电场调控双层石墨烯纳米带的电子结构和光学性质

利用基于密度泛函理论的第一性原理方法,研究了外加电场作用下双层AA堆垛的Armchair边缘石墨烯纳米带(BAGNRs)的电子结构和光学性质. BAGNRs具有半导体特性,其带隙随带宽(宽度为4～12个碳原子)的增加而振荡性减小.当施加电场后,BAGNRs的带隙随着电场强度的增加而逐渐减小,带隙越大对电场值的变化越敏感.当电场值为0.5 V/?时,所有BAGNRs的带隙都为零. BAGNRs具有各向异性的光学性质,其介电函数在垂直极化方向为半导体特性,而在平行极化方向为金属特性.在外加电场的作用下,BAGNRs的介电函数、吸收系数、折射系数、反射系数、电子能量损失系数和光电导率,其峰值向低能量区域移动,即产生红移现象.电场增强了能带间的跃迁几率.纳米带宽度对这些光学性质参数具有不同程度的影响.研究结果解释了电场调控BAGNRs光学性质的规律和微观机理.

The electronic structures and optical properties of bilayer graphene nanoribbons in external electric fields

The electronic structures and optical properties of AA-stacked bilayer armchair edge graphene nanoribbons (BAGNRs) subject to the influences of a perpendicular electric field are investigated by using first-principles calculations based on density functional theory. We find that the BAGNRs have semiconductive characteristics, and the band gaps decrease oscillationally with the increase of the nanoribbon widths (4 to 12 carbon atoms) of BAGNRs. When the electric fields are applied on the BAGNRs, the band gaps of BAGNRs decrease with the increase of electric field intensity, and the bigger band gap is more sensitive to the electric field intensity. All the band gaps of different width BAGNRs are zero when the electric field intensity reaches to 0.5v/A. The dielectric functions of BAGNRs are of semiconductor in the vertical polarization direction while of metal in the parallel polarization direction showing that the BAGNRs have anisotropic optical properties. For the dielectric functions, absorption coefficients, electron energy loss spectra, optical conductivities, reflectivities and the refraction indexes of BAGNRs, under the external electric field their spectrum peaks move to lower energy zone, indicating red-shifted spectra. The electric field enhances the interband transition. These optical property parameters are influenced differently by the widths of BAGNRs. The research results explain the microscopic mechanism of the electronic structures and optical properties of BAGNRs in the external electric field.