Interface Engineering of Au(111) for the Growth of 1T′-MoSe<sub>2</sub>

Phase-controlled synthesis of two-dimensional transition-metal dichalcogenides (TMDCs) is of great interest due to the distinct properties of the different phases. However, it is challenging to prepare metallic phase of group-VI TMDCs due to their metastability. At the monolayer level, interface engineering can be used to stabilize the metastable phase. Here, we demonstrate the selective growth of either single-layer 1H- or 1T′-MoSe<sub>2</sub> on Au(111) by molecular-beam epitaxy; the two phases can be unambiguously distinguished using scanning tunnelling microscopy and spectroscopy. While the growth of 1H-MoSe<sub>2</sub> is favorable on pristine Au(111), the growth of 1T′-MoSe<sub>2</sub> is promoted by the predeposition of Se on Au(111). The selective growth of the 1T′-MoSe<sub>2</sub> on Se-pretreated Au(111) is attributed to the Mo intercalation induced stabilization of the 1T′ phase, which is supported by density functional theory calculations. In addition, 1T′ twin boundaries and 1H–1T′ heterojunctions were observed and found to exhibit enhanced tunnelling conductivity. The substrate pretreatment approach for phase-controlled epitaxy could be applicable to other group-VI TMDCs grown on Au (111).