Metal-conductive polymer hybrid nanostructures: preparation and electrical properties of palladium-polyimidazole nanowires

A simple, convenient method for the formation of hybrid metal conductive polymer nanostructures is described. Polyimidazole (PIm) has been templated on λ-DNA via oxidative polymerisation of imidazole using FeCl3 to produce conductive PIm DNA nanowires. The PIm DNA nanowires were decorated with Pd (Pd PIm DNA) by electroless reduction of with NaBH4 in the presence of PIm DNA; the choice of imidazole was motivated by the potential Pd(II) binding site at the pyridinic N atom. The formation of PIm DNA and the presence of metallic Pd on Pd PIm DNA nanowires were verified by FTIR, UV-vis and XPS spectroscopy techniques. AFM studies show that the nanowires have diameters in the range 5-45 nm with a slightly greater mean diameter (17.1 0.75 nm) for the Pd-decorated nanowires than the PIm DNA nanowires (14.5 0.89 nm). After incubation for 24 h in the polymerisation solution, the PIm DNA nanowires show a smooth, uniform morphology, which is retained after decoration with Pd. Using a combination of scanned conductance microscopy, conductive AFM and two-terminal measurements we show that both types of nanowire are conductive and that it is possible to discriminate different possible mechanisms of transport. The conductivity of the Pd PIm DNA nanowires, (0.1-1.4 S cm−1), is comparable to the PIm DNA nanowires (0.37 0.029 S cm−1). In addition, the conductance of Pd PIm DNA nanowires exhibits Arrhenius behaviour (Ea = 0.43 0.02 eV) as a function of temperature in contrast to simple Pd DNA nanowires. These results indicate that although the Pd crystallites on Pd PIm DNA nanowires decorate the PIm polymer, the major current pathway is through the polymer rather than the Pd.