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

• Published in: Synthetic metals Vol. 159; no. 3; pp. 177 - 181
• Main Authors: Kulkarni, P., McCullough, L.A., Kowalewski, T., Porter, L.M.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.02.2009; Elsevier
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Conduction mechanism; Electronic structure and electrical properties of surfaces, interfaces, thin films and low-dimensional structures; Electronic transport in multilayers, nanoscale materials and structures; Exact sciences and technology; Nanostructured carbon films; Physics; Porous; Variable-range hopping; Conduction mechanism; Nanostructured carbon films; Variable-range hopping; Porous; Work functions; Electrical conductivity; Hall effect; Nanostructures; Majority carrier; Temperature effects; Ohmic contacts; Microstructure; Carrier mobility; Chemical synthesis; IV characteristic; Carrier density; Activation energy
• ISSN: 0379-6779; 1879-3290
• DOI: 10.1016/j.synthmet.2008.08.015

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 × 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.