Interface Engineering of Au(111) for the Growth of 1T'-MoSe2.

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'-MoSe2 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-MoSe2 is favorable on pristine Au(111), the growth of 1T'-MoSe2 is promoted by the predeposition of Se on Au(111). The selective growth of the 1T'-MoSe2 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).