title: Two new phases of monolayer group-IV monochalcogenides and their piezoelectric properties.
abstract: Two stable structural phases of the monolayer group-IV monochalcogenides GeS, GeSe, SnS and SnSe have been found using first-principles calculations, and will be called as A-MX and H-MX. It is found that these two new phases are energetically nearly degenerate with the pristine phase Z-MX and are semiconductors for all four group-IV monochalcogenides. The band gaps of A-MX range from 1.62 eV to 1.86 eV, while H-MX exhibits wider band gaps in the range from 2.21 eV to 2.47 eV. Moreover, both of them exhibit significant piezoelectric properties. The piezoelectric coefficient of A-MX is about 1-2 orders of magnitude higher than those of other frequently used piezoelectric materials, showing obvious anisotropic characters, while that of H-MX is isotropic and comparable with those of other piezoelectric materials.
authors.affiliation: Department of Applied Physics, Nanjing University of Science and Technology, Nanjing, 210094, China.
authors.forename: Ting
authors.initials: T
authors.lastname: Hu
authors.affiliation: Group of Computational Condensed Matter Physics, National Laboratory of Solid State Microstructures and Department of Physics, Nanjing University, Nanjing 210093, P. R. China. jdong@nju.edu.cn.
authors.forename: Jinming
authors.initials: J
authors.lastname: Dong