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 F₂ at 200 °C, (2) gaseous BrF₃ at room temperature, and (3) CF₄ 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 F₂ and BrF₃ produces small fully fluorinated areas and short fluorinated chains, respectively, while the treatment with CF₄ plasma results in various attached species, including single or paired fluorine atoms and -CF₃ groups. The results demonstrate a possibility of different patterning of carbon surfaces through choosing the fluorination method.