Photonic crystals of close-packed arrays of air spheres in a dielectric background of titania have been fabricated with a novel ceramic technique. Unlike previous methods, ordering of the spheres and the formation of the titania network are performed simultaneously. The photonic crystals exhibit a reflectance peak and a uniform color at the position of the first stop band. The wavelength of the reflectance peak scales very well with the sphere size.

A novel architecture with high‐aspect‐ratio nanoscale metallic periodic patterns is fabricated as transparent electrodes. The structure shows high visible light transmission and has superior electrical conductivity compared to standard indium tin oxide (ITO) coated glass. A proof‐of‐principle organic photovoltaic device is successfully fabricated with the electrode.

3D micropatterning of materials can create advanced mechanical, chemical, or electromagnetic functionalities not observed in bulk. This is especially true for 3D periodic structures, called photonic crystals, which significantly modify optical properties of materials for light having wavelengths close to the periodicity of the patterning. [1][2][3] Among them, a 3D metallic photonic crystal (MPC), usually in a woodpilelike pattern, [4] has recently attracted attention because it can produce efficient thermal emitters and photovoltaic devices [5] through tailoring of the absorption spectrum. [6,7] However, its fabrication is still problematic because of challenges in 3D microfabrication at optical scales. In this letter, we report a nonphotolithographic fabrication method using soft lithography [8] and electrodeposition to produce highly layered full-metallic structures with excellent structural fidelity. By adding a homogeneous monolithic backplane to the conventional woodpile structure, the difficulty of alignment in layer-by-layer fabrication is alleviated, while preserving characteristic highly enhanced thermal radiation in a tailorable range of frequencies.Although the tailored enhancement of absorption has been observed from woodpile MPCs fabricated by semiconductor processing, [6,7] obstacles in multilayer alignment and intricate processing still remain. As an alternative approach, direct laser writing [9,10] could be considered to create a template for woodpile MPCs. As in all approaches using a template, metalinfiltration is a critical step because of the complex 3D geometry of the template. Electrodeposition has strong potential for complete bottom-up filling rather than vapor-phase deposition, which often results in voids from blocked channels. [11,12] However, a number of requirements must be satisfied, including: complete wetting of the template, slow deposition to prevent hydrogen generation at the cathode, and good chemical and mechanical stability of the template under electrolytes. Additionally, the surface of the conducting substrate cannot have any insulating residue impeding current flow after forming the template. It is not clear whether other approaches using photolithography, including direct laser writing, are adequate for the fabrication of woodpile metallic structures using electrodeposition. Recently, we reported a soft lithographic technique, called two-polymer microtransfer molding, [13] for the fabrication of layer-by-layer polymer microstructures using nonoptical additive processing. With this technique, a photocurable polyurethane prepolymer (J91, Summers Optical) is filled in linear microchannels of a polydimethylsiloxane-based elastomeric mold (Sylgard 184, Dow Corning) and solidified. The surface of the prefilled polymer is coated with a photocurable polymetacrylate prepolymer (SK9, Summers Optical) as an adhesive layer and the assembly is placed in contact with an indium-tin-oxide (ITO)-coated glass. Then, after curing the adhesive layer and peeling off the elastomeric mold, a l...

Very uniform 2 μm-pitch square microlens arrays (μLAs), embossed on the blank glass side of an indium-tinoxide (ITO)-coated 1.1 mm-thick glass, are used to enhance light extraction from organic light-emitting diodes (OLEDs) by ~100%, significantly higher than enhancements reported previously. The array design and size relative to the OLED pixel size appear to be responsible for this enhancement. The arrays are fabricated by very economical soft lithography imprinting of a polydimethylsiloxane (PDMS) mold (itself obtained from a Ni master stamp that is generated from holographic interference lithography of a photoresist) on a UV-curable polyurethane drop placed on the glass. Green and blue OLEDs are then fabricated on the ITO to complete the device. When the μLA is ~15 × 15 mm 2 , i.e., much larger than the ~3 × 3 mm 2 OLED pixel, the electroluminescence (EL) in the forward direction is enhanced by ~100%. Similarly, a 19 × 25 mm 2 μLA enhances the EL extracted from a 3 × 3 array of 2 × 2 mm 2 OLED pixels by 96%. Simulations that include the effects of absorption in the organic and ITO layers are in accordance with the experimental results and indicate that a thinner 0.7 mm thick glass would yield a ~140% enhancement. Abstract: Very uniform 2 μm-pitch square microlens arrays (μLAs), embossed on the blank glass side of an indium-tin-oxide (ITO)-coated 1.1 mm-thick glass, are used to enhance light extraction from organic lightemitting diodes (OLEDs) by ~100%, significantly higher than enhancements reported previously. The array design and size relative to the OLED pixel size appear to be responsible for this enhancement. The arrays are fabricated by very economical soft lithography imprinting of a polydimethylsiloxane (PDMS) mold (itself obtained from a Ni master stamp that is generated from holographic interference lithography of a photoresist) on a UV-curable polyurethane drop placed on the glass. Green and blue OLEDs are then fabricated on the ITO to complete the device. When the μLA is ~15 × 15 mm 2 , i.e., much larger than the ~3 × 3 mm 2 OLED pixel, the electroluminescence (EL) in the forward direction is enhanced by ~100%. Similarly, a 19 × 25 mm 2 μLA enhances the EL extracted from a 3 × 3 array of 2 × 2 mm 2 OLED pixels by 96%. Simulations that include the effects of absorption in the organic and ITO layers are in accordance with the experimental results and indicate that a thinner 0.7 mm thick glass would yield a ~140% enhancement. Keywords

A regenerable calcium-based sorbent was prepared by pelletizing either powdered limestone or calcium sulfate hemihydrate and then coating the pellets with an optimum mixture of powdered alumina and limestone. The pellets were subsequently calcined and treated at high temperature to produce pellets with a calcium oxide core surrounded by a strong, inert porous shell. The crushing strength of the core-in-shell pellets was directly proportional to the shell thickness. The performance characteristics of the sorbent were determined by employing a thermogravimetric analysis system to measure the rate of reaction of individual pellets with small concentrations of H2S at high temperature. The reaction was rapid and directly proportional to H2S concentration. The reaction rate was not affected greatly by the thickness of the pellet shell or by temperature in the range of 840−920 °C. However, the rate was more rapid for hemihydrate-based pellets than for limestone-based pellets. The hemihydrate-based pellets also had the advantage of withstanding repeated loading and regeneration without suffering a significant loss of reactivity, whereas the limestone-based pellets did suffer markedly. A regenerable calcium-based sorbent was prepared by pelletizing either powdered limestone or calcium sulfate hemihydrate and then coating the pellets with an optimum mixture of powdered alumina and limestone. The pellets were subsequently calcined and treated at high temperature to produce pellets with a calcium oxide core surrounded by a strong, inert porous shell. The crushing strength of the core-in-shell pellets was directly proportional to the shell thickness. The performance characteristics of the sorbent were determined by employing a thermogravimetric analysis system to measure the rate of reaction of individual pellets with small concentrations of H 2 S at high temperature. The reaction was rapid and directly proportional to H 2 S concentration. The reaction rate was not affected greatly by the thickness of the pellet shell or by temperature in the range of 840-920°C. However, the rate was more rapid for hemihydrate-based pellets than for limestone-based pellets. The hemihydrate-based pellets also had the advantage of withstanding repeated loading and regeneration without suffering a significant loss of reactivity, whereas the limestone-based pellets did suffer markedly. Keywords Chemical and Biological Engineering

Layer-by-layer three-dimensional photonic crystals are fabricated by low-temperature atomic layer deposition of titanium dioxide on a polymer template created by soft lithography. With a highly conformal layer of titanium dioxide, a significantly enhanced photonic band gap effect appears at 3.1μm in transmittance and reflectance. From optical investigations of systematically shifted structures, the robust nature of the photonic band gap with respect to structural fluctuations is confirmed experimentally. With angle-resolved Fourier-transform spectroscopy, the authors also demonstrate that the fabricated photonic crystal can be a diffraction-free device as the photonic band gap exists over the diffracting regime.

No abstract

We present an efficient method of fabricating freestanding three-dimensional metallic photonic crystals using soft lithography. Low cost and ease of fabrication are achieved through gold sputter deposition on a freestanding woodpile polymer template. We compare experimental results to theoretical calculations for tetragonal and face-centered-tetragonal structures as a function of the number of layers. The photonic crystals behave like full metallic structures with a photonic band edge at a wavelength of 3.5μm. The rejection rates of the structures are about 10dB/layer.