Robust doping of single-walled carbon nanotubes with ionic liquids: experiment and first-principles modeling†

Single-walled carbon nanotubes (SWCNTs) have considerable application potential. Due to their unique electrical properties, they are expected to become critical components of future microelectronics. However, their ability to propagate charge, commonly gauged by measuring electrical conductivity, is still unsatisfactory. One of the most straightforward methods of improving this property involves doping, which affects the Fermi level of the material. Unfortunately, it is not uncommon that the potent doping agents only improve the electrical conductivity of SWCNTs briefly before they either degrade or evaporate from the material. In particular, it is especially undesired in the case of halogen-based dopants, which improve the electrical properties of SWCNTs substantially, but, at the same time, they are often highly volatile. To alleviate this problem, we designed and thoroughly examined a SWCNT doping platform based on ionic liquids, which are well-known for their stability and negligible vapor pressure. Our experimental results demonstrated that the electrical properties of the material were considerably improved, and the enhancement did not deteriorate over time. First-principles modeling based on density functional theory and non-equilibrium Green's function formalism provided insights into the mechanisms responsible for this enhanced and sustained performance.