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We demonstrate the functionalization of 2-D photonic crystal structures operating at ∼ 1.5 μm with colloidal PbSe quantum dots and examine the modified photoluminescence from the functionalized photonic crystal. Using spin coating and airbrushing, monodisperse PbSe quantum dots were deposited from hexanes on lithographically patterned GaAs photonic crystal substrates. The effectiveness of patterning the PbSe quantum dots via standard liftoff process was examined. The near-IR photoluminescence spectra of quantum dot-functionalized photonic crystals were studied. We found that the photoluminescence peak became attenuated by approximately a factor of five and exhibited a narrow peak width (50 nm vs. 120 nm) compared to PbSe deposited on unpatterned GaAs, suggesting that there is some coupling between the quantum dots and the photonic crystal. Future work to improve the coupling and detection efficiency is proposed.
Photonic crystals are of interest for GHz transmission applications, including rapid switching, GHz filters, and phased-array technology. 3D fabrication by Robocasting enables moldless printing of high solid loading slurries into structures such as the “woodpile” structures used to fabricate dielectric photonic band gap crystals. In this work, tunable dielectric materials were developed and printed into woodpile structures via solid freefrom fabrication (SFF) toward demonstration of tunable photonic crystals. Barium strontium titanate ceramics possess interesting electrical properties including high permittivity, low loss, and high tunability. This paper discusses the processing route and dielectric characterization of (BaxSr1-XTiO3):MgO ceramic composites, toward fabrication of tunable dielectric photonic band gap crystals.
Micromolding is a recently developed technique for fabricating parts in the millimeter size range with minimum features and dimensional tolerances less than 10 μm. This degree of precision is achieved by fabricating a master using the LiGA process. The molds made from the master are then filled with powder of the desired material to form parts that are then released from the mold and sintered to high density. Currently, molds are made of either poly(methyl)methacrylate (PMMA) or poly(dimethylsiloxane) (silicone rubber, PDMS). The PMMA molds must be dissolved to release the parts using a solvent that limits the choice of binder used to hold together the powder in the part. The PDMS molds are soft and therefore not suitable for lapping the parts prior to removal from the mold. Recently, two new types of molds materials have been investigated that can be removed utilizing a phase change, either melting or sublimation. The development of these new mold materials, which allow a wider choice of binders, will be described.
Robocasting is a freeform fabrication technique for dense ceramics and composites that is based on layer-wise deposition of highly loaded colloidal slurries. The process is essentially binderless with less than 1% organics and parts can be fabricated, dried, and completely sintered in less than 24 hours. This review will highlight materials developments for structural applications and modelling of slurry flow. Fabrication of preforms for alumina / metal composites will be discussed as well as techniques for multimaterial deposition in both graded structures and discrete placement of fugitive materials.
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