신종화 교수

The refractive index of natural transparent materials is limited to 2-3 throughout the visible wavelength range. Wider controllability of the refractive index is desired for novel optical applications such as nanoimaging and integrated photonics. We report that metamaterials consisting of period and symmetry-tunable self-assembled nanopatterns can provide a controllable refractive index medium for a broad wavelength range, including the visible region. Our approach exploits the independent contr

The authors introduce a general mechanism, based on electrostatic and magnetostatic considerations, for designing three-dimensional isotropic metamaterials that possess an enhanced refractive index over an extremely large frequency range. The mechanism allows nearly independent control of effective electric permittivity and magnetic permeability without the use of resonant elements.

The practical limits of coinage-metal-based plasmonic materials demand sustainable, abundant alternatives with a wide plasmonic range of the solar energy spectrum. Aluminum (Al) is an emerging alternative, but its instability in aqueous environments critically limits its applicability to various light-harvesting systems. Here, we report a design strategy to achieve a robust platform for plasmon-enhanced light harvesting using Al nanostructures. The incorporation of mussel-inspired polydopamine n

Effective surface enhancement of Raman scattering (SERS) requires strong near-field enhancement as well as effective light collection of plasmonic structures. To this end, plasmonic nanoparticle (NP) arrays with narrow gaps or sharp tips have been suggested as desirable structures. We present a highly dense and uniform Au nanoscale gap array enabled by the customized design of NP shape and arrangement employing block copolymer self-assembly. Block copolymer self-assembly in thin films offers uni

Core-shell plasmonic nanohybrids are synthesized through a simple solutionbased process utilizing mussel-inspired polydopamine (PDA). The multi-purpose PDA not only facilitates plasmonic metal formation, but also serves as a scaffold to incorporate photosensitizers around the metal cores, as well as an adhesive between the nanohybrids and the substrate. The resulting plasmonic assembly exhibits highly enhanced light absorption in photo catalytic systems to augment artificial photosynthesis.

Abstract Metamaterials can possess extraordinary properties not readily available in nature. While most of the early metamaterials had narrow frequency bandwidth of operation, many recent works have focused on how to implement exotic properties and functions over broad bandwidth for practical applications. Here, we provide two definitions of broadband operation in terms of effective material properties and device functionality, suitable for describing materials and devices, respectively, and ove

The refractive index is the fundamental property of all optical materials and dictates Snell's law, propagation speed, wavelength, diffraction, energy density, absorption and emission of light in materials. Experimentally realized broadband refractive indices remain <40, even with intricately designed artificial media. Herein, we demonstrate a measured index >1,800 resulting from a mesoscopic crystal with a dielectric constant greater than three million. This gigantic enhancement effect originat

Ingenious solutions to reduce energy consumption and improve power efficiency are the need of the hour to tackle climate change. Radiative cooling is being extensively studied as a potential route for passive cooling and energy harvesting. However, to achieve almost complete solar reflection necessary for daytime sub-ambient cooling, the visual appearance of radiative coolers proposed so far has primarily been limited to being either diffusive white or mirror-like, which may be undesirable in re

It has been shown that a metal film with a one-dimensional array of subwavelength cut-through slits can be accurately modeled as an anisotropic and uniform metamaterial film with nondispersive electric permittivity [epsimacr] and magnetic permeability [mumacr] tensors. This model has an interesting scaling property: The values for the thickness Lmacr can be chosen at arbitrarily, provided that [epsimacr] and [mumacr] are scaled accordingly. The analytical expressions of the corrections due to ne

Common materials show a limited range of refractive indices over the visible and infrared wavelengths, and their values are not easily tunable once the material is chosen. Here, self-assembled metal nanoparticle arrays are proposed as an effective optical material with a large range of possible refractive indices that are nearly dispersionless over broad wavelength ranges. The material can be potentially fabricated over a large curved surface, and the resulting index is even more tunable by vari

Recent advances in metasurfaces and optical nanostructures have enabled complex control of incident light with optically thin devices. However, it has thus far been unclear whether it is possible to achieve complete linear control of coherent light transmission, that is, independent control of polarization, amplitude, and phase for both input polarization states, with just a single, thin nanostructure array. Here, it is proved possible, and a universal metasurface is proposed, a bilayer array of

We consider three-dimensional structures consisting of multiple interlocking, disconnected metal networks. We show that, in the low-frequency limit, these systems support photonic bands with linear dispersion relation. The number of such photonic bands is directly controlled by the number of networks and can be arbitrarily large. We construct a non-Maxwellian effective medium for these systems. The effective medium supports multicomponent effective fields, with the numbers of field components de

We introduce the theoretical criterion for achieving three-dimensional self-collimation of light in a photonic crystal. Based on this criterion, we numerically demonstrate a body-center-cubic structure that supports wide-angle self-collimation and is directly compatible with the recently developed holographic fabrication technique. We further show that both bends and beam splitters can be introduced into this structure by the use of interfaces.

High-resolution (10 nm), high-areal density, high-aspect ratio (>5), and morphologically complex nanopatterns are fabricated from a single conventional block copolymer (BCP) structure with a 70 nm scale resolution and an aspect ratio of 1, through the secondary-sputtering phenomenon during the Ar-ion-bombardment process. This approach provides a foundation for the design of new routes to BCP lithography.

Smart chromatic materials with optical transmittances that can be modified by light scattering upon external stimuli are attracting extensive interest because of their appealing applications in smart windows, privacy protection, electronic displays, etc. However, the development of these scatterers, which are mostly activated by electric fields, is hindered by their intrinsic energy consumption, slow responses, and poor stability. Recently, mechanoresponsive scatterers based on a strain-driven r