Electrical properties of a single microcoiled carbon fiber

Regular microcoiled carbon fibers with a double helix structure have been synthesized by the catalytic pyrolysis of acetylene at 750–790°C using Ni powder as a catalyst and thiophene as a promotor. The measurements by a standard four-probe technique of resistance, I-V curves, and magnetoresistance of a single microcoiled fiber are presented. I-V curves and the temperature dependence of the resistance are in accordance with Mott-David [Electronic Processes in Noncrystalline Materials (Oxford University Press, Oxford, 1979), 2nd ed., p. 32] variable range hopping above 13K and Shklovskii-Efros [Electronic Properites of Doped Semiconductors (Springer, Berlin, 1984), p. 202]; Pollak-Shklovshii [Hopping Transport in Solids, (North-Holland, Amsterdam, 1991), 273] variable range hopping below 13K. In addition, a positive magnetoresistance with H2-dependence behavior is observed at low temperature.