An international joint research group including Specially Appointed Professor Hiroaki Misawa of the Research Institute for Interdisciplinary Science at Okayama University, Postdoctoral Researcher Yaolong Li and Professor Yasutaka Matsuo of the Research Institute for Electronic Science at Hokkaido University, Associate Professor Xu Shi of the Institute for Integrated Innovation at Hokkaido University, and Professor Qihuang Gong of Peking University demonstrated that a nanostructure made from the two-dimensional material molybdenum(IV) dichloride oxide (MoOCl2) can both strongly focus light and efficiently store specific wavelengths. The achievement could lead to high-sensitivity optical sensors, ultra-compact optical switches, and optical information processing devices. The findings were published in ACS Nano.
The left panel shows an electron micrograph of MoOCl2 nanodisks arranged on a substrate, and the lower-left schematic shows the device structure consisting of a MoOCl2 nanodisk on an Au reflective film and a glass substrate. The graph on the right shows the reflectance spectra measured for two light-polarization directions. Depending on the polarization of incident light, the same nanostructure can switch between a light-concentrating resonance and a light-trapping resonance.
Provided by Hiroaki Misawa, Okayama University
The research group processed MoOCl2 into a disk-shaped nanostructure and placed it on a gold thin film. The gold thin film acts as a reflective film, enhancing the function of efficiently "storing" specific colors of light within the MoOCl2 nanostructure. Through this design, they simultaneously achieved within a single MoOCl2 nanostructure both a resonance that strongly "focuses" light like a metal and a resonance that efficiently "stores" specific colors of light.
This nanodisk is placed on the gold thin film reflective layer. Changing the polarization direction of light causes the resonance that strongly "focuses" light like a metal and the resonance that efficiently "stores" specific colors of light to appear individually. In other words, two different light functions can be switched within a single nanostructure.
The two resonances do not blend together and can be switched independently simply by changing the oscillation direction (polarization direction) of the light. Furthermore, by adjusting the size and shape of the nanostructure, they also succeeded in overlapping the two resonances in the same wavelength region. Even in this case, the respective functions did not mix and could be selectively controlled by polarization.
Measurements using photoemission electron microscopy also revealed that the locations where light concentrates strongly differ between the two resonances. In the resonance that strongly "focuses" light, light concentrates at the top of the nanostructure. In the resonance that "stores" light, light concentrates near the interface between MoOCl2 and the gold thin film. This means that within a single nanostructure, not only the way light gathers but also the location where light operates can be switched.
Misawa commented, "We demonstrated that the functions of 'focusing' and 'storing' light can coexist within a single small nanostructure and that they can be switched between. I hope this achievement will lead to new designs for high-sensitivity optical sensors and optical information processing devices."
Journal Information
Publication: ACS Nano
Title: Coexistence of Metal and Dielectric Resonance Modes in a Single Nanostructure of a Hyperbolic Material
DOI: 10.1021/acsnano.6c06696
This article has been translated by JST with permission from The Science News Ltd. (https://sci-news.co.jp/). Unauthorized reproduction of the article and photographs is prohibited.