FEB 17,2009
Tomorrow's fuel-cell vehicles may be powered by enzymes that consume cellulose from woodchips or grass and exhale hydrogen.

Researchers at Virginia Tech, Oak Ridge National Laboratory (ORNL), and the University of Georgia have produced hydrogen gas pure enough to power a fuel cell by mixing 14 enzymes, one coenzyme, cellulosic materials from nonfood sources, and water heated to about 90 degrees (32 degrees Celsius).

The group announced three advances from their "one pot" process: 1) a novel combination of enzymes, 2) an increased hydrogen generation rate -- to as fast as natural hydrogen fermentation, and 3) a chemical energy output greater than the chemical energy stored in sugars – the highest hydrogen yield reported from cellulosic materials. "In addition to converting the chemical energy from the sugar, the process also converts the low-temperature thermal energy into high-quality hydrogen energy – like Prometheus stealing fire," said Percival Zhang, assistant professor of biological systems engineering in the College of Agriculture and Life Sciences at Virginia Tech.

"It is exciting because using cellulose instead of starch expands the renewable resource for producing hydrogen to include biomass," said Jonathan Mielenz, leader of the Bioconversion Science and Technology Group at ORNL.

The researchers used cellulosic materials isolated from wood chips, but crop waste or switchgrass could also be used. "If a small fraction – 2 or 3 percent – of yearly biomass production were used for sugar-to-hydrogen fuel cells for transportation, we could reach transportation fuel independence," Zhang said. (He added that the 3 percent figure is for global transportation needs. The U.S. would actually need to convert about 10 percent of biomass – which would be 1.3 billion tons of usable biomass).

The research is supported by the Air Force Office of Scientific Research; Zhang's DuPont Young Professor Award, and the U.S. Department of Energy.

Courtesy: www.sciencedaily.com

To understand friction on a very small scale, a team of University of Wisconsin-Madison engineers had to think big.

Friction is a force that affects any application where moving parts come into contact; the more surface contact there is, the stronger the force. At the nanoscale — mere billionths of a meter — friction can wreak havoc on tiny devices made from only a small number of atoms or molecules. With their high surface-to-volume ratio, nanomaterials are especially susceptible to the forces of friction.

But researchers have trouble describing friction at such small scales because existing theories are not consistent with how nanomaterials actually behave. Through computer simulations, the group demonstrated that friction at the atomic level behaves similarly to friction generated between large objects. Five hundred years after Leonardo da Vinci discovered the basic friction laws for large objects, the UW-Madison team has shown that similar laws apply at the nanoscale.

The team, which was led by Izabela Szlufarska, an assistant professor of materials science and engineering, and included materials science and engineering graduate student Yifei Mo and mechanical engineering assistant professor Kevin Turner, published its findings in the Feb. 26 issue of the journal Nature.

Current nanoscale friction theories are based on the idea that nanoscale surfaces are smooth, but, in reality, the surfaces resemble a mountain range, where each peak corresponds to an atom or a molecule.

The UW-Madison team performed computer simulations that looked at nanoscale materials as a collection of atoms, monitoring their positions and interactions throughout the entire sliding process. "For the first time, we modeled friction at length scales very similar to experiments, while maintaining atomic resolution and realistic interactions between atoms," say Szlufarska.

The team discovered simple laws of nanoscale friction. They found that friction is proportional to the number of atoms that interact between two nanoscale surfaces. The researchers' simulations showed that, at the nanoscale, materials in contact behave more like large rough objects rubbing against each other, rather than as two perfectly smooth surfaces, as was previously imagined. "When you look at it closely, the surface is made of atoms, so the contact is actually rough," says Szlufarska.

The team's simulation data correlates very well with recorded experimental data — something that previous models have failed to accomplish. Szlufarska hopes to use the simulations as a tool to understand what mechanisms contribute to friction on both the nano- and macroscale.

"Nobody is able to predict friction or design materials with desired friction properties — we measure a lot of friction coefficients for different materials, but it's not really clear how to relate them to the properties of the material," she explains. "The origin of friction is really an open and growing research field."

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Need to store electricity more efficiently? Put it behind bars.

That's essentially the finding of a team of Rice University researchers who have created hybrid carbon nanotube metal oxide arrays as electrode material that may improve the performance of lithium-ion batteries.

With battery technology high on the list of priorities in a world demanding electric cars and gadgets that last longer between charges, such innovations are key to the future. Electrochemical capacitors and fuel cells would also benefit, the researchers said.

The team from Pulickel Ajayan's research group published a paper this week describing the proof-of-concept research in which nanotubes are grown to look – and act – like the coaxial conducting lines used in cables. The coax tubes consist of a manganese oxide shell and a highly conductive nanotube core.

"It's a nice bit of nanoscale engineering," said Ajayan, Rice's Benjamin M. and Mary Greenwood Anderson Professor in Mechanical Engineering and Materials Science.

"We've put in two materials – the nanotube, which is highly electrically conducting and can also absorb lithium, and the manganese oxide, which has very high capacity but poor electrical conductivity," said Arava Leela Mohana Reddy, a Rice postdoc researcher. "But when you combine them, you get something interesting."

That would be the ability to hold a lot of juice and transmit it efficiently. The researchers expect the number of charge/discharge cycles such batteries can handle will be greatly enhanced, even with a larger capacity.

"Although the combination of these materials has been studied as a composite electrode by several research groups, it's the coaxial cable design of these materials that offers improved performance as electrodes for lithium batteries," said Ajayan.

"At this point, we're trying to engineer and modify the structures to get the best performance," said Manikoth Shaijumon, also a Rice postdoc. The microscopic nanotubes, only a few nanometers across, can be bundled into any number of configurations. Future batteries may be thin and flexible. "And the whole idea can be transferred to a large scale as well. It is very manufacturable," Shaijumon said.

The hybrid nanocables grown in a Rice-developed process could also eliminate the need for binders, materials used in current batteries that hold the elements together but hinder their conductivity.

The paper was written by Reddy, Shaijumon, doctoral student Sanketh Gowda and Ajayan. It appears in the online version of the American Chemical Society's Nano Letters.

The project is supported by funding from the Hartley Family Foundation.

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Journal reference:

1. Reddy et al. Coaxial MnO2/ Carbon Nanotube Array Electrodes for High-Performance Lithium Batteries. Nano Letters, 2009; 090202085144070 DOI: 10.1021/nl803081j

Scientists in Arizona and New Jersey are reporting that aerogels, a super-lightweight solid sometimes called “frozen smoke,” may serve as the ultimate sponge for capturing oil from wastewater and effectively soaking up environmental oil spills.

In the new study, Robert Pfeffer and colleagues point out that the environmental challenges of oil contamination go beyond widely publicized maritime oil spills like the Exxon Valdez incident.

Experts estimate that each year people dump more than 200 million gallons of used oil into sewers, streams, and backyards, resulting in polluted wastewater that is difficult to treat. Although there are many different sorbent materials for removing used oil, such as activated carbon, they are often costly and inefficient. Hydrophobic silica aerogels are highly porous and absorbent material, and seemed like an excellent oil sponge.

The scientists packed a batch of tiny aerogel beads into a vertical column and exposed them to flowing water containing soybean oil to simulate the filtration process at a wastewater treatment plant. They showed that the aerogel beads absorbed up to 7 times their weight and removed oil from the wastewater at high efficiency, better than many conventional sorbent materials.

FEB 16,2009
MIT researchers who study the structure of protein-based materials with the aim of learning the key to their lightweight and robust strength have discovered that the particular arrangement of proteins that produces the sturdiest product is not the arrangement with the most built-in redundancy or the most complicated pattern.

Instead, the optimal arrangement of proteins in the rope-like structures they studied is a repeated pattern of two stacks of four bundled alpha-helical proteins.

This composition of two repeated hierarchies (stacks and bundles) provides great strength—the ability to withstand mechanical pressure without giving way—and great robustness—the ability to perform mechanically, even if flawed. Because the alpha-helical protein serves as the building block of many common materials, understanding the properties of those materials has been the subject of intense scientific inquiry since the protein's discovery in the 1940s.

In a paper published in the Jan. 27 online issue of Nanotechnology, Markus Buehler and Theodor Ackbarow describe a model of the protein’s performance, based on molecular dynamics simulations. With their model they tested the strength and robustness of four different combinations of eight alpha-helical proteins: a single stack of eight proteins, two stacks of four bundled proteins, four stacks of two bundled proteins, and double stacks of two bundled proteins. Their molecular models replicate realistic molecular behavior, including hydrogen bond formation in the coiled spring-like alpha-helical proteins.

“The traditional way of designing materials is to consider properties at the macro level, but a more efficient way of materials’ design is to play with the structural makeup at the nanoscale,” said Buehler, the Esther and Harold E. Assistant Professor in the Department of Civil and Environmental Engineering. “This provides a new paradigm in engineering that enables us to design a new class of materials.”

More and more frequently, natural protein materials are being used as inspiration for the design of synthetic materials that are based on nanowires and carbon nanotubes, which can be made to be much stronger than biological materials. Buehler and Ackbarow's work demonstrates that by rearranging the same number of nanoscale elements into hierarchies, the performance of a material can be radically changed. This could eliminate the need to invent new materials for different applications.

In a follow-up study, Buehler and CEE graduate students Zhao Qin and Steve Cranford ran similar tests using more than 16,000 elements instead of eight. They found that 98 percent of the randomly arranged rope-like structures did not meet the optimal performance level of the self-assembled natural molecules, which made up the other 2 percent of the structures. The most successful of those again utilized the bundles of four alpha-helical proteins.

That analysis shows that random arrangements of elements typically lead to inferior performance, and may explain why many engineered materials are not yet capable of combining disparate properties such as robustness and strength.

“Only a few specific nanostructured arrangements provide the basis for optimal material performance, and this must be incorporated in the material design process,” said Buehler.

This work is funded by the Army Research Office, a National Science Foundation CAREER Award, and the Air Force Office of Scientific Research. Ackbarow, a graduate student at the Max Planck Institute of Colloids and Interfaces in Potsdam, Germany, was supported in this work by the German National Academic Foundation, the Hamburg Foundation for research studies abroad and the Dr. Juergen Ulderup Foundation.

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FEB 4,2009
UV light-enhanced tooth bleaching is not only a con, but is dangerous to your eyes and skin, says a Royal Society of Chemistry journal.

The light treatment gives absolutely no benefit over bleaching without UV, and damages skin and eyes up to four times as much as sunbathing, reports a study in Photochemical & Photobiological Sciences.

Those looking to match Tom Cruise’s glittering pearly-whites would be better off ignoring claims of better bleaching with UV light treatment.

The treatment is at least as damaging to skin and eyes as sunbathing in Hyde Park for a midsummer’s afternoon – one lamp actually gave four times that level of radiation exposure.

And as with sunbathing, fair-skinned or light-sensitive people are at even greater risk, said lead author Ellen Bruzell of the Nordic Institute of Dental Materials.

Bruzell also found that bleaching damaged teeth. She saw more exposed grooves on the enamel surface of bleached teeth than on unbleached teeth. These grooves make the teeth more vulnerable to mechanical stress.

Tooth bleaching is one of the most popular cosmetic dental treatments available. It uses a bleaching agent – usually hydrogen peroxide – to remove stains such as those from red wine, tea and coffee, and smoking.

UV light is claimed to further activate the oxidation process, improving bleaching efficiency. The authors of this Photochemical & Photobiological Sciences article say there is very little substantive evidence to support this claim, and their new study finds no benefit to using UV light.

Courtesy: www.sciencedaily.com

FEB 23,2009
“One of the most important problems in materials science solved,” reports Professor Peter Oppeneer of Uppsala University. Together with three colleagues, he has managed to explain the hitherto unsolved riddle in materials science known as ‘the hidden order' - how a new phase arises and why.

This is a discovery that can be of great importance to our understanding of how new material properties occur, how they can be controlled and exploited in the future.

For a long time researchers have attempted to develop the superconducting materials of the future that will be able to conduct energy without energy losses, something of great importance to future energy production. But one piece of the puzzle has been missing. There are several materials that evince a clear phase shift in all thermodynamic properties when the temperature falls below a certain transitional temperature, but no one has been able to explain the new collective order in the material. Until now, it has been called the hidden order.

"The hidden order was discovered 24 years ago, and for all these years scientists have tried to find an explanation, but so far no one has succeeded. This has made the question one of the hottest quests in materials science. And now that we can explain how the hidden order in materials occurs, in a manner that has never been seen before, we have solved one of the most important problems of our day in this scientific field," says Professor Peter Oppeneer.

Four physicists from Uppsala University, led by Peter Oppeneer and in collaboration with John Mydosh from the University of Cologne, who discovered the hidden order 24 years ago, show through large-scale calculations how the hidden order occurs. Extremely small magnetic fluctuations prompt changes in the macroscopic properties of the material, so an entirely new phase arises, with different properties.

"Never before have we seen the so-called ‘magnetic spin excitations' produce a phase transition and the formation of a new phase. In ordinary material this excitation cannot change the phase and properties of the material because it is too weak. But now we have shown that this is in fact possible," says Peter Oppeneer.

What explains in detail all of the physical phenomena in the hidden order is a computer-based theory. Among other applications, it can be used to better understand high-temperature superconducting materials and will thus be important in the development of new superconducting materials and future energy production.

Courtesy: www.sciencedaily.com

New plastics may soon replace metals in auto bodies. Designers are beginning to discover a whole new world of possibilities offered by materials that can be bent into futuristic shapes.

DETROIT--Imaginations are let loose on car designs of the future. Now, young, creative minds are pushing automotive design to its limits, using every shape, color and size in their creations.

Designers and engineers who take their dreams and turn them into reality create these new cars of the future.

Chris Piscitelli's zest for cars started when he was just a kid. "My father is an old car enthusiast, so I grew up around it." Piscitelli is a design student at the College for Creative Studies in Detroit. As he got older, he learned his love of cars could be linked with his artistic talent.

"I have a passion for cars and design, so it was just natural for me to get into automotive design," Piscitelli says.

Now, Chris is part of a future generation of car designers learning to put new materials to use in exciting, futuristic ways. "We're supposed to stress the use of a lot of the new plastics and things that you do with plastics that you couldn't necessarily do with say, you know, steel," Piscitelli tells Ivanhoe.

Plastic is easy to mold so using materials engineering, Chris used the advantages of plastic by heating it so the long, spaghetti-like molecules slide over each other to form new shapes, giving us durable, cost-effective, lightweight plastics with sleek curves.

Jim Kolb, vice president of American Plastics Council in Troy says, "The limitations that some metals have in forming parts -- are overcome with the use of plastics."

Plastic concepts have caught the eye of car companies who see the future of car design in students like Piscitelli. "We're able to push the limit with the project, and so to make something that was, you know, kind of futuristic and, you know, out there, but also could be seen on the road," Piscitelli says. His concept car may not be road-ready right now, but it's a nice sneak peak at what the future holds.

Car manufacturers are working to make affordable plastic cars available to consumers.

New steel technologies are offering better looks, performance and protection for cars. To make new steel alloys, metallurgical engineers are mixing different kinds of metals like nickel, with iron to make a lighter, stronger, more-flexible automobile.

PITTSBURGH--High gas prices are forcing consumers to fork over fistfuls of cash at the pump. In fact, AAA says prices are now a dollar more than this time last year. Now, a new car technology might offer some relief when filling up your car at the pump.

Rising gas prices are hitting Andy Carson where it hurts -- his wallet. "I think gas prices are going to have a tremendous effect on my decision on what car I'm going to buy," Carson says. Fuel economy is playing a big part in his decision. Now, new high-tech materials for cars may produce a car to fit his budget.

Richard Fruehan, a metallurgical engineer from Carnegie Mellon University in Pittsburgh, says, "These very new steels have unique properties. This will enable us to use these steels in automobiles and reduce the weight of the automobiles and get the resulting fuel economy."

New steel technologies offer better looks, performance and protection for cars. Fruehan says, "The result will be a car that lasts longer, a car that gets better fuel economy and a car that is safe for the passenger." To make new steel materials, metallurgical engineers mix different kinds of metals, like nickel with iron to make a lighter, stronger, more-flexible product. "These steels are more coatable to resist corrosion, so the steels that we're pitting in are much better," Fruehan says.

Improved materials for cars could be the answer to gas mileage sticker-shock and give Andy Carson an upgrade. "I get good gas mileage now, but I think I can do a lot better," he says. But for now, he's paying the price at the pump and hopes for relief down the road.

If you think the United States prices are high, in Europe, they pay $7 a gallon. So experts say now is the time to tackle the problem.

Coutesy: www.sciencedaily.com

When moisture condenses on a cool surface, droplets can form that are the right size to scatter light, fogging up glass. A new polymer coating draws droplets into nanopores and transforms them into a transparent sheet, improving vision.

BOSTON--If you're all fogged up, a new discovery may have you seeing more clearly. Fog is not just a weather nuisance for drivers; it can cause problems just about everywhere. Now, a new anti-fog glass coating is clearing the way for consumers.

Your bathroom mirror, eyeglasses, and your car windshield all fall victim to fog. It can happen anywhere moisture condenses on a cool surface.

Michael Rubner, a materials chemist and professor of Polymer Material Science at Massachusetts Institute of Technology in Boston, says, "When they condense they are just the right size to scatter light. If light gets scattered you can't see through those glasses anymore."

Michael created a polymer coating, made from different materials that transform the opaque droplets of water into a transparent sheet. "All of the process that we use to create these coatings is done with water," he says.

The process begins by dipping the glass into a solution of negatively charged tiny glass particle. After, it's dipped into another solution with positively charged polymers. Michael says: "We're forming what we call nanopores. The pores are so small that you can't see them with your eyes. They don't scatter light. But they're large enough so that when you put a drop of water onto the surface, it's drawn into those pores and spread across the surface instantaneously."

The effect allows you to continue seeing clearly through the piece of coated glass. This not only helps you at home, but even the military is looking for fog-free glass. Thomas Long, from Fosta-Tek Optics in Leominster, Mass., says, "The soldiers are faced with either having a foggy field of vision or taking those glasses off to improve their vision, but then being vulnerable to fragments of shrapnel ending their eyesight."

Michael says his coating promises to be long lasting for soldiers out in the field and to drivers just trying to see their way home. He's trying to find a cost-effective way to mass market the polymer coating and hopes it will be available in the next few years.

Courtesy: www.sciencedaily.com

New materials for car bodies may soon transform the auto industry. Auto engineers can mold these carbon-fiber-reinforced plastics into virtually any shape. The materials are both strong and light -- increasing fuel efficiency and safety at the same time.

TROY, Mich.-- Cars built entirely out of plastic could be the wave of the future, making metal a thing of the past when it comes to cars.

New, innovative cars made almost entirely of plastic are paving the way for what you may be driving in the future. Guan Chew, a mechanical engineer at Porsche Engineering Services in Troy, Mich., says, "With plastics you can design cars which are very bold, and that gives you an advantage to sell nicer cars."

Plastics have gained a lot of ground over traditional metals used in cars, making it possible to build almost an entire vehicle completely of non-metal material. Paul Ritchie, CEO and engineer at Porsche Engineering Services, says: "The Carrera GT is what we would refer to as a proving ground for one of our new materials. It's made essentially from reinforced plastic."

Mechanical engineers use a lightweight, high-strength aerospace material called carbon-fiber-reinforced plastic. It's used in the doors, hoods, fenders, chasis and also in support frames for the engine and transmission.

"You can mold the plastics into very complicated shapes that maybe you can't do in steel," Chew says. Looks aren't the only perks of plastic; plastics help cars lose weight to go farther on fuel.

New materials, like plastic, are usually tested on high-end vehicles first. Once the materials are proven to be more efficient and cost effective, they eventually filter down to affordable consumer vehicles.

Transporting energy without any loss, travelling in magnetically levitated trains, carrying out medical imaging (MRI) with small-scale equipment: all these things could come true if we had superconducting materials that worked at room temperature. Researchers at CNRS have now taken another step forward on the road leading to this ultimate goal. They have revealed the metallic nature of a class of so-called critical high-temperature superconducting materials.

This result, which was published in the 31 May 2007 issue of the journal Nature, has been eagerly awaited for 20 years. It paves the way to an understanding of this phenomenon and makes it possible to contemplate its complete theoretical description.

Superconductivity is a state of matter characterized by zero electrical resistance and impermeability to a magnetic field. For instance, it is already used in medical imaging (MRI devices), and could find spectacular applications in the transport and storage of electrical energy without loss, the development of transport systems based on magnetic levitation, wireless communication and even quantum computers.

However, for now, such applications are limited by the fact that superconductivity only occurs at very low temperatures. In fact, it was only once a way of liquefying helium had been developed, which requires a temperature of 4.2 kelvins (-269 °C), that superconductivity was discovered, in 1911 (a discovery for which the Nobel Prize was awarded two years later.)

Since the end of the 1980s (Nobel Prize in 1987), researchers have managed to obtain 'high temperature' superconducting materials: some of these compounds can be made superconducting simply by using liquid nitrogen (77 K, or -196 °C). The record critical temperature (the phase transition temperature below which superconductivity occurs) is today 138 K (-135 °C).

This new class of superconductors, which are easier and cheaper to use, has given fresh impetus to the race to find ever higher critical temperatures, with the ultimate goal of obtaining materials which are superconducting at room temperature. However, until now, researchers have been held back by some fundamental questions. What causes superconductivity at microscopic scales" How do electrons behave in such materials"

Researchers at the National Laboratory for Pulsed Magnetic Fields2, working together with researchers at Sherbrooke, have observed 'quantum oscillations', thanks to their experience in working with intense magnetic fields. They subjected their samples to a magnetic field of as much as 62 teslas (a million times stronger than the Earth's magnetic field), at very low temperatures (between 1.5 K and 4.2 K).

The magnetic field destroys the superconducting state, and the sample, now in a normal state, shows an oscillation of its electrical resistance as a function of the magnetic field. Such an oscillation is characteristic of metals: it means that, in the samples that were studied, the electrons behaved in the same way as in ordinary metals.

The researchers will be able to use this discovery, which has been eagerly awaited for 20 years, to improve their understanding of critical high-temperature superconductivity, which until now had resisted all attempts at modeling it. The discovery has been effective in sorting out the many theories which had emerged to explain the phenomenon, and provides a firm foundation on which to build a new theory. It will make it possible to design more efficient materials, with critical temperatures closer to room temperature.

Reference: Quantum oscillations and the Fermi surface in an underdoped high-Tc superconductor, Nicolas Doiron-Leyraud, Cyril Proust, David LeBoeuf, Julien Levallois, Jean-Baptiste Bonnemaison, Ruixing Liang, D. A. Bonn, W. N. Hardy, Louis Taillefer, Nature, 31 May 2007, Vol 447, pp 565-568.

A new paper published in the Journal of the American Chemical Society (JACS) by a team led by professor Francesc Illas of the UB’s Department of Physical Chemistry and director of the Laboratory of Computational Materials Science (CMSL) will help to broaden our understanding of the nature of superconducting materials and of the origin of the superconductivity phenomenon in high critical temperature materials.

Other participants in the study are Ibério de P. R. Moreira (UB) and Jacek C. Wojdel, currently at the ICMAB-CSIC. The study was carried out with the collaboration of the Barcelona Supercomputing Center (BSC) and the Catalonia Supercomputing Centre (CESCA).

Superconductors are materials that conduct electrical current with zero resistance at low temperatures. Superconductivity was discovered in 1911, and the researchers in this area of solid state physics have been regular recipients of the Nobel Physics Prize: H. K. Onnes (1913), who discovered this extraordinary phenomenon; J. Bardeen, L. Cooper and R. Schrieffer (1972), for the BCS Theory of Superconductivity, which explains how electron pairs are formed (Cooper pairs) and how they conduct electrical current with zero resistance; J.C. Bednorz and K.A. Müller (1987), for their work with ceramic superconducting materials (copper oxides or cuprates) at temperatures above 35 K (-238 ºC) and beyond the boiling point of liquid nitrogen (-196 ºC).

“No theory has been able to account properly for high temperature superconductivity, although it seems to bear a strong relationship with the magnetic properties of materials,” explains Francesc Illas, who is also director of the UB’s Institute of Theoretical and Computational Chemistry (IQTCUB).

In 2008, the discovery of a new family of high critical temperature iron and arsenic superconductors (AsFe) marked a second major revolution in the world of superconductivity. The new compounds, which do not contain copper (Cu) but which have oxygen (O), fluor (F) or arsenic (As) and iron (Fe), will help scientists to solve some of the mysteries in the area of solid state physics.

But are these two high temperature superconductor families really so different? For Francesc Illas, “the main purpose of our work is to stress that these new materials are not as different from cuprates as originally thought. This point is fundamental for defining a unified approach to the two families of superconducting materials.”

According to the new study, the two families of superconducting materials share a similar electronic structure: specifically, Fe and As compounds are antiferromagnetic and exhibit a strong spin frustration, that is, strong magnetic interactions that make the interpretation of experiments difficult.

Another innovation mentioned in the article is the use of sophisticated techniques such as hybrid functionals for the study of electronic structure. “In cuprates,” says Illas, “the most commonly used methodologies are standard LDA (Local Density Approximation) and GGA (Generalized Gradient Approximation), which predict these systems to have a strong metallic character. However, experimental studies on the undoped parent compounds – superconductivity only appears when doping these materials – have shown that cuprates have insulating properties and are antiferromagnetic, but not metallic”. Therefore, the study of these systems will require more elaborate methods than the standard LDA and GGA methods to obtain a satisfactory description of their electronic structure and properties.

According to the experts, studying the electronic structure of the new FeAs based compounds using LDA and GGA also gives erroneous results, as in the case of cuprates. “These techniques,” says Illas, “are unable to give an accurate description of strongly correlated systems (cuprates, new superconductor families, and so on); these limitations have been frequently described in the literature.” More sophisticated approaches are necessary to describe the electronic structure and properties of these magnetic materials.

The discovery of high critical temperature superconductivity is one of the most remarkable chapters in modern science. It is a major breakthrough in developing new technologies and compounds in solid state physics and materials science. Physics experts dream of establishing a satisfactory theoretical model of the electronic structure in order to understand the formation of the superconducting phase, and then to be able to synthesize superconductors at room temperature. This objective seems attainable but not in a near future. For the time being, the most realistic approach is to try to understand the properties of undoped superconducting parent compounds and to progressively understand the effect of doping in the electronic structure of these materials, an area of research in which Illas’s group is one of the leaders in Spain.

An international team including scientists from the London Centre for Nanotechnology (LCN) have just published findings in the journal 'Proceedings of the National Academy of Sciences' (PNAS) demonstrating the dramatic effects of quantum mechanics in a simple magnet.

The importance of the work lies in establishing how a conventional tool of material science -- neutron beams produced at particle accelerators and nuclear reactors -- can be used to produce images of the ghostly entangled states of the quantum world.

At the nano scale, magnetism arises from atoms behaving like little magnets called 'spins'. In ferromagnets -- the kind that stick to fridge doors -- all of these atomic magnets point in the same direction. In antiferromagnets, the spins were thought to spontaneously align themselves opposite to the adjacent spins, leaving the material magnetically neutral overall.

The new research shows that this picture is not correct because it ignores the uncertainties of quantum mechanics. In particular, at odds with everyday intuition, the quantum-mechanical physical laws which operate on the nano-scale allow a spin to simultaneously point both up and down. At the same time, two spins can be linked such that even though it is impossible to know the direction of either by itself, they will always point in opposite directions -- in which case they are 'entangled'.

With their discovery, the researchers demonstrate that neutrons can detect entanglement, the key resource for quantum computing.

One of the lead authors of the work, Professor Des McMorrow from the LCN, comments: "When we embarked on this work, I think it is fair to say that none of us were expecting to see such gigantic effects produced by quantum entanglement in the material we were studying. We were following a hunch that this material might yield something important and we had the good sense to pursue it."

The researchers' next steps will be to pursue the implications for high temperature superconductors, materials carrying electrical currents with no heating and which bear remarkable similarities to the insulating antiferromagnets they have studied, and the design of quantum computers.

Collaborative research between scientists in the UK and USA has led to a major breakthrough in the understanding of antiferromagnets, published in this week's Nature. Scientists at the London Centre for Nanotechnology, the University of Chicago and the Center for Nanoscale Materials at Argonne National Laboratory have used x-rays to see the internal workings of antiferromagnets for the very first time.

Unlike conventional magnets, antiferromagnets (such as the metal chromium) are materials which exhibit 'secret' magnetism, undetectable at a macroscopic level. Instead, their magnetism is confined to very small regions where atoms behave as tiny magnets. They spontaneously align themselves opposite to adjacent atoms, leaving the material magnetically neutral overall.

Professor Gabriel Aeppli, Director of the London Centre for Nanotechnology, said: "People have been familiar with ferromagnets for hundreds of years and they have countless everyday uses; everything from driving electrical motors to storing information on hard disk drives. We haven't been able to make the same strides with antiferromagnets because we weren't able to look inside them and see how they were ordered.

"This breakthrough takes our understanding of the internal dynamics of antiferromagnets to where we were ninety years ago with ferromagnets. Once you can see something, it makes it that much easier to start engineering it."

The magnetic characteristics of ferromagnets have been studied by scientists since Greek antiquity, enabling them to build up a detailed picture of the regions - or "magnetic domains" - into which they are divided. However, antiferromagnets remained a mystery because their internal structure was too fine to be measured.

The internal order of antiferromagnets is on the same scale as the wavelength of x-rays (below 10 nanometers). The latest research used x-ray photon correlation spectroscopy to produce 'speckle' patterns; holograms which provide a unique 'fingerprint' of a particular magnetic domain configuration.

Dr. Eric D. Isaacs, Director of the Center for Nanoscale Materials, said: "Since the discovery of x-rays over 100 years ago, it has been the dream of scientists and engineers to use them to make holographic images of moving objects, such as magnetic domains, at the nanoscale.

"This has only become possible in the last few years with the availability of sources of coherent x-rays, such as the Advanced Photon Source, and the future looks even brighter with the development of fully coherent x-ray sources called Free Electron Lasers over the next few years."

In addition to producing the first antiferromagnet holograms, the research also showed that their magnetic domains shift over time, even at the lowest of temperatures. The most likely explanation for this can be found in quantum mechanics and the experiments open the door to the future exploitation of antiferromagnets in emerging technologies such as quantum computing.

"The key finding of our research provides information on the stability of domain walls in antiferromagnets," said Oleg Shpyrko, lead author on the publication and researcher at the Center for Nanoscale Materials. "Understanding this is the first step towards engineering antiferromagnets into useful nanoscale devices that exploit it."

Work at the London Centre for Nanotechnology was funded by a Royal Society Wolfson Research Merit Award and the Basic Technologies program of Research Councils UK. Work at the Center for Nanoscale Materials and the Advanced Photon Source was supported by the DOE Office of Science, Office of Basic Energy Sciences. The work at the University of Chicago was supported by the National Science Foundation.

Imagine unloading a pile of bricks onto the ground and watching the bricks assemble themselves into a level, straight wall in only a few minutes. While merely a fantasy for builders in the everyday world, these types of self-assembled structures are a reality for those who build materials in the nanoworld.

Michael C. Tringides, a senior physicist at the U.S. Department of Energy's Ames Laboratory, has shown that nanoscale "straight wall" lead islands on silicon are spontaneously and quickly created by unusually mobile atoms.

Several years ago, Tringides' research group was the first to observe that lead atoms deposited on a silicon surface at low temperatures self-organize into uniform-height island nanostructures. The laws of quantum mechanics – specifically, Quantum Size Effects – determine why lead atoms stack up to create uniform islands while other nanostructure systems organize into islands that vary in height.

How the lead-on-silicon islands organized into uniform-height islands remained a mystery until Tringides' team made the surprising discovery that when lead atoms move along the surface of a silicon substrate, the lead atoms exhibit a liquid-like motion instead of the typical random-type diffusion observed in other systems. The liquid-like motion of atoms was observed using scanning tunneling microscopy at Ames Lab and low energy electron microscopy performed by collaborators in Hong Kong.

"One big surprise was that the atoms were moving a lot at such a low temperature: 150 degrees Kelvin or minus 123 degrees Celsius," said Tringides. "The other surprise was that the atoms weren't moving randomly like individual atoms as we would expect. In this particular case, it seemed like the whole layer of lead atoms was moving like a liquid.

Fluid-like motion of the lead atoms explains why the layer moves so easily and forms uniform islands so quickly.

"When applying nanotechnology, it's very important to be able to make nanostructures of the same dimension using a method that others can easily replicate," said Tringides. "And, it's important that the growth process is fast."

Tringides' work succeeds in terms of uniformity and speed. The lead islands self-organize on silicon in only two to three minutes. Also, better understanding of how the lead islands grow will help researchers see if other systems show the same liquid-like behavior at low temperatures.

With such promising findings in hand, Tringides' team, which includes associate scientist Myron Hupalo and graduate students Steven Binz and Jizhou Chen, further investigated the possible use of these unusual lead islands on silicon as templates to study typical atomic processes, such as adsorption, nucleation and atom bonding. These processes are important in the study of reactivity and catalysis.

During those experiments, Tringides' group made another unexpected discovery. Normally atomic processes depend on an element's chemical nature, but the group found that when it came to lead islands, quantum mechanics had another surprise in store: The atomic processes depend dramatically on whether the island height is odd or even rather than its chemical nature. Tringides' group made this intriguing observation in a large lead island that had formed over a step on the original silicon surface. The top of the large island was flat as expected.

"But, the part of the island sitting on the higher terrace of silicon was four layers high, and the other part of the island sitting on the lower terrace was five layers," said Tringides.

The group studied nucleation on this unusual island by adding a very small amount of lead to its surface, creating many new small islands on top of the large island. Examination revealed that the density of the new islands was 60 times higher on the four-layer part of the island than on the five-layer part even though the two parts of the island were connected, suggesting that atom bonding is easier on the four-layer islands.

"The island was made up of the same element, lead, throughout," said Tringides. "So, we would expect the two parts of the island to communicate with each other, and atoms should be able to easily move from left to right and right to left among both halves of the island, so the density of the new small islands should have been the same in both parts."

Instead, the two halves of the island behaved like two separate islands. The four-layer section of the island has similar characteristics to independent four-layer islands, and the five-layer section behaved like other five-layer islands.

"For the purpose of growing materials, the two-part island indicates that we may not have to change the element to create variation in material properties," said Tringides. "Instead, we may be able to just change the height of the island."

"This is promising because it's easier to change the geometry of an island than to go out and find a new, exotic material," he added.

Tringides plans further experiments using gas adsorption to test the relationship between material reactivity and island height.

The Department of Energy's Office of Science, Basic Energy Sciences Office funded the work.

Scientists have perfected a technique for very accurately measuring and controlling the electromagnetic waves within some of the shortest laser pulses ever made, says new research. Being able to fully understand and control these laser pulses represents an important step towards using them to track and manipulate electrons in leading-edge research at the sub-atomic level.

The study, published in Nature Physics, focused on extremely short laser pulses, less than 10 femtoseconds long - a femtosecond is one million-billionth of a second. These laser pulses can allow scientists to move and control the electrons in atoms and molecules, and to understand, for example, how molecules are formed. To achieve this reliably, the pulse of electromagnetic waves emitted from the laser must be controlled and measured with a precision which, until now, has been very hard to achieve.

The team of physicists from Imperial College London attained an unprecedented level of accurate measurement by firing the femtosecond laser pulse into a sample of gas, which responds by emitting an x-ray pulse which is even shorter in duration - up to 10 times shorter than the original laser pulse. The researchers found that the spectrum of the x-ray pulse has encoded within it all the information necessary to precisely reconstruct the waveform of the original laser pulse. Through careful measurements and some 'intelligent' software designed specifically for this purpose, the researchers were therefore able, for the first time, to measure the waveform of individual femtosecond pulses.

Dr John Tisch, one of the Imperial research team, said: "This measurement technique is so accurate that we can determine the position of a peak in the pulse of electromagnetic waves from the laser with a precision of a mere 0.05 femtoseconds - in other words, 50 attoseconds. Also, the measurement can be made on individual pulses rather than by looking at the average properties of many pulses, so this is an important step forwards."

Dr Tisch explains that not only will this new technique lead to a greater ability to use short laser pulses for accurate sub-atomic level research, but it also sheds new light on the extremely short x-ray pulses emitted in response: "The x-ray pulses we used in the measurement process of our research are of great interest in their own right," he says. "They are on the attosecond timescale, which is even shorter than a femtosecond - just one billion-billionth of a second. They are a new tool for scientists to probe even faster motion than the femtosecond pulses that triggered them."

The research team have recently received a four-year £2.5 million grant from the EPSRC to take this research to the next stage. Professor Jonathan Marangos explains: "Now we've perfected this technique, we are going to look into using our accurate measurements and control of these lasers to manipulate electrons and control quantum processes."

The research was funded by a Basic Technology Programme grant from RCUK.

Lawrence Livermore National Laboratory scientists for the first time have validated the idea of using extremely short and intense X-ray pulses to capture images of objects such as proteins before the X-rays destroy the sample.

At the same time, the team also established a speed record of 25 femtoseconds for flash imaging.

The new method will be applicable to atomic-resolution imaging of complex biomolecules when even more powerful X-ray lasers, currently under construction, are available. The technique will allow scientists to gain insight into the fields of materials science, plasma physics, biology and medicine.

Using the free-electron laser at Deutsches Elektronen-Synchrotron (DESY) in Hamburg, Livermore scientists, as part of an international collaboration led by LLNL's Henry Chapman and Janos Hajdu of Uppsala University, were able to record a single diffraction pattern of a nanostructured object before the laser destroyed the sample. A Livermore-developed computer algorithm was then used to recreate an image of the object based on the recorded diffraction pattern. This "lensless" imaging technique could be applied to atomic-resolution imaging because it is not limited by the need to build a high-resolution lens. The flash images could resolve features 50 nanometers in size, which is about 10 times smaller than what is achievable with an optical microscope.

Theory predicts that a single diffraction pattern may be recorded from a large macromolecule, a virus or a cell with an ultra-short and extremely bright X-ray pulse before the sample explodes and turns into a plasma. This means that scientists could better understand the structure of macromolecular proteins without crystallizing them and thus allow rapid study of all classes of proteins.

Livermore scientists, along with colleagues at Uppsala University in Sweden, DESY, Technische Universität Berlin, the Center for Biophotonics Science and Technology at UC Davis, Stanford Synchrotron Radiation Laboratory, and private firm Spiller X-ray Optics of Livermore, conducted the first experimental demonstration of this theory.

Computer simulations based on four different models suggest that a near-atomic resolution structure could be achieved by well-thought out choice of pulse length and intensity of X-ray wavelength before the sample is stripped of its electrons and is destroyed. However, up until now, there had been no experimental verification of the technique.

The experimental demonstration of "flash diffractive imaging" uses the first soft X-ray FEL (free electron laser) in the world located at the FLASH facility at DESY. FLASH generates high-power soft X-ray pulses by the principle of self-amplification of spontaneous emission. The pulses are 10 million times brighter than today's brightest X-ray sources, synchrotrons. In addition, this experiment showed that it only takes a 25-femtosecond pulse duration to capture the image.

There has been a question whether the diffraction pattern recorded under these circumstances could be reconstructed to obtain undamaged sample information.

"These results could become a standardized method," Chapman said. "This imaging could be applied at the cellular, sub-cellular and down on to single molecule scale."

Other Livermore authors include Anton Barty, Michael Bogan, Sebastien Boutet, Matthias Frank, Stefan Hau-Riege, Stefano Marchesini, Bruce Woods, Saša Bajt, Henry Benner, Richard London, Richard Lee and Abraham Szoke.

The work was funded by a Laboratory Directed Research and Development strategic initiative proposal for "biological imaging with fourth-generation light sources."

The research appears in the Nov. 12 online edition of Nature Physics. It will appear on the cover of the December hard copy issue of Nature Physics.

This research was funded in part by the National Science Foundation's Center for Biophotonics Science and Technology (CBST) headquartered at the UC Davis Medical Center in Sacramento. CBST is a multi-institutional research center established in 2002 by LLNL and UC Davis researchers and is dedicated to the development and application of photonic instrumentation and methods to address important problems in the biomedical technology sector.

Founded in 1952, Lawrence Livermore National Laboratory is a national security laboratory, with a mission to ensure national security and apply science and technology to the important issues of our time. Lawrence Livermore National Laboratory is managed by the University of California for the U.S. Department of Energy's National Nuclear Security Administration.

A new imaging technique developed by researchers at the University of Illinois overcomes the limit of diffraction and can reveal the atomic structure of a single nanocrystal with a resolution of less than one angstrom (less than one hundred-millionth of a centimeter).

Optical and electronic properties of small assemblages of atoms called quantum dots depend upon their electronic structure – not just what's on the surface, but also what's inside. While scientists can calculate the electronic structure, they need to know where the atoms are positioned in order to do so accurately.

Getting this information, however, has proved to be a challenge for nanocrystals like quantum dots. Mapping out the positions of atoms requires clues provided by the diffraction pattern. But quantum dots are so small, the clues provided by diffraction alone are not enough.

By combining two sources of information – images and diffraction patterns taken with the same electron microscope – researchers at the U. of I. can achieve sub-angstrom resolution of structures that were not possible before.

"We show that for cadmium-sulfide nanocrystals, the improved image resolution allows a determination of their atomic structures," said Jian-Min (Jim) Zuo, a professor of materials science and engineering at the U. of I., and corresponding author of a paper that describes the high-resolution imaging system in the February issue of Nature Physics.

Images from electron microscopy can resolve individual atoms in a nanocrystal, but the atoms soon suffer radiation damage, which limits the length of observations. Patterns from X-ray diffraction can be used to determine the structure of large crystals, but not for nanocrystals, which are too small and don't diffract well.

To achieve sub-angstrom resolution, Zuo and colleagues developed a reiterative algorithm that processes and combines shape information from the low-resolution image and structure information from the high-resolution diffraction pattern. Both the image and the diffraction pattern are taken with the same transmission-electron microscope.

"The low-resolution image provides the starting point by supplying missing information in the central beam and supplying essential marks for aligning the diffraction pattern," said Zuo, who also is a researcher at the university's Frederick Seitz Materials Research Laboratory. "Our phase-retrieval algorithm then reconstructs the image."

To demonstrate the technique, the researchers took a new look at cadmium-sulfide quantum dots.

"We chose cadmium-sulfide quantum dots because of their size-dependent optical and electronic properties, and the importance of atomic structure on these properties," Zuo said. "Cadmium-sulfide quantum dots have potential applications in solar energy conversion and in medical imaging."

Using the reiterative algorithm, the smallest separation between the cadmium and sulfide atomic columns was measured at 0.84 angstroms, the researchers report.

"Since low-resolution images can be obtained from different sources, our technique is general and can be applied to non-periodic structures, such as interfaces and local defects," Zuo said. "Our technique also provides a basis for imaging the three-dimensional structure of single nanoparticles."

With Zuo, co-authors of the paper are former doctoral student and lead author Weijie Huang (now at Dow Chemical Co.), U. of I. professor of materials science and engineering Moonsub Shim, former postdoctoral research associate Bin Jiang (now at FEI Co.), and former doctoral student Kwan-Wook Kwon (now at LAM Research).

The U.S. Department of Energy, the American Chemical Society and the National Science Foundation funded the work.

In the world of nanomaterials, scientists and engineers can create new structures with tiny building blocks as small as one billionth of a meter.

But in order to construct new materials and devices, researchers first need to understand how these tiny units interact with each other.

One such building block is graphite oxide, which is often used to make graphene — a hotly studied material that scientists believe could be used to produce low-cost carbon-based transparent and flexible electronics. Like graphene, graphite oxide is essentially a sheet that is only one atom thick, but can be as wide as tens of micrometers.

Jiaxing Huang, assistant professor of materials science and engineering at Northwestern University, and his research group at the McCormick School of Engineering and Applied Science set out to investigate how these graphite-oxide sheets assemble. Their results, published as the cover article in the Jan. 26 issue of the Journal of the American Chemical Society, surprised them.

“We were very curious how these extremely thin two-dimensional sheets interact with each other,” Huang says. “This knowledge can also help to prepare better graphene thin films.”

Huang and his group studied the sheets by putting them onto a water surface — a process called Langmuir-Blodgett assembly, which makes the sheets stay flat and allows scientists to move them around.

The effect reminded the researchers of water lilies on a pond, and Huang asked his sister to help to create a Chinese water painting similar to that of Claude Monet’s series of paintings “Water Lilies” to demonstrate the idea. The artwork was chosen as one of the first illustrated covers for the 130-year-old journal.

Researchers used a barrier to push the sheets together to see how they would interact and then “fished” the interacting sheets off the water surface using glass slides or silicon wafers. Huang and his colleagues expected to see that individual sheets had stacked one upon the other, like a shuffled deck of cards. Instead they found that the edges of the graphite oxide sheets rumpled as they were pushed together.

“This was quite a surprise for us,” Huang says. “Now we understand that electrostatic repulsion is the dominant interaction when these sheets are pushed together in this edge-to-edge geometry. This prevents graphite oxide layers from overlapping with each other.”

When squeezed even further, the sheets eventually formed an interlocking structure that becomes a continuous membrane.

This film — consisting of flat, non-overlapping single layers tiling over large areas — has been very difficult to achieve by conventional thin-film processing techniques such as drop casting or spraying.

This breakthrough could have two immediate technological impacts. “Because we can keep them close to each other and still keep them flat, it provides high coverage of the surface with the single layers — which in turn will translate into high successful yield in graphene device fabrication,” Huang says. “On the other hand, the continuous graphite oxide monolayer can be made into a transparent conductor after conversion to graphene.”

Now, after studying how they interact edge-to-edge, Huang hopes to study face-to-face contact of the graphene-based materials. Stacking graphene sheets directly on top of each other will form graphite and lose the advantages of the single-atom-thick graphene materials. But Huang hopes to find a way to stack graphene without making graphite, which could create functional materials for energy-related applications such as electrodes for batteries, ultracapacitors and fuel cells.

“If we are good at making these tiny building blocks and if we can control how they assemble, we will create a lot of wonderful new things,” Huang says.

In addition to Huang, co-authors of the paper include National Science Foundation graduate research fellow Laura Cote and postdoctoral fellow Franklin Kim, both of whom, according to Huang, “did a wonderful job” to create the high-quality graphite oxide sheets used in the experiment.

Materials Chemists Apply Photonic Crystals to Forensics

Photonic crystals -- materials with precise patterns of gaps that make them reflect only selected wavelengths of light -- could soon replace the traditional ink-based fingerprinting. In a new silica-based, photonic-crystal material, the spacing of the gaps changes in response to pressure applied. Corresponding changes in its color reveal fingerprints with high precision -- not only the ridges in the skin, but also the depth of the ridges, the shape of the finger, and the mechanical properties of the skin.

TORONTO -- Increased airport security ... Better police forensics work ... Even improved bridge and building safety. These are all the tremendous possibilities stemming from a new material that's 20 times thinner than a strand of human hair.

Imagine a security system that relied on something unique to every single person -- his fingerprint. Now, scientists have developed a material that makes those prints nearly impossible to forge.

At the University of Toronto inside a science lab, Materials Chemist Andre Arsenault starts from scratch making new crystals. The raw materials are a lot like opal gemstones, which reflect light.

"Opal gemstone is very nice because you get all these multi-faceted color effects," Arsenault tells DBIS.

But these crystals are microscopic. Inside a flask, they form millions of tiny silica circles. Chemists fill the spaces with a synthetic rubber and then dissolve the silica, leaving behind a thin, honeycomb-like structure called a photonic crystal. When you press on it, the holes get closer together, changing the wavelength of light that's reflected.

"As you start pressing, you're gonna gradually go through the rainbow toward the blue. So you're gonna go red, orange, yellow, green, blue, purple," Arsenault says.

With a traditional ink fingerprint, the only thing that can be seen is the ridges on the finger. Full-color prints provide so much more. "You can get information about the depth of the ridges on the people's fingers," Arsenault says. "You can get information about the shape of people's fingers, as well as even the mechanical properties of the skin."

He even made a rubber replica of his fingerprint, which might fool a traditional fingerprint scan. The new material picked up the fake.

Researchers say the photonic crystal material is inexpensive to make and could be used to improve sensors in a number of consumer products.

Researchers “tune” graphene’s properties by growing it on different surfaces.

Researchers at Rensselaer Polytechnic Institute have discovered a new method for controlling the nature of graphene, bringing academia and industry potentially one step closer to realizing the mass production of graphene-based nanoelectronics.

Graphene, a one-atom-thick sheet of carbon, was discovered in 2004 and is considered a potential heir to copper and silicon as the fundamental building blocks of nanoelectronics.

With help from an underlying substrate, researchers for the first time have demonstrated the ability to control the nature of graphene. Saroj Nayak, an associate professor in Rensselaer’s Department of Physics, Applied Physics, and Astronomy, along with Philip Shemella, a postdoctoral research associate in the same department, have determined that the chemistry of the surface on which graphene is deposited plays a key role in shaping the material’s conductive properties. The results are based on large-scale quantum mechanical simulations.

Results show that when deposited on a surface treated with oxygen, graphene exhibits semiconductor properties. When deposited on a material treated with hydrogen, however, graphene exhibits metallic properties.

“Depending on the chemistry of the surface, we can control the nature of the graphene to be metallic or semiconductor,” Nayak said. “Essentially, we are ‘tuning’ the electrical properties of material to suit our needs.”

Conventionally, whenever a batch of graphene nanostructures is produced, some of the graphene is metallic, while the rest is semiconductor. It would be nearly impossible to separate the two on a large scale, Nayak said, yet realizing new graphene devices would require that they be comprised solely of metallic or semiconductor graphene. The new method for “tuning” the nature of graphene is a key step to making this possible, he said.

Graphene’s excellent conductive properties make it attractive to researchers. Even at room temperature, electrons pass effortlessly, near the speed of light and with little resistance. This means a graphene interconnect would likely stay much cooler than a copper interconnect of the same size. Cooler is better, as heat produced by interconnects can have negative effects on both a computer chip’s speed and performance.

Results of the study were published this week in the paper “Electronic structure and band-gap modulation of graphene via substrate surface chemistry” in Applied Physics Letters, and are featured on the cover of the journal’s January 19 issue.

Large-scale quantum simulations for the study were run on Rensselaer’s supercomputing system, the Computational Center for Nanotechnology Innovations (CCNI).

Researchers received funding for the project from the New York State Interconnect Focus Center at Rensselaer.

University of Maryland physicists have shown that in graphene the intrinsic limit to the mobility, a measure of how well a material conducts electricity, is higher than any other known material at room temperature. Graphene, a single-atom-thick sheet of graphite, is a new material which combines aspects of semiconductors and metals.

Their results, published online in the journal Nature Nanotechnology, indicate that graphene holds great promise for replacing conventional semiconductor materials such as silicon in applications ranging from high-speed computer chips to biochemical sensors.

A team of researchers led by physics professor Michael S. Fuhrer of the university's Center for Nanophysics and Advanced Materials, and the Maryland NanoCenter said the findings are the first measurement of the effect of thermal vibrations on the conduction of electrons in graphene, and show that thermal vibrations have an extraordinarily small effect on the electrons in graphene.

In any material, the energy associated with the temperature of the material causes the atoms of the material to vibrate in place. As electrons travel through the material, they can bounce off these vibrating atoms, giving rise to electrical resistance. This electrical resistance is "intrinsic" to the material: it cannot be eliminated unless the material is cooled to absolute zero temperature, and hence sets the upper limit to how well a material can conduct electricity.

In graphene, the vibrating atoms at room temperature produce a resistivity of about 1.0 microOhm-cm (resistivity is a specific measure of resistance; the resistance of a piece material is its resistivity times its length and divided by its cross-sectional area). This is about 35 percent less than the resistivity of copper, the lowest resistivity material known at room temperature.

"Other extrinsic sources in today's fairly dirty graphene samples add some extra resistivity to graphene," explained Fuhrer, "so the overall resistivity isn't quite as low as copper's at room temperature yet. However, graphene has far fewer electrons than copper, so in graphene the electrical current is carried by only a few electrons moving much faster than the electrons in copper."

In semiconductors, a different measure, mobility, is used to quantify how fast electrons move. The limit to mobility of electrons in graphene is set by thermal vibration of the atoms and is about 200,000 cm2/Vs at room temperature, compared to about 1,400 cm²/Vs in silicon, and 77,000 cm²/Vs in indium antimonide, the highest mobility conventional semiconductor known.

"Interestingly, in semiconducting carbon nanotubes, which may be thought of as graphene rolled into a cylinder, we've shown that the mobility at room temperature is over 100,000 cm²/Vs" said Fuhrer (T. Dürkop, S. A. Getty, Enrique Cobas, and M. S. Fuhrer, Nano Letters 4, 35 (2004)).

Mobility determines the speed at which an electronic device (for instance, a field-effect transistor, which forms the basis of modern computer chips) can turn on and off. The very high mobility makes graphene promising for applications in which transistors much switch extremely fast, such as in processing extremely high frequency signals.

Mobility can also be expressed as the conductivity of a material per electronic charge carrier, and so high mobility is also advantageous for chemical or bio-chemical sensing applications in which a charge signal from, for instance, a molecule adsorbed on the device, is translated into an electrical signal by changing the conductivity of the device.

Graphene is therefore a very promising material for chemical and bio-chemical sensing applications. The low resitivity and extremely thin nature of graphene also promises applications in thin, mechanically tough, electrically conducting, transparent films. Such films are sorely needed in a variety of electronics applications from touch screens to photovoltaic cells.

Fuhrer and co-workers showed that although the room temperature limit of mobility in graphene is as high as 200,000 cm²/Vs, in present-day samples the actual mobility is lower, around 10,000 cm²/Vs, leaving significant room for improvement. Because graphene is only one atom thick, current samples must sit on a substrate, in this case silicon dioxide.

Trapped electrical charges in the silicon dioxide (a sort of atomic-scale dirt) can affect the electrons in graphene and reduce the mobility. Also, vibrations of the silicon dioxide atoms themselves can also have an effect on the graphene which is stronger than the effect of graphene's own atomic vibrations. This so-called "remote interfacial phonon scattering" effect is only a small correction to the mobility in a silicon transistor, but because the phonons in graphene itself are so ineffective at scattering electrons, this effect becomes very important in graphene.

"We believe that this work points out the importance of these extrinsic effects, and creates a roadmap for finding better substrates for future graphene devices in order to reduce the effects of charged impurity scattering and remote interfacial phonon scattering." Fuhrer said.

"Intrinsic and Extrinsic Performance Limits of Graphene Devices on SiO₂," J. H. Chen, C. Jang, S. Xiao, M. Ishigami, M. S. Fuhrer (will appear in Nature Nanotechnology online March 23, 2008)