Charge doping induced reversible multistep structural phase transitions and electromechanical actuation in two-dimensional 1T’-MoS2
The 1T’ phase of transition metal dichalcogenides (TMDs) is a low symmetry charge density wave (CDW) phase, which can be viewed as a periodically distorted structure (Peierls distortion) of the high symmetry 1T phase. In this paper, using density functional theory (DFT) calculations, we report that the positive charge (hole) injection is an effective method to modulate the Peierls distortion of MoS2 1T’ for new CDW phase and superior electromechanical properties. A new stable CDW phase is discovered at hole doping level of 0.10 h+/atom, named as 1Tt ’. The hole charging and discharging can induce a reversible phase transition of MoS2 among the three phases, 1T, 1T’ and 1Tt ’. Such reversible phase transition leads to superior electromechanical properties including a strain output as high as −5.8% with a small hysteresis loop, multi-step super-elasticity, and multi-shape memory effect, which are valuable in active electromechanical device designs at nanoscale. In-depth analysis on the change of electronic structure under hole doping was performed to understand the new CDW phase and the observed phase transition. Using charge doping to modulate the Peierls distortion in two-dimensional materials can serve as a general concept for nano-active material designs.