Chemical and Electronic Structure of Interfaces with Conjugated Polymers: Systems of Interest in Molecular Electronics Applications
The doping of conjugated polymers by electronic oxidation or reduction leads to the high electrical conductivity of conducting polymers. In the doping process, electronic charge is transferred either to (reduction) or from (oxidation) the conjugated polymer. The electrons transferred are stored in new electronic states, the energies of which fall with in the otherwise forbidden electron energy gap of the pristine (undoped) polymer. In polymers with a degenerate ground state, such as polyacetylene, spinless charged solitons are formed, while for polymers having a non-degenerate ground state, such as poly(para-phenylenevinylene), the charges are accommodated in singly-charged polarons or doubly-charged spinless bipolarons [1,2]. In this work, n-type doping is studied, since the addition of electrons can be studied by photoelectron spectroscopy, where added holes (the absence of electrons) is more difficult. In the doping of non-degenerate ground state polymers, the very first electrons go into polaron states. As the number of polarons increases, with increased doping, bipolarons may be formed, depending upon which form of charge storage species has the lowest energy in the particular polymer system, and a polaron-bipolaron transition takes place.
KeywordsSodium Atom Ultraviolet Photoelectron Spectroscopy Rubidium Atom Polaron State Bipolaron State
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