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

Abstract

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.

Two-dimensional layered MSi2N4 (M = Mo, W) as promising thermal management materials: a comparative study

“…2 2D MoSi 2 N 4 was reported to exhibit semiconducting behavior, high carrier mobility, high strength, and excellent ambient stability. 1,2 In addition to that, due to its noncentrosymmetric hexagonal structure and unique electronic structure, several new physical properties such as second harmonic generation, 3 valley pseudospin 4,5 and piezoelectricity 6 were proposed in this system. However, these research studies are mainly focused on the electronic properties instead of the phononic properties of MoSi 2 N 4 , which is of great significance in reliable operation with applications in electronics.…”

Coexistence of intrinsic piezoelectricity and nontrivial band topology in monolayer InXO (X = Se and Te)

“…The softest direction is along the (100) direction, while the hardest direction is along the (110) direction, and the corresponding Young's moduli is 79.94 Nm −1 and 101.36 Nm −1 . The maximum value of Young's moduli is less than that of many 2D materials 15,18,55 , which means that the monolayer Li 2 Fe 2 SSe has extraordinary flexibility. For Poisson's ratios, the minima is along the (110) direction (0.179), while the maxima is along the (100) direction (0.352).…”

Valley polarization transition driven by biaxial strain in Janus $\mathrm{GdClF}$ monolayer

“…The calculated results show that Young's moduli C 2D , shear modulus G 2D and Poisson's ratio ν of GdClF monolayer are 57.15 Nm −1 , 22.32 Nm −1 and 0.281, respectively. The C 2D is less than those of many 2D materials 38,[41][42][43][44][45] , which means that GdClF monolayer can be easily tuned by strain.…”

“…This is the same with ones of Janus monolayer MoSSe 41 . For 2D materials, by using Voigt notation with only considering the in-plane strain and stress [41][42][43][44][45] , the piezoelectric stress, strain and elastic tensors can be re-…”