CAFM on conjugated polymer nanofibers: Capable of assessing one fiber mobility

Abstract

Poly(3-alkylthiophene) (P3AT) nanofibers (NFs) are interesting as building blocks for future organic electronic devices but also as a model system to examine transport mechanisms in semiconducting polymers. However, due to the technical problem of making good contacts at the nanometer scale, electrical characterizations on one isolated P3AT NF are rare. Here, using Conductive Atomic Force Microscopy (CAFM), charge transport investigations along the length (p-p stacking direction) and the height (alkyl chain direction) of one single NF are reported. Firstly, by developing a transistor structure with one electrode being the CAFM tip, we measured the longitudinal mobility: mu(L) = 0.07 +/- 0.03 cm(2) V(-1) s(-1). Secondly, charge transport along the NF height was done in a sandwich structure and led to a transversal mobility of mu(T) similar to 10(-5)-10(-6) cm(2) V(-1) s(-1) where mu(T) was found to decrease with increasing alkyl side chain length. With CAFM charge transport anisotropy in P3AT NF is thus evidenced at the nanometer scale, since we find at least four orders of magnitude difference between mu(L) and mu(T). (C) 2011 Elsevier B. V. All rights reserved.