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Interfaces with polymers
The interfaces formed between polymers and metals as well as between two polymers, poly(vinylidene fluoride with trifluoroethylene) (PVDF-TrFE) and polyaniline, have been investigated. The interfaces are proven to be diffusive for the former case and the metal atoms dope into the polymer systems, while in the later case, the interface between these two polymers is demonstrated to be abrupt. ^ With the aid of angle resolved photoemission spectroscopy, I have demonstrated that the polyaniline thin films have preferential orientations depending on both the substrates and the film thickness. This is important since it shows the conductance of the films depends on the molecular orientation. The aromatic rings stay coplanar for thin polyaniline films on gold, resulting in larger conductance, but tilt out with increasing thickness or on silicon substrates, resulting in smaller conductance. ^ The doping effects have been carefully explored for polyaniline using angle integrated photoemission spectroscopy, X-ray photoemission spectroscopy and inverse photoemission spectroscopy. With sodium doping, the valence bands, conduction bands as well as the characteristic core levels of polyaniline show consistent shifts to the higher binding energy. Sodium, as an electron donor, when added to the polyaniline system, results in increased electron populations in the polyaniline bands—effectively filling the almost completely filled band. In the case of iodine doping, all the states shifted to lower binding energy. Iodine, as an electron acceptor, effectively depletes the electron population in the occupied bands of polyaniline. ^ Based on the different semiconductor character of PVDF-TrFE and polyaniline as well as the abrupt interface between them, a simple p-n heterojunction was fabricated with excellent rectification properties. ^
Chemistry, Polymer|Physics, Condensed Matter
Xu, Bo, "Interfaces with polymers" (2002). ETD collection for University of Nebraska - Lincoln. AAI3074112.