Active Asymmetric Electron-Transfer Effect on the Enhanced Piezoelectricity in MoTO (T = S, Se, or Te) Monolayers and Bilayers

Abstract

Development of piezoelectric materials is limited partly due to the incompleteness of internal mechanism and the lack of vertical piezoelectricity. Herein, we theoretically identify the stable MoTO (T = S, Se, or Te) monolayers and bilayers. When two elements are given but another element can be changed, the larger the electronegativity difference ratio R ratio is, the stronger the piezoelectricity will be. Vertical piezoelectric coefficient d 33 of the MoTeO bilayer reaches 38.907 pm/V, which is 12 times larger than that of the bulk GaN. The “active asymmetric electron-transfer” strategy mainly contributes to the spontaneous remarkable piezoelectricity of MoTO. Importantly, we proposed the new method for calculating the piezoelectric coefficients of two-dimensional (2D) materials, which corresponds to the fact that 2D materials have a certain thickness. This study not only provides novel extraordinary candidates for energy conversion and touch-sensor nanodevices but also promotes a deeper understanding of piezoelectricity of 2D materials.

Piezoelectricity and valley polarization in a semilithiated 2H-TiTe2 monolayer with near room-temperature ferromagnetism

“…Due to the repulsive interaction between the Li adatoms, however, the relaxed lattice constant and Ti–Te up /Ti–Te dn bond lengths are elongated to 3.90 and 2.89/2.81 Å, respectively. Similar to monolayers of Janus 2H-TMDCs, 28–32 Li@2H-TiTe 2 adopts the C 3v point group thanks to the breaking of reflection symmetry. To assess the stability of the semilithiated system, we first calculate the phonon dispersion with a 3 × 3 × 1 supcell.…”

“…By contrast, asymmetric surface functionalization strategy like resultant 2D Janus materials is found both theoretically and experimentally to be more efficient to produce intrinsic vertical piezoelectricity due to the breaking of out-of-plane reflection symmetry. 28–34…”

Novel valley character and tunable quasi-half-valley metal state in Janus monolayer VSiGeP4

“…Two-dimensional (2D) systems have attracted a lot of public attention because of their excellent, fascinating, and convincing traits, and they possess enormous potential for the development of new electronic devices. 1–7 The valley is a new degree of freedom in 2D systems besides charge and spin, broadening the horizons in spintronic, valleytronic, and functional devices. 8–17 The valley can be denoted by the local extrema in the valence band (VB) and conduction band (CB): that is, valence band maximum (VBM) and conduction band minimum (CBM).…”

Switch effect on controlled water splitting by biaxial strain regulating the promising two-dimensional Janus X2PAs (X = Si, Ge and Sn) photocatalyst

“…2D materials with Janus geometry have garnered much attention for their new properties arising from the broken out-of-plane symmetry. 10,15–24 Interestingly, Yang's group has proposed a new photocatalytic model with an intrinsic dipole that can relieve restriction on the bandgap requirement of photocatalysts. 25 The potential applications of Janus materials in photocatalysis have been revealed in the past.…”