Two-dimensional Janus Si dichalcogenides: a first-principles study

Abstract

Strong structural asymmetry is actively explored in two-dimensional (2D) materials, because it can give rise to many interesting physical properties. Motivated by the recent synthesis of monolayer $\mathrm{Si_2Te_2}$, we explore...

Giant intrinsic piezoelectricity in 2D hybrid organic–inorganic perovskites [C6H11NH3]2MX4 (M = Ge, Sn, Pb; X = Cl, Br, I)

“…From the illustration in Fig. 6(a), it is clear that compared with other 2D monolayers, 27,29,53–60 [C 6 H 11 NH 3 ] 2 MX 4 have larger piezoelectric stress coefficients e ij . It means that they shall have larger out-of-plane piezoelectric coefficients d 31 and d 32 according to formula (4).…”

“…53,54 In particular, the out-of-plane piezoelectric coefficients ( d 31 = 82.720 pm V −1 ; d 32 = −36.139 pm V −1 ) of [C 6 H 11 NH 3 ] 2 SnBr 4 are the largest among the six investigated systems. This value is 2 orders of magnitude larger than other reported 2D monolayers which include 2D Buckled hexagonal III–V compounds ( d 31 = d 32 = 0.016–0.568 pm/V), 27 Janus structures of quintuple Bi 2 X 3 (X = S, Se) monolayers (| d 31 | = | d 32 | = 0.18–0.20 pm V −1 ), 29 Janus niobium oxydihalide, NbOXY (X, Y = Cl, Br, I and X ≠ Y) ( d 31 = 0.002–0.074 pm V −1 ; d 32 = 0.26–0.34 pm V −1 ), 53 2D M 2 CO 2 (M = Sc, Y, La) MXenes ( d 31 = d 32 = 0.42–1.16 pm V −1 ), 54 Janus transition metal dichalcogenides ( d 31 = d 32 = 0.007–0.028 pm V −1 ), 48 two-dimensional Janus Si dichalcogenides ( d 31 = d 32 = 0.157–0.31 pm V −1 ), 55 Janus group-III chalcogenide monolayers ( d 31 = d 32 = 0.007–0.46 pm V −1 ), 56 group-IV(A) Janus dichalcogenide monolayers ( d 31 = d 32 = 0.11–0.26 pm V −1 ), 57 Janus structures in semiconducting group IVB dichalcogenide monolayers (2D-NS MXY) ( d 31 = d 32 = 0.004–0.414 pm V −1 ), 58 and 2D monolayer Li-based ternary chalcogenides LiMX 2 (M = Al, Ga and In; X = S, Se and Te) ( d 31 = d 32 = 0.05–1.62 pm V −1 ). 46,59 In addition, [C 6 H 11 NH 3 ] 2 SnBr 4 does not contain Pb element, and there is no Pb pollution when it is used in the piezoelectronic device.…”

“…From the illustration in Fig. 6(a), it is clear that compared with other 2D monolayers, 27,29,[53][54][55][56][57][58][59][60] value indicates that the lattice will stretch (compress) along the a-axis (b-axis) when the applied electric field is along the c-axis direction. The significant difference between the intramolecular bond energies (Fig.…”

Novel Piezoelectricity in Two-Dimensional Metallic/Semimetallic Materials with Out-of-Plane Polarization

“…Fourth, it can be combined with flexoelectricity; e.g., the piezoelectricity of semiconducting 2H-MoTe 2 can be turned by surface corrugation-mediated flexoelectricity . Fifth, it can be combined with the Rashba effect. ,, For example, CrSSe and CrSeTe monolayer are materials with both Rashba spin splitting and piezoelectricity, which may become efficient micronano spintronics …”

“…21 Fifth, it can be combined with the Rashba effect. 11,22,23 For example, CrSSe and CrSeTe monolayer are materials with both Rashba spin splitting and piezoelectricity, which may become efficient micronano spintronics. 22 Graphene and many other 2D materials (such as silicene and germanene, 24,25 graphynes, 26 borophene, 27,28 FeB 2 monolayer, 29 t-BN, 30 and M 3 X 2 31 ) constitute a special class of 2D materials called Dirac materials due to their characteristic cone-like band structure near the Fermi level, and the resulting low-energy excitations behave as massless Dirac fermions, 14,32,33 which further leads to various novel phenomena and properties such as fractional quantum Hall effect 34,35 and ultrahigh carrier mobility.…”