Anode-Supported SOFC Performs Well at Intermediate Operating Temperatures with a Lanthanum Ferrite-Based Cathode
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RESEARCH/RESEARCHERS Nanoscale Technique Prints Metal Films with Reusable Stamps and Tailored Surface Chemistry Traditional nanolithographic techniques such as electron-beam or deep-UV nanolithography are limited to patterning small regions of specialized materials on rigid, ultraflat inorganic substrates. These restrictions are unacceptable for nascent applications in fields such as plastic electronics and biotechnology. Consequently, researchers are aggressively investigating alternative “soft lithography” methods, such as near-field phase-shift lithography, microcontact printing, and dip-pen lithography. In the July 15 issue of Applied Physics Letters, Y.-L. Loo and co-workers at Lucent Technologies described a nanotransfer printing (nTP) technique that is used to transfer metal films with features as small as 100 nm from the raised regions of a stamp onto substrates. This is reminiscent of woodcut printing, but on the nanometer scale. The high-resolution method is fast, can cover large areas, provides good adhesion, and is conducted under ambient conditions. Moreover, unlike its competing technologies, this soft lithography method is a one-step process and purely additive: It does not require any etching, resists, or postpatterning deposition. The scientists produced rigid stamps by conventional patterning and etching of hard substrates such as glass or GaAs and created flexible stamps by casting a prepolymer of poly(dimethysiloxane) (PDMS) in a patterned resist mold. They “inked” the stamp simply by evaporating the desired metal. Substrates can also be either rigid or conformal, and materials have included silicon dioxide and PDMS. Intimate contact between the film and the substrate transfers the metal film through a common condensation reaction between hydroxyl (–OH) groups present on both surfaces. In order to accumulate the hydroxyl groups, the researchers applied either oxygen plasma or UV radiation to the native oxides. This surface-chemistry restriction on the materials is not severe. Thus far, the researchers have successfully used nTP to print films of aluminum, whose surface spontaneously oxidizes, and, surprisingly, gold, after dusting it with titanium to obtain the requisite oxide layer. “By exploiting other interfacial chemistries,” Loo said, “nanotransfer printing may be suitable for patterning a wide range of single- and multilayer conducting, dielectric, and semiconducting films.” To appraise nTP’s potential application to plastic electronics, the scientists patterned
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Au/Ti contacts and interconnects for organic transistors and complementary inverter circuits. The devices performed as well as top-contact devices fabricated with conventional shadow-mask gold electrodes. RICHARD N. LOUIE
Diblock Copolypeptide Amphiphiles Form Rapidly Recovering Hydrogels Protein-based hydrogels are used in a number of applications including drug delivery, tissue replacement, and cosmetics. Researchers at the University of California, Santa Barbara and the University of Delaware, Newark have synthesized dibl
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