Electronic structure of highly crystalline polyaniline by study of tunneling conduction in n+-Si/self-assembled monolayer/polyaniline heterostructures |
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Affiliation: | 1. Technical Physics and Prototype Engineering Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400 085, India;2. Institut d’Electronique, Micro-electronique et Nanotechnologie – CNRS, Molecular Nanostructures and Devices group, BP 60069, Avenue Poincare, F-59652, Villeneuve d’Ascq cedex, France |
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Abstract: | Highly crystalline polyaniline (PANI) films were deposited on degenerated silicon (n+-Si) substrates covered with its native oxide (SiO2), surface modified with amino-silane self-assembled monolayers (SAM). Scanning electron microscopy studies reveal formation of single crystal domains scattered all over the surface of film. Height and current images obtained using current-sensing AFM (C-AFM) exhibit pyramidal topography of crystallites, and inhomogeneous conductivity. As the native oxide and SAM acts as a very thin insulating layer (<2 nm) between the metal-like substrate (degenerated Si) and the PANI film, it forms n+-Si/SiO2/SAM/PANI metal-insulator-semiconductor (MIS) heterostructure. C-AFM probe was used for I–V measurements on the MIS structures and study the tunneling conduction across it. The conductance spectra derived from I–V characteristics corroborates well with the polaron-lattice band structure of doped PANI with presence of polaron bands between the HOMO-LUMO energy gap. These polaron bands are well-resolved from our C-AFM measurements and they are located about 0.25 eV below the LUMO and above the HOMO. |
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