The peculiarities of dynamic current-voltage and charge-voltage loops and transient currents of melanin under pulse hydration

TL;DR

This study investigates how pulse hydration affects the electrical properties of melanin, revealing unique dynamic current-voltage and charge-voltage behaviors, and models these effects with nonlinear circuits, highlighting melanin's potential for sensing applications.

Contribution

It provides the first detailed analysis of pulse hydration effects on melanin's electrical characteristics and models these effects with nonlinear circuits, advancing understanding of melanin-based sensors.

Findings

Pulse hydration sharply increases conductance and capacitance.

Distinct hump-like, knee-like, and step-like features appear in I-V, Q-V, and I-t curves.

Modeling with nonlinear circuits explains the observed behaviors.

Abstract

Melanin is a biopolymer with unique set of applicable physical and chemical properties. The impact of a moisture-saturated air pulse (~1 s) on dynamic current-voltage (I-V-), charge-voltage (Q-V-) and transient (I-t-) characteristics of fungal melanin thin layers was investigated. The pulse hydration gives rise to sharp increase of conductance and capacitance (by I-V-loops and I-t-curves swing), transferred charge (by Q-V-loops swing) and causes the appearance of the following peculiarities: hump-like on I-V-loops, knee-like on I-V-curves and step-like on I-t-curves. General shape of I-V-loops was modelled under low hydration by linear series-parallel RC-circuit and under high hydration by the circuit with anti-series Zener diodes as nonlinear elements. By processing of bipolar I-V-loops and I-t-curves allowing for unipolar ones, the maxima of displacement current - voltage loops were revealed and their similarity to current maxima observed under ionic space charge transfer in metal-insulator-semiconductor structures and under polarization reversal in ferroelectrics is discussed. Corresponding processing of bipolar Q-V-loops evidences general shape of obtained dielectric displacement - voltage loops characteristic to ion-conducting materials. As a reason of observed transformations, the appearance of temporal polar media with reversible ferroelectric-like polarization and ionic space charge transfer is considered. Obtained results disclose the functional capabilities of melanin based sensing devices operating in dynamic mode for both hydration and driving voltage.