Large out-of-plane piezoelectricity of VIA group functionalized MXenes thin films for MEMS

Abstract

The integration of piezoelectric and micro-electro-mechanical system (MEMS) technologies is promoting the rapid development of the MEMS industry. However, due to the lack of excellent in-plane and out-of-plane piezoelectric coefficients, good ambient temperature stability, and high mechanical durability, the reported two-dimensional piezoelectric thin films are facing severe challenges in the development of MEMS. Therefore, based on density functional theory calculations, we simulated the VIA group (the sixth main family in the periodic table of elements) functional MXenes, namely, Sc2CXY (Sc2COS, Sc2COSe, Sc2CSO, and Sc2CSeO). The results show that this kind of material has good dynamic, thermal, and mechanical stability. Importantly, the structure exhibits good in-plane and out-of-plane piezoelectric effects due to the inversion asymmetry, bandgap adjustability, flexibility, and different electronegativity. Among them, the piezoelectric strain value of d33 is one to three orders of magnitude higher than that of d22 or d31, which makes these materials can become a strong candidate for advanced equipment such as nano-wearable electronics, robot bionic skin, and piezoelectric products for MEMS.

Intrinsic Coupling between Piezoelectric and Electronic Transport Properties in Janus γ-GeSnXO (X = S, Se) Monolayers with Vertical Piezoelectricity

“…Based on first-principles density functional theory, in the following research, we explored the piezoelectric effect of the Janus γ-GeSnXO monolayer. Next, the formation energy of γ-GeSnXO was calculated according to the formula normalΔ E = ( E − n 1 × E 1 − n 2 × E 2 − n 3 × E 3 − n 4 × E 4 ) / n E is the total energy of the γ-GeSnXO sheets, E 1 , E 2 , E 3 , and E 4 are the per atom crystal energy of Ge, Sn, S/Se, and O in the solid phase, respectively, n 1 , n 2 , n 3 , and n 4 are the numbers of each element in the unit cell, and n is the total number of atoms. The formation energy determines the stability of matter.…”

First-Principles Investigation of Two-Dimensional CuPP-Grid Molecular Sieves for C4 Hydrocarbon Purification by a Double-Bond Effect

“…The Grimme’s DFT-D2 van der Waals (vdW) correction was employed for evaluating the interaction between molecules and the CuPP-Grid molecular sieve . To fully optimize all atomic positions, the convergence criteria for force and plane-wave cutoff energy were set to 0.02 eV/Å and 10 –5 eV, respectively. − The thermal stability of CuPP-Grid was verified by performing ab initio molecular dynamics (AIMD) simulation using a Nosé–Hoover thermostat. In an NVT ensemble, the temperature was set as 300 K and the AIMD simulation lasted for 5 ps with a time step of 1 fs.…”

2D layered BP/InSe and BP/Janus In2SeX (X = S or Te) type-II van der Waals heterostructures for photovoltaics: insight from first-principles calculations

“…15–17 Moreover, 2D Janus MoSSe can be successfully synthesized by sulfurization of MoSe 2 or selenization of MoS 2 . 18,19 Compared to pristine 2D materials, 2D Janus materials lose their mirror symmetry and generate an internal vertical electric field, giving rise to many new phenomena such as enhanced out-of-plane piezoelectric coefficients, 20–22 increased carrier mobility, 23,24 and significant Rashba splitting. 24–27 First-principles calculations also predicted that some 2D Janus materials are intrinsically ferromagnetic, such as Janus FeXY (X, Y = Cl, Br, and I, X ≠ Y) 28 and Janus Cr 2 I 3 X 3 (X = Br, Cl) monolayers.…”