NIST TechBeat Blue/Yellow Banner NIST logo--go to NIST home page Search NIST web space go to NIST home page go to A-Z subject index Contact NIST skip navigation

April 21, 2005

  In This Issue:
bullet Chip-scale Refrigerators Cool Bulk Objects

Portable Radiation Detectors Generally Meet Standards

bullet Nanomagnets Bend the Rules
bullet Dogs and Robots Share NIST Special Test Arena
bullet X-Rays Shine Light on High-Intensity Gas Lamps
bullet Data Effort Improves Flow Toward 'Greener' Chemistry
bullet Meeting to Explore Possible Gene Expression Consortium

[NIST Tech Beat Search] [Credits] [NIST Tech Beat Archives] [Media Contacts] [Subscription Information]

blue divider

Chip-scale Refrigerators Cool Bulk Objects

This colorized scanning electron micrograph shows a cube of germanium attached to a membrane. The four small light blue rectangles at the midpoints of the membrane perimeter are chip-scale refrigerators that cooled the cube and membrane to only a few hundred thousandths of a degree above absolute zero.

Click here to download a higher resolution version of this image.

Image credit: N. Miller, A. Clark/NIST

Chip-scale refrigerators capable of reaching temperatures as low as 100 milliKelvin have been used to cool bulk objects for the first time, researchers at the National Institute of Standards and Technology (NIST) report. The solid-state refrigerators have applications such as cooling cryogenic sensors in highly sensitive instruments for semiconductor defect analysis and astronomical research.

The work is featured in the April 25, 2005, issue of Applied Physics Letters.* The NIST-designed refrigerators, each 25 by 15 micrometers, are sandwiches of a normal metal, an insulator and a superconducting metal. When a voltage is applied across the sandwich, the hottest electrons "tunnel" from the normal metal through the insulator to the superconductor. The temperature in the normal metal drops dramatically and drains electronic and vibrational energy from the objects being cooled.

The researchers used four pairs of these sandwiches to cool the contents of a silicon nitrate membrane that was 450 micrometers on a side and 0.4 micrometers thick. A cube of germanium 250 micrometers on a side was glued on top of the membrane. The cube is about 11,000 times larger than the combined volume of the refrigerators. This is roughly equivalent to having a refrigerator the size of a person cool an object the size of the Statue of Liberty. Both objects were cooled down to about 200 mK, and further improvements in refrigerator performance are possible, according to the paper.

The refrigerators are fabricated using common chip-making lithography methods, making production and integration with other microscale devices straightforward. The devices are much smaller and less expensive than conventional equipment used for cooling down to 100 mK, a target temperature for optimizing the performance of cryogenic sensors. These sensors take advantage of unusual phenomena that occur at very low temperatures to detect very small differences in X-rays given off by nanometer-scale particles, enabling users such as the semiconductor industry to identify the particles. The work was supported in part by the National Aeronautics and Space Administration and NIST's Office of Microelectronics Programs.

*A.M. Clark, N.A. Miller, A. Williams, S.T. Ruggiero, G.C. Hilton, L.R. Vale, J.A. Beall, K.D. Irwin, J.N. Ullom. Cooling of Bulk Material by Electron-Tunneling Refrigerators. Applied Physics Letters. April 25, 2005.

Media Contact:
Laura Ost,, (301) 975-4034 or Gail Porter,,
(301) 975-3392



blue divider

Portable Radiation Detectors Generally Meet Standards

NIST researcher Leticia Pibida uses a hand-held radiation detection device to check the cargo of truck trailer.

© Robert Rathe

To receive a high-resolution version of this image, contact Gail Porter.

Portable radiation detectors generally perform well enough to meet new consensus standards but provide inaccurate readings for certain types of radiation, according to recent tests by the National Institute of Standards and Technology (NIST).

The results, reported in the May issue of the journal Health Physics,* are based on NIST tests of 31 commercial detectors, including hand-held survey meters; electronic personal alarming detectors (similar to pagers); and radionuclide identifiers (specialized devices that can identify specific radioactive materials). A number of federal, state and local agencies are using such instruments as part of homeland security-related efforts to detect and identify radioactive materials.

Researchers compared the devices' exposure rate readings to NIST measurements for different energy and intensity levels produced by NIST's calibrated gamma ray and X-ray beam lines. The responses of the majority of the detectors agreed with NIST-measured values, within acceptable uncertainties, for tests with gamma rays. This performance meets requirements established by new American National Standards Institute (ANSI) standards, adopted by the Department of Homeland Security (DHS) in 2004. However, there was a large discrepancy between most detectors' readings and the NIST values for the lowest-energy X-rays. For instance, readings by 14 detectors were roughly 40 to 100 percent below the NIST value. The deviations were much larger than those stated in manufacturers' specifications.

The tests are intended to help first responders and government agencies make better use of existing equipment and acquire the right equipment for emergency response, and to encourage manufacturers to better design and characterize their instruments. The tests were performed as part of the NIST program to support the development of the new ANSI standards (see
as well as to support the NIST Office of Law Enforcement Standards and DHS in testing detectors for their use by first responders.

*L. Pibida, R. Minniti, M. O'Brien, and M. Unterweger. Test of Radiation Detectors used in Homeland Security Applications. Health Physics. May. Vol. 88, Number 5. Posted online April 13, 2005.

Media Contact:
Laura Ost,, (301) 975-4034 or Gail Porter,,
(301) 975-3392


blue divider

Nanomagnets Bend the Rules

Nanocomposite materials seem to flout conventions of physics. In the latest example of surprising behavior, reported* April 15 by scientists at the National Institute of Standards and Technology (NIST) and Brookhaven National Laboratory, a class of nanostructured materials that are key components of computer memories and other important technologies undergo a previously unrecognized shift in the rate at which magnetization changes at low temperatures.

The team suggests that the apparent anomaly described as an “upturn” in magnetization may be due to the quantum mechanical process known as Bose-Einstein condensation. They maintain that, in nanostructured magnets, energy waves called magnons coalesce into a common ground state and, in effect, become one. This collective identity, the researchers say, results in magnetic behavior seemingly at odds with a long-standing theory.

The new finding could prompt a reassessment of test methods used to predict technologically important properties of "ferromagnetic" materials. The results also could point the way to marked improvements in the performance of microwave devices. Magnets are integral to these devices, used in a variety of communication and defense technologies.

Ferromagnets, including iron, cobalt, nickel and many tailor-made materials, become magnetic when exposed to an external magnetic field. As the strength of the external field increases, the materials become more magnetic, an atomic-level, temperature-influenced process called magnetic saturation. When the external field is removed, ferromagnets undergo an internal restructuring and the acquired magnetization decays, or fades, very slowly at a rate that increases with temperature.

Determined through accelerated testing methods, the temperature dependence of magnetic saturation and the rate of magnetization decay are key concerns in the design of permanent magnets, hard disks and other magnetic data storage systems.

For further information, see

*E. Della Torre, L.H. Bennett, and R.E. Watson, Extension of the Bloch T3/2 Law to Magnetic Nanostructures: Bose-Einstein Condensation. Physical Review Letters. April 15, 2005.

Media Contact:
Mark Bello,, (301) 975-3776


blue divider

Dogs and Robots Share NIST Special Test Arena

Police Officer Michael Millsaps Jr. of the Amtrak Police Department rewards his dog Bak for finding a hidden gun under debris at the NIST reference test arena for urban search and rescue and explosive ordnance disposal robots.

The white transmitters worn by both Millsaps and Bak can be used to track and record their movements as they proceed through the arena. Similar transmitters are attached to rescue robots and are used to analyze searching performance.

Photo by Gail Porter/NIST

Click here to download a higher resolution version of this image.

Bomb and drug sniffing dogs are regular visitors to the National Institute of Standards and Technology (NIST) for training, not for emergency work. Every month as many as 10 to 20 dogs and their handlers from federal agencies as well as from local county and municipal police departments visit the arenas that NIST uses to test and evaluate urban search and rescue and explosive ordnance disposal robots.

The arenas represent a building in various stages of collapse and provide a robot testing site for both pre- and post-disaster scenarios. The jumble of concrete collapsed walls and fallen debris also offers just the right challenge to sharpen the skills of the dogs who hunt for hidden drugs or patrol potential terrorist targets.

Small samples of explosive materials or narcotics are first hidden amid the rubble. Then individual dogs, under the watchful eyes of their handlers who are in a sense in training as well, seek out firearms, ammunition, explosives and chemical compounds used to build explosives or drugs such as cocaine or heroin. Once the dog finds the "hide," he or she sits silently, at attention, in front of the cache.

The individual dogs are trained in locating drugs or explosives, not both. Handlers must know why a dog is sitting, and in a real situation whether the find is safe to pick up. Success brings a shout of "That's my Boy," a rough, affectionate head tussle, a brief pulling match over a toy with the handler, and then the hunt goes on until all the hidden explosives or drugs are found.

"A dog just wants to play," said Sergeant Rick Hawkins of the NIH Police Department who coordinates the multi-agency K-9 visits to NIST. "When we go home we look at our paycheck. A dog has his toy and that's what he works for." Hawkins' six-year-old black Labrador, Flyer, is trained to find narcotics.

The police trainers appreciate having a unique indoor facility that challenges the dogs' skills and that is available on a regular basis. At the same time, the NIST robotics experts benefit from observing police techniques for systematically searching for explosives.

In April, NIST experts helped with the 2005 RoboCup German Open international competition in Paderborn, Germany, that used a newly constructed version of the NIST arenas to test the performance of the latest rescue robots.

A brief video describing the training of both dogs and robots at the NIST arena is available at: (Requires RealPlayer)
Audio file for the visually impaired (Requires RealPlayer)

Media Contact:
John Blair,, (301) 975-4261



blue divider

X-Rays Shine Light on High-Intensity Gas Lamps

Scientists perform a series of calculations to transform X-ray intensity data (left, a montage of five separate images) into an image of the spatial distribution of mercury atoms in a high-intensity discharge lamp (right). Blue indicates the lowest density of atoms, red the highest.

Click here to download a higher resolution version of this image.

An X-ray technique developed by physicists at the National Institute of Standards and Technology (NIST) is helping to improve the design and energy efficiency of the bright white lights often used to illuminate stadiums, roads and many other settings.

High-intensity gas discharge (HID) lamps produce 26 percent of the nation's light output, but, as a result of their high energy efficiency, consume only 17 percent of the electricity used for lighting. Continuing improvements in energy efficiency and other features will reduce electricity use and the negative environmental effects of power generation. Improved efficiency could save lots of money: HID lamps consume roughly 4 percent of U.S. electricity, equivalent to about $10 billion annually.

The NIST technique uses X-ray imaging to improve understanding of the complex science underlying the HID lamp's design. Such lamps have two electrodes in a ceramic tube that contains small amounts of mercury and metal-halide salts. An electric current between the electrodes heats the lamp, vaporizing the mercury and metal-halide salts and producing a gas of electrically charged particles, or plasma. Metal atoms, excited by collisions with electrons in the plasma, emit light at many different wavelengths, producing a bright, white light.

In the NIST technique, an HID lamp is placed in an intense beam of X-rays. The X-rays penetrate the lamp's ceramic housing but are partially absorbed by the mercury gas in the lamp, casting a shadow in the beam. A special digital camera behind the lamp captures a high-resolution, two-dimensional image of this X-ray shadow showing the density of mercury atoms in the discharge. From the mercury distribution, the temperature distribution in the lamp also can be determined. This technique has been used to quantify processes that consume power without producing light.

Researchers now are demonstrating that this technique can be implemented in industrial laboratories using small-scale X-ray sources. This project provides measurement support to universities participating in the Advanced Light Source Research Program-II (ALITE-II) of the Electric Power Research Institute. The goals of the consortium are to make significant improvements in lighting technology by combining the resources of university, industry and government laboratories in pre-competitive research.

*J.J. Curry and C.J. Sansonetti. X-Ray Absorption Imaging of High-Pressure Lighting Plasmas. IEEE Transactions on Plasma Science. April 2005

Media Contact:
Laura Ost,, (301) 975-4034



blue divider

Data Effort Improves Flow Toward 'Greener' Chemistry

Molecular "space filling" models demonstrate the difference in size for the positively charged "cation" (top image) and the negatively charged "anion" (bottom left) that combine to form a promising ionic liquid. It is still a mystery how the much smaller water molecule (right) can have such a large effect on the viscosity of such ionic liquids.

Click here to download a higher resolution version of this image.

Jeopardy answer: Death Valley and "ionic liquids." Correct question: Where does a little bit of water make a whole lot of difference?

Scientists at the National Institute of Standards and Technology (NIST) report* that flow properties for a relatively new class of alternative solvents called ionic liquids are extremely sensitive to tiny amounts of water. For example, for one of these solvents, just a 0.01 percent increase in water dissolved into a sample, caused a 1 percent decrease in flow resistance—a 100-fold effect. The finding should be helpful in the design of new industrial processes such as chemical separations that are both more efficient and more environmentally friendly.

Ionic liquids are salts. Just like table salt, ionic liquids consist of two components, one positively and one negatively charged. Unlike most simple salts, however, most of these new solvents are liquid at room temperature.

"People in industry are very interested in using ionic liquids because unlike most organic solvents, they don't evaporate and they are not flammable," explains NIST's Jason Widegren, lead author on the paper.

However, before ionic fluids can be used widely in industrial processes, reliable property data on characteristics like flow resistance (viscosity), density and thermal conductivity must be collected.

The new data help explain why reproducible measurements of viscosity for ionic liquids have been very difficult to achieve and published results have differed by 30 percent or more. Even the slightest contamination of samples with water vapor absorbed from the air dramatically affects measurements. The NIST group avoided these problems by carefully drying their samples and measuring water content both before and after each viscosity measurement.

The NIST work is part of a larger effort, conducted in conjunction with the International Union of Pure and Applied Chemistry, to perform "round robin" thermophysical property testing on the most promising ionic fluids and make the resulting data available to the scientific community.

*J. A. Widegren, A. Laesecke, and J. W. Magee. The effect of dissolved water on the viscosities of hydrophobic room-temperature ionic liquids. Chemical Communications, 2005, 1610-1612.

Media Contact:
Gail Porter,, (301) 975-3392


blue divider

Meeting to Explore Possible Gene Expression Consortium

The National Institute of Standards and Technology (NIST) will a host a meeting on May 16, 2005, in Boulder, Colo., to explore the possibility of creating a NIST-industry consortium focused on gene expression metrology.

Parallel and closely related advances over the last few years in the sequencing of whole genomes and the development of so-called gene microarrays have fueled an explosive growth in data on genes and their functions. Gene microarrays use thousands or tens of thousands of short lengths of single-strand DNA, fixed in a grid about the size of a postage stamp, to rapidly measure gene activity. It’s a powerful technology, but one that has evolved rapidly, and in advance of any underlying scientific infrastructure to quantitatively evaluate the quality of individual experimental results.

As a consequence, it has become difficult to reconcile the results of microarray experiments at different labs using different equipment. Lack of a gene expression measurement infrastructure is undermining confidence in microarray-based test results.

To address this problem, NIST is hosting the May 16 meeting to assess industry interest in establishing a Consortium on Gene Expression Metrology. The consortium would develop universal measurement methods to characterize microarray performance, including measures of signal-to-noise ratio, signal-to-background ratio, dynamic range (from minimum to maximum quantifiable amount), and selectivity/specificity.

Interested parties should contact Marc Salit,, (301) 975-3646.

Media Contact:
Michael Baum,, (301) 975-2763



blue divider

Return to NIST News Page)

Editor: Gail Porter

Date created:4/19/05
Date updated:4/19/05