Carrier Doping into Single-Walled Carbon Nanotubes through Encapsulation of Fluorinated Fullerenes

The fluorinated fullerene C60Fx (x ≈ 42) was synthesized by heating C60 fullerene in a fluorine gas atmosphere. Subsequently, the encapsulation of C60Fx within single-walled carbon nanotubes (SWCNTs) was achieved by placing C60Fx and SWCNTs inside a glass tube and subjecting them to further heat treatment under vacuum conditions. The formation of SWCNTs encapsulating C60Fx (C60Fx@SWCNT) was confirmed through various techniques, including transmission electron microscopy, X-ray diffraction experiments, Raman scattering experiments, and X-ray photoelectron spectroscopy. Furthermore, measurements of the electrical conductivity and the Seebeck coefficient of the C60Fx@SWCNT revealed that SWCNTs were hole-doped as a result of the encapsulation of C60Fx. Similar measurement was conducted for SWCNTs containing tetracyanoquinodimethane (TCNQ), and it was observed that C60Fx had the larger hole-doping effect per molecule than TCNQ. Additionally, it was demonstrated that C60Fx@SWCNT functions effectively as oxygen reduction electrodes.