Two-dimensional (2D) semiconducting transition metal dichalcogenides (TMDs) represent the ultimate thickness for scaling down channel materials. They provide a tantalizing solution to push the limit of semiconductor technology nodes in the sub-1 nm range. One key challenge with 2D semiconducting TMD channel materials is to achieve large-scale batch growth on insulating substrates of single crystals with spatial homogeneity and compelling electrical properties. Recent studies have claimed the epitaxy growth of wafer-scale, single-crystal 2D TMDs on a c-plane sapphire substrate with deliberately engineered off-cut angles. It has been postulated that exposed step edges break the energy degeneracy of nucleation and thus drive the seamless stitching of mono-oriented flakes. Here we show that a more dominant factor should be considered: in particular, the interaction of 2D TMD grains with the exposed oxygen–aluminium atomic plane establishes an energy-minimized 2D TMD–sapphire configuration. Reconstructing the surfaces of c-plane sapphire substrates to only a single type of atomic plane (plane symmetry) already guarantees the single-crystal epitaxy of monolayer TMDs without the aid of step edges. Electrical results evidence the structural uniformity of the monolayers. Our findings elucidate a long-standing question that curbs the wafer-scale batch epitaxy of 2D TMD single crystals—an important step towards using 2D materials for future electronics. Experiments extended to perovskite materials also support the argument that the interaction with sapphire atomic surfaces is more dominant than step-edge docking.
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The data from this study are available from the corresponding authors on reasonable request.
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J.-H.F. and V.T. are indebted to the financial support from the University of Tokyo and the Japan Society for the Promotion of Science (JSPS, 23H00253). V.T. is beholden to the support from the King Abdullah University of Science and Technology (KAUST) Office of Sponsored Research (OSR) under award CCF-3079 and Office of Technology Development under the RTF grant. L.-J.L. acknowledges support from the Jockey Club Hong Kong to the JC STEM lab of 3DIC and the Research Grant of the Council of Hong Kong (CRS_PolyU502/22). Y.W. and L.-J.L. acknowledge support from the University of Hong Kong and the National Key R&D Project of China (2022YFB4044100). J.-H.F. and V.T. acknowledge KAUST Core Labs and the National Synchrotron Radiation Research Center (NSRRC) for support for the STEM imaging and LEED characterization. Y.-J.L. acknowledges support from AS-CDA-108-M08 Academia Sinica. J.-H.F. and V.T. dedicate this work to Ibrahim Alnami, who passed away before completing this project.
The authors declare no competing interests.
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Fu, JH., Min, J., Chang, CK. et al. Oriented lateral growth of two-dimensional materials on c-plane sapphire. Nat. Nanotechnol. 18, 1289–1294 (2023). https://doi.org/10.1038/s41565-023-01445-9
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