Formation of Planar Metasurfaces in Oxide Thin Films via Synchronized Ionic Gating

Ionic gating using ionic liquids or ionic solids allows for the electrical control of the properties of oxide thin films, electrostatically in some cases, or, very often, via electrochemical changes in the composition of the film [1]. Here we show the possibility of creating metasurfaces from a single oxide layer via ionic gating through lithographically defined arrays of orifices in a resist layer that is deposited on top of the oxide layer. We demonstrate the creation of designer optical metasurfaces from initially insulating layers of of VO₂ and SrCoO_2.5. Synchronized ionic gating through periodic arrays of orifices, shaped in the form of antennae, allows for the formation of arrays of metallic islands in an insulating host. Planar optical metasurfaces are thereby formed that display anomalous optical reflection of light [2]. For the case of VO₂, the anomalous optical reflection can be actively tuned by both electric-field and temperature. Moreover, the synchronized local ionic gating of a ferromagnetic La_0.67Sr_0.33MnO₃ film leads to the electrical formation of magnetic metasurfaces. i.e., all-oxide artificial spin ice structures through collective interactions between magnetic nano-islands. Our findings open a new path towards the creation of complex electronic, magnetic, and optical metasurfaces via synchronized local ionic gating.
[1] J. Jeong, N. Aetukuri, T. Graf, T. D. Schladt, M. G. Samant, and S. S. P. Parkin, "Suppression of Metal-Insulator Transition in VO₂ by Electric Field–Induced Oxygen Vacancy Formation," Science, 339, 1402-1405 (2013).
[2] H. Han et al., "All-Oxide Metasurfaces Formed by Synchronized Local Ionic Gating," Adv. Mater. 36, 2401064 (2024).