Investigation of electrical properties of nanostructured carbon films derived from block copolymers

Electrical properties of nanostructured carbon (ns-C) films fabricated by pyrolysis of PAN-b-PBA copolymers were investigated. Films having cylindrical morphology and pyrolyzed at 400,500 and 600 C were investigated. Both carbide forming (Zr,Ti) and non-carbide forming (Cu, Pt) metals spanning a wide range of electron work functions (4.1-5.5 eV) formed ohmic contacts to the ns-C films in the as-deposited state. The conductivity of the ns-C films increased roughly three orders of magnitude for every 100 C increase in the pyrolysis temperature. Hall-effect measurements showed that the films pyrolyzed at 600 C were n-type with a majority carrier concentration and mobility of 5.8 x 10(18) cm(-3) and 0.97 cm(2)/V s, respectively. Current-voltage measurements as a function of temperature (I-V-T) were performed on films pyrolyzed at 600 C, whereas films pyrolyzed at 400 and 500 C were too resistive for reliable resistivity-temperature and Hall-effect measurements. The resistivity as a function of temperature was analyzed by using the reduced activation energy method and was determined to follow variable-range hopping (VRH) mechanisms at and below room temperature. The data indicates a crossover from Efros-Shklovskii VRH [J. Phys. C 8. (1975) L49] to Mott VRH [J. Non-Cryst. Solids 1, (1968) 1] at temperatures above 100 K. (C) 2008 Elsevier B.V. All rights reserved.