Fe, Al, N, S co-doping as a tool for regulating the optical properties of (8,0) single-walled carbon nanotubes: a first principle study

A first principles study on the influence of co-doping on several optical porperties of a (8, 0) single-walled carbon nanotube (SWCNT) is introduced in this study. Density functional theory (DFT) is used to calculate the optical properties of a pristine (8, 0) SWCNT and SWCNTs co-doped with aluminum (Al) and sulphur (S); iron(Fe) and sulphur (S); Al, S and nitrogen (N); and Fe, S and N, which is achieved by the cambridge sequential total energy package (CASTEP). Distinct optical properties of the pristine and co-doped SWCNTs were calculated and compared, which includes the dielectric function, refractive index, reflectivity, absorption, conductivity and loss function. For the dielectric function, refractive index and reflectivity, the values of optical porperties are highest for SWCNT co-doped with Al and S, while the nonadjacent element Fe is introduced, the values sharply decline for SWCNT co-doped with Fe and S. However, when nitrogen is added to two kinds of co-doped SWCNTs, the optical properties are almost the same; this phenomenon shows that the nitrogen element can weaken the influence of other co-doped elements. For absorption, conductivity and loss function, a reduction can be observed as a result of co-doping irrespective of the nature of the incident light and the variety of doping element. It is also observed that the polycrystalline media in the incident light path has an influence on the optical properties. It can be concluded that co-doping can be used as a new method for controlling the optical properties of modified carbon nanotubes. This is of great value for the design of sensitive optical elements based on SWCNTs.