What happened in the first trillionth of a trillionth of a trillionth of a second after the Big Bang? Super-sensitive microwave detectors, built at the National Institute of Standards and Technology (NIST), may soon help scientists find out. The new sensors, described on Saturday at a meeting of the American Physical Society (APS) in Denver,* were made for a potentially ground-breaking experiment scheduled for a year from now to make new measurements of the cosmic microwave background (CMB)—the faint afterglow of the Big Bang that still fills the universe.
The experiment, a collaboration of NIST, Princeton University, the University of Colorado at Boulder, and the University of Chicago, will take place in the Chilean desert. A large array of powerful NIST sensors on a telescope will look for subtle fingerprints in the CMB from primordial gravitational waves—ripples in the fabric of space-time from the violent birth of the universe more than 13 billion years ago. Such waves are believed to have left a faint but unique imprint on the direction of the CMB’s electric field, called the “B-mode polarization.” These waves—never before confirmed through measurements—are potentially detectable today, if sensitive enough equipment is used.
“This is one of the great measurement challenges facing the scientific community over the next 20 years, and one of the most exciting ones as well,” says Kent Irwin, the NIST physicist leading the project.
If found, these waves would be the clearest evidence yet in support of the “inflation theory,” which suggests that all of the currently observable universe expanded rapidly from a subatomic volume, leaving in its wake the telltale cosmic background of gravitational waves.
The experiment depends on new NIST microwave detectors that are designed to measure not only the intensity but also the polarization of the microwave background. The B-mode polarization signals may be more than a million times fainter than the temperature signals. To detect such subtle patterns, the NIST detectors will collect significant amounts of radiation efficiently and will be free of moving parts and traditional sources of systematic error, such as vibration and magnetic interference. The NIST team previously built superconducting amplifiers and cameras for CMB experiments at the South Pole, in balloon-borne observatories, and on the Atacama Plateau in Chile.
New Study: Home Energy Savings Are Made in the Shade
Shade trees positioned near houses in Sacramento, Calif., such as those in this photo, can significantly affect electricity use. Tree cover on the west and south sides of Sacramento homes reduced average summertime electricity demand by more than 5 percent, according to a study by NIST and the USDA.
Trees positioned to shade the west and south sides of a house may decrease summertime electric bills by 5 percent on average, according to a recent study* of California homes by researchers from the National Institute of Standards and Technology (NIST) and the U.S. Department of Agriculture (USDA).
The first large-scale study of its kind, the research paper considers the effects of shade on 460 single-family homes in Sacramento during the summer of 2007 and provides hard statistics showing how well-placed shade trees can reduce energy costs and atmospheric carbon, as well.
“People have known for a long time that trees have multiple benefits for people, but we’ve quantified one of them for the first time using actual billing data and put a dollar value on it,” said NIST’s David Butry, who authored the paper with Geoffrey Donovan of the USDA Forest Service’s Pacific Northwest Research Station.
The study’s findings included:
Planting trees on the west and south sides of a house decreased summertime electricity use, but planting them on the north actually increased it. Those on the east had no effect.
Fast-growing trees provide better help than do smaller ones, and placement of the trees, particularly the distance from the house, is a significant factor.
A London plane tree, planted on the west side of a house, can reduce carbon emissions from summertime electricity use by an average of 31 percent over 100 years.
This last finding was particularly significant to Butry, who said that trees not only reduce the carbon produced by the local gas or coal-fired power generator, but also remove carbon dioxide—a greenhouse gas—from the atmosphere.
“Trees sequester carbon in addition to providing shade,” Butry said. “We measured how much these shade trees reduced the carbon created by burning fuels to produce the electricity, and found that the trees also sequestered an equivalent amount of carbon on top of that. So there’s a double benefit.”
Utility companies from as far away as South Korea and South Africa have contacted the team about expanding the study, which was limited to a single season in a single city.
“It would be really interesting to look at how the effect varies across regions of the U.S. and of the world, and to see what happens in wintertime,” Butry said. “Sacramento Municipal Utility was very helpful in providing us with the data we needed. But future studies will depend on who has data and shares it with us.”
* G.H. Donovan and D.T. Butry. The value of shade: Estimating the effect of urban trees on summertime electricity use. Energy and Buildings June, 2009, 662-668. doi: 10.1016/j.enbuild.2009.01.002.
High Rise Fire Study Provides Insight Into Deadly Wind-Driven Fires
A fan recreates a wind-driven fire outside of the Governors Island apartment building. The wind pushes the fire into the public hallway, making conditions too dangerous for firefighters (see inset). Firefighters use a “floor below nozzle” to suppress the fire from the apartment below. Within one minute the temperature in the corridor drops from 1000 degrees C (800 degrees F) to 100 degrees C (200 degrees F), and firefighters can now do their job (see inset).
Fire researchers at the National Institute of Standards and Technology (NIST) have just published two reports providing details of how wind affects fires in high-rise buildings. A set of instructional DVDs based on the research is available for firefighter training, and will lead to improved safety for civilian and firefighters.
While much is known about wind’s impact on outdoor blazes, little has been known about how a fire rapidly turns into a “blowtorch” —firefighter’s parlance—when a blast of wind enters through a broken window, particularly in high-rise buildings.
Thousands of high-rise apartment fires occur annually. Beginning in one room, a fire can quickly spread smoke, heat and gases through hallways and stairwells, limiting the occupants’ chances to escape and the firefighters’ ability to rescue them. NIST researchers conducted a series of experiments to study the effect of wind on high-rise fires—buildings seven stories and taller—and potential techniques for fighting these fires.
Eight experiments were conducted in NIST’s Large Fire Laboratory, where conditions were controlled and measured. “These tests demonstrated that wind and a simple room and contents’ fire can be extended when wind and an open vent are present,” explained Fire Protection Engineer Dan Madrzykowski. “The temperatures in the flow path reached at least 400 degrees C (752 degrees F)—far higher than a firefighter in full protective gear can survive,” said Madrzykowski.
An abandoned apartment building on Governor’s Island, New York, provided a real-life laboratory for fire researchers studying wind-driven fires and tactics to combat them. The Statue of Liberty can be seen to the left of the island.
The researchers also conducted field experiments in an abandoned seven-story building on Governors Island, New York. The results confirmed the laboratory findings—that conditions created by wind can push hot gases and smoke from the apartment of origin into the public corridors and stairwells.
Researchers experimented with techniques that had a significant impact on reducing the hazardous conditions. For example, firefighters placed a fire-resistant material over windows to block the wind. They also used a “floor below nozzle” that allowed them to spray water through a broken window from the apartment below. The importance of controlling the doors inside a building to interrupt the flow path and stop the spread of fire gases was demonstrated many times during the experiments.
Both projects were supported by the Department of Homeland Security’s Federal Emergency Management Agency Assistance to Firefighter Research and Development Grant Program and the United States Fire Administration.
A double DVD set on the research is available for teaching purposes. It includes a video overview, both reports, a PowerPoint presentation summarizing the results, training videos, and video documentation of all of the experiments. The information is available at www.fire.gov. The DVD set can be ordered by emailing a request to madrzy@nist.gov.
Vise Squad: Putting the Squeeze on a Crystal Leads to Novel Electronics
The arrangement between atoms of a film of strontium titanate and the single crystal of silicon on which it was made is shown on the left. When sufficiently thin, the strontium titanate can be strained to match the atom spacing of the underlying silicon and becomes ferroelectric. On the right, this schematic has been written into such a film utilizing the ability of a ferroelectric to store data in the form of a reorientable electric polarization.
A clever materials science technique that uses a silicon crystal as a sort of nanoscale vise to squeeze another crystal into a more useful shape may launch a new class of electronic devices that remember their last state even after power is turned off. Computers that could switch on instantly without the time-consuming process of “booting” an operating system is just one of the possibilities, according to a new paper by a team of researchers spanning four universities, two federal laboratories and three corporate labs.*
Almost exactly two years ago, a team led by Joseph Woicik of NIST and several other federal, academic and industrial laboratories combined precision X-ray spectroscopy data from the NIST beamlines at the National Synchrotron Light Source with theoretical calculations to demonstrate that by carefully layering a thin film of strontium titanate onto a pure silicon crystal, they could distort the titanium compound into something it normally wasn’t—a so-called “ferroelectric” compound that might serve as a fast, efficient medium for data storage.** The new paper adds a key experimental and technological demonstration—the ability to write, read, store and erase patterned bits of data in the strontium titanate film.
In contrast to a traditional data storage material, which records data as a pattern of magnetic regions pointing in different directions, a ferroelectric can do the same with tiny regions of polarized electric charges. Ferroelectric memories are used, for example, in “smart cards” for subway systems. Ferroelectric structures that could be built directly onto silicon crystals, the most common materials base for consumer electronics, have been sought for years for a variety of applications, including nonvolatile memory (data that is not lost when power is turned off) and temperature or pressure sensors integrated into silicon-based microelectronics. One of the potentially biggest prizes would be ferroelectric transistors that could retain their logic state (“on” or “off”) without power, which could enable computers that switch on instantly without needing a boot stage.
The breakthrough originated with researcher Hao Li of Motorola, Inc., who succeeded in depositing the metal oxide directly onto silicon with no intervening layer of silicon oxide producing “coherency” between the two crystal structures—the unique matching up perfectly of one atom to the next across the metal-oxide/Si interface. This is a difficult trick both because silicon is highly reactive to oxidation and because the crystal spacing of the two materials does not normally match. Guided by precision X-ray diffraction data from NIST, Li developed a finely controlled method of depositing the strontium titanate in stages, gradually building up layers that were only a few molecules thick. The result, X-ray data showed, was that the silicon atoms literally squeezed the cubic strontium-titanate crystal to make it fit, distorting it into an oblong shape. That distortion creates a structural instability in the film that makes the compound a ferroelectric.
While theoretical calculations and spectroscopic data demonstrated that the distorted crystal behaved like a ferroelectric, proof of the ferroelectric functionality waited on the new work led by Cornell University professor Darrell Schlom, whose team used a technique called piezoresponse force microscopy to write, read and erase polarized domains in the strontium titanate film.
Researchers from Cornell, the University of Pittsburgh, NIST, Pennsylvania State University, Northwestern University, Motorola, the Energy Department’s Ames Laboratory, Intel Corporation, and Tricorn Tech contributed to the latest paper. X-ray diffraction data were taken at the Advanced Photon Source, Argonne National Laboratory. The research was funded in part by the Office of Naval Research and the National Science Foundation.
* M.P. Warusawithana, C. Cen, C.R. Sleasman, J.C. Woicik, Y. Li, L.F. Kourkoutis, J.A. Klug, H. Li, P. Ryan, L.-P. Wang, M. Bedzyk, D.A. Muller, L.-Q. Chen, J. Levy and D.G. Schlom. A ferroelectric oxide made directly on silicon. Science V 324 17 April 17, 2009. DOI: 10.1126/science.1169678.
** J.C. Woicik, E.L. Shirley, C.S. Hellberg, K.E. Andersen, S. Sambasivan, D.A. Fischer, B.D. Chapman, E.A. Stern, P. Ryan, D.L. Ederer and H. Li. Ferroelectric distortion in SrTiO3 thin films on Si (001) by x-ray absorption fine structure spectroscopy: Experiment and first-principles calculations. Physical Review B 75, Rapid Communications, 140103 April 24, 2007. DOI: 10.1103/PhysRevB.75.140103.
New Nanotube Coating Enables Novel Laser Power Meter
Carbon nanotubes (black coating in photo, right) form the inner lining of NIST’s new laser power meter, enabling the copper instrument to withstand the intensity of military lasers while precisely measuring their power. Laser light is distributed evenly inside the water-cooled cavity by a mirror (diagonal component at center of graphic).
The U.S. military can now calibrate high-power laser systems, such as those intended to defuse unexploded mines, more quickly and easily thanks to a novel nanotube-coated power measurement device developed at the National Institute of Standards and Technology (NIST).
The new laser power meter, tested at a U.S. Air Force base last week, will be used to measure the light emitted by 10-kilowatt (kW) laser systems. Light focused from a 10 kW laser is more than a million times more intense than sunlight reaching the Earth. Until now, NIST-built power meters, just like the lasers they were intended to measure, were barely portable and operated slowly. The new power meter is much smaller—about the size of a crock pot rather than a refrigerator. It also features a new design that enables it to make continuous power measurements.
A key innovation is the use of a sprayed-on coating of carbon nanotubes—tiny cylinders made of carbon atoms—which conduct heat hundreds of times better than conventional detector coating materials.
In the new power meter, laser light is absorbed in a cone-shaped copper cavity, where a spinning mirror directs the light over a large area and distributes the heat uniformly. The cavity is lined with a NIST-developed coating made of multiwalled carbon nanotubes held together by a potassium silicate (water glass) binder, and surrounded by a water jacket. The coating absorbs light and converts it to heat. The resulting rise in water temperature generates a current, which is measured to determine the power of the laser.
NIST has developed and maintained optical power standards for decades. In recent years, NIST researchers have experimented with a variety of coatings made of nanotubes because they offer an unusual combination of desirable properties, including intense black color for maximum light absorption. Designing a detector to collect and measure all of the power from a laser intended to significantly alter its target is a significant challenge. The new power meter uses the latest version of NIST’s nanotube coating,* which absorbs light efficiently, is more stable than some conventional coatings such as carbon black, and resists laser damage as effectively as commercial ceramic coatings.
Among other test results, NIST has found that multiwalled carbon nanotubes perform better than single-walled nanotubes. Researchers are continuing to seek nanotube formulas that are durable and easy to apply, like enamel paint, but have even higher damage thresholds than today’s coatings.
NIST’s nanotube coating technology already has been transferred to industry for use in commercial products. Development of the new power meter was funded by the Air Force.
* C.L. Cromer, K.E. Hurst, X. Li and J.H. Lehman. Black optical coating for high-power laser measurements from carbon nanotubes and silicate. Optics Letters. January 15, 2009, Vol. 34, No. 2.
Terahertz Waves Are Effective Probes for IC Heat Barriers
Credit: Shutterstock
By modifying a commonly used commercial infrared spectrometer to allow operation at long-wave terahertz frequencies, researchers at the National Institute of Standards and Technology (NIST) discovered an efficient new approach to measure key structural properties of nanoscale metal-oxide films used in high-speed integrated circuits. Their technique, described in a recent paper,* could become an important quality-control tool to help monitor semiconductor manufacturing processes and evaluate new insulating materials.
Chip manufacturers deposit complicated mazes of layered metallic conductor and semiconconductor films interlaced with insulating metal oxide nanofilms to form transistors and conduct heat. Because high electrical leakage and excess heat can cause nanoscale devices to operate inefficiently or fail, manufacturers need to know the dielectric and mechanical properties of these nanofilms to predict how well they will perform in smaller, faster devices.
Manufacturers typically assay the structure of metal oxide films using X-ray spectroscopy and atomic force microscopy, both tedious and time-consuming processes. NIST researchers discovered that they could extract comparable levels of detail about the structural characteristics of these thin films by measuring their absorption of terahertz radiation, which falls between the infrared and microwave spectral regions.
Although terahertz spectroscopy is known to be very sensitive to crystal and molecular structure, the degree to which the metal oxide films absorbed the terahertz light was a surprise to NIST researchers.
“No one thought nanometer-thick films could be detected at all using terahertz spectroscopy, and I expected that the radiation would pass right through them,” says Ted Heilweil, a NIST chemist and co-author of the paper. “Contrary to these expectations, the signals we observed were huge.”
The NIST team found that the atoms in the films they tested move in concert and absorb specific frequencies of terahertz radiation corresponding to those motions. From these absorbed frequencies the team was able to extrapolate detailed information about the crystalline and amorphous composition of the metal oxide films, replete with structures that could affect their function.
The team’s experiments showed that a 40 nanometer thick hafnium oxide film grown at 581 kelvin (307 degrees Celsius) had an amorphous structure with crystalline regions spread throughout; nanofilms grown at lower temperatures, however, were consistently amorphous. According to Heilweil, an approximately 5 nanometer film thickness is the detection limit of the terahertz method, and the efficacy of the technique depends to some degree on the type of metal oxide, though the group noted that all metal-oxide materials surveyed exhibit distinct spectral characteristics.
* E. Heilweil, J. Maslar, W. Kimes, N. Bassim and P. Schenck. Characterization of metal-oxide nanofilm morphologies and composition by terahertz transmission spectroscopy. Optics Letters. 34 (9), 1360–1362 (2009).
The National Institute of Standards and Technology (NIST) last week issued its first reference materials to support the new and growing field of tissue engineering for medicine. The new NIST materials are samples of a typical tissue scaffold material that have been measured and documented by NIST for three different degrees of porosity.
Three-dimensional tissue scaffolds, under development for some years, are biodegradable materials that are meant to be implanted in the body to provide a structurally sound framework for the patient’s cells to implant and grow, in time repairing damaged tissue. The scaffolds are meant to be absorbed gradually by the body and replaced by normal tissue. Today they are used most commonly to help repair damaged bone, but other applications being studied.
In addition to biocompatibility and biodegradability, successful 3-D tissue scaffolds have a number of physical requirements. Porosity or pore size is one key factor. The pores in the scaffold must be large enough to permit cells to infuse the structure and receive nutrients, but healthy cell growth also depends on the cell’s immediate surroundings. If the pores are too large or spaced too far apart, cells will be unable to build the proper connections.
The three new NIST reference materials are disks approximately 20 millimeters across and 5 millimeters high formed of crisscrossed layers polyester struts approximately 200 micrometers in diameter. Varying the spacing of the struts in each layer resulted in three different average porosities for the disks: 47 percent (average strut spacing of 200 micrometers), 60 percent (300 micrometers), and 69 percent (450 micrometers). These span the common range of pore sizes typically required for tissue engineering applications.
The biodegradable polymer, polycaprolactone, originally was used for sutures, and was chosen for being relatively strong and stable when not exposed to water or sunlight. The material has been approved by the Food and Drug Administration for use in tissue engineering implants, but the NIST reference materials are not meant for use in the body.
The release of these reference materials culminates a multi-year effort involving input from the FDA, the National Institutes of Health and ASTM Working Group WK6507 “Reference Scaffolds for Tissue Engineering.”
Standard Reference Materials are among the most widely distributed and used products from NIST. The agency prepares, analyzes and distributes more than a thousand different materials that are used throughout the world to check the accuracy of instruments and test procedures used in manufacturing, clinical chemistry, environmental monitoring, electronics, criminal forensics and dozens of other fields. For more information, see NIST’s SRM Web page at http://ts.nist.gov/measurementservices/referencematerials.
NIST Issues Draft Guide for Automating Computer Security Verification
The National Institute of Standards and Technology (NIST) has issued for public comment a draft publication describing a new method to automate the task of verifying computer security settings. Known as the Security Content Automation Protocol (SCAP), the specification has recently been incorporated into software scanners for checking security settings in federal computers.
The new publication provides an overview of SCAP, discusses programs for ensuring that products implement SCAP properly and recommends how federal agencies and other organizations can use SCAP effectively.
“You can do a lot of things with SCAP,” said NIST computer scientist Matthew Barrett, the publication’s lead author. “An organization can express vulnerability assessment instructions in a machine-readable format, and SCAP-validated tools can use that information to automate many computer security activities.”
In July 2008, the Office of Management and Budget required federal agencies to use SCAP-validated products to measure compliance with the Federal Desktop Core Configuration (FDCC), a mandated group of security settings for federal computers that run Windows XP and Vista. SCAP lists known security-related configuration problems and software flaws and can identify these vulnerabilities and evaluate results to determine FDCC compliance. The scan results are in a standardized format consistent across agencies and readable by other SCAP tools.
Organizations also can use SCAP to automate technical compliance with other information technology requirements, such as the Federal Information Security Management Act (FISMA). SCAP can be used to map high-level FISMA “controls”—for example, identifying, reporting and correcting information system flaws—to low-level rules—such as making sure patches for financial software are up to date.
SCAP incorporates six open specifications, including a dictionary of names for security-related software flaws; naming conventions for hardware, operating systems and applications; and a specification for exchanging technical details on how to check systems for security-related issues. SCAP combines the specifications and incorporates two XML-based programming languages for manipulating SCAP-based information.
Vendors are incorporating SCAP into their products, such as those that check for security issues. NIST also manages programs for validating third-party software tools to ensure they properly incorporate SCAP and for accrediting outside laboratories that perform validation tests of SCAP tools. Although developed for the federal government, SCAP can be used by other organizations.
Physicist James C. Bergquist, a Fellow at the National Institute of Standards and Technology (NIST) whose research helped usher in the age of optical atomic clocks, has been elected a member of the National Academy of Sciences. Election to the academy is considered one of the highest honors that can be accorded a U.S. scientist or engineer. New members are elected by current members in recognition of their distinguished and continuing achievements in original research.
Bergquist is a world leader in laser science and optical frequency standards, the basis for the next generation of atomic clocks. Bergquist’s experimental clock based on a single mercury ion (electrically charged atom) is the world’s most precise timepiece, and would neither gain nor lose 1 second in 2 billion years. The mercury ion clock was the first clock to have a smaller measurement uncertainty than atomic clocks based on cesium atoms, which are still the international standard. (See “Mercury Atomic Clock Keeps Time with Record Accuracy.”) Bergquist has pioneered a long string of advances in measurement science with broad applications, including the development of lasers with the world’s narrowest linewidth (band of emitted frequencies) and techniques required for quantum information processing, among many other breakthroughs.
A Colorado native, Bergquist has worked at the NIST Boulder Labs since 1978. He received his doctorate in physics from the University of Colorado. Bergquist’s previous honors include three Department of Commerce gold medals, the American Physical Society’s Herbert P. Broida Prize and Arthur Schawlow Prize in Laser Science, NIST’s Edward Uhler Condon Award and Samuel Wesley Stratton Award, the Optical Society of America’s William F. Meggers Award, and the IEEE’s I. I. Rabi Award. He joins seven other NIST scientists who are members of the NAS, a private organization of scientists and engineers established in 1863 dedicated to the furtherance of science and its use for the general welfare. See the NAS release, “72 New Members Chosen By Academy.”
Daniel Madrzykowski
Credit: NIST
NIST Researcher Dan Madrzykowski Named Fire Service Instructor of the Year
Daniel Madrzykowski of the National Institute of Standards and Technology was named George D. Post Instructor of the Year for 2009 by the International Society of Fire Service Instructors and Fire Engineering. Madrzykowski was recognized for his work to improve firefighter safety through research, education and training. He is a leader in applying science to firefighting operations, specifically his research on the application of fire dynamics tools, and applying this scientific knowledge to save the lives of firefighters. He also studies firefighter line-of-duty deaths to help establish the root causes of an incident in an effort to learn lessons that will improve life safety and prevent future losses.
Madrzykowski was presented the award for transferring his knowledge and experience to the classroom. He has delivered fire dynamics programs across the country and has developed a variety of training discs to put these lessons in the hands of fire company officers and instructors worldwide. Madrzykowski’s newest DVD program is on his recently completed wind driven fire research. More information is available at www.fire.gov.
NIST Physicists Win European and Optics Society Awards
Jun Ye, a NIST Fellow working at JILA, a joint institute of NIST and the University of Colorado at Boulder, has received the 2009 European Frequency and Time Award. Ye was honored for his pioneering work in establishing a neutral atom optical lattice clock, narrow linewidth lasers, femtosecond spectroscopy, and phase-coherent transmission of frequencies via optical fibers. The award was presented in April during the joint European Frequency and Time Forum and IEEE International Frequency Control Symposium held in France.
The award, described at http://www.eftf-ifcs-2009.com/awards-announcement.html, recognizes exceptional contributions as judged on the basis of initiative and creativity, quality of work, degree of success obtained as well as the worldwide scientific impact on the time and frequency community.
Leo Hollberg, a physicist and group leader who recently retired from NIST Boulder, will receive the 2009 William F. Meggers Award from the Optical Society of America (OSA). The award recognizes outstanding work in spectroscopy and is named after a physicist who worked at NIST from 1914 to 1958. Hollberg was cited for his seminal contributions to the development of diode lasers as powerful spectroscopic tools, development of femtosecond frequency combs, and demonstration of unique quantum effects in the interaction between light and atoms.
