of the MoS2 monolayer related by a 60° rotation is quite small for both surfaces, indicating that the two orientations of MoS2 exist with almost the same amount on the α-Al2O3(0001) regardless of the termination. This result suggests that it is essentially difficult to obtain large-scale MoS2 with a single domain on the α-Al2O3(0001) by chemical vapor deposition.