Two-dimensional MoS₂ electromechanical actuators

We investigate the electromechanical properties of two-dimensional MoS₂ monolayers with 1H, 1T, and 1T′ structures as a function of charge doping by using density functional theory. We find isotropic elastic moduli in the 1H and 1T structures, while the 1T′ structure exhibits an anisotropic elastic modulus. Moreover, the 1T structure is shown to have a negative Poisson's ratio, while Poisson's ratios of the 1H and 1T′ are positive. By charge doping, the monolayer MoS₂ shows a reversible strain and work density per cycle ranging from -0.68% to 2.67% and from 4.4 to 36.9 MJ m^-3, respectively, making them suitable for applications in electromechanical actuators. We also examine the stress generated in the MoS₂ monolayers and we find that 1T and 1T′ MoS₂ monolayers have relatively better performance than 1H MoS₂ monolayer. We argue that such excellent electromechanical performance originate from the electrical conductivity of the metallic 1T and semimetallic 1T′ structures and also from their high Young's modulus of about 150-200 GPa.