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

Abstract

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 $785\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ and UV-visible-NIR absorption spectra. Peaks of metallic SWCNTs with small diameters less than $1.1\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ 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 $1.1\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ were still retained after fluorination. Moreover, the D-band decreased after annealing at $900\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$, 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 $1.1\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$. The absorption data also demonstrated the similar diameter dependence in the selectivity to the Raman spectra.