Fabrication of Polyaniline (PANI) through Parallel Nanopores: Charge Transport Properties of PANI@SiO2 Nanopore Molecular Junctions

Aniline is electropolymerized through mesoporous silica nanopores (100 nm-long, 3 nm in diameter) orthogonally oriented on indium-tin oxide (ITO). Only a few polyaniline (PANI) wires are accommodated in the nanochannels and their growth is electrochemically controlled. The electronic transport properties of PANI@SiO2 are studied by Conductive Atomic Force Microscopy (C-AFM), using a Pt-coated C-AFM tip. Three different behaviors are observed. First, linear I/V curves are obtained when PANI is deposited in the nanopores with material spilling over the silica membrane; electron transport occurs through many PANI@SiO2 channels and the overall conductance is high. Second, flat I/V curves are recorded, indicating "insulator" behavior when the SiO2 nanopores are not fully filled by PANI wires. Thirdly, non-linear I/V curves, which are quantitatively highly reproducible and independent of the point probed, are obtained. These are attributed to the formation of molecular junctions where the C-AFM tip in contact with the nanopores acts as the top electrode and vertical PANI wires just fill the SiO2 channels. The size of the top electrode and the reproducilility of the I/V suggest that the C-AFM is seeing about 5 nanopores each filled with one or two PANI wires.