Orientated Lateral Growth of Two-Dimensional Materials on C-plane Sapphire

Two-dimensional (2D) semiconducting transition metal dichalcogenides (TMDs) representing the ultimate thickness scaling of channel materials provide a solution to tantalizingly push the limit of technology nodes in the sub-1-nm range. One key challenge with 2D semiconducting TMDs channel materials is the large-scale batch growth on insulating substrates with continuous single crystallinity, spatial homogeneity, and compelling electrical properties. Recent studies have claimed the epitaxy growth of wafer-scale, single-crystal 2D TMDs on C-plane sapphire substrate with deliberately engineered off-cut angles. It has been predominately postulated that exposed step edges break the energy degeneracy of nucleation and thus drive the seamless stitching of mono-oriented flakes. In this talk, I will discuss a more dominant factor that should be considered. The interaction of 2D TMDs grains with the exposed oxygen-aluminum atomic plane establishes an energy-minimized 2D TMD-sapphire configuration. Reconstructing the surfaces of C-plane sapphire substrates to only a single type (symmetry) of atomic planes already guarantees the single-crystal epitaxy of monolayer TMDs without the aid of step edges. Electrical results also evidence the structural uniformity of the monolayers. Our new experimental findings elucidate the long-standing question that curbs the wafer-scale batch epitaxy of 2D TMDs single crystals, an important step toward using 2D materials for future electronics. Experiments extended to other materials like graphydine, and perovskites also support the argument that the interaction with sapphire atomic surfaces is more dominant than the step edge docking.