Preferential etching of metallic single-walled carbon nanotubes with small diameter by fluorine gas

We have introduced a new approach to selectively remove metallic single-walled carbon nanotubes (SWCNTs) using a gas phase reaction by fluorine gas, followed by a heat treatment. The metallicity of the treated samples was characterized by the resonant Raman spectra with three wavelengths of 514, 633, and 7850.3em0exnm and UV-visible-NIR absorption spectra. Peaks of metallic SWCNTs with small diameters less than 1.10.3em0exnm in the radial breathing mode of Raman spectra were greatly suppressed with fluorination and completely disappeared after heat treatment. On the other hand, the semiconducting SWCNTs with small diameters less than 1.10.3em0exnm were still retained after fluorination. Moreover, the D-band decreased after annealing at 9000.2em0ex^∘C, which was associated with the release of fluorine atoms during heat treatment. The removal of metallic SWCNTs was not observed at SWCNTs with diameters greater than 1.10.3em0exnm. The absorption data also demonstrated the similar diameter dependence in the selectivity to the Raman spectra.