Metastable phase control of two-dimensional transition metal dichalcogenides on metal substrates

Phase control of two-dimensional (2D) transition metal dichalcogenides (TMDs) is important from both scientific and engineering aspects. However, up to now it remains a challenge to stabilize the metastable phase of TMDs under ambient conditions. Herein, via systematic first-principles calculations, we demonstrate that by the appropriate choice of metal substrate as a support for the transferred layer, the metastable phase of MoS2 can be effectively stabilized. By screening 15 widely used metal substrates, we found that Mo(001), W(001) and Hf(0001) surfaces not only stabilize the metastable 1T' phase against the common 2H phase, but also prevent the structural transformation of 1T' -> 2H by increasing the transition barrier. Remarkably, we reveal the crucial role of charge transfer from the metal surface to Mo d-orbitals of MoS2 that influences the electron occupation of atomic orbitals associated with crystal splitting, which provides an excellent descriptor to determine the stability of the metastable phase. We also propose a novel field-effect transistor made from a single MoS2 layer with a semiconducting 2H phase region connected to two metallic 1T phase regions in contact with a metal electrode (Mo, W, Hf), which exhibits an ideal Schottky-barrier-free interface. These findings are generally applicable, offering an attractive and practical approach to engineer the phase transition of 2D TMDs and design novel nanodevices with multi-functionalities.