Effects of polymerization media on the nanoscale conductivity and current-voltage characteristics of chemically synthesized polyaniline films

A current sensing atomic force microscope (CS-AFM) was used to probe the conducting homogeneity and band structures of fully doped polyaniline (PANI) films prepared from in situ chemical polymerization/deposition of aniline on indium tin oxide in various inorganic acids. The charge transport properties of PANI films depend on the film thickness as well as polymerization medium. Fluctuations in conductivity are observed on all acid-doped PANI films and the conducting homogeneity was dependent on the film thickness: the conductivity of thick film is more uniform. The current-voltage (I-V) characteristics of all thick (>200 nm) films displayed a metal-like behavior and conductivity as high as 40 S/cm was detected in high conducting regions of film thicker than 400 nm. Whereas thin (<120 nm) films revealed insulating, semiconducting, and semimetal conducting, wide distribution in conductivity and interband distances (estimated from the I-V ordI/dV-V curves) was found. The interband distances is 0-1.35, 0-1.0, and 0-0.78 eV for thin PANI film prepared from HCl(aq), HClO(4)(aq), and H2SO4(aq), respectively. PANI film (260 nm) prepared from H2SO4(aq) revealed fiberlike morphology, and compared to PANI films prepared from HCl(aq) and HClO4(aq) with similar thickness, it has higher average nanoscale conductivity but lower bulk conductivity. This result could be direct evidence which supports that the bulk conductivity of PANI depended on the carriers hopping between the conducting domains.