Effect of vacancy defect and strain on the structural, electronic and magnetic properties of carbon nitride 2D monolayers by DFTB method
Taoufik Sakhraoui
Abstract
Abstract We investigate the electronic and magnetic properties of C <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mi> </mml:mi> <mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">n</mml:mi> </mml:mrow> </mml:mrow> </mml:msub> </mml:math> N <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mi/> <mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">m</mml:mi> </mml:mrow> </mml:mrow> </mml:msub> </mml:math> (C 6 N 6 , C 2 N, C 3 N and C 3 N 4 ) using density functional tight-binding (DFTB) method. We find that these compounds are dynamically stable and their electronic band gaps are in the range of 0.59–3.28 eV. We show that the electronic structure is modulated by strain and the semiconducting behavior is well preserved except for C 3 N at +5% biaxial strain, where a transition from semiconductor to metal was observed. Under +3% biaxial strain, C 3 N 4 undergoes a transition from an indirect (K-Γ) to a direct (Γ-Γ) band gap. Moreover, band gap of C 2 N transforms from direct (Γ-Γ) to indirect (M-Γ) under +4% biaxial strain. However, no change in the nature of the band gap of C 6 N 6 . Further, when the studied materials under uniaxial tensile strain, their bandgaps reduce. Our theoretical study showed that an indirect-to-direct nature transition may occur for C 6 N 6 and for C 3 N 4 , which broadens their applications. On the other hand, magnetism is observed in all N-vacancy defected C <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mi> </mml:mi> <mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">n</mml:mi> </mml:mrow> </mml:mrow> </mml:msub> </mml:math> N <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mi/> <mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">m</mml:mi> </mml:mrow> </mml:mrow> </mml:msub> </mml:math> , which encourages its application in spintronic. Moreover, calculations of formation energies indicate that N-vacancy is energetically more favorable than C-vacancy in both C 2 N and C 3 N 4 . Opposite behavior found for C 6 N 6 and C 3 N.