First Principles Study of Properties of Functionalized MXENE (Ti2N) and Defect onMXENE Mono-Layers

Abstract

The evolution of structural and electronic properties of graphene-like titanium nitride MXene has been studied with different functional groups (-F, -O, -H, and -OH)

employing

first principles electronic structure calculations. The calculated formation and cohesive energies reveal the chemical stability of all MXenes and MAX phase. The bare MXene exhibits same hexagonal symmetry as its parent bulk MAX phase. The surface terminated species are distributed randomly on the surface of bare MXene with preferred locations between Ti atoms. The MAX phase and all the studied defect free functionalized MXenes are metallic in nature except for oxygen terminated one, which is found to be 100% spin polarized half-metallic. Additionally, the bare MXene is nearly half-metallic ferromagnet. The spin orbit coupling (SOC) only significantly influences in the bare MXene and trivially influences with O and N defected MXenes. The strain effect influences the Fermi level thereby shifting towards the lower energy state under compression and toward higher energy state under tensile strain in Ti . These properties are reversed in the case of Ti 2 N, Ti 2 NF 2 , and Ti . The halfmetallic

nature changes to semi-metallic under 1% compression and completely destroyed under 2% compression. The variable topological phenomena have been studied

in pristine, strained, and defected MXenes.

Interestingly, the band structure of Ti 2 N(OH) remarkably transforms from half-metallic to semi-conducting (with large band gap of 1.73 eV) in 12.5% Ti, weakly semi-conducting in 5.5% Ti, and topological semi-metal in 12.5% oxygen. The N defect with 25% converts from half-metallic to metallic with certain topological features. Further, the 12.5% Co substitution in Ti preserves the half-metallic character, whereas Mn substitution allows to convert half-metallic into weak semi-metallic preserving ferromagnetic (FM) character. However, Cr substitution converts half-metallic FM to half-metallic anti-ferromagnetic (AFM) character. 2 2 NO 2 2 NH 2 NO 2 2