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

Nov. 17, 2005

  In This Issue:
bullet Additives May Save Energy for Cooling Big Buildings

Copper Ridges Nearly Double X-ray Sensor Performance

bullet NIST Seeking Cure for Electronics-Killing Whiskers
  Quick Links:
bullet Two Universities Get Grants for Precision Measurements
bullet Nobel Laureate Wins Presidential Rank Award
bullet Virgil Gligor to Receive NIST/NSA Security Award

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

blue divider

Additives May Save Energy for Cooling Big Buildings (Amended 11/22/2005)
Cooling tower for commercial air conditioning unit
NIST laboratory experiments have demonstrated that adding small amount of additives to refrigerants may significantly improve the efficiency of commercial air conditioning.

Photo by Gail Porter/NIST

View a high resolution version of this image.

A National Institute of Standards and Technology (NIST) researcher has come up with a method designed to improve the energy efficiency of water chillers that cool the nation’s large commercial buildings. The NIST method, if confirmed through experiments with full-scale chiller systems, could save as much as 1 percent of the 320 billion kWh of electricity used annually by chillers or an equivalent 5.5 million barrels of oil per year, according to Mark Kedzierski, the NIST mechanical engineer who developed the technique.

The advance builds on past NIST research designed to optimize mixtures of chiller refrigerants with lubricants. The researchers discovered that some lubricants, when injected in small amounts, can significantly enhance evaporator heat transfer, increasing the efficiency of chillers. When they studied the process more closely they found the most efficient heat transfer occurred when the added oil’s surface tension, viscosity, composition and chemical characteristics complemented those of the chiller’s base lubricant.

In a recent paper* describing the method, Kedzierski describes how the right additive forms a very thin covering on an evaporator surface, which produces enhanced bubbling during boiling. The improved conversion of the refrigerant molecules into vapor molecules increases the chiller’s cooling capacity similar to a heat pump.

Kedzierski developed rules for the selection of the different types of oil additives according to the type of chiller lubricant, making successful energy enhancement less of a hit-or-miss proposition. Laboratory work is under way testing the energy enhancing potential of several oil and lubricant combinations that have been identified by the rules.

“The leap from a successful laboratory experiment to an everyday large-scale cooling application is a big one. NIST wants to see this theory translated into products germane to manufacturers as soon as possible,” Kedzierski said. “We welcome private-sector interest in the theory and its application.”

*M. Kedzierski. Method and transport properties for enhancing the nucleative heat transfer of refrigerant chiller evaporators. PriorArt Database, Online publication date, Sept. 28, 2005. The NIST theory and research is also described at (.pdf; download Acrobat Reader).

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



blue divider


Copper Ridges Nearly Double X-ray Sensor Performance

Scientist testing ultra cold refrigerator

Project leader Kent Irwin installs superconducting materials in an ultra-cold refrigerator for testing. These materials are used to make high-performance X-ray sensors for astronomy and materials research applications.

©Geoffrey Wheeler

For a high-resolution version of this photo contact

A series of copper ridges nearly doubles the resolution of experimental X-ray sensors, enabling more precise identification of the X-ray “fingerprints” of different atoms, researchers at the National Institute of Standards and Technology (NIST) report. The sensors are expected to be powerful tools for astronomy, such as in determining the temperature and motion of matter in space, and for semiconductor materials analysis, helping to differentiate between nanoscale contaminant particles on silicon wafers.

The new design, described in the Nov. 7 issue of Applied Physics Letters,* can measure X-ray energies with an uncertainty of only 2.4 electron volts (eV), breaking through a long-standing 4.5 eV plateau in the performance of superconducting "transition edge" sensors (TES). The cryogenic sensors absorb individual X-rays and measure the energy based on the resulting rise in temperature. The temperature is measured with a bilayer of normal metal (copper) and superconducting metal (molybdenum) that changes resistance in response to the heat from the radiation. The new TES design performs about 40 times better than conventional X-ray sensors made of silicon and lithium.

Layout of the NIST transition-edge sensor showing 5 copper ridges
The NIST "transition-edge sensor" is made of layers of molybdenum and copper with a coating of bismuth to increase the X-ray stopping power. The five copper ridges shown in this colorized photo enhance the sensor's performance.

Image credit: NIST

View a high resolution version of this image. 

The primary design change was the addition of five copper ridges patterned on the sensor, perpendicular to the current flow, which blunts or softens the change in resistance from superconducting to normal. NIST holds a patent on the sensor design concept.** The gentler transition reduces unexplained “noise” that degrades measurement precision. A second change was a reduction in device size from 400 to 250 micrometers square, which increases the rise in temperature caused by the X-rays, to better match the broader temperature range of the change in resistance.

NIST researchers expect to further improve sensor performance to reach the 2 eV resolution goal set by the National Aeronautics and Space Administration (NASA). NASA plans to mount TES sensors on a telescope sent into space on a satellite mission still under development. Improved sensor performance will enable scientists to better measure tiny shifts in X-ray frequency caused by the motion of atoms in space, for example. The latest NIST work was supported in part by NASA and the NIST Office of Microelectronics Programs.

* J.N. Ullom, J.A. Beall, W.B. Doriese, W.D. Duncan, L. Ferreira, G.C. Hilton, K.D. Irwin, C.D. Reintsema and L.R. Vale. 2005. Optimized transition-edge x-ray microcalorimeter with 2.4 eV energy resolution at 5.9 keV. Applied Physics Letters. Nov. 7.

** Superconducting transition-edge sensor with weak links, Hilton, Irwin, Martinis and Wollman, US6239431, Issued May 29, 2001.

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


blue divider

NIST Seeking Cure for Electronics-Killing Whiskers

Tin-Copper Whisker

Pure tin hillock

Top: Colorized scanning electron micrograph (SEM) shows a "whisker" on the surface of a tin-copper alloy. The image was taken 176 days after the alloy was electroplated onto a tiny cantilever beam.

Bottom: Micrograph of a "hillock" on an electrodeposited surface of pure tin (10 times the magnification of top image).

Image credit:NIST/Boettinger et al., Acta Materialia,5033-5050

View a high resolution version of top image.

View a high resolution version of bottom image.

Environmental groups around the world have been campaigning for years to replace lead-containing solders and protective layers on electronic components with non-hazardous metals and alloys. In response, the European Union (EU) will ban the use of lead (and five other hazardous substances) in all electrical and electronic equipment sold in EU nations starting in July 2006. U.S. manufacturers must comply with this requirement in order to market their products overseas.

However, pure electroplated tin and lead-free tin alloys tend to spontaneously grow metallic whiskers (thin filament-like structures often several millimeters long) during service. These defects can lead to electrical shorts and failures across component leads and connectors.

Whiskers—and more benign raised formations called hillocks—are believed to be a metal’s means of relieving stress generated by the electroplating process, so National Institute of Standards and Technology (NIST) researchers—working with the International Electronics Manufacturing Initiative (iNEMI)—have been trying to identify the origins of such stresses and better understand the resulting mechanisms for whisker and hillock growth. In a recent paper in Acta Materialia,* they reported that the surfaces of tin-copper deposits developed extremely long whiskers while pure tin deposits (the simplest lead-free plating finish) only produced hillocks. By comparison, the soon-to-be-banned tin-lead deposits did not form either type of deformity (a characteristic known since the 1960s).

The NIST researchers determined that whiskers and hillocks form when the boundaries between individual grains in a deposit have a column-shaped structure. If the boundaries move laterally, hillocks form. When copper impurities hold the columnar boundaries immobile, whiskers are the result. A tin-lead deposit possesses randomly structured boundaries that do not create either of these actions.

Based on these findings, the NIST researchers are exploring ways of eliminating the stresses and creating deposit structures without column grains that elicit whiskers and hillocks. One possibility involves using an alternating current on/current off electroplating process instead of the traditional continuous current method. This could disrupt the formation of columnar boundaries, yielding a structure similar to that of a tin-lead deposit but without lead’s environmental danger.

* Boettinger W.J., Johnson C.E., Bendersky L.A., Moon K-W, Williams M.E. and Stafford G.R. Whisker and hillock formation on Sn, Sn-Cu and Sn-Pb electrodeposits. Acta Materialia Vol. 53, Issue 19, pp. 5033-5050 (November 2005)

Media Contact:
Michael E. Newman,, (301) 975-3025



blue divider

Quick Links

Two Universities Get Grants for Precision Measurements

NIST has awarded two new Precision Measurement Grants to promote fundamental research in measurement science in U.S. colleges and universities. One grant was made to Edmund G. Myers of Florida State University (Tallahassee, Fla.) to carry out a sensitive measurement of the difference between the mass of tritium and helium-3, at the level of one part in 1011. This information will provide a constraint on the interpretation of tritium beta-decay experiments, which, in turn, will provide an improved upper limit on the mass of the electron anti-neutrino. This has important consequences for both fundamental physics and astrophysics. The other grant was awarded to David Weiss of Pennsylvania State University to carry out an ultraprecise search for an electric dipole moment of the electron at the level of 3×10-32 e m, a 500-fold improvement over the current limit. The experiment is expected to help put limits on possible extensions of the Standard Model, currently the most fundamental theory of matter, which plays a key role in understanding of nature.

The grants are awarded for three years, with an initial year funding of $50,000. The funding may be renewed at $50,000 per year for up to two additional years, for a total of $150,000, at the discretion of NIST. Over the 35-year history of the program, four PMG awardees have gone on to win Nobel Prizes. For more information, see or contact Peter Mohr, (301) 975-3217,



blue divider

Nobel Laureate wins Presidential Rank Award

NIST Fellow William D. Phillips, 1997 Nobel Laureate in physics, is a distinguished recipient of a 2005 Presidential Rank Award for exceptional long-term accomplishments, the most prestigious award given to senior executives and senior professionals in federal service. According to the federal Office of Personnel Management, winners are “strong leaders who achieve results and consistently demonstrate strength, integrity, industry, and a relentless commitment to excellence in public service.” Award winners are chosen through a rigorous selection process. They are nominated by their agency heads, evaluated by boards of private citizens, and approved by the President. For more information, see



blue divider

Virgil Gligor to Receive NIST/NSA Security Award

Dr. Virgil Gligor, one of the country’s pioneering figures in computer security, will be presented with the 2006 National Information Systems Security Award by the National Institute of Standards and Technology and the National Security Agency in a ceremony at the 26th Annual Computer Security Applications Conference in Tucson, Ariz. on Dec. 6, 2005.

The award recognizes individuals for scientific or technological breakthroughs, outstanding leadership, highly distinguished authorship or significant long-term contributions in the computer security field.

Gligor, a professor of electrical and computer engineering at the University of Maryland, College Park, Md., will receive the prestigious award for his outstanding contributions to advance computer security technology. Gligor has been a leader in computer security research and education for 30 years in a broad range of areas including access control mechanisms, penetration analysis, denial-of-service protection, cryptographic protocols, and applied cryptography.

For more information on Gligor and past award winners as well as on the computer security applications conference, see

(Return to NIST News Page)

Editor: Gail Porter

Date created:11/17/05
Date updated: 11/17/05