Chemically Synthesized Electromagnetic Metal Oxide Nanoresonators

Abstract Metal oxide nanostructures represent a large class of dielectric nanomaterials with high or moderate refractive indexes. Dielectric nanomaterials have recently attracted much attention in the field of all‐dielectric nanophotonics. They can support both electric and magnetic resonances without suffering from high losses or heating as their plasmonic counterparts. Although various intriguing optical effects have been discovered on dielectric nanostructures, a real challenge in this field is the difficulty in the production of dielectric nanostructures with well‐defined geometry, smooth surface, moderate/high refractive indexes, and good crystallinity. In this work, using an aerosol spray method and subsequent thermal treatment, smooth‐surfaced metal oxide spheres that span a broad size range from 100 nm to several micrometers in diameter and a relatively wide refractive index range from 2 to 2.35 in the visible region have been successfully synthesized. In particular, they are shown to support strong electric and magnetic resonances of different orders in excellent agreement with Mie theory, which is a signature of their outstanding optical performance. The findings offer many possibilities for a wide variety of low‐loss optical components, from Mie‐type nanoresonators and whispering gallery cavities to micrometer lenses.