Ferroelectric-like behaviour of melanin: Humidity effect on current-voltage characteristics

• Current-voltage dependences (IV-D) of ITO/melanin layer/ITO structures were studied.
• Hysteresis voltages of quasistatic IV-D are near to water decomposition potentials.
• Short wet air pulse gives rise to displacement current maxima on dynamic IV-D.
• Modelling of IV-D by series-parallel RC-circuit with Zener diodes was performed.
• As a reason reversible ionic transfer and ferroelectric polarization are considered.

The influence of low vacuum on quasistatic current-voltage (I–V) dependences and the impact of wet air pulse on dynamic bipolar I-V-loops and unipolar I-V-curves of fungal melanin thin layers have been studied for the first time.The threshold hysteresis voltages of I–V dependences are near to the standard electrode potentials of anodic water decomposition.Short wet air pulse impact leads to sharp increase of the current and appearance of “hump”-like and “knee”-like features of I-V-loops and I-V-curves, respectively.By treatment of I-V-loop allowing for I-V-curve shape the maxima of displacement current are revealed. The peculiarities of I-V-characteristics were modelled by series-parallel RC-circuit with Zener diodes as nonlinear elements.As a reason of appearance of temporal polar media with reversible ferroelectric-like polarization and ionic space charge transfer is considered the water-assisted dissociation of some ionic groups of melanin monomers that significantly influences electrophysical parameters of melanin nanostructures.

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