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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Mimicking Growth Of Dizzy Dendrites

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Crystals are more than just pretty faces. Many of the useful properties associated with metal alloys or polymer blends—like strength, flexibil-ity and clarity—stem from a material’s specific crystal microstructure.

In a recent issue of Nature Materials, NIST researchers described work with collaborators in Hungary and France using computer simulations of crystal growth to advance understanding of how foreign particles—either additives or impurities—affect crystal growth patterns. They found that computer simulations developed to predict the crystal growth of metal alloys matched up remarkably well with microscope images of actual crystals grown in polymer films with thicknesses far below that of a human hair.

Randomly dispersed foreign particles in both the simulation and the real materials produced
what the researchers dubbed “dizzy dendrites.” In both cases, the tree-like branches in the crystals tend to curve and split, instead of forming the straight, symmetric patterns typical of pure crystals. (See graphics above. Left—dizzy dendrite grown in a polymer blend. Right—computer simulation of a metal alloy dizzy dendrite.)

Further simulations indi-cated that rotating the particles in concert during the solidification process produced spiraling dendrites. Alternating strips of particles with first one and then another orientation produced zig-zagging patterns. The researchers suggest that experimentalists may be able to reproduce the crystal patterns seen in these more complex simulations. Possible methods include imprinting the crystal-growing surface with a patterned roller (like those used to make a patterned pie crust) or using external electromagnetic fields or laser pulses to orient particles in specific directions.

Contact: James Warren, (301) 975-6139.

Progress Toward a ‘Super Molecule’

A team of researchers at JILA, a joint institute of NIST and the University of Colorado at Boulder, report in the July 3 edition of the journal Nature an important step toward creating a “super molecule,” a blend of thousands of molecules acting in unison. Such a blend of molecules would provide physicists with an excellent tool for studying molecular quantum mechanics and superconductivity.

At temperatures of only 150 nanoKelvin above absolute zero, the team used lasers and a carefully tuned magnetic field to pair potassium atoms belonging to a class of particles called fermions into loosely joined molecules belonging to a class of particles, called bosons. Surprisingly, the researchers report, the number of molecules produced is very large—with about a quarter million (50 percent) of the atoms within the original cloud pairing up.

“This work,” Jin notes, “could help us understand the basic physics behind supercon-ductivity and especially high-temperature superconductivity.” Superconductivity is a property in which electrons (a fermion particle) move through a metal with no resistance. The experiments may lead to creation
of fermion superfluids made from gases that would be much easier to study than solid superconductors.

“Our experiments,” Jin continues, “produced the lowest molecular binding energy that has been measured spectroscopically.” In other words, the atom pairs forming each molecule are hanging onto one another by their proverbial fingertips. They also are spaced very far apart by molecular standards. The researchers measured the amount of energy required to hold the molecules together by breaking the molecular bond with a relatively low-energy radio wave. Most molecular bonds require higher-energy light waves to break them apart.

The atoms, a form of potassium with one extra neutron (the isotope of potassium with a molecular weight of 40 rather than the more common 39), are classified as fermions. Fermions are the particles most people are familiar with—i.e., protons, neutrons, electrons—and they obey one basic rule. No
fermion can be in exactly the same state at exactly the same time and place as another fermion. Hence, no two things made of ordinary matter can be in exactly the same place at exactly the same time.

The molecules formed from these potassium atoms, however, are bosons. Unlike fermions, bosons can be in exactly the same energy state in exactly the same time and space. Light waves or photons are the most commonly known bosons, and laser light is an example of how bosons can behave in unison.

Creation of a “super atom,” or Bose-Einstein condensate (BEC), earned JILA scientists Eric Cornell and Carl Wieman the 2001 Nobel Prize in physics. BECs are the atomic equivalent of lasers.
Funded by NIST and the National Science Foundation, the current work builds on these earlier experiments.

Contact: Deborah Jin, (303) 492-0256, jind@boulder.nist.gov.

Software to Cool Summer’s Heat

New software developed by NIST can help cooling system manufacturers meet Department of Energy goals calling for a 20 percent increase in energy efficiency of residential air conditioners by 2006. Manufacturing engineers can use the software, called EVAP-COND, to improve evaporators and condensers, two types of heat exchangers that are essential components of every air conditioner.

The software simulations depict the performance of evaporators and condensers working with any one of 10 cooling agents, including new generation atmospheric ozone-safe hydrofluorocarbon fluids and “natural refrigerants,” such as carbon dioxide or propane.

The Windows-based program can be downloaded from www2.bfrl.nist.gov/software/evap-cond/.

Improving Control of Quantum Dots

A light bulb isn’t very useful without a reliable on/off switch. The same holds true for quantum dots. These ultra-tiny electronic nanostructures someday may serve as the ones and zeros used by a superfast quantum computer, but first physicists must improve methods for turning them “on” and “off.”

Researchers from NIST and the National Renewable Energy Laboratory (NREL) have developed a way to measure accurately the amount of laser light needed to shift electrons in a particular type of quantum dot between two discrete states, a low energy, ground state and a higher energy, excited state. (See June 23 Applied Physics Letters online.)

The strength of the interaction between quantum dots and electromagnetic waves like laser light is affectionately known in physical science circles as the “dipole moment.” Loosely translated, it’s a number that tells you how easy the dots are to excite. The new NIST/NREL technique meas-ures the dipole moment directly by enclosing the dots in a cav-ity where a pulse of laser light can pass over them repeatedly. The ability to measure accurately the dipole moment for quantum dots made of different materials should help nanotechnology researchers optimize these structures for a variety of applications, including both quantum computing and quantum communications.

In a separate study, NIST researchers used a method that helps calculate the growth of cracks to predict how quantum dots assemble and stack themselves on semiconductor materials. (See July 15 Physical Review B.)

The insight could aid development of more reliable methods for fabricating lasers, sensors and other devices that exploit quantum dots’ special electronic properties.

The minuscule structures already are the basis for some lasers. Yet, difficulties in making quantum dots of uniform size and precisely positioning them on a substrate remain formidable. These obstacles stand in the way of an array of faster, more powerful electronic and photonic devices.

Two NIST researchers borrowed a mathematical concept that explains how cracks grow in a solid, such as the Earth’s crust or an airplane wing. The concept, called the elastic energy release rate, accounts for how energy is apportioned as a crack advances. The scientists found that the rate also accounts for how self-assembling quantum dots will position and align themselves among their neighbors—those next door and those living below. For cube-shaped quantum dots, at least, the equation predicts the most “energetically favorable” location for a quantum dot. The theory can be used, for example, to predict the optimal depth for embedding quantum dots that will be overlain by another array of dots.
Contact: Kevin Silverman, (303) 497-7948, silverman@boulder.nist.gov or Vinod Tewary, (303) 497-5753, tewary@boulder.nist.gov.

New Network for First Responders

First responders would like to be able to send messages simultaneously to all the emergency workers at the scene of a disaster if necessary, but lack of interoperability among various types of radio equipment prevents them from doing so today.

In the future, first responders converging on a disaster scene may be able to quickly and easily exchange emergency messages and data using a wireless ad hoc network recently developed and tested by NIST scientists and engineers. NIST’s work in this area is part of the federal government’s efforts to improve first responder communications in light of the Sept. 11 terrorist attacks.

The network consists of personal digital assistants (PDAs) equipped with wireless local area network (WLAN) cards. Transmission routes among the PDAs are established automatically and without need for networking infrastructure at the emergency site as the first responders arrive on the scene. The network may use any nearby PDA to relay messages to others at the scene and allows transmission of voice, text, video, and sensor data. If a worker leaves the disaster scene or a device is destroyed, the network automatically reorganizes itself.

Small video screens can display the names of workers and their roles. In buildings equipped with radios at reference locations, the network would determine the locations of first responders and track their movements. The devices also could receive information from smoke, heat, or vibration sensors embedded in smart buildings that could be transmitted by wireless sensor networks or distributed by first responders during emergencies.

Contact: Nader Moayeri, (301) 975-3767.

Tool Measures Nanoscale Forces

How do you weigh a dust mite? Or determine the force required to pull a molecule apart? Such tasks require a device that measures nanonewtons—forces 1 billion times smaller than the force required to hold an apple against Earth’s gravity. Nanonewton forces are estimated with atomic force microscopes and instruments that measure the properties of ultrathin coatings like those used on computer hard drives or turbine blades. But the accuracy of such estimates is unknown because they haven’t been calibrated with force standards based on the kilogram, the internationally accepted unit of mass.

Luckily, there is hope on the horizon. In a paper presented June 4 at the annual conference of the Society of Experimental Mechanics in Charlotte, N.C., NIST engineers describe a prototype instrument that reliably measures forces as small as tens of nanonewtons and simultaneously ties those measurements to forces a thousand times larger based on the kilogram.

The device works by connecting a well-calibrated spring-loaded scale with a set of electrodes that generates an electrostatic force. The instrument balances the downward force produced by a one-milligram mass artifact by keeping the distance between the electrodes constant but varying the amount of voltage between them. The result is a force determination accurate to a few parts in 10,000 that is measured with voltage, electrical capacitance, and distance (the location of the electrodes as measured in wavelengths of laser light).

The NIST researchers hope to extend the instrument's resolution to tens of piconewtons (trillionths of a newton).

Contact: Jon Pratt, (301) 975-5470.

Tooth, Heal Thyself

Dentists beware: Teeth soon may be smart enough to fix themselves. “Smart materials” invented at NIST soon may be available that stimulate repair of defective teeth. Laboratory studies show that these composites, made of amorphous calcium phosphate embedded in polymers, can efficiently promote re-growth of tooth structures. In the presence of saliva-like solutions the material releases calcium and phosphate ions, forming a crystalline calcium phosphate similar to the mineral found naturally in teeth and bone. Developed through a long-standing partnership between NIST and the American Dental Association (ADA), these bioactive, biocompatible materials are described in the May/June NIST Journal of Research. Plans are being made for clinical trials, and several companies have expressed interest in licensing the patented material. Initial applications include adhesive cements for orthodontic braces and anti-cavity liners underneath conventional fillings. The work is funded through a grant from the National Institute of Dental and Craniofacial Research. Contact: Joseph Antonucci, (301) 975-6794.

Novel Spectroscopic Method Detects Terrorist Threats

A novel technique that uses far-infrared (terahertz) radiation to rapidly identify bulk or airborne materials inside sealed paper or plastic containers has been demonstrated by NIST scientists and SPARTA Inc.,
of Rosslyn, Va. The technology has potential applications in homeland security, such as detection of explosives in the mail or other non-metallic portable containers. The method involves directing a far-infrared light source at a sample in a closed container, detecting the light transmitted through the materials, and then analyzing the light that was absorbed by the sample while making adjustments for the light absorbed by the container. Two years of experiments have demonstrated that the technique detects aerosols, pharmaceutical powders, most gases, several explosives, and other common materials. The researchers have compiled a database of spectral characteristics for more than 100 materials. Further research aims to increase the sensitivity and throughput speed. Contact: Edwin Heilweil, (301) 975-2370 or Matt Campbell, (703) 797-3021, matt_campbell@rosslyn.sparta.com.

Tiny Bubbles Make a Chemist Feel Fine

NIST chemists reported in the June 24 online edition of Langmuir that a process called microboiling shows promise for quick, simple, and inexpensive chemical sensing. The process involves the formation of tiny vapor bubbles on a 200-nanometer-thick film of precious metal immersed in water and heated rapidly. By coating the metal microheater with a single layer of water-repelling molecules, the scientists dramatically altered the microboiling behavior. Bubbles formed more obviously and at lower temperatures, and the water in immediate contact with the metal got much hotter. The finding means that changes in boiling behavior should be useful for detecting specific substances. The water surrounding a microheater designed to bond with DNA or proteins, for example, might boil at a different temperature if the target molecules were attached to the coating. A change can be measured in just 5 microseconds. The technique can detect surfactants, such as those used in detergents, and may be useful for lab-on-a-chip devices. Potential spin-offs include designer coatings for boilers and heat exchangers and microheaters that simplify chemical manufacturing. Contact: Michael Tarlov, (301) 975-2058.

Peanut Butter Standard Spreads Quality

NIST recently issued Standard Reference Material (SRM) 2387, a peanut butter sample characterized with state-of-the-art measurement methods to provide values for fat, protein, vitamins, minerals, and other analytes it contains. It can be used by food manufacturers to validate production and quality control procedures, as well as to ensure accurate labeling of product content. The new SRM is the first NIST food-matrix reference material with values assigned for 18 individual amino acids—the building blocks of proteins—and for aflatoxins, carcinogenic substances produced by mold in crops. It also is the only SRM that is high in both fat content and protein, making it useful in evaluating the fat and protein content of other food products. SRM 2387 already has found a scientific use in evaluating allergen test kits. Even a trace of peanut protein can cause serious reactions, including death, if someone is highly allergic. Contact: Katherine Sharpless, (301) 975-3121.

Military Communications—The military uses thousands of miles of optical fibers on ships, planes and land-based installations to transmit voice and data. To ensure reliable communications, they needed a simple, highly accurate way to measure the amount of light delivered by these glass “wires” at key points in the transmission system. Working with ILX Lightwave Corp. of Bozeman, Mont., NIST researchers came up with a system capable of world-class optical measurements with push-button convenience. Measurement uncertainty is half that of previous optical fiber power detectors. The new systems now are being shipped to military calibration centers. Contact: John Lehman, (303) 497-3654, lehman@boulder.nist.gov.

Advanced Technologies—In the last several months, NIST’s Advanced Technology Program has announced 23 new awards to private-sector companies and joint ventures for cost-shared development of novel technologies. Research proj-ects receiving funding will focus on improved blade technology for wind turbines, virus-resistant tissues for skin grafts, and methods for operating a car’s devices through conversational speech among other topics. For details on the new awards, see www.nist.gov/news. Background information on ATP, is available at www.atp.nist.gov.

Miniature Mix-ups—A new NIST project aims to stir up materials research by adapting “lab-on-a-chip” technology to mix and evaluate experimental concoctions at a rapid clip, hastening improvements in products ranging from paints to shampoos to plastics. Initially, researchers at the NIST Combinatorial Methods Center (NCMC) and several of the NCMC’s company members plan to rev up the search for new or better emulsions—often complex formulations that are the basis for U.S. product markets totaling more than $50 billion. NCMC researchers have designed and tested credit-card-sized prototypes tailored for viscous materials research. Features include mixers, pumps, reservoirs and computer control of the flow of sample droplets through a network of millimeter-wide channels. Contact: Alamgir Karim, (301) 975-6588.

About Technology at a Glance:

NIST is an agency of the US Department of Commerce's Technology Administration. NIST develops and promotes measurement, 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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