Self-assembly of monolayer-thick alumina particle-epoxy composite films.

Monolayer-thick composite films composed of alpha-alumina and Spurr's epoxy were prepared via a self-assembly process known as fluid forming. The process makes use of a high-spreading-tension fluid composed of volatile and nonvolatile components to propel particles across the air-water interface within a water bath. Continuous addition of the particle suspension builds a 2D particle film at the air-water interface. The spreading fluid compresses the film into a densely packed array against a submerged substrate. The assembled monolayer is deposited onto the substrate by removing the substrate from the bath. A dispersion containing a narrow size distribution, 10 microm alpha-alumina particles, light mineral oil, and 2-propanol was spread at the air-water interface and the alumina particles were assembled into densely packed arrays with an aerial packing fraction (APF) of 0.88. However, when mineral oil was replaced by Spurr's epoxy nonuniform films with low packing density resulted. It was found that replacing 2-propanol with a mixture of 2-propanol and 1-butanol with a volume ratio of 4:1 produced uniform, densely packed alumina/epoxy composite films. The role of the solvent mixture will be discussed.

Microstructured optical fibers as high-pressure microfluidic reactors.

Deposition of semiconductors and metals from chemical precursors onto planar substrates is a well-developed science and technology for microelectronics. Optical fibers are an established platform for both communications technology and fundamental research in photonics. Here, we describe a hybrid technology that integrates key aspects of both engineering disciplines, demonstrating the fabrication of tubes, solid nanowires, coaxial heterojunctions, and longitudinally patterned structures composed of metals, single-crystal semiconductors, and polycrystalline elemental or compound semiconductors within microstructured silica optical fibers. Because the optical fibers are constructed and the functional materials are chemically deposited in distinct and independent steps, the full design flexibilities of both platforms can now be exploited simultaneously for fiber-integrated optoelectronic materials and devices.