First Principles Study On The Mechanical And Electrical Properties Of Monolayer H-BN

Monolayer hexagonal boron nitride(h-BN)is a two-dimensional nano material with wide band gap.It is widely used in micro nano electromechanical systems,optoelectronic devices,field effect transistors and other fields because of its excellent mechanical,electrical and optical properties.However,it is inevitable that there will be some defects in the process of material preparation,which will affect the properties of the material.Therefore,in this thesis,the first principle method is used to study the mechanical and electrical properties of intrinsic and monolayer h-BN with vacancy defects.The main research contents and innovations of this thesis include as following,(1)The mechanical response of the intrinsic monolayer h-BN under uniaxial strain in different chiral directions was studied by first principles method.The results showed that the monolayer h-BN was anisotropic.The theoretical strengths of the zigzag and armchair were97.4 GPa and 82.1 GPa respectively,the young’s modulus were 757.7 GPa and 775.2 GPa respectively,and the critical strains were 0.28 and 0.18 respectively;The zigzag direction had a better ability to bear strain,which was related to the higher atomic density parallel to the serrated direction.(2)The mechanical properties of monolayer h-BN with vacancy defects under uniaxial tensile strain were studied by first principles method.The results showed that the existence of vacancy defects will change the position of atoms near the vacancy,and distort the lattice,thus weakening the mechanical properties of h-BN;Compared with the intrinsic system,the theoretical strength of V_B system in the direction of zigzag and armchair was reduced by23.8%and 15.6%respectively;The theoretical strength of V_N system in two directions decreased by 19%and 22.3%respectively;With the increase of vacancy concentration,Young’s modulus and theoretical strength decreased.(3)The electrical properties of monolayer h-BN with intrinsic and vacancy defects were studied.It was found that the intrinsic monolayer h-BN was an indirect band gap semiconductor material without strain;Uniaxial tensile strain played a certain role in regulating the energy band of the intrinsic monolayer h-BN,and the band gap gradually decreased with the increase of strain;The existence of vacancy defects lead to impurity energy levels in monolayer h-BN,which reduces its band gap.In this thesis,the mechanical and electrical characteristics of monolayer h-BN are deeply discussed through theoretical calculation,which provides theoretical basis and data reference for the application of monolayer h-BN in micro nano electromechanical devices,nano electronic devices,optoelectronic devices and other related fields in the future.