Potassium doping in the double-walled carbon nanotubes at room temperature

The room-temperature chemical doping of potassium (K) in the double-walled carbon nanotubes (DWCNTs) was achieved. The phenanthrene/K complex in 1,2-dimethylethyl ether solution was used for the K-doping. Doping concentration of K in the DWCNTs was 3.2 at %. The K 2p spectrum comprises two peak components at binding energies of K 2p_3/2 (293 eV) and K 2p _1/2 (296 eV), which can be ascribed to the K oxides and cations, respectively. This indicates that the K-doping exhibits a strong charge transfer interaction with carbon atoms and the oxygen atoms at the interface of K/phenanthrene and DWCNTs. Many defects were observed on the wall of the K-doped DWCNTs, resulting in rugged graphite sheets. Also, sometimes cutting appeared on the cross of graphite layers. It was found from the thermogravimetric analysis (TGA) and Raman analysis that the crystallinity of DWCNTs decreased due to K-doping. The room-temperature chemical K-doping strongly influenced the crystalline perfection and defect degree of DWCNTs. The K-doped DWCNTs showed the lower turn-on electric field and the higher emission current density compared to the undoped DWCNTs.