Phase engineering of nanomaterials (PEN) has demonstrated great potential in the fields of catalysis, electronics, energy storage and conversion, and condensed matter physics. Our work provides useful insights for understanding the stability of 2D heterostructures and interfaces between chemically, structurally, and electronically different phases. In this paper, we demonstrate how the thermodynamics of mixing in the MoReSe₂ system during CVD growth dictates the formation more » of atomically sharp interfaces between MoSe₂ and ReSe₂, which can be confirmed by high-resolution scanning transmission electron microscopy imaging, revealing zigzag selenium-terminated interface between the epitaxial 2H and 1T' lattices. Herein, we address this problem via a CVD technique to grow thermodynamically stable heterostructure of 2H/1T' MoSe₂–ReSe₂ using conventional transition metal phase diagrams as a reference. The 2D TMDC heterostructures at the present stage face difficulties being implemented in these applications because of lack of large and sharp heterostructure interfaces. Two-dimensional (2D) transition metal dichalcogenide (TMDC) heterostructures have been proposed as potential candidates for a variety of applications like quantum computing, neuromorphic computing, solar cells, and flexible field effective transistors. = 1T/2H heterostructures and provide vital insights into the other 2D hybrid materials. Finally, we report the energetics of the 2H to 1T' transition with several other more » adatoms, Ag, Au, Ni, Pt and Pd, but none of them are as effective as Cu in inducing the transition. The main atomic mechanism of the structural transition is the gliding of S atoms on the upper surface. This difference reflects the higher electronegativity of Cu, which also indicates that Cu-modified MoS 2 can be expected to be less chemically reactive than MoS 2 with alkali metal adatoms. Charge donation to the 1T' phase by Cu stabilizes it with respect to the 2H structure and importantly, it also reduces the energy barrier between the 2H and 1T' structures. This is distinct from the behavior in the 2H phase, where Cu does not donate any charge, and it is also distinct from alkali metal adsorption, where charge is donated to both 2H and 1T' MoS 2. Cu adsorption results in effective n-type doping of MoS 2 by charge transfer from Cu in the case of the 1T' phase. We report, based on first principles calculations, that the adsorption of metal atom Cu on the surface can induce the phase transition of MoS 2 from the semiconducting 2H to the metallic 1T' phase. In this paper, the electronic properties of MoS 2 are strongly controlled by the structure, providing a route to their modulation.
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