Effect of the fluorination technique on the surface-fluorination patterning of double-walled carbon nanotubes

Double-walled carbon nanotubes (DWCNTs) are fluorinated using (1) fluorine F(2) at 200 °C, (2) gaseous BrF(3) at room temperature, and (3) CF(4) radio-frequency plasma functionalization. These have been comparatively studied using transmission electron microscopy and infrared, Raman, X-ray photoelectron, and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. A formation of covalent C–F bonds and a considerable reduction in the intensity of radial breathing modes from the outer shells of DWCNTs are observed for all samples. Differences in the electronic state of fluorine and the C–F vibrations for three kinds of the fluorinated DWCNTs are attributed to distinct local surroundings of the attached fluorine atoms. Possible fluorine patterns realized through a certain fluorination technique are revealed from comparison of experimental NEXAFS F K-edge spectra with quantum-chemical calculations of various models. It is proposed that fluorination with F(2) and BrF(3) produces small fully fluorinated areas and short fluorinated chains, respectively, while the treatment with CF(4) plasma results in various attached species, including single or paired fluorine atoms and –CF(3) groups. The results demonstrate a possibility of different patterning of carbon surfaces through choosing the fluorination method.