Nanotechnology (Commonwealth Union) – Metallic nanostructures are extremely tiny metal objects that are used in a variety of applications such as medicine where they can play a key role in diagnostics. They also have great use in catalysis, energy production and more. As the potential of nanotechnology continues to expand, the possible role metallic nanostructures could possibly be crucial for the variety of applications.
Metallic nanostructures have great cpacity of concentrating light within extremely small spaces, whereas dielectric nanostructures are particularly effective at trapping light while keeping energy losses low. Bringing these two advantages together has typically involved complex hybrid structures, where the resulting optical modes interact and become difficult to manipulate separately. As a result, creating both types of resonance within a single nanostructure while avoiding unwanted interference has remained a significant challenge in nanophotonics, restricting progress toward small, multifunctional optical technologies.
A study team headed by Special Appointment Professor Hiroaki Misawa of the study Institute for Interdisciplinary Science, Advanced Research Field at Okayama University in Japan has developed a potential answer to this problem. The team collaborated with Dr. Xu Shi and Professor Yasutaka Matsuo at Hokkaido University in Japan, and Dr. Yaolong Li and Professor Qihuang Gong at Peking University in China and Hokkaido University in Japan.
They built nanostructures on the basis of MoOCl2, which is a natural hyperbolic material in two dimensions, with extraordinary optical properties. MoOCl2 is a metal along one of the crystallographic directions, while it is a dielectric along the perpendicular direction. The unique anisotropy opens up the possibility for the existence of two fundamentally different optical resonances in the same nanostructure.
The study appeared online in June this year, prior to appearing in the Volume 20, Issue 26 of ACS Nano on July 7, 2026.
To investigate these properties, the researchers produced arrays of MoOCl₂ nanodisks on a reflective gold film. They examined the structures through spectroscopy, finite-difference time-domain simulations and photoemission electron microscopy. The underlying gold layer functions as a mirror, strengthening confinement of the dielectric resonance while maintaining the plasmonic response. Since the two resonances arise from separate crystallographic axes, they do not hybridize, allowing each mode to be manipulated independently with minimal crosstalk.
The researchers also observed substantial differences between the optical properties of the two resonances. By modifying the geometry of the nanostructures, the team was able to bring the two resonances together at the same wavelength while retaining independent control through polarization. The pronounced difference was attributed to the distinct locations of the optical hotspots associated with the two resonances within the nanostructure.
Professor Misawa indicated that they had the desire to independently control the light-concentrating abilities of metallic nanostructures together with the light-trapping function of dielectric nanostructures inside a single structure.
He further pointed out that MoOCl₂ provided this unique opportunity due to the fact that its optical response is altered with crystal direction, permitting two completely different resonance modes to coexist with no interference with each other.
The ability to selectively activate two independent resonances by simply changing the polarization of incoming light could make it easier to develop highly integrated optical components. The researchers say the approach could have potential applications in high-sensitivity optical and chemical sensing, ultra-compact optical switches, optical communications, optical information processing, nonlinear photonics, and multifunctional metasurfaces designed to manipulate light reflection, polarization, and propagation with greater flexibility.
According to Professor Misawa, the study presents a novel method for creating multifunctional nanophotonic devices by utilising a single nanostructure instead of intricate hybrid arrangements.
Researchers of the study highlighted the fact that finding a single MoOCl₂ nanostructure shows great possibilities to nanophotonic engineering which deals with the nature of light interactions at a nanoscale.
