Electrical conductivity of single polycrystalline-amorphous carbon nanocoils

Polycrystalline-amorphous carbon nanocoils (CNCs) have been synthesized by thermal chemical vapor deposition. The electrical conductivity of a single CNC is investigated over a wide temperature range from 4 to 300 K by employing the four-probe method. It is found that the smaller the line diameter of the CNC, the bigger the size of the crystalline grain, which results in the better crystallinity and conductivity. Moreover, the temperature behavior of rho(T) reveals that the intrinsic electric-transport mechanisms through a single helical CNC are mainly due to a combination conduction processes of the thermal activation, the nearest-neighbor hopping, and variable range hopping. Meanwhile, the dominate electron transport mechanisms crossover from one mode to another with the circumstance temperature. Notably, it follows Mott variable range hopping and Efros-Shklovskii variable range hopping at low temperature. The model transition zones which are related to the crystallinity of the CNCs are also discussed in each temperature regime. (C) 2015 Elsevier Ltd. All rights reserved.