Charge-induced electromechanical actuation of Mo- and W-dichalcogenide monolayers

Using first-principle density functional calculations, we investigate electromechanical properties of two-dimensional MX₂ (M = Mo, W; X = S, Se, Te) monolayers with the 1H and 1T structures as a function of charge doping for both electron and hole doping. We find that by increasing the atomic number, Z_X, of X atoms (Z_S < Z_Se < Z_Te), the work density per cycle of the MX₂ monolayers are increased and decreased for the 1H and 1T structures, respectively. On the other hand, the work density per cycle of the WX₂ monolayers are higher than that of the MoX₂ monolayers for both the 1H and 1T structures. Therefore, WTe₂ and WS₂ monolayers for the 1H and 1T structures, respectively, have the best electromechanical performances in the MX₂ compounds. In addition, the MX₂ monolayers show a reversible strain up to 3%, which is higher than that of graphene (∼1%). Our results provide an important insight into the electromechanical properties of the MX₂ monolayers, which are useful for artificial muscles applications.