Electric Property Change of Single-Walled Carbon Nanotube by the Encapsulation of Aliphatic Thiols.

The encapsulation of single-walled carbon nanotubes (SWNTs) with aliphatic thiol compounds with a relatively small amount of ionization energy achieves n-type doping of SWNTs. Thiol compounds encapsulated inside nanotubes in vacuum drastically change the electric properties of SWNTs by a charge transfer between the two species. The simplicity of the synthetic process offers a viable route for large-scale production of SWNTs with controlled doping states by using mat-type SWNTs. Optical characterization (Raman and near-infrared spectrum) and electric property (conductivity) reveals that a charge transfer between the SWNTs and compounds occurs through the difference in the ionization energy and electron affinity. We confirm an electron density change in SWNTs through optical spectroscopy and conductivity measurement in vacuum. X-ray photoelectron spectroscopy also reveals that the compounds are predominantly encapsulated inside SWNTs.