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Modulating Peierls distortion of 1T_prime MoS2 via charge doping: a new charge density wave phase, reversible phase transition, and excellent electromechanical properties

The 1T_prime phase of transition metal dichalcogenides (TMDs) is a low symmetry charge density wave (CDW) phase, which can be regarded 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_prime for new CDW phase and superior electromechanical properties. A new stable CDW phase is discovered at hole doping level of ~ 0.10h+/atom, named as 1Tt_prime. The hole charging and discharging can induce a reversible phase transition of MoS2 among the three phases, 1T, 1T_prime and 1Tt_prime. 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.