Schematic showing that ultrahigh refractive index metamaterials assembled with nanoparticles can be fabricated and used as optical materials. Credit: POSTECH
We all look in the mirror at least once a day to see our reflection. Mirrors are used not only in everyday life, but also in cutting-edge technologies such as semiconductor processing and high-resolution displays. Recently, a powerful reflective Bragg mirror based on high-index metamaterials has been developed that reflects only the desired light.
A research team led by Professor Gi-Ra Yi (Department of Chemical Engineering) at POSTECH with the research team led by Professors Seok Joon Kwon and Pil Jin Yoo (School of Chemical Engineering) at Sungkyunkwan University jointly developed an ultra-high refractive index metamaterial from a tight packing of gold nanospheres and a reflector that combines the metamaterial with a polymer.
Metamaterials – with properties that do not exist in nature – can be engineered to have a negative (-) or ultra-high refractive index. However, high refractive index metamaterials still have limitations from design to fabrication.
To overcome this problem, the research team developed a metamaterial that is uniformly arranged with gaps at the 1-nanometer level by assembling spherical gold nanoparticles. This material, which maximizes light-matter interaction, registers the highest refractive index in the visible and near-infrared regions. The 2D superstructures show the highest refractive index of 7.8
A Distributed Bragg Reflector (DBR), which is made by overlaying these metamaterials and low-refractive-index polymer layers, reflects highly specific wavelengths.
In addition, the research team established the theory of a plasmonic percolation model that could explain the extremely high refractive index. Because it theoretically explains the ultra-high refractive index of metamaterials that could not be explained in previous studies, the development of related research areas is expected in the future.
This research is also attracting attention from academia and industry for its applicability in precision semiconductor processes and high-resolution displays.
The study was published in Advanced materials.
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Dong-In Shin et al, Percolated plasmonic nanosphere superlattices with 1 nm gap as high-index metamaterials, Advanced materials (2022). DOI: 10.1002/adma.202203942
Provided by Pohang University of Science and Technology (POSTECH)
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