Synthesis of fullerene encased single-walled carbon nanotube by means of electro-chemistry

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By using the electro-chemistry method, doping of Fullerenes within the single-wall carbon nanotube (SWNT) was carried out from the toluene solution of C60 with electrolyte of lithium-perchiorate in DMF. Reduction voltage of ca. -0.5 V for C_<60> fullerene was applied in order to dope the fullerene molecules to SWNT mats, which were attached on the both ends of the Pt-plate electrodes. As results, SWNT mat attached on the positive electrode fully encases the C_<60> molecules. On the other hand, SWNT mat on the negative electrode rarely encases the fullerene ; most of the fullerenes were on the outside of the tube and Li was attached on the surface. These facts suggest that the anion of C_<60> was approached to the positive electrode due to electrostatic force and was efficiently encased within the SWNT. Thermal polymerization of C_<60> molecules, which is progressed in the nanotube space, was investigated detailedly by using Raman scattering spectroscopy in order to clarify the polymerization process from the array structure of C_<60> molecules to the tubular structure. As a result, 0.7 nm diameter tubes were formed inside the host tube and the diameter of the tube was changed to large diameters in order to match the inter-tube-wall separation with the van der Waals distance. We proposed a diameter transformation model for the inner tubes, which is based on forming the (9,0) zig-zag tube at first. Experiments of bromine doping to the double-wall carbon nanotubes were also carried out in the present program, and we found that the electrons can be transferred to the bromine molecules from the outer tubes, but they cannot be transferred from the inner tubes. This fact was also supported by the theoretical arguments based on the self-consistent tight, binding model calculation, which was carried out as the collaboration work with the group at Pennsylvania State University.