Figure 1.

(a) A schematic diagram showing the concept of MBE growth monolayer MoS₂ on a sapphire substrate. (b,c) Optical image of the epitaxial MoS₂ taken in bright field (b) and dark field (c) regimes. MoS₂ covers more than 97% of the surface. (d) SEM image of the epitaxial MoS₂ revealing the high crystallinity of the samples with the characteristic crystallite size 6 ± 2 μm. (e) The AFM topography map of MoS₂ surface with a scan area of 17.5 × 10 μm². Root mean square roughness of MoS₂ is 0.5 nm in areas without defects. (f) The AFM topography map and the cross-sectional profile of the edge of epitaxial MoS₂ along the green line, giving the MoS₂ layer thickness of ~0.9 nm. The scan area was 5.5 × 2 μm².