Intrinsic piezoelectricity in monolayer MSi2N4 (M = Mo, W, Cr, Ti, Zr and Hf)

Motived by experimentally synthesized (Hong Y. L. et al., Science, 369 (2020) 670), the intrinsic piezoelectricity in monolayer ( , W, Cr, Ti, Zr and Hf) are studied by density functional theory (DFT). Among the six monolayers, has the best piezoelectric strain coefficient d(11) of 1.24 pm/V, and the second is 1.15 pm/V for . Taking as a example, strain engineering is applied to improve d(11). It is found that tensile biaxial strain can enhance d(11) of , and the d(11) at 4% strain can improve by 107% with respect to the unstrained one. By replacing the N by P or As in , the d(11) can be raised substantially. For and , the d(11) is as high as 4.93 pm/V and 6.23 pm/V, which is mainly due to smaller and very small minus or positive ionic contribution to piezoelectric stress coefficient e(11) with respect to . The discovery of this piezoelectricity in monolayer enables active sensing, actuating and new electronic components for nanoscale devices, and is recommended for experimental exploration.