N-type doping effect of single-walled carbon nanotubes with aromatic amines

Abstract

We investigated the chemical doping of the single-walled carbon nanotubes (SWCNTs) networks by a treatment with aromatic amines. Adsorption and intercalation of amine molecules in bundled SWCNTs leads to typical n-type doping observed already for alkali metals. The electron donation to SWCNTs is demonstrated by the X-ray-induced photoelectron spectra (XPS), where the carbon C Is peak observed at 284.4 eV for the sp(2) carbon in pristine samples is shifted by up to 0.3 eV to higher binding energy upon chemical treatment. The development of a Breit-Wigner-Fano component on the lower energy side of the G mode in the Raman spectrum as well as a shift of the G(+) to lower frequency provide evidence for charge accumulation in the nanotube pi system, and indication for the n-type doffing. The spectroscopic changes are accompanied by the modification of the electrical properties of the SWCNTs. A reduction of conductivity depends on the doping level and implies the decreasing concentration of the charge carriers in the naturally p-doped tubes. Comparing the two selected n-type dopants, the tetramethyl-p-phenylenediamine, shows more pronounced changes in the XPS and the Raman spectra than tetramethylpyrazine, indicating that the sp(3) hybridization of nitrogen in the amine groups attached to phenyl ring is much more effective in interaction with the tube it system than the sp(2) hybridization of nitrogen in the aromatic pyrazine ring. (c) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim