Optical and electronic properties of iodine and bromine doped chirality enriched (12,1) and (13,2) single-walled carbon nanotubes

Abstract

We present transmission measurements on chirality enriched semiconducting (12,1) and (13,2) single-walled carbon nanotubes (CE-s-SWCNTs) and CE-s-SWCNTs doped with iodine (I2@CE-s-SWCNTs) and bromine (Br2@CE-s-SWCNTs) in wide frequency range from 0.1 to 40 THz. The real part of the optical conductivity σreal(ω) was fitted using Drude-Lorentz model. The Drude (D) term in the CE-s-SWCNTs was attributed to the presence of metallic tubes traces in the sample. The D/scattering rate(γD) ratio was increased by a factor of 1.13 and 2.35 with iodine and bromine p-doping, respectively. This increase was compensated by large increase in D term leading to an increase in the optical conductivity at the DC limit (σDC), growing from 186 Ω−1cm−1 for the CE-s-SWCNTs to 203 and 426 Ω−1cm−1 for the I2@CE-s-SWCNTs and Br2@CE-s-SWCNTs, respectively. In addition, the plasmon peak was shifted to higher frequencies and gains more spectral weight with doping. The calculated optical parameters determine that iodine and bromine create acceptor levels above the top of the CE-s-SWCNTs valence band by 0.04 and 0.08 eV, respectively, shifting the Fermi level. The high σDC value of the Br2@CE-s-SWCNTs is due to the higher electronegativity of bromine which enables removal of more electrons from the valence band of CE-s-SWCNTs to bromine acceptor levels.