Monday, March 31, 2008

Carbon Nanotubes Outperform Copper Nanowires as Interconnects

Saroj Nayak — Assistant Professor of Physics, Rensselaer Polytechnic Institute

Saroj Nayak — Assistant Professor of Physics, Rensselaer Polytechnic Institute. Education: — Ph.D., Physical Science, Jawaharlal Nehru University, India, 1995

Career Highlights: Before joining the faculty at Rensselaer in 2000, Nayak was a Princeton Materials Institute Junior Fellow at Princeton University. He is a member of the American Physical Society and of the Materials Research Society.

Research Interests: Nayak's research interests involve the interface of physics, chemistry, and engineering. His principal areas of focus on the study of atomic and electronic structure of matters using the state of the art ab initio electronic structure calculation methods to classical and quantum molecular dynamics simulations and Monte Carlo methods. The two major recent focuses of Nayak's research are the study of nanostructured materials and simulations of biological molecules using electronic structure methods.
Scientists create robust quantum models to compare key characteristics of copper and CNTs

Troy, N.Y. — Researchers at Rensselaer Polytechnic Institute have created a road map that brings academia and the semiconductor industry one step closer to realizing carbon nanotube interconnects, and alleviating the current bottleneck of information flow that is limiting the potential of computer chips in everything from personal computers to portable music players.

To better understand and more precisely measure the key characteristics of both copper nanowires and carbon nanotube bundles, the researchers used advanced quantum-mechanical computer modeling to run vast simulations on a high-powered supercomputer. It is the first such study to examine copper nanowire using quantum mechanics rather than empirical laws.

After crunching numbers for months with the help of Rensselaer’s Computational Center for Nanotechnology Innovations, the most powerful university-based supercomputer in the world, the research team concluded that the carbon nanotube bundles boasted a much smaller electrical resistance than the copper nanowires. This lower resistance suggests carbon nanotube bundles would therefore be better suited for interconnect applications.

“With this study, we have provided a road map for accurately comparing the performance of copper wire and carbon nanotube wire,” said Saroj Nayak, an associate professor in Rensselaer’s Department of Department of Physics, Applied Physics, and Astronomy, who led the research team. “Given the data we collected, we believe that carbon nanotubes at 45 nanometers will outperform copper nanowire.”

The research results will be featured in the March issue of Journal of Physics: Condensed Matter.

Because of the nanoscale size of interconnects, they are subject to quantum phenomena that are not apparent and not visible at the macroscale, Nayak said. Empirical and semi-classical laws cannot account for such phenomena that take place on the atomic and subatomic level,
and, as a result, models and simulations based on those models cannot be used to accurately predict the behavior and performance of copper nanowire. Using quantum mechanics, which deals with physics at the atomic level, is more difficult but allows for a fuller, more accurate model.

“If you go to the nanoscale, objects do not behave as they do at the macroscale,” Nayak said. “Looking forward to the future of computers, it is essential that we solve problems with quantum mechanics to obtain the most complete, reliable data possible.”

The size of computer chips has shrunk dramatically over the past decade, but has recently hit a bottleneck, Nayak said. Interconnects, the tiny copper wires that transport electricity and information around the chip and to other chips, have also shrunk. As interconnects get smaller, the copper’s resistance increases and its ability to conduct electricity degrades. This means fewer electrons are able to pass through the copper successfully, and any lingering electrons are expressed as heat. This heat can have negative effects on both a computer chip’s speed and performance.

Researchers in both industry and academia are looking for alternative materials to replace copper as interconnects. Carbon nanotube bundles are a popular possible successor to copper, Nayak said, because of the material’s excellent conductivity and mechanical integrity. It is generally accepted that a quality replacement for copper must be discovered and perfected in the next five to 10 years in order to further perpetuate Moore’s Law – an industry mantra that states the number of transistors on a computer chip, and thus the chip’s speed, should double every 18-24 months.

Nayak said there are still many challenges to overcome before mass-produced carbon nanotube interconnects can be realized. There are still issues concerning the cost of efficiency of creating bulk carbon nanotubes, and growing nanotubes that are solely metallic rather than their current state being of partially metallic and partially semiconductor. More study will also be required, he said, to model and simulate the effects of imperfections in carbon nanotubes on the electrical resistance, contact resistance, capacitance, and other vital characteristics of a nanotube interconnect.

Rensselaer graduate student Yu Zhou and postdoctoral research assistant Subbalakshmi Sreekala are co-authors of the paper. Materials science and engineering professor Pulickel Ajayan, who is now at Rice University, is also a co-author.

Funding for this project was provided by the New York State Interconnect Focus Center.

About Rensselaer - Rensselaer Polytechnic Institute, founded in 1824, is the nation’s oldest technological university. The university offers bachelor’s, master’s, and doctoral degrees in engineering, the sciences, information technology, architecture, management, and the humanities and social sciences. Institute programs serve undergraduates, graduate students, and working professionals around the world. Rensselaer faculty are known for pre-eminence in research conducted in a wide range of fields, with particular emphasis in biotechnology, nanotechnology, information technology, and the media arts and technology. The Institute is well known for its success in the transfer of technology from the laboratory to the marketplace so that new discoveries and inventions benefit human life, protect the environment, and strengthen economic development.

Contact: Michael Mullaney 518-276-6161 Rensselaer Polytechnic Institute

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Sunday, March 30, 2008

Physicists discover how fundamental particles lose track of quantum mechanical properties

David Awschalom, Professor of Physics, University of California(New Orleans, La.) –– In today’s Science Express, the advance online publication of the journal Science, researchers report a series of experiments that mark an important step toward understanding a longstanding fundamental physics problem of quantum mechanics. The scientists presented their findings at the annual meeting of the American Physical Society.
The problem the physicists addressed is how a fundamental particle in matter loses track of its quantum mechanical properties through interactions with its environment.

The research was performed by scientists at the California NanoSystems Institute at the University of California, Santa Barbara and the U. S. Department of Energy Ames Laboratory in Iowa.

At the quantum level things like particles or light waves behave in ways very different from what scientists expect in a human-scale world. In the quantum world, for example, an electron can exist in two places at the same time, what is called a "superposition" of states, or spin up and down at the same time.

Quantum mechanics in computing could lead to communication with no possible eavesdropping, lightning-fast database searches, and code-cracking ability.

The answer to the problem the researchers have tackled is key to unraveling how the classical world in which we live emerges from all the interacting quantum particles in matter. This scientific query surrounds the basic quantum dynamics of a single particle spin coupled to a collection, or bath, of random spins. This scenario describes the underlying behavior of a broad class of materials around us, ranging from quantum spin tunneling in magnetic molecules to nuclear magnetic resonance in semiconductors.

“We were stunned by these unexpected experimental results, and extremely excited by the ability to control and monitor single quantum states, especially at room temperature,” said author David Awschalom, a professor of physics at UC Santa Barbara. Awschalom is affiliated with the California NanoSystems Institute at UCSB and is the Director of the Center for Spintronics & Quantum Computation, also at the university.

Recently the issue of how fundamental particles lose track of quantum mechanical properties through interaction with the environment has gained crucial importance in the field of quantum information. In this area, robust manipulation of quantum states promises enormous speedups over classical computation. Keeping track of the quantum phase is essential for keeping the quantum information, and insight into loss of the phase will greatly help to mitigate this process.

Experimental work on this subject has thus far been hindered by the lack of high-fidelity coherent control of a single spin in nature and our inability to directly influence the bath dynamics.

In a collaboration between physicists in Awschalom’s research group at UCSB and Slava Dobrovitski, a visiting scientist from Ames Laboratory in Iowa, a series of experiments were undertaken that utilized electron spins in diamond to investigate different regimes of spin-bath interactions, and provide much information about the decoherence dynamics.

The scientists use diamond crystals to study a single electron spin tied to an adjustable collection of nearby spins. Two features of diamond that make this system viable for unprecedented investigations into the coherent dynamics are the precise optical control of a single spin that is unique to diamond, and the magnetic tunability of the spin-bath and intrabath dynamics with small permanent magnets. Their team’s observations contain a number of extraordinary discoveries, such as the time-dependent disappearance and reappearance of quantum oscillations of the spins in the diamond lattice.

“To our surprise, when looking at longer times, the oscillations disappeared then re-appeared,” said co-author Ronald Hanson, a postdoctoral student at UCSB during this period who is now a professor at the Kavli Institute of Nanoscience Delft, at Delft University of Technology, in the Netherlands. “At first it looked like an artifact, but repeated measurements reproduced this behavior.”

The problem of a single spin coupled to a bath of spins has been the subject of an intense international research effort, as this conceptual framework describes the physical behavior of a number of real systems. Among others, these include atomic and electronic spins that are prime candidates for implementing quantum information processors and coherent spintronics devices.

A series of direct experiments coupled to theoretical simulations demonstrate that spins in diamond serve as a nearly ideal, adjustable, model of central spin.

“This work demonstrates a rare level of synergy between experiment, analytical theory, and computer simulations,” said Dobrovitski. “These three constituents all agree, support, and complement each other. Together, they give a lucid qualitative picture of what happens with spin centers in diamond, and, at the same time, provide a quantitatively accurate description. This agreement is hard to anticipate in advance for such complex systems, where many nuclear and electron quantum spins interact with each other.”

Studies of the quantum dynamics of spins in diamond is an emerging topic involving several leading research groups worldwide. It may also be important in the context of recent interest in possible carbon-based electronic devices employing carbon nanotubes and/or graphene. ###

Awschalom won the APS Oliver E. Buckley Prize for fundamental contributions to experimental studies of quantum spin dynamics and spin coherence in condensed matter systems. Awschalom’s other honors include the Agilent Europhysics Prize, the AAAS Newcomb-Cleveland Prize, the Outstanding Investigator Prize from the Materials Research Society, and the Magnetism Prize of the International Union of Pure and Applied Physics. He is a member of the National Academy of Sciences.

Awschalom earned his B.S. in physics at the University of Illinois at Urbana-Champaign, and his Ph.D. in experimental physics at Cornell University. He joined the UC Santa Barbara faculty as a professor of physics in 1991. His research has been chronicled in his more than 300 scientific journal articles, and has also been featured in The New York Times, The Wall Street Journal, San Francisco Chronicle, Dallas Morning News, Discover magazine, Scientific American, Physics World, and New Scientist. His research focuses on optical and magnetic interactions in semiconductor quantum structures, spin dynamics and coherence in condensed matter systems, macroscopic quantum phenomena in nanometer-scale magnets, and quantum information processing in the solid state.

Contact: Gail Gallessich 805-893-7220 University of California - Santa Barbara

David Awschalom can be reached at (805) 893-2121, or at

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Saturday, March 29, 2008

Modern physics is critical to global warming research

Caption: Even a highly simplified model of the Earth's atmosphere shows great complexity in jet streams and macroturbulence. Mathematical approaches that focus on average statistics rather than detailed patterns can deepen our understanding of climate and climate change. Credit: Brad Marston / Brown University. Usage Restrictions: Please give full credit to the image author and institution if used.
PROVIDENCE, R.I. [Brown University] — Science has come a long way with predicting climate. Increasingly sophisticated models and instruments can zero in on a specific storm formation or make detailed weather forecasts – all useful to our daily lives. But to understand global climate change, scientists need more than just a one-day forecast. They need a deeper understanding of the complex and interrelated forces that shape climate.

This is where modern physics can help, argues Brad Marston, professor of physics at Brown University. Marston is working on sets of equations that can be used to more accurately explain climate patterns. Marston will explain his research as part of a panel discussion titled “The Physics of Climate and Climate Change,” scheduled for 2:30 p.m. on March 11, 2008, at the American Physical Society’s meeting in New Orleans. Marston will also take part in a 1 p.m. press conference prior to the presentation.

“Climate is a statement about the statistics of weather, not the day-to-day or minute-by-minute fluctuations,” Marston said. “That’s really the driving concept. We know we can’t predict the weather more than a couple of weeks out. But we can turn that to our advantage, by using statistical physics to look directly at the climate itself.” Take the drying of Lake Mead in the western United States. Scientists think the lake, which straddles Nevada and Arizona, may already be getting less rain due to shifting weather patterns caused by a warming world.
Computer models can follow those rainfall patterns and forecast the likely effects on the lake. But current models obscure the larger mechanisms – such as shifting storm tracks – that can drive changes in rainfall.

“If we’re just mesmerized by the details of the model,” Marston said, “we could be missing the big picture of why it’s happening.”

Marston’s statistical approach can be used to help crack the code of complicated, dynamic atmospheric processes poorly understood through models, such as convection, cloud formation, and macroturbulence, which refers to the currents, swirls and eddies in the global atmosphere. More fundamentally, Marston said this approach can help to deepen understanding of what is happening in today’s climate and what those changes can mean for climate in the future.

“We’re trying to make the models more robust, to give better insights into what is actually going on,” he said.

Marston’s research, on which he teamed with former Brown undergraduate Emily Conover and Tapio Schneider of the California Institute of Technology, was selected last fall for publication in the Journal of the Atmospheric Sciences. Marston’s ultimate research goal is to create a more realistic rendering of the global atmospheric system that can be used to understand the atmosphere of the past and to gauge future changes.

“We’re improving the statistical methods themselves, so that they’re more accurate,” Marston said. “At the same time we are applying the methods to progressively more complete models of the Earth’s atmosphere.” ###

Editors: Brown University has a fiber link television studio available for domestic and international live and taped interviews and maintains an ISDN line for radio interviews. For more information, call the Office of Media Relations at (401) 863-2476.

Contact: Richard Lewis 401-863-3766 Brown University

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Friday, March 28, 2008

The 2008 PhysicsCentral Nanobowl Winners! VIDEO

Grand Prize Champion
Nanobowl X^-IX

Prize: Nanotrophy and $1,000 (normal-sized cash)

The Nanobowl NanotrophyThe Nanobowl Nanotrophy

A nanoscale trophy will be created in silicon and metal, which will be visible only under super high magnification electron or scanning microscopes.
At such minuscule dimensions, the width of the features will be about a thousand times thinner than a strand of human hair!

The trophy is being made right now by physicists of the Craighead research group at Cornell University in Ithaca , NY. Detailed Images of Nanotrophy

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Thursday, March 27, 2008

Copolymers block out new approaches to microelectronics at NIST

Co-Polymers; MicroelectronicsTitle: Co-Polymers; Microelectronics. Description: A novel technique for controlling the orientation of nanostructures (red and blue) is to use disordered, roughened substrates. Silica nanoparticles (orange), cast onto silicon substrates (grey), create "tunable" substrates which can control self-assembly, despite inherent disorder. *MSEL

Subjects (names): Topics/Categories: Nanotechnology--Materials. Type: Graphic, scientific data. Source: National Institute of Standards and Technology. Credit Line as it should appear in print: Credit: NIST. AV Number: 08MSEL002. Date Created: March 2008. Date Entered: 3/7/2008
In response to the electronics industry’s rallying cry of “smaller and faster,” the next breakthroughs in the electronics size barrier are likely to come from microchips and data storage devices created out of novel materials such as organic molecules and polymers. With innovative measurement techniques and new ways to position the molecules, NIST researchers reported at the March Meeting of the American Physical Society how they have improved manipulation of so-called block copolymers—polymers made of a mixture of two or more different molecule building blocks that are tethered at a junction point—which can form arrays of tiny dots that could be used as the basis for electronic components that pack terabytes (1000 gigabytes) of memory in something as small as a pack of gum.

One of the challenges in polymer nanotechnology is how to control their self-assembly—a hard-to-control process for materials which require precision. An important recent NIST accomplishment has been in developing accurate measurements of thin film polymeric nanostructure in 3-D.
(Ironically, while determining atomic structure is well-established, measuring the slightly larger internal structure of the polymers—on the order of 10 to 20 nanometers—is much harder.) Ron Jones, together with colleagues from NIST, the University of Maryland and IBM, has used NIST’s neutron scattering and reflectivity facility to deflect neutrons off block copolymer films from many different angles. By combining the many 2-D neutron scattering pictures into a single composite scattering pattern, this technique provides the first quantitative method for imaging the 3-D internal structure of thin film polymeric nanostructures using neutron scattering—a crucial tool to see if the nanoscale polymer structures are in their required positions.1

NIST researchers also have developed new insights on how best to nudge these self-assembling material into those positions. August Bosse will report on computer simulations that model how the polymers assemble when they are placed on templates lined with troughs separated by crests.2 When a heated zone is swept across the template, the polymer molecules assemble into almost defect free, well-aligned lines faster over the entire template, an important feature for nanotech manufacturing applications.3 Sangcheol Kim (working with a team that included researchers from the University of Maryland and IBM) has found that changing the surface chemistry of the template by making some parts hydrophillic and some parts hydrophobic also can elegantly control the dimension of the block-copolymer pattern relative to the chemical template.4

And last, with all this emphasis on precise placement, NIST researcher Kevin Yager, has learned that sometimes sloppier is better. By purposely roughening up his templates with a sprinkling of chemically modified nanoparticle silica, he has forced block copolymers into standing perpendicular to the template—a feat that is generally considered tough to manage but important for nanotech applications.5 Of course, the inner structure of the polymers are not orderly with this technique, but for those applications where only the surface needs to be smooth, this is an ideal, inexpensive way to achieve vertical structures.


1 R. Jones, X. Zhang, S. Kim, A. Karim, R. Briber and H. Kim. Orientation distribution for thin film block copolymers. Presented at the March Meeting of the American Physical Society, March 12, 2008, New Orleans, La. Session: Q22.00007.

2 A. Bosse, R. Jones and A. Karim. Fluctuation-induced line-edge roughness in nano-confined block copolymer thin films. Presented at the March Meeting of the American Physical Society, March 11, 2008, New Orleans, La. Session: L22.00010.

3 A. Karim. INVITED TALK. Templated Self-Assembly of Block Copolymer Thin Films. Presented at the March Meeting of the American Physical Society, March 10, 2008, New Orleans, La. Session: B4.00002.

4 S. Kim, H-J. Lee, R.L. Jones, A. Karim, R.M. Briber and H-C. Kim. Precise control of 3-dimensional block copolymer assembly using 2-dimensional chemical templates. Presented at the March Meeting of the American Physical Society, March 10, 2008, New Orleans, La. Session: A25.00010.

5 K. Yager, A. Karim and E. Amis. Disordered nanoparticle interfaces for defect-tolerance in the self-assembly of block-copolymers. Presented at the March Meeting of the American Physical Society, March 12, 2008, New Orleans, La. Session: P18.00001.

Contact: Michael Baum 301-975-2763 National Institute of Standards and Technology (NIST)

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Wednesday, March 26, 2008

Nanomaterials show unexpected strength under stress

Nanoscale Ductility

Title: Nanoscale Ductility - Description: NIST researchers have shown that substances such as silica that are brittle in bulk exhibit ductile behavior at the nanoscale. Computer simulations demonstrate the material extension and necking that occurs during the separation of amorphous silica nanoparticles.

Subjects (names): Topics/Categories: Nanotechnology--Materials Type: Graphic/illustration. Source: National Institute of Standards and Technology
Credit Line as it should appear in print: Credit: NIST. AV Number: 08MSEL003. Date Created: March 2008. Date Entered: 3/7/2008
In yet another twist on the strangeness of the nanoworld, researchers at the National Institute of Standards and Technology (NIST) and the University of Maryland-College Park have discovered that materials such as silica that are quite brittle in bulk form behave as ductile as gold at the nanoscale. Their results may affect the design of future nanomachines.

NIST scientists Pradeep Namboodiri and Doo-In Kim and colleagues first demonstrated* the latest incongruity between the macro and micro worlds this past fall with direct experimental evidence for nanoscale ductility. In a new paper** presented today at the March Meeting of the American Physical Society, NIST researchers Takumi Hawa and Michael Zachariah and guest researcher Brian Henz
shared the insights they gained into the phenomenon through their computer simulations of nanoparticle aggregates.

At the macroscale, the point at which a material will fail or break depends on its ability to maintain its shape when stressed. The atoms of ductile substances are able to shuffle around and remain cohesive for much longer than their brittle cousins, which contain faint structural flaws that act as failure points under stress.

Nanoscale Ductility

Title: Nanoscale Ductility. Description: NIST researchers have shown that substances such as silica that are brittle in bulk exhibit ductile behavior at the nanoscale. Computer simulations demonstrate the material extension and necking that occurs during the separation of crystalline silica nanoparticles.

Topics/Categories: Nanotechnology--Materials, Type: Graphic/illustration. Source: National Institute of Standards and Technology. Credit Line as it should appear in print: Credit: NIST. AV Number: 08MSEL004. Date Created: March 2008. Date Entered: 3/7/2008
At the nanoscale, these structural flaws do not exist, and hence the materials are nearly “perfect.” In addition, these objects are so small that most of the atoms that comprise them reside on the surface. According to Namboodiri and Kim, the properties of the surface atoms, which are more mobile because they are not bounded on all sides, dominate at the nanoscale. This dominance gives an otherwise brittle material such as silica its counterintuitive fracture characteristics.

“The terms ‘brittle’ and ‘ductile’ are macroscopic terminology,” Kim says. “It seems that these terms don’t apply at the nanoscale.”

Using an atomic force microscope (AFM), Kim and Namboodiri were able to look more closely at interfacial fracture than had been done before at the nanoscale.
They found that the silica will stretch as much as gold or silver and will continue to deform beyond the point that would be predicted using its bulk-scale properties.

Hawa, Henz and Zachariah’s simulations reaffirmed their study and added some additional details. They showed that both nanoparticle size and morphology—whether the material is basically crystalline or amorphous, for example—have an effect on the observed ductility and tensile strength because those factors influence the mobility of surface atoms. In the simulations, the smaller the particles in the aggregate the more ductile the material behaved. Crystalline structures exhibited greater strength when stressed and deformed long after the critical yield point observed macroscopically.

Namboodiri explained that although the work is very basic, these findings might one day inform the design of microelectronic mechanical devices. ###

* N. Pradeep, D-I. Kim, J. Grobelny, T. Hawa, B. Henz, and M. R. Zachariah. Ductility at the nanoscale: Deformation and fracture of adhesive contacts using atomic force microscopy. Applied Physics Letters, published online 15 November 2007.

** T. Hawa, B. Henz, and M. Zachariah. Computer simulations of nanoparticle aggregate fracture. Presented Wednesday, March 12, 2008, at the 2008 APS meeting in New Orleans, La.

Contact: Mark Esser 301-975-2767 National Institute of Standards and Technology (NIST)

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Tuesday, March 25, 2008

All Done With Mirrors: NIST Microscope Tracks Nanoparticles in 3-D VIDEO

Title: Nanoparticles; Microscope Design - Description: Heart of the orthogonal tracking microscope system developed at NIST is this nanoparticle solution sample well etched in silicon. Careful orientation of the silicon crystal makes it possible to chemically etch angled sides in the well so smooth they act as mirrors.

In this configuration, four side views of a nanoparticle floating in solution (left) are reflected up. A microscope above the well sees the real particle (center, right) and four reflections that show the particle's vertical position.

Topics/Categories: Nanotechnology--Nanomanufacturing. Type: Graphic, illustration. Source: National Institute of Standards and Technology. Credit Line as it should appear in print: Credit: NIST. AV Number: 08CNST001. Date Created: March 2008. Date Entered: 3/7/2008
A clever new microscope design allows nanotechnology researchers at the National Institute of Standards and Technology (NIST) to track the motions of nanoparticles in solution as they dart around in three dimensions. The researchers hope the technology, which NIST plans to patent, will lead to a better understanding of the dynamics of nanoparticles in fluids and, ultimately, process control techniques to optimize the assembly of nanotech devices.

While some nanoscale fabrication techniques borrow from the lithography and solid state methods of the microelectronics industry, an equally promising approach relies on “directed self-assembly.” This capitalizes on physical properties and chemical affinities of nanoparticles in solutions to induce them to gather and arrange themselves in desired structures at desired locations. Potential products include extraordinarily sensitive chemical and biological sensor arrays, and new medical and diagnostic materials based on “quantum dots” and other nanoscale materials.
But when your product is too small to be seen, monitoring the assembly process is difficult.

Microscopes can help, but a microscope sees a three-dimensional fluid volume as a 2-D plane. There’s no real sense of the “up and down” movement of particles in its field of view except that they get more or less fuzzy as they move across the plane where the instrument is in focus. To date, attempts to provide a 3-D view of the movements of nanoparticles in solution largely have relied on that fuzziness. Optics theory and mathematics can estimate how far a particle is above or below the focal plane based on diffraction patterns in the fuzziness. The math, however, is extremely difficult and time consuming and the algorithms are imprecise in practice.

One alternative, NIST researchers reported at the annual meeting of the American Physical Society,* is to use geometry instead of algebra. Specifically, angled side walls of the microscopic sample well act as mirrors to reflect side views of the volume up to the microscope at the same time as the top view. (The typical sample well is 20 microns square and 15 microns deep.) The microscope sees each particle twice, one image in the horizontal plane and one in the vertical. Because the two planes have one dimension in common, it’s a simple calculation to correlate the two and figure out each particle’s 3-D path. “Basically, we reduce the problem of tracking in 3-D to the problem of tracking in 2-D twice,” explains lead author Matthew McMahon.

The 2-D problem is simpler to solve—several software techniques can calculate and track 2-D position to better than 10 nanometers. Measuring the nanoparticle motion at that fine scale—speeds, diffusion and the like—will allow researchers to calculate the forces acting on the particles and better understand the basic rules of interaction between the various components. That in turn will allow better design and control of nanoparticle assembly processes.

* M. McMahon, A. Berglund, P. Carmichael, J. McClelland and J.A. Liddle. Orthogonal tracking microscopy for nanofabrication research. Paper presented on Monday, March 10, 2008, 1:03 p.m., at the 2008 March Meeting of the American Physical Society, New Orleans, La., March 10-14, 2008.

Contact: Michael Baum 301-975-2763 National Institute of Standards and Technology (NIST)

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Monday, March 24, 2008

Purdue leads center to simulate behavior of micro-electromechanical systems

Jayathi Y. Murthy and Dipali Pradhan

Caption: Jayathi Y. Murthy (standing), a professor in Purdue's School of Mechanical Engineering, works with graduate student Dipali Pradhan on a computer simulation to analyze how heat is transferred through a silicon nanowire. Murthy will lead a new center based at Purdue's Discovery Park to develop advanced simulations of microelectromechanical systems for commercial and defense applications. Credit: Purdue News Service photo/David Umberger. Usage Restrictions: None.
WEST LAFAYETTE, Ind. - The National Nuclear Security Administration has awarded a $17 million cooperative agreement for a research center at Purdue University's Discovery Park to develop advanced simulations for commercial and defense applications, Purdue officials announced Friday.

The center will focus on the behavior and reliability of miniature switches and is one of five new Centers of Excellence chosen by the NNSA.

About 35 researchers at Purdue, including faculty members, software professionals and students, will be involved in the new Center for Prediction of Reliability, Integrity and Survivability of Microsystems, or PRISM. The University of Illinois, Urbana-Champaign, and the University of New Mexico will collaborate in the center.
"The center takes advantage of Purdue's interdisciplinary strengths and considerable expertise in computational modeling and nanotechnology," Purdue President France A. Córdova said.

The center will advance the emerging field of "predictive science," or applying computational simulations to predict the behavior of complex systems, said Jayathi Y. Murthy, director of the new center and a professor in Purdue's School of Mechanical Engineering.

Caption: This is an image of a tiny switch called a radio-frequency micro-electromechanical system. The device has a length of about 400 microns, or millionths of a meter, or roughly four times the width of a human hair. The National Nuclear Security Administration will award a $17 million cooperative agreement for a research center at Purdue's Discovery Park to develop advanced simulations to perfect the devices for commercial and defense applications. Credit: Dimitrios Peroulis, Purdue School of Electrical and Computer Engineering, Birck Nanotechnology Center. Usage Restrictions: None.
The new centers will develop advanced science and engineering models and software for simulations needed to predict the reliability and durability of "micro-electromechanical systems," or MEMS. Researchers also will develop methods associated with the emerging disciplines of verification and validation and uncertainty quantification.

"The goal of these emerging disciplines is to enable scientists to make precise statements about the degree of confidence they have in their simulation-based predictions," Murthy said.

PRISM will be based at the Birck Nanotechnology Center and also is affiliated with the Energy Center, both in Purdue's Discovery Park.
The center is funded with $17 million over five years from the NNSA's Office of Advanced Simulation and Computing through its Predictive Science Academic Alliance Program. Purdue and its partners also are providing $4.2 million in matching funds for the center.

PRISM and the other four newly selected centers will focus on unclassified applications of interest to NNSA and its three national laboratories: Lawrence Livermore, Los Alamos and Sandia.

Under PRISM, the miniature switches, called MEMS devices, are being created to replace conventional switches and other electronic components. MEMS are machines that combine electronic and mechanical components on a microscopic scale.

The MEMS are far lighter and smaller than the conventional technology and could be manufactured in large quantities at low cost, Murthy said.

"Research is needed, however, to improve the reliability, ruggedness and durability of the devices," she said.

The new simulations will make it possible to accurately predict how well the MEMS devices would stand up to the rigors of varying and extreme environments and how long they would last in the field. Devices in many environments must withstand crushing gravitational forces, temperature extremes, radiation and shocks from impact.

"Reliability pertains to long-term performance," Murthy said. "Improving the integrity and survivability relate to the fact that MEMS get used in very adverse conditions. You don't want the MEMS to fail before the systems in which they are embedded are deployed. MEMS have many potential important applications in civilian and defense applications."

For example, the switches can be used to turn radio signals on and off for a variety of purposes in national defense and for routing satellite communications. Potential civilian applications include cell phones and other telecommunications products, automotive sensors, and liquid-crystal-display projectors for large screens.

The technology will make it possible to reduce the size of switching equipment from several inches to 1 millimeter, or thousandth of a meter.

"Even though MEMS have a big size, weight and cost advantage, they are not really reliable enough yet," Murthy said.

A major challenge is creating "multiscale" simulations that bridge a broad range of size and time scales associated with objects measured in nanometers, or billionths of a meter, to objects measured in millimeters.

One problem is that matter behaves differently on the scale of nanometers than it does in the ordinary macro world of meters. Another complication is that important failure phenomena in MEMS may occur over a range of time scales, ranging from billionths of a second to several months.

The center will focus on creating simulations to unite these sizes and time scales, capturing the entire workings of a design, from its nanometer-scale layout to its macro-scale features. The research will draw on expertise and facilities affiliated with Purdue's Network for Computational Nanotechnology, based at the Birck Nanotechnology Center, and the Rosen Center for Advanced Computing, a division of Purdue's Office of Information Technology. The NNSA's national laboratory personnel will be advisers and collaborators in this research effort.

The research will concentrate on specific types of MEMS, called radio frequency MEMS, and particularly a device called a metal-dielectric contacting MEMS. The tiny switches have a length of about 400 microns, or millionths of a meter, or roughly four times the width of a human hair. The devices, switches used to turn on and off radio frequency signals, are made of a thin metal membrane located on top of a dielectric contact.

During operation, the membrane snaps on top of the contact, altering an electronic property called capacitance and switching off the radio signal, in effect turning off the device.

Researchers in the center will create a simulation system called MEMOSA to accurately model the devices. The metal membrane constantly hitting the contact forms cracks and defects. Whereas the defects are formed in regions a few hundred nanometers long, components in the device are 100 times larger, complicating the job of creating accurate simulations.

In addition to multiscale considerations, another complicating factor is that device operation involves the interaction of mechanical, electrical and thermal factors. The devices are made of various types of materials, which also have to be incorporated into simulations.

Creating the simulations will require the expertise of researchers from materials science, electrical engineering, mechanical engineering, aeronautics and astronautics, mathematics, computer science, and computer architecture.

The researchers will have access to unclassified supercomputers at the three NNSA national labs to run the large-scale simulations. These systems will be at the petascale computing level.

"Petascale computing is the leading edge, the fastest computing that will be possible in the near future," Murthy said. "Right now, the state of the art is terascale computing, a thousand times slower."

Researchers also will use computer resources on the nanoHUB, an Internet-based science gateway that provides access to advanced simulation and software tools. The nanoHub is part of the Network for Computational Nanotechnology at Purdue. Facilities and hardware provided by Purdue's Office of Information Technology also will be utilized extensively. ###

Writers: Emil Venere, (765) 494-4709,, Phillip Fiorini, (765) 496-3133, (765) 427-3009 (cell),

Sources: France A. Cordóva, (765) 494-9708, Jayathi Y. Murthy, (765) 494-5701,, Jay Gore, interim director of Purdue's Energy Center, (765) 494-2122,, Ananth Grama, Purdue professor of computer science, (765) 494-6964,

Related Web sites:Contact: Phillip Fiorini 765-496-3133 Purdue University

Sunday, March 23, 2008

Assembly technique for tiny wires may eventually help detect cancer and other diseases

Professor Theresa Mayer

Theresa S. Mayer received the B.S. degree in Electrical Engineering from Virginia Tech in 1988, and the M.S. and Ph.D. degrees in Electrical Engineering from Purdue University in 1989 and 1993. In 1994, she joined the Department of Electrical Engineering at Penn State University-University Park, where she is a Professor.

Dr. Mayer was appointed as an Associate Director of the Penn State University Materials Research Institute in 2006, where she serves as the Technical Director of Penn State Nanofabrication Facility. She is also the Director of the Penn State Site of the National Science Foundation National Nanotechnology Infrastructure Network (NSF-NNIN). Her interests are in the areas of nanoscale electronic and optical device fabrication, integration, and characterization.

Her group currently has funded projects in semiconductor nanowire electronics, self-assembly of chemical and biological sensors on CMOS chips, metallo- and all-dielectric metamaterials, and molecular electronic devices. Prof. Mayer was a Kodak Fellow (1990-1993) and the recipient of a National Science Foundation CAREER Award (1995), and a Penn State Engineering Society Outstanding Teaching Award (2000).

She served as the General Chair of the IEEE Device Research Conference and the Chair of the Gordon Research Conference on the Chemistry and Physics of Nanostructure Fabrication in 2006. Dr. Mayer holds 5 U.S. Patents and is the co-author of over 90 journal publications.
Bottom-up manufacturing may hold the key to production of tiny medical devices capable of testing for multiple molecules like viruses or cancer markers, according to an interdisciplinary team of Penn State researchers.

"Diagnostic chips can be made more useful by assembling, at predetermined locations on the chip, large numbers of nanowires pretreated off chip," says Rustom B. Bhiladvala, research assistant professor, electrical engineering. "Using this new bottom-up method, our group has demonstrated that thousands of single wires can be successfully aligned and anchored to form tiny diving board resonator arrays."

The traditional top-down process begins with silicon and carves nanoresonator devices from the material. This approach works well and produces many devices that are nearly identical, but the process has limitations. The addition of chemical probes or other changes in the existing materials must be done after the devices are fabricated on the chips.

The bottom-up method, although not producing identical devices, is more flexible. In bottom-up fabrication, researchers manufacture nanowires off chip using any inorganic or organic material that will produce nanowires. They can attach probe molecules to the wires off chip, using a variety of chemicals and they can attach each group of nanowires and their probes to the chips in the numbers and at the locations desired.

"We can achieve high device integration yields, but the devices are not as uniform as top-down manufactured devices," says Theresa S. Mayer, professor of electrical engineering. "However, we can access materials that are not easy to integrate into the devices with top-down methods. We can also integrate wires treated off-chip with entirely different probe molecules that are attached to the wires using condition optimized for that molecule."

The researchers described their bottom-up method using fabrication of a resonator array in the current issue of Nature Nanotechnology. They fabricated these proof-of-concept chips with nanowires made of single crystal silicon or polycrystalline rhodium attached at one end and suspended over a depression. This type of device can detect target molecules when they bind to the probe molecules on the nanowires and change the wire's vibration.

To create the bottom-up diving board resonators, the researchers used a layer of photoresist – a light-sensitive material which, when exposed to light, can then be easily removed chemically – to create an array of tiny rectangular wells on the chip. These wells were aligned above an insulated electrode on the chip surface. A solution of nanowires, with probes already attached, flows over the chip surface while the electrodes produce an electric field. The electric field grabs the nanowires and pulls them to the surface where they align perpendicular to the electrode. The aligned nanowires skate along the electrodes and when they reach a well, drop down into it.
Once a wire is in a well, that wire repels other wires allowing, for the most part, only one wire per well. The number of wires in the solution is controlled depending on the number of wells so only a few wires remain on the chip outside the wells.

"One of the biggest challenges of self assembly is whether we can control where the wires go and control the defects," says Mayer, associate director of Penn State's Material Research Institute and director of Penn State's site of the National Science Foundation's National Nanotechnology Infrastructure Network. "This new method allows integration of the nanowires with high yield."

In the case of the resonators, once the wires are in the depressions, the researchers switch to a top-down approach, placing a layer of a different photoresist on top of the chip and removing a small cube of photoresist around the tip where the wire anchor will be built. The researchers then electro-deposit metal into the tiny square holes, anchoring the nanowire in place. They dissolve the photoresist, leaving the suspended nanowire and at the same time removing the nanowires that did not make it into wells.

By choosing the well depth and the thickness of the original photoresist layer, the researchers can adjust the height of the resonator above the chip surface. An added benefit of bottom-up fabrication is that the nanowires with their probe molecules retain their functionality after integration. The researchers also showed that, after the resonator chip arrays were fabricated, target molecules did selectively bind to only those nanowires treated with the correct probe molecules.

The researchers tested many silicon and rhodium nanoresonators by measuring their vibration at high vacuum and found that the electroplated anchors were uniform, not too far from rigid and did not show high energy losses. They also found that both types of wires show negligible effects of air damping at pressures as high as about a thousandth of an atmosphere, which can be reached using small and inexpensive vacuum pumps. They showed that both nanowire dimensions and material properties affect the loss due to air damping at one atmosphere. The quality of the response at this modest vacuum is such that these resonators are strong candidates for sensitive resonance-based detection schemes.

"Bottom-up fabrication is an entirely new nanomanufacturing approach and we need to create devices that have properties that match what we can now make using top-down fabrication," says Mayer. "Our vision is to make large arrays of nano size devices with multiple probes for multiple targets by placing different groups of functionalized nanowires sequentially on chips." ###

The researchers included Bhiladvala; Mayer; Mingwei Li, graduate student, electrical engineering; Thomas J. Morrow, graduate student and James A. Sioss, recent Ph.D. recipient, chemistry; Kok-Keong Lew, recent Ph.D. recipient in materials science and engineering; Joan M. Redwing, professor of materials science and engineering and electrical engineering and Christine D. Keating, associate professor of chemistry.

The National Institutes of Health and the NSF provided support for this research. Members of the research team have filed a provisional patent on this assembly process.

Contact: A'ndrea Elyse Messer 814-865-9481 Penn State

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Saturday, March 22, 2008

Researchers engineer new polymers to change their stiffness and strength when exposed to liquids

Sea Cucumber in its Natural Habitat

Caption: Sea cucumbers inspired the design of chemo-responsive nanocomposite with adaptive mechanical properties. Credit: F. Carpenter. Usage Restrictions: None.
Case Western Reserve University, VA researchers publish findings in Science

CLEVELAND -- An interdisciplinary team of researchers from the departments of macromolecular science and engineering and biomedical engineering at the Case School of Engineering and the Louis Stokes Cleveland Department of Veterans Affairs Medical Center has published ground-breaking work on a new type of polymer that displays chemoresponsive mechanic adaptability -- meaning the polymer can change from hard to soft plastic and vice versa in seconds when exposed to liquid -- in the March 7, 2008, issue of Science, one of the world's most prestigious scholarly journals covering all aspects of science.
Jeffrey R. Capadona, associate investigator at the VA's Advanced Platform Technology (APT) Center, graduate student Kadhiravan Shanmuganathan, and Case Western Reserve University professors and APT investigators Dustin Tyler (biomedical engineering), Stuart Rowan (macromolecular science) and Christoph Weder (macromolecular science) have unveiled a radically new approach for developing polymer nanocomposites which alter their mechanical properties when exposed to certain chemical stimuli.

"We can engineer these new polymers to change their mechanical properties -- in particular stiffness and strength -- in a programmed fashion when exposed to a specific chemical," says Weder, one of the senior authors of the paper.

"The materials on which we reported in Science were designed to change from a hard plastic -- think of a CD case -- to a soft rubber when brought in contact with water," adds Rowan, who has been Weder's partner on the project for almost six years.

"Our new materials were tailored to respond specifically to water and to exhibit minimal swelling, so they don't soak up water like a sponge," saud Shanmuganathan.

In their new approach, the team used a biomimetic approach -- or mimicking biology -- copying nature's design found in the skin of sea cucumbers.

"These creatures can reversibly and quickly change the stiffness of their skin. Normally it is very soft, but, for example, in response to a threat, the animal can activate its 'body armor' by hardening its skin," explains Capadona, who has a sea cucumber in his aquarium. Marine biologists have shown in earlier studies that the switching effect in the biological tissue is derived from a distinct nanocomposite structure in which highly rigid collagen nanofibers are embedded in a soft connective tissue. The stiffness is mediated by specific chemicals that are secreted by the animal's nervous system and which control the interactions among the collagen nanofibers. When connected, the nanofibers form a reinforcing network which increases the overall stiffness of the material considerably, when compared to the disconnected (soft) state.

Building on their recent success on the fabrication of artificial polymer nanocomposites containing rigid cellulose nanofibers, which earned them the December 2007 cover of Nature Nanotechnology, the team mimicked the architecture nature 'designed' for the sea cucumbers and created artificial materials that display similar mechanical morphing characteristics.

The Case Western Reserve/VA team is specifically interested in using such dynamic mechanical materials in biomedical applications, for example as adaptive substrates for intracortical microelectrodes. These devices are being developed as part of 'artificial nervous systems' that have the potential to help treat patients that suffer from medical conditions such as Parkinson's disease, stroke or spinal cord injuries, i.e., disorders in which the body's interface to the brain is compromised. A problem observed in experimental studies is that the quality of the brain signals recorded by such microelectrodes usually degrades within a few months after implantation, making chronic applications challenging. One hypothesis for this failure is that the high stiffness of these electrodes, which is required for their insertion, causes damage to the surrounding, very soft brain tissue over time. "We believe that electrodes that use mechanically adaptive polymer as substrate could alleviate this problem" explains Dustin Tyler, who specializes in neural interfacing and functional electrical stimulation. The development and testing of experimental microelectrodes that involve the new adaptive materials is currently underway. "That's why we designed our first materials to respond to water" explains Weder. "This allows the rigid electrodes to become soft when implanted into the water-rich brain" he adds. ###

The Department of Veterans Affairs and the VA Rehabilitation R&D Center of Excellence in Advanced Platform Technology (APT) played an important role in uniting Weder and Rowan with Capadona and Tyler, to conduct research in the area of adaptive nanocomposite materials, which are now fabricated by the new process. The APT center is a cohesive intellectual community that offers its investigators the opportunity to meet regularly, have discussions within and outside of their fields, participate in list-servs, and attend educational and scientific conferences. It allows access to state-of-the-art facilities including MEMS design and fabrication, mixed signal and wireless communication laboratories, telemetry laboratories, support staff and other technical and clinical resources.

Science is the world's leading multidisciplinary, peer-reviewed journal that publishes significant original scientific research, plus reviews and analyses of current research and science policy.

About Case Western Reserve University

Case is among the nation's leading research institutions. Founded in 1826 and shaped by the unique merger of the Case Institute of Technology and Western Reserve University, Case is distinguished by its strengths in education, research, service, and experiential learning. Located in Cleveland, Case offers nationally recognized programs in the Arts and Sciences, Dental Medicine, Engineering, Law, Management, Medicine, Nursing, and Social Work.

About research at the Louis Stokes Cleveland VA Medical Center - The Cleveland VA Medical Center has several large, well-funded research and development programs in:
  • biomedical research
  • health services research
  • clinical and cooperative studies
  • rehabilitation research
There are also two VA-funded centers of excellence:
  • Functional Electrical Stimulation (FES) Center
  • Advance Platform Technology Center
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Friday, March 21, 2008

New technique takes a big step in examination of small structures VIDEO

The Network for Computational Nanotechnology FULL STREAMING VIDEO - is a network of 6 universities working together to connect theory, experiment, and computation in a way that makes a difference to the future of nanotechnology.

Bacteriophage Epsilon15

Caption: Shown is an image of bacteriophage Epsilon15 studied by Wen Jiang, an assistant professor of biological sciences at Purdue. The bacteriophage is shown at a resolution of 4.5 angstrom -- the highest resolution achieved for a living organism of this size. Credit: Graphic/Wen Jiang lab. Usage Restrictions: None.
WEST LAFAYETTE, Ind. - A team led by a Purdue University researcher has achieved images of a virus in detail two times greater than had previously been achieved.

Wen Jiang, an assistant professor of biological sciences at Purdue, led a research team that used the emerging technique of single-particle electron cryomicroscopy to capture a three-dimensional image of a virus at a resolution of 4.5 angstroms. Approximately 1 million angstroms would equal the diameter of a human hair.

"This is one of the first projects to refine the technique to the point of near atomic-level resolution," said Jiang, who also is a member of Purdue's structural biology group.
"This breaks a threshold and allows us to now see a whole new level of detail in the structure. This is the highest resolution ever achieved for a living organism of this size."

Details of the structure of a virus provide valuable information for development of disease treatments, he said.

"If we understand the system - how the virus particles assemble and how they infect a host cell - it will greatly improve our ability to design a treatment," Jiang said. "Structural biologists perform the basic science and provide information to help those working on the clinical aspects."

A paper detailing the work was published in the Feb. 28 issue of Nature.

Roger Hendrix, a professor of biological sciences at the University of Pittsburgh, said what is learned about viruses can be applied to many other biological systems.

"Understanding the proteins that create the structure of a virus gives us insight into the tiny biological machines found throughout our bodies," he said. "Getting to 4.5 angstrom using this technique is a watershed of sorts because it is the first time we can actually trace the polypeptide chain - the backbone of proteins. Now we can see the tiny gears and levers that allow the proteins to move and interact as they carry out their intricate biological roles."

The imaging technique, called cryo-EM, has the added benefit of maintaining the sample being studied in a state very similar to its natural environment. Other imaging techniques used regularly, such as X-ray crystallography, require the sample be manipulated.

"This method offers a new approach for modeling the structure of proteins in other macromolecular assemblies, such as DNA, at near-native states," Jiang said. "The sample is purified in a solution that is very similar to the environment that would be found in a host cell. It is as if the virus is frozen in glass and it is alive and infectious while we examine it."

In addition to Jiang, Matthew L. Baker, Joanita Jakana and Wah Chiu from Baylor College of Medicine, and Peter R. Weigele and Jonathan King from Massachusetts Institute of Technology worked on the project, which was funded by the National Institutes of Health and the National Science Foundation.

The team obtained a three-dimensional map of the capsid, or protein shell, of the epsilon15 bacteriophage, a virus that infects bacteria and is a member of a family of viruses that are the most abundant life forms on Earth, Jiang said.

Other methods of determining the structure could not be used for this family of virus. None had been successfully crystallized, and the complexity of members of this family had prevented evaluation through the genome sequence alone.

"This demonstration shows that cryo-EM is doable and is a major step in reaching the full potential of this technique," he said. "The goal is to have it reach a 3 to 4 angstrom resolution, which would allow us to clearly see the amino acids that make up a protein."

In electron microscopy, a beam of electrons takes the place of the light beam used in a conventional microscope. The use of electrons instead of light allows the microscope to "see" in much greater detail.

Cryo-EM cools specimens to temperatures well below the freezing point of water. This decreases damage from the electron beam and allows the specimens to be examined for a longer period of time. Longer exposure time allows for sharper, more detailed images.

Researchers using cryo-EM had obtained images at a resolution of 6-9 angstroms but could not differentiate between smaller elements of the structure spaced only 4.5 angstroms apart.

"There are different elements that make up the protein building blocks of the virus," Jiang said. "It is like examining a striped blanket. From a distance, the stripes blur together and the blanket appears to be one solid color. As you get closer you can see the different stripes, and if you use a magnifying glass you can see the strands of string that make up the material. The resolution needs to be smaller than the distance between the strands of thread in order to see two separate strands.

"By being able to zoom in, researchers were able to see components that blurred together at the earlier achieved resolution."

Cryo-EM requires high-end electron microscopes and powerful computing resources. The research team used the Baylor College of Medicine's cryoelectron microscope. It is expected that Purdue will install a state-of-the-art cryoelectron microscope in 2009.

In 2006 Purdue received a $2 million grant from the National Institute of Health to purchase the microscope. It will be installed in Hockmeyer Hall of Structural Biology, expected to open in 2009.

Computer programs are used to extract the signal from the microscope and to combine thousands of two-dimensional images into an accurate three-dimensional image that maps the structure of the virus. This requires use of a large data set and could not have been done without the resources of Purdue's Office of Information Technology, or ItaP, Jiang said.

Jiang used Purdue's Condor program - which links computers including desktop machines and large, powerful research computers - to create the largest distributed computing network at a university.

"ITaP provided us with computational power at the supercomputer scale that was necessary for this work," he said. "Purdue's Condor program allowed us to take advantage of the power of 7,000 computers. This was a critical element to our success."

Jiang plans to continue to refine every step of the process to improve the capabilities of the technique and to examine more medically relevant virus species.

Purdue's structural biology group studies a diverse group of problems, including cellular signaling pathways, RNA catalysis, bioremediation, molecular evolution, viral entry, viral replication and viral pathogenesis. Researchers use a combination of X-ray crystallography, electron cryomicroscopy, NMR spectroscopy, and advanced computational and modeling tools to study these problems. ###

Contact: Elizabeth K. Gardner 765-494-2081 Purdue University

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Thursday, March 20, 2008

UD's Appelbaum wins NSF Career Award for research on silicon spintronics

Ian Appelbaum, Spintronics Researcher, University of Delaware

Caption: Ian Appelbaum, University of Delaware assistant professor of electrical and computer engineering, is the recipient of the Faculty Early Career Development Award from the National Science Foundation for his research on spintronics. Credit: Jon Cox/University of Delaware. Usage Restrictions: Image must include credit to University of Delaware.
Ian Appelbaum, assistant professor of electrical and computer engineering at the University of Delaware, has received the prestigious Faculty Early Career Development Award from the National Science Foundation for his pioneering research in the exciting next evolution of electronics known as spintronics.

This emerging field focuses on harnessing the magnet-like spin property of electrons to produce electronics ranging from computers to cell phones that are faster, yet use less energy than today's power-hogging devices.

The highly competitive funding award, designed to support the integrated research and educational activities of faculty early in their careers, is bestowed on those scientists and engineers deemed most likely to become the academic leaders of the 21st century. Fewer than 20 percent of the proposals submitted by faculty from across the nation to the annual competition are funded.

The five-year, $400,000 award will support Appelbaum's research and companion education project on silicon spintronics.

“It was really great to receive this award,” Appelbaum says. “It will enable us to continue our work to prove that silicon--the world's top semiconductor--can be used in spintronic applications.
Spintronic devices will offer a number of advantages in the future,” Appelbaum notes. “These lower-power, instant-on electronics will allow increased device portability and are especially important in light of today's increasing energy costs and its environmental impact.”

Silicon is the workhorse material of the electronics industry, the transporter of electrical current in computer chips and transistors. Silicon also had been predicted to be a superior semiconductor for spintronics, yet demonstrating the element's ability to conduct the spin of electrons, referred to as “spin transport,” had eluded scientists until Appelbaum and his research group, with a colleague from Cambridge NanoTech, published their results in the scientific journal Nature in May 2007.

The UD research group made international headlines as the first to demonstrate spin transport in silicon using a novel hot-electron detection technique.

Appelbaum's research group then showed how their device design could be used as a spin field-effect transistor. The design was featured on the cover of the scientific journal Applied Physics Letters in June 2007.

More recently, Appelbaum and his team showed that an electron's spin can be transported a marathon distance in the world of microelectronics--through a 350-micron-thick silicon wafer. That major advance was reported in the Oct. 26, 2007, issue of Physical Review Letters, published by the American Physical Society.

The former research was funded by grants from the U.S. Office of Naval Research and the Defense Advanced Research Projects Agency (DARPA) of the U.S. Department of Defense.

Now, with NSF's support, Appelbaum and his group will continue to explore the fundamental development of the silicon chips, transistors and integrated circuits required for a potential new industry. Ultimately, the research may lead to the development of a whole new logic architecture for electronics, Appelbaum says.

“While almost all work in the field has focused on compound semiconductors, there are clear benefits from leveraging the enormous existing capital investment in silicon,” Appelbaum says. “Furthermore, silicon has an intrinsically long spin lifetime, making it even more attractive for applications where spins must survive through many clock cycles and across complex circuits,” he says.

A complementary education component to the research project will include the training of graduate students and under-represented undergraduates in diverse aspects of science and engineering, including semiconductor device design, processing and measurement, and spintronics.

Also, research fellowships for minority undergraduate students will be fostered through a partnership with the local Louis Stokes Alliance for Minority Participation (LSAMP) and the Resources to Insure Successful Engineers (RISE) program at UD. Summer research internship opportunities for Delaware high school teachers will be offered, too, according to Appelbaum.

“The education component is designed to help us advance UD's research strengths in engineering and spintronics, as well as in nanotechnology,” Appelbaum says. “By exposing high-school teachers to modern nanotechnology concepts, we hope to excite their students' interest in pursuing advanced technology degrees.”

Appelbaum also plans to offer his successful course “Magnetism and Spintronics” (ELEG423) through a distance-learning format. ###

Appelbaum earned his bachelor's degree summa cum laude in physics and mathematics at Rensselaer Polytechnic Institute and his Ph.D. in physics at the Massachusetts Institute of Technology. He was a postdoctoral fellow at Harvard University for one year before joining the UD faculty in 2005.
Appelbaum is the author or co-author of more than 30 peer-reviewed journal articles. He is a member of the Materials Research Society and a life member of the American Physical Society.
Contact: Tracey Bryant 302-831-8185 University of Delaware

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Wednesday, March 19, 2008

Surface dislocation nucleation: Strength is but skin deep at the nanoscale, Penn engineers discover

Atomic configuration of nucleation

Caption: Atomic configuration of nucleation (blue atom group) in the surface layer of a square copper nanowire (yellow and green atoms) under uniaxial stress. Nucleation occurs at a partial dislocation in the surface layer. Colors refer to the breaking of local inversion symmetry. Credit: Physical Review Letters and Ju Li, Department of Materials Science in the School of Engineering and Applied Science at Penn. Usage Restrictions: None.
PHILADELPHIA –- For centuries, engineers have bent and torn metals to test their strength and ductility. Now, materials scientists at the University of Pennsylvania School of Engineering and Applied Science are studying the same metals but at nanoscale sizes in the form of wires a thousand times thinner than a human hair. This work has enable Penn engineers to construct a theoretical model to predict the strength of metals at the nanoscale. Using this model, they have found that, while metals tend to be stronger at nanoscale volumes, their strengths saturate at around 10-50 nanometers diameter, at which point they also become more sensitive to temperature and strain rate. Such prediction of different strength regimes of nano-solids is important for future application and engineering design of nanotechnology.
Such small-volume materials with relatively large surface areas are now routinely employed in microchips and nanoscience and technology, and their mechanical properties can differ vastly from their macroscale counterparts. Typically, smaller is stronger. A gold wire 200 nanometers in diameter can be 50 times stronger per area than centimeter-sized single-crystal gold. Engineers investigated the "smaller is stronger" trend.

Ju Li, an associate professor in the Department of Materials Science and Engineering at Penn, and his collaborators at the Georgia Institute of Technology have combined transition state theory, explicit atomistic energy landscape calculation and computer simulation to establish a theoretical framework to predict the strengths of small-volume materials. Unlike previous models, their prediction can be directly compared with experiments performed at realistic temperature and loading rates. This research appeared as a cover article in Volume 100 of Physical Review Letters.

Their study demonstrated that the free, exterior surface of nanosized materials can be fertile breeding grounds of dislocations at high stresses. Dislocations are string-like defects whose movements give rise to plastic flow, or shape change, of solids. In large-volume materials, it is easy for dislocations to multiply and entangle and to maintain a decent population inside; however, in small-volume materials, dislocations could show up and then exit the sample, one at a time. To initiate and sustain plastic flow in this case, dislocations need to be frequently nucleated fresh from the surface.

Since surface is itself a defect, researchers asked to what degree the measured strength of a small-volume material reflects surface properties and surface-mediated processes, particularly when the sample size is in the range of tens of nanometers. Li and his team modeled tiny bits of gold and copper to investigate the probabilistic nature of surface dislocation nucleation. The study showed that the activation volume associated with surface dislocation nucleation is characteristically in the range of 1–10 times the atomic volume, much smaller than that of many conventional dislocation processes. Small activation volumes will lead to sensitive temperature and strain-rate dependence of the critical stress, providing an upper bound to the size-strength relation.

From this, the team predicted that the "smaller is stronger" trend will saturate at wire diameters 10-50 nanometers for most metals. For comparison, computers now contain microchips with 45 nanometer strained silicon features. Associated with this saturation in strength is a transition in the rate-controlling mechanism, from collective dislocation dynamics to single dislocation nucleation. ###

The National Science Foundation-funded study was performed by Li and Amit Samanta of Penn and, from Georgia Tech, Ting Zhu and Ken Gall of the Woodruff School of Mechanical Engineering and Austin Leach of the School of Materials Science and Engineering.

Contact: Jordan Reese 215-573-6604 University of Pennsylvania

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Tuesday, March 18, 2008

Physicists discover gold can be magnetic on the nanoscale

Planar Gold Cluster

Caption: Three-dimensional (a) and planar 20-atom gold clusters (b), showing top and side views, with the gold atoms depicted as yellow spheres, adsorbed on an MgO 8-layer film (Mg atoms in green and O atoms in red), which itself is supported by an underlying silver substrate (not shown). The calculations were performed under the influence of an electric field of 1 volt per nanometer. The excess electronic charge distribution is superimposed on the atomic structure as a blue cloud. The planar structure (b) is the favorable one under these conditions, while without the electric field the 3-D cluster (a) is the more stable one. Credit: Uzi Landman/Georgia Tech. Usage Restrictions: With Credit.

Gold Nanowire

Caption: The atomic structure of a gold nanowire containing 5 gold atoms (depicted by yellow spheres), with an embedded oxygen molecule (depicted by red spheres), stretched between two gold tip electrodes (gold leads that connect to the electrodes are not shown). Excess electronic charge on the incorporated oxygen atoms is depicted by blue clouds. Credit: Uzi Landman/Georgia Tech. Usage Restrictions: With Credit.
Physicists at the Georgia Institute of Technology have made important findings regarding gold on the nanoscale. They found that applying an electrical field on a surface-supported gold nanocluster changes its structure from a three-dimensional one to a planar flat structure. In another paper, they relate their discovery that gold in this size regime can be made magnetic through oxygenation of gold nanowires. They also found that up to a certain length, oxygenated gold nanowires behave as a conducting metal, but beyond that, they become insulators. This marks the first time on the nanoscale that such a metal-to-insulation transition has been found on the nanoscale. Both findings are important predictions that could some day be implemented as control parameters governing the chemical and physical material properties employed in nanotechnology.

The researchers focused their theoretical investigations on gold nanostructures because of the well known chemical inertness of gold in the bulk form, allowing one to maintain samples with minimal influence on the environment.

“However, we again find that small is different,” said Uzi Landman, Regents’ and Institute Professor, holder of the F.E. Callaway Chair, and director of the Center for Computational Materials Science, repeating a phrase that he coined and has used often for close to two decades. “On the nanoscale, even gold becomes a potent catalyst, exhibiting new and surprising, chemical, mechanical, electrical and magnetic behavior, which could not have been extrapolated or predicted on the basis of our knowledge about this substance in the bulk form. Some of these systems may find technological uses in nanocatalysis and as chemical and electrical sensors,” Landman added.

For the first study, which appears in the February 8 edition of Physical Review Letters,
Landman and Research Scientist Bokwon Yoon performed first-principles quantum mechanical computer simulations of a 20-atom gold nanocluster adsorbed on the surface of a film of magnesium oxide (MgO), an insulator which itself is supported by an underlying metallic silver substrate. The optimal configuration of the adsorbed gold nanocluster depends on the thickness of the underlying MgO film, and for an eight-layer film it was found to be a three-dimensional four-sided pyramid, with one of the sides contacting the magnesium oxide surface.

However, the researchers discovered that under the influence of an externally applied electric field, the aforementioned three-dimensional shape of the gold nanocluster is no longer the energetically favored structure. Instead, the optimal structure becomes a flat planar 20-atom gold island spread on the MgO surface.

Turning off the applied field or reversing it’s direction results in reverting the structure back to the pyramidal one. The origin of the nanocluster morphological change was found to relate to accumulation of excess electronic charge at the interface between the cluster and the magnesium oxide film. This excess charge, which stabilizes the planar nanocluster structure, originates from the underlying silver substrate, and it’s ability to penetrate to the cluster interface through the eight-layer thick MgO film depends on the presence of the externally applied driving electric field.

The researchers also discovered that the chemical activity of the adsorbed gold nanocluster varied significantly under the influence of the applied field, enhancing the low-temperature catalytic oxidation of CO to carbon dioxide.

“We found that we can change in a controllable manner the physical as well as the chemical properties of the adsorbed nanostructure by applying an external voltage across the supported gold nanocluster,” said Landman. “ I believe that this finding may introduce a potent control parameter into the chemistry of materials. The newly proposed method for tuning and controlling the structure and reactivity of nanostructures through the application of external electric fields may open novel directions and increase the range and applications of nanocatalytic systems and chemically based sensors and catalytic switches.”

The second finding, which appears in the February 1 edition of the same journal, answers the question of what happens when a nanowire of gold is pulled in the presence of oxygen. In these studies Landman, Postdoctoral Fellow Chun Zhang and Senior Research Scientist Robert Barnett used first-principles simulations and quantum electrical transport calculations. They found that oxygenated gold nanowires exhibit different properties, depending on whether the oxygen is incorporated in a molecular form or as individual atoms. Indeed, some of these theoretical results offer a new interpretation of recent laboratory experiments on oxygenated gold nanowires.

In the case of incorporation of molecular oxygen into the gold nanowire, the simulations revealed that the nanowires can be stretched to a significantly longer extent than pure gold nanowires – in other words, the adsorbed oxygen molecule serves as a reinforcing clamp.

Furthermore, the simulations predict that up to a certain stretching distance (typically up to wires that resemble a stretched necklace of about six gold atoms and an embedded oxygen molecule), such nanowires will conduct electrons similar to a pure gold nanowire. These results have been confirmed experimentally. Moreover, the simulations predict that oxygenated gold nanowires extended beyond a length of about six gold atoms become insulating. The conducting state can be restored by a slight contraction of the wire, thus allowing distance - dependent sensitive metal-to-insulator nano-switching.

When individual oxygen atoms, rather than an oxygen molecule, are incorporated in the gold nanowire, the elongation range was found to be limited and the electrical conductance was predicted to be lower than in the previous case of molecular oxygen incorporation. However, a surprising finding was made for such wires, predicting the emergence of magnetism with the magnetic moments localized on the embedded oxygens and on the neighboring gold nanowire atoms.

“It’s a very exotic thing,” said Landman of the phenomenon. “Finding materials that have magnetic properties when their bulk form doesn’t have those properties is very interesting from a fundamental point of view, and may have certain future technological applications.” ###

Contact: David Terraso 404-385-2966 Georgia Institute of Technology

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