Metastable 1T′-phase group VIB transition metal dichalcogenide crystals

Metastable 1T′-phase transition metal dichalcogenides (1T′-TMDs) with semi-metallic natures have attracted increasing interest owing to their uniquely distorted structures and fascinating phase-dependent physicochemical properties. However, the synthesis of high-quality metastable 1T′-TMD crystals, especially for the group VIB TMDs, remains a challenge. Here, we report a general synthetic method for the large-scale preparation of metastable 1T′-phase group VIB TMDs, including WS₂, WSe₂, MoS₂, MoSe₂, WS_2xSe_2(1−x) and MoS_2xSe_2(1−x). We solve the crystal structures of 1T′-WS₂, -WSe₂, -MoS₂ and -MoSe₂ with single-crystal X-ray diffraction. The as-prepared 1T′-WS₂ exhibits thickness-dependent intrinsic superconductivity, showing critical transition temperatures of 8.6 K for the thickness of 90.1 nm and 5.7 K for the single layer, which we attribute to the high intrinsic carrier concentration and the semi-metallic nature of 1T′-WS₂. This synthesis method will allow a more systematic investigation of the intrinsic properties of metastable TMDs.