New Material to Remove Radioactive Gas from Spent Nuclear Fuel

This illustration of a metal-organic framework, or MOF, shows the metal center bound to organic molecules. Each MOF has a specific framework determined by the choice of metal and organic. Sandia chemists identified a MOF whose pore size and high surface area can separate and trap radioactive iodine molecules from a stream of spent nuclear fuel. (Credit: Image courtesy of Sandia National Laboratories)

Science Daily  — Research by a team of Sandia chemists could impact worldwide efforts to produce clean, safe nuclear energy and reduce radioactive waste.

The discovery could be applied to nuclear fuel reprocessing or to clean up nuclear reactor accidents. A characteristic of nuclear energy is that used fuel can be reprocessed to recover fissile materials and provide fresh fuel for nuclear power plants. Countries such as France, Russia and India are reprocessing spent fuel.The Sandia researchers have used metal-organic frameworks (MOFs) to capture and remove volatile radioactive gas from spent nuclear fuel. "This is one of the first attempts to use a MOF for iodine capture," said chemist Tina Nenoff of Sandia's Surface and Interface Sciences Department.

The process also reduces the volume of high-level wastes, a key concern of the Sandia researchers. "The goal is to find a methodology for highly selective separations that result in less waste being interred," Nenoff said.

Part of the challenge of reprocessing is to separate and isolate radioactive components that can't be burned as fuel. The Sandia team focused on removing iodine, whose isotopes have a half-life of 16 million years, from spent fuel.

They studied known materials, including silver-loaded zeolite, a crystalline, porous mineral with regular pore openings, high surface area and high mechanical, thermal and chemical stability. Various zeolite frameworks can trap and remove iodine from a stream of spent nuclear fuel, but need added silver to work well.

"Silver attracts iodine to form silver iodide," Nenoff said. "The zeolite holds the silver in its pores and then reacts with iodine to trap silver iodide."

But silver is expensive and poses environmental problems, so the team set out to engineer materials without silver that would work like zeolites but have higher capacity for the gas molecules. They explored why and how zeolite absorbs iodine, and used the critical components discovered to find the best MOF, named ZIF-8.

"We investigated the structural properties on how they work and translated that into new and improved materials," Nenoff said.

MOFs are crystalline, porous materials in which a metal center is bound to organic molecules by mild self-assembly chemical synthesis. The choice of metal and organic result in a very specific final framework.

The trick was to find a MOF highly selective for iodine. The Sandia researchers took the best elements of the zeolite Mordenite -- its pores, high surface area, stability and chemical absorption -- and identified a MOF that can separate one molecule, in this case iodine, from a stream of molecules. The MOF and pore-trapped iodine gas can then be incorporated into glass waste for long-term storage.

The Sandia team also fabricated MOFs, made of commercially available products, into durable pellets. The as-made MOF is a white powder with a tendency to blow around. The pellets provide a stable form to use without loss of surface area, Nenoff said.

Sandia has applied for a patent on the pellet technology, which could have commercial applications.

The Sandia researchers are part of the Off-Gas Sigma Team, which is led by Oak Ridge National Laboratory and studies waste-form capture of volatile gasses associated with nuclear fuel reprocessing. Other team members -- Pacific Northwest, Argonne and Idaho national laboratories -- are studying other volatile gases such as krypton, tritium and carbon.

The project began six years ago and the Sigma Team was formalized in 2009. It is funded by the U.S. Department of Energy Office of Nuclear Energy.

Sandia's iodine and MOFs research was featured in two recent articles in the Journal of the American Chemical Societyauthored by Nenoff and team members Dorina Sava, Mark Rodriguez, Jeffery Greathouse, Paul Crozier, Terry Garino, David Rademacher, Ben Cipiti, Haiqing Liu, Greg Halder, Peter Chupas, and Karena Chapman. Chupas, Halder and Chapman are from Argonne.

"The most important thing we did was introduce a new class of materials to nuclear waste remediation," said Sava, postdoctoral appointee on the project.

Nenoff said another recent paper in Industrial & Engineering Chemistry Research shows a one-step process that incorporates MOFs with iodine in a low-temperature, glass waste form. "We have a volatile off-gas capture using a MOF and we have a durable waste form," Nenoff said.

Nenoff and her colleagues are continuing their research into new and optimized MOFs for enhanced volatile gas separation and capture.

"We've shown that MOFs have the capacity to capture and, more importantly, retain many times more iodine than current materials technologies," said Argonne's Chapman.

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The above story is reprinted from materials provided by DOE/Sandia National Laboratories, via News wise.

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Journal References:

1. Karena W. Chapman, Dorina F. Sava, Gregory J. Halder, Peter J. Chupas, Tina M. Nenoff. Trapping Guests within a Nanoporous Metal–Organic Framework through Pressure-Induced Amorphization. Journal of the American Chemical Society, 2011; 133 (46): 18583 DOI:10.1021/ja2085096
2. Dorina F. Sava, Mark A. Rodriguez, Karena W. Chapman, Peter J. Chupas, Jeffery A. Greathouse, Paul S. Crozier, Tina M. Nenoff. Capture of Volatile Iodine, a Gaseous Fission Product, by Zeolitic Imidazolate Framework-8.Journal of the American Chemical Society, 2011; 133 (32): 12398 DOI: 10.1021/ja204757x

Bilayer Graphene Works as an Insulator: Research Has Potential Applications in Digital and Infrared Technologies

ScienceDaily  — A research team led by physicists at the University of California, Riverside has identified a property of "bilayer graphene" (BLG) that the researchers say is analogous to finding the Higgs boson in particle physics.

BLG is formed when two graphene sheets are stacked in a special manner. Like graphene, BLG has high current-carrying capacity, also known as high electron conductivity. The high current-carrying capacity results from the extremely high velocities that electrons can acquire in a graphene sheet.Graphene, nature's thinnest elastic material, is a one-atom thick sheet of carbon atoms arranged in a hexagonal lattice. Because of graphene's planar and chicken wire-like structure, sheets of it lend themselves well to stacking.

The physicists report online Jan. 22 in Nature Nanotechnology that in investigating BLG's properties they found that when the number of electrons on the BLG sheet is close to 0, the material becomes insulating (that is, it resists flow of electrical current) -- a finding that has implications for the use of graphene as an electronic material in the semiconductor and electronics industries.

"BLG becomes insulating because its electrons spontaneously organize themselves when their number is small," said Chun Ning (Jeanie) Lau, an associate professor of physics and astronomy and the lead author of the research paper. "Instead of moving around randomly, the electrons move in an orderly fashion. This is called 'spontaneous symmetry breaking' in physics, and is a very important concept since it is the same principle that 'endows' mass for particles in high energy physics."

Lau explained that a typical conductor has a huge number of electrons, which move around randomly, rather like a party with ten thousand guests with no assigned seats at dining tables. If the party only has four guests, however, then the guests will have to interact with each other and sit down at a table. Similarly, when BLG has only a few electrons the interactions cause the electrons to behave in an orderly manner.

New quantum particle

Allan MacDonald, the Sid W. Richardson Foundation Regents Chair in the Department of Physics at The University of Texas at Austin and a coauthor on the research paper, noted that team has measured the mass of a new type of massive quantum particle that can be found only inside BLG crystals.

"The physics which gives these particles their mass is closely analogous to the physics which makes the mass of a proton inside an atomic nucleus very much larger than the mass of the quarks from which it is formed," he said. "Our team's particle is made of electrons, however, not quarks."

MacDonald explained that the experiment the research team conducted was motivated by theoretical work which anticipated that new particles would emerge from the electron sea of a BLG crystal.

"Now that the eagerly anticipated particles have been found, future experiments will help settle an ongoing theoretical debate on their properties," he said.

Practical applications

An important finding of the research team is that the intrinsic "energy gap" in BLG grows with increasing magnetic field.

In solid state physics, an energy gap (or band gap) refers to an energy range in a solid where no electron states can exist. Generally, the size of the energy gap of a material determines whether it is a metal (no gap), semiconductor (small gap) or insulator (large gap). The presence of an energy gap in silicon is critical to the semiconductor industry since, for digital applications, engineers need to turn the device 'on' or conductive, and 'off' or insulating.

Single layer graphene (SLG) is gapless, however, and cannot be completely turned off because regardless of the number of electrons on SLG, it always remains metallic and a conductor.

"This is terribly disadvantageous from an electronics point of view," said Lau, a member of UC Riverside's Center for Nanoscale Science and Engineering. "BLG, on the other hand, can in fact be turned off. Our research is in the initial phase, and, presently, the band gap is still too small for practical applications. What is tremendously exciting though is that this work suggests a promising route -- trilayer graphene and tetralayer graphene, which are likely to have much larger energy gaps that can be used for digital and infrared technologies. We already have begun working with these materials."

Lau and MacDonald were joined in the research by J. Velasco Jr. (the first author of the research paper), L. Jing, W. Bao, Y. Lee, P. Kratz, V. Aji, M. Bockrath, and C. Varma at UCR; R. Stillwell and D. Smirnov at the National High Magnetic Field Laboratory, Tallahassee, Fla.; and Fan Zhang and J. Jung at The University of Texas at Austin.

The research was supported by grants from the National Science Foundation, Office of Naval Research, FENA Focus Center, and other agencies.

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The above story is reprinted from materials provided by University of California - Riverside.

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Journal Reference:

1. J. Velasco, L. Jing, W. Bao, Y. Lee, P. Kratz, V. Aji, M. Bockrath, C. N. Lau, C. Varma, R. Stillwell, D. Smirnov, Fan Zhang, J. Jung, A. H. MacDonald. Transport spectroscopy of symmetry-broken insulating states in bilayer graphene. Nature Nanotechnology, 2012; DOI:10.1038/nnano.2011.251

Graphene 'Invisible' to Water: How the Extreme Thinness of Graphene Enables Near-Perfect Wetting Transparency

Graphene is the thinnest material known to science. The nanomaterial is so thin, in fact, water often doesn’t even know it’s there. A new study from Rensselaer Polytechnic Institute shows how the extreme thinness of graphene enables near-perfect wetting transparency. The findings could help inform a new generation of graphene-based flexible electronic devices. Additionally, the research suggests a new type of heat pipe that uses graphene-coated copper to cool computer chips. (Credit: Rensselaer/Koratkar)

ScienceDaily (Jan. 23, 2012) — Graphene is the thinnest material known to science. The nanomaterial is so thin, in fact, water often doesn't even know it's there.

Results of the study were published in the journal Nature Materials. The findings could help inform a new generation of graphene-based flexible electronic devices. Additionally, the research suggests a new type of heat pipe that uses graphene-coated copper to cool computer chips.Engineering researchers at Rensselaer Polytechnic Institute and Rice University coated pieces of gold, copper, and silicon with a single layer of graphene, and then placed a drop of water on the coated surfaces. Surprisingly, the layer of graphene proved to have virtually no impact on the manner in which water spreads on the surfaces.

The discovery stemmed from a cross-university collaboration led by Rensselaer Professor Nikhil Koratkar and Rice Professor Pulickel Ajayan.

"We coated several different surfaces with graphene, and then put a drop of water on them to see what would happen. What we saw was a big surprise -- nothing changed. The graphene was completely transparent to the water," said Koratkar, a faculty member in the Department of Mechanical, Aerospace, and Nuclear Engineering and the Department of Materials Science and Engineering at Rensselaer. "The single layer of graphene was so thin that it did not significantly disrupt the non-bonding van der Waals forces that control the interaction of water with the solid surface. It's an exciting discovery, and is another example of the unique and extraordinary characteristics of graphene."

Results of the study are detailed in the Nature Materials paper "Wetting transparency of graphene."

Essentially an isolated layer of the graphite found commonly in our pencils or the charcoal we burn on our barbeques, graphene is single layer of carbon atoms arranged like a nanoscale chicken-wire fence. Graphene is known to have excellent mechanical properties. The material is strong and tough and because of its flexibility can evenly coat nearly any surface. Many researchers and technology leaders see graphene as an enabling material that could greatly advance the advent of flexible, paper-thin devices and displays. Used as a coating for such devices, the graphene would certainly come into contact with moisture. Understanding how graphene interacts with moisture was the impetus behind this new study.

The spreading of water on a solid surface is called wetting. Calculating wettability involves placing a drop of water on a surface, and then measuring the angle at which the droplet meets the surface. The droplet will ball up and have a high contact angle on a hydrophobic surface. Inversely, the droplet will spread out and have a low contact angle on a hydrophilic surface.

The contact angle of gold is about 77 degrees. Koratkar and Ajayan found that after coating a gold surface with a single layer of graphene, the contact angle became about 78 degrees. Similarly, the contact angle of silicon rose from roughly 32 degrees to roughly 33 degrees, and copper increased from around 85 degrees to around 86 degrees, after adding a layer of graphene.

These results surprised the researchers. Graphene is impermeable, as the tiny spaces between its linked carbon atoms are too small for water, or a single proton, or anything else to fit through. Because of this, one would expect that water would not act as if it were on gold, silicon, or copper, since the graphene coating prevents the water from directly contacting these surfaces. But the research findings clearly show how the water is able to sense the presence of the underlying surface, and spreads on those surfaces as if the graphene were not present at all.

As the researchers increased the number of layers of graphene, however, it became less transparent to the water and the contact angles jumped significantly. After adding six layers of graphene, the water no longer saw the gold, copper, or silicon and instead behaved as if it was sitting on graphite.

The reason for this perplexing behavior is subtle. Water forms chemical or hydrogen bonds with certain surfaces, while the attraction of water to other surfaces is dictated by non-bonding interactions called van der Waals forces. These non-bonding forces are not unlike a nanoscale version of gravity, Koratkar said. Similar to how gravity dictates the interaction between Earth and the sun, van der Waals forces dictate the interaction between atoms and molecules.

In the case of gold, copper, silicon, and other materials, the van der Waals forces between the surface and water droplet determine the attraction of water to the surface and dictate how water spreads on the solid surface. In general, these forces have a range of at least several nanometers. Because of the long range, these forces are not disrupted by the presence of a single-atom-thick layer of graphene between the surface and the water. In other words, the van der Waals forces are able to "look through" ultra-thin graphene coatings, Koratkar said.

If you continue to add additional layers of graphene, however, the van der Waals forces increasingly "see" the carbon coating on top of the material instead of the underlying surface material. After stacking six layers of graphene, the separation between the graphene and the surface is sufficiently large to ensure that the van der Waals forces can now no longer sense the presence of the underlying surface and instead only see the graphene coating. On surfaces where water forms hydrogen bonds with the surface, the wetting transparency effect described above does not hold because such chemical bonds cannot form through the graphene layer.

Along with conducting physical experiments, the researchers verified their findings with molecular dynamics modeling as well as classical theoretical modeling.

"We found that van der Waals forces are not disrupted by graphene. This effect is an artifact of the extreme thinness of graphene -- which is only about 0.3 nanometers thick," Koratkar said. "Nothing can rival the thinness of graphene. Because of this, graphene is the ideal material for wetting angle transparency."

"Moreover, graphene is strong and flexible, and it does not easily crack or break apart," he said. "Additionally, it is easy to coat a surface with graphene using chemical vapor deposition, and it is relatively uncomplicated to deposit uniform and homogeneous graphene coatings over large areas. Finally, graphene is chemically inert, which means a graphene coating will not oxidize away. No single material system can provide all of the above attributes that graphene is able to offer."

A practical application of this new discovery is to coat copper surfaces used in dehumidifiers. Because of its exposure to water, copper in dehumidifier systems oxidizes, which in turn decreases its ability to transfer heat and makes the entire device less efficient. Coating the copper with graphene prevents oxidation, the researchers said, and the operation of the device is unaffected because graphene does not change the way water interacts with copper. This same concept may be applied to improve the ability of heat pipes to dissipate heat from computer chips, Koratkar said.

"It's an interesting idea. The graphene doesn't cause any significant change to the wettability of copper, and at the same time it passivates the copper surface and prevents it from oxidizing," he said.

Along with Koratkar and Ajayan, co-authors of the paper are Yunfeng Shi, assistant professor in the Department of Materials Science and Engineering at Rensselaer; Rensselaer mechanical engineering graduate students Javad Rafiee, Abhay Thomas, and Fazel Yavari; Rensselaer physics graduate student Xi Mi; and Rice mechanical and materials engineering graduate student Hemtej Gullapalli.

This research was supported in part by the Advanced Energy Consortium (AEC); the National Science Foundation (NSF); and the Office of Naval Research (ONR) graphene Multidisciplinary University Research Initiative (MURI).

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Journal Reference:

1. Javad Rafiee, Xi Mi, Hemtej Gullapalli, Abhay V. Thomas, Fazel Yavari, Yunfeng Shi, Pulickel M. Ajayan, Nikhil A. Koratkar. Wetting transparency of graphene. Nature Materials, 2012; DOI: 10.1038/NMAT3228

Vaccines to Boost Immunity Where It Counts, Not Just Near Shot Site

ScienceDaily (Jan. 22, 2012) — Researchers at Duke University Medical Center have created synthetic nanoparticles that target lymph nodes and greatly boost vaccine responses, said lead author Ashley St. John, PhD, a researcher at Duke-NUS Graduate Medical School.

The current study used mice to show it is possible to shift the delivery path directly to the lymph nodes.Currently all other adjuvants (substances added to vaccines to help to boost the immune response) are thought to enhance immunity at the skin site where the vaccine is injected rather than going to the lymph nodes, where the most effective immune reactions occur.

The researchers based their strategy on their observation that mast cells, which are cells that are found in the skin that fight infections, also communicate directly to the lymph nodes by releasing nanoparticles called granules.

"Our strategy is unique because we have based our bioengineered particles on those naturally produced by mast cells, which effectively solve the same problem we are trying to solve of combating infection," said St. John, who is in the Duke-NUS Program in Emerging Infectious Diseases.

The synthetic granules consist of a carbohydrate backbone that holds tiny, encapsulated inflammatory mediators such as tumor necrosis factor (TNF). These particles, when injected, mimic the attributes of the granules found in natural cells, and the synthetic particles also target the draining lymph nodes and provide for the timed release of the encapsulated material.

Traditional vaccine adjuvants may help antigens (the small part of a pathogen that is injected during vaccination that the body reacts to) to persist so the body can have an immune reaction and build antibodies so that when a real pathogen, such as the flu virus arrives, it will be conquered. Alternatively, adjuvants may activate cells called dendritic cells, which pick up pathogen parts and must travel from the skin to lymph nodes where immune reactions are initiated.

The Duke team, however, has created a vaccine adjuvant of nanoparticles that are capable of traveling from the point of injection to the lymph nodes where they act on many cell types of the immune system to spur the right reaction for a greatly increased immune response.

The researchers found that they could use this adjuvant in vaccinations of mice with the influenza A virus.

In levels of flu virus exposure that would be lethal in typical mice, the vaccinated mice were able to fight off the disease and had an increased survival rate, thanks to the effective immune response the particles stimulated.

The researchers also showed they could load the same type of particles with a different immune factor, IL-12, that directed a response toward a different set of lymphocytes. This is an important finding since certain types of infections require specialized responses to be overpowered by the body.

St. John said the flexibility of the synthetic particles and their ability to target certain lymph nodes represented a new avenue of personalized medical treatment -- personalized vaccines.

Senior author Soman Abraham, PhD, professor of pathology, immunology and molecular genetics and microbiology at Duke in Durham, NC, and emerging infectious diseases at Duke-NUS, is cautiously optimistic that the mast-cell-inspired synthetic particles could make their way into human use soon.

"It should not be long because all the individual cytokines (immune system factors) and additional materials loaded into these particles are already FDA approved for use in humans," Abraham said. "There is a lot of interest in nanoparticle-based therapy, but we are basing our materials on our observation of mast cells in nature. This is an informed application to deliver the right material to the right place in the body to get the most effective immune reaction."

Other authors include Herman Staats and Cheryl Chan of Duke Pathology who contributed to the vaccination studies, and Kam Leong, who contributed to the design of the synthetic particles, of the Pratt School of Engineering at Duke.

Funding came from the National Institutes of Health.

Researchers ink nanostructures with tiny 'soldering iron'

ScienceDaily (Nov. 7, 2011) — Researchers with the U.S. Department of Energy (DOE)'s Lawrence Berkeley National Laboratory (Berkeley Lab) have shed light on the role of temperature in controlling a fabrication technique for drawing chemical patterns as small as 20 nanometers. This technique could provide an inexpensive, fast route to growing and patterning a wide variety of materials on surfaces to build electrical circuits and chemical sensors, or study how pharmaceuticals bind to proteins and viruses.

One way of directly writing nanoscale structures onto a substrate is to use an atomic force microscope (AFM) tip as a pen to deposit ink molecules through molecular diffusion onto the surface. Unlike conventional nanofabrication techniques that are expensive, require specialized environments and usually work with only a few materials, this technique, called dip-pen nanolithography, can be used in almost any environment to write many different chemical compounds. A cousin of this technique -- called thermal dip-pen nanolithography -- extends this technique to solid materials by turning an AFM tip into a tiny soldering iron.

Dip-pen nanolithography can be used to pattern features as small as 20 nanometers, more than forty thousand times smaller than the width of a human hair. What's more, the writing tip also performs as a surface profiler, allowing a freshly-writ surface to be imaged with nanoscale precision immediately after patterning.

"Tip-based manufacturing holds real promise for precise fabrication of nanoscale devices," says Jim DeYoreo, interim director of Berkeley Lab's Molecular Foundry, a DOE nanoscience research center. "However, a robust technology requires a scientific foundation built on an understanding of material transfer during this process. Our study is the first to provide this fundamental understanding of thermal dip-pen nanolithography."

In this study, DeYoreo and coworkers systematically investigated the effect of temperature on feature size. Using their results, the team developed a new model to deconstruct how ink molecules travel from the writing tip to the substrate, assemble into an ordered layer and grow into a nanoscale feature.

"By carefully considering the role of temperature in thermal dip-pen nanolithography, we may be able to design and fabricate nanoscale patterns of materials ranging from small molecules to polymers with better control over feature sizes and shapes on a variety of substrates," says Sungwook Chung, a staff scientist in Berkeley Lab's Physical Biosciences Division, and Foundry user working with DeYoreo. "This technique helps overcome fundamental length scale limitations without the need for complex growth methods."

DeYoreo and Chung collaborated with a research team from the University of Illinois at Urbana-Champaign that specializes in fabricating specialized tips for AFMs. Here, these collaborators developed a silicon-based AFM tip with a gradient of charge-carrying atoms sprinkled into the silicon such that a higher number reside at the base while fewer sit at the tip. This makes the tip heat up when electricity flows through it, much like the burner on an electric stove.

This 'nanoheater' can then be used to heat up inks applied to the tip, causing them to flow to the surface for fabricating microscale and nanoscale features. The group demonstrated this by drawing dots and lines of the organic molecule mercaptohexadecanoic acid on gold surfaces. The hotter the tip, the larger the feature size the team could draw.

"We are excited about this collaboration with Berkeley Lab, which combines their remarkable nanoscience capabilities with our technology to control temperature and heat flow on the nanometer scale," says co-author William P. King, a University of Illinois professor of mechanical sciences and engineering. "Our ability to control the temperature within a nanometer-scale spot enabled this study of molecular-scale transport. By tuning the hotspot temperature, we can probe how molecules flow to a surface."

"This thermal control over tip-to-surface transfer developed by Professor King's group adds versatility by enabling on-the-fly variations in feature size and patterning of both liquid and solid materials," DeYoreo adds.

Chung is the lead author and DeYoreo the corresponding author of a paper reporting this research in the journal Applied Physics Letters. The paper is titled "Temperature-dependence of ink transport during thermal dip-pen nanolithography." Co-authoring the paper with Chung, DeYoreo and King were Jonathan Felts and Debin Wang.

This work at the Molecular Foundry was supported by DOE's Office of Science and the Defense Advanced Research Projects Agency.

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The perfect clone: Researchers hack RFID smartcards

ScienceDaily (Nov. 3, 2011) — Professional safecrackers use a stethoscope to find the correct combination by listening to the clicks of the lock. Researchers at the Ruhr-University Bochum have now demonstrated how to bypass the security mechanisms of a widely used contactless smartcard in a similar way. Employing so-called "Side-Channel Analysis" the researchers of the Chair for Embedded Security (Prof. Dr.-Ing. Christof Paar) can break the cryptography of millions of cards that are used all around the world.

Mathematically secure

RFID smartcards (Radio Frequency Identification) of the type DESFire MF3ICD40 are widely employed in payment and access control systems. The security of these cards is based on Triple-DES, a cipher that is unbreakable from a purely mathematic point of view. DESFire cards are for instance used by the public transport agencies in Melbourne, San Francisco and Prague. The DESFire MF3ICD40 is manufactured by NXP, the former semiconductor division of Philips Electronics.

Fluctuations of the magnetic field

A person is identified as a passenger, employee or customer when his RFID smartcard is placed in the proximity of a reader. To guarantee the necessary level of security, a secret key is stored on the integrated chip inside the card. But just like for the safe, the security mechanism produces the electronic equivalent of the clicks of a mechanic lock. "We measured the power consumption of the chip during the encryption and decryption with a small probe," says David Oswald. The fluctuations of the electro-magnetic field allow the researchers to conclude to the full 112-bit secret key of the smartcard.

Low cost, big damage

Having extracted the keys, an attacker can create an unlimited number of undetectable clones of a given card. The required time and effort are quite low: "For our measurements, we needed a DESFire MF3ICD40 card, an RFID reader, the probe and an oscilloscope to measure the power consumption," says Oswald. This equipment only costs a few thousand euros. Having obtained knowledge on the characteristic properties of the smartcard, the attack takes three to seven hours. The manufacturer NXP confirmed the security hole in the meanwhile and recommends his customers to upgrade to a newer version of the card.

Insufficient countermeasures

Already back in 2008, researchers around Prof. Dr.-Ing. Christof Paar used Side-Channel Analysis to break supposedly secure systems. Three years ago, garage and car doors "mysteriously" opened for the researchers of the Chair for Embedded Security. The employed KeeLoq RFID system -- which customers and manufacturers trusted blindly before -- turned out to be highly susceptible to Side-Channel Analysis, researchers said.

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Wet and mild: Researchers take the temperature of Mars' past

ScienceDaily (Oct. 13, 2011) — Researchers at the California Institute of Technology (Caltech) have directly determined the surface temperature of early Mars for the first time, providing evidence that's consistent with a warmer and wetter Martian past.

By analyzing carbonate minerals in a four-billion-year-old meteorite that originated near the surface of Mars, the scientists determined that the minerals formed at about 18 degrees Celsius (64 degrees Fahrenheit). "The thing that's really cool is that 18 degrees is not particularly cold nor particularly hot," says Woody Fischer, assistant professor of geobiology and coauthor of the paper, published online in the Proceedings of the National Academy of Sciences (PNAS) on October 3. "It's kind of a remarkable result."

Knowing the temperature of Mars is crucial to understanding the planet's history -- its past climate and whether it once had liquid water. The Mars rovers and orbiting spacecraft have found ancient deltas, rivers, lakebeds, and mineral deposits, suggesting that water did indeed flow. Because Mars now has an average temperature of -63 degrees Celsius, the existence of liquid water in the past means that the climate was much warmer then. But what's been lacking is data that directly points to such a history. "There are all these ideas that have been developed about a warmer, wetter early Mars," Fischer says. "But there's precious little data that actually bears on it." That is, until now.

The finding is just one data point -- but it's the first and only one to date. "It's proof that early in the history of Mars, at least one place on the planet was capable of keeping an Earthlike climate for at least a few hours to a few days," says John Eiler, the Robert P. Sharp Professor of Geology and professor of geochemistry, and a coauthor of the paper. The first author is Itay Halevy, a former postdoctoral scholar who's now at the Weizmann Institute of Science in Israel.

To make their measurement, the researchers analyzed one of the oldest known rocks in the world: ALH84001, a Martian meteorite discovered in 1984 in the Allan Hills of Antarctica. The meteorite likely started out tens of meters below the Martian surface and was blown off when another meteorite struck the area, blasting the piece of Mars toward Earth. The potato-shaped rock made headlines in 1996 when scientists discovered tiny globules in it that looked like fossilized bacteria. But the claim that it was extraterrestrial life didn't hold up upon closer scrutiny. The origin of the globules, which contain carbonate minerals, remained a mystery.

"It's been devilishly difficult to work out the process that generated the carbonate minerals in the first place," Eiler says. But there have been countless hypotheses, he adds, and they all depend on the temperature in which the carbonates formed. Some scientists say the minerals formed when carbonate-rich magma cooled and crystallized. Others have suggested that the carbonates grew from chemical reactions in hydrothermal processes. Another idea is that the carbonates precipitated out of saline solutions. The temperatures required for all these processes range from above 700 degrees Celsius in the first case to below freezing in the last. "All of these ideas have merit," Eiler says.

Finding the temperature through independent means would therefore help narrow down just how the carbonate might have been formed. The researchers turned to clumped-isotope thermometry, a technique developed by Eiler and his colleagues that has been used for a variety of applications, including measuring the body temperatures of dinosaurs and determining Earth's climate history.

In this case, the team measured concentrations of the rare isotopes oxygen-18 and carbon-13 contained in the carbonate samples. Carbonate is made out of carbon and oxygen, and as it forms, the two rare isotopes may bond to each other -- clumping together, as Eiler calls it. The lower the temperature, the more the isotopes tend to clump. As a result, determining the amount of clumping allows for a direct measurement of temperature.

The temperature the researchers measured -- 18 ± 4 degrees Celsius -- rules out many carbonate-formation hypotheses. "A lot of ideas that were out there are gone," Eiler says. For one, the mild temperature means that the carbonate must have formed in liquid water. "You can't grow carbonate minerals at 18 degrees other than from an aqueous solution," he explains. The new data also suggests a scenario in which the minerals formed from water that filled the tiny cracks and pores inside rock just below the surface. As the water evaporated, the rock outgassed carbon dioxide, and the solutes in the water became more concentrated. The minerals then combined with dissolved carbonate ions to produce carbonate minerals, which were left behind as the water continued to evaporate.

Could this wet and warm environment have been a habitat for life? Most likely not, the researchers say. These conditions wouldn't have existed long enough for life to grow or evolve -- it would have taken only hours to days for the water to dry up. Still, these results are proof that an Earthlike environment once existed in at least one particular spot on Mars for a short time, the researchers say. What that implies for the global geology of Mars -- whether this rock is representative of Martian history or is just an isolated artifact -- is an open question.

The research described in the PNAS paper, "Carbonates in the Martian meteorite Allan Hills 84001 formed at 18 ± 4 °C in a near-surface aqueous environment," was supported by a Texaco Postdoctoral Fellowship, NASA, and the National Science Foundation.

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Journal Reference:

I. Halevy, W. W. Fischer, J. M. Eiler. Carbonates in the Martian meteorite Allan Hills 84001 formed at 18   4  C in a near-surface aqueous environment. Proceedings of the National Academy of Sciences, 2011; 108 (41): 16895 DOI: 10.1073/pnas.1109444108

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Wet and mild: Researchers take the temperature of Mars' past

ScienceDaily (Oct. 13, 2011) — Researchers at the California Institute of Technology (Caltech) have directly determined the surface temperature of early Mars for the first time, providing evidence that's consistent with a warmer and wetter Martian past.

By analyzing carbonate minerals in a four-billion-year-old meteorite that originated near the surface of Mars, the scientists determined that the minerals formed at about 18 degrees Celsius (64 degrees Fahrenheit). "The thing that's really cool is that 18 degrees is not particularly cold nor particularly hot," says Woody Fischer, assistant professor of geobiology and coauthor of the paper, published online in the Proceedings of the National Academy of Sciences (PNAS) on October 3. "It's kind of a remarkable result."

Knowing the temperature of Mars is crucial to understanding the planet's history -- its past climate and whether it once had liquid water. The Mars rovers and orbiting spacecraft have found ancient deltas, rivers, lakebeds, and mineral deposits, suggesting that water did indeed flow. Because Mars now has an average temperature of -63 degrees Celsius, the existence of liquid water in the past means that the climate was much warmer then. But what's been lacking is data that directly points to such a history. "There are all these ideas that have been developed about a warmer, wetter early Mars," Fischer says. "But there's precious little data that actually bears on it." That is, until now.

The finding is just one data point -- but it's the first and only one to date. "It's proof that early in the history of Mars, at least one place on the planet was capable of keeping an Earthlike climate for at least a few hours to a few days," says John Eiler, the Robert P. Sharp Professor of Geology and professor of geochemistry, and a coauthor of the paper. The first author is Itay Halevy, a former postdoctoral scholar who's now at the Weizmann Institute of Science in Israel.

To make their measurement, the researchers analyzed one of the oldest known rocks in the world: ALH84001, a Martian meteorite discovered in 1984 in the Allan Hills of Antarctica. The meteorite likely started out tens of meters below the Martian surface and was blown off when another meteorite struck the area, blasting the piece of Mars toward Earth. The potato-shaped rock made headlines in 1996 when scientists discovered tiny globules in it that looked like fossilized bacteria. But the claim that it was extraterrestrial life didn't hold up upon closer scrutiny. The origin of the globules, which contain carbonate minerals, remained a mystery.

"It's been devilishly difficult to work out the process that generated the carbonate minerals in the first place," Eiler says. But there have been countless hypotheses, he adds, and they all depend on the temperature in which the carbonates formed. Some scientists say the minerals formed when carbonate-rich magma cooled and crystallized. Others have suggested that the carbonates grew from chemical reactions in hydrothermal processes. Another idea is that the carbonates precipitated out of saline solutions. The temperatures required for all these processes range from above 700 degrees Celsius in the first case to below freezing in the last. "All of these ideas have merit," Eiler says.

Finding the temperature through independent means would therefore help narrow down just how the carbonate might have been formed. The researchers turned to clumped-isotope thermometry, a technique developed by Eiler and his colleagues that has been used for a variety of applications, including measuring the body temperatures of dinosaurs and determining Earth's climate history.

In this case, the team measured concentrations of the rare isotopes oxygen-18 and carbon-13 contained in the carbonate samples. Carbonate is made out of carbon and oxygen, and as it forms, the two rare isotopes may bond to each other -- clumping together, as Eiler calls it. The lower the temperature, the more the isotopes tend to clump. As a result, determining the amount of clumping allows for a direct measurement of temperature.

The temperature the researchers measured -- 18 ± 4 degrees Celsius -- rules out many carbonate-formation hypotheses. "A lot of ideas that were out there are gone," Eiler says. For one, the mild temperature means that the carbonate must have formed in liquid water. "You can't grow carbonate minerals at 18 degrees other than from an aqueous solution," he explains. The new data also suggests a scenario in which the minerals formed from water that filled the tiny cracks and pores inside rock just below the surface. As the water evaporated, the rock outgassed carbon dioxide, and the solutes in the water became more concentrated. The minerals then combined with dissolved carbonate ions to produce carbonate minerals, which were left behind as the water continued to evaporate.

Could this wet and warm environment have been a habitat for life? Most likely not, the researchers say. These conditions wouldn't have existed long enough for life to grow or evolve -- it would have taken only hours to days for the water to dry up. Still, these results are proof that an Earthlike environment once existed in at least one particular spot on Mars for a short time, the researchers say. What that implies for the global geology of Mars -- whether this rock is representative of Martian history or is just an isolated artifact -- is an open question.

The research described in the PNAS paper, "Carbonates in the Martian meteorite Allan Hills 84001 formed at 18 ± 4 °C in a near-surface aqueous environment," was supported by a Texaco Postdoctoral Fellowship, NASA, and the National Science Foundation.

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by California Institute of Technology.

Journal Reference:

I. Halevy, W. W. Fischer, J. M. Eiler. Carbonates in the Martian meteorite Allan Hills 84001 formed at 18   4  C in a near-surface aqueous environment. Proceedings of the National Academy of Sciences, 2011; 108 (41): 16895 DOI: 10.1073/pnas.1109444108

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Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

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Internet security: Researchers break W3C standard

ScienceDaily (Oct. 19, 2011) — Standards are supposed to guarantee security, especially in the WWW. The World Wide Web Consortium (W3C) is the main force behind standards like HTML, XML, and XML Encryption. But implementing a W3C standard does not mean that a system is secure. Researchers from the chair of network and data security have found a serious attack against XML Encryption. "Everything is insecure," is the uncomfortable message from Bochum.

Standard for large integration projects

XML stands for "eXtensible Markup Language," and is the industry standard for platform-independent data exchange. Companies like IBM, Microsoft and Redhat Linux use XML standards for integrating Webservice projects for large customers. XML Encryption was designed to protect the confidentiality of the exchanged data. Reason enough to have a closer look at its security.

Weak chaining of ciphertext blocks

Juraj Somorovsky and Tibor Jager exploited a weakness in the CBC mode for the chaining of different ciphertext blocks. "We were able to decrypt data by sending modified ciphertexts to the server, by gathering information from the received error messages." The attack was tested against a popular open source implementation of XML Encrytion, and against the implementations of companies that responded to the responsible disclosure -- in all cases the result was the same: the attack works, XML Encryption is not secure.

Details of the attack are presented at this year's ACM Conference on Computer and Communications Security (http://www.sigsac.org/ccs/CCS2011/techprogram.shtml).

No simple solution available

„There is no simple patch for this problem," states Somorovsky. "We therefore propose to change the standard as soon as possible." The researchers informed all possibly affected companies through the mailing list of W3C, following a clear responsible disclosure process. With some companies there were intensive discussions on workarounds.

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View the original article here

Progress in quantum computing: Researchers control rate of photon emission from luminescent imperfections in diamond

ScienceDaily (Oct. 12, 2011) — Engineers and physicists at Harvard have managed to capture light in tiny diamond pillars embedded in silver, releasing a stream of single photons at a controllable rate.

The advance represents a milestone on the road to quantum networks in which information can be encoded in spins of electrons and carried through a network via light, one photon at a time.

The finding was published in Nature Photonics, appearing online Oct. 9.

"We can make the emission of photons faster, which will allow us to do more processing per second -- for example, more computations -- in the future quantum network," explains principal investigator Marko Loncar, Associate Professor of Electrical Engineering at the Harvard School of Engineering and Applied Sciences (SEAS).

The device Loncar's research team has built consists of parallel rows of tiny, nanofabricated diamond posts, embedded in a layer of silver, that can each act as a single photon source.

By removing the silver wrapping from their nanostructures, the team was also able to achieve a slower release of photons, which is of interest for probing the dynamics of the quantum system.

The breakthrough takes advantage of imperfections in the diamond's crystal lattice, where carbon atoms are replaced by other elements. To the naked eye, these imperfections can appear as discolorations in the diamond, turning it yellow in the case of nitrogen. Occasionally, there is also a vacancy (missing carbon atom) next to the nitrogen atom.

Each nitrogen-vacancy imperfection can serve as a nearly perfect quantum emitter, capable of emitting red photons one by one, even at room temperature. The technology is a promising candidate for realization of scalable, on-chip quantum networks.

"The color centers in diamond are very interesting as qubits for quantum information processing, where they can be used as memory to store information," says Loncar. "More importantly, they can be interrogated -- they can be written into and read out -- with light."

Loncar's team fabricates diamond posts that contain negatively charged nitrogen vacancy centers, which can absorb light and hold its energy for a given amount of time, finally releasing it in the form of photons.

"The rate at which photons are emitted can be controlled by carefully nano-engineering the center's surrounding," says co-author Irfan Bulu, a research associate in the Loncar group. Attaining fine control of that release, however, has been difficult.

"One of the main challenges has been the efficiency with which you can write information into the spin of these color centers, as well as the efficiency with which you can collect photons emitted from the color centers," explains co-author Jennifer Choy, a graduate student in Loncar's lab at SEAS. "The other challenge has been the rate -- how quickly you can perform these processes."

Previous work from Loncar's group solved the collection efficiency problem by using diamond nanowires to channel and direct the flow of photons. The new research manipulates the radius of diamond pillars and adds the silver coating. The diamond-silver construction acts as an optical nanoresonator, creating a strong electromagnetic field around the emitter and offering a new level of control over the rate of emission.

Moreover, the device functions at room temperature -- an essential requirement for practical computing applications -- and the nanostructured chips are fully scalable.

"We've designed everything in parallel in a massive system, which allows us to make thousands or millions of devices with more or less the same properties, and we use conventional microfabrication and nanofabrication techniques, unlike what has been done in this field before," says Birgit Hausmann, a graduate student in Loncar's lab at SEAS and one of the co-authors.

In addition to Loncar, Choy, Hausmann, and Bulu, co-authors included Tom Babinec, a graduate student at SEAS; Mughees Khan, a staff scientist at the Wyss Institute for Biologically Inspired Engineering at Harvard; Patrick Maletinsky, a fellow of the Department of Physics at Harvard; and Amir Jacoby, Professor of Physics in the Harvard Faculty of Arts and Sciences.

The work was supported by grants and fellowships from the U.S. Department of Defense, the Defense Advanced Research Projects Agency (DARPA) QuEST program, the National Science Foundation (NSF), the King Abdullah University of Science and Technology (KAUST), the Sloan Foundation, and the NSF-supported Nanoscale Science and Engineering Center (NSEC) at Harvard. Fabrication took place at the NSF-supported Center for Nanoscale Systems (CNS) at Harvard.

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Harvard University.

Journal Reference:

Jennifer T. Choy, Birgit J. M. Hausmann, Thomas M. Babinec, Irfan Bulu, Mughees Khan, Patrick Maletinsky, Amir Yacoby, Marko Loncar. Enhanced single-photon emission from a diamond–silver aperture. Nature Photonics, 2011; DOI: 10.1038/nphoton.2011.249

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Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Ancient supernovas discovered: 10-billion-year-old exploding stars were a source of Earth's iron, researchers say

ScienceDaily (Oct. 7, 2011) — Supernovas -- stars in the process of exploding -- open a window onto the history of the elements of Earth's periodic table as well as the history of the universe. All of those heavier than oxygen were formed in nuclear reactions that occurred during these explosions.

The most ancient explosions, far enough away that their light is reaching us only now, can be difficult to spot. A project spearheaded by Tel Aviv University researchers has uncovered a record-breaking number of supernovas in the Subaru Deep Field, a patch of sky the size of a full moon. Out of the 150 supernovas observed, 12 were among the most distant and ancient ever seen.

The discovery sharpens our understanding of the nature of supernovas and their role in element formation, say study leaders Prof. Dan Maoz, Dr. Dovi Poznanski and Or Graur of TAU's Department of Astrophysics at the Raymond and Beverly Sackler School of Physics and Astronomy. These "thermonuclear" supernovas in particular are a major source of iron in the universe.

The research, which appears in the Monthly Notices of the Royal Astronomical Society this month, was done in collaboration with teams from a number of Japanese and American institutions, including the University of Tokyo, Kyoto University, the University of California Berkeley, and Lawrence Berkeley National Laboratory.

A key element of the universe

Supernovas are nature's "element factories." During these explosions, elements are both formed and flung into interstellar space, where they serve as raw materials for new generations of stars and planets. Closer to home, says Prof. Maoz, "these elements are the atoms that form the ground we stand on, our bodies, and the iron in the blood that flows through our veins." By tracking the frequency and types of supernova explosions back through cosmic time, astronomers can reconstruct the universe's history of element creation.

In order to observe the 150,000 galaxies of the Subaru Deep Field, the team used the Japanese Subaru Telescope in Hawaii, on the 14,000-foot summit of the extinct Mauna Kea volcano. The telescope's light-collecting power, sharp images, and wide field of view allowed the researchers to overcome the challenge of viewing such distant supernovas.

By "staring" with the telescope at the Subaru Deep Field, the faint light of the most distant galaxies and supernovas accumulated over several nights at a time, forming a long and deep exposure of the field. Over the course of observations, the team "caught" the supernovas in the act of exploding, identifying 150 supernovas in all.

Sourcing man's life-blood

According to the team's analysis, thermonuclear type supernovas, also called Type-la, were exploding about five times more frequently 10 billion years ago than they are today. These supernovas are a major source of iron in the universe, the main component of Earth's core and an essential ingredient of the blood in our bodies.

Scientists have long been aware of the "universal expansion," the fact that galaxies are receding from one another. Observations using Type-Ia supernovas as beacons have shown that the expansion is accelerating, apparently under the influence of a mysterious "dark energy" -- the 2011 Nobel Prize in Physics will be awarded to three astronomers for this work. However, the nature of the supernovas themselves is poorly understood. This study improves our understanding by revealing the range of the ages of the stars that explode as Type-Ia supernovas. Eventually, this will enhance their usefulness for studying dark energy and the universal expansion, the researchers explain.

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by American Friends of Tel Aviv University.

Journal Reference:

K. Maguire, M. Sullivan, R. C. Thomas, P. Nugent, D. A. Howell, A. Gal-Yam, I. Arcavi, S. Ben-Ami, S. Blake, J. Botyanszki, C. Buton, J. Cooke, R. S. Ellis, I. M. Hook, M. M. Kasliwal, Y.-C. Pan, R. Pereira, P. Podsiadlowski, A. Sternberg, N. Suzuki, D. Xu, O. Yaron, J. S. Bloom, S. B. Cenko, S. R. Kulkarni, N. Law, E. O. Ofek, D. Poznanski, R. M. Quimby. PTF10ops - a subluminous, normal-width light curve Type Ia supernova in the middle of nowhere. Monthly Notices of the Royal Astronomical Society, 2011; DOI: 10.1111/j.1365-2966.2011.19526.x

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Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Internet security: Researchers break W3C standard

ScienceDaily (Oct. 19, 2011) — Standards are supposed to guarantee security, especially in the WWW. The World Wide Web Consortium (W3C) is the main force behind standards like HTML, XML, and XML Encryption. But implementing a W3C standard does not mean that a system is secure. Researchers from the chair of network and data security have found a serious attack against XML Encryption. "Everything is insecure," is the uncomfortable message from Bochum.

Standard for large integration projects

XML stands for "eXtensible Markup Language," and is the industry standard for platform-independent data exchange. Companies like IBM, Microsoft and Redhat Linux use XML standards for integrating Webservice projects for large customers. XML Encryption was designed to protect the confidentiality of the exchanged data. Reason enough to have a closer look at its security.

Weak chaining of ciphertext blocks

Juraj Somorovsky and Tibor Jager exploited a weakness in the CBC mode for the chaining of different ciphertext blocks. "We were able to decrypt data by sending modified ciphertexts to the server, by gathering information from the received error messages." The attack was tested against a popular open source implementation of XML Encrytion, and against the implementations of companies that responded to the responsible disclosure -- in all cases the result was the same: the attack works, XML Encryption is not secure.

Details of the attack are presented at this year's ACM Conference on Computer and Communications Security (http://www.sigsac.org/ccs/CCS2011/techprogram.shtml).

No simple solution available

„There is no simple patch for this problem," states Somorovsky. "We therefore propose to change the standard as soon as possible." The researchers informed all possibly affected companies through the mailing list of W3C, following a clear responsible disclosure process. With some companies there were intensive discussions on workarounds.

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Note: If no author is given, the source is cited instead.

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Researchers discover material with graphene-like properties

ScienceDaily (Oct. 14, 2011) — After the Nobel Prize in Physics was awarded to two scientists in 2010 who had studied the material graphene, this substance has received a lot of attention. Together with colleagues from Korea, Dr. Frederik Wolff-Fabris from the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) has now developed and analyzed a material which possesses physical properties similar to graphene. Its structure also resembles iron pnictides, i.e. high temperature superconductors, and it definitely has a promising future: Due to the position of the individual components in the Periodic Table of Elements, some of the atoms can simply be replaced by foreign atoms.

This creates new materials which can be superconductive, magnetic, or behave like topological insulators.

Earlier this year, Dr. Jun Sung Kim came from South Korea to use HZDR's Dresden High Magnetic Field Laboratory to analyze a number of material samples in high magnetic fields. For the first time ever, he and his colleague from Dresden, Dr. Frederik Wolff-Fabris, studied the metal SrMnBi2 and observed something amazing: The material consisting of the three elements strontium, manganese, and bismuth behaves physically similar to the "magical material" graphene.

Due to its composition and the position of its elements in the Periodic Table, SrMnBi2 permits simple and uncomplicated doping with foreign atoms. Inserting small amounts of foreign atoms alters the physical properties of a material. This might result in the creation of new magnets or superconductors.

SrMnBi2 is currently also in the focus of other research groups; but only the use of ultra-high magnetic fields, such as those generated in the Dresden High Magnetic Field Laboratory, permitted these precise results and, thus, a publication in the scientific journal Physical Review Letters. Later this year, Dr. Jun Sung Kim will return to Dresden to conduct additional experiments on SrMnBi2 with Dr. Wolff-Fabris.

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Helmholtz Association of German Research Centres.

Journal Reference:

Joonbum Park, G. Lee, F. Wolff-Fabris, Y. Koh, M. Eom, Y. Kim, M. Farhan, Y. Jo, C. Kim, J. Shim, J. Kim. Anisotropic Dirac Fermions in a Bi Square Net of SrMnBi2. Physical Review Letters, 2011; 107 (12) DOI: 10.1103/PhysRevLett.107.126402

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View the original article here

Progress in quantum computing: Researchers control rate of photon emission from luminescent imperfections in diamond

ScienceDaily (Oct. 12, 2011) — Engineers and physicists at Harvard have managed to capture light in tiny diamond pillars embedded in silver, releasing a stream of single photons at a controllable rate.

The advance represents a milestone on the road to quantum networks in which information can be encoded in spins of electrons and carried through a network via light, one photon at a time.

The finding was published in Nature Photonics, appearing online Oct. 9.

"We can make the emission of photons faster, which will allow us to do more processing per second -- for example, more computations -- in the future quantum network," explains principal investigator Marko Loncar, Associate Professor of Electrical Engineering at the Harvard School of Engineering and Applied Sciences (SEAS).

The device Loncar's research team has built consists of parallel rows of tiny, nanofabricated diamond posts, embedded in a layer of silver, that can each act as a single photon source.

By removing the silver wrapping from their nanostructures, the team was also able to achieve a slower release of photons, which is of interest for probing the dynamics of the quantum system.

The breakthrough takes advantage of imperfections in the diamond's crystal lattice, where carbon atoms are replaced by other elements. To the naked eye, these imperfections can appear as discolorations in the diamond, turning it yellow in the case of nitrogen. Occasionally, there is also a vacancy (missing carbon atom) next to the nitrogen atom.

Each nitrogen-vacancy imperfection can serve as a nearly perfect quantum emitter, capable of emitting red photons one by one, even at room temperature. The technology is a promising candidate for realization of scalable, on-chip quantum networks.

"The color centers in diamond are very interesting as qubits for quantum information processing, where they can be used as memory to store information," says Loncar. "More importantly, they can be interrogated -- they can be written into and read out -- with light."

Loncar's team fabricates diamond posts that contain negatively charged nitrogen vacancy centers, which can absorb light and hold its energy for a given amount of time, finally releasing it in the form of photons.

"The rate at which photons are emitted can be controlled by carefully nano-engineering the center's surrounding," says co-author Irfan Bulu, a research associate in the Loncar group. Attaining fine control of that release, however, has been difficult.

"One of the main challenges has been the efficiency with which you can write information into the spin of these color centers, as well as the efficiency with which you can collect photons emitted from the color centers," explains co-author Jennifer Choy, a graduate student in Loncar's lab at SEAS. "The other challenge has been the rate -- how quickly you can perform these processes."

Previous work from Loncar's group solved the collection efficiency problem by using diamond nanowires to channel and direct the flow of photons. The new research manipulates the radius of diamond pillars and adds the silver coating. The diamond-silver construction acts as an optical nanoresonator, creating a strong electromagnetic field around the emitter and offering a new level of control over the rate of emission.

Moreover, the device functions at room temperature -- an essential requirement for practical computing applications -- and the nanostructured chips are fully scalable.

"We've designed everything in parallel in a massive system, which allows us to make thousands or millions of devices with more or less the same properties, and we use conventional microfabrication and nanofabrication techniques, unlike what has been done in this field before," says Birgit Hausmann, a graduate student in Loncar's lab at SEAS and one of the co-authors.

In addition to Loncar, Choy, Hausmann, and Bulu, co-authors included Tom Babinec, a graduate student at SEAS; Mughees Khan, a staff scientist at the Wyss Institute for Biologically Inspired Engineering at Harvard; Patrick Maletinsky, a fellow of the Department of Physics at Harvard; and Amir Jacoby, Professor of Physics in the Harvard Faculty of Arts and Sciences.

The work was supported by grants and fellowships from the U.S. Department of Defense, the Defense Advanced Research Projects Agency (DARPA) QuEST program, the National Science Foundation (NSF), the King Abdullah University of Science and Technology (KAUST), the Sloan Foundation, and the NSF-supported Nanoscale Science and Engineering Center (NSEC) at Harvard. Fabrication took place at the NSF-supported Center for Nanoscale Systems (CNS) at Harvard.

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Harvard University.

Journal Reference:

Jennifer T. Choy, Birgit J. M. Hausmann, Thomas M. Babinec, Irfan Bulu, Mughees Khan, Patrick Maletinsky, Amir Yacoby, Marko Loncar. Enhanced single-photon emission from a diamond–silver aperture. Nature Photonics, 2011; DOI: 10.1038/nphoton.2011.249

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Ceramics researchers shed light on metal embrittlement

ScienceDaily (Sep. 26, 2011) — Why does a solid metal that is engineered for ductility become brittle, often suddenly and with dramatic consequences, in the presence of certain liquid metal impurities? The phenomenon, known as liquid metal embrittlement, or LME, has baffled metallurgists for a century.

Now, a team of ceramics researchers has shed light on LME by obtaining atomic-scale images of unprecedented resolution of the grain boundaries, or internal interfaces, where LME occurs.

In doing so, says Martin Harmer, professor of materials science and engineering at Lehigh University, the researchers have achieved the first direct observation in a metal system of a bilayer grain boundary phase transition.

The study suggests that interior interfaces can undergo transitions similar to the solid-to-liquid and liquid-to-gas phase transitions that occur in larger, "bulk" materials.

It also paves the way for scientists to prevent LME by strengthening the chemical bonds of the materials present at grain boundaries.

"This is a very exciting discovery," says Harmer, who directs Lehigh's Center for Advanced Materials and Nanotechnology. "It gives us a much clearer understanding of the atomic mechanism of LME and it promises to improve our ability to control and fine-tune the properties of metals and other materials during fabrication."

Harmer and his colleagues reported their findings Sept. 23 in Science magazine.

Their 18-month study was funded by the U.S. Navy. The group will continue its work, with a focus on rectifying LME-related problems in metals, with help from a five-year, $7.5 million grant through the Department of Defense's Multidisciplinary University Research Initiative program. That project involves researchers from Lehigh, Carnegie-Mellon, Clemson, Illinois and Kutztown universities.

The common ground of ceramics and metals

Many of the consequences of LME affect everyday life, says Harmer.

A steel highway signpost can crack because LME weakened it by the molten zinc alloy applied to the steel during fabrication. Mercury and gallium, both liquid at room temperature, cause normally corrosion-resistant aluminum to become brittle. And concerns over LME make nuclear power plant operators hesitate to switch from water to liquid metal coolant, whose higher boiling point and ability to absorb radiation give it superior and more reliable cooling properties.

Harmer, who has spent 30 years studying ceramics, became interested in LME after he and his students in 2006 identified six grain-boundary "complexions," each with a distinct rate of grain growth, in the ceramic alumina.

He described complexions, and their influence on material properties, in an article titled "The Phase Behavior of Interfaces," which was published April 8 in the Perspective section of Science.

The discovery of grain-boundary complexions in ceramics, Harmer says, prompted him to seek insight into the embrittlement of metals.

"Our ideas on complexions can be tested more rigorously with metals than with ceramics because metals are simpler systems than ceramics," he says.

Harmer's group examined a nickel-bismuth alloy using Lehigh's JEOL 2200 FS aberration-corrected scanning transmission electron microscope (STEM), which has unparalleled imaging capabilities. The group employed a technique called high-angle annular dark-field imaging (HAADF), which focuses a beam of electrons only 1 angstrom (0.1 nm) wide on a sample.

Previous studies had revealed the existence of four interfacial phases at grain boundaries (GB) in metals -- a clean, or intrinsic GB, a monolayer/submonolayer, a nanometer-thick intergranular film, and a complete GB wetting film.

The aberration-corrected STEM revealed two additional GB phases -- a bilayer and a trilayer.

"A bilayer had been seen before in a ceramic system," says Harmer, "but no one had seen such examples of the bi- and trilayers in metals."

The aberration-corrected STEM pinpointed the bilayer of bismuth atoms at the grain boundary as the source of a weak atomic-scale bond in the nickel-bismuth alloy.

"The bonding is so weak that the grains come apart almost like the opening of a slippery zipper," says Harmer.

"There is a very strong bond between bismuth and nickel, so it had never been clear why the alloy is prone to embrittlement. But the bonds between bismuth atoms are weak. We are the first group to see the formation of a bismuth bilayer that weakens this material."

A comprehensive study

Harmer described his group's study as "exhaustive." The researchers examined 12 independent interfaces and took care to exclude artificial "imaging artifacts" introduced by experimental error or by technology.

They also attempted to ensure that their images represented the 3-D nature of nickel-bismuth.

"When you project a 3-D image onto a 2-D film, distortions can result. To avoid this, we imaged at different depths on the sample. By looking sequentially at these images and their structural thickness, we were able to rule out artifacts that give the illusion of a bilayer."

In contrast with previous studies, most of which looked at synthetic bi-crystals, Harmer's group examined polycrystalline nickel which resembles industrial materials.

"Real grain boundaries are typically less symmetrical and have higher energy than synthetic bi-crystals," says Harmer, "and they show other differences as well."

The group plans next to attempt to experiment with the chemistry of nickel-bismuth GBs to produce a more ductile behavior.

"Perhaps combining the bismuth with other elements that bond at the interface will prove effective," says Harmer.

A new aberration-corrected microscope that Lehigh is acquiring in early 2012 -- the JEOL ARM2200F STEM -- will improve the group's ability to do atomic-scale chemical analysis of grain boundaries, says Harmer.

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Lehigh University, via EurekAlert!, a service of AAAS.

Journal References:

J. Luo, H. Cheng, K. M. Asl, C. J. Kiely, M. P. Harmer. The Role of a Bilayer Interfacial Phase on Liquid Metal Embrittlement. Science, 2011; 333 (6050): 1730 DOI: 10.1126/science.1208774M. P. Harmer. The Phase Behavior of Interfaces. Science, 2011; 332 (6026): 182 DOI: 10.1126/science.1204204

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