We synthesized 4,5-bis(octadecylthio)-4 0 ,5 0 -bis(ethylcarbamoyl)tetrathiafulvalene and measured the electrical conductivity of its perchlorate (ClO 4 À )-doped nanofibers, which have double and triple helix structures. The nanostructure of the bis(octadecylthio)-TTF-diamide and its ClO 4 À -doped fibers in a 3 : 1 ratio was deduced in relation to the X-ray crystal structure of bis(methylthio)-TTF-diamide. The doubly coiled nanofibers form when initially formed spiral ribbons of lamellarly arranged TTFdiamide perchlorate split in the middle, and a further split of the double helix produces the triplex structure. Temperature-dependent conductance and current-voltage (I-V) characteristics of the coiled fibers were measured in the temperature (T) range of 70-300 K. The conductance decreased with a decrease in T, and the I-V characteristics were nonlinear over the entire T range. The results were analyzed by using a modified fluctuation-induced tunneling conduction model, where the barrier height and width were linearly dependent on the electric field.

Magnetoresistance ͑MR͒ and magnetothermoelectric power ͑MTEP͒ of iodine-doped single-walled carbon nanotubes ͑I@SWNT͒ under magnetic fields up to 14 T are investigated from room temperature ͑300 K͒ down to 1.6 K. Our results on resistivity and thermoelectricpower ͑TEP͒ in a zero magnetic field are similar to those reported by Grigorian et al. ͓Phys. Rev. Lett. 80, 5560 ͑1998͔͒ The positive sign of the TEP values indicates that the majority of the carriers in the I@SWNT are holes. The broad enhancement of TEP at temperatures of 30-200 K shows quasilinear temperature dependence and is consistent with sharply varying density of states near the Fermi level with additional contribution from the spin-orbit scattering in the normal metallic characteristics of the I@SWNT. For T Ͻ 7 K, MR is negative and it decreases with H 2 followed by the H 1/2 dependence at around H = 2 T which is characteristic for the weak localization. In the range 7 KϽ T Ͻ 70 K, MR is positive at low magnetic field and becomes negative at higher magnetic field. The negative MR in the high magnetic fields decreases linearly. At T Ն ϳ 100 K, MR is positive up to 14 T, which could be the result of spin-orbit scattering in the I@SWNT. The MTEP decreases under magnetic field at T Ͻ 90 K. The reduction in MTEP is originated from the delocalization of electron wave functions under the magnetic field. At T Ͼ 90 K, the thermal fluctuation dominates the effect of magnetic fields resulting the MTEP to be the same as the zero magnetic field TEP.

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