Strain-induced band modulation and excellent stability, transport and optical properties of penta-MP2 (M = Ni, Pd, and Pt) monolayers.

Vipin Kumar,Debesh R Roy

doi:10.1039/d0na00503g

Abstract

First principle calculations utilizing density functional theory were carried out to investigate the electronic, transport and optical properties of penta-MP2 (M = Ni, Pd and Pt) monolayer compounds under applied uniaxial and biaxial tensile strains. With an optimum magnitude of applied strain, we found band gap transitions in penta-MP2 monolayers from zero/narrow to the semiconductor regime, wherein band gaps were noticed to be firmly dependent on the applied uniaxial and biaxial tensile strains. In this study, the PBE approach was used primarily to evaluate electronic properties, from where the identified architectures of penta-MP2 with maximum obtained bandgaps under respective optimum strains were assessed through the HSE06 method of calculation for better estimation of band gaps and optical properties. Prior to HSE calculations, we affirmed our assessment for the stability and reliability of the compounds under uniaxial and biaxial strains of up to 15% through phonon spectrum and elastic calculations. A distinct transition was also noted from semiconductor to metal for all compounds after the applied optimum uniaxial and biaxial strains. The optical absorption spectra in all the stretched penta-MP2 compounds reached the order of 106 cm−1, with significant peaks belonging to the IR and visible regions; this indicates promising applications of these materials in high-performance solar energy and good hot mirror materials. The enhanced I–V responses under uniaxial and biaxial tensile strains using the non-equilibrium Green's function (NEGF) approach confirm the usefulness of the strained state of the considered penta-MP2 monolayers. The results show that tuning electronic properties, I–V characteristics and optical properties of stretched penta-MP2 compounds under tensile strain merits significant future applications in optoelectronic devices and as good hot mirror materials.

Highlights

The discovery of graphene in 2004 encouraged substantial scienti c efforts in the research community to explore two-dimensional (2D) materials, as they exhibit outstanding physical, mechanical, electronic, optical and transport properties
Employing density functional perturbation theory (DFPT)[63] interfaced with phonopy[64] code, we evaluated the dynamical strength using the small displacement method of atoms with 4 Â 4 Â 1 supercells for all the considered structures, and the phonon spectra were determined using the obtained second order force constant
The calculated energy loss spectrum L(u) for NiP2 was found to be quite large at 2.9 eV photon energy, whereas a much lower peak was observed at 1.4 eV for the polarization in the parallel direction

Summary

Introduction

We have performed a systematic investigation of the electronic properties of a series of monolayer penta-MP2 (M 1⁄4 Ni, Pd and Pt) compounds under tensile strains of up to 15% using density functional theory (DFT).[50] Initially, we considered the Perdew–Burke–Ernzerhof (PBE)[51,52] approach for bandgap modulation to nd the maximum bandgap value with respect to a particular amount of strain in the uniaxial and biaxial directions. It is well known that PBE-DFT usually underestimates electronic band gaps To overcome this issue, we employed a very popular hybrid functional, Heyd–Scuseria–Ernzerhof (HSE06),[53,54] to obtain more accurate band gap values. T(E,V) 1⁄4 Tr[aR(E,V)GR(E,V)aL(E,V)GL(E,V)GA(E,V)] (3) where a and GA denote the coupling matrix of the electrodes and the Green's function of the central region, respectively

Results and discussion

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Concluding remarks