Eur. Phys. J. E (2009) 28: 285-291
https://doi.org/10.1140/epje/i2008-10437-9

Regular Article

Structural, electrical, electronic and optical properties of melanin films

¹ Department of Physics, Camerino University, Via Madonna delle Carceri, 62032, Camerino, Italy
² Department of MCAB, Camerino University, Via Gentile III da Varano, 62032, Camerino, Italy
³ Department of Physics, L’Aquila University, Via Vetoio, 67010, Coppito, Italy

^* e-mail: mamatimin.abbas@unicam.it

Received: 15 January 2008
Revised: 18 November 2008
Accepted: 19 December 2008
Published online: 3 February 2009

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 states along the stacked planar secondary structure.