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.