Trapping sunlight with silicon nanowires

Solar cells made from silicon are projected to be a prominent factor in future renewable green energy equations, but so far the promise has far exceeded the reality. While there are now silicon photovoltaics that can convert sunlight into electricity at impressive 20 percent efficiencies, the cost of this solar power is prohibitive for large-scale use. Researchers with the Lawrence Berkeley National Laboratory (Berkeley Lab), however, are developing a new approach that could substantially reduce these costs. The key to their success is a better way of trapping sunlight.

"Through the fabrication of thin films from ordered arrays of vertical silicon nanowires we've been able to increase the light-trapping in our solar cells by a factor of 73," says chemist Peidong Yang, who led this research.

Caption: A radial p-n junction consists of a layer of n-type silicon forming a shell around a p-type silicon nanowire core. This geometry turns each individual nanowire into a photovoltaic cell. Credit: Image courtesy of Peidong Yang. Usage Restrictions: None. Caption: This photovoltaic cell is comprised of 36 individual arrays of silicon nanowires featuring radial p-n junctions. The color dispersion demonstrates the excellent periodicity present over the entire substrate. Credit: Photo courtesy of Peidong Yang. Usage Restrictions: None.

"Since the fabrication technique behind this extraordinary light-trapping enhancement is a relatively simple and scalable aqueous chemistry process, we believe our approach represents an economically viable path toward high-efficiency, low-cost thin-film solar cells." Yang holds joint appointments with Berkeley Lab's Materials Sciences Division, and the University of California Berkeley's Chemistry Department. He is a leading authority on semiconductor nanowires - one-dimensional strips of materials whose width measures only one-thousandth that of a human hair but whose length may stretch several microns. "Typical solar cells are made from very expensive ultrapure single crystal silicon wafers that require about 100 micrometers of thickness to absorb most of the solar light, whereas our radial geometry enables us to effectively trap light with nanowire arrays fabricated from silicon films that are only about eight micrometers thick," he says. "Furthermore, our approach should in principle allow us to use metallurgical grade or "dirty" silicon rather than the ultrapure silicon crystals now required, which should cut costs even further." Yang has described this research in a paper published in the journal Nano Letters, which he co-authored with Erik Garnett, a chemist who was then a member of Yang's research group. The paper is titled "Light Trapping in Silicon Nanowire Solar Cells." Generating Electricity from Sunlight At the heart of all solar cells are two separate layers of material, one with an abundance of electrons that functions as a negative pole, and one with an abundance of electron holes (positively-charged energy spaces) that functions as a positive pole.

When photons from the sun are absorbed, their energy is used to create electron-hole pairs, which are then separated at the interface between the two layers and collected as electricity.

Because of its superior photo-electronic properties, silicon remains the photovoltaic semiconductor of choice but rising demand has inflated the price of the raw material. Furthermore, because of the high-level of crystal purification required, even the fabrication of the simplest silicon-based solar cell is a complex, energy-intensive and costly process.

Yang and his group are able to reduce both the quantity and the quality requirements for silicon by using vertical arrays of nanostructured radial p-n junctions rather than conventional planar p-n junctions. In a radial p-n junction, a layer of n-type silicon forms a shell around a p-type silicon nanowire core. As a result, photo-excited electrons and holes travel much shorter distances to electrodes, eliminating a charge-carrier bottleneck that often arises in a typical silicon solar cell. The radial geometry array also, as photocurrent and optical transmission measurements by Yang and Garrett revealed, greatly improves light trapping.

"Since each individual nanowire in the array has a p-n junction, each acts as an individual solar cell," Yang says. "By adjusting the length of the nanowires in our arrays, we can increase their light-trapping path length."

While the conversion efficiency of these solar nanowires was only about five to six percent, Yang says this efficiency was achieved with little effort put into surface passivation, antireflection, and other efficiency-increasing modifications.

"With further improvements, most importantly in surface passivation, we think it is possible to push the efficiency to above 10 percent," Yang says.

Combining a 10 percent or better conversion efficiency with the greatly reduced quantities of starting silicon material and the ability to use metallurgical grade silicon, should make the use of silicon nanowires an attractive candidate for large-scale development.

As an added plus Yang says, "Our technique can be used in existing solar panel manufacturing processes." ###

This research was funded by the National Science Foundation's Center of Integrated Nanomechanical Systems.

Berkeley Lab is a U.S. Department of Energy national laboratory located in Berkeley, California. It conducts unclassified scientific research for DOE's Office of Science and is managed by the University of California. Visit our website at www.lbl.gov.

Contact: Lynn Yarris lcyarris@lbl.gov 510-486-5375 DOE/Lawrence Berkeley National Laboratory

Helping hydrogen: Student inventor tackles challenge of hydrogen storage VIDEO

$30,000 Lemelson-MIT Collegiate Student Prizes awarded to inventive students nationwide; 4 leading institutes celebrate 2010 winners.

Troy, N.Y. – Determined to play a key role in solving global dependency on fossil fuels, Javad Rafiee, a doctoral student in the Department of Mechanical, Aerospace, and Nuclear Engineering at Rensselaer Polytechnic Institute, has developed a new method for storing hydrogen at room temperature.

Rafiee has created a novel form of engineered graphene that exhibits hydrogen storing capacity far exceeding any other known material.

Caption: Innovations in composites manufacturing, graphene-based hydrogen storage, and more efficient LEDs faced off for this year's $30,000 Lemelson-MIT Rensselaer Student Prize. Watch the three finalists, Casey Hoffman, Javad Rafiee, and Jiuru Xu explain their projects. Credit: Rensselaer. Usage Restrictions: please include video credit. Caption: Determined to play a key role in solving global dependency on fossil fuels, Javad Rafiee, a doctoral student at Rensselaer Polytechnic Institute, has developed a new method for storing hydrogen at room temperature. Rafiee has created a novel form of engineered graphene that exhibits hydrogen storing capacity far exceeding any other known material. For this innovation, which brings the world a step closer to realizing the widespread adoption of clean, abundant hydrogen as a fuel for transportation vehicles, Rafiee is the winner of the 2010 $30,000 Lemelson-MIT Rensselaer Student Prize. Credit: Rensselaer/Kris Qua. Usage Restrictions: Please include Photo Credit.

For this innovation, which brings the world a step closer to realizing the widespread adoption of clean, abundant hydrogen as a fuel for transportation vehicles, Rafiee is the winner of the 2010 $30,000 Lemelson-MIT Rensselaer Student Prize. He is among the four 2010 $30,000 Lemelson-MIT Collegiate Student Prize winners announced today. "Invention is the key ingredient of progress, and the Lemelson-MIT Rensselaer Student Prize rallies our students to innovate world-changing solutions for the grand challenges facing all people of all nations," said Rensselaer President Shirley Ann Jackson. "Javad Rafiee has the vision of a robust national hydrogen economy and a world less dependent on oil and gasoline. I applaud his efforts toward this noble goal, and congratulate him on this prestigious award. I thank all of the Lemelson-MIT Rensselaer Collegiate Student Prize winners and finalists for their effort, zeal, and for being ambassadors of progress." Rafiee is the fourth recipient of the Lemelson-MIT Rensselaer Student Prize. The prize, first given in 2007, is awarded annually to a Rensselaer senior or graduate student who has created or improved a product or process, applied a technology in a new way, redesigned a system, or demonstrated remarkable inventiveness in other ways. "This year's winners from the Massachusetts Institute of Technology, California Institute of Technology, Rensselaer Polytechnic Institute, and University of Illinois at Urbana-Champaign shine light on the significance of collegiate invention. They have the ability to transform seemingly implausible ideas into reality and are the true entrepreneurial leaders of their generation," said Joshua Schuler, executive director of the Lemelson-MIT Program. Enabling Greener Transportation with Graphene Hydrogen storage has proven to be a significant bottleneck to the advancement and proliferation of fuel cell and hydrogen technologies in cars, trucks, and other applications. Rafiee has developed a new method for manufacturing and using graphene, an atom-thick sheet of carbon atoms arranged like a nanoscale chain-link fence, to store hydrogen.

His solution is inexpensive and easy to produce.

With adviser and Rensselaer Professor Nikhil Koratkar, Rafiee used a combination of mechanical grinding, plasma treatment, and annealing to engineer the atomic structure of graphene to maximize its hydrogen storage capacity. This new graphene has exhibited a hydrogen storage capacity of 14 percent by weight at room temperature – far exceeding any other known material.

This 14-percent capacity surpasses the U.S. Department of Energy 2015 target of realizing a material with hydrogen storage capacity of 9 percent by weight at room temperature. Rafiee said his graphene is also one of the first known materials to surpass the Department of Energy's 2010 target of 6 percent.

Rafiee's graphene exhibits three critical attributes that result in its unique hydrogen storage capacity. The first is high surface area. Graphene's unique structure, only one atom thick, means that each of its carbon atoms is exposed to the environment and, in turn, to the hydrogen gas. The second attribute is low density. Graphene has one of the highest surface area-per-unit masses in nature, far superior to even carbon nanotubes and fullerenes

The third attribute is favorable surface chemistry. After oxidizing graphite powder and mechanically grinding the resulting graphite oxide, Rafiee synthesized the graphene by thermal shock followed by annealing and exposure to argon plasma. These treatments play an important role in increasing the binding energy of hydrogen to the graphene surface at room temperature, as hydrogen tends to cluster and layer around carbon atoms.

Talented Engineer

Rafiee joined Rensselaer in 2008, following an internship at the City University of Hong Kong and earning his bachelor's and master's degrees in mechanical and manufacturing engineering from the University of Tabriz in Iran. At Rensselaer, Rafiee and his brother, Mohammad, joined the research group of Mechanical, Aerospace, and Nuclear Engineering Professor Nikhil Koratkar.

"Javad is extremely knowledgeable, has great confidence in his abilities, and has demonstrated a very high level of creativity and originality. However, it is his deep passion and enthusiasm for research and discovery coupled with his amazing drive and energy that differentiates him from his peers," Koratkar said. "This passion and excitement for discovery and innovation is not something that can be taught or learned. It is an intrinsic quality of an individual – either you have it or you don't – and Javad is the most intellectually curious student I have ever had the privilege to advise here at Rensselaer."

In his time at Rensselaer, Rafiee has authored five, and co-authored three, journal papers in various disciplines, ranging from materials science and mechanical engineering, to computer science and urology.

Rafiee is from Tehran, Iran, and expects to earn his doctorate in 2011. Following graduation, he and his brother plan to start their own business with a focus on clean energy and green manufacturing.

Lemelson-MIT Collegiate Student Prizes

In addition to Rafiee's pioneering work, the other winners of the annual Lemelson-MIT Collegiate Student Prize were announced today at their respective universities:

* Lemelson-MIT Student Prize winner Erez Lieberman-Aiden demonstrated creativity and innovation across several disciplines, most recently with his invention of "Hi-C", a three-dimensional genome sequencing method that will enable an entirely new understanding of cell state, genetic regulation and disease.
* Lemelson-MIT Caltech Student Prize winner Heather Agnew contributed to the development of an innovative technique that creates inexpensive, stable, highly reliable biochemical compounds that have the potential to replace antibodies used in many standard diagnostic tests.
* Lemelson-MIT Illinois Student Prize winner Jonathan Naber and the Illini Prosthetics Team developed an affordable, durable, extremely functional prosthetic arm for people in underdeveloped countries, made from recycled materials. ###

ABOUT THE LEMELSON-MIT PROGRAM
celebrating innovation, inspiring youth

The Lemelson-MIT Program recognizes the outstanding inventors and innovators transforming our world, and inspires young people to pursue creative lives and careers through innovation.

Jerome H. Lemelson, one of U.S. history's most prolific inventors, and his wife, Dorothy, founded the Lemelson-MIT Program at the Massachusetts Institute of Technology in 1994. It is funded by The Lemelson Foundation and administered by the School of Engineering. The Foundation sparks, sustains, and celebrates innovation and the inventive spirit. It supports projects in the U.S. and developing countries that nurture innovators and unleash invention to advance economic, social, and environmentally sustainable development. To date, The Lemelson Foundation has donated or committed more than U.S. $150 million in support of its mission.

ABOUT THE LEMELSON-MIT RENSSELAER STUDENT PRIZE

The Lemelson-MIT Rensselaer Student Prize is awarded to a student who has demonstrated remarkable inventiveness and innovation.

Contact: Michael Mullaney mullam@rpi.edu 518-276-6161 Rensselaer Polytechnic Institute

Vigilance needed in nanotechnology

University of Calgary chemist finds right mix of tools to measure nanomaterials in blood vessels

University of Calgary chemistry professor David Cramb is a step closer to helping solve a complex problem in nanotechnology: the impact nanoparticles have on human health and the environment.

Cramb, director of the Faculty of Science's nanoscience program, and his researchers have developed a methodology to measure various aspects of nanoparticles in the blood stream of chicken embryos.

Dr. David T. Cramb Director, Nanoscience Program Professor, Department of Chemistry

"With the boom in nanomaterials production there is an increasing possibility of environmental and/or human exposure. Thus there is a need to investigate their potential detrimental effects," says Cramb. "We have developed very specialized tools to begin measuring such impacts." Nanoparticles are particles or groups of atoms or molecules nanometers in size. One millimetre (or the diameter of the head of a pin) is equal to one-million nanometres. Nanoparticles are already used in the cosmetics industry and are being developed for drug delivery, diagnostic imaging and tissue engineering, to name only a few applications. It is estimated investments in nanotechnology globally will reach about $12 trillion US by 2012.

Cramb is looking for ways to help answer questions including: If embryos are exposed to nanoparticles, where will the nanoparticles go? How will the embryo respond? What regulatory approaches can be recommended to mitigate accidental exposure? How can nanotechnology be made green and sustainable?

"Bioaccumulation studies involving embryos are being conducted in our laboratory," says Cramb. "These studies are important since chronic nanotoxicity in an adult organism could be related to exposure during the development process. Additionally, acute exposure may affect embryonic viability."

Cramb and his researchers studied motion and light induced changes in nanoparticles by focusing a laser beam into a blood vessel containing nanoparticles and measuring fluorescence. (The measurements provide a determination of particles aggregation in the vessel). This is unique because it has never been done in a live embryo. The results will now allow measurement and understanding of uptake into embryonic tissues. ###

The Organization for Economic Co-operation and Development is leading a global effort to develop research that will help member states to implement sound, science-based regulatory frameworks for the burgeoning nanotechnology industry. NSERC and Canadian Institutes of Health Research (CHRP - Collaborative Health Research Projects Program) have provided $600,000 disbursed over three years to fund research in this area by a team including the research groups of Cramb, Kristina Rinker and Sarah Childs of the University of Calgary and Warren Chan of the University of Toronto.

Contact: Leanne Yohemas leanne.yohemas@ucalgary.ca 403-220-5144 University of Calgary

Sorting device for analyzing biological reactions puts the power of a lab in a researcher's pocket VIDEO

Microfluidic technology increases efficiency, reduces costs, and could be a boon for synthetic biology.

CAMBRIDGE, Mass., March 2010 – Fictional candy maker Willy Wonka called his whimsical device to sort good chocolate eggs from bad, an eggucator. Likewise, by determining what enzymes and compounds to keep and which to discard, scientists are aiming to find their own golden eggs: more potent drugs and cleaner sources of energy.

Toward that end, Harvard researchers and a team of international collaborators demonstrated a new microfluidic sorting device that rapidly analyzes millions of biological reactions.

Caption: The sorted drops move up the field gradient created by the electrodes by dielectrophoresis and are pulled into the keep channel. The movie is recorded at 4,000 frames s-1 and shows the result of sorting a demonstration emulsion containing fluorescein (light drops) or bromophenol blue 1 percent by weight in water. Credit: Jeremy Agresti, Harvard School of Engineering and Applied Sciences. Usage Restrictions: None. Caption: The microfluidic sorting device removes inactive and unwanted compounds, dumping the drops into a "bad egg" bin, and guides the others into a "keep" container. Specifically, as the drops flow through the channels they eventually encounter a junction (a two-channel fork). The device identifies the desired drops by using a laser focused on the channel before the fork to read a drop's fluorescence level. The drops with greater intensity of fluorescence (those exhibiting the highest levels of activity) are pulled towards the keep channel by the application of an electrical force, a process known as dielectrophoresis. Credit: Courtesy of Jeremy Agresti, Harvard School of Engineering and Applied Sciences. Usage Restrictions: None.

Smaller than an iPod Nano, the device analyzes reactions a 1,000-times faster and uses 10 million-fold less volumes of reagent than conventional state-of-the-art robotic methods. The scientists anticipate that the invention could reduce screening costs by 1 million-fold and make directed evolution, a means of engineering tailored biological compounds, more commonplace in the lab. "Our finding is not so much a scientific discovery, but the first demonstration of a new technology," says project leader Jeremy Agresti, a former research associate in the lab of co-author David Weitz, Mallinckrodt Professor of Physics and of Applied Physics in the Harvard School of Engineering and Applied Sciences (SEAS) and Department of Physics. "What limits new areas of research in biology and biotechnology is the ability to assay or to do experiments on many different variables in parallel at once." The team's technology, first reported in the February 8th online Early Edition of the Proceedings of the National Academy of Sciences, bypasses conventional limitations through the use of drop-based microfluidics, squeezing tiny capsules of liquid through a series of intricate tubes, each narrower than a single human hair. "Each microscopic drop can trap an individual cell and thus it becomes like a miniature test tube," explains Amy Rowat, a postdoctoral fellow at SEAS. "The drops are coated with a surfactant, or stabilization molecule, that prevents the drops from coalescing with each other and also prevents the contents from sticking to the wall of the drops."

To sort, the system removes inactive and unwanted compounds, dumping the drops into a "bad egg" bin, and guides the others into a "keep" container. Specifically, as the drops flow through the channels they eventually encounter a junction (a two-channel fork). Left alone, the drops will naturally flow towards the path of least fluidic resistance, or the waste channel.

The device identifies the desired drops by using a laser focused on the channel before the fork to read a drop's fluorescence level. The drops with greater intensity of fluorescence (those exhibiting the highest levels of activity) are pulled towards the keep channel by the application of an electrical force, a process known as dielectrophoresis.

"Our concept was to build a miniature laboratory for performing biological experiments quickly and efficiently," explains collaborator Adam Abate, a postdoctoral fellow in applied physics at SEAS. "To do this we needed to construct microfluidic versions of common bench-top tasks, such as isolating cells in a compartment, adding reagents, and sorting the good from the bad. The challenge was to do this with microscopic drops flowing past at thousands per second."

"The sorting process is remarkably efficient and fast. By shrinking down the reaction size to 10 picoliters of volumes, we increased the sorting speed by the same amount," adds Agresti. "In our demonstration with horseradish peroxidase, we evolved and improved an already efficient enzyme by sorting through 100 million variants and choosing the best among them."

In particular, the researchers were struck by the ability to increase the efficiency of an already efficient enzyme to near its theoretical maximum, the diffusion limit, where the enzyme can produce products as quickly as a new substrate can bump into it.

Using conventional means, the sorting process would have taken several years. Such a dramatic reduction of time could be a boon for the burgeoning field of synthetic biology. For example, a biofuels developer could use the device to screen populations of millions of organisms or metabolic pathways to find the most efficient producer of a chemical or fuel. Likewise, scientists could speed up the pace of drug development, determining the best chemical candidate compounds and then evolving them based upon desired properties.

"The high speed of our technique allows us to go through multiple cycles of mutation and screening in a very short time," says Agresti. "This is the way evolution works best. The more generations you can get through, the faster you can make progress." ###

Agresti, Rowat, and Abate's co-authors included Keunho Ahn from SEAS; Eugene Antipov and Alexander M. Klibanov, both from MIT; Jean-Christophe Baret and Andrew D. Griffiths, both from the Université de Strasbourg; and Manuel Marquez from YNano LLC.

The authors acknowledge the support by the Human Frontier Science Program; the National Science Foundation through the Harvard Materials Research Science and Engineering Center; the Centre National de la Recherche Scientifique; the Massachusetts Life Sciences Center; and the Agence National de la Recherche.

Contact: Michael Patrick Rutter mrutter@seas.harvard.edu 617-496-3815 Harvard University

Greener memory from random motion

Heat helps in low power data storage scheme. Random thermal fluctuations in magnetic memory can be harnessed to reduce the energy required to store information, according to an experiment reported in the current issue of Physical Review Letters. The development could lead to computer memory that operates at significantly lower power than conventional devices. Markus Münzenberg of Universität Göttingen and Jagadeesh Moodera of MIT describe the potential route to greener magnetic memory in a Viewpoint in the latest issue of APS Physics (physics.aps.org).

Heat is usually a problem when it comes to storing digital data. At the microscopic level, the molecules and atoms of anything at a temperature above absolute zero are in constant motion.

Caption: This is a schematic of data storage in (left) converntional magnetic memory and (right) thermally assisted memory. Credit: Illustration: Alan Stonebraker, APS. Usage Restrictions: None.

Because magnetic memory relies on controlling and measuring the orientation of tiny magnetic particles, the jostling that comes about as components warm up can potentially scramble data. Thermal issues are a major concern as researchers build increasingly dense and fast magnetic memory. But heat isn't entirely bad, according to a collaboration of Italian and American physicists that has shown that random thermal motions can be helpful for writing magnetic data. Essentially, they found that applying an electrical current that should be too modest to record data can still be effective for writing information because thermal motion gives an added boost to help orient magnetic particles.

The researchers confirmed the effect by measuring magnetic fluctuations as the particles that make up memory were being aligned. Thermal motions are random, which in turn causes random variations in the amount of time it takes for magnetic particles to line up. The fact that alignment times ranged from one to a hundred billionths of a second made it clear that random, temperature-dependent motion must be at work in helping to flip the particles.

The experimental confirmation of the thermal effects on magnetic memory points the way to new, thermally-assisted data writing schemes. The advances could reduce the power required to store information, potentially helping to ensure that future PCs are increasingly green machines. ###

Contact: James Riordon riordon@aps.org 301-209-3238 American Physical Society

The proof's in the bubbles

Molecular imaging technique uses ultrasound and microscopic bubbles to target cancer cells

Reston, Va.—An imaging technique combining ultrasound and specially modified contrast agents may allow researchers to noninvasively detect cancer and show its progression, according to research published in the March issue of The Journal of Nuclear Medicine (JNM). The technique enables researchers to visualize tumor activity at the molecular level.

"We hope this technique might be helpful for the early detection of disease," said Juergen K. Willmann, M.D., lead author of the study and assistant professor of radiology at Stanford University School of Medicine. "It may help save lives by finding cancer—such as breast, ovarian or pancreatic cancer—in the very early stages, when it is still curable."

In the study, researchers intravenously injected microbubbles—gas-filled spheres small enough to travel through vessels—into mice with cancers. The microbubbles, which were paired with a new peptide (a molecule that consists of a chain of amino acids), were designed to travel through the vascular system and attach to integrin—a well-characterized molecular marker that acts as a "red flag" for tumor vessel growth, or angiogenesis. Tumor vessel growth occurs when active tumor cells create certain pathways to provide the tumor with a sufficient supply of oxygen, nutrients and other factors needed for growth.

Once the gas-filled microbubbles seek out the cancers and attach to their vessel walls, they send out strong signals that are picked up by standard clinical ultrasound scanners. The imaging signals produced by the microbubbles are reflected back to the ultrasound transducer and illuminate the areas that outline the tumor, thus providing researchers with a sonogram of tumor vessel growth on a molecular level.

"Ultrasound holds great promise for the application of molecular imaging because it is widely available, relatively inexpensive and safe. There is no exposure to radiation and repetitive imaging is not a concern," said Dr. Willmann. "Furthermore, the targeted microbubbles have great potential for translation from bench to bedside—which will be explored in future studies," said Sanjiv Gambhir, M.D., Ph.D., director of the molecular imaging program at Stanford.

Contrast-enhanced ultrasound can be used to image blood perfusion in organs, to measure blood flow rate in the heart and other organs and to perform other applications—such as characterization of focal lesions in the liver. Current interest is focused on modifying contrast agents to make them specifically useful for molecular imaging. The microbubbles, paired with the new peptide that binds to tumor vessel cells as studied in the current research, may be more effective than antibody molecules, which are time-intensive to produce, are costly and may cause adverse reactions in patients.

Noninvasive imaging strategies such as the one described in the JNM study may be particularly helpful for diagnosing cancer in its earliest stages as well as for developing therapeutic agents to treat cancer and monitoring whether treatment is working. ###

Authors of "Targeted Contrast-Enhanced Ultrasound Imaging of Tumor Angiogenesis with Contrast Microbubbles Conjugated to Integrin-Binding Knottin Peptides" include Juergen K. Willmann, Richard H. Kimura, Nirupama Deshpande, Amelie M. Lutz, Jennifer R. Cochran, and Sanjiv S. Gambhir of the Molecular Imaging Program at Stanford, Department of Radiology, School of Medicine, Stanford University, Stanford, Calif.

About SNM—Advancing Molecular Imaging and Therapy

SNM is an international scientific and medical organization dedicated to raising public awareness about what molecular imaging is and how it can help provide patients with the best health care possible. SNM members specialize in molecular imaging, a vital element of today's medical practice that adds an additional dimension to diagnosis, changing the way common and devastating diseases are understood and treated.

SNM's more than 17,000 members set the standard for molecular imaging and nuclear medicine practice by creating guidelines, sharing information through journals and meetings and leading advocacy on key issues that affect molecular imaging and therapy research and practice. For more information, visit www.snm.org.

Contact: Amy Shaw ashaw@snm.org 703-652-6773 Society of Nuclear Medicine

University of Pennsylvania Joins International Collaboration in Government/Academics to Research “Soft Matter”

PHILADELPHIA –- The University of Pennsylvania’s Laboratory for Research on the Structure of Matter has entered into a multi-year agreement with specialty chemical producer Rhodia and the French National Center for Scientific Research to launch an international, public-private research collaboration in soft condensed matter.

The collaboration between academia, government and industry brings together a diverse team of world-class scientists with complementary expertise for understanding, manipulating and creating novel soft materials. The joint effort will focus on developing new, sustainable technologies in the field of soft condensed matter, a science at the interface of chemistry, biology, physics and nanotechnology.

Soft condensed matter research focuses on easily deformable materials whose physics are often dominated by entropy. Liquids, colloids, polymers, foams, surfactants, liquid crystals and gels are examples of soft materials.

Penn will benefit from an industrial platform on which to test new breakthroughs in material science, particularly at the nanoscale. It is called the COMPASS collaboration, for Complex Assemblies of Soft Matter. Penn will also gain access to the formulation expertise of a variety of visiting scientists.

“Our research collaborations have always benefited from a multi-disciplinary approach,” Arjun Yodh, the James M. Skinner Professor of Science and director of the LRSM, said. “The COMPASS collaboration with Rhodia and CNRS will enable Penn to continue to build on that approach to take advantage of major research capabilities well beyond our traditional boundaries.”

Initial projects will explore renewable and sustainable ingredients for consumer products in home and personal-care markets. Others projects will address broadly critical issues such as water scarcity for agriculture and novel printable electronic solutions for energy transfer and storage.

Exploratory research will create soft materials, such as fluids or gels, with unique properties based on various natural or synthetic ingredients. Researchers will focus on developing new materials with improved cost effectiveness and performance, novel functional attributes and sustainable technologies for application in a range of consumer products and industrial formulations, including body wash, shampoo, paints, lubricants, viscosifiers and printable electronics.

“This collaboration illustrates how world-class researchers, international outreach and industrial know-how can accelerate the pace of research and move basic science into the consumer and industrial world,” Steven J. Fluharty, vice provost for research at Penn, said.

Research will be conducted in Penn’s LRSM and Rhodia’s Center for Research and Technology in Bristol, Pa. CNRS researchers will work at both locations. As many as 20 researchers will work in the collaboration.

“This agreement brings together some of the best research talent and facilities in the world,” Paul-Joël Derian, Rhodia’s vice president and worldwide director of research, said. “Together we are exploring practical research applications to improve the sustainability of everyday products. Equally important, we will concentrate on finding new solutions for critical challenges in agriculture and energy that affect the developing world as well as advanced societies.” ###

Contact: Jordan Reese jreese@upenn.edu 215-573-6604 University of Pennsylvania

New graphene 'nanomesh' could change the future of electronics

Graphene, a one-atom-thick layer of a carbon lattice with a honeycomb structure, has great potential for use in radios, computers, phones and other electronic devices. But applications have been stymied because the semi-metallic graphene, which has a zero band gap, does not function effectively as a semiconductor to amplify or switch electronic signals.

While cutting graphene sheets into nanoscale ribbons can open up a larger band gap and improve function, 'nanoribbon' devices often have limited driving currents, and practical devices would require the production of dense arrays of ordered nanoribbons — a process that so far has not been achieved or clearly conceptualized.

Yu Huang

But Yu Huang, a professor of materials science and engineering at the UCLA Henry Samueli School of Engineering and Applied Science, and her research team, in collaboration with UCLA chemistry professor Xiangfeng Duan, may have found a new solution to the challenges of graphene. In research to be published in the March issue of Nature Nanotechnology (currently available online), Huang's team reveals the creation of a new graphene nanostructure called graphene nanomesh, or GNM. The new structure is able to open up a band gap in a large sheet of graphene to create a highly uniform, continuous semiconducting thin film that may be processed using standard planar semiconductor processing methods.

"The nanomeshes are prepared by punching a high-density array of nanoscale holes into a single or a few layers of graphene using a self-assembled block copolymer thin film as the mask template," said Huang.

The nanomesh can have variable periodicities, defined as the distance between the centers of two neighboring nanoholes. Neck widths, the shortest distance between the edges of two neighboring holes, can be as low as 5 nanometers.

This ability to control nanomesh periodicity and neck width is very important for controlling electronic properties because charge transport properties are highly dependent on the width and the number of critical current pathways.

Using such nanomesh as the semiconducting channel, Huang and her team have demonstrated room-temperature transistors that can support currents nearly 100 times greater than individual graphene nanoribbon devices, but with a comparable on-off ratio. The on-off ratio is the ratio between the currents when a device is switched on or switched off. This usually reveals how effectively a transistor can be switched off and on.

The researchers have also shown that the on-off ratio can be tuned by varying the neck width.

"GNMs can address many of the critical challenges facing graphene, as well as bypass the most challenging assembly problems," Huang said. "In conjunction with recent advances in the growth of graphene over a large-area substrate, this concept has the potential to enable a uniform, continuous semiconducting nanomesh thin film that can be used to fabricate integrated devices and circuits with desired device size and driving current.

"The concept of the GNM therefore points to a clear pathway towards practical application of graphene as a semiconductor material for future electronics. The unique structural and electronic characteristics of the GNMs may also open up exciting opportunities in highly sensitive biosensors and a new generation of spintronics, from magnetic sensing to storage," she said. ###

The study was funded in part by Huang's UCLA Henry Samueli School of Engineering and Applied Science Fellowship.

The UCLA Henry Samueli School of Engineering and Applied Science, established in 1945, offers 28 academic and professional degree programs, including an interdepartmental graduate degree program in biomedical engineering. Ranked among the top 10 engineering schools at public universities nationwide, the school is home to seven multimillion-dollar interdisciplinary research centers in wireless sensor systems, nanotechnology, nanomanufacturing and nanoelectronics, all funded by federal and private agencies.

For more news, visit the UCLA Newsroom and follow us on Twitter.

Contact: Wileen Wong Kromhout wwkromhout@support.ucla.edu 310-206-0540 University of California - Los Angeles

Nanotechnologists from Penn collaborate to form near-frictionless diamond material

PHILADELPHIA –- Researchers at the University of Pennsylvania, the University of Wisconsin-Madison and IBM Research-Zürich have fabricated an ultra sharp, diamond-like carbon tip possessing such high strength that it is 3,000 times more wear-resistant at the nanoscale than silicon.

The end result is a diamond-like carbon material mass-produced at the nanoscale that doesn't wear. The new nano-sized tip, researchers say, wears away at the rate of one atom per micrometer of sliding on a substrate of silicon dioxide, much lower than that for a silicon oxide tip which represents the current state-of-the-art. Consisting of carbon, hydrogen, silicon and oxygen molded into the shape of a nano-sized tip and integrated on the end of a silicon microcantilever for use in atomic force microscopy, the material has technological implications for atomic imaging, probe-based data storage and as emerging applications such as nanolithography, nanometrology and nanomanufacturing.

Caption: This is an SEM image of a silicon microcantilever with an ultrasharp tip of diamond-like carbon with silicon. Credit: Harish Bhaskaran, IBM. Usage Restrictions: None.

The importance of the discovery lies not just in its size and resistance to wear but also in the hard substrate against which it was shown to perform well when in sliding contact: silicon dioxide. Because silicon –- used in almost all integrated circuit devices –- oxidizes in atmosphere forming a thin layer of its oxide, this system is the most relevant for nanolithography, nanometrology and nanomanufacturing applications. Probe-based technologies are expected to play a dominant role in many such technologies; however, poor wear performance of many materials when slid against silicon oxide, including silicon oxide itself, has severely limited usefulness to the laboratory.

Researchers built the material from the ground up, rather than coating a nanoscale tip with wear-resistant materials. The collaboration used a molding technique to fabricate monolithic tips on standard silicon microcantilevers. A bulk processing technique that has the potential to scale up for commercial manufacturing is available.

Robert Carpick, professor in the Department of Mechanical Engineering and Applied Mechanics at Penn, and his research group had previously shown that carbon-based thin films, including diamond-like carbon, had low friction and wear at the nanoscale; however, it has been difficult to fabricate nanoscale structures made out of diamond-like carbon until now.

Understanding friction and wear at the nanoscale is important for many applications that involve nanoscale components sliding on a surface.

"It is not clear that materials that are wear-resistant at the macroscale exhibit the same property at the nanoscale," lead author Harish Bhaskaran, who was a postdoctoral research at IBM during the study, said.

Defects, cracks and other phenomena that influence material strength and wear at macroscopic scales are less important at the nanoscale, which is why nanowires can, for example, show higher strengths than bulk samples. ###

The study, published in the current edition of the journal Nature Nanotechnology, was conducted collaboratively by Carpick and postdoctoral researcher Papot Jaroenapibal of the Department of Mechanical Engineering and Applied Mechanics in Penn's School of Engineering and Applied Science; Bhaskaran, Bernd Gotsmann, Abu Sebastian, Ute Drechsler, Mark A. Lantz and Michel Despont of IBM Research-Zürich; and Yun Chen and Kumar Sridharan of the University of Wisconsin. Jaroenapibal currently works at Khon Kaen University in Thailand, and Bhaskaran currently works at Yale University.

Research was funded by a European Commission grant and the Nano/Bio Interface Center of the University of Pennsylvania through the National Science Foundation.

Contact: Jordan Reese jreese@upenn.edu 215-573-6604 University of Pennsylvania

Scientists glimpse nanobubbles on super nonstick surfaces

Could lead to design of water-shedding materials for applications in energy, medicine and more

UPTON, NY — Scientists at the U.S. Department of Energy's Brookhaven National Laboratory have obtained the first glimpse of miniscule air bubbles that keep water from wetting a super non-stick surface. Detailed information about the size and shape of these bubbles — and the non-stick material the scientists created by "pock-marking" a smooth material with cavities measuring mere billionths of a meter — is being published online today in the journal Nano Letters.

"Our results explain how these nanocavities trap tiny bubbles which render the surface extremely water repellent," said Brookhaven physicist and lead author Antonio Checco.

Brookhaven physicist Antonio Checco

The research could lead to a new class of non-stick materials for a range of applications, including improved-efficiency power plants, speedier boats, and surfaces that are resistant to contamination by germs. Non-stick surfaces are important to many areas of technology, from drag reduction to anti-icing agents. These surfaces are usually created by applying coatings, such as Teflon, to smooth surfaces.

But recently — taking the lead from observations in nature, notably the lotus leaf and some varieties of insects — scientists have realized that a bit of texture can help. By incorporating topographical features on surfaces, they've created extremely water repellant materials.

"We call this effect 'superhydrophobicity,'" said Brookhaven physicist Benjamin Ocko. "It occurs when air bubbles remain trapped in the textured surfaces, thereby drastically reducing the area of liquid in contact with the solid." This forces the water to ball up into pearl shaped drops, which are weakly connected to the surface and can readily roll off, even with the slightest incline.

"To get the first glimpse of nanobubbles on a superhydrophobic surface we created a regular array of more than a trillion nano-cavities on an otherwise flat surface, and then coated it with a wax-like surfactant," said Charles Black, a physicist at Brookhaven's [http://www.bnl.gov/cfn/] Center for Functional Nanometerials .

This coated, nanoscale textured surface was much more water repellant than the flat surface alone, suggesting the existence of nanobubbles. However, because the nanoscale is not accessible using ordinary microscopes, little is known about these nanobubbles.

To unambiguously prove that these ultra-small bubbles were present, the Brookhaven team carried out x-ray measurements at the [http://www.nsls.bnl.gov] National Synchrotron Light Source . "By watching how the x-rays diffracted, or bounced off the surface, we are able to image extremely small features and show that the cavities were mostly filled with air," said Brookhaven physicist Elaine DiMasi.

Checco added, "We were surprised that water penetrates only about 5 to 10 nanometers into the cavities — an amount corresponding to only 15 to 30 layers of water molecules — independent of the depth of the cavities. This provides the first direct evidence of the morphology of such small bubbles."

According to the scientists' observations, the bubbles are only about 10 nanometers in size — about ten thousand times smaller than the width of a single human hair. And the team's results conclusively show that these tiny bubbles have nearly flat tops. This is in contrast to larger, micrometer-sized bubbles, which have a more rounded top.

"This flattened configuration is appealing for a range of applications because it is expected to increase hydrodynamic slippage past the nanotextured surface," Checco said. "Moreover, the fact that water hardly penetrates into the nano-textures, even if an external pressure is applied to the liquid, implies that these nanobubbles are very stable."

Therefore, in contrast to materials with larger, micrometer-sized textures, the surfaces fabricated by the Brookhaven team may exhibit more stable superhydrophobic properties.

"These findings provide a better understanding of the nanoscale aspects of superhydropobicity, which should help to improve the design of future superhydrophobic non-stick surfaces," Checco said. ###

This research is funded by the DOE Office of Science. Tommy Hofmann, a former Brookhaven physicist now at Helmholtz Zentrum Berlin, also contributed to this work.

One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. Brookhaven is operated and managed for DOE's Office of Science by Brookhaven Science Associates, a limited-liability company founded by the Research Foundation of State University of New York on behalf of Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit, applied science and technology organization.

Contact: Karen McNulty Walsh kmcnulty@bnl.gov 631-344-8350 DOE/Brookhaven National Laboratory

Nanotechnology Tackles Major Problems Associated with Chemotherapy – Side Effects and Drug Resistance

Additional research focuses on practical application of nanotechnology across a wide range of fields including homeland defense and the environment.

Huixin He, associate professor of nanoscale chemistry at Rutgers University, Newark, and Tamara Minko, professor at the Rutgers Ernest Mario School of Pharmacy, have developed a nanotechnology approach that potentially could eliminate the problems of side effects and drug resistance in the treatment of cancer. Under traditional chemotherapy, cancer cells, like bacteria, can develop resistance to drug therapy, leading to a relapse of the disease.

As reported in the December 21, 2009, issue of the journal Small, He, Minko and their co-researchers, including investigators from Merck & Co. and Carl Zeiss SMT, a global nanotechnology firm, have designed nanomaterials that allow for the delivery of both a chemical (doxorubicin) to destroy cancer cells and a genetic drug to prevent drug resistance.

Huixin He

When administered to drug-resistant ovarian cancer cells, the treatment was more than 130 times lethal than when doxorubicin was administrated alone. “The drug can only be released when it is inside the cancer cells,” He said. “This controlled internal release mechanism can dramatically eliminate side effects associated with anticancer drugs to normal tissues.” Battling Aggressive Breast Cancer with Nanotubes In related research, Professor He and another team of co-researchers have developed single-walled carbon nanotubes that hold the potential of providing a more effective means for detecting and selectively destroying aggressive breast cancer cells.

In a paper published in BMC Cancer late last year, the researchers showed that by chemically bonding a special antibody onto the nanotubes and taking advantage of two unique properties of carbon nanotubes, single cancer cells can be detected and selectively eradicated while leaving the nearby normal cells unharmed. The uniqueness of this approach is that it is more easily extended to other types of cancer cells. He’s research in the areas of cancer detection and treatment is funded in part with grants from the National Science Foundation and National Cancer Institute.

Research Focuses on Practical Applications Across a Wide Range of Fields

The application of He’s research is far and wide. He and members of her lab at Rutgers are working on the practical application of nanomaterials as a diagnostic tool for Parkinson’s disease. Other research is focused on the development of a platform to detect the presence of chemical warfare agents for homeland defense. He and her lab members are also working on nanotechnology to measure iron ions in ocean atmosphere dust and sea water, which is critical for the study of greenhouse gases and climate change.

At Rutgers, He teaches undergraduate courses in analytical chemistry and graduate courses in electrochemical analytical chemistry. She is the recipient of the 2009 Rutgers Presidential Fellowship for Teaching Excellence.

Media Contact: Helen Paxton 973-353-5262 E-mail: paxton@andromeda.rutgers.edu

Princeton scientists find an equation for materials innovation

Princeton engineers have made a breakthrough in an 80-year-old quandary in quantum physics, paving the way for the development of new materials that could make electronic devices smaller and cars more energy efficient.

By reworking a theory first proposed by physicists in the 1920s, the researchers discovered a new way to predict important characteristics of a new material before it's been created. The new formula allows computers to model the properties of a material up to 100,000 times faster than previously possible and vastly expands the range of properties scientists can study.

Caption: Princeton Professor Emily Carter and graduate student Chen Huang developed a new way of predicting important properties of substances. The advance could speed the development of new materials and technologies. Credit: Frank Wojciechowski/Princeton University. Usage Restrictions: Please credit Frank Wojciechowski/Princeton University.

"The equation scientists were using before was inefficient and consumed huge amounts of computing power, so we were limited to modeling only a few hundred atoms of a perfect material," said Emily Carter, the engineering professor who led the project. "But most materials aren't perfect," said Carter, the Arthur W. Marks '19 Professor of Mechanical and Aerospace Engineering and Applied and Computational Mathematics. "Important properties are actually determined by the flaws, but to understand those you need to look at thousands or tens of thousands of atoms so the defects are included. Using this new equation, we've been able to model up to a million atoms, so we get closer to the real properties of a substance."

By offering a panoramic view of how substances behave in the real world, the theory gives scientists a tool for developing materials that can be used for designing new technologies. Car frames made from lighter, strong metal alloys, for instance, might make vehicles more energy efficient, and smaller, faster electronic devices might be produced using nanowires with diameters tens of thousands of times smaller than that of a human hair.

Paul Madden, a chemistry professor and provost of The Queen's College at Oxford University, who originally introduced Carter to this field of research, described the work as a "significant breakthrough" that could allow researchers to substantially expand the range of materials that can be studied in this manner. "This opens up a new class of material physics problems to realistic simulation," he said.

The new theory traces its lineage to the Thomas-Fermi equation, a concept proposed by Llewellyn Hilleth Thomas and Nobel laureate Enrico Fermi in 1927. The equation was a simple means of relating two fundamental characteristics of atoms and molecules. They theorized that the energy electrons possess as a result of their motion -- electron kinetic energy -- could be calculated based how the electrons are distributed in the material. Electrons that are confined to a small region have higher kinetic energy, for instance, while those spread over a large volume have lower energy.

Understanding this relationship is important because the distribution of electrons is easier to measure, while the energy of electrons is more useful in designing materials. Knowing the electron kinetic energy helps researchers determine the structure and other properties of a material, such as how it changes shape in response to physical stress. The catch was that Thomas and Fermi's concept was based on a theoretical gas, in which the electrons are spread evenly throughout. It could not be used to predict properties of real materials, in which electron density is less uniform.

The next major advance came in 1964, when another pair of scientists, Pierre Hohenberg and Walter Kohn, another Nobel laureate, proved that the concepts proposed by Thomas and Fermi could be applied to real materials. While they didn't derive a final, working equation for directly relating electron kinetic energy to the distribution of electrons, Hohenberg and Kohn laid the formal groundwork that proved such an equation exists. Scientists have been searching for a working theory ever since.

Carter began working on the problem in 1996 and produced a significant advance with two postdoctoral researchers in 1999, building on Hohenberg and Kohn's work. She has continued to whittle away at the problem since. "It would be wonderful if a perfect equation that explains all of this would just fall from the sky," she said. "But that isn't going to happen, so we've kept searching for a practical solution that helps us study materials."

In the absence of a solution, researchers have been calculating the energy of each atom from scratch to determine the properties of a substance. The laborious method bogs down the most powerful computers if more than a few hundred atoms are being considered, severely limiting the amount of a material and type of phenomena that can be studied.

Carter knew that using the concepts introduced by Thomas and Fermi would be far more efficient, because it would avoid having to process information on the state of each and every electron.

As they worked on the problem, Carter and Chen Huang, a doctoral student in physics, concluded that the key to the puzzle was addressing a disparity observed in Carter's earlier work. Carter and her group had developed an accurate working model for predicting the kinetic energy of electrons in simple metals. But when they tried to apply the same model to semiconductors -- the conductive materials used in modern electronic devices -- their predictions were no longer accurate.

"We needed to find out what we were missing that made the results so different between the semiconductors and metals," Huang said. "Then we realized that metals and semiconductors respond differently to electrical fields. Our model was missing this."

In the end, Huang said, the solution was a compromise. "By finding an equation that worked for these two types of materials, we found a model that works for a wide range of materials."

Their new model, published online Jan. 26 in Physical Review B, a journal of the American Physical Society, provides a practical method for predicting the kinetic energy of electrons in semiconductors from only the electron density. The research was funded by the National Science Foundation.

Coupled with advances published last year by Carter and Linda Hung, a graduate student in applied and computational mathematics, the new model extends the range of elements and quantities of material that can be accurately simulated.

The researchers hope that by moving beyond the concepts introduced by Thomas and Fermi more than 80 years ago, their work will speed future innovations. "Before people could only look at small bits of materials and perfect crystals," Carter said. "Now we can accurately apply quantum mechanics at scales of matter never possible before." ###

Contact: Chris Emery cemery@princeton.edu 609-258-4597 Princeton University, Engineering School

Researchers gain detailed insight into failing heart cells using new nano-technique

Researchers have been able to see how heart failure affects the surface of an individual heart muscle cell in minute detail, using a new nanoscale scanning technique developed at Imperial College London. The findings may lead to better design of beta-blockers, the drugs that can slow the development of heart failure, and to improvements in current therapeutic approaches to treating heart failure and abnormal heart rhythms.

Heart failure is a progressive and serious condition in which the heart is unable to supply adequate blood flow to meet the body's needs. Hormones such as adrenaline, which are activated by the body in an attempt to stimulate the weak heart, eventually produce further damage and deterioration.

Image of living cardiac muscle cells taken using new scanning ion conductance microscopy technology (image courtesy of Science/AAAS).

Symptoms include shortness of breath, difficulty in exercising and swollen feet. In the new study, published today in the journal Science and funded by the Wellcome Trust and the Leducq Foundation, researchers were able to analyse individual regions on the surface of the heart muscle cell in unprecedented detail, using live nanoscale microscopy. They used a new technique called scanning ion conductance microscopy (SICM), which gives an image of the surface of the cardiac muscle cell at more detailed levels than those possible using conventional live microscopy.

This enabled the researchers to see fine structures such as minute tubes (t- tubules), which carry electrical signals deep into the core of the cell. They could also see that the muscle cell surface is badly disrupted in heart failure.

There are two types of receptors for adrenaline. The first, beta1AR, strongly stimulates the heart to contract and it can also induce cell damage in the long term. The second, beta2AR, can slightly stimulate contraction but it also has special protective properties. For today's study, the researchers combined SICM with new chemical probes which give fluorescent signals when beta1AR or beta2AR is activated.

They found that the beta2AR receptors are normally anchored in the t-tubules, but in those cells damaged by heart failure they change location and move into the same space as beta1AR receptors. The researchers believe that this altered distribution of receptors might affect the beta2AR receptors' ability to protect cells, and lead to more rapid degeneration of the failing heart.

One of the most important categories of drugs for slowing the development of heart failure are the beta-blockers, which prevent adrenaline from affecting the heart cells by targeting the beta receptors. The new finding increases understanding of what happens to the two receptors in heart failure and could lead to the design of improved beta-blockers. It may eventually help resolve an existing debate about whether it is better to block the beta2AR receptors as well as the beta1AR.

Dr Julia Gorelik, corresponding author of the study from the National Heart and Lung Institute at Imperial College London, said: "Our new technique means we can get a real insight into how individual cells are disrupted by heart failure. Using our new nanoscale live-cell microscopy we can scan the surface of heart muscle cells to much greater accuracy than has been possible before and to see tiny structures that affect how the cells function.

"Through understanding what's happening on this tiny scale, we can ultimately build up a really detailed picture of what's happening to the heart during heart failure and long term, this should help us to tackle the disease. The main question for our future research will be to understand whether drugs can prevent the beta2-AR from moving in the cell and how this might help us to fight heart failure," added Dr Gorelik.

For the study, the researchers looked at single living cardiac muscle cells in a culture dish, taken from healthy or failing rat hearts. They stimulated the beta1AR and beta2AR receptors using drugs applied via nanopipette inside the t-tubules on the heart muscle cell. -ends-

For further information please contact: Laura Gallagher Research Media Relations Manager Imperial College London e-mail: gallagher@imperial.ac.uk Telephone: +44 (0)207 594 8432 or ext. 48432 Out of hours duty Press Officer: +44 (0)7803 886 248

Study quantifies the electron transport effects of placing metal contacts onto graphene

Making contact: Using large-scale supercomputer calculations, researchers have analyzed how the placement of metallic contacts on graphene changes the electron transport properties of the material as a factor of junction length, width and orientation. The work is believed to be the first quantitative study of electron transport through metal-graphene junctions to examine earlier models in significant detail.

Information on the ways in which attaching metal contacts affects electron transport in graphene will be important to scientists studying the material – and to designers who may one day fabricate electronic devices from the carbon-lattice material.

Caption: Georgia Tech researchers Markus Kindermann, Mei-Yin Chou and Salvador Barraza-Lopez (left to right) pose with graphics from their calculation of metal contacts on graphene. Credit: Georgia Tech Photo. Usage Restrictions: None. Caption: This figure illustrates the atomistic arrangement of aluminum and carbon atoms in the junctions studied by the Georgia Tech team. Credit: Georgia Tech image. Usage Restrictions: None.

"Graphene devices will have to communicate with the external world, and that means we will have to fabricate contacts to transport current and data," said Mei-Yin Chou, a professor and department chair in the School of Physics at the Georgia Institute of Technology. "When they put metal contacts onto graphene to measure transport properties, researchers and device designers need to know that they may not be measuring the instrinsic properties of pristine graphene. Coupling between the contacts and the material must be taken into account." Information on the effects of metal contacts on graphene was reported in the journal Physical Review Letters on February 19th. The research was supported by the U.S. Department of Energy, and involved interactions with researchers at the National Science Foundation (NSF)-supported Materials Research Science and Engineering Center (MRSEC) at Georgia Tech. Using large-scale, first-principles calculations done at two different NSF-supported supercomputer centers, the Georgia Tech research team – which included postdoctoral fellows Salvador Barraza-Lopez and Mihajlo Vanevic, and assistant professor Markus Kindermann – conducted detailed atomic-level calculations of aluminum contacts grown on graphene.

The calculations studied two contacts up to 14 nanometers apart, with graphene suspended between them. In their calculations, the researchers allowed the aluminum to grow as it would in the real world, then studied how electron transfer was induced in the area surrounding the contacts.

"People have been able to come up with phenomenological models that they use to find out what the effects are with metallic contacts," Chou explained. "Our calculations went a few steps farther because we built contacts atom-by-atom. We built atomistically-resolved contacts, and by doing that, we solved this problem at the atomic level and tried to do everything consistent with quantum mechanics."

Because metals typically have excess electrons, physically attaching the contacts to graphene causes a charge transfer from the metal. Charge begins to be transferred as soon as the contacts are constructed, but ultimately the two materials reach equilibrium, Chou said.

The study showed that charge transfer at the leads and into the freestanding section of the material creates an electron-hole asymmetry in the conductance. For leads that are sufficiently long, the effect creates two conductance minima at the energies of the Dirac points for the suspended and clamped regions of the graphene, according to Barraza-Lopez.

"These results could be important to the design of future graphene devices," he said. "Edge effects and the impact of nanoribbon width have been studied in significant detail, but the effects of charge transfer at the contacts may potentially be just as important."

The researchers modeled aluminum, but believe their results will apply to other metals such as copper and gold that do not form chemical bonds with graphene. However, other metals such as chromium and titanium do chemically alter the material, so the effects they have on electron transport may be different.

Beyond the new information provided by the calculations, the research further proposes quantitative models that can be used under certain circumstances to describe the impact of the contacts.

"Earlier models had been based on physical insights, but nobody really knew how faithfully they described the material," Kindermann said. "This is the first calculation to show that these earlier models apply under certain circumstances for the systems that we studied."

Data from the study may one day help device designers engineer graphene circuits by helping them understand the effects they are seeing.

"When we modify graphene, we need to understand what changes occur as a result of adding materials," added Chou. "This is really fundamental research to understand these effects and to have a numerical prediction for what is going on. We are helping to understand the basic physics of graphene." ###

This research was supported by Department of Energy grant DE-FG02-97ER45632. Comments and conclusions in this article are those of the researchers and do not necessarily reflect the views of the Department of Energy.

Contact: John Toon jtoon@gatech.edu 404-894-6986 Georgia Institute of Technology Research News

Brown physicist discovers odd, fluctuating magnetic waves

PROVIDENCE, R.I. [Brown University] — At the quantum level, the forces of magnetism and superconductivity exist in an uneasy relationship. Superconducting materials repel a magnetic field, so to create a superconducting current, the magnetic forces must be strong enough to overcome the natural repulsion and penetrate the body of the superconductor. But there's a limit: Apply too much magnetic force, and the superconductor's capability is destroyed.

This relationship is pretty well known. But why it is so remains mysterious. Now physicists at Brown University have documented for the first time a quantum-level phenomenon that occurs to electrons subjected to magnetism in a superconducting material.

Caption: Brown University physicist Vesna Mitrovic and colleagues have discovered magnetic waves that fluctuate when exposed to certain conditions in a superconducting material. The find may help scientists understand more fully the relationship between magnetism and superconductivity. Credit: Lauren Brennan, Brown University. Usage Restrictions: None.

In a paper published in Physical Review Letters, Vesna Mitrovic, joined by other researchers at Brown and in France, report that at under certain conditions, electrons in a superconducting material form odd, fluctuating magnetic waves. Apply a little more magnetic force, and those fluctuations cease: The electronic magnets form repeated wave-like patterns promoted by superconductivity. The discovery may help scientists understand more fully the relationship between magnetism and superconductivity at the quantum level. The insight also may help advance research into superconducting magnets, which are used in magnetic resonance imaging (MRI) and a host of other applications.

"If you don't understand [what is happening at] the quantum [level], how can you design a more powerful magnet?" asked Mitrovic, assistant professor of physics.

When a magnetic field is applied to a superconducting material, vortices measured in nanometers (1 billionth of a meter) pop up. These vortices, like super-miniature tornadoes, are areas where the magnetic field has overpowered the superconducting field state, essentially suppressing it. Crank up the magnetic field and more vortices appear. At some point, the vortices are so widespread the material loses its superconducting ability altogether.

At an even more basic level, sets of electrons called Cooper pairs (named for Brown physicist Leon Cooper, who shared a Nobel Prize for the discovery) form superconductivity. But scientists believe there also are other electrons that are magnetically oriented and spin on their own axes like little globes; these electrons are tilted at various angles on their imaginary axes and move in a repeating, linear pattern that resembles waves, Mitrovic and her colleagues have observed.

"These funny waves most likely appear because of superconductivity, but the reason why is still unsettled," Mitrovic said.

Adding to the mystery, Mitrovic and fellow researchers, including Brown graduate student Georgios Koutroulakis and former Brown postdoctoral associate Michael Stewart, saw that the waves fluctuated under certain conditions. After nearly three years of experiments at Brown and at the national magnetic field laboratory in Grenoble, France, Mitrovic's team was able to produce the odd waves consistently when testing a superconducting material — cerium-cobalt-indium5 (CeCoIn5) — at temperatures close to absolute zero and at about 10 Tesla of magnetic force.

The waves appeared to be sliding, Mitrovic said. "It's as if people are yanking on the wave," she added. Mitrovic and her colleagues also observed that when more magnetic energy is added, the fluctuations disappear and the waves resume their repeating, linear patterns.

The researchers next want to understand why these fluctuations occur and whether they crop up in other superconducting material. ###

The research was funded by the National Science Foundation and a European Community grant, as well as the Alfred P. Sloan Foundation.

Contact: Richard Lewis Richard_Lewis@Brown.edu 401-863-3766 Brown University

Stressed nanomaterials display unexpected movement

Johns Hopkins researchers have discovered that, under the right conditions, newly developed nanocrystalline materials exhibit surprising activity in the tiny spaces between the geometric clusters of atoms called nanocrystals from which they are made.

This finding, detailed recently in the journal Science, is important because these nanomaterials are becoming more ubiquitous in the fabrication of microdevices and integrated circuits. Movement in the atomic realm can affect the mechanical properties of these futuristic materials -- making them more flexible and less brittle -- and may alter the material's lifespan.

"As we make smaller and smaller devices, we've been using more nanocrystalline materials that have much smaller crystallites -- what materials scientists call grains -- and are believed to be much stronger," said Kevin Hemker, professor and chair of Mechanical Engineering in Johns Hopkins' Whiting School of Engineering and senior author of the Science article.

Caption: Mechanical engineer Kevin Hemker, seated between models representing how atoms are packed within an individual grain in a material, holds a silicon wafer onto which nanocrystalline aluminum thin film specimens have been deposited. Credit: Will Kirk/JHU. Usage Restrictions: None.

"But we have to understand more about how these new types of metal and ceramic components behave, compared to traditional materials. How do we predict their reliability? How might these materials deform when they are subjected to stress?" The experiments conducted by a former undergraduate research assistant and supervised by Hemker focused on what happens in regions called grain boundaries. A grain or crystallite is a tiny cluster of atoms arranged in an orderly three-dimensional pattern. The irregular space or interface between two grains with different geometric orientations is called the grain boundary. Grain boundaries can contribute to a material's strength and help it resist plastic deformation, a permanent change of shape.

Nanomaterials are believed to be stronger than traditional metals and ceramics because they possess smaller grains and, as a result, have more grain boundaries.

Most scientists have been taught that these grain boundaries do not move, a characteristic that helps the material resist deformation. But when Hemker and his colleagues performed experiments on nanocrystalline aluminum thin films, applying a type of force called shear stress, they found an unexpected result. "We saw that the grains had grown bigger, which can only occur if the boundaries move," he said, "and the most surprising part of our observation was that it was shear stress that had caused the boundaries to move."

"The original view," Hemker said, "was that these boundaries were like the walls inside of a house. The walls and the rooms they create don't change size; the only activity is by people moving around inside the room. But our experiments showed that in these nanomaterials, when you apply a particular type of force, the rooms do change size because the walls actually move."

The discovery has implications for those who use thin films and other nanomaterials to make integrated circuits and microelectromechanical systems, commonly called MEMS. The boundary movement shown by Hemker and his colleagues means that the nanomaterials used in these products likely possess more plasticity, higher reliability and less brittleness, but also reduced strength.

"As we move toward making things at much smaller sizes, we need to take into account how activity at the atomic level affects the mechanical properties of the material," Hemker said. "This knowledge can help the microdevice makers decide on the proper size for their components and can lead to better predictions about how long their products will last." ###

The journal article describing this discovery was inspired by a Johns Hopkins master's thesis produced by Tim Rupert, then a combined bachelor's/master's degree student in mechanical engineering. Rupert, who is now a doctoral student at MIT, is lead author of the Science piece. Along with Hemker, the co-authors are Daniel Gianola, a former doctoral student and postdoctoral fellow in Hemker's lab who is now an assistant professor of materials science and engineering at the University of Pennsylvania; and Y. Gan of the Karlsruhe Institute of Technology in Germany.

Funding for the research was provided by the U.S. Department of Energy and the National Science Foundation.

Digital color photo of the Kevin Hemker available; contact Phil Sneiderman.

Related links:

• Kevin Hemker's Lab Page: www.me.jhu.edu/hemker/MicroNano/
• Johns Hopkins Department of Mechanical Engineering: www.me.jhu.edu/

Contact: Phil Sneiderman prs@jhu.edu 443-287-9960 Johns Hopkins University

Quantum leap for phonon lasers

Physicists take a big step toward practical sound-based laser analogues.

Physicists have taken major step forward in the development of practical phonon lasers, which emit sound in much the same way that optical lasers emit light. The development should lead to new, high-resolution imaging devices and medical applications. Just as optical lasers have been incorporated into countless, ubiquitous devices, a phonon laser is likely to be critical to a host of as yet unimaginable applications.

Two separate research groups, one located in the US and the other in the UK, are reporting dramatic advances in the development of phonon lasers in the current issue of Physical Review Letters.

Caption: These are schemes for phonon amplification and lasing: (Top) Two coupled microcavities are excited by an optical pulse traveling through an optical fiber (blue). (Center) Pump photons entering through the fiber are converted to lower energy photons and coherent phonons. At a threshold pump power, phonon gain exceeds phonon loss resulting in phonon lasing. (Bottom) Phonon amplification in a superlattice. Tunneling of electrons from one quantum well to the next is accompanied by phonon emission. When a strong phonon wave is applied, it leads to phonon amplification. Credit: Alan Stonebraker. Usage Restrictions: None.

The papers are highlighted with a Viewpoint by Jacob Khurgin of Johns Hopkins University in the February 22 issue of Physics (http://physics.aps.org). Light and sound are similar in various ways: they both can be thought of in terms of waves, and they both come in quantum mechanical units (photons in the case of light, and phonons in the case of sound). In addition, both light and sound can be produced as random collections of quanta (consider the light emitted by a light bulb) or orderly waves that travel in coordinated fashion (as is the case for laser light). Many physicists believed that the parallels imply that lasers should be as feasible with sound as they are with light. While low frequency sound in the range that humans can hear (up to 20 kilohertz) is easy to produce in either a random or orderly fashion, things get more difficult at the terahertz (trillions of hertz) frequencies that are the regime of potential phonon laser applications. The problem stems from the fact that sound travels much slower than light, which in turn means that the wavelength of sound is much shorter than light at a given frequency. Instead of resulting in orderly, coherent phonon lasers, miniscule structures that can produce terahertz sound tend to emit phonons randomly. Researchers at Caltech have overcome the problem by assembling a pair of microscopic cavities that only permit specific frequencies of phonons to be emitted. They can also tune the system to emit phonons of different frequencies by changing the relative separation of the microcavities. The group from the UK's University of Nottingham took a different approach. They built their device out of electrons moving through a series of structures known as quantum wells. As an electron hops from one quantum well to the next, it produces a phonon. So far, the Nottingham group has not demonstrated a true phonon lasing, but their system amplifies high-frequency sound in a way that suggests it could be it a key component in future phonon laser designs. Regardless of the approach, the recent developments are landmark breakthroughs on the route to practical phonon lasers. Phonon lasers would have to go a long way to match the utility of their optical cousins, but the many applications that physicists have in mind already,

including medical imaging, high precision measurement devices, and high-energy focused sound, suggest that sound-based lasers may have a future nearly as bright as light lasers. ###

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Contact: James Riordon riordon@aps.org 301-209-3238 American Physical Society