Fig. 2: Cyclic voltammograms and charge transfer at interfaces.
From: Electrochemical ohmic memristors for continual learning
a Schematic of energy diagram of the OE/oxide/OE system with one Schottky interface and one ohmic-like interface. The Schottky interface is positively biased, providing high electronic current. b Schematic of energy diagram of Schottky system when the Schottky interface is under reverse bias. This results in a high energy barrier and blocks the electron movement through the SE/oxide interface. c Schematic of energy diagram of the OE/oxide/OE system with dual ohmic-like interfaces under positively biased and reverse biased (d). In these cases, due to the low Schottky energy barrier and lower level of electrode passivation, higher electronic currents can flow through the metal/oxide interface, regardless of the applied voltage polarity. For all systems, when the top electrode (Schottky electrode SE, or ohmic electrode) is anodically polarized (a, c), the Fermi level of the redox system (EF, REDOX) is shifted, electrons are transferred from the occupied states (RED) to metal. Oxidation currents are generated during the anode process. Under the reverse biased condition, electrons are transferred from metal to unoccupied states (OX), reduction process occurred at the cathodic interface. e Cyclic voltammograms measured in Schottky system-based memristive devices (Pt,Cu/Ta2O5/Ta). The current densities show diode-like behavior. High currents are observed in positively biased condition (region I, energy diagram shown in a), and low currents in reverse bias condition (region II, energy diagram shown in b). The inset shows the current-voltage characteristics under high-revolution CV sweeps, indicating the presence of ionic currents originated from electrochemical redox reactions (region II). f Cyclic voltammograms in ohmic memristive systems. The high current densities shown at both positive (region III, energy diagram shown in c) and negative biased region (region IV, energy diagram shown in d) suggest that the Schottky-like barriers at metal/oxide interfaces are highly reduced. The pronounced current densities peaks imply strong redox processes at OE/oxide interfaces (see also Supplementary Figs. 17 and 18).
