Scanning tunneling microscopy and spectroscopy of polyaniline: Evidence for chain-folded lamellae with anomalous deformability

Abstract

Scanning tunneling microscopy reveals a distinct lamellar morphology on the surfaces of emeraldine base (EB-II) and its protonated salt (ES-II) films. From this, we derived a chain-folded lamella structural model that may help reconcile the "3D granular metal" with the "quasi-ID metallic chain" conduction models developed for this class of conducting polymers. Current-voltage tunneling spectroscopy (TS) experiments show a finite density of states at the Fermi energy for all the samples, indicating the importance of tunneling to disordered surface states. Current-tip displacement TS experiments reveal an anomalous slow current decay for samples protonated beyond the insulator-metal percolation transition. We related this to significant tip intrusion into the film surface owing to high elasticity in the c axis of the protonated lattice. We also briefly highlighted the importance of tunneling resistance set point, and the roles of surface mobility and deformability, in relation to tunneling to and from these organic polymer surfaces.