Synthesis and characterization of uniform 3R phase bilayer MoS2 on sapphire

Bilayer (BL) two-dimensional transition metal dichalcogenides (TMDs) exhibit excellent properties in carrier mobility, state density, and room temperature stability, which attract considerable attention. However, previous efforts on synthesis BL TMDs have lacked homogeneity and control over the number of layers. Here, we demonstrate an effective and controllable approach to synthesize highly uniform 3R phase BL MoS2 on a c-plane sapphire substrate. The number of MoS2 layer can be controlled by adjusting the confinement distance, sapphire step height (annealing temperature), and growth temperature. These influencing factors have been thoroughly investigated. Raman and PL analyses demonstrate bilayer properties and remarkable uniformity. SHG and HAADF-STEM measurements reveal 3R stacking structure of BL MoS2. Furthermore, field-effect-transistor (FET) devices fabricated using BL MoS2 domains exhibit high carrier mobility and on/off ratio. This work provides an efficient method for layer-controlled MoS2 growth and offers new insights into the growth mechanism of BL MoS2.