Transport properties of alkali-doped multi walled carbon nanotubes

In this work we propose a study on electrical properties of multiwalled carbon nanotubes (MWCNT) doped with the most commonly used alkali metals. We report resistivity measurements of MWCNT exposed to doping with Li, Na, K and Cs. Our results show that, increasing the alkali exposure, the resistance of the doped sample decreases denoting a progressive sample metallization. The changes in resistivity, contrary to that observed for single walled carbon nanotubes (SWCNT) in our previous work, are independent upon the alkali properties but appear related to alkali intercalation effects in the MWCNT random network. The doping effects have been also controlled by X-ray photo electron spectroscopy (XPS). The spectra confirm the absence of chemical bonds between carbon nanotubes and alkali, validating the hypothesis of intercalation of alkali in the interstitial channels between the tubes. Our results are also confirmed by comparison between SEM images of single walled and multiwalled carbon nanotubes.