Rubbing a dry powder of particles in one direction between two rubbery substrates is found to be a quick and highly reproducible, yet inexpensive fabrication technique for assembling particle monolayers with perfect spatial registry on flat or curved surfaces. The optimum rubbing conditions - pressure and speed - for a single-crystal monolayer are shown to depend on particle size. Potential applications are in biosensors, photovoltaics, and light manipulators.

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We report thermal radiation antennas that sustain large emissivity at a broad range of wavelengths and angles, as well as maintaining their emissivity at high temperatures (up to 1300 K) under atmospheric pressure. Two-dimensional arrays composed of tungsten (W) cones with high aspect ratio were fabricated by laser interference lithography followed by deep reactive-ion etching, then optically characterized by measuring the broadband (λ = 500–2500 nm) absorptivity spectra. The fabricated W radiation antennas yielded greater absorptivity in visible to near-infrared wavelengths by increasing the aspect ratio of the cones, resulting in a near two-fold enhancement in average absorptivity compared to a reference planar W substrate. The measured absorptivity spectra were reproduced well by electromagnetic simulations with the experimental optical constants of W. Electromagnetic simulations also verified that such broadband increases in absorptivity are mostly caused by the enlarged scattering cross-section of individual cones. A 120 nm-thick conformal alumina coating prepared by atomic layer deposition was employed to prevent surface oxidation of the fabricated W radiation antennas, which additionally improved their absorptivity through an amplified antenna effect. These experimental and theoretical findings are generalizable to different infrared spectra by simply scaling up the antenna structures, and thus will be extensively utilized in thermal radiation applications such as solar steamers, thermophotovoltaics, and radiative coolers.

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Breaking the total internal reflection far above a critical angle (i.e., outcoupling deep-trap guided modes) can dramatically improve existing light-emitting devices. Here, we report a deep-trap guided modes outcoupler using densely arranged microstructured hollow cavities. Measurements of the leaky mode dispersions of hollow-cavity gratings accurately quantify the wavelength-dependent outcoupling strength above a critical angle, which is progressively improved over the full visible spectrum by increasing the packing density. Comparing hollow- and filled-cavity gratings, which have identical morphologies except for their inner materials (void vs. solid sapphire), reveals the effectiveness of using the hollow-cavity grating to outcouple deep-trap guided modes, which results from its enhanced transmittance at near-horizontal incidence. Scattering analysis shows that the outcoupling characteristics of a cavity array are dictated by the forward scattering characteristics of their individual cavities, suggesting the importance of a rationally designed single cavity. We believe that a hollow-cavity array tailored for different structures and spectra will lead to a technological breakthrough in any type of light-emitting device.