Nanoparticles Conjugated with Tobacco Mosaic Virus Form Electronic Memory Device
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crystal device to present the different faces to the incident light. This technique offers a new, potentially easier, and more effective approach for the fabrication of highly ordered photonic crystals than currently used. According to the researchers, further refinement of this method may yield even greater advantages by shortening fabrication time and further reducing defects. KRISTA NIECE
New Coating Method Produces Arrays of Orthogonally Tilted Nanopores in Ceramic Films Surfactant-templated thin mesoporous ceramic films with hexagonally closepacked (hcp) cylindrical nanopores aligned perpendicular to the substrate attract more interest than films with pores aligned parallel to the substrate surface in fields such as membrane separations, sensors, and catalysis, because their channels are accessible to larger solutes. V.R. Koganti and S.E. Rankin from the University of Kentucky, D. Dunphy of Sandia National Laboratories, V. Gowrishankar and M.D. McGehee from Stanford University, and X. Li and J. Wang from Argonne National Laboratory have demonstrated that a chemically neutral sacrificial copolymer layer directed the orientation of orthogonally tilted hcp pores in surfactant-templated silica and titania films. As reported in the November 8, 2006, issue of Nano Letters (p.2567; DOI:10.1021/ nl061992v), chemically neutral layers were formed by coating clean glass substrates with PEO-r-PPO copolymer (PEO—poly (ethylene oxide); PPO—poly (propylene oxide)) and cross-linking the films by an isocyanate hydroxyl reaction at 120ºC overnight. Then, a film of silica sol was dip-coated onto the substrates, with P123 (PEO-co-PPO-co-PEO) as a surfactant pore template and tetraethylorthosilicate as a silica precursor. The films were aged and dried at 40ºC for 24 h and 100ºC for 24 h, and calcined in air at 500ºC. The researchers controlled the thickness of the silica films by diluting the original sol in ethanol. Similarly, surfactant-templated titania films were produced by dip-coating titania sols, prepared by adding a solution of P123 in ethanol to a mixture of titanium(IV) ethoxide and concentrated HCl, onto PEO-r-PPO copolymer-modified surfaces. Titania films were aged in a highly humid environment at 4ºC for 2 h and calcined at 400ºC. X-ray diffraction and grazing incidence small-angle x-ray scattering patterns confirmed that the films contained hcp chan-
nels tilted perpendicular to the substrate so long as the film thickness was below a critical value between 70 nm and 100 nm. Thicker films (up to 240 nm thick) could be completely oriented by sandwiching them between two PEO-r-PPO–modified substrates. Direct observation by electron microscopy corroborated these results. Because the cross-linked PEO-PPO layer masks substrate-specific effects, the researchers said that orthogonally tilted hcp nanopore ceramic films can be deposited on substrates of any curvature and size onto or into which the PEO-PPO layer can be deposited. Other ceramic precursors may allow extension of this approach to other applications, including
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