石墨炔型BC_xN(x=1,2)的力学性质、电子结构和光学性质

The mechanical properties, electronic structure and optical properties of graphyne-BC_xN(x=1,2)

本文采用基于密度泛函的第一性原理研究了石墨炔型α-BC2N,β-BCN,γ-BC2N的结构稳定性、力学性质、电子结构和光学性质.结合能和声子谱验证了三种新结构是稳定存在的.研究力学性质时发现,γ-BC2N泊松比仅有0.41,垂直于平面的方向具有较好的抗压缩能力;α-BC2N,β-BCN的泊松比较大,可用作柔性薄膜材料.三种材料的带隙值分别是2.541, 0.241和1.711 e V,均是直接带隙半导体.这是因为B, N原子的介入打破了原有结构对称性,从而打开了石墨炔的带隙值.三种半导体的带隙值受应变的调控,均随应变值的增加而带隙变窄.光学性质表明新结构可对相当宽的能量范围内的光子产生响应.其中,α-BC2N和γ-BC2N的光子吸收行为从可见光区开始,而β-BCN则可吸收从红外持续到紫外能量范围内的光子.同时,三种材料的反射率都很低,光子透过率很强,可用做吸波材料.

In this paper,the structural stability,mechanical properties,electronic structure and optical properties ofα-BC2 N,β-BCN andγ-BC2 N were studied by the first-principles based on density functional theory.Cohesive energy and phonon spectra verify that these structures are stable.When studying the mechanical properties,it is found that theγ-BC2 N Poisson’s ratio is 0.41,which has better resistance to compression in the direction perpendicular to the plane;the Poisson ofα-BC2 N andβ-BCN is relatively large and can be used as a flexible film material.The band-gap values of the three materials are 2.541,0.241 and 1.711 eV,respectively,which are direct band-gap semiconductors.B and N atoms break the original structure symmetry,and band gap values of these structures are enlarged.The band gap values of the three semiconductors are regulated by strain,and the band gaps are narrowed as the strain value increases.Optical properties indicate that the new structure can respond to photons in a fairly wide range of energies.Among them,the photon absorption behavior ofα-BC2 N andγ-BC2 N starts from the visible region,whileβ-BCN absorbs photons from the infrared to the ultraviolet energy range.At the same time,the reflectivity of the three materials is very low,the photon transmittance is very strong,and it can be used as an absorbing material.