Nanophysicists find unexpected magnetic effect

Kondo effect noted in single-atom contacts of pure ferromagnets

HOUSTON -- Spanish and U.S. physicists studying nanoelectronics have found that size really does matter when it comes to predicting the behavior of electrical contacts that are just one atom wide.

In new research appearing this week in the journal Nature, physicists at Spain's University of Alicante and at Rice University in Houston have found that single-atom contacts made of ferromagnetic metals like iron, cobalt and nickel behave very differently than do slightly larger versions that are on the order of the devices used in today's electronic gadgets.

"We've found that the last atom in the line, the one out there on the very end, doesn't want to align itself and behave like we expect it to," said study co-author Doug Natelson, associate professor of physics and astronomy at Rice. "What this shows is that you can really alter what you think of as a defining property of these metals just by reducing their size."

Doug Natelson

The findings center on the "Kondo effect," one of the most studied and well documented phenomena in magnetic materials. Scientists learned early in the study of electromagnetism that normal metals, like copper, conduct electricity better as they became colder. But in the 1930s, scientists found that adding even trace amounts of ferromagnetic metals like iron would throw off this effect. In the 1960s, Japanese physicist Jun Kondo explained the effect: while cooling normal metals results in fewer vibrations among atoms,

and thus less electrical resistance, mobile electrons in the metals tend to align their spins in the opposite direction of the spins of electrons in a magnetic atom. Thus, at low temperatures, an electron moving past a magnetic impurity will tend to flip its spin and therefore get deflected from its path. This explains why even tiny magnetic impurities can cause electrical resistance to rise, in spite of further cooling.

Based on decades of experimental evidence, physicists would not ordinarily expect the Kondo effect to play a role in wires and contacts made entirely of ferromagnetic metals like iron, cobalt and nickel. Yet that is precisely what co-authors Maria Reyes Calvo and Carlos Untiedt found occurring in experiments in Untiedt's laboratory in Alicante, Spain, in 2008. Calvo, a graduate student, was working with single-atom ferromagnetic contacts that were created by lowering and raising the tip of a scanning tunneling microscope onto a surface.

Untiedt knew that Natelson worked on similar-sized systems that were created in a wholly different way, by laying down metals on a flat surface. So Untiedt arranged for a travel grant from the Spanish government and Natelson agreed to oversee Calvo's recreation of the study at Rice.

"Reyes was a very quick study, and within just a few weeks she had mastered our technique for making single-atom junctions," Natelson said. "She conducted dozens of experiments on junctions made of cobalt and nickel, and we saw the characteristic Kondo effect in the conductance, just as she had seen in Spain."

Co-authors Joaquín Fernández-Rossier and Juan José Palacios, both of the University of Alicante, and David Jacob of Rutgers University. provided a theoretical framework to help explain the unexpected effect. Natelson said the team's discovery is yet another example of the unique types of effects that characterize nanotechnology.

"The fact that this atom is all by itself at the surface is what makes it behave so differently, and it shows that engineers need to be mindful of surface effects in anything they design at this level," Natelson said. ###

The research was supported by the European Union's Seventh Framework Program, the National Science Foundation, the Packard Foundation and the W.M. Keck Foundation.

Contact: Jade Boyd jadeboyd@rice.edu 713-348-6778 Rice University

New security and medical sensor devices made possible by metallic nanostructures

Scientists have designed tiny new sensor structures that could be used in novel security devices to detect poisons and explosives, or in highly sensitive medical sensors, according to research published tomorrow (8 April) in Nano Letters.

The new 'nanosensors', which are based on a fundamental science discovery in UK, Belgian and US research groups, could be tailor-made to instantly detect the presence of particular molecules, for example poisons or explosives in transport screening situations, or proteins in patients' blood samples, with high sensitivity.

The researchers were led by Imperial College London physicists funded by the Engineering and Physical Sciences Research Council. The team showed that by putting together two specific 'nanostructures' made of gold or silver, they can make an early prototype device which, once optimised, should exhibit a highly sensitive ability to detect particular chemicals in the immediate surroundings.

An image of the metallic ring and disk. The scale bar shows 200 nanometres.

The nanostructures are each about 500 times smaller than the width of a human hair. One is shaped like a flat circular disk while the other looks like a doughnut with a hole in the middle. When brought together they interact with light very differently to the way they behave on their own. The scientists have observed that when they are paired up they scatter some specific colours within white light much less, leading to an increased amount of light passing through the structure undisturbed.

This is distinctly different to how both structures scatter light separately. This decrease in the interaction with light is in turn affected by the composition of molecules in close proximity to the structures. The researchers hope that this effect can be harnessed to produce sensor devices.

Lead researcher on the project Professor Stefan Maier from Imperial's Department of Physics, and an Associate of Imperial's Institute for Security Science and Technology, said:

"Pairing up these structures has a unique effect on the way they scatter light – an effect which could be very useful if, as our computer simulations suggest, it is extremely sensitive to changes in surrounding environment. With further testing we hope to show that it is possible to harness this property to make a highly sensitive nanosensor."

Metal nanostructures have been used as sensors before, as they interact very strongly with light due to so-called localised plasmon resonances. But this is the first time a pair with such a carefully tailored interaction with light has been created.

The device could be tailored to detect different chemicals by decorating the nanostructure surface with specific 'molecular traps' that bind the chosen target molecules. Once bound, the target molecules would change the colours that the device absorbs and scatters, alerting the sensor to their presence. The team's next step is to test whether the pair of nanostructures can detect chosen substances in lab experiments.

Professor Maier concludes: "This study is a beautiful example of how concepts from different areas of physics fertilise each other – in essence our nanosensor system is a classical analogue of electromagnetically induced transparency, a famous phenomenon from quantum mechanics."

The research was conducted by the team at Imperial College London in collaboration with IMEC and the Catholic University in Leuven, Belgium, and Rice University in Houston, Texas. -Ends-

For more information please contact: Danielle Reeves, Imperial College London press office. Tel: +44 (0)20 7594 2198. Out-of-hours duty press office: +44 (0)7803 886248
Email: Danielle.reeves@imperial.ac.uk

Notes to editors:

1. 'Fano Resonances in Individual Coherent Plasmonic Nanocavities', Nano Letters, Issue 4, April 8 2009.

Niels Verellen, Yannick Sonnefraud, Heidar Sobhani, Feng Hao, Victor V. Moshchalkov, Pol Van Dorpe, Peter Nordlander, and Stefan A. Maier.

-IMEC, Kapeldreef 75, 3001 Leuven, Belgium.
-INPAC-Institute for Nanoscale Physics and Chemistry, Nanoscale Superconductivity and Magnetism and Pulsed Fields Group, K. U. Leuven Celestijnenlaan 200 D, B-3001 Leuven, Belgium.
-Experimental Solid State Group, Physics Department, Imperial College, London SW7 2AZ, U.K.
-Laboratory for Nanophotonics, Department of Physics and Astronomy, M.S. 61, Rice University, Houston, Texas 77005-1892

2. About Imperial College London

Consistently rated amongst the world's best universities, Imperial College London is a science-based institution with a reputation for excellence in teaching and research that attracts 13,000 students and 6,000 staff of the highest international quality.

Innovative research at the College explores the interface between science, medicine, engineering and business, delivering practical solutions that improve quality of life and the environment - underpinned by a dynamic enterprise culture.

Since its foundation in 1907, Imperial's contributions to society have included the discovery of penicillin, the development of holography and the foundations of fibre optics. This commitment to the application of research for the benefit of all continues today, with current focuses including interdisciplinary collaborations to improve health in the UK and globally, tackle climate change and develop clean and sustainable sources of energy.

Website: www.imperial.ac.uk

3. About the Engineering and Physical Sciences Research Council

The Engineering and Physical Sciences Research Council (EPSRC) is the UK's main agency for funding research in engineering and the physical sciences. The EPSRC invests more than £740 million a year in research and postgraduate training, to help the nation handle the next generation of technological change.

Website: www.epsrc.ac.uk

Contact: Danielle Reeves danielle.reeves@imperial.ac.uk 44-207-594-2198 Imperial College London

MIT virus battery could power cars, electronic devices

CAMBRIDGE, Mass--For the first time, MIT researchers have shown they can genetically engineer viruses to build both the positively and negatively charged ends of a lithium-ion battery.

The new virus-produced batteries have the same energy capacity and power performance as state-of-the-art rechargeable batteries being considered to power plug-in hybrid cars, and they could also be used to power a range of personal electronic devices, said Angela Belcher, the MIT materials scientist who led the research team.

The new batteries, described in the April 2 online edition of Science, could be manufactured with a cheap and environmentally benign process: The synthesis takes place at and below room temperature and requires no harmful organic solvents, and the materials that go into the battery are non-toxic.

Angela Belcher holds a display of the virus-built battery she helped engineer. The battery -- the silver-colored disc -- is being used to power an LED. Photo / Donna Coveney

In a traditional lithium-ion battery, lithium ions flow between a negatively charged anode, usually graphite, and the positively charged cathode, usually cobalt oxide or lithium iron phosphate. Three years ago, an MIT team led by Belcher reported that it had engineered viruses that could build an anode by coating themselves with cobalt oxide and gold and self-assembling to form a nanowire. In the latest work, the team focused on building a highly powerful cathode to pair up with the anode, said Belcher, the Germeshausen Professor of Materials Science and Engineering and Biological Engineering. Cathodes are more difficult to build than anodes because they must be highly conducting to be a fast electrode, however, most candidate materials for cathodes are highly insulating (non-conductive).

To achieve that, the researchers, including MIT Professor Gerbrand Ceder of materials science and Associate Professor Michael Strano of chemical engineering, genetically engineered viruses that first coat themselves with iron phosphate, then grab hold of carbon nanotubes to create a network of highly conductive material.

Because the viruses recognize and bind specifically to certain materials (carbon nanotubes in this case), each iron phosphate nanowire can be electrically "wired" to conducting carbon nanotube networks. Electrons can travel along the carbon nanotube networks, percolating throughout the electrodes to the iron phosphate and transferring energy in a very short time.

The viruses are a common bacteriophage, which infect bacteria but are harmless to humans.

The team found that incorporating carbon nanotubes increases the cathode's conductivity without adding too much weight to the battery. In lab tests, batteries with the new cathode material could be charged and discharged at least 100 times without losing any capacitance. That is fewer charge cycles than currently available lithium-ion batteries, but "we expect them to be able to go much longer," Belcher said.

The prototype is packaged as a typical coin cell battery, but the technology allows for the assembly of very lightweight, flexible and conformable batteries that can take the shape of their container.

Last week, MIT President Susan Hockfield took the prototype battery to a press briefing at the White House where she and U.S. President Barack Obama spoke about the need for federal funding to advance new clean-energy technologies.

Now that the researchers have demonstrated they can wire virus batteries at the nanoscale, they intend to pursue even better batteries using materials with higher voltage and capacitance, such as manganese phosphate and nickel phosphate, said Belcher. Once that next generation is ready, the technology could go into commercial production, she said. ###

Lead authors of the Science paper are Yun Jung Lee and Hyunjung Yi, graduate students in materials science and engineering. Other authors are Woo-Jae Kim, postdoctoral fellow in chemical engineering; Kisuk Kang, recent MIT PhD recipient in materials science and engineering; and Dong Soo Yun, research engineer in materials science and engineering.

The research was funded by the Army Research Office Institute of the Institute of Collaborative Technologies, and the National Science Foundation through the Materials Research Science and Engineering Centers program.

Contact: Elizabeth Thomson thomson@mit.edu 617-258-5402 Massachusetts Institute of Technology

Researchers Peer into Nanowires to Measure Dopant Properties

EVANSTON, Ill. --- Semiconductor nanowires -- tiny wires with a diameter as small as a few billionths of a meter -- hold promise for devices of the future, both in technology like light-emitting diodes and in new versions of transistors and circuits for the next generation of electronics. But in order to utilize the novel properties of nanowires, their composition must be precisely controlled, and researchers must better understand just exactly how the composition is determined by the synthesis conditions.

Nanowires are synthesized from elements that form bulk semiconductors, whose electrical properties are in turn controlled by adding minute amounts of impurities called dopants. The amount of dopant determines the conductivity of the nanowire.

Assistant Professor, Department of Materials Science and Engineering, Northwestern University. 3019 Cook Hall, 2220 Campus Drive, Evanston, IL 60208 Office: (847) 491-2232. Lab: (847) 491-4959. Fax: (847) 491-7820 E-mail: lauhon@northwestern.edu

But because nanowires are so small -- with diameters ranging from 3 to 100 nanometers -- researchers have never been able to see just exactly how much of the dopant gets into the nanowire during synthesis. Now, using a technique called atom probe tomography, Lincoln Lauhon, assistant professor of materials science and engineering at Northwestern University’s McCormick School of Engineering and Applied Science, has provided an atomic-level view of the composition of a nanowire. By precisely measuring the amount of dopant in a nanowire, researchers can finally understand the synthesis process on a quantitative level and better predict the electronic properties of nanowire devices.

“We simply mapped where all the atoms were in a single nanowire, and from the map we determined where the dopant atoms were,” said Lauhon. “The more dopant atoms you have, the higher the conductivity.”

Previously, researchers could not measure the amount of dopant and had to judge the success of the synthesis based on indirect measurements of the conductivity of nanowire devices. That meant that variations in device performance were not readily explained.

“If we can understand the origin of the electrical properties of nanowires, and if we can rationally control the conductivity, then we can specify how a nanowire will perform in any type of device,” said Lauhon. “This fundamental scientific understanding establishes a basis for engineering.”

He and his group performed the research at Northwestern’s Center for Atom Probe Tomography, which uses a Local Electrode Atom Probe™ microscope to dissect single nanowires and identify their constituents. This instrumentation software allows 3-D images of the nanowire to be generated, so Lauhon could see from all angles just how the dopant atoms were distributed within the nanowire.

In addition to measuring the dopant in the nanowire, Lauhon’s colleague, Peter Voorhees, Frank C. Engelhart Professor of Materials Science and Engineering at Northwestern, created a model that relates the nanowire doping level to the conditions during the nanowire synthesis. The researchers performed the experiment using germanium wires and phosphorous dopants -- and they will soon publish results using silicon -- but the model provides guidance for nanowires made from other elements, as well.

“This model uses insight from Lincoln’s experiment to show what might happen in other systems,” Voorhees says. “If nanowires are going to be used in device applications, this model will provide guidance as to the conditions that will enable us to add these elements and control the doping concentrations.”

Both professors will continue working on this research to broaden the model.

“We would like to establish the general principles for doping semiconductor nanowires,” said Lauhon.

The paper is titled “Direct Measurement of Dopant Distribution in an Individual Vapour-liquid-solid Nanowire.” In addition to Lauhon and Voorhees, the other authors are Daniel E. Perea, Eric R. Hemesath, Edwin J. Schwalbach and Jessica L. Lensch-Falk, all from Northwestern.

The Office of Naval Research and the National Science Foundation supported the research.

Contact: Kyle Delaney k-delaney@northwestern.edu 847-467-4010 Northwestern University

Magnetic nano-'shepherds' organize cells

DURHAM, N.C. -- The power of magnetism may address a major problem facing bioengineers as they try to create new tissue -- getting human cells to not only form structures, but to stimulate the growth of blood vessels to nourish that growth.

A multidisciplinary team of investigators from Duke University, Case Western Reserve University and the University of Massachusetts, Amherst created an environment where magnetic particles suspended within a specialized solution act like molecular sheep dogs. In response to external magnetic fields, the shepherds nudge free-floating human cells to form chains which could potentially be integrated into approaches for creating human tissues and organs.

The cells not only naturally adhere to each other upon contact, the researchers said, but the aligned cellular configurations may promote or accelerate the creation and growth of tiny blood vessels.

Caption: The process of forming cell chains using magnetic particles is shown in this photo. Credit: Duke University/Case Western Reserve University/University of Mass. Amherst. Usage Restrictions: None. Caption: This photo shows Duke's Ben Yellen, left, and Randall Erb. Credit: Duke University. Usage Restrictions: None.

"We have developed an exciting way of using magnetism to manipulate human cells floating freely in a solution containing magnetic nanoparticles" said Randall Erb, fourth-year graduate student in the laboratory of Benjamin Yellen, assistant professor of Mechanical Engineering and Materials Science, at Duke University's Pratt School of Engineering. "This new cell assembly process holds much promise for tissue engineering research and offers a novel way to organize cells in an inexpensive, easily accessible way." Melissa Krebs, third-year biomedical engineering graduate student at Case Western and Erb's sister, co-authored a paper appearing online in advance of the May publication of Nano Letters, a journal published by the American Chemical Society. "The cells have receptors on their surfaces that have an affinity for other cells," Krebs said. "They become sticky and attach to each other. When endothelial cells get together in a linear fashion, as they did in our experiments, it may help them to organize into tiny tubules."

The iron-containing nanoparticles used by the researchers are suspended within a liquid known as a ferrofluid. One of the unique properties of these ferrofluids is that they become highly magnetized in the presence of external magnetism, which allows researchers to readily manipulate the chain formation by altering the strength of the magnetic field.

At the end of the process, the nanoparticles are simply washed away, leaving a linear chain of cells. That the cells remain alive, healthy and relatively unaltered without any harmful effects from the process is one of the major advances of the new approach over other strategies using magnetism.

"Others have tried using magnetic particles either within or on the surface of the cells," Erb said. "However, the iron in the nanoparticles can be toxic to cells. Also, the process of removing the nanoparticles afterward can be harmful to the cell and its function."

The key ingredient for these studies was the synthesis of non-toxic ferrofluids by colleagues Bappaditya Samanta and Vincent Rotello at the University of Massachusetts, who developed a method for coating the magnetic nanoparticles with bovine serum albumin (BSA), a protein derived from cow blood. BSA is a stable protein used in many experiments because it is biochemically inert. In these experiments, the BSA shielded the cells from the toxic iron.

"The other main benefit of our approach is that we are creating three-dimensional cell chains without any sophisticated techniques or equipment," Krebs said. "Any type of tissue we'd ultimately want to engineer will have to be three-dimensional."

For their experiments, the researchers used human umbilical vein endothelial cells. Others types of cells have also been used, and it appears to the researchers that this new approach can work with any type of cell.

"While still in the early stages, we have shown that we can form oriented cellular structures," said Eben Alsberg, assistant professor of Biomedical Engineering and Orthopedic Surgery at Case Western and senior author of the paper. "The next step is to see if the spatial arrangement of these cells in three dimensions will promote vascular formation. A major hurdle in tissue engineering has been vascularization, and we hope that this technology may help to address the problem." ###

The research was supported by the National Institutes of Health, the National Science Foundation and Case Western.

Contact: Richard Merritt richard.merritt@duke.edu 919-660-8414 Duke University

Engineers develop method to disperse chemically modified graphene in organic solvents VIDEO

AUSTIN, Texas — A method for creating dispersed and chemically modified graphene sheets in a wide variety of organic solvents has been developed by a University of Texas at Austin engineering team led by Professor Rod Ruoff, opening the door to use graphene in a host of important materials and applications such as conductive films, polymer composites, ultracapacitors, batteries, paints, inks and plastic electronics.

Graphene is a unique atom-thick, carbon-based material. Its unusual combination of very high mechanical stiffness and strength, high and tunable electrical and thermal conductivity, and the fact that chemists can alter its chemistry readily means it has applications in nanoelectronics, solar cell devices and energy storage devices such as batteries and ultracapacitors.

Of critical importance to many of these possible applications is the dispersion of graphene or chemically modified graphene in solvents that can, for example, coat products to make them stronger, stiffer and improve thermal and electrical conductivity.

Rod Ruoff

"A part of our research group has avidly pursued developing an understanding of how to readily make colloidal dispersions of graphene in a wide variety of solvents from water to various organic liquids," said Ruoff, professor of mechanical engineering who holds the Cockrell Family Regents Chair in Engineering #7.

"The solvents and the chemical functionality of the graphene, and thus how the graphene disperses, has allowed us to develop important rules for the research and technology communities.

"By using 'solubility parameters' ubiquitously applied by industry to determine the solvents most likely to dissolve certain materials or to create good colloids, the researchers have developed a set of solubility parameters for chemically modified graphenes," Ruoff added. "We believe that this approach will have exceptional utility for technology transition in use of colloidal suspensions of graphene sheets."

The findings were detailed in the paper "Colloidal Suspensions of Highly Reduced Graphene Oxide in a Wide Variety of Organic Solvents" which will be published in the April issue of the journal Nano Letters. It was co-authored by Sungjin Park, Jinho An, Inhwa Jung, Richard D. Piner, Sung Jin An, Xuesong Li, Aruna Velamakanni and Ruoff, all of the Department of Mechanical Engineering at the university.

Park and Ruoff, who is one of the scientific community's foremost authorities in the study of graphene, have also written the article "Chemical Methods for the Production of Graphenes," which appeared in the March 29 issue of Nature Nanotechnology. It's an extensive review of various methods of making graphene through chemical methods, which also discusses colloidal suspensions of graphene and how they are made.

Funding for the colloidal suspension research was provided by The University of Texas at Austin and the Texas Nanotechnology Research Superiority Initiative.

Learn more about Ruoff's work.

For more information, contact: Daniel Vargas, Cockrell School of Engineering, 512-471-7541; Rodney Ruoff, Department of Mechanical Engineering, Cockrell School of Engineering, 512-471-4691.

Contact: Rod Ruoff r.ruoff@mail.utexas.edu 512-471-4691 University of Texas at Austin

DNA-Based Assembly Line for Precision Nano-Cluster Construction VIDEO

Method could lead to rapid, reliable assembly of new biosensors and solar cells

UPTON, NY - Building on the idea of using DNA to link up nanoparticles - particles measuring mere billionths of a meter - scientists at the U.S. Department of Energy's (DOE) Brookhaven National Laboratory have designed a molecular assembly line for predictable, high-precision nano-construction. Such reliable, reproducible nanofabrication is essential for exploiting the unique properties of nanoparticles in applications such as biological sensors and devices for converting sunlight to electricity. The work will be published online March 29, 2009, by Nature Materials.

The Brookhaven team has previously used DNA, the molecule that carries life's genetic code, to link up nanoparticles in various arrangements, including 3-D nano-crystals.

The idea is that nanoparticles coated with complementary strands of DNA - segments of genetic code sequence that bind only with one another like highly specific Velcro - help the nanoparticles find and stick to one another in highly specific ways. By varying the use of complementary DNA and strands that don't match, scientists can exert precision control over the attractive and repulsive forces between the nanoparticles to achieve the desired construction. Note that the short DNA linker strands used in these studies were constructed artificially in the laboratory and don't "code" for any proteins, as genes do.

Using DNA to assemble nanoclusters: (a) (1) DNA linker strands (squiggly lines) are used to attach DNA-coated nanoparticles to a surface. (2) Linker strands are attached to the top side of the nanoparticle. (b) (3a) A nanoparticle of a second type with complementary DNA encoding recognizes the exposed linker strands and attaches to the surface-anchored nanoparticle. (4a and 5a) The assembled structure is released from the surface support, resulting in a two-particle, dimer cluster. (c) (3b) Alternatively, the immobilized particles produced in step (a) are released from the surface, leaving the opposite-side linker strands free to bind with multiple particles (4b) to form asymmetric "Janus" clusters.

The latest advance has been to use the DNA linkers to attach some of the DNA-coated nanoparticles to a solid surface to further constrain and control how the nanoparticles can link up. This yields even greater precision, and therefore a more predictable, reproducible high-throughput construction technique for building clusters from nanoparticles. "When a particle is attached to a support surface, it cannot react with other molecules or particles in the same way as a free-floating particle," explained Brookhaven physicist Oleg Gang, who led the research at the Lab's Center for Functional Nanomaterials. This is because the support surface blocks about half of the particle's reactive surface. Attaching a DNA linker or other particle that specifically interacts with the bound particle then allows for the rational assembly of desired particle clusters. "By controlling the number of DNA linkers and their length, we can regulate interparticle distances and a cluster's architecture," said Gang. "Together with the high specificity of DNA interactions, this surface-anchored technique permits precise assembly of nano-objects into more complex structures." Instead of assembling millions and millions of nanoparticles into 3-D nanocrystals, as was done in the previous work, this technique allows the assembly of much smaller structures from individual particles. In the Nature Materials paper, the scientists describe the details for producing symmetrical, two-particle linkages, known as dimers, as well as small, asymmetrical clusters of particles - both with high yields and low levels of other, unwanted assemblies.

"When we arrange a few nanoparticles in a particular structure, new properties can emerge," Gang emphasized. "Nanoparticles in this case are analogous to atoms, which, when connected in a molecule, often exhibit properties not found in the individual atoms. Our approach allows for rational and efficient assembly of nano-'molecules.' The properties of these new materials may be advantageous for many potential applications."

For example, in the paper, the scientists describe an optical effect that occurs when nanoparticles are linked as dimer clusters. When an electromagnetic field interacts with the metallic particles, it induces a collective oscillation of the material's conductive electrons. This phenomenon, known as a plasmon resonance, leads to strong absorption of light at a specific wavelength.

"The size and distance between the linked particles affect the plasmonic behavior," said Gang. By adjusting these parameters, scientists might engineer clusters for absorbing a range of wavelengths in solar-energy conversion devices. Modulations in the plasmonic response could also be useful as a new means for transferring data, or as a signal for a new class of highly specific biosensors.

Asymmetric clusters, which were also assembled by the Brookhaven team, allow an even higher level of control, and therefore open new ways to design and engineer functional nanomaterials. ###

Because of its reliability and precision control, Brookhaven's nano-assembly method would be scalable for the kind of high-throughput production that would be essential for commercial applications. Brookhaven Lab has applied for a patent on the assembly method as well as several specific applications of the technology. For information about the patent or licensing this technology, contact Kimberley Elcess at (631) 344-4151, or elcess@bnl.gov.

In addition to Gang, the team included materials scientist Dmytro Nykypanchuk, summer student Marine Cuisinier, and biologist Daniel (Niels) van der Lelie, all from Brookhaven, and former Brookhaven chemist Matthew Maye, now at Syracuse University. Their work was funded by DOE's Office of Science and through a Goldhaber Distinguished Fellowship sponsored by Brookhaven Science Associates.

The Center for Functional Nanomaterials at BNL is one of the five DOE Nanoscale Science Research Centers (NSRCs), premier national user facilities for interdisciplinary research at the nanoscale. Together the NSRCs comprise a suite of complementary facilities that provide researchers with state-of-the-art capabilities to fabricate, process, characterize, and model nanoscale materials, and constitute the largest infrastructure investment of the National Nanotechnology Initiative. The NSRCs are located at DOE's Brookhaven, Argonne, Lawrence Berkeley, Oak Ridge, and Sandia and Los Alamos National Laboratories. For more information about the DOE NSRCs, please visit http://nano.energy.gov.

Related Links

DNA Technique Yields 3-D Crystalline Organization of Nanoparticles, 1/30/2008:
www.bnl.gov/bnlweb/pubaf/pr/PR_display

New DNA-Based Technique For Assembly of Nano- and Micro-sized Particles, 9/12/2007:
www.bnl.gov/bnlweb/pubaf/pr/PR_display

Nanoparticle Assembly Enters the Fast Lane, 10/11/2006:
www.bnl.gov/bnlweb/pubaf/pr/PR_display

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.

Visit Brookhaven Lab's electronic newsroom for links, news archives, graphics, and more: www.bnl.gov/newsroom

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

New molecular force probe stretches molecules, atom by atom

CHAMPAIGN, Ill. — Chemists at the University of Illinois have created a simple and inexpensive molecular technique that replaces an expensive atomic force microscope for studying what happens to small molecules when they are stretched or compressed.

The researchers use stiff stilbene, a small, inert structure, as a molecular force probe to generate well-defined forces on various molecules, atom by atom.

"By pulling on different pairs of atoms, we can explore what happens when we stretch a molecule in different ways," said chemistry professor Roman Boulatov. "That information tells us a lot about the properties of fleeting structures called transition states that govern how, and how fast, chemical transformations occur."

Roman Boulatov Department of Chemistry University of Illinois, A554 Chemical & Life Sciences Lab, 600 South Mathews Avenue, Urbana, IL 61801 (217)333-4968 Fax: (217)244-3186 boulatov@illinois.edu. WEB: Boulatov Group

Boulatov, research associate Qing-Zheng Yang, postdoctoral researcher Daria Khvostichenko, and graduate students Zhen Huang and Timothy Kucharski describe the molecular force probe and present early results in a paper accepted for publication in Nature Nanotechnology. The paper is to be posted on the journal's Web site on Sunday (March 29). Similar to the force that develops when a rubber band is stretched, restoring forces occur in parts of molecules when they are stretched. Those restoring forces contain information about how much the molecule was distorted, and in what direction. The molecular force probe allows reaction rates to be measured as a function of the restoring force in a molecule that has been stretched or compressed. This information is essential for developing a chemomechanical kinetic theory that explains how force affects rates of chemical transformations. Such a theory will help researchers better understand a host of complex phenomena, from the operation of motor proteins that underlie the action of muscles, to the propagation of cracks in polymers and the mechanisms by which living cells sense forces in their surroundings.

"Localized reactions offer the best opportunity to gain fundamental insights into the interplay of reaction rates and molecular restoring forces," Boulatov said, "but these reactions are extremely difficult to study with a microscopic force probe."

Microscopic force probes, which are utilized by atomic force microscopes, are much too large to grab onto a single pair of atoms. Measuring microns in size, the probe tips contact many atoms at once, smearing experimental results.

"By replacing microscopic force probes with small molecules like stiff stilbene, we can study the relationship between restoring force and reaction rate for localized reactions," Boulatov said. "The more accurately we know where our probe acts, the better control we have over the distortion, and the easier it is to interpret the results."

Using conventional methods, Boulatov and his students first attach stiff stilbene to a molecule they wish to study. Then they irradiate the resulting molecular assembly with visible light. The light causes the stilbene to change from a fully relaxed shape to one that exerts a desired force on the molecule. The chemists then measure the reaction rate of the molecule as a function of temperature, which reveals details of what caused the reaction to accelerate.

One type of chemical transformation the researchers studied is the breaking of one strong (covalent) chemical bond at a time. The experimental results were sometimes counterintuitive.

"Unlike a rubber band, which will always break faster when stretched, pulling on some chemical bonds doesn't make them break any faster; and sometimes it's a bond that you don't pull on that will break instead of the one you do pull," Boulatov said. "That's because experiences in the macroscopic world do not map particularly well to the molecular world."

Molecules do not live in a three-dimensional world, Boulatov said. Molecules populate a multi-dimensional world, where forces applied to a pair of atoms can act in more than three dimensions.

"Even small molecules will stretch and deform in many different ways," Boulatov said, "making the study of molecular forces even more intriguing." ###

Funding was provided by the National Science Foundation, the U.S. Air Force Office of Scientific Research, the American Chemical Society Petroleum Research Fund and the U. of I. The National Center for Supercomputing Applications and the U.S. Department of Defense High-Performance Computing Modernization Program provided computational resources.

Contact: James E. Kloeppel, Physical Sciences Editor kloeppel@illinois.edu 217-244-1073 University of Illinois at Urbana-Champaign

Quantum dots and nanomaterials: Ingredients for better lighting and more reliable power

TEMPE, Ariz. – Imagine flexible lighting devices manufactured by using printing techniques. Imagine solar power sources equally as reliable and as portable as any conventional power source.

Such advances are among aims of research at Arizona State University to find ways of more effectively harnessing solar power and producing more energy-efficient, durable and custom-designed light sources. The work is now drawing support from two international corporations.

U.S.-based Solterra Renewable Technologies Inc. and Nitto Denko Corp. of Japan are investing more than $3.7 million through grants to help fund the research led by ASU engineering professor Ghassan Jabbour.

Ghassan Jabbour, Professor School of Materials Email: jabbour@asu.edu Phone: (480) 727-7002

Jabbour's work focuses on the use of nanomaterials and quantum dots in solar cells and solid state lighting. Technical advances in this area "will open the way for a new wave of more efficient and portable power and light sources in as many shapes and varieties as designers can imagine," he says. Jabbour, who teaches in ASU's School of Materials, is doing his research through the Advanced Photovoltaics Center, which he directs. The center is part of the Arizona Institute for Renewable Energy at ASU. Jabbour also is director of optoelectronics research for the Flexible Display Center, part of the university's Ira A. Fulton School of Engineering.

Illuminating printing processes

Work funded by the grants will include the study of the materials science, physics and engineering solutions necessary to produce the next generation of solar cells, which will cost less to produce and perform more efficiently, Jabbour says.

The project is an example of the economic benefit a research university can bring to its state. Each year, Arizona universities contribute nearly $1 billion into the Arizona economy from their research, most of which is funded by the U.S. government and entities from outside the state. Research money brought in by universities is restricted money that can be used only for the research activity it supports. It cannot be used to compensate for cuts in other parts of the university's budget.

The quantum dots/solar cells project already has brought a small company to open new operations at the ASU Research Park. Given the increasing interest in solar energy and the means to produce it at lower costs, the company can be expected to grow rapidly, Jabbour says.

One of the major scientific and engineering challenges of Ghassan's project involves how to employ printing techniques to fabricate low-cost alternatives to current solar cells. Research articles on printed organic solar cells written by Jabbour and other members of his team continue to be cited by fellow researchers more than any other articles in the area of printed ultra-thin solar cell research. (Ultra-thin means it involves materials less than 100 times the thickness of a typical human hair.)

Printing is a viable method for mass production of solar cells. Some printing techniques, such as silk-screen printing (commonly used to print logos, numbers and pictures on textiles), are already used in some aspects of solar cell manufacturing.

Printing allows for large numbers of solar-cell devices to be manufactured rapidly, thus eventually bringing down costs.

"In our work, we will be investigating various techniques such as inkjet printing, screen printing, and roll-to-roll, which is similar to newspaper printing techniques, to see what works best for solar cell manufacturing," Jabbour says.

The power of photons

The material science and engineering aspect of the projects involves experiments with materials that exhibit unique properties at the nanoscale, specifically materials that use photons to achieve more efficient conversion of energy into electricity. The materials also have a broader absorption spectrum of incident solar light – meaning they can make more effective use of solar light for conversion into electricity.

"It's traditional to generate one electron-hole pair for every absorbed photon in most solar cells," Jabbour says, but researchers in his lab are working on generating more multiple electron-hole pairs per photon to achieve increased power-conversion efficiency. This is accomplished by producing a higher number of electrons for each absorbed photon from incident light.

In most bulk semiconducting materials, Jabbour explains, absorption of an incident photon (light quanta) with the right energy can excite an electron enough to move it across an energy band gap – thus resulting in an electron-hole pair. But the same photon might generate more than one electron-hole pair if the material is made into much smaller dimensions – such as the size of a quantum dot.

Quantum dots are small particles about few nanometers (a billionth of a meter) in size. By adjusting the particles' physical dimensions, their optical and electronic properties can be fine-tuned. Through such a process, the resulting characteristics of the materials are different than the characteristics of the same material in bulk size, Jabbour explains.

The challenge is how to extract most of the charges from the dots to transfer in the form of electrical current to the device being powered by the solar cell, he says.

Recent results of 3 percent in power conversion in this area are encouraging. Such an efficiency will continue to climb as better materials and device structures are being developed, which is a part of Jabbour's work supported by the grants.

Energy conservation goals

More efficient solar cells are only one part of the solution to the nation's growing energy needs. Just as important is making efficient use of energy in conventional systems, Jabbour says.

The two technologies he and his team are working on are interrelated, involving both energy generation and energy conservation. Although there is a strong push for alternative energy, including solar energy, Jabbour says much can be accomplished by focusing on research to lower the power consumption of conventional technologies. This work involves the area of solid state lighting.

One of the corporate grants is supporting work directly aimed at understanding the materials and device physics of nanoscale structures for low-power, nanothick solid state lighting applications.

The materials used are hybrid nanomaterials targeting white-light emission from a single building block. The light source made out of these materials also will have a nano-range thickness and can be operated at high brightness (equivalent to a ceiling lamp) using a 9-volt battery source. Just as with solar cells, these light sources will also be printable in the future, Jabbour says.

Flexibility in lighting devices

"The beauty of these two projects is their compatibility with rugged substrates, including flexible ones," he says.

A substrate is a material on which circuits or other small devices are formed or fabricated. Flexible substrates (for example, plastic, thin metal foils, or cloth) allow for more durable lights that also weigh less than conventional lighting devices and can be produced in a variety of shapes.

"Imagine a light that is made on a roll that can be cut into various shapes according to the desire of the user," Jabbour says. Such an advance is still far off, but not impossible. In fact, he points out, printed lights made out of inorganic phosphors that operate at about 120 to 150 volts are already available. The drawback is that currently they can be operated only at such high voltages.

The two technologies promise to provide low-cost, high-efficiency solar cells and solid state lights that can be made on thin flexible substrates, resulting in light-weight durable modules that are easier to place on roof tops (for example, solar-cell arrays) and indoors (lamps and similar lighting devices). ###

• SOURCE: Ghassan Jabbour, jabbour@asu.edu Professor, School of Materials. Director, Advanced Photovoltaics Center (480)727-8930
• MEDIA CONTACT: Joe Kullman, joe.kullman@asu.edu (480) 965-8122 direct line (480) 773-1364 mobile
• Ira A. Fulton School of Engineering. Arizona State University. Tempe, Arizona USA. www.fulton.asu.edu/fulton/

Contact: Joe Kullman, joe.kullman@asu.edu 480-965-8122. Arizona State University

University of Miami physicist develops battery using new source of energy

His discovery is a 'proof of principle' of the existence of a 'spin battery'

CORAL GABLES, FL. — Researchers at the University of Miami and at the Universities of Tokyo and Tohoku, Japan, have been able to prove the existence of a "spin battery," a battery that is "charged" by applying a large magnetic field to nano-magnets in a device called a magnetic tunnel junction (MTJ). The new technology is a step towards the creation of computer hard drives with no moving parts, which would be much faster, less expensive and use less energy than current ones. In the future, the new battery could be developed to power cars. The study will be published in an upcoming issue of Nature and is available in an online advance publication of the journal.

Caption: The top is a graphic representation of the overall device structure. The diameter is roughly that of a human hair. The bottom is a magnified image of the central part. The white spots are atoms and the white circles are the nano-magnets, the "working part" of the device. Credit: Pham Nam Hai. Usage Restrictions: None.

The device created by University of Miami Physicist Stewart E. Barnes, of the College of Arts and Sciences and his collaborators can store energy in magnets rather than through chemical reactions. Like a winding up toy car, the spin battery is "wound up" by applying a large magnetic field --no chemistry involved. The device is potentially better than anything found so far, said Barnes. "We had anticipated the effect, but the device produced a voltage over a hundred times too big and for tens of minutes, rather than for milliseconds as we had expected," Barnes said. "That this was counterintuitive is what lead to our theoretical understanding of what was really going on." The secret behind this technology is the use of nano-magnets to induce an electromotive force. It uses the same principles as those in a conventional battery, except in a more direct fashion.

The energy stored in a battery, be it in an iPod or an electric car, is in the form of chemical energy. When something is turned "on" there is a chemical reaction which occurs and produces an electric current. The new technology converts the magnetic energy directly into electrical energy, without a chemical reaction. The electrical current made in this process is called a spin polarized current and finds use in a new technology called "spintronics."

The new discovery advances our understanding of the way magnets work and its immediate application is to use the MTJs as electronic elements which work in different ways to conventional transistors. Although the actual device has a diameter about that of a human hair and cannot even light up an LED (light-emitting diode--a light source used as electronic component), the energy that might be stored in this way could potentially run a car for miles. The possibilities are endless, Barnes said.

"There are magnets hidden away in many things, for example there are several in a mobile telephone, many in a car, and they are what keeps your refrigerator closed," he said. "There are so many that even a small change in the way we understand of how they work, and which might lead to only a very small improvement in future machines, has a significant financial and energetic impact." ###

The University of Miami's mission is to educate and nurture students, to create knowledge, and to provide service to our community and beyond. Committed to excellence and proud of the diversity of our University family, we strive to develop future leaders of our nation and the world. www.miami.edu.

Contact: Marie Guma-Diaz m.gumadiaz@umiami.edu 305-284-1601 University of Miami

Nanowires may lead to better fuel cells

The creation of long platinum nanowires at the University of Rochester could soon lead to the development of commercially viable fuel cells.

Described in a paper published today in the journal Nano Letters, the new wires should provide significant increases in both the longevity and efficiency of fuel cells, which have until now been used largely for such exotic purposes as powering spacecraft. Nanowire enhanced fuel cells could power many types of vehicles, helping reduce the use of petroleum fuels for transportation, according to lead author James C. M. Li, professor of mechanical engineering at the University of Rochester.

"People have been working on developing fuel cells for decades. But the technology is still not being commercialized," says Li. "Platinum is expensive, and the standard approach for using it in fuel cells is far from ideal. These nanowires are a key step toward better solutions."

Electron microscope view of platinum nanowires with beads. Electron microscope view of platinum nanowires without beads

The platinum nanowires produced by Li and his graduate student Jianglan Shui are roughly ten nanometers in diameter and also centimeters in length—long enough to create the first self-supporting "web" of pure platinum that can serve as an electrode in a fuel cell. Much shorter nanowires have already been used in a variety of technologies, such as nanocomputers and nanoscale sensors. By a process known as electrospinning—a technique used to produce long, ultra-thin solid fibers—Li and Shui were able to create platinum nanowires that are thousands of times longer than any previous such wires. "Our ultimate purpose is to make free-standing fuel cell catalysts from these nanowires," says Li. Within a fuel cell the catalyst facilitates the reaction of hydrogen and oxygen, splitting compressed hydrogen fuel into electrons and acidic hydrogen ions.

Electrons are then routed through an external circuit to supply power, while the hydrogen ions combine with electrons and oxygen to form the "waste" product, typically liquid or vaporous water.

Platinum has been the primary material used in making fuel cell catalysts because of its ability to withstand the harsh acidic environment inside the fuel cell. Its energy efficiency is also substantially greater than that of cheaper metals like nickel.

Prior efforts in making catalysts have relied heavily on platinum nanoparticles in order to maximize the exposed surface area of platinum. The basic idea is simple: The greater the surface area, the greater the efficiency. Li cites two main problems with the nanoparticle approach, both linked to the high cost of platinum.

First, individual particles, despite being solid, can touch one another and merge through the process of surface diffusion, combining to reduce their total surface area and energy. As surface area decreases, so too does the rate of catalysis inside the fuel cell.

Second, nanoparticles require a carbon support structure to hold them in place. Unfortunately, platinum particles do not attach particularly well to these structures, and carbon is subject to oxidization, and thus degradation. As the carbon oxidizes over time, more and more particles become dislodged and are permanently lost.

Li's nanowires avoid these problems completely.

With platinum arranged into a series of centimeter long, flexible, and uniformly thin wires, the particles comprising them are fixed in place and need no additional support. Platinum will no longer be lost during normal fuel cell operation.

"The reason people have not come to nanowires before is that it's very hard to make them," says Li. "The parameters affecting the morphology of the wires are complex. And when they are not sufficiently long, they behave the same as nanoparticles."

One of the key challenges Li and Shui managed to overcome was reducing the formation of platinum beads along the nanowires. Without optimal conditions, instead of a relatively smooth wire, you end up with what looks more like a series of interspersed beads on a necklace. Such bunching together of platinum particles is another case of unutilized surface area.

"With platinum being so costly, it's quite important that none of it goes to waste when making a fuel cell," says Li. "We studied five variables that affect bead formation and we finally got it—nanowires that are almost bead free."

His current objective is to further optimize laboratory conditions to obtain fewer beads and even longer, more uniformly thin nanowires. "After that, we're going to make a fuel cell and demonstrate this technology," says Li. ###

About the University of Rochester

The University of Rochester (www.rochester.edu) is one of the nation's leading private universities. Located in Rochester, N.Y., the University gives students exceptional opportunities for interdisciplinary study and close collaboration with faculty through its unique cluster-based curriculum. Its College of Arts, Sciences, and Engineering is complemented by the Eastman School of Music, Simon School of Business, Warner School of Education, Laboratory for Laser Energetics, Schools of Medicine and Nursing, and the Memorial Art Gallery.

Contact: Evan Wendel evan.wendel@rochester.edu 585-275-2671 University of Rochester

Turning sunlight into liquid fuels

Berkeley Lab researchers create a nano-sized photocatalyst for artificial photosynthesis.

Berkeley, CA - For millions of years, green plants have employed photosynthesis to capture energy from sunlight and convert it into electrochemical energy. A goal of scientists has been to develop an artificial version of photosynthesis that can be used to produce liquid fuels from carbon dioxide and water. Researchers with the U.S. Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) have now taken a critical step towards this goal with the discovery that nano-sized crystals of cobalt oxide can effectively carry out the critical photosynthetic reaction of splitting water molecules.

Caption: Under the fuel through artificial photosynthesis scenario, nanotubes embedded within a membrane would act like green leaves, using incident solar radiation (Hγ) to split water molecules (H2O), freeing up electrons and oxygen (O2) that then react with carbon dioxide (CO2) to produce a fuel, shown here as methanol (CH3OH). The result is a renewable green energy source that also helps scrub the atmosphere of excessive carbon dioxide from the burning of fossil fuels. Credit: Robert Flavio, Berkeley Lab Public Affairs. Usage Restrictions: None. Caption: Feng Jiao (left) and Heinz Frei, chemists with Berkeley Lab's Physical Biosciences Division, have been investigating metal oxide catalysts for the production of liquid fuels through artificial photosynthesis. Credit: photo by Roy Kaltschmidt, Berkeley Lab Public Affairs. Usage Restrictions: None.

"Photooxidation of water molecules into oxygen, electrons and protons (hydrogen ions) is one of the two essential half reactions of an artifical photosynthesis system - it provides the electrons needed to reduce carbon dioxide to a fuel," said Heinz Frei, a chemist with Berkeley Lab's Physical Biosciences Division, who conducted this research with his postdoctoral fellow Feng Jiao. "Effective photooxidation requires a catalyst that is both efficient in its use of solar photons and fast enough to keep up with solar flux in order to avoid wasting those photons. Clusters of cobalt oxide nanocrystals are sufficiently efficient and fast, and are also robust (last a long time) and abundant. They perfectly fit the bill." Frei and Jiao have reported the results of their study in the journal Angewandte Chemie, in a paper entitled: "Nanostructured Cobalt Oxide Clusters in Mesoporous Silica as Efficient Oxygen-Evolving Catalysts." This research was performed through the Helios Solar Energy Research Center (Helios SERC), a scientific program at Berkeley Lab under the direction of Paul Alivisatos, which is aimed at developing fuels from sunlight. Frei serves as deputy director of Helios SERC. Artificial photosynthesis for the production of liquid fuels offers the promise of a renewable and carbon-neutral source of transportation energy, meaning it would not contribute to the global warming that results from the burning of oil and coal. The idea is to improve upon the process that has long-served green plants and certain bacteria by integrating into a single platform light-harvesting systems that can capture solar photons and catalytic systems that can oxidize water – in other words, an artificial leaf.

"To take advantage of the flexibility and precision by which light absorption, charge transport and catalytic properties can be controlled by discrete inorganic molecular structures, we have been working with polynuclear metal oxide nanoclusters in silica," Frei said. "In earlier work, we found that iridium oxide was efficient and fast enough to do the job, but iridium is the least abundant metal on earth and not suitable for use on a very large scale. We needed a metal that was equally effective but far more abundant."

Green plants perform the photooxidation of water molecules within a complex of proteins called Photosystem II, in which manganese-containing enzymes serve as the catalyst. Manganese-based organometallic complexes modeled off Photosystem II have shown some promise as photocatalysts for water oxidation but some suffer from being water insoluble and none are very robust. In looking for purely inorganic catalysts that would dissolve in water and would be far more robust than biomimetic materials, Frei and Jiao turned to cobalt oxide, a highly abundant material that is an an important industrial catalyst. When Frei and Jiao tested micron-sized particles of cobalt oxide, they found the particles were inefficient and not nearly fast enough to serve as photocatalysts. However, when they nano-sized the particles it was another story.

"The yield for clusters of cobalt oxide (Co3O4) nano-sized crystals was about 1,600 times higher than for micron-sized particles," said Frei, "and the turnover frequency (speed) was about 1,140 oxygen molecules per second per cluster, which is commensurate with solar flux at ground level (approximately 1,000 Watts per square meter)."

Frei and Jiao used mesoporous silica as their scaffold, growing their cobalt nanocrystals within the naturally parallel nanoscale channels of the silica via a technique known as "wet impregnation." The best performers were rod-shaped crystals measuring 8 nanometers in diameter and 50 nanometers in length, which were interconnected by short bridges to form bundled clusters. The bundles were shaped like a sphere with a diameter of 35 nanometers. While the catalytic efficiency of the cobalt metal itself was important, Frei said the major factor behind the enhanced efficiency and speed of the bundles was their size.

"We suspect that the comparatively very large internal area of these 35 nanometer bundles (where catalysis takes place) was the main factor behind their increased efficiency," he said, "because when we produced larger bundles (65 nanometer diameters), the internal area was reduced and the bundles lost much of that efficiency gain."

Frei and Jiao will be conducting further studies to gain a better understanding of why their cobalt oxide nanocrystal clusters are such efficient and high-speed photocatalysts and also looking into other metal oxide catalysts. The next big step, however, will be to integrate the water oxidation half reaction with the carbon dioxide reduction step in an artificial leaf type system.

"The efficiency, speed and size of our cobalt oxide nanocrystal clusters are comparable to Photosystem II," said Frei. "When you factor in the abundance of cobalt oxide, the stability of the nanoclusters under use, the modest overpotential and mild pH and temperature conditions, we believe we have a promising catalytic component for developing a viable integrated solar fuel conversion system. This is the next important challenge in the field of artificial photosynthesis for fuel production." ###

The Helios Solar Energy Research Center is supported by the Director, Office of Science, Office of Basic Energy Sciences of the U.S. Department of Energy.

Berkeley Lab is a U.S. Department of Energy national laboratory located in Berkeley, California. It conducts unclassified scientific research 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

Nanotubes find niche in electric switches

Study finds nanotube structures could improve electric motors

HOUSTON -- New research from Rice University and the University of Oulu in Oulu, Finland, finds that carbon nanotubes could significantly improve the performance of electrical commutators that are common in electric motors and generators.

The research, which appeared online this month in the journal Advanced Materials, finds that "brush contact" pads made of carbon nanotubes had 10 times less resistance than did the carbon-copper composite brushes commonly used today. Brush contacts are an integral part of "commutators," or spinning electrical switches used in many battery-powered electrical devices, such as cordless drills.

Caption: Pads of nanotube "forests" were tested as brush contacts. Credit: P. Ajayan/Rice University. Usage Restrictions: Must credit.

"The findings show that nanotubes have a great deal of practical relevance as brush contacts," said lead researcher Pulickel Ajayan, Rice's Benjamin M. and Mary Greenwood Anderson Professor in Mechanical Engineering and Materials Science. "The technology is widely used in industry, both in consumer gadgets as well as larger electrical machinery,

so this could be a very interesting, near-term application for nanotubes." The combination of mechanical and electrical properties of nanotubes makes this possible.

The carbon nanotubes used in the study are hollow tubes of pure carbon that are about 30 nanometers in diameter. By comparison, a human hair is about 100,000 nanometers in diameter. In addition to being small, nanotubes are also extremely lightweight and durable, and they are excellent conductors of heat and electricity.

Because of these properties, the researchers decided to test nanotubes as brush contacts. Brush contacts are conducting pads held against a spinning metal disc or rod by spring-loaded arms. Current is passed from the spinning disc through the brush contacts to other parts of the device.

To test the feasibility of using carbon nanotube brush contacts, the research team replaced the ordinary copper-carbon composite brushes of an electric motor with small blocks that contain millions of carbon nanotubes. Under an electron microscope, these millimeter-square blocks look like a tightly packed forest.

From Ajayan's previous work, the team knew that these nanotube forests react something like a "memory foam" pillow; they regain their shape very quickly after they are compressed.

"This elasticity is something that's not found in existing composites that are used for brush contacts, and that's the essence of why the nanotube brush contacts perform better: They keep much more of their surface area in contact with the spinning disc," said Robert Vajtai, faculty fellow at Rice. Vajtai worked on the study with Ajayan and a group of researchers in Finland led by University of Oulu Researcher Krisztian Kordas.

The team believes that the improved contact between the surface of the spinning disc and the brush accounts for the 90 percent reduction in lost energy. ###

Co-authors on the paper also included Geza Toth, Jani Mäklin, Niina Halonen, Jaakko Palosaari, Jari Juuti and Heli Jantunen, all of the University of Oulu, and Gregory Sawyer of the University of Florida.

Support for the research was provided by the Academy of Finland, the University of Oulu's Micro and Nanotechnology Center, the Air Force Office of Scientific Research and the Semiconductor Research Corporation.

Contact: Jade Boyd jadeboyd@rice.edu 713-348-6778 Rice University

Iowa State researchers developing clean, renewable energy for ethanol industry

AMES, Iowa – Iowa State University researchers are working to produce clean, renewable energy by developing a new, low-emissions burner and a new catalyst for ethanol production.

Both technologies will use the synthesis gas – a mixture of carbon monoxide and hydrogen – produced by the gasification of discarded seed corn, switchgrass, wood chips and other biomass.

The burner will be designed to efficiently and cleanly burn biomass-based gas. The catalyst will be designed to convert the synthesis gas directly into ethanol.

The project is supported by a two-year, $2.37 million grant from the Iowa Power Fund, a state program to advance energy innovation and independence.

Caption: Song-Charng Kong, an Iowa State University assistant professor of mechanical engineering who studies combustion, is leading a research project that aims to develop new, clean and renewable energy technologies that complement the ethanol industry. Credit: Bob Elbert/Iowa State University, Usage Restrictions: None.

Song-Charng Kong, an Iowa State assistant professor of mechanical engineering, is leading the project. The research team also includes Robert C. Brown, the Iowa Farm Bureau Director of Iowa State's Bioeconomy Institute, an Anson Marston Distinguished Professor in Engineering and the Gary and Donna Hoover Chair in Mechanical Engineering; Victor Lin, a professor of chemistry, director of Iowa State's Center for Catalysis, director of Chemical and Biological Sciences for the U.S. Department of Energy's Ames Laboratory and founder of Catilin Inc., an Ames-based company that produces catalysts for biodiesel production; Samuel Jones, an assistant scientist for the Center for Sustainable Environmental Technologies; plus seven graduate students and two post-doctoral researchers.

The project also includes two industrial partners: Frontline BioEnergy, an Ames-based company that builds commercial-scale gasification systems; and Hawkeye Energy Holdings, an Ames-based ethanol producer with plants in Iowa Falls, Fairbank, Menlo and Shell Rock.

"We're excited about this research," Brown said. "This project partners the thermochemical conversion of biomass with ethanol production."

The project will move ethanol production beyond the fermentation of simple sugars in corn kernels. The researchers' idea is to use heat and oxygen to gasify biomass and produce a medium Btu gas (called synthesis gas) that a new catalyst can convert directly into ethanol. They'll also generate the gas using air to make a low Btu gas (called producer gas) that can be used in gas-fired heating and drying equipment.

"We're not intending to replace grain ethanol production," Brown said. "We want to complement it."

The burner

Kong, who is leading development of the new burner, said the technology could replace natural gas in conventional ethanol production. That would provide ethanol plants with a clean and renewable source of steam and heat.

Synthesis and producer gases have been used in burners designed for natural gas and other fuels. But Kong said the biomass-based gases aren't the same kind of fuel.

Biomass, for example, contains fixed nitrogen from the air and from fertilizers used to produce the biomass. Gasifying biomass releases the fixed nitrogen as ammonia in the generated gases. Improperly burning gases containing ammonia could produce nitrogen oxide emissions. Such emissions aren't acceptable in most industrial facilities under EPA regulations because they can contribute to smog and acid rain.

Kong's goal is to develop a burner that will minimize the emission of such pollutants while maximizing combustion efficiency.

He'll start by studying a conventional gas burner now at the Iowa Energy Center's Biomass Energy Conversion Facility in Nevada. He'll use that baseline data to develop computer models of the burner's performance. He'll use those models to test new designs that optimize the combustion of producer gas from biomass. And then he'll build and test a new burner at the energy center's facility.

"We're not doing a laboratory study," Kong said. "We're doing a real-world study. This will be helpful in developing a new and clean way to use renewable energy."

The catalyst

Lin, who's leading the development of a new catalyst for ethanol production, said it may be possible to efficiently produce liquid fuel directly from synthesis gas.

The key will be carbon-based nanoparticles just a few billionths of a meter wide. The particles are made from graphite and carry a transition metal that produces a chemical reaction. That reaction converts synthesis gas to ethanol.

Lin said there is an existing chemical catalyst that can convert synthesis gas to ethanol. But that catalyst has a very low yield of ethanol, produces greenhouse gases such as methane, needs heat up to 540 degrees Fahrenheit and requires high pressures.

Lin said the new catalyst should work at lower temperatures and pressures while delivering a higher yield of ethanol.

Could the technology be commercially viable?

"It's premature to say whether we have a realistic chance of that or not," Lin said. "But I can say this has shown some exciting preliminary results."

Benefits

The three Iowa State researchers said the project has potential to do a lot more than develop new technologies and patents.

A project summary says using biomass to produce ethanol and provide heat for ethanol production can reduce the nation's dependence on foreign oil, reduce the carbon footprint of ethanol plants, increase the plants' renewable energy ratio, boost the profitability of biorefineries and put energy dollars into local economies.

John Reardon, the research and development manager for Frontline BioEnergy, said an ethanol plant that produces 100 million gallons per year could buy enough biomass to add $10 million per year to the local economy. He also said repowering conventional ethanol plants with biomass-based gas could create more than a thousand new engineering and construction jobs over a 10-year conversion period.

Brown said all that can add up to "a potential evolution of the ethanol industry." ###

Contacts:

Song-Charng Kong, Mechanical Engineering, (515) 294-3244, kong@iastate.edu
Robert C. Brown, Bioeconomy Institute, (515) 294-7934, rcbrown@iastate.edu
Victor Lin, Chemistry and Ames Laboratory, (515) 294-3135, vsylin@iastate.edu
John Reardon, Frontline BioEnergy, (515) 292-1200
Nicholas T. Ryan, Hawkeye Energy Holdings, (515) 663-6404
Mike Krapfl, News Service, (515) 294-4917, mkrapfl@iastate.edu

Contact: Song-Charng Kong kong@iastate.edu 515-294-3244 Iowa State University

Spinning carbon nanotubes spawns new wireless applications

Lighter, cheaper, safer -- a team of researchers at the University of Cincinnati, known for their world record-breaking carbon nanotubes, has discovered new applications of use to both military and consumer audiences.

The University of Cincinnati has long been known for its world-record-breaking carbon nanotubes. Now researchers at the University of Cincinnati have discovered new uses by spinning carbon nanotubes (CNTs) into longer fibers with additional useful properties.

Breakthroughs Without Broken Threads

Taking technology that has already been proven to grow carbon nanotubes of world-record breaking lengths, researchers Vesselin Shanov and Mark Schulz in the UC College of Engineering NanoWorld Lab have now found new applications by spinning these fibers into strong threads.

Caption: Using the spun carbon nanotubes, UC physicist David Mast was able to broadcast AM and FM radio, video and get four bars of service on his cell phone. Credit: Lisa Britton/UC photographic services. Usage Restrictions: None. Caption: Mark Schulz, David Mast and Vesselin Shanov (left to right) from the University of Cincinnati have created new applications for spun carbon nanotubes for both military and consumer use. Credit: Lisa Britton/UC photographic services, Usage Restrictions: None. Caption: University of Cincinnati physicist David Mast replaced the antenna in his cell phone with a "nano antenna" made from spun carbon nanotubes, made in the UC labs of Mark Schulz and Vesselin Shanov. Credit: Lisa Britton/UC Photographic Services, Usage Restrictions: None.

David Mast, from UC's McMicken College of Arts and Sciences, saw possibilities in the threads. Mast, an associate professor of physics, took a 25-micron carbon nanotube thread and created a dipole antenna using double-sided transparent tape and silver paste. He was immediately successful in transmitting radio signals. "It transmitted almost as well as the copper did, but at about one ten-thousandth of the weight," says Mast. "Then I decided to dismantle my cell phone," says Mast. He created a cell phone antenna, using CNT thread and tape. Ripping the back off his own cell phone, he tore out the phone's original antenna and replaced it with his home-made one. With the "nano-antenna" or "nantenna," he was able to get four to five "bars" of service, compared to none when he removed it. "That was a very pleasant surprise, how easy it was to do," Mast says. "The hardest thing is to manipulate them. They float on ambient air." From there it was an easy leap to video, in which he was again successful. "I want to now set up a wireless webcam for the lab using these thread antennas soMast says that the key to the new applications is the quality of the material that Schulz and Shanov came up with using multi-wall carbon nanotubes. "They spin thread that is of such high quality, it opens the door to incredible possibilities," says Mast. "This is just one of many potential applications." Schulz explains that the carbon nanotube threads work well as an antenna because of something called the "skin effect." "The electrons transfer well because they want to go to the surface," he says. "Instead of traveling through a bulk mass, they are traveling across a skin." "Copper wire is a bulk material," Shanov points out. "With carbon nanotubes, all the atoms are on the surface of these carbon structures and the tubes themselves are hollow, so the CNT thread is small and light." "Carbon thread that is a fraction of the weight of current copper conductors and antennas could directly apply and would be significant to aerospace activities — commercial, military and space," he adds. "On any aircraft, there are about several hundred pounds of copper as cables and wiring."

Mast points out that the threads have what he calls an "immensely high tensile strength — perhaps five times that of steel and yet they are less dense than steel."

Now that the team has shown the feasibility of such applications, the next steps will be to work on improvements (such as making yarn out of several threads) and to find industries that will commercialize CNT thread.

Mast's next step was going to be to buy a new cell phone. However, he says, "it works so well now that I decided to just upgrade to a new antenna made of carbon nanotube yarn." ###

This research was funded by the National Science Foundation (with technical monitors Shaochen Chen, Shih-Chi Liu, and K. Jimmy Hsia), and North Carolina A&T SU (collaborators Jag Sankar and Sergey Yarmolenko) through their NSF-ERC (technical monitor Lynn Preston) and ONR-CNN (technical monitor Ignacio Perez) projects.

Contact: Wendy Beckman wendy.beckman@uc.edu 513-556-1826 University of Cincinnati