Wavelength-Selective Three-Dimensional Thermal Emitters via Imprint Lithography and Conformal Metallization.

Metallic photonic crystals (MPCs) exhibit wavelength-selective thermal emission enhancements and are promising thermal optical devices for various applications. Here, we report a scalable fabrication strategy for MPCs suitable for high-temperature applications. Well-defined double-layer titanium dioxide (TiO2) woodpile structures are fabricated using a layer-by-layer soft-imprint method with TiO2 nanoparticle ink dispersions, and the structures are subsequently coated with high purity, conformal gold films via reactive deposition from supercritical carbon dioxide. The resulting gold-coated woodpile structures are effective MPCs and exhibit emissivity enhancements at a selective wavelength. Gold coatings deposited using a cold-wall reactor are found to be smoother and result in a greater thermal emission enhancement compared to those deposited using a hot-wall reactor.

Direct Imprinting of Scalable, High-Performance Woodpile Electrodes for Three-Dimensional Lithium-Ion Nanobatteries.

The trend of device downscaling drives a corresponding need for power source miniaturization. Though numerous microfabrication methods lead to successful creation of submillimeter-scale electrodes, scalable approaches that provide cost-effective nanoscale resolution for energy storage devices such as on-chip batteries remain elusive. Here, we report nanoimprint lithography (NIL) as a direct patterning technique to fabricate high-performance TiO2 nanoelectrode arrays for lithium-ion batteries (LIBs) over relatively large areas. The critical electrode dimension is below 200 nm, which enables the structure to possess favorable rate capability even under discharging current densities as high as 5000 mA g-1. In addition, by sequential imprinting, electrodes with three-dimensional (3D) woodpile architecture were readily made in a "stack-up" manner. The height of architecture can be easily controlled by the number of stacked layers while maintaining nearly constant surface-to-volume ratios. The result is a proportional increase of areal capacity with the number of layers. The structure-processing combination leads to efficient use of the material, and the resultant specific capacity (250.9 mAh g-1) is among the highest reported. This work provides a simple yet effective strategy to fabricate nanobatteries and can be potentially extended to other electroactive materials.

Strain-tunable one dimensional photonic crystals based on zirconium dioxide/slide-ring elastomer nanocomposites for mechanochromic sensing.

We demonstrate the fabrication and performance of tunable, elastic organic/inorganic composite one-dimensional photonic crystals (1DPCs) in the visible spectrum. By controlling the composition of high refractive index metal oxide nanoparticle/polymer composites, a refractive index difference of 0.18 between the filled and unfilled polymer layers can be achieved while maintaining desirable flexibility and elasticity. This index contrast is achieved with a loading of 70 wt % zirconium dioxide nanoparticles within a slide-ring elastomer matrix, which is composed of topologically cross-linked polyrotaxane polyols. The large refractive index contrast enables high reflectivity while simultaneously minimizing the number of layers necessary, compared to purely polymer systems. Because the films are both flexible and elastic, these nanocomposite 1DPCs can function as colorimetric strain sensors. We demonstrate the sensing behavior of these 1DPCs by applying over 40% strain, resulting in a visible color shift across the visible spectrum from red to blue. 1DPCs of just 6 periods maintain reflectance of 40% throughout the visible spectrum, with a tensile mechanochromic sensitivity (Δλ/Δεmax) as high as -6.05 nm/%.