Technology at a Glance is a quarterly newsletter from the National Institute of Standards and Technology reporting on research results, funding programs, and manufacturing extension and technology services. If you have comments or general questions about this newsletter or if you would like to receive the four-page, color newsletter in hard copy, please email your mailing address to Gail Porter, editor, or call (301) 975-3392. About Technology at a Glance.

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‘Hot’ Movies Help Optimize Sensors

It will never run in theaters, but this colorful movie has a cult following all the same.

The “thermal contour” movie reveals what happens to a microhotplate, a NIST-developed technology that shows promise for a variety of gas-sensing applications, when it is heated and cooled. The devices are attractive for use in low-cost gas sensors, which might be used, for example, to detect freshness of food products or the leakage or presence of harmful chemicals.

The small size and fast heating speed of these tiny, micromachined devices previously made it difficult to measure dynamic temperature distribution, so NIST researchers used a new high-speed transient thermal imaging system (originally developed by NIST to study heating in power semiconductor devices) to make the movies.

The imaging system collects temperature information every microsecond for each 15 micrometer square of space on the microhotplate. The system works by successively acquiring temperature response as a function of time at each coordinate of the device being tested, and by using a coordinate-translation scheme to move between points. The thermal responses at different points are reconstructed to make the thermal contour movie. The colors in the graphic [above] indicate temperatures on a microhotplate surface where white is the hottest and blue is the coolest.

Components include an infrared microscope set up to “stare” at a 15 micrometer region of the device being tested. A digitizing oscilloscope is used for data acquisition. A temperature controller is used to maintain the test device at a desired temperature and to facilitate calibration of the emissions with a light chopper. A coordinate motion controller is used to change coordinates on the device. And sophisticated computer-controlled instrumentation with a high-level user interface is used to make the high-speed thermal image measurements.

NIST researchers found that the thermal imaging system can be used to optimize the design of microhotplates, which consist of a heater, a metal thermometer/heat distribution plate, and electrical contacts, all separated by insulating layers.

Contact: Allen Hefner, (301) 975-2071.

Solar Energy Home Runs on Ribbons

In a new twist on the American dream, a “Zero-Energy Cottage” demonstrates how a homeowner might do away with those pesky utility bills.

The 1,700-square-foot, two-bedroom, two-bath house features a number of environmentally friendly designs, materials, and systems, including solar electric panels made by Evergreen Solar of Marlboro, Mass. The company developed an innovative approach to making its technology with co-funding from NIST’s Advanced Technology Program. Designed to generate as much energy as it needs, the cottage is a project of the Captain Planet Foundation, which supports environmental projects for kids.

Evergreen Solar makes solar panels—which convert sunlight to electricity—using a patented “String Ribbon” technique. Ultrathin crystalline silicon is produced directly from molten silicon, a streamlined process that avoids the waste and cost of slicing solid material blocks. String Ribbon yields more than twice as many solar cells per pound of silicon as typical methods, according to the company.

The three-year project overcame significant technical challenges, including development of an active after-heater concept for precise control of thermal gradients and stresses in the silicon as it is formed and cools. Ribbon thickness was reduced from 300 micrometers to less than 100 micro-meters, while the width was doubled to 8 centimeters. These thinner, wider solar-grade ribbons also can be grown faster with the after heater.

As a result of the project, Evergreen Solar more than doubled furnace output and attracted venture capital funding to build a new manufacturing plant. The company has shipped more than 10,000 panels, which are used worldwide for both grid-connected and remote power applications. They were used in California to meet demand spurred by the recent energy crisis, for example, and installed on Tokyo’s World Trade Center.

Contact: Rex D’Agostino, (508) 357-2221, Web site: www.evergreensolar.com.

Circuits Sized Without Contact

A novel electrical technique for measuring the widths (or critical dimensions) of features patterned on the photomasks used in semiconductor manufacturing has been developed by a NIST guest researcher from George Washington University based on concepts originating at NIST. This technique—which can provide measurements applicable to integrated circuits with 0.18-micrometer lines, the state of the art—offers a potentially less expensive alternative to conventional industrial metrology methods.

Test structures are included in the designs patterned on photomasks so that suppliers and users can measure parameters, such as width, of selected features. The new technique measures the conduction characteristics of specific features on the test structures,and their widths are derived from this information. The relationship between electrical behavior and size has long been used to determine linewidth; the innovation here is that the electric signals are measured without physically contacting the test structure, reducing the danger of damaging or contaminating the mask.

An alternating-current (AC) signal is delivered using a specially designed sensor located in close proximity to, but not contacting, the test structure.

Analysis of this AC signal provides a measure of the capacitance (a conductive device’s capability to store electrical energy) between the sensor and the test structure.

From this measurement, the feature width is derived. Although the procedure appears straightforward, turning this concept into a practical tool proved difficult.

The new test device was fabricated by VTT in Finland with pioneering manufacturing methods. A major achievement of the project was finding a way to reduce the effects of “stray” capacitance and, thereby, improve the signal-to-noise ratio.

Contact: Richard Allen, (301) 975-5026.

Ion Beam Analyses Trace Quantities

From semiconductor chips to radioactive elements, a variety of materials and surfaces are routinely characterized by secondary ion mass spectrometry (SIMS), which offers high sensitivity, monolayer (single atom thickness) sampling depth, and high spatial resolution. In SIMS, a surface is bombarded in a vacuum with an energetic primary ion beam to produce characteristic “secondary ion” signals that provide information on the surface composition of the sample (ions are atoms possessing a net electrical charge). NIST is a leader in the development and application of SIMS, which is used for chemical analysis of the elemental and molecular composition of a variety of industrially relevant materials, including semiconductors, metals, polymers and pharmaceuticals.

Now, NIST has a rare new SIMS instrument, one of only three of its type in the United States, that offers superior sensitivity in detecting and distinguishing among elements at trace levels with micrometer spatial resolution. The new instrument (called an IMS 1270), offers very high secondary ion transmission combined with high mass resolution and the ability to simultaneously detect selected isotopes (isotopes are atomic species of the same element with different masses). This capability makes it especially useful for the precise measurement of isotope ratios for elements at trace level concentrations. The room-sized instrument is currently undergoing acceptance testing at NIST. Whereas the two other IMS 1270s in this county are used primarily to characterize geological materials, NIST scientists plan to apply their instrument to a variety of basic research, standards, and industrial problems.

For instance, the new instrument will be used to explore ultrahigh sensitivity measurements of the abundance of dopant elements and metals in silicon wafers for semiconductor manufacturing applications. Studies are planned to examine the distribution of chemotherapeutic agents in tissue cell cultures using molecules tagged with isotopic tracers. Other possible uses include investigation of the need for standards and measurement methods for geochemical applications, such as the analysis of samples from energy exploration sites.

Contact: Albert Fahey, (301) 975-2185.

Getting the Drop on Fire Quenchers

The behavior of tiny droplets of new liquid fire suppressants may play a big role in fire-fighting effectiveness. The new suppressants are proposed to replace halon suppressants now being phased out because they cause damage to stratospheric ozone.

The effectiveness of a suppressant depends on many factors. Do the droplets evaporate quickly or cling to a hot surface? Do they spread, shrink, splash, or levitate? Liquid droplet interactions with surfaces have been studied for more than 100 years, but the complicated fluid mechanics process is still not well understood. Moreover, few studies have addressed what happens to water droplets containing fire-suppressing additives.

NIST researchers are studying the collision dynamics of single droplets, about 2.7 mm in diameter, as they strike a heated stainless steel surface. In one set of experiments, the behavior of pure water was compared to that of a solution with salt-containing additives (30 percent sodium acetate trihydrate). The researchers recorded what happened to the droplets at different impact energies and at different surface temperatures using a high-speed digital camera.

Among the findings, for both water (left column of photos) and additive-containing droplets (right column), the disk-shaped liquid film formed on the surface after impact grew in diameter at higher impact velocity, possibly providing increased surface cooling. The presence of the additive influenced the collision dynamics greatly at low impact energy (top two photos), but less so as the velocity increased (bottom two photos). This suggests that for high-velocity impact, knowing the evolution of liquid film diameter for water impact may be sufficient to determine the amount of surface cooling. These findings are important in fire suppression because droplets impinging on surfaces from sprinklers and pressure nozzles are expected to have relatively higher impact energies.

Contact: Samuel Manzello, (301) 975-6891.

Building Plastic Biochip Devices

There may well be a plastic biochip in your future, thanks in part to NIST. Microfluidics devices, also known as “lab-on-a-chip” systems, are miniaturized chemical and biochemical analyzers that one day may be used for quick, inexpensive tests in physicians’ offices.

Most microfluidics devices today are made of glass materials. Cheaper, disposable devices could be made of plastics, but their properties are not yet well understood.

NIST is contributing to the development of these plastic microfluidics. One study looked at how fluids flowed in plastic microchannels by tracking fluorescent dye in the fluids. NIST researchers also developed an easy technique for accurately measuring fluid temperatures—an important parameter for chemical reactions.

A third project spawned a method for concentrating and separating an ionic (charged) substance in solution within microchannels. The technique concentrates the substance as much as 10,000-fold or more, making it easier to detect in ultrasmall quantities (nanoliters—a billionth of a liter—or less).

Finally, NIST staff designed a novel system to overcome the difficult problem of slow mixing in microfluidics devices. The mixer consists of a T-shaped microchannel imprinted in plastic that is modified with a laser to create a series of slanted wells. The wells speed the mixing of two streams entering the passage.

Contact: Laurie Loscascio, (301) 975-3130.

Computers Based on Ion Traps?

Quantum computers—using the properties of quantum systems rather than transistors to perform calculations or store information—someday could solve problems in seconds that would take months on today’s best supercomputers. A plausible architecture for a quantum computer was proposed recently by a team of current and former NIST scientists. The design reported in the journal Nature is based on the use of electromagnetic traps where ions (electrically charged atoms) can be stored, observed, and manipulated—techniques that NIST has played a leading role in developing. The paper proposes an architecture consisting of a large number of small, interconnected ion traps. By changing the operating voltages in these traps, researchers can confine a few ions in each trap or shuttle them from trap to trap, creating both memory and logical processing regions. A pair of interconnected ion traps that efficiently transports ions and that maintains stable electronic states has been demonstrated, indicating that the method is a practical system for building a quantum computer. Contact: David Wineland, (303) 497-5286.

Chocolate Standard Raises the ‘Bar’ on Accuracy

Chocoholics, rejoice. Now there’s a way to know more precisely than ever how much fat (and other constituents) are in chocolate and similar foods. NIST has issue Standard Reference Material (SRM) 2384, Baking Chocolate, which has been characterized with state-of-the-art measurement methods to show how much fat, protein, carbohydrates, individual fatty acids, elements, vitamins, and other components it contains. The baking chocolate SRM is the first standard to contain a high proportion of fat—more than 50 percent. A high-fat food standard has been identified as a priority by manufacturers. Because of this high fat content, the new SRM can be analyzed by manufacturers of chocolate and by quality assurance labs of companies that produce other fatty products, such as black olives and potato chips. This SRM also is the first to have values assigned for antioxidants and caffeine. Contact: Katherine Sharpless, (301) 975-3121.

Bugs in Your Software

Software bugs, or errors, are so prevalent and so detrimental that they cost the U.S. economy an estimated $59.5 billion annually, according to a study commissioned by NIST. Over half of the costs are borne by software users, and the remainder by software developers/vendors. The study also found that, although all errors cannot be removed, an estimated $22.2 billion in error costs could be eliminated by earlier and more effective identification and removal of software defects. These are the savings associated with finding an increased percentage (but not 100 percent) of errors closer to the development stages in which they are introduced. Currently, over half of all errors are not found until “downstream” in the development process or during post-sale software use. NIST funded the study, which was conducted by the Research Triangle Institute in North Carolina, as part of a joint planning process with industry to help identify and assess technical approaches that would improve software-testing capabilities. Copies of the 309-page report can be obtained at www.nist.gov/director/prog-ofc/report02-3.pdf.

Vibrations May Warn of Structural Collapses

NIST fire researchers are working to design an early warning system for building collapses. In May 2002, NIST, cooperating with local fire departments, set fires in vacant stores in a shopping center in Woodbridge, Va., that was scheduled to be demolished. Fire engineers from NIST and NIST grantee Harvey Mudd College (Claremont, Calif.) tested the capability of highly sensitive motion detectors to detect pre-collapse vibrations of walls in the lightweight steel frame building during fires large enough to cause collapse of steel deck roofs. The researchers hope to develop a methodology for interpreting the vibration data, which are being analyzed at Harvey Mudd, to enable the development of warning devices. A device that uses this technology could be attached to burning buildings by firefighters or installed into a structure permanently, to provide advanced warning of unsafe structures. The NIST experiment was part of a two-year series sponsored by the U.S. Fire Administration. Contact: Dave Evans, (301) 975-6897.

International Cooperation—NIST led five federal agencies participating with businesses and universities in the U.S.-Japan Joint Optoelectronics Project. Over seven years, the project provided a unique venue for fostering international cooperation and progress in a competitive high-technology field while protecting intellectual property. The project, part of Japan’s Real World Computing Partnership, encouraged advanced research by providing access to devices not yet commercially available. It led to more than 100 research publications, new research efforts, products, patents, and increased trade between the two countries. Single copies of the final report are available at no charge by calling (301) 975-NIST (6478) or sending an e-mail to inquiries@nist.gov.

Ceramic Machining— Understanding of ceramic machining processes, particularly machining damage characterization, was improved greatly through the NIST Ceramic Machining Consortium, which recently concluded its 10-year program. About 40 industrial and academic organizations participated. Payoffs included exact quantification of residual machining crack damage depths in silicon nitride, a major revision to the standard specimen preparation procedure in the widely used ASTM standard method for flexural strength testing of advanced ceramics, and a new standard test method for evaluating the effect of surface grinding on strength. Contact: George Quinn, (301) 975-5765.

Standards Symposium—Proceedings are now available for the NIST Centennial Standards Symposium—Standards in the Global Economy: Past, Present, and Future, which focused on a variety of topics, including information technology; semiconductors and optical sensing; transportation, materials, and manufacturing; and building and construction. Speakers included three former NIST directors and representatives from ANSI, ASTM, ASME, ISO, IEC, and other public and private-sector organizations. For a paper copy, send an e-mail to Mary Jo DiBernardo at maryjo.dibernardo@nist.gov. Also available online at http://ts.nist.gov/ts/htdocs/210/gsig/sp974-pdf/sp974-toc.htm.

About Technology at a Glance:

NIST is an agency of the US Department of Commerce's Technology Administration. NIST develops and promotes measurements, standards, and technology to enhance productivity, facilitate trade, and improve the quality of life. Technology at a Glance is produced by Public and Business Affairs, NIST, 100 Bureau Dr., Stop 3460, Gaithersburg, Md. 20899-3460. Any mention of commercial products is for information only; it does not imply recommendation or endorsement by NIST. Technology at a Glance Editor: Gail Porter, (301) 975-3392, email: gail.porter@nist.gov. For patent information, call (301) 975-3084.

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