Calculations Indicate that 2D Photonic Crystals Based upon Archimedean-Like Tilings Have Nearly Isotropic Properties
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microscopy showed that the dried products prepared by both acid and base catalysis consist of aggregates of fibers ~200 µm long and 150–600 nm in diameter. Similar fiber aggregates were observed for the assemblies produced by the organogelator alone, proving its role as the template. The fibers produced by acid-catalyzed polymerization were smooth, while those produced by basecatalyzed polymerization had rough surfaces. This difference was ascribed to the production of TiO2 particles during basecatalyzed polymerization. Unlike the dried product, the calcined samples exhibited fiber structures only when the polymerization was basecatalyzed. This result is consistent with the presence of anionic propagation species during base-catalyzed sol-gel polymerization. These negatively charged intermediates adsorb onto the positively charged organogelator template, and the polymerization proceeds along the template. Transmission electron micrographs of the calcined base-catalyzed product show that the nanofibers are hollow and have internal diameters of 50–150 nm. X-ray diffraction studies of the calcined nanofibers show that they have the desired anatase structure. GREGORY KHITROV
Research Laboratory said that the technique’s compatibility with standard semiconductor batch-processing tools should allow future microfluidic devices to be made quickly and cheaply in a microchip factory.
Calculations Indicate that 2D Photonic Crystals Based upon Archimedean-Like Tilings Have Nearly Isotropic Properties Radius of curvature: 52 µm
Radius of curvature: 8 µm
Low-Temperature Process Produces Microcanals for Microfluidic Chips Researchers at Sandia National Laboratories have developed a microchip processing technique that creates raised microscopic canals on chips, through which liquids or gases can flow from one chip feature to another. The raised hemispherical canals, 8–100 µm in diameter, have been created on silicon, glass, and quartz surfaces. Some of the canals have been made with curvatures with radii as small as 8 µm. These canals can be small enough and curvy enough that some liquids or gases pass easily through them and others pass more slowly. This ability to distinguish among fluidic materials is useful for chemical-separation applications, the most common use of microfluidic devices. To make the canals, the researchers pattern a thin layer of photoresist on the wafer’s surface using a conventional photo mask and light, then develop away areas of photoresist exposed to the light, leaving a network of photoresist ridges on the wafer’s surface that eventually becomes the canals’ interiors. Next, they heat the wafer to a relatively low temperature of 100°C for about 20 s, which causes the square-edged ridges to slump into a hemispherical shape. A 2-µm-
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Microscopic views of raised hemispherical canals 8–100 µm in diameter.
thick film of silicon oxynitride is deposited over the rounded photoresist, and the entire wafer is soaked in an acetone bath until the remaining photoresist is dissolved, leaving hollow tunnels on
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