Probing electrochemically induced resistive switching of TiO2 using SPM techniques

Abstract

Resistive switching on the nanoscale is an emerging research field and Scanning Probe Microscopy (SPM) is a powerful tool for studies in this area. Under the SPM tip, the electrical field is very high due to the small tip radius on the order of tens of nanometers, and this can enable a range of ionic/electrochemical phenomena during the resistive switching of the materials under the SPM tip. Although the ionic/electrochemical phenomena have long been considered vital for the resistive switching of materials, a few pieces of experimental evidence, as well as the decoupling of the effects of the electrochemical processes at different stages, are still needed. In this work, we applied SPM based techniques to study resistive switching as well as the electrochemical phenomena during the resistive switching of the TiO₂ thin films prepared using Pulse Laser Deposition (PLD). It was found that the reversible or irreversible electrochemical processes initiated at different voltages can promote or degrade the resistive switching behavior of TiO₂. Combined with an electrical cell with environmental control, these electrochemical processes have been shown to require the involvement of moisture; the accumulation of oxygen vacancies, protons, and hydroxyls at the tip/TiO₂ junction may contribute to the promoting effect of the reversible electrochemical process on resistive switching, while the oxygen vacancy ordering and the injection of protons and hydroxyls into the lattice may lead to the irreversible electrochemical process. This work provides a detailed insight into the characteristics, origins, and the effects of the electrochemical phenomena on resistive switching performance, and will provide a further understanding of the electrochemical phenomena in various functional materials.