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. 2019 Mar 26:7:162.
doi: 10.3389/fchem.2019.00162. eCollection 2019.

Evidence of Unprecedented High Electronic Conductivity in Mammalian Pigment Based Eumelanin Thin Films After Thermal Annealing in Vacuum

Ludovico Migliaccio  1 , Paola Manini  1 , Davide Altamura  2 , Cinzia Giannini  2 , Paolo Tassini  3 , Maria Grazia Maglione  3 , Carla Minarini  3 , Alessandro Pezzella  4
Affiliations

Evidence of Unprecedented High Electronic Conductivity in Mammalian Pigment Based Eumelanin Thin Films After Thermal Annealing in Vacuum

Ludovico Migliaccio et al. Front Chem. .

Abstract

Melanin denotes a variety of mammalian pigments, including the dark electrically conductive eumelanin and the reddish, sulfur-containing, pheomelanin. Organic (bio)electronics is showing increasing interests in eumelanin exploitation, e.g., for bio-interfaces, but the low conductivity of the material is limiting the development of eumelanin-based devices. Here, for the first time, we report an abrupt increase of the eumelanin electrical conductivity, revealing the highest value presented to date of 318 S/cm. This result, obtained via simple thermal annealing in vacuum of the material, designed on the base of the knowledge of the eumelanin chemical properties, also discloses the actual electronic nature of this material's conduction.

Keywords: charge transport; electrical conductivity; eumelanin; melanins; molecular orientation; organic (bio)electronics; vacuum thermal treatment.

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Figures

Figure 1
Figure 1
UV-Vis absorptivity (percent absorbance/film thickness) of the films at the different process stages: (red, circles) DHI; (black, squares) DHI-eumelanin (film after AISSP); (blue, triangles) HVAE (film after thermal annealing in vacuum: 600°C; 2 h; 10−6 mbar).
Figure 2
Figure 2
Pictorial model of the polyindole packing evolution during the high vacuum annealing. Water molecules and carboxylic groups are evidenced, to show their reduction in the material as the process temperature increases.
Figure 3
Figure 3
GIWAXS 2D patterns of (A) HVAE film (processed at 600°C for 2 h) and (B) DHI-eumelanin film. 1D radial cuts along (C) the out-of-plane and (D) the in-plane directions, obtained from the 2D maps in (A,B).
Figure 4
Figure 4
Conductivity of vacuum annealed eumelanin thin films vs. the annealing temperature and (inset) vs. the annealing time at 600°C temperature. Data are listed in the table. All the measurements were performed in air at room temperature. Errors of each point are indicated inside the plots symbols.
See this image and copyright information in PMC

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