The effect of grain boundaries on the electron relaxation rate is significant even for large area noble metal films and more so for plasmonic nanostructures. Optical spectroscopy and X-ray diffraction show a substantial improvement in plasmon resonance quality for square-particle nanoantennas after annealing due to an enlarged grain size from 22 to 40 nm and improved grain boundaries described by the electron reflection coefficient. The electron relaxation rate due to the grains is shown to decrease by a factor of 3.2.

Infrared wavelength selective thermal emission based on Tamm plasmon polaritons (TPPs) is experimentally demonstrated. Unlike conventional TPP structures having a thin metal layer on a DBR, the proposed structure has a thick metal under a DBR which is more robust for thermal radiation. The number of DBR pairs is a critical factor to maximize the narrowband emission: It has to satisfy the impedance matching condition, which varies with the choice of metal film. The proposed structure can achieve twice higher Q-factor for the measured emissivity compared to typical plasmonic thermal emitters. The structure is one dimensional, only consists of multilayers, and free from nano-patterning, offering a practical design in applications such as gas sensing, narrowband IR sources and in thermophotovoltaics. TOC

High-refractive-index (HRI) nanostructures support optically induced electric dipole (ED) and magnetic dipole (MD) modes that can be used to control scattering and achieve narrowband absorption. In this work, a high-absorptance device is proposed and realized by using amorphous silicon nanoantenna (a-Si NA) arrays that suppress backward and forward scattering with engineered structures and in particular periods. The overlap of ED and MD resonances, by designing an array with a specific period and exciting lattice resonances, is experimentally demonstrated. The absorptance of a-Si NA arrays increases 3-fold in the near-infrared range in comparison to unpatterned silicon films. Nonradiating a-Si NA arrays can achieve high absorptance with a small resonance bandwidth (Q = 11.89) at a wavelength of 785 nm. The effect is observed not only due to the intrinsic loss of material but by overlapping the ED and MD resonances.

We present comprehensive studies on thin diffraction lenses made of arrays of subwavelength, parallel nanoslits in a gold film. Such a nanoslit lens can operate either as a conventional convex or concave lens. The lenses can be designed to focus linearly polarized light with polarization either perpendicular (TM-lens) or parallel to the slits (TE-lens), while the orthogonal polarization diverges when passing through the lens. The designs of each lens are initially built on the dispersion relations for wave propagation through a parallel-plate waveguide. Both TM- and TE-lenses were realized experimentally, and full-wave numerical simulations fully support the experimental results.

Artificial color pixels based on dielectric Mie resonators are appealing for scientific research as well as practical design. Vivid colors are imperative for displays and imaging. Dielectric metasurface-based artificial pixels are promising candidates for developing flat, flexible, and/or wearable displays. Considering the application feasibility of artificial color pixels, wide color gamuts are crucial for contemporary display technology. To achieve a wide color gamut, ensuring the purity and efficiency of nanostructure resonance peaks in the visible spectrum is necessary for structural color design. Low-loss dielectric materials are suitable for achieving vivid colors with structural color pixels. However, high-order Mie resonances prevent color pixels based on dielectric metasurfaces from efficiently generating highly saturated colors. In particular, fundamental Mie resonances (electric/magnetic dipole) for red can result in not only a strong resonance peak at 650 nm but also high-order Mie resonances at shorter wavelengths, which reduces the saturation of the target color. To address these problems, we fabricated silicon nitride metasurfaces on quartz substrates and applied Rayleigh anomalies at relatively short wavelengths to successfully suppress high-order Mie resonances, thus creating vivid color pixels. We performed numerical design, semianalytic considerations, and experimental proof-of-concept examinations to demonstrate the performance of the silicon nitride metasurfaces. Apart from traditional metasurface designs that involve transmission and reflection modes, we determined that lateral light incidence on silicon nitride metasurfaces can provide vivid colors through long-range dipole interactions; this can thus extend the applications of such surfaces to eyewear displays and guided-wave illumination techniques.