Effects of potassium on the supramolecular structure and electronic properties of eumelanin thin films.

Patrizia Borghetti, Andrea Goldoni, Carla Castellarin-Cudia, Loredana Casalis, Fabian Herberg, Luca Floreano, Albano Cossaro, Alberto Verdini, Ralph Gebauer, Prasenjit Ghosh, Luigi Sangaletti

Index: Langmuir 26(24) , 19007-13, (2010)

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Abstract

The role of potassium in the formation of synthetic eumelanin aggregates is investigated by atomic force microscopy and soft-X-ray spectroscopy. Control over the thin film granularity is achieved by using K salts, in both drop casting and electrodeposition of eumelanin thin films. Further control over orientation is made possible by a suitable choice of the substrate: evidence of self-assembly is found for thin films deposited on gold. Finally, it is shown that the potassium content affects not only the samples morphology, but also the low-lying states in the valence band, where a transfer of spectral weight across the HOMO-LUMO gap is observed, disclosing possible applications of this multifunctional biomacromolecule.