Tunneling spectroscopy and spectroscopic imaging of granular metallicity of polyaniline

The band-gap electronic structures of two forms of the conducting polymer polyaniline, emeraldine base (EB) and emeraldine salt (ES), have been studied. Tunneling spectroscopy measurements show that ES is metallic in nature with a finite electron density of state at the Fermi energy (EF), while EB behaves as an insulator with a gap at EF in agreement with theoretical calculations. These results allowed us to obtain direct evidence of the granular metallicity of ES by spectroscopic imaging. The spectroscopic images show different spatial distributions of nanometer-sized metallic particles in ES and EB samples, providing important information needed in studying electrical conductivities of conducting polymers.