Near-field imaging of domain switching in in-operando VO$_{2}$ devices

TL;DR

This study employs scattering scanning near-field optical microscopy to investigate nanoscale domain switching in in-operando VO₂ devices, revealing the origin of switching behavior and domain persistence with high spatial resolution.

Contribution

It demonstrates the use of near-field optical microscopy to probe electronic structure and domain dynamics in VO₂ devices under operational conditions, providing new insights into their switching mechanisms.

Findings

Discontinuities in I(V) are due to insulating-to-metallic domain switching.

Metallic domains form continuous paths at threshold voltage.

Metallic domains persist after bias removal, with boundary regions forming.

Abstract

Experimental insight in the nanoscale dynamics underlying switching in novel memristive devices is limited owing to the scarcity of techniques that can probe the electronic structure of these devices. Scattering scanning near-field optical microscopy is a relatively novel approach to probe the optical response of materials with a spatial resolution well below the diffraction limit. We use this non-invasive tool to demonstrate that it provides detailed information on the origin and memory behaviour of ultra-thin films of vanadium dioxide. Simultaneously recorded $I(V)$ characteristics and near-field maps show that discontinuities in the I(V) characteristics arise from the sudden switching of insulating domains to metallic domains. At the threshold voltage, the domains form a continuous current path. The metallic domains persist once the bias voltage is removed, but narrow monoclinic regions appear around the domain boundaries. The key advantage of our approach is that it provides detailed information on the electronic structure at length scales raging from tens of nanometers up to tens of microns and is easily applied under \textit{in operando} conditions.