Electronic and Optical Properties of Carbon Nanoribbons

Abstract

Low-dimensional materials have attracted considerable research interest from both theoretical and experimental perspectives. These materials exhibit novel physical and chemical properties due to confinement in low dimensions. Narrow graphene nanoribbons (GNRs) exhibit a significant band gap, and their optical properties are expected to be fundamentally different from those of the parent material, graphene. Unlike graphene, the optical response of GNRs can be tuned by the ribbon width and the directly related band gap. Using density functional theory in the generalized gradient approximation, we studied the electronic band structures and optical properties of graphene nanoribbons passivated with hydrogen atoms. Calculations showed that the band gap decreases with increasing nanoribbon width. This band gap is determined by both quantum confinement and the edge effect. The complex permittivity, complex refractive index, absorption coefficient, and reflectance of 9-AGNR graphene nanoribbon were calculated. The maximum peak values of the real and imaginary parts of the permittivity function are shifted toward lower frequencies. The maximum peak of the absorption coefficient is also shifted toward the blue region of the spectrum. Optical absorption is caused by interband transitions located near the point. The reflectance has three closely spaced peaks located in the red, visible, and blue regions of the spectrum, respectively.