Tunneling spectroscopy and spectroscopic imaging of granular metallicity of polyaniline

The band-gap electronic structures of two forms of the conducting polymer p olyaniline, emeraldine base (EB) and emeraldine salt (ES), have been studie d. Tunneling spectroscopy measurements show that ES is metallic in nature w ith a finite electron density of state at the Fermi energy (E-F), while EB behaves as an insulator with a gap at E-F in agreement with theoretical cal culations. These results allowed us to obtain direct evidence of the granul ar metallicity of ES by spectroscopic imaging. The spectroscopic images sho w different spatial distributions of nanometer-sized metallic particles in ES and EB samples, providing important information needed in studying elect rical conductivities of conducting polymers. (C) 1999 American Institute of Physics. [S0003-6951(99)04905-0].