Sneak Previews

Medicine benefits from micropatterning development

Developers of medical devices regularly face the challenge of making their products biocompatible and suitable for implantation into the human body. This challenge becomes especially difficult when the products are computer "biochips." Biochips are a class of microscopic devices called micro-electro-mechanical systems (MEMS). BioMEMs are MEMS that are being developed for a variety of medical applications, such as monitoring glucose levels in diabetics, chemical and genetic screening of blood, and analyzing food products. The trouble with bioMEMS is the attaching of biological entities such as cells or DNA to a computer chip. Nicholas A. Peppas, a professor of chemical and biomedical engineering at Purdue University, and Rashid Bashir, an assistant professor of electrical and computer engineering at the university, are developing a new micropatterning technique that is used for "gluing" biological entities to computer chips. The professors form their copolymer glue with two layers of thin film. Patterns are created on the copolymer's surface by applying a mask and then irradiating the surface. Specific cells stick to the polymer, depending on the design of the patterns. So far, the smallest patterns are approximately 5 microns in length. Peppas and Bashir are working on development of smaller sizes. For more information, visit http://ChE.www.ecn.purdue.edu/ChE/Fac_Staff/Fac.Staff/peppas or http://ECE.www.ecn.purdue.edu/ECE/People/Faculty/ bashir .

Laser tracks Earth's atmosphere

Jn Kang, a professor of electrical and computer engineering at Johns Hopkins, is working with engineers at NASA to design a fiber-optic laser that will shoot ultraviolet beams at the Earth's atmosphere from a satellite. When the light strikes molecules of ozone, sulfur, and carbon dioxide, it bounces back to the satellite carrying a wavelength absorption "fingerprint" which reveals information about the Earth's atmospheric content. Kang is developing the prototype, which is part of a Lidar system that will be launched into space within the next three years. Lidar systems use light for radar instead of radio waves. Kang's prototype is about the size of a laptop computer. "It weighs much less than conventional lasers," he says. "That's attractive to spacecraft designers because weight is an important factor." Contact Kang at Johns Hopkins University, 3003 N. Charles St., Baltimore, MD 21218-2690; call (410) 516-8186; fax (410) 516-7160; or e-mail jkang@jhu.edu .

The ultimate miniaturization limit

As engineers strive to make electronic devices smaller and faster, they are approaching the atomic level where quantum mechanics become a limiting factor. Uzi Landman, the director of the Georgia Tech Center for Computational Materials Science, is providing clues about how these small-scale devices will work by conducting research on the properties of silicon nanowires a few atoms in diameter. Results of the work help engineers understand how quantum mechanics affect materials on this very small scale, which helps engineers design tomorrow's electronic devices. "Our trade secret is simulations of such nano-scale devices, and prediction of methods for their preparation," says Landman. The Georgia Tech research team simulated silicon nanowires etched from bulk silicon or self-assembled from clusters containing 24 atoms of silicon. Wires were connected to aluminum leads. The experiments produced data on the nanowires' electrical conductance, the influence of a silicon-metal interface, and the role that doping with aluminum atoms has in changing material properties. For example, the research suggests a way of overcoming some of the anticipated problems involved in doping the silicon used in small electronic devices. Doping of semiconductors is routinely used for tuning and optimizing device characteristics. However, in nanoscale devices, it's reasonable to expect large variations of dopant concentrations from device to device. Designers need to be aware of these variations for determining the performance of such devices. Landman believes nanowires made from silicon clusters could offer a solution. "Advanced theoretical methods of electron structure calculations for systems of up to several thousand electrons are essential for predicting properties," says Landman. For more information on Landman's research, e-mail Uzi.Landman@physics.gatech.edu , call (404) 894-3368, or fax (404) 894-7747.

Universal language for exchanging product information

Until recently, Lockheed Martin manually transmitted large volumes of engineering data via hard copy bid packages to potential suppliers. Data often had to be re-entered into different systems, resulting in time delays and errors. Each of the 27 sets of F-16 manuals, which are translated for use among 19 different air forces from different countries, includes hundreds of documents totaling approximately 50,000 pages. By changing the medium from paper to electronic manuals, all data can now be placed on a single laptop computer hard drive. Using the electronic media reduces cost, storage space, and airlift requirements for deployments. Using STEP, the global Standard for The Exchange of Product model data, Lockheed Martin data can be electronically sent to suppliers. What once could take weeks is now accomplished in minutes. STEP, also known as ISO 10303, was brought about through the efforts of the National Institute of Standards and Technology's efforts to create a universal, unambiguous language for exchanging product information. For more information on NIST's involvement with STEP, call (301) 975-3524 or go to www.nist.gov .

Sensitive sensors

Nancy Foster-Mills, Tom Autry, and Jim Amonette are researchers at Pacific Northwest National Laboratories (PNNL) developing sensors for non-destructive, real-time monitoring of chemical mixtures. "These photoacoustic sensors are 100 to 1,000 times more sensitive than conventional absorption spectroscopy technologies," says Foster-Mills. Using the new sensor, she worked with the U.S. Department of Energy (DOE) to determine how minerals in the soil take up the pollutant chromate. The soil analysis, which also helped determine the concentration of chromate at a DOE site, provides results in seconds. "Other technologies might take minutes or hours," says Foster-Mills. The sensor works when light of the appropriate wavelength shines on a soil sample and excites molecules in the mixture. As molecules return to their relaxed state, they emit heat, which creates a pressure wave through the sample. When researchers measure the pressure wave with the sensor, they determine how much of a given chemical is in the sample. The sensor's potential applications include routine analysis of chemicals in situations where non-destructive, real-time monitoring in-situ is needed. PNNL is seeking partners to develop the photoacoustic sensor. Contact PNNL at Box 999, 902 Battelle Blvd., Richland, WA 99352; call (509) 375-2121; or visit www.pnl.gov/breakthroughs .

Superconducting wire

Engineers and scientists from Los Alamos, Oak Ridge, and Argonne National Labs are collaborating with the University of Wisconsin and American Superconductor to advance a new high-temperature superconducting wire that lacks resistance when cooled. The high-temperature superconducting materials are ceramics, but ceramics produced with conventional processing methods are brittle and not always durable enough for electrical applications. The new superconducting wires use a "powder-in-tube" fabrication technique that synthesizes and packs powder into a silver or silver alloy tube. A series of deformation steps, including wire drawing, transforms the tube into a length of wire. Lengths of individual wires are bundled together into a larger silver tube. After additional deformation processes occur, fine elements of ceramic material run the length of the wire. Subsequent heat-treating converts the wire's ingredients into filaments of superconducting material. American Superconductor is building a wire-manufacturing facility dedicated to the manufacture of the wire product and hopes to begin production of it in January of 2002. For more information, call (505) 665-9206 or go to http://www.lanl.gov .