River Water and Salty Ocean Water Used to Generate Electricity

Anywhere freshwater enters the sea, such as river mouths or estuaries, could be potential sites for a power plant using such a battery, said Yi Cui, associate professor of materials science and engineering, who led the research team.

The theoretical limiting factor, he said, is the amount of freshwater available."We actually have an infinite amount of ocean water; unfortunately we don't have an infinite amount of freshwater," he said.

As an indicator of the battery's potential for producing power, Cui's team calculated that if all the world's rivers were put to use, their batteries could supply about 2 terawatts of electricity annually -- that's roughly 13 percent of the world's current energy consumption.

The battery itself is simple, consisting of two electrodes -- one positive, one negative -- immersed in a liquid containing electrically charged particles, or ions. In water, the ions are sodium and chlorine, the components of ordinary table salt.

Initially, the battery is filled with freshwater and a small electric current is applied to charge it up. The freshwater is then drained and replaced with seawater. Because seawater is salty, containing 60 to 100 times more ions than freshwater, it increases the electrical potential, or voltage, between the two electrodes. That makes it possible to reap far more electricity than the amount used to charge the battery.

"The voltage really depends on the concentration of the sodium and chlorine ions you have," Cui said."If you charge at low voltage in freshwater, then discharge at high voltage in sea water, that means you gain energy. You get more energy than you put in."

Once the discharge is complete, the seawater is drained and replaced with freshwater and the cycle can begin again."The key thing here is that you need to exchange the electrolyte, the liquid in the battery," Cui said. He is lead author of a study published in the journal Nano Letters earlier this month.

In their lab experiments, Cui's team used seawater they collected from the Pacific Ocean off the California coast and freshwater from Donner Lake, high in the Sierra Nevada. They achieved 74 percent efficiency in converting the potential energy in the battery to electrical current, but Cui thinks with simple modifications, the battery could be 85 percent efficient.

To enhance efficiency, the positive electrode of the battery is made from nanorods of manganese dioxide. That increases the surface area available for interaction with the sodium ions by roughly 100 times compared with other materials. The nanorods make it possible for the sodium ions to move in and out of the electrode with ease, speeding up the process.

Other researchers have used the salinity contrast between freshwater and seawater to produce electricity, but those processes typically require ions to move through a membrane to generate current. Cui said those membranes tend to be fragile, which is a drawback. Those methods also typically make use of only one type of ion, while his battery uses both the sodium and chlorine ions to generate power.

Cui's team had the potential environmental impact of their battery in mind when they designed it. They chose manganese dioxide for the positive electrode in part because it is environmentally benign.

The group knows that river mouths and estuaries, while logical sites for their power plants, are environmentally sensitive areas.

"You would want to pick a site some distance away, miles away, from any critical habitat," Cui said."We don't need to disturb the whole system, we just need to route some of the river water through our system before it reaches the ocean. We are just borrowing and returning it," he said.

The process itself should have little environmental impact. The discharge water would be a mixture of fresh and seawater, released into an area where the two waters are already mixing, at the natural temperature.

One of Cui's concerns is finding a good material for the negative electrode. He used silver for the experiments, but silver is too expensive to be practical.

His group did an estimate for various regions and countries and determined that South America, with the Amazon River draining a large part of the continent, has the most potential. Africa also has an abundance of rivers, as do Canada, the United States and India.

But river water doesn't necessarily have to be the source of the freshwater, Cui said.

"The water for this method does not have to be extremely clean," he said. Storm runoff and gray water could potentially be useable.

A power plant operating with 50 cubic meters of freshwater per second could produce up to 100 megawatts of power, according to the team's calculations. That would be enough to provide electricity for about 100,000 households.

Cui said it is possible that even treated sewage water might work.

"I think we need to study using sewage water," he said."If we can use sewage water, this will sell really well."

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First Practical Nanogenerator Produces Electricity With Pinch of the Fingers

"This development represents a milestone toward producing portable electronics that can be powered by body movements without the use of batteries or electrical outlets," said lead scientist Zhong Lin Wang, Ph.D."Our nanogenerators are poised to change lives in the future. Their potential is only limited by one's imagination."

The latest improvements have resulted in a nanogenerator powerful enough to drive commercial liquid-crystal displays, light-emitting diodes and laser diodes. By storing the generated charges using a capacitor, the output power is capable to periodically drive a sensor and transmit the signal wirelessly.

"If we can sustain the rate of improvement, the nanogenerator may find a broad range of other applications that require more power," he added. Wang cited, for example, personal electronic devices powered by footsteps activating nanogenerators inside the sole of a shoe; implanted insulin pumps powered by a heart beat; and environmental sensors powered by nanogenerators flapping in the breeze.

Wang and colleagues demonstrated commercial feasibility of the latest nanogenerator by using it to power an LED light and a liquid crystal display like those widely used in many electronic devices, such as calculators and computers. The power came from squeezing the nanogenerator between two fingers.

The key to the technology is zinc oxide (ZnO) nanowires. ZnO nanowires are piezoelectric -- they can generate an electric current when strained or flexed. That movement can be virtually any body movement, such as walking, a heartbeat, or blood flowing through the body. The nanowires can also generate electricity in response to wind, rolling tires, or many other kinds of movement.

The diameter of a ZnO nanowire is so small that 500 of the wires can fit inside the width of a single human hair. Wang's group found a way to capture and combine the electrical charges from millions of the nanoscale zinc oxide wires. They also developed an efficient way to deposit the nanowires onto flexible polymer chips, each about a quarter the size of a postage stamp. Five nanogenerators stacked together produce about 1 micro Ampere output current at 3 volts -- about the same voltage generated by two regular AA batteries (about 1.5 volts each).

"While a few volts may not seem like much, it has grown by leaps and bounds over previous versions of the nanogenerator," said Wang, a scientist at Georgia Institute of Technology."Additional nanowires and more nanogenerators, stacked together, could produce enough energy for powering larger electronics, such as an iPod or charging a cell phone."

Wang said the next step is to further improve the output power of the nanogenerator and find a company to produce the nanogenerator. It could hit the market in three to five years, he estimated. The device's first application is likely to be as a power source for tiny environmental sensors and sensors for infrastructure monitoring.

The scientists acknowledge funding from the Defense Advanced Research Projects Agency (of the U.S. Department of Defense), the Department of Energy, the National Institutes of Health and the National Science Foundation, and the U.S. Air Force.

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Researchers Make First Perovskite-Based Superlens for the Infrared

The unique optical properties of metamaterials, which include the ability to bend light backwards -- a property known as negative refraction -- arise from their structure rather than their chemical composition. However, metamaterials can be difficult to fabricate and tend to absorb a relatively high percentage of photons that would otherwise be available for imaging.

Now, researchers with the U.S. Department of Energy (DOE)'s Lawrence Berkeley National Laboratory (Berkeley Lab) have fabricated a superlens from perovskite oxides that are simpler and easier to fabricate than metamaterials, and are ideal for capturing light in the mid-infrared range, which opens the door to highly sensitive biomedical detection and imaging. It is also possible that the superlensing effect can be selectively turned on/off, which would open the door to highly dense data writing and storage.

"We have demonstrated a superlens for electric evanescent fields with low absorption losses using perovskites in the mid-infrared regime," says Ramamoorthy Ramesh, a materials scientist with Berkeley Lab's Materials Sciences Division, who led this research."Spectral studies of the lateral and vertical distributions of evanescent waves around the image plane of our lens show that we have achieved an imaging resolution of one micrometer, about one-fourteenth of the working wavelength."

Ramesh, who also holds appointments with the University of California Berkeley's Department of Materials Science and Engineering and the Department of Physics, is the senior author of a paper in the journalNature Communicationstitled"Near-field examination of perovskite-based superlenses and superlens-enhanced probe-object coupling."

Conventional lenses create images by capturing the propagating light waves emitted by an object under illumination and then bending these captured light waves into focus. No matter how perfect a conventional lens is, the smallest image it can ever resolve is about half the wavelength of the illuminating (incident) light -- a restriction known as the"diffraction limit." Superlenses overcome the diffraction limit by capturing the evanescent light waves, which carry detailed information about features on an object that are significantly smaller than the wavelengths of incident light. Because evanescent waves dissipate or"vanish" after traveling a very short distance, conventional lenses seldom ever see them.

"A superlens made out of a metamaterial focuses propagating waves and reconstructs evanescent waves arising from the illuminated objects in the same plane to produce an image with sub-wavelength resolution," says Susanne Kehr, a former member of Ramesh's Berkeley research group and now with the University of Saint Andrews in the United Kingdom."Our perovskite-based superlens doesn't focus propagating waves, but instead reconstructs evanescent fields only. These fields generate the sub-wavelength images that we study with near-field infrared microscopy."

Kehr is one of two leading authors of theNature Communicationspaper, along with Yongmin Liu, a metamaterials expert in the research group of Xiang Zhang, who also worked on this study. In 2005, Zhang, who holds joint appointments with Berkeley Lab and the University of California, Berkeley, led the first experimental demonstration of a superlens at optical frequencies.

Kehr and Liu say that perovskites hold a number of advantages over metamaterials for superlensing. The perovskites they used to make their superlens, bismuth ferrite and strontium titan¬ate, feature a low rate of photon absorption and can be grown as epitaxial multilayers whose highly crystalline quality reduces interface roughness so there are few photons lost to scattering. This combination of low absorption and scattering losses significantly improves the imaging resolution of the superlens.

"In addition, perovskites display a wide range of fascinating properties, such as ferroelectricity and piezoelectricity, superconductivity and enormous magnetoresistance that might inspire new functionalities of perovskite-based superlenses, such as non-volatile memory, microsensors and microactu¬ators, as well as applications in nanoelectronics," says Liu."Bismuth ferrite, in particular, is multiferroic, meaning it simultaneously displays both ferroelectric and ferromagnetic properties, and therefore is a good candidate to allow for electric and magnetic tunability."

This research represents the first application of perovskite materials to superlensing. One of the biggest challenges was to find the right combination of perovskites that would make an effective superlens. The perovskite thin films they fabricated were grown by pulsed-laser deposition and found to be single phase and fully epitaxial. However, this too was a challenge, as Kehr explains.

"Our superlenses consisted of a layer of bismuth ferrite and a layer of strontium titan¬ate with thicknesses of 200 and 400 nanometers, respectively, which is rather thick for epitaxial growth with pulsed laser deposition," she says."At these thicknesses, accurate thickness and flat interfaces become a problem."

A combination of near-field infrared microscopy with a tunable free-electron laser provided a first of its kind highly detailed study of the spatial and spectral near-field responses of the superlens. This study led to the observation of an enhanced coupling between the illuminated objects -- rectangles of strontium ruthenate on a strontium titanate substrate -- and a near-field scattering probe -- a metal-coated atomic-force microscope tip with a typical radius of 50 nanometers.

"At certain distances between the probe and the surface of the object, we observed a maximum number of evanescent fields," Ramesh says."Comparisons with numerical simulations indicate that this maximum originates from an enhanced coupling between probe and object, which might be applicable for multifunctional circuits, infrared spectroscopy and thermal sensors."

In theirNature Communicationspaper, Ramesh and his co-authors say that the multiferroic bismuth ferrite layer should make their superlens tunable through the application of an external electric field. This tunability could be used to change the superlensing wavelength or sharpen the final image, but even more importantly, might be used to turn the superlensing effect on and off.

"The ability to switch superlensing on and off for a certain wavelength with an external electric field would make it possible to activate and deactivate certain local areas of the lens," Kehr says."This is the concept of data-storage, with writing by electric fields and optical read-outs."

Liu says that the mid-infrared spectral region at which their superlens functions is prized for biomedical applications.

"Most biomolecules have specific absorption and radiation features in this range that depend on their chemical composition and therefore yield a fingerprint in the spectra," he says."However, compared with optical wavelengths, there are significant limitations in the basic components available today for biophotonic delivery in the mid-infrared. Our superlens has the potentials to eliminate these limitations."

This research was carried out by an international collaboration of scientists. In addition to Kehr, Liu and Ramesh, other co-authors of the paper"Near-field examination of perovskite-based superlenses and superlens-enhanced probe-object coupling," were Lane Martin, Pu Yu, Martin Gajek, Seung-Yeul Yang, Chan-Ho Yang, Marc Wenzel, Rainer Jacob, Hans-Georg von Ribbeck, Manfred Helm, Xiang Zhang and Lukas Eng.

The broad range of expertise represented by these co-authors was critical to the success of the research, as Kehr explains.

"Our perovskite oxide superlens was designed and grown in Ramesh's group, but the idea for a perovskite superlens originated with Lukas Eng at the University of Technology in Dresden," she says."A collaboration at Dresden between Eng and Manfred Helm provided the expertise for combining near-field infrared microscopy and free-electron laser technologies, and Yongmin and Xiang Zhang provided the expertise in optics for interpreting our results."

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Debut of the First Practical 'Artificial Leaf'

"A practical artificial leaf has been one of the Holy Grails of science for decades," said Daniel Nocera, Ph.D., who led the research team."We believe we have done it. The artificial leaf shows particular promise as an inexpensive source of electricity for homes of the poor in developing countries. Our goal is to make each home its own power station," he said."One can envision villages in India and Africa not long from now purchasing an affordable basic power system based on this technology."

The device bears no resemblance to Mother Nature's counterparts on oaks, maples and other green plants, which scientists have used as the model for their efforts to develop this new genre of solar cells. About the shape of a poker card but thinner, the device is fashioned from silicon, electronics and catalysts, substances that accelerate chemical reactions that otherwise would not occur, or would run slowly. Placed in a single gallon of water in a bright sunlight, the device could produce enough electricity to supply a house in a developing country with electricity for a day, Nocera said. It does so by splitting water into its two components, hydrogen and oxygen.

The hydrogen and oxygen gases would be stored in a fuel cell, which uses those two materials to produce electricity, located either on top of the house or beside it.

Nocera, who is with the Massachusetts Institute of Technology, points out that the"artificial leaf" is not a new concept. The first artificial leaf was developed more than a decade ago by John Turner of the U.S. National Renewable Energy Laboratory in Boulder, Colorado. Although highly efficient at carrying out photosynthesis, Turner's device was impractical for wider use, as it was composed of rare, expensive metals and was highly unstable -- with a lifespan of barely one day.

Nocera's new leaf overcomes these problems. It is made of inexpensive materials that are widely available, works under simple conditions and is highly stable. In laboratory studies, he showed that an artificial leaf prototype could operate continuously for at least 45 hours without a drop in activity.

The key to this breakthrough is Nocera's recent discovery of several powerful new, inexpensive catalysts, made of nickel and cobalt, that are capable of efficiently splitting water into its two components, hydrogen and oxygen, under simple conditions. Right now, Nocera's leaf is about 10 times more efficient at carrying out photosynthesis than a natural leaf. However, he is optimistic that he can boost the efficiency of the artificial leaf much higher in the future.

"Nature is powered by photosynthesis, and I think that the future world will be powered by photosynthesis as well in the form of this artificial leaf," said Nocera, a chemist at Massachusetts Institute of Technology in Cambridge, Mass.

Nocera acknowledges funding from The National Science Foundation and Chesonis Family Foundation.

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Snapshots of Laser Driven Electrons

Flocking behavior does not only exist among birds, insects or fish; the microcosm offers similar phenomena, too. A team of scientists including Ferenc Krausz and his employees Laszlo Veisz and Alexander Buck of the Laboratory of Attosecond Physics (LAP) at the Max-Planck-Institut für Quantenoptik (MPQ) and the Ludwig-Maximilians-Universität (LMU Munich), in cooperation with colleagues from the Friedrich Schiller University Jena, succeeded in the first observation of laser-accelerated fast electron swarms in conjunction with a plasma wave consisting of positively charged helium ions and slow background electrons.

This way, the physicists managed to observe in real-time how electrons form bunches under the influence of strong laser pulses and how they behave in the slipstream during their flight. The findings facilitate the development of new electron and light sources with which, for example, the structure of atoms and molecules can be explored. In medicine, this knowledge helps the development of new X-ray sources whose resolution will be much higher than current devices allow.

When short laser pulses irradiate e.g. helium atoms their structure is heavily disturbed. If the light is strong enough, electrons are pulled out of the atoms and the helium atoms become ions. This mixture of electrons and ions is called plasma which may support wave structures -the so called electron plasma waves- when exposed to strong light. In laser physics this process and these waves are used under special conditions to rapidly accelerate a small number of the electrons to close to the speed of light and to control them.

A team from the Laboratory of Attosecond Physics at the MPQ and the LMU Munich, in cooperation with the Friedrich Schiller University Jena, succeeded in taking snapshots of both the accelerated electron bunches and the plasma wave produced by the strong laser light that drives them.

In their experiments, the laser physicists focused a laser pulse on a helium gas jet (or flow of helium gas) from a specially designed nozzle. The pulse only lasts a few femtoseconds (one femtosecond corresponds to millionth of a billionth second, 10^-15seconds). The flash of light consists of only a few wave cycles and around one billion billion light particles (photons). Its highest power is focused to a very short moment -- the duration of the flash of light -- and a tiny area. The high-intensity laser pulse tears out all the electrons from the atoms, leaving behind a plasma composed of free electrons and Helium nuclei. In this cocktail the electrons are much lighter than the helium ions; as a result they are pushed aside. While the laser pulse sweeps across the system the ions remain stationary and the released electrons oscillate around one location. Together the particles form a plasma wave; one oscillation of this structure takes around 20 femtoseconds.

In the plasma wave, gigantic electric fields are formed, which are 1000 times stronger than those generated in the world's largest particle accelerators. A small number of the electrons take advantage of these fields, fly as a swarm behind the laser pulse in its slipstream and accelerate to close to the speed of light. In this process, every accelerated electron has almost the same energy.

Physicists have long been aware of this phenomenon and it has been demonstrated in earlier experiments. The Japanese laser physicist Toshiki Tajima already described this process in 1970. Today Tajima works as a researcher in the excellence cluster Munich-Centre for Advanced Photonics. However, up to now it has only been possible to individually observe the electron swarm or the whole plasma wave with reduced resolution.

The laser physicists from Garching succeeded in recording both phenomena with a high-resolution image of the plasma wave. The process was documented in snapshots with the same light pulse also responsible for accelerating the electrons. The physicists had previously split the laser pulse so that a small portion of it illuminated the system of free electrons and ions perpendicularly to the electron beam. The periodic structure of the plasma wave refracts and partially deflects the light.″We observe the deflection and thereby image the plasma wave as a modulation of brightness onto a camera,″ explains Laszlo Veisz, the research-group leader of the LAP team. In doing so the researchers achieve a unique spatial and temporal resolution in the femtosecond range. The electron swarm produces strong magnetic fields that the physicists also record and thus determine its position and duration. Eventually, a film describing the acceleration of the electrons results from the combination of both measurement methods.

″The obtained improved knowledge about laser-driven electron acceleration helps us in the development of new X-ray sources of unprecedented quality, not only for basic research but also for medicine,″ explains Ferenc Krausz.

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High-Temperature Superconductor Spills Secret: A New Phase of Matter?

"Our findings point to management and control of this other phase as the correct path toward optimizing these novel superconductors for energy applications, as well as searching for new superconductors," said Zhi-Xun Shen of the Stanford Institute for Materials and Energy Science (SIMES), a joint institute of the Department of Energy's SLAC National Accelerator Laboratory and Stanford University. Shen led the team of researchers that made the discovery; their findings appear in the March 25 issue ofScience.

Superconductors are materials that conduct electricity with 100 percent efficiency, losing nothing to resistance. Currently used in medical imaging, highly efficient electrical generators and maglev trains, they have the potential to become a truly transformative technology; energy applications would be just one beneficiary. This promise is hampered by one thing, though: they work only at extremely low temperatures. Although research over the past 25 years has developed"high-temperature superconductors" that work at warmer temperatures, even the warmest of them -- the cuprates -- must be chilled half-way to absolute zero before they will superconduct.

The prospect of being able to dramatically increase that working temperature, thus making superconductors easier and cheaper to use, has kept interest in the cuprates at the boiling point. But to change something you have to understand it, and a puzzle called the pseudogap has stood in the way.

One hallmark of a superconductor is a so-called"energy gap" that appears when the material transitions into its superconducting phase. The gap in electron energies arises when electrons pair off at a lower energy to do the actual job of superconducting electric current.

When most of these materials warm to the point that they can no longer superconduct, the electron pairs split up, the electrons start to regain their previous energies, and the gap closes. But in the cuprates, the gap persists even above superconducting temperatures. This is the pseudogap, and it doesn't fully disappear until a second critical temperature called T* (pronounced"T-star") is reached. T* can be 100 degrees higher than the temperature at which superconductivity begins.

The electrons in the pseudogap state aren't superconducting -- so what are they doing? That's the puzzle that's had condensed matter physicists scratching their heads for two decades.

"A clear answer as to whether such a gap is just an extension of superconductivity or a harbinger of another phase is a critical step in developing better superconductors," Shen said.

In work done at SLAC's Stanford Synchrotron Radiation Lightsource, Lawrence Berkeley National Laboratory's Advanced Light Source and Stanford University, Shen's team looked at a sample of a cuprate superconductor from the inside out. They examined electronic behavior at the sample's surface, thermodynamic behavior in the sample's interior, and changes to the sample's dynamic properties over time using a trifecta of measurement techniques never before employed together.

"There is much to be said about using the same material and three different techniques to tackle the problem," commented condensed matter physicist Sudip Chakravarty of the University of California Los Angeles, who was not involved in the research."Even after decades of research this is a key unanswered question."

The team's findings: electrons in the pseudogap phase are not pairing up. They reorganize into a distinct yet elusive order of their own. In fact, the new order is also present when the material is superconducting; it had been overlooked before, masked by the behavior of superconducting electron pairs.

Simply knowing the pseudogap indicates a new phase of matter provides a clear signpost for follow-up research, according to Ruihua He, a post-doctoral researcher at the Advanced Light Source and first author of the paper. He outlined the next steps:"First to-do: uncover the nature of the pseudogap order. Second to-do: determine whether the pseudogap order is friend or foe to superconductivity. Third to-do: find a way to promote the pseudogap order if it's a friend and suppress it if it's a foe."

According to Makoto Hashimoto, a coauthor on the paper and SSRL staff scientist, their work"makes the high-temperature superconductor roadmap much clearer than before, and a good roadmap is important for any big science project."

This advance was made possible by a strong collaboration between Shen's team and teams of researchers from SIMES (led by Aharon Kapitulnik), LBNL (led by Joseph Orenstein) and the ALS (led by Zahid Hussain), the sample growers from the National Institute of Advanced Industrial Science and Technology (led by Hiroshi Eisaki), as well as SIMES theorists Steve Kivelson and Thomas Devereaux.

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Smaller Particles Could Make Solar Panels More Efficient

The results are published in the April issue of the journalACS Nano.

The advance provides evidence to support a controversial idea, called multiple-exciton generation (MEG), which theorizes that it is possible for an electron that has absorbed light energy, called an exciton, to transfer that energy to more than one electron, resulting in more electricity from the same amount of absorbed light.

Quantum dots are human-made atoms that confine electrons to a small space. They have atomic-like behavior that results in unusual electronic properties on a nanoscale. These unique properties may be particularly valuable in tailoring the way light interacts with matter.

Experimental verification of the link between MEG and quantum dot size is a hot topic due to a large degree of variation in previously published studies. The ability to generate an electrical current following MEG is now receiving a great deal of attention because this will be a necessary component of any commercial realization of MEG.

For this study, Lusk and collaborators used a National Science Foundation (NSF)-supported high performance computer cluster to quantify the relationship between the rate of MEG and quantum dot size.

They found that each dot has a slice of the solar spectrum for which it is best suited to perform MEG and that smaller dots carry out MEG for their slice more efficiently than larger dots. This implies that solar cells made of quantum dots specifically tuned to the solar spectrum would be much more efficient than solar cells made of material that is not fabricated with quantum dots.

According to Lusk,"We can now design nanostructured materials that generate more than one exciton from a single photon of light, putting to good use a large portion of the energy that would otherwise just heat up a solar cell."

The research team, which includes participation from the National Renewable Energy Laboratory, is part of the NSF-funded Renewable Energy Materials Research Science and Engineering Center at the Colorado School of Mines in Golden, Colo. The center focuses on materials and innovations that will significantly impact renewable energy technologies. Harnessing the unique properties of nanostructured materials to enhance the performance of solar panels is an area of particular interest to the center.

"These results are exciting because they go far towards resolving a long-standing debate within the field," said Mary Galvin, a program director for the Division of Materials Research at NSF."Equally important, they will contribute to establishment of new design techniques that can be used to make more efficient solar cells."

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Better Batteries for Electric Cars

Electric cars are the future -- a view shared by government and the automotive industry alike.  By 2020, a million passenger cars with an electric drive should be on the roads in Germany. The ADAC, the German motoring organization, found out in a survey, 74 percent of those surveyed would buy an electric car if they did not have to compromise in terms of cost, comfort and safety.

Consumers are not willing to compromise one iota when it comes to range. Around one third of drivers are looking for a range of at least 500 kilometers. And here is the crux: A lack of charging stations and limited battery life have so far prevented compact electric vehicles from going mainstream. The lithium-ion batteries used by most automakers are simply too heavy, too expensive and go flat too quickly. New materials should improve the performance, service life and safety of the energy storage device, yet the development of these kinds of materials is time-consuming and costly. In the Fraunhofer System Research for Electromobility (FSEM) project, researchers from the Fraunhofer Institute for Industrial Mathematics ITWM in Kaiserslautern are developing software to simulate lithium-ion batteries, which should in turn speed up this process and make it more efficient. The new software is dubbed BEST, short for Battery and Electrochemistry Simulation Tool.

A lithium-ion battery consists of two porous electrodes kept apart by a separator filled with electrolyte. Lithium ions flow between the electrodes when the battery is charged and discharged."Battery performance depends on the materials used in the components. These materials need to work in harmony with each other," explains Jochen Zausch, a scientist in the Complex Fluids group at Fraunhofer ITWM."Various material combinations can be simulated using our software, enabling us to come up with the ideal mix. The kind of trial-and-error testing done in the past is no longer necessary."

The Fraunhofer ITWM researchers have managed to simulate on macroscopic and microscopic level the entire battery cell as well as the transport and reaction processes of the lithium ions themselves."We can show the microscopic structure of the electrodes. Every individual pore measuring 10 micrometers can be seen -- something none of today's off-the-shelf programs can do. The position and shape of the electrodes can also be varied," says Zausch. By resolving the structure of the electrodes in three dimensions, parameters such as lithium ion concentrations and current density can be calculated. For these computations a specializes"Finite Volume" code is used that was developed and implemented at the ITWM. The distribution of the current flow provides an indication of heat production in the battery. Therefore, the software can pinpoint possible hotspots that may overheat and can lead to ignition of the battery. Aging effects can also be assessed using BEST. After all, temperature development within the battery affects its service life. The scientists intend to upgrade the program to include aging models which would make these kinds of studies even easier to conduct.

"Ultimately, BEST should help both automakers and manufacturers of electric storage devices to build robust, safe batteries with greater range and, at the same time, improved acceleration," says Zausch in conclusion. The software can be seen at the Hannover Messe from April 4 to 8.

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Nanomodified Surfaces Seal Leg Implants Against Infection

"You need to close (the area) where the bacteria would enter the body, and that's where the skin is," said Thomas Webster, associate professor of engineering and orthopaedics at Brown University.

Webster and a team of researchers at Brown may have come across the right formula to deter bacterial migrants. The group reports two ways in which it modified the surface of titanium leg implants to promote skin cell growth, thereby creating a natural skin layer and sealing the gap where the device has been implanted into the body. The researchers also created a molecular chain to sprinkle skin-growing proteins on the implant to hasten skin growth.

The findings are published in theJournal of Biomedical Materials Research A.

The researchers, including Melanie Zile, a Boston University student who worked in Webster's lab as part of Brown's Undergraduate Teaching and Research Awards program, and Sabrina Puckett, who earned her engineering doctorate last May, created two different surfaces at the nanoscale, dimensions less than a billionth of a meter.

In the first approach, the scientists fired an electron beam of titanium coating at the abutment (the piece of the implant that is inserted into the bone), creating a landscape of 20-nanometer mounds. Those mounds imitate the contours of natural skin and trick skin cells into colonizing the surface and growing additional keratinocytes, or skin cells.

Webster knew such a surface, roughened at the nanoscale, worked for regrowing bone cells and cartilage cells, but he was unsure whether it would be successful at growing skin cells. This may be the first time that a nanosurface created this way on titanium has been shown to attract skin cells.

The second approach, called anodization, involved dipping the abutment into hydrofluoric acid and giving it a jolt of electric current. This causes the titanium atoms on the abutment's surface to scurry about and regather as hollow, tubular structures rising perpendicularly from the abutment's surface. As with the nanomounds, skin cells quickly colonize the nanotubular surface.

In laboratory (in vitro) tests, the researchers report nearly a doubling of skin cell density on the implant surface; within five days, the keratinocyte density reached the point at which an impermeable skin layer bridging the abutment and the body had been created.

"You definitely have a complete layer of skin," Webster said."There's no more gap for the bacteria to go through."

To further promote skin cell growth around the implant, Webster's team looked to FGF-2, a protein secreted by the skin to help other skin cells grow. Simply slathering the abutment with the proteins doesn't work, as FGF-2 loses its effect when absorbed by the titanium. So the researchers came up with a synthetic molecular chain to bind FGF-2 to the titanium surface, while maintaining the protein's skin-cell growing ability. Not surprisingly, in vitro tests showed the greatest density of skin cells on abutment surfaces using the nanomodified surfaces and laced with FGF-2. Moreover, the nanomodified surfaces create more surface area for FGF-2 proteins than would be available on traditional implants.

The next step is to perform in vivo studies; if they are successful, human trials could begin, although Webster said that could be years away.

The U.S. Department of Veterans Affairs and the U.S. National Science Foundation funded the research.

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Simulating Tomorrow's Accelerators at Near the Speed of Light

But realizing the promise of laser-plasma accelerators crucially depends on being able to simulate their operation in three-dimensional detail. Until now such simulations have challenged or exceeded even the capabilities of supercomputers.

A team of researchers led by Jean-Luc Vay of Berkeley Lab's Accelerator and Fusion Research Division (AFRD) has borrowed a page from Einstein to perfect a revolutionary new method for calculating what happens when a laser pulse plows through a plasma in an accelerator like BELLA. Using their"boosted-frame" method, Vay's team has achieved full 3-D simulations of a BELLA stage in just a few hours of supercomputer time, calculations that would have been beyond the state of the art just two years ago.

Not only are the recent BELLA calculations tens of thousands of times faster than conventional methods, they overcome problems that plagued previous attempts to achieve the full capacity of the boosted-frame method, such as violent numerical instabilities. Vay and his colleagues, Cameron Geddes of AFRD, Estelle Cormier-Michel of the Tech-X Corporation in Denver, and David Grote of Lawrence Livermore National Laboratory, publish their latest findings in the March, 2011 issue of the journalPhysics of Plasma Letters.

Space, time, and complexity

The boosted-frame method, first proposed by Vay in 2007, exploits Einstein's Special Theory of Relativity to overcome difficulties posed by the huge range of space and time scales in many accelerator systems. Vast discrepancies of scale are what made simulating these systems too costly.

"Most researchers assumed that since the laws of physics are invariable, the huge complexity of these systems must also be invariable," says Vay."But what are the appropriate units of complexity? It turns out to depend on how you make the measurements."

Laser-plasma wakefield accelerators are particularly challenging: they send a very short laser pulse through a plasma measuring a few centimeters or more, many orders of magnitude longer than the pulse itself (or the even-shorter wavelength of its light). In its wake, like a speedboat on water, the laser pulse creates waves in the plasma. These alternating waves of positively and negatively charged particles set up intense electric fields. Bunches of free electrons, shorter than the laser pulse,"surf" the waves and are accelerated to high energies.

"The most common way to model a laser-plasma wakefield accelerator in a computer is by representing the electromagnetic fields as values on a grid, and the plasma as particles that interact with the fields," explains Geddes, a member of the BELLA science staff who has long worked on laser-plasma acceleration."Since you have to resolve the finest structures -- the laser wavelength, the electron bunch -- over the relatively enormous length of the plasma, you need a grid with hundreds of millions of cells."

The laser period must also be resolved in time, and calculated over millions of time steps. As a result, while much of the important physics of BELLA is three-dimensional, direct 3-D simulation was initially impractical. Just a one-dimensional simulation of BELLA required 5,000 hours of supercomputer processor time at Berkeley Lab's National Energy Research Scientific Computing Center (NERSC).

Choosing the right frame

The key to reducing complexity and cost lies in choosing the right point of view, or"reference frame." When Albert Einstein was 16 years old he imagined riding along in a frame moving with a beam of light -- a thought experiment that, 10 years later, led to his Special Theory of Relativity, which establishes that there is no privileged reference frame. Observers moving at different velocities may experience space and time differently and even see things happening in a different order, but calculations from any point of view can recover the same physical result.

Among the consequences are that the speed of light in a vacuum is always the same; compared to a stationary observer's experience, time moves more slowly while space contracts for an observer traveling near light speed. These different points of view are called Lorentz frames, and changing one for another is called a Lorentz transformation. The"boosted frame" of the laser pulse is the key to enabling calculations of laser-plasma wakefield accelerators that would otherwise be inaccessible.

A laser pulse pushing through a tenuous plasma moves only a little slower than light through a vacuum. An observer in the stationary laboratory frame sees it as a rapid oscillation of electromagnetic fields moving through a very long plasma, whose simulation requires high resolution and many time steps. But for an observer moving with the pulse, time slows, and the frequency of the oscillations is greatly reduced; meanwhile space contracts, and the plasma becomes much shorter. Thus relatively few time steps are needed to model the interaction between the laser pulse, the plasma waves formed in its wake, and the bunches of electrons riding the wakefield through the plasma. Fewer steps mean less computer time.

Eliminating instability

Early attempts to apply the boosted-frame method to laser-plasma wakefield simulations encountered numerical instabilities that limited how much the calculation frame could be boosted. Calculations could still be speeded up tens or even hundreds of times, but the full promise of the method could not be realized.

Vay's team showed that using a particular boosted frame, that of the wakefield itself -- in which the laser pulse is almost stationary -- realizes near-optimal speedup of the calculation. And it fundamentally modifies the appearance of the laser in the plasma. In the laboratory frame the observer sees many oscillations of the electromagnetic field in the laser pulse; in the frame of the wake, the observer sees just a few at a time.

Not only is speedup possible because of the coarser resolution, but at the same time numerical instabilities due to short wavelengths can be suppressed without affecting the laser pulse. Combined with special techniques for interpreting the data between frames, this allows the full potential of the boosted-frame principle to be reached.

"We produced the first full multidimensional simulation of the 10 billion-electron-volt design for BELLA," says Vay."We even ran simulations all the way up to a trillion electron volts, which establishes our ability to model the behavior of laser-plasma wakefield accelerator stages at varying energies. With this calculation we achieved the theoretical maximum speedup of the boosted-frame method for such systems -- a million times faster than similar calculations in the laboratory frame."

Simulations will still be challenging, especially those needed to tailor applications of high-energy laser-plasma wakefield accelerators to such uses as free-electron lasers for materials and biological sciences, or for homeland security or other research. But the speedup achieves what might otherwise have been virtually impossible: it puts the essential high-resolution simulations within reach of new supercomputers.

This work was supported by the U.S. Department of Energy's Office of Science, including calculations with the WARP beam-simulation code and other applications at the National Energy Research Scientific Computing Center (NERSC).

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Tying the Knot With Computer-Generated Holograms: Winding Optical Path Moves Matter

Optical traps can be used to confine and manipulate small objects -- ranging in size from a few nanometers to several hundred micrometers -- in 3-D. They work because variations in the intensity of the light produce forces that push small objects toward bright regions. The trapping of small objects is widely used for a broad range of research applications in biophysics, condensed matter physics and medical diagnostics.

Ordinary optical traps use Gaussian laser beams that focus to a spot. The beams being used to create extended optical traps focus instead to curves, much like the bright patterns on the bottom of swimming pools. And these bright curves can be tied in knots.

Knotted traps are made by imprinting a computer-generated hologram on the wavefronts of an otherwise ordinary beam of light. NYU undergraduate student Elisabeth Shanblatt and NYU physicist David Grier, the authors of theOptics Expresspaper, use a"liquid-crystal spatial light modulator" to project their holograms. This is essentially the first cousin of a conventional LCD television screen. The spatial light modulator imprints a calculated pattern of phase shifts onto the light. When the modified beam is brought to a focus with a high-power lens, the region of maximum intensity takes the form of a 3-D curve. This curve can cross over and through itself to trace out a knot. Moreover, the same hologram can redirect the light's radiation pressure to have a component along the curve, so that the total optical force"threads the knot."

When Shanblatt and Grier began this investigation, they thought that creating knots would be a compelling and aesthetically pleasing demonstration of their method's power. Once the knots actually worked, they realized that there are very few -- if any -- other practical ways to create knotted force fields. Previously reported knotted vortex fields have intensity minima along the knot, rather than the intensity maxima, or"bright knots" that can be created using the computer-generated holograms.

Shanblatt was working on a project with Grier investigating these holographic optical traps, when they discovered a method for projecting holographic optical traps along arbitrary curves in 3-D, with amplitude and phase profiles independently specified.

"The knotted optical force fields we created use intensity gradients to hold microscopic objects in place and phase gradients to thread them through the knot," says Shanblatt, describing their method."These optical knots are a special type of a very general class of 3-D optical traps that can be created using holographic techniques."

Ordinary optical traps have current applications in biophysics, where they are used as surgical tools and to probe the elastic properties of biomolecules, and in condensed matter physics, where they assemble nanomaterials into 3-D functional structures and gauge the forces between microscopic objects. Extended optical traps are especially handy in moving small objects such as biological cells through microfluidic lab-on-a-chip devices. And they can be used to measure very small interactions among such objects, which is helpful for medical diagnostic tests.

Perhaps the most exciting and futuristic potential application the NYU team sees for their method is to create knotted current loops of charged particles in high-temperature plasmas. This is a long-sought-after goal for developing fusion energy as a practical power source.

How can their knots of light solve problems of fusion energy? Fusion reactors work by slamming light atomic nuclei into each other so hard that the nuclei fuse into heavier elements, releasing lots of energy. The best way to accomplish this, Grier says, is to heat the atoms to a high enough temperature so that they can overcome all of the barriers to fusion. At these temperatures, the atoms' electrons ionize and the gas becomes a plasma.

This is doubly good, notes Grier, because you can pass large electric currents through the plasma, therefore heating it still more."You can also act on the currents with magnetic fields to contain the hot plasma, preventing it from destroying its physical container. These fusion plasmas are literally as hot as the core of the sun," he adds.

A problem occurs when currents flowing through plasma in a fusion reactor become unstable; this is similar to what occurs when the currents flowing through the plasma in a neon sign flicker. The currents thrash around, cool the plasma, damage the container, and generally prevent the process from generating useful energy.

"If the currents in a plasma are tied into a knot, the knot can eliminate most, if not all, of these instabilities because the magnetic field lines generated by the knotted current can't pass though each other," explains Grier.

Shanblatt and Grier believe that projecting a knotted optical force field into a plasma might prove to be a good way to initiate a knotted current loop. If so, the knotted current could then be ramped up by other conventional means. The result? Perhaps, a stable, high-temperature plasma capable of producing bountiful fusion energy.

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Batteries Charge Quickly and Retain Capacity, Thanks to New Structure

Braun's group developed a three-dimensional nanostructure for battery cathodes that allows for dramatically faster charging and discharging without sacrificing energy storage capacity. The researchers' findings will be published in the March 20 advance online edition of the journalNature Nanotechnology.

Aside from quick-charge consumer electronics, batteries that can store a lot of energy, release it fast and recharge quickly are desirable for electric vehicles, medical devices, lasers and military applications.

"This system that we have gives you capacitor-like power with battery-like energy," said Braun, a professor of materials science and engineering."Most capacitors store very little energy. They can release it very fast, but they can't hold much. Most batteries store a reasonably large amount of energy, but they can't provide or receive energy rapidly. This does both."

The performance of typical lithium-ion (Li-ion) or nickel metal hydride (NiMH) rechargeable batteries degrades significantly when they are rapidly charged or discharged. Making the active material in the battery a thin film allows for very fast charging and discharging, but reduces the capacity to nearly zero because the active material lacks volume to store energy.

Braun's group wraps a thin film into three-dimensional structure, achieving both high active volume (high capacity) and large current. They have demonstrated battery electrodes that can charge or discharge in a few seconds, 10 to 100 times faster than equivalent bulk electrodes, yet can perform normally in existing devices.

This kind of performance could lead to phones that charge in seconds or laptops that charge in minutes, as well as high-power lasers and defibrillators that don't need time to power up before or between pulses.

Braun is particularly optimistic for the batteries' potential in electric vehicles. Battery life and recharging time are major limitations of electric vehicles. Long-distance road trips can be their own form of start-and-stop driving if the battery only lasts for 100 miles and then requires an hour to recharge.

"If you had the ability to charge rapidly, instead of taking hours to charge the vehicle you could potentially have vehicles that would charge in similar times as needed to refuel a car with gasoline," Braun said."If you had five-minute charge capability, you would think of this the same way you do an internal combustion engine. You would just pull up to a charging station and fill up."

All of the processes the group used are also used at large scales in industry so the technique could be scaled up for manufacturing.

They key to the group's novel 3-D structure is self-assembly. They begin by coating a surface with tiny spheres, packing them tightly together to form a lattice. Trying to create such a uniform lattice by other means is time-consuming and impractical, but the inexpensive spheres settle into place automatically.

Then the researchers fill the space between and around the spheres with metal. The spheres are melted or dissolved, leaving a porous 3-D metal scaffolding, like a sponge. Next, a process called electropolishing uniformly etches away the surface of the scaffold to enlarge the pores and make an open framework. Finally, the researchers coat the frame with a thin film of the active material.

The result is a bicontinuous electrode structure with small interconnects, so the lithium ions can move rapidly; a thin-film active material, so the diffusion kinetics are rapid; and a metal framework with good electrical conductivity.

The group demonstrated both NiMH and Li-ion batteries, but the structure is general, so any battery material that can be deposited on the metal frame could be used.

"We like that it's very universal, so if someone comes up with a better battery chemistry, this concept applies," said Braun, who is also affiliated with the Materials Research Laboratory and the Beckman Institute for Advanced Science and Technology at Illinois."This is not linked to one very specific kind of battery, but rather it's a new paradigm in thinking about a battery in three dimensions for enhancing properties."

The U.S. Army Research Laboratory and the Department of Energy supported this work. Visiting scholar Huigang Zhang and former graduate student Xindi Yu were co-authors of the paper.

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Spintronics: Enhancing the Magnetism

Now, researchers with the U.S. Department of Energy (DOE) Lawrence Berkeley National Laboratory (Berkeley Lab) have been able to enhance spontaneous magnetization in special versions of the popular multiferroic material bismuth ferrite. What's more, they can turn this magnetization"on/off" through the application of an external electric field, a critical ability for the advancement of spintronic technology.

"Taking a novel approach, we've created a new magnetic state in bismuth ferrite along with the ability to electrically control this magnetism at room temperature," says Ramamoorthy Ramesh, a materials scientist with Berkeley Lab's Materials Sciences Division, who led this research."An enhanced magnetization arises in the rhombohedral phases of our bismuth ferrite self-assembled nanostructures. This magnetization is strain-confined between the tetragonal phases of the material and can be erased by the application of an electric field. The magnetization is restored when the polarity of the electric field is reversed."

Ramesh, who also holds appointments with the University of California Berkeley's Department of Materials Science and Engineering and the Department of Physics, is the corresponding author of a paper in the journalNature Communications.

Magnetoelectronic or spintronic devices store data through electron spin and its associated magnetic moment rather than the electron charge-based storage of today's electronic devices. Spin, a quantum mechanical property arising from the magnetic moment of a spinning electron, carries a directional value of either"up" or"down" that can be used to encode data in the 0s and 1s of the binary system. In addition to the size, speed and capacity advantages over electronic devices, the data storage in spintronic devices does not disappear when the electric current stops.

Multiferroics are prime candidate materials for future spintronic devices because they can simultaneously exhibit both electric and magnetic properties. Bismuth ferrite, a multiferroic composed of bismuth, iron and oxygen (BFO), has been thrust into the spintronic spotlight thanks in part to a surprising discovery in 2009 by Ramesh and his research group. They found that although bismuth ferrite is an insulator, running through its crystals are two-dimensional sheets called"domain walls" that conduct electricity. Ramesh and his group subsequently found that application of a large epitaxial strain (compression in the direction of a material's crystal planes) changes the bismuth ferrite crystal structure from its natural rhombohedral phase into a tetragonal phase. Partial relaxation of the strain creates a stable nanoscale mixture of the rhombohedral and tetragonal phases.

In this new research, Ramesh and his group have deployed epitaxial strain to create bismuth ferrite films that are a mix of highly distorted rhombohedral and tetragonal phases, in which the rhombohedral phases are mechanically confined by regions of the tetragonal phases. The magnetic moments that spontaneously arise in these special films occur within the distorted rhombohedral phase rather than at the phase interfaces and are significantly stronger than the magnetic moment that occurs in conventional bismuth ferrite.

"Normal bismuth ferrite films typically show a spontaneous magnetization of 6 to 8 electromagnetic units/cubic centimeter, which is too small for applications in a real device," says Qing (Helen) He, who was the lead author on theNatureCommunications paper."By setting our bismuth ferrite films in this special mixed phase state, we can enhance the spontaneous magnetization to approximately 30 to 40 electromagnetic units/cubic centimeter, which is large enough to be used in real devices."

Ramesh, He and their co-authors discovered that the enhanced spontaneous magnetization in their special bismuth ferrite films can be controlled through the use of an external electric field without any noticeable current passing through the film. The ability to turn the magnetization on/off in these films opens the door to their use in spintronic devices as the on/off states can serve as the 1 and 0 states of data storage. That these on/off states can be achieved without an electric current is a significant added advantage.

"In the typical magnetic memory device, the magnetic state of the material is set by an external magnetic field that is generated from the current flowing through an electromagnet," says He."Current flow needs to be driven with a lot of power and at the same time generates waste heat. Therefore, using an electric field instead of a current to control the magnetization saves energy."

The discovery that the magnetization of these special bismuth ferrite films can be controlled with an electric field was largely made possible by the use of PhotoEmission Electron Microscopy (PEEM) at Berkeley Lab's Advanced Light Source (ALS), a DOE Office of Science national user facility for synchrotron radiation. The PEEM3 microscope at ALS beamline 11.0.1 is one of the world's best instruments for studying ferromagnetic and antiferromagnetic nanoscale domains.

In addition to Ramesh and He, other co-authors of the paper were Ying-Hao Chu, John Heron, Seung-Yeul Yang, Wen-I Laing, Chang-Yang Kuo, Hong-Ji Lin, Pu Yu, Chen-Wei Liang, Robert Zeches, Wei-Chen Kuo, Jenh-Yih Juang, Chien-Te Chen, Elke Arenholz and Andreas Scholl.

This research was primarily supported by the DOE Office of Science.

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Graphene Cloak Protects Bacteria, Leading to Better Images

Vikas Berry, assistant professor of chemical engineering at Kansas State University, and his research team are wrapping bacteria with graphene to address current challenges with imaging bacteria under electron microscopes. Berry's method creates a carbon cloak that protects the bacteria, allowing them to be imaged at their natural size and increasing the image's resolution.

Graphene is a form of carbon that is only one atom thick, giving it several important properties: it's impermeable, it's the strongest nanomaterial, it's optically transparent and it has high thermal conductance.

"Graphene is the next-generation material," Berry said."Although only an atom thick, graphene does not allow even the smallest of molecules to pass through. Furthermore, it's strong and highly flexible so it can conform to any shape."

Berry's team has been researching graphene for three years, and Berry recently saw a connection between graphene and cell imaging research. Because graphene is impermeable, he decided to use the material to preserve the size of bacterial cells imaged under high-vacuum electron microscopes.

The research results appear in the paper"Impermeable Graphenic Encasement of Bacteria," which was published in a recent issue ofNano Letters, a monthly scientific journal published by the American Chemical Society. The team's preliminary research appeared in Nature News in 2010.

The current challenge with cell imaging occurs when scientists use electron microscopes to image bacterial cells. Because these microscopes require a high vacuum, they remove water from the cells. Biological cells contain 70 to 80 percent water, and the result is a severely shrunk cell. As a result, it is challenging to obtain an accurate image of the cells and their components in their natural state.

But Berry and his team created a solution to the imaging challenge by applying graphene. The graphene acts as an impermeable cloak around the bacteria so that the cells retain water and don't shrink under the high vacuum of electron microscopes. This provides a microscopic image of the cell at its natural size.

The carbon cloaks can be wrapped around the bacteria using two methods. The first method involves putting a sheet of graphene on top of the bacteria, much like covering up with a bed sheet. The other method involves wrapping the bacteria with a graphene solution, where the graphene sheets swaddle the bacteria. In both cases the graphene sheets were functionalized with a protein to enhance binding with the bacterial cell wall.

Under the high vacuum of an electron microscope, the wrapped bacteria did not change in size for 30 minutes, giving scientists enough time to observe them. This is a direct result of the high strength and impermeability of the graphene cloak, Berry said.

Graphene's other extraordinary properties enhance the imaging resolution in microscopy. Its electron-transparency enables a clean imaging of the cells. Since graphene is a good conductor of heat and electricity, the local electronic-charging and heating is conducted off the graphene cloak, giving a clear view of the bacterial cell well. Unwrapped bacterial cells appear dark with an indistinguishable cell wall.

"Uniquely, graphene has all the properties needed to image bacteria at high resolutions," Berry said."The project provides a very simple route to image samples in their native wet state."

The process has potential to influence future research. Scientists have always had trouble observing liquid samples under electron microscopes, but using carbon cloaks could allow them to image wet samples in a vacuum. Graphene's strong and impermeable characteristics ensure that wrapped cells can be easily imaged without degrading them. Berry said it might be possible in the future to use graphene to keep bacterium alive in a vacuum while observing its biochemistry under a microscope.

The research also paves the way for enhanced protein microscopy. Proteins act differently when they are dry and when they are in an aqueous solution. So far most protein studies have been conducted in dry phases, but Berry's research may allow proteins to be observed more in aqueous environments.

"This research could be the point of evolution for processing of sensitive samples with graphene to achieve enhanced imaging," Berry said.

Other researchers involved in the project include Daniel Boyle, research assistant professor in biology; Nihar Mohanty, doctoral student in chemical engineering, India; Ashvin Nagaraja, former master's student in electrical engineering; and Monica Fahrenholtz, a May 2010 chemical engineering graduate from Clearwater.

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Electric Grid Reliability: Increasing Energy Storage in Vanadium Redox Batteries by 70 Percent

In a paper published by the journalAdvanced Energy Materials,researchers at the Department of Energy's Pacific Northwest National Laboratory found that adding hydrochloric acid to the sulfuric acid typically used in vanadium batteries increased the batteries' energy storage capacity by 70 percent and expanded the temperature range in which they operate.

"Our small adjustments greatly improve the vanadium redox battery," said lead author and PNNL chemist Liyu Li."And with just a little more work, the battery could potentially increase the use of wind, solar and other renewable power sources across the electric grid."

Unlike traditional power, which is generated in a reliable, consistent stream of electricity by controlling how much coal is burned or water is sent through dam turbines, renewable power production depends on uncontrollable natural phenomena such as sunshine and wind. Storing electricity can help smooth out the intermittency of renewable power while also improving the reliability of the electric grid that transmits it. Vanadium batteries can hold on to renewable power until people turn on their lights and run their dishwashers. Other benefits of vanadium batteries include high efficiency and the ability to quickly generate power when it's needed as well as sit idle for long periods of time without losing storage capacity.

A vanadium battery is a type of flow battery, meaning it generates power by pumping liquid from external tanks to the battery's central stack, or a chamber where the liquids are mixed. The tanks contain electrolytes, which are liquids that conduct electricity. One tank has the positively-charged vanadium ion V5+ floating in its electrolyte. And the other tank holds an electrolyte full of a different vanadium ion, V2+. When energy is needed, pumps move the ion-saturated electrolyte from both tanks into the stack, where a chemical reaction causes the ions to change their charge, creating electricity.

To charge the battery, electricity is sent to the vanadium battery's stack. This causes another reaction that restores the original charge of vanadium ions. The electrical energy is converted into chemical energy stored in the vanadium ions. The electrolytes with their respective ions are pumped back into to their tanks, where they wait until electricity is needed and the cycle is started again.

A battery's capacity to generate electricity is limited by how many ions it can pack into the electrolyte. Vanadium batteries traditionally use pure sulfuric acid for their electrolyte. But sulfuric acid can only absorb so many vanadium ions.

Another drawback is that sulfuric acid-based vanadium batteries only work between about 50 and 104 degrees Fahrenheit (10 to 40 Celsius). Below that temperature range, the ion-infused sulfuric acid crystallizes. The larger concern, however, is the battery overheating, which causes an unwanted solid to form and renders the battery useless. To regulate the temperature, air conditioners or circulating cooling water are used, which causes up to 20 percent energy loss and significantly increasing the battery's operating cost, the researchers noted.

Wanting to improve the battery's performance, Li and his colleagues began searching for a new electrolyte. They tried a pure hydrochloric acid electrolyte, but found it caused one of the vanadium ions to form an unwanted solid. Next, they experimented with various mixtures of both hydrochloric and sulfuric acids. PNNL scientists found the ideal balance when they mixed 6 parts hydrochloric acid with 2.5 parts sulfuric acid. They verified the electrolyte and ion molecules present in the solution with a nuclear magnetic resonance instrument and the Chinook supercomputer at EMSL, DOE's Environmental Molecular Sciences Laboratory at PNNL.

Tests showed that the new electrolyte mixture could hold 70 percent more vanadium ions, making the battery's electricity capacity 70 percent higher. The discovery means that smaller tanks can be used to generate the same amount of power as larger tanks filled with the old electrolyte.

And the new mixture allowed the battery to work in both warmer and colder temperatures, between 23 and 122 degrees Fahrenheit (-5 to 50 Celsius), greatly reducing the need for costly cooling systems. At room temperature, a battery with the new electrolyte mixture maintained an 87 percent energy efficiency rate for 20 days, which is about the same efficiency of the old solution.

The results are promising, but more research is needed, the authors noted. The battery's stack and overall physical structure could be improved to increase power generation and decrease cost.

"Vanadium redox batteries have been around for more than 20 years, but their use has been limited by a relatively narrow temperature range," Li said."Something as simple as adjusting the batteries' electrolyte means they can be used in more places without having to divert power output to regulate heat."

This research was supported by DOE's Office of Electricity Delivery and Energy Reliability and internal PNNL funding.

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Room-Temperature Spintronic Computers Coming Soon? Silicon Spin Transistors Heat Up and Spins Last Longer

"Electronic devices mostly use the charge of the electrons -- a negative charge that is moving," says Ashutosh Tiwari, an associate professor of materials science and engineering at the University of Utah."Spintronic devices will use both the charge and the spin of the electrons. With spintronics, we want smaller, faster and more power-efficient computers and other devices."

Tiwari and Ph.D. student Nathan Gray report their creation of room-temperature, spintronic transistors on a silicon semiconductor this month in the journalApplied Physics Letters. The research -- in which electron"spin" aligned in a certain way was injected into silicon chips and maintained for a record 276 trillionths of a second -- was funded by the National Science Foundation.

"Almost every electronic device has silicon-based transistors in it," Gray says."The current thrust of industry has been to make those transistors smaller and to add more of them into the same device" to process more data. He says his and Tiwari's research takes a different approach.

"Instead of just making transistors smaller and adding more of them, we make the transistors do more work at the same size because they have two different ways {electron charge and spin} to manipulate and process data," says Gray.

A Quick Spin through Spintronics

Modern computers and other electronic devices work because negatively charged electrons flow as electrical current. Transistors are switches that reduce computerized data to a binary code of ones or zeros represented by the presence or absence of electrons in semiconductors, most commonly silicon.

In addition to electric charge, electrons have another property known as spin, which is like the electron's intrinsic angular momentum. An electron's spin often is described as a bar magnet that points up or down, which also can represent ones and zeroes for computing.

Most previous research on spintronic transistors involved using optical radiation -- in the form of polarized light from lasers -- to orient the electron spins in non-silicon materials such as gallium arsenide or organic semiconductors at supercold temperatures.

"Optical methods cannot do that with silicon, which is the workhorse of the semiconductor and electronics industry, and the industry doesn't want to retool for another material," Tiwari says.

"Spintronics will become useful only if we use silicon," he adds.

The Experiment

In the new study, Tiwari and Gray used electricity and magnetic fields to inject"spin polarized carriers" -- namely, electrons with their spins aligned either all up or all down -- into silicon at room temperature.

Their trick was to use magnesium oxide as a"tunnel barrier" to get the aligned electron spins to travel from one nickel-iron electrode through the silicon semiconductor to another nickel-iron electrode. Without the magnesium oxide, the spins would get randomized almost immediately, with half up and half down, Gray says.

"This thing works at room temperature," Tiwari says."Most of the devices in earlier studies have to be cooled to very low temperatures" -- colder than 200 below zero Fahrenheit -- to align the electrons' spins either all up or all down."Our new way of putting spin inside the silicon does not require any cooling."

The experiment used a flat piece of silicon about 1 inch long, about 0.3 inches wide and one-fiftieth of an inch thick. An ultra-thin layer of magnesium oxide was deposited on the silicon wafer. Then, one dozen tiny transistors were deposited on the silicon wafer so they could be used to inject electrons with aligned spins into the silicon and later detect them.

Each nickel-iron transistor had three contacts or electrodes: one through which electrons with aligned spins were injected into the silicon and detected, a negative electrode and a positive electrode used to measure voltage.

During the experiment, the researchers send direct current through the spin-injector electrode and negative electrode of each transistor. The current is kept steady, and the researchers measure variations in voltage while applying a magnetic field to the apparatus

"By looking at the change in the voltage when we apply a magnetic field, we can find how much spin has been injected and the spin lifetime," Tiwari says.

A 328 Nanometer, 276 Picosecond Step for Spintronics

For spintronic devices to be practical, electrons with aligned spins need to be able to move adequate distances and retain their spin alignments for an adequate time.

During the new study, the electrons retained their spins for 276 picoseconds, or 276 trillionths of a second. And based on that lifetime, the researchers calculate the spin-aligned electrons moved through the silicon 328 nanometers, which is 328 billionths of a meter or about 13 millionths of an inch.

"It's a tiny distance for us, but in transistor technology, it is huge," Gray says."Transistors are so small today that that's more than enough to get the electron where we need it to go."

"Those are very good numbers," Tiwari says."These numbers are almost 10 times bigger than what we need {for spintronic devices} and two times bigger than if you use aluminum oxide" instead of the magnesium oxide in his study.

He says Dutch researchers previously were able to inject aligned spins into silicon using aluminum oxide as the"tunneling medium," but the new study shows magnesium oxide works better.

The new study's use of electronic spin injection is much more practical than using optical methods such as lasers because lasers are too big for chips in consumer electronic devices, Tiwari says.

He adds that spintronic computer processors require little power compared with electronic devices, so a battery that may power an electronic computer for eight hours might last more than 24 hours on a spintronic computer.

Gray says spintronics is"the next big step to push the limits of semiconductor technology that we see in every aspect of our lives: computers, cell phones, GPS (navigation) devices, iPods, TVs."

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Ferroelectric Materials Discovery Could Lead to Better Memory Chips

In ferroelectric memory the direction of molecules' electrical polarization serves as a 0 or a 1 bit. An electric field is used to flip the polarization, which is how data is stored.

With his colleagues at U-M and collaborators from Cornell University, Penn State University, and University of Wisconsin, Madison, Xiaoqing Pan, a professor in the U-M Department of Materials Science and Engineering, has designed a material system that spontaneously forms small nano-size spirals of the electric polarization at controllable intervals, which could provide natural budding sites for the polarization switching and thus reduce the power needed to flip each bit.

"To change the state of a ferroelectric memory, you have to supply enough electric field to induce a small region to switch the polarization. With our material, such a nucleation process is not necessary," Pan said."The nucleation sites are intrinsically there at the material interfaces."

To make this happen, the engineers layered a ferroelectric material on an insulator whose crystal lattices were closely matched. The polarization causes large electric fields at the ferroelectric surface that are responsible for the spontaneous formation of the budding sites, known as"vortex nanodomains."

The researchers also mapped the material's polarization with atomic resolution, which was a key challenge, given the small scale. They used images from a sub-angstrom resolution transmission electron microscope at Lawrence Berkeley National Laboratory. They also developed image processing software to accomplish this.

"This type of mapping has never been done," Pan said."Using this technique, we've discovered unusual vortex nanodomains in which the electric polarization gradually rotates around the vortices."

This research is funded by the Department of Energy, the National Science Foundation and the U.S. Army Research Office.

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Materials Identified That May Deliver More 'Bounce'

The alloys could be used in springier blood vessel stents, sensitive microphones, powerful loudspeakers, and components that boost the performance of medical imaging equipment, security systems and clean-burning gasoline and diesel engines.

While these nanostructured metal alloys are not new -- they are used in turbine blades and other parts demanding strength under extreme conditions -- the Rutgers researchers are pioneers at investigating these new properties.

"We have been doing theoretical studies on these materials, and our computer modeling suggests they will be super-responsive," said Armen Khachaturyan, professor of Materials Science and Engineering in the Rutgers School of Engineering. He and postdoctoral researcher Weifeng Rao believe these materials can be a hundred times more responsive than today's materials in the same applications.

Writing in the March 11 issue of the journalPhysical Review Letters, the researchers describe how this class of metals with embedded nanoparticles can be highly elastic, or"springy," and can convert electrical and magnetic energy into movement or vice-versa. Materials that exhibit these properties are known among scientists and engineers as"functional" materials.

One class of functional materials generates an electrical voltage when the material is bent or compressed. Conversely, when the material is exposed to an electric field, it will deform. Known as piezoelectric materials, they are used in ultrasound instruments; audio components such as microphones, speakers and even venerable record players; autofocus motors in some camera lenses; spray nozzles in inkjet printer cartridges; and several types of electronic components.

In another class of functional materials, changes in magnetic fields deform the material and vice-versa. These magnetorestrictive materials have been used in naval sonar systems, pumps, precision optical equipment, medical and industrial ultrasonic devices, and vibration and noise control systems.

The materials that Khachaturyan and Rao are investigating are technically known as"decomposed two-phase nanostructured alloys." They form by cooling metals that were exposed to high temperatures at which the nanosized particles of one crystal structure, or phase, are embedded into another type of phase. The resulting structure makes it possible to deform the metal under an applied stress while allowing the metal to snap back into place when the stress is removed.

These nanostructured alloys might be more effective than traditional metals in applications such blood vessel stents, which have to be flexible but can't lose their"springiness." In the piezoelectric and magnetorestrictive components, the alloy's potential to snap back into shape after deforming -- a property known as non-hysteresis -- could improve energy efficiency over traditional materials that require energy input to restore their original shapes.

In addition to potentially showing responses far greater than traditional materials, the new materials may be tunable; that is, they may exhibit smaller or larger shape changes and output force based on varying mechanical, electrical or magnetic input and the material processing.

The researchers hope to test the results of their computer simulations on actual metals in the near future.

The Rutgers team collaborated with Manfred Wittig, professor of Materials Science and Engineering at the University of Maryland. Their research was funded by the National Science Foundation and the U.S. Department of Energy.

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Electromechanical Circuit Sets Record Beating Microscopic 'Drum'

Described in the March 10 issue ofNature, the NIST experiments created strong interactions between microwave light oscillating 7.5 billion times per second and a"micro drum" vibrating at radio frequencies 11 million times per second. Compared to previously reported experiments combining microscopic machines and electromagnetic radiation, the rate of energy exchange in the NIST device -- the"coupling" that reflects the strength of the connection -- is much stronger, the mechanical vibrations last longer, and the apparatus is much easier to make.

Similar in appearance to an Irish percussion instrument called a bodhrán, the NIST drum is a round aluminum membrane 100 nanometers thick and 15 micrometers wide, lightweight and flexible enough to vibrate freely yet larger and heavier than the nanowires typically used in similar experiments.

"The drum is so much larger than nanowires physically that you can make this coupling strength go through the roof," says first author John Teufel, a NIST research affiliate who designed the drum."The drum hits a perfect compromise where it's still microscale but you can couple to it strongly."

The NIST experiments shifted the microwave energy by 56 megahertz (MHz, or million cycles per second) per nanometer of drum motion, 1,000 times more than the previous state of the art.

"We turned up the rate at which these two things talk to each other," Teufel says.

The drum is incorporated into a superconducting cavity cooled to 40 milliKelvin, a temperature at which aluminum allows electric current to flow without resistance -- a quantum property. Scientists apply microwaves to the cavity. Then, by applying a drive tone set at the difference between the frequencies of the microwave radiation particles (photons) and the drum, researchers dramatically increase the overall coupling strength to make the two systems communicate faster than their energy dissipates. The microwaves can be used to measure and control the drum vibrations, and vice versa. The drum motion will persist for hundreds of microseconds, according to the paper, a relatively long time in the fast-paced quantum world.

In engineering terms, the drum acts as a capacitor -- a device that holds electric charge. Its capacitance, or ability to hold charge, depends on the position of the drum about 50 nanometers above an aluminum electrode. When the drum vibrates, the capacitance changes and the mechanical motion modulates the properties of the electrical circuit. The same principle is at work with a microphone and FM radio, but here the natural drum motion, mostly at one frequency, is transmitted to the listener in the lab.

The experiment is a step towards entanglement -- a curious quantum state linking the properties of objects -- between the microwave photons and the drum motion, Teufel says. The apparatus has the high coupling strength and low energy losses needed to generate entanglement, he says. Further experiments will address whether the mechanical drumbeats obey the rules of quantum mechanics, which govern the behavior of light and atoms.

The drum is a key achievement in NIST's effort to develop components for superconducting quantum computers and quantum simulations, while also working toward the widely sought scientific goal of making the most precise measurements possible of mechanical motion.

Quantum computers, if they can be built, could solve certain problems that are intractable today. The microwave and radiofrequency signals in the new electromechanical circuit could be used to represent quantum information. NIST scientists plan to combine the new circuit with superconducting quantum bits to create and manipulate motion of relatively large objects on the smallest (quantum) scales.

The experiment reported inNatureis a prelude to cooling the drum to its"ground state," or lowest-energy state. Starting from the ground state, the drum could be manipulated for the applications mentioned above. In addition, such control would enable tests of the boundary between the everyday classical and quantum worlds. The drum also has possible practical applications such as measuring length and force with sensitivities at levels of attometers (billionths of a billionth of a meter) and attonewtons (billionths of a billionth of a newton), respectively.

As a non-regulatory agency, NIST promotes U.S. innovation and industrial competitiveness by advancing measurement science, standards and technology in ways that enhance economic security and improve our quality of life.

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Extremely Fast Magnetic Random Access Memory (MRAM) Computer Data Storage Within Reach

An invention made by the Physikalisch-Technische Bundesanstalt (PTB) changes this situation: A special chip connection, in association with dynamic triggering of the component, reduces the response from -- so far -- 2 ns to below 500 ps. This corresponds to a data rate of up to 2 GBit (instead of the approx. 400 MBit so far). Power consumption and the thermal load will be reduced, as well as the bit error rate. The European patent is just being granted this spring; the US patent was already granted in 2010. An industrial partner for further development and manufacturing such MRAMs under licence is still being searched for.

Fast computer storage chips like DRAM and SRAM (Dynamic and Static Random Access Memory) which are commonly used today, have one decisive disadvantage: in the case of an interruption of the power supply, the information stored on them is irrevocably lost. The MRAM promises to put an end to this. In the MRAM, the digital information is not stored in the form of an electric charge, but via the magnetic alignment of storage cells (magnetic spins). MRAMs are very universal storage chips because they allow -- in addition to the non-volatile information storage -- also faster access, a high integration density and an unlimited number of writing and reading cycles.

However, the current MRAM models are not yet fast enough to outperform the best competitors. The time for programming a magnetic bit amounts to approx. 2 ns. Whoever wants to speed this up, reaches certain limits which have something to do with the fundamental physical properties of magnetic storage cells: during the programming process, not only the desired storage cell is magnetically excited, but also a large number of other cells. These excitations -- the so-called magnetic ringing -- are only slightly attenuated, their decay can take up to approx. 2 ns, and during this time, no other cell of the MRAM chip can be programmed. As a result, the maximum clock rate of MRAM is, so far, limited to approx. 400 MHz.

Until now, all experiments made to increase the velocity have led to intolerable write errors. Now, PTB scientists have optimized the MRAM design and integrated the so-called ballistic bit triggering which has also been developed at PTB. Here, the magnetic pulses which serve for the programming are selected in such a skilful way that the other cells in the MRAM are hardly magnetically excited at all. The pulse ensures that the magnetization of a cell which is to be switched performs half a precision rotation (180°), while a cell whose storage state is to remain unchanged performs a complete precision rotation (360°). In both cases, the magnetization is in the state of equilibrium after the magnetic pulse has decayed, and magnetic excitations do not occur any more.

This optimal bit triggering also works with ultra-short switching pulses with a duration below 500 ps. The maximum clock rates of the MRAM are, therefore, above 2 GHz. In addition, several bits can be programmed at the same time which would allow the effective write rate per bit to be increased again by more than one order. This invention allows clock rates to be achieved with MRAM which can compete with those of the fastest volatile storage components.

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Student Innovation Transmits Data and Power Wirelessly Through Submarine Hulls

Lawry, a student in the Department of Electrical, Computer, and Systems Engineering at Rensselaer, is one of three finalists for the 2011$30,000 Lemelson-MIT Rensselaer Student Prize. 

Lawry's project is titled"A High-Performance System for Wireless Transmission of Power and Data Through Solid Metallic Enclosures," and his faculty adviser is Gary Saulnier, professor of electrical, computer, and systems engineering at Rensselaer.

In our increasingly tetherless world, wires have been all but replaced by more convenient wireless connections in homes and offices -- everything from phones and accessing the Internet to keyboards and printers. In the area of defense, a progression from wired to wireless systems presents an opportunity to improve the safety of naval vessels. Presently, to install critical safety sensors on the exterior of ships and submarines, the U.S. Navy is forced to drill holes in the hull through which cables for data and power transmission are run. Each hole increases the risk of potentially serious issues, including leaks and structural failure. Additionally, installing these sensors on commissioned vessels requires the use of a drydock or cofferdam, which can take months and cost millions of dollars.

Lawry's invention solves this problem. Unlike conventional electromagnetic wireless systems, which are ineffective at transmitting power and data through vessel hulls because of the"Faraday cage" shielding effects they present, his patent-pending system uses ultrasound -- high-frequency acoustic waves -to easily propagate signals through thick metals and other solids. Piezoelectric transducers are used to convert electrical signals into acoustic signals and vice versa, allowing his system to form wireless electrical bridges across these barriers. Lawry's clever design features separate non-interfering ultrasonic channels for independent data and power transmission.

With this new system, Lawry has demonstrated the simultaneous, continuous delivery of 50 watts of power and 12.4 megabytes per second (Mbps) of data through a 2.5-inch-thick solid steel block in real time. These results far surpass all known previously published systems capable of simultaneous data and power transmission through metal. With only minor modifications, Lawry said he's confident his design will have the capacity to support much higher power levels and data rates. His invention uses a powerful communication technology that allows the transmission system to adapt to non-ideal conditions and mechanical variations over time. This is critical for ensuring successful operation of the system in real-world conditions outside of a controlled laboratory environment.

Lawry's complex combination of electronic and acoustic hardware, signal generation and detection technology, and power generation and collection equipment shares many characteristics with a state-of-the-art communications system such as a cellular phone. Using the three main building blocks of electrical engineering -- power, communications, and computing -- Lawry has developed a system that can communicate through a thick metal wall without the need for a battery or any supplemental power source. This means sensors on the outer hull of submarines can be made to work with systems on the other side of the wall for many years without the need for human intervention.

In addition to the hulls of ships and submarines, Lawry said his wireless data and power system could benefit many other applications where it is necessary or advantageous to continually power and monitor sensor networks in isolated environments. For example, his system could be used to power and communicate with sensors in nuclear reactors, chemical processing equipment, oil drilling equipment and pipelines, armored vehicles, un-manned underwater deep-sea exploration vehicles, or even space shuttles and satellites.

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Probing Atomic Chicken Wire: Mounting Graphene on Boron Nitride Dramatically Improves Electronic Properties

In addition to potential applications in integrated circuits, solar cells, miniaturized bio devices and gas molecule sensors, the material has attracted the attention of physicists for its unique properties in conducting electricity on an atomic level.

Graphene has very little resistance and allows electrons to behave as massless particles like photons, or light particles, while traveling through the hexagonal grid at very high speeds.

The study of the physical properties and potential applications of graphene, however, has suffered from a lack of suitable carrier materials that can support a flat graphene layer while not interfering with its electrical properties.

Researchers in the University of Arizona's physics department along with collaborators from the Massachusetts Institute of Technology and the National Materials Science Institute in Japan have now taken an important step forward toward overcoming those obstacles.

They found that by placing the graphene layer on a material almost identical in structure, instead of the commonly used silicon oxide found in microchips, they could significantly improve its electronic properties.

Substituting silicon wafers with boron nitride, a graphene-like structure consisting of boron and nitrogen atoms in place of the carbon atoms, the group was the first to measure the topography and electrical properties of the resulting smooth graphene layer with atomic resolution.

The results are published in the advance online publication ofNature Materials.

"Structurally, boron nitride is basically the same as graphene, but electronically, it's completely different," said Brian LeRoy, an assistant professor of physics and senior author of the study."Graphene is a conductor, boron nitride is an insulator."

"We want our graphene to sit on something insulating, because we are interested in studying the properties of the graphene alone. For example, if you want to measure its resistance, and you put it on metal, you're just going to measure the resistance of the metal because it's going to conduct better than the graphene."

Unlike silicon, which is traditionally used in electronics applications, graphene is a single sheet of atoms, making it a promising candidate in the quest for ever smaller electronic devices. Think going from a paperback to a credit card.

"It's as small as you can shrink it down," LeRoy said."It's a single layer, you'll never get half a layer or something like that. You could say graphene is the ultimate in making it small, yet it 's still a good conductor."

Stacked upon each other, 3 million sheets of graphene would amount to only 1 millimeter. The thinnest material on Earth, graphene brought the 2010 Nobel Prize to Andre Geim and Konstantin Novoselov, who were able to demonstrate its exceptional properties with relation to quantum physics.

"Using a scanning tunneling microscope, we can look at atoms and study them," he added."When we put graphene on silicon oxide and look at the atoms, we see bumps that are about a nanometer in height."

While a nanometer -- a billionth of a meter -- may not sound like much, to an electron whizzing along in a grid of atoms, it's quite a bump in the road.

"It's basically like a piece of paper that has little crinkles in it," LeRoy explains."But if you put the paper, in this case the graphene, on boron nitride, it's much flatter. It smooths out the bumps by an order of magnitude."

LeRoy admits the second effect achieved by his research team is a bit harder to explain.

"When you have graphene sitting on silicon oxide, there are trapped electric charges inside the silicon oxide in some places, and these induce some charge in the overlying graphene. You get quite a bit of variation in the density of electrons. If graphene sits on boron nitride, the variation is two orders of magnitude less."

In his lab, LeRoy demonstrates the first -- and surprisingly low-tech -- step in characterizing the graphene samples: He places a tiny flake of graphite -- the stuff that makes up pencil"lead" -- on sticky tape, folds it back on itself and peels it apart again, in a process reminiscent of a Rorschach Test.

"You fold this in half," he explained,"and again, and again, until it gets thin. Graphene wants to peel off into these layers, because the bonds between the atoms in the horizontal layer are strong, but weak between atoms belonging to different layers. When you put this under an optical microscope, there will be regions with one, two, three, four or more layers. Then you just search for single-layer ones using the microscope."

"It's hard to find the sample because it's very, very small," said Jiamin Xue, a doctoral student in LeRoy's lab and the paper's leading author."Once we find it, we put it between two gold electrodes so we can measure the conductance."

To measure the topography of the graphene surface, the team uses a scanning tunneling microscope, which has an ultrafine tip that can be moved around.

"We move the tip very close to the graphene, until electrons start tunneling to it," Xue explained."That's how we can see the surface. If there is a bump, the tip moves up a bit."

For the spectroscopic measurement, Xue holds the tip at a fixed distance above the sample. He then changes the voltage and measures how much current flows as a function of that voltage and any given point across the sample. This allows him to map out different energy levels across the sample.

"You want as thin an insulator as possible," LeRoy added."The initial idea was to pick something flat but insulating. Because boron nitride essentially has the same structure as graphene, you can peel it into layers in the same way. Therefore, we use a metal as a base, put a thin layer of boron nitride on it and then graphene on top."

The UA portion of this research was funded by the U.S. Army Research Office and the National Science Foundation.

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