Recently it was discovered that periodic lattices of metamaterial scatterers show optical activity, even if the scatterers or lattice show no 2D or 3D chirality, if the illumination breaks symmetry. We demonstrate that such "pseudochirality" is intrinsic to any single planar metamaterial scatterer and in fact has a well-defined value at a universal bound. We argue that in any circuit model, a nonzero electric and magnetic polarizability derived from a single resonance automatically imply strong bi-anisotropy, i.e., magnetoelectric cross polarizability at the universal bound set by energy conservation. We confirm our claim by extracting polarizability tensors and cross sections for handed excitation from transmission measurements on near-infrared split ring arrays, and electrodynamic simulations for diverse metamaterial scatterers.
We propose a dielectric nanoresonator geometry consisting of hollow dielectric nanocylinders which support geometrical resonances. We fabricate such hollow Si particles with an outer diameter of 108-251 nm on a Si substrate, and determine their resonant modes with cathodo-luminescence (CL) spectroscopy and optical dark-field (DF) scattering measurements. The scattering behavior is numerically investigated in a systematic fashion as a function of wavelength and particle geometry. We find that the additional design parameter as a result of the introduction of a center gap can be used to control the relative spectral spacing of the resonant modes, which will enable additional control over the angular radiation pattern of the scatterers. Furthermore, the gap offers direct access to the enhanced magnetic dipole modal field in the center of the particle.
Randomly packed particles in granular matter, ubiquitous in nature and industry, usually defy simple predictions for the optimal amorphous packing density because jammed granules are strongly correlated. While mixing different granular shapes seems to be a further complication, we discovered in simulations that binary rodsphere mixtures harbor a surprisingly simple dependence of packing volume fraction on mixture composition. This isochoric ideality covers the entire composition range and is experimentally validated by mixtures of sphero-cylindrical TicTac sweets and spherical beads: their joint random packing volume is indeed independent of the segregation state. Isochoric ideality occurs in a rod-shape range that includes the unique aspect ratio, which universally maximizes rod-sphere packing densities and suggests a novel amorphous analog of a plastic crystal, namely rod-sphere mixtures with completely uncorrelated particle orientations.The puzzle of dense amorphous particle packings has caught the close attention of mathematicians and scientists from many different disciplines. In particular, non-spherical particles and their mixtures, jammed into random packings, are abundant and occur on widely different length scales. Macroscopic instances of anisotropic granular matter, among many others, are the grains in solidifying igneous rocks, various grains in food (rice, pasta's, TicTac sweets, etc.), ceramic bulk powders, catalyst pellets, and reinforcing fibers in industry.1-6 On the sub-micron length scale anisometric colloids such as rods and platelets form dense random packings and glasses, 4,7-13 while protein filaments may randomly pack in animal cells.14 Essential questions are how tight one can pack particles in jammed amorphous packings and how to optimize the corresponding random close packing (RCP) density. In quest of the optimal or densest random packing, particle non-sphericity has proven to be an effective means to maximize the RCP density. Recent studies on random packing of sphero-cylinders 15 and ellipsoids 16,17 revealed an intriguing non-monotonic dependence of the RCP density on the particle elongation. Starting from the Bernal random sphere packing, the RCP density first raises to a maximum for nearly spherical particles and only beyond this maximum the random packing density monotonically decreases with particle aspect ratio. So far, this peculiar maximum has only been observed for monodisperse granules 15-17 and colloids. 9 As polydispersity in size and shape is often unavoidable, one important question is how to optimize packing densities of granular mixtures, which ideally could be predicted from densities of the monodisperse components. It is therefore of fundamental and practical interest to investigate for such mixtures the existence of a density maximum and the universality, if any, in its location or magnitude.We uncover the universality in jamming of rather short spherocylinders of length L (including two hemi-spherical caps at both ends) and diameter D by investigating the RCP of...
The renowned yellow phosphor yttrium aluminum garnet (YAG) doped with trivalent cerium has found its way into applications in many forms: as powder of micron sized crystals, as a ceramic, and even as a single crystal. However, additional technological advancement requires providing this material in new form factors, especially in terms of particle size. Where many materials have been developed on the nanoscale with excellent optical properties (e.g., semiconductor quantum dots, perovskite nanocrystals, and rare earth doped phosphors), it is surprising that the development of nanocrystalline YAG:Ce is not as mature as for these other materials. Control over size and shape is still in its infancy, and optical properties are not yet at the same level as other materials on the nanoscale, even though YAG:Ce microcrystalline materials exceed the performance of most other materials. This review highlights developments in synthesis methods and mechanisms and gives an overview of the state of the art morphologies, particle sizes, and optical properties of YAG:Ce on the nanoscale.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.