title: Structural, electrical, electronic and optical properties of melanin films.
abstract: We present thick, uniform and rather flat melanin films obtained using spray deposition. The morphology of the films was investigated using Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). Temperature-dependent electrical resistance of melanin thin films evidenced a semiconductor-like character and a hysteretic behavior linked to an irreversible process of water molecule desorption from the melanin film. X-ray Photoelectron Spectroscopy (XPS) was carried out to analyze the role of the functional groups in the primary and secondary structure of the macromolecule, showing that the contribution of the 5,6-dihydroxyindole-2-carboxylic acid (DHICA) subunit to the molecule is about 35%. Comparison of the optical absorption of the thick (800nm) and thin (80nm) films showed a spectral change when the thickness increases. From in vacuum photoconductivity (PC) measured at controlled temperatures, we suggest that the melanin films exhibit a possible charge transport mechanism by means of delocalized pi states along the stacked planar secondary structure.
authors.affiliation: CNISM - Department of Physics, Camerino University, Camerino (MC), Italy. mamatimin.abbas@unicam.it
authors.forename: M
authors.initials: M
authors.lastname: Abbas
authors.forename: F
authors.initials: F
authors.lastname: D'Amico
authors.forename: L
authors.initials: L
authors.lastname: Morresi
authors.forename: N
authors.initials: N
authors.lastname: Pinto
authors.forename: M
authors.initials: M
authors.lastname: Ficcadenti
authors.forename: R
authors.initials: R
authors.lastname: Natali
authors.forename: L
authors.initials: L
authors.lastname: Ottaviano
authors.forename: M
authors.initials: M
authors.lastname: Passacantando
authors.forename: M
authors.initials: M
authors.lastname: Cuccioloni
authors.forename: M
authors.initials: M
authors.lastname: Angeletti
authors.forename: R
authors.initials: R
authors.lastname: Gunnella
mesh_terms: D001703:Biophysics / Q000379:methods*; D004583:Electrons; D006801:Humans; D007211:Indoles / Q000737:chemistry; D008027:Light; D008422:Materials Testing; D008543:Melanins / Q000737:chemistry*; D008855:Microscopy, Electron, Scanning / Q000379:methods; D016252:Microscopy, Scanning Tunneling / Q000379:methods; D008968:Molecular Conformation; D055095:Optics and Photonics; D011108:Polymers / Q000737:chemistry; D013057:Spectrum Analysis / Q000379:methods; D014965:X-Rays
chemical_list: D007211:Indoles; D008543:Melanins; D011108:Polymers; C030692:5,6-dihydroxy-2-indolylcarboxylic acid