A co-op team led by Professor Sang Ouk Kim and Professor Jonghwa Shin from the Department of Material Science and Engineering at KAIST has developed a high-tunable metamaterial that is able to control its refractive index at a wide range using a process called block copolymer self-assembly that produces desired material shapes and patterns at the nanoscale.

     Light travels in a straight line through various media, such as air, water, or glass, but changes its path angle as it enters a different medium. Each medium has its unique refractive index, which determines various properties of light, such as the emission, absorption, velocity, attenuation, refraction, and diffraction. The efficiency of many devices, ranging from optical communication systems to high-resolution imaging, depend on high refractive indices of the media.

     Unfortunately, refractive indices of natural transparent materials span at most 2.0 to 3.0. To combat such limitation, the researchers launched into the investigation of metamaterials to maximize refractive index. A metamaterial is a synthetic composite material with a structure that exhibits properties not typically found in natural materials. It is especially valuable for the management of refractive indices, but little research have been conducted in the visible light spectrum, which many optical devices use.

     In lieu of the lack in research, the team aimed to harness the independent control of permittivity and permeability in nanoscale materials to change the refractive index. The researchers precisely manipulated interatomic distance, which was uniformly less than 5 nm, through block copolymer self-assembly, which uses pattern shrinkage on block copolymer nanopatterns to vary and increase the refractive index. The method enhanced the refractive index up to 5.10.

     Using the ability to freely control materials’ refractive indices, scientists can construct the structure in a preferred way. The metamaterial could be applied to LED displays in order to increase their display efficiency or to solar cells to maximize energy efficiency. Professor Kim stated, “The fact that we can control the behavior of visible light implies that we can greatly improve the efficiency of solar cells or devices like LED displays. Previously impossible developments in scientific equipment like ultra-high magnification microscopes or ultra-high resolution semiconductors are now achievable.”

     The study was published in the scientific journal Nature Communications on September 27.