Structural Defects Introduced Into Carbon Nanotubes Could Lead The Way To Carbon Nanotube Circuits

ScienceDaily (Jan. 15, 2009) — Structural defects introduced into carbon nanotubes could lead the way to carbon nanotube circuits, research led by Vincent Meunier of Oak Ridge National Laboratory's Computer Science and Mathematics Division shows.

Individual carbon nanotubes are excellent conductors of electricity, but that conductivity goes away when they are connected together into circuits because the junctions act as barriers, and the connections are effective insulators.

However, work conducted at the Department of Energy's Center for Nanophase Materials Sciences at ORNL and Mexico's National Laboratory for Nanoscience and Nanotechnology Research shows that imperfections in the carbon lattice structure, which is typically hexagonal, improve conductivity between nanotubes.

The finding could lead to nanoscale circuits that enable more compact and more powerful computers made of carbon nanotube materials that outperform silicon.

The research is published in the journal ACS Nano. The work is supported by the Division of Materials Sciences and Engineering, DOE Office of Basic Energy Sciences.

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Adapted from materials provided by DOE/Oak Ridge National Laboratory.

Cerium Oxide Nanotubes Get Noticed

ScienceDaily (Mar. 30, 2006) — Chemists and materials scientists often study "nanotubes" -- capsule-shaped molecules only a few billionths of a meter (nanometers) in width. In nanotube form, many materials take on useful, unique properties, such as physical strength and excellent conductivity. Carbon nanotubes are the most widely investigated variety. Now, in pioneering research, scientists at the U.S. Department of Energy's Brookhaven National Laboratory have created and investigated the properties of nanotubes made of a different, yet equally interesting material: cerium oxide.

Brookhaven chemist Wei-Qiang Han. (Image courtesy of Brookhaven National Laboratory)

"Cerium oxide nanotubes have potential applications as catalysts in vehicle emission-control systems and even fuel cells," says Brookhaven chemist Wei-Qiang Han, the lead scientist involved in the work. "But until very recently, they haven't been studied."

Han and his colleagues are in the midst of ongoing research into the structure and properties of cerium oxide nanotubes. As part of this, they have devised a method to synthesize cerium oxide nanotubes of high quality. First, they allow the compounds cerium nitrate and ammonia hydroxide to chemically react. Initially, this reaction forms "one-dimensional" nanostructures, such as rods and sheets, made of the intermediate product cerium hydroxide. The intermediate product is then quickly cooled to zero degrees Celsius, which freezes those structures into place. By letting the chemical reaction proceed over a long period of time, a process called "aging," the hydrogen is eventually removed from the intermediate product and a large quantity of the desired end product -- cerium oxide nanotubes -- is formed.

Han will explain this synthesis method at the American Chemical Society National Meeting in Atlanta, Georgia. His talk will take place at 3:00 p.m. on Tuesday, March 28, 2006, in Room B403 of the Georgia World Congress Center.

During his talk, Han will also discuss his group's recent study -- how cerium oxide nanotubes release oxygen ions when immersed in a low-oxygen environment, a process that is critical to the nanotubes' effectiveness as catalysts. To do this, the researchers have used several techniques. These include "transmission electron microscopy," a very powerful imaging technique, and two x-ray techniques, which they performed at Brookhaven's National Synchrotron Light Source.

"We're interested in studying oxygen-atom vacancies in cerium oxide nanotubes because, when combined with their other surface features, these vacancies may make them more functional and effective in the applications mentioned," Han said.

This work was funded by the Office of Basic Energy Sciences within the U.S. Department of Energy's Office of Science.

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Adapted from materials provided by Brookhaven National Laboratory.

Flower-shaped Nanoparticles May Lead To Better Batteries For Portable Electronics

ScienceDaily (Sep. 16, 2008) — Want more power and longer battery life for that cell phone, laptop, and digital music player? "Flower power" may be the solution. Chemists are reporting development of flower-shaped nanoparticles with superior electronic performance than conventional battery materials.

These "nanoflowers" may power next-generation electronic devices, say the scientists in a report scheduled for the Oct. 8 issue of ACS' Nano Letters, a monthly journal.

Gaoping Cao and colleagues point out that nanoflowers are not new. Researchers have developed various types of flower-shaped nanoparticles using different materials, including manganese oxide, the key metallic ingredient that powers conventional batteries. However, older-generation nanoflowers were not suitable for electronic products of the future, which will demand more power and longer battery life, the researchers say.

In the new study, scientists first grew clusters of carbon nanotubes, strands of pure carbon 50,000 times thinner than a human hair, that are known to have superior electrical conductivity. The scientists then deposited manganese oxide onto the nanotubes using a simple, low-cost coating technique called "electrodeposition," resulting in nano-sized clusters that resemble tiny dandelions under an electron microscope. The result was a battery system with higher energy storage capacity, longer life, and greater efficiency than conventional battery materials, the researchers say.

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Journal reference:

1. Zhang, Hao, Cao, Gaoping, Wang, Zhiyong, Yang, Yusheng, Shi, Zujin, and Gu, Zhennan. Growth of Manganese Oxide Nanoflowers on Vertically-Aligned Carbon Nanotube Arrays for High-Rate Electrochemical Capacitive Energy Storage. Nano Letters, 2008; 8 (9): 2664 DOI: 10.1021/nl800925j

Adapted from materials provided by American Chemical Society, via EurekAlert!, a service of AAAS.

Gold, Copper Nanoparticles Take Center Stage In The Search For Hydrogen Production Catalysts

ScienceDaily (Mar. 29, 2007) — X-ray studies at the U.S. Department of Energy's (DOE) Brookhaven National Laboratory are pointing the way to less costly and more efficient catalysts for improving the performance of fuel cells. The studies, which will be presented by Brookhaven chemist Jose Rodriguez at the 233rd National Meeting of the American Chemical Society, show that copper can be substituted for gold in reactions that keep fuel cells functioning longer while eliminating unwanted byproducts.

Chemist Jose Rodriguez (Credit: Image courtesy of DOE/Brookhaven National Laboratory)

With the goal of efficient fuel cell operation in mind, researchers first need to turn their attention to hydrogen, which is one of the leading energy sources being investigated by scientists sponsored by the DOE as part of its mission to ensure the nation's future energy needs. A major problem facing today's most promising fuel-cell technologies is that the same hydrogen-rich materials feeding the reaction often contain high levels of carbon monoxide (CO), which is formed during hydrogen production. Within a fuel cell, CO "poisons" the expensive platinum catalysts that convert hydrogen into electricity, deteriorating their efficiency over time and requiring their replacement.

Rodriguez will discuss how the use of gold and copper nanoparticles might provide a solution to this problem at the National Meeting. "We're trying to find a catalyst that achieves two things: produces hydrogen while removing a large amount of CO," Rodriguez said.

One way to eliminate the CO byproduct is to combine it with water to produce hydrogen gas and carbon dioxide in a process known as the "water-gas shift" reaction. With the assistance of proper catalysts, the water-shift reaction can convert nearly 100 percent of the CO into carbon dioxide. Using catalyst characterization techniques at Brookhaven's National Synchrotron Light Source (NSLS), Rodriguez and coworkers Jonathan Hanson and Jan Hrbek found that nanoparticles of either gold or copper, supported on a metal, can perform this catalytic role. In particular, they found that the greatest catalytic activity is achieved with extremely small nanoparticles -- less than 4 nanometers (4 billionths of a meter) -- supported on the metal cerium oxide, or ceria.

"Metal nanoparticles alone are not able to do the catalysis," Rodriguez said. "But when you put them on the ceria, you see tremendous catalytic activity."

At the nanoscale, gold has long been known to exhibit chemical reactivity that makes it a potent catalyst. The problem, however, comes with its hefty price tag. "We wanted a material that was less expensive," Rodriguez said. "We wanted to see if we could replace the gold with copper." Using x-ray diffraction, absorption, and spectroscopy studies at the NSLS, Rodriguez's group showed that the substitution is indeed possible. Although gold nanoparticles continue to show the greatest catalytic activity, copper is almost as reactive and its cost is much lower.

This research was funded by the Office of Basic Energy Sciences within the DOE's Office of Science.

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Adapted from materials provided by DOE/Brookhaven National Laboratory.

Ceria Nanoparticles Catalyze Reactions For Cleaner-Fuel Future

ScienceDaily (Apr. 2, 2005) — SAN DIEGO, CA - Experiments on ceria (cerium oxide) nanoparticles carried out at the U.S. Department of Energy’s Brookhaven National Laboratory may lead to catalytic converters that are better at cleaning up auto exhaust, and/or to more-efficient ways of generating hydrogen — a promising zero-emission fuel for the future. Brookhaven chemist Jose Rodriguez will present results from two studies exploring the composition, structure, and reactivity of these versatile nanoparticles during the 229th National Meeting of the American Chemical Society on Tuesday, March 15, at 8:15 a.m. in room Del Mar A of the Hyatt Regency, San Diego, California.

After using a novel technique to synthesize the ceria nanoparticles, Rodriguez and coworkers Xianqin Wang and Jonathan Hanson used bright beams of x-rays at the National Synchrotron Light Source to study how their composition, structure, and reactivity changed in response to doping with zirconium in one case, and impregnation with gold in another.

“In a catalytic converter, ceria acts as a buffer, absorbing or releasing oxygen depending on the conditions of the engine to maintain the catalyst in its optimum operating condition for converting harmful emissions such as carbon monoxide and nitrogen oxide to carbon dioxide and nitrogen gas,” Rodriguez said. Others have found that adding zirconium improves ceria’s ability to store and release oxygen.

The synchrotron studies at Brookhaven explain why: Zirconium changes the ceria’s structure to increase the number of oxygen “vacancies” — or places for oxygen uptake and release. Furthermore, Rodriguez says, “the ceria nanoparticles we studied have much better performance, higher chemical reactivity, than the bulk form of ceria currently used in catalytic converters.” Thus, this research holds promise for more-efficient catalytic converters — and cleaner air.

In the second study, Wang, Hanson, and Rodriguez deposited gold on the surface of ceria nanoparticles and used x-rays at the synchrotron to determine the catalyst’s “active phase” — the conformation responsible for the catalytic activity — in the conversion of water and carbon monoxide to hydrogen gas and carbon dioxide. This “water-gas shift” reaction is important for generating hydrogen, which can be used for chemical transformations and as a fuel in a hydrogen-based economy. Hydrogen is one of the leading energy sources being investigated by scientists sponsored by the Department of Energy as part of its mission to ensure the nation’s future energy needs.

“In both cases, we are learning about the fundamental conditions necessary for optimal operation of the catalysts,” Rodriguez said. “This kind of knowledge eventually will lead to a rational design of even more effective catalysts.”

This research was funded by the Office of Basic Energy Sciences within the U.S. Department of Energy’s Office of Science.

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Adapted from materials provided by Brookhaven National Laboratory.

Nanoparticle Offers Promise For Treating Glaucoma

ScienceDaily (June 19, 2007) — A unique nanoparticle made in a laboratory at the University of Central Florida is proving promising as a drug delivery device for treating glaucoma, an eye disease that can cause blindness and affects millions of people worldwide.

Glaucoma affects millions of people and if left untreated can cause blindness. (Credit: Jerry Klein)

“The nanoparticle can safely get past the blood-brain barrier making it an effective non-toxic tool for drug delivery,” said Sudipta Seal, an engineering professor with appointments in UCF’s Advanced Materials Processing and Analysis Center and the Nanoscience Technology Center.

Seal and his colleagues from North Dakota State University note in the article that while barely 1-3 percent of existing glaucoma medicines penetrate into the eye, earlier experiments with nanoparticles have shown not only high penetration rates but also little patient discomfort. The miniscule size of the nanoparticles makes them less abrasive than some of the complex polymers now used in most eye drops.

Seal and his team created a specialized cerium oxide nanoparticle and bound it with a compound that has been shown to block the activity of an enzyme (hCAII) believed to play a central role in causing glaucoma.

The disease involves abnormally high pressure of the fluid inside the eye, which, if left untreated, can result in damage to the optic nerve and vision loss. High pressure occurs, in part, because of a buildup of carbon dioxide inside the eye, and the compound blocks the enzyme that produces carbon dioxide.

Seal and a team of collaborators including Sanku Mallik, of North Dakota State University, developed the research on using nanoparticles as a delivery mechanism for the compound after supervising a student summer project at UCF. Duke University undergraduate Serge Reshetnikov spent a summer studying nanoscience on UCF’s Orlando campus as part of a Research Experience for Undergraduates (REU) project funded by the National Science Foundation. Reshetnikov started looking into the possibilities of using nanoparticles as drug delivery tools. Subsequent research with his advisors led to the specific application for glaucoma.

In their paper on the research, which was also supported by the National Science Foundation, Seal and Mallik note the results are “very promising” and that their nanoparticle configuration offers seemingly limitless possibilities as a non-toxic drug delivery tool.

The findings will be published in an article appearing in the June 28 issue of the Journal of Physical Chemistry C.

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Adapted from materials provided by University of Central Florida.

Tracking Down The Effect Of Nanoparticles

ScienceDaily (Apr. 12, 2009) — Cerium oxide is a ceramic nano-abrasive. Scientists have now examined, under conditions close to reality, what happens when it is breathed in and deposited on the lung surface. Initially, the result was rather reassuring.

Cell cultures of lung epithelial cells (in the right-hand box) were exposed to an aerosol of cerium oxide nanoparticles in a special glove box. During the exposure of the cell cultures, the nanoparticles were freshly produced by flame synthesis in the left half of the box. (Credit: Image courtesy of ETH Zurich)

Synthetic nanoparticles are ubiquitous in today's world: either as an additive to building materials, whose properties they improve; in cosmetics, mainly in sun creams and toothpaste; or in foodstuffs, to thicken them or brighten their color. However, nano-safety research, i.e. knowledge of how nanoparticles interact with their environment and specifically with a living organism, is still largely in its infancy.

However, this is one of the central topics for the research group led by Wendelin Stark, Assistant Professor at the Institute for Chemical and Bio-engineering of ETH Zurich. The group carries out tests over and over again to investigate the effect nanoparticles have on their surroundings.

Conditions close to reality

Together with the research group led by Peter Gehr, Professor of Histology at the University of Bern, the scientists have now used a completely new method and a new type of lung cell culture to examine how cerium oxide nanoparticles act on the cells. The aim was to study the toxicity of cerium oxide, which is used in large amounts as an abrasive, mainly in the manufacture of semiconductor chips. Although, as a rule, this takes place in a hermetically sealed room from which people are excluded, the researchers now simulated a situation in which ceramic nanomaterial is inhaled directly, for example if nanoparticles are manufactured without protection or the powder is handled incorrectly.

The researchers did this by using what is called flame spray synthesis to spray cerium oxide nanoparticles in a closed glove box, thus simulating aerosols. A fan distributed the aerosols uniformly in the box, about 2.5 cubic meters in size, in which the aerosols were sprayed on to the cultured lung cells for ten, twenty and thirty minutes. The ETH researches hit upon the idea when they spoke to Barbara Rothen-Rutishauser, a scientist from Bern and first author of the paper. She told them about the new type of cell culture.

The innovative aspect of the method is the special cell culture combined with the use of flame spray synthesis. The cell culture of lung epithelial cells grows on a permeable membrane. The lower surface of the epithelial cells is immersed in a medium and their upper surface is covered with a natural liquid layer. Thus the cell culture is very similar to the surface of the lung. As a result of the aerosol production, the spray process is also close to reality. The combination of these two techniques showed how inhaled nanoparticles are deposited on the lung surface. In conventional methods for such experiments up to now, cell cultures were bathed in nanoparticle solutions. However, this can cause the nanoparticles to agglomerate, which alters their properties; moreover, the lung surface is wet in a different way. Consequently, the behavior of the cells might also change.

No cell death

The scientists chose cerium oxide for their study, mainly because the material does not occur physiologically in cells, meaning that only the effect of the nanoparticle on the cell is observed. The longer the cultures were sprayed for, the more nanoparticles were deposited on the lung cells. The scientists observed that the cells were not destroyed, i.e. they did not die. However, the permeability of the cell layer increased. Therefore, the researchers suspect that certain structures of particular proteins that seal the interstices between the epithelial cells had altered under the influence of the nanoparticles. The production of a substance in the cell which is associated with oxidative stress and which could result in DNA damage could also be observed.

Long-term effects unknown

Robert Grass, group leader in Wendelin Stark’s group, explains: “However, we were unable to observe the effect of the particles on the cells over a prolonged time.” This is because the cultures must be subjected to further processing to allow them to be examined under a microscope. In a next step, the researchers plan to replicate even more realistic conditions by using what are known as triple cell co-cultures that simulate human cellular respiratory tract barriers. For example, they want to find out how the body’s phagocytes and “waste disposal agents”, known as macrophages, deal with nanoparticles.

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Journal reference:

1. Rothen-Rutishauser et al. Direct Combination of Nanoparticle Fabrication and Exposure to Lung Cell Cultures in a Closed Setup as a Method To Simulate Accidental Nanoparticle Exposure of Humans. Environmental Science & Technology, 2009; 43 (7): 2634 DOI: 10.1021/es8029347

Adapted from materials provided by ETH Zurich.

Measuring The Immeasurable: Bond Strength Of Materials Linked To Heat Transfer

ScienceDaily (Apr. 13, 2009) — The speed at which heat moves between two materials touching each other is a potent indicator of how strongly they are bonded to each other, according to a new study by researchers at Rensselaer Polytechnic Institute.

Researchers at Rensselaer Polytechnic Institute have discovered there is a strong correlation between the speed at which heat moves between two touching materials and how strongly those materials are bonded together. The study shows that this flow of heat from one material to another can be dramatically altered by "painting" a thin atomic layer between materials. Changing the interface fundamentally alters the way the materials interact. (Credit: Rensselaer/Rahul Godawat)

Additionally, the study shows that this flow of heat from one material to another, in this case one solid and one liquid, can be dramatically altered by "painting" a thin atomic layer between materials. Changing the interface fundamentally changes the way the materials interact.

"If you have a nanoparticle that is inside a liquid solution, you can't just 'peel away' the liquid to measure how strongly it is bonded to the surrounding molecules," said Pawel Keblinski, professor in Rensselaer's Department of Materials Science and Engineering, who co-led the study. "Instead, we show that you can measure the strength of these bonds simply by measuring the rate of heat flow from the nanoparticle to the surrounding liquid."

"Interfaces are an exciting new frontier for doing fundamental studies of this type. If you peek into complex biological systems – a cell, for example – they contain a high density of interfaces, between different proteins or between protein and water," said Shekhar Garde, the Elaine and Jack S. Parker Professor and head of Rensselaer's Department of Chemical and Biological Engineering, who co-led the study with Keblinski. "Our approach possibly provides another handle to quantify how proteins talk to each other or with the surrounding water."

Results of the study, titled "How wetting and adhesion affect thermal conductance of a range of hydrophobic to hydrophilic aqueous solutions," were published April 13 in Physical Review Letters.

Keblinski and Garde used extensive molecular dynamics simulations to measure the heat flow between a variety of solid surfaces and water. They simulated a broad range of surface chemistries and showed that thermal conductance, or how fast heat is transferred between a liquid and a solid, is directly proportional to how strongly the liquid adhered to the solid.

"In the case of a mercury thermometer, thermal expansion correlates directly with temperature," Keblinski said. "What we have done, in a sense, is create a new thermometer to measure the interfacial bonding properties between liquids and solids."

"We can use this new technique to characterize systems that are very difficult or impossible to characterize by other means," Garde said.

This fundamental discovery, which helps to better understand how water sticks to or flows past a surface, has implications for many different heat transfer applications and processes including boiling and condensation. Of particular interest is how this discovery can benefit new systems for cooling and displacing heat from computer chips, a critical issue currently facing the semiconductor industry, Garde said.

More generally, the authors said the study sheds new light on the behavior of water at various solid interfaces, which has direct implications ranging from the binding of proteins and other molecules to surfaces, to biological self-assembly in interfacial environments.

Co-authors of the paper include materials science and engineering graduate student Natalia Shenogina, along with chemical and biological engineering graduate student Rahul Godawat.

Financial support for this project was provided by the U.S. National Science Foundation Nanoscale Science and Engineering Center Grant, in addition to support from U.S. Air Force Office of Scientific Research Multidisciplinary University Research Initiative.

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Adapted from materials provided by Rensselaer Polytechnic Institute.

Peering Into Nanowires To Measure Dopant Properties

ScienceDaily (Apr. 13, 2009) — 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 next generation of electronics.

Atom-by-atom mapping of a germanium nanowire by atom probe tomography. Left: 3D reconstruction of an individual Ge nanowire with each green sphere representing an individual Ge atom. The dimensions are 50x50x100 nm3. The region enclosed by the red box is displayed at upper right, with single atomic planes visible in the center of the image. The grey spheres are phosphorous dopant atoms used to control the conductivity. (The dimensions are 5x25x15 nm3). The region enclosed by the blue box is displayed in the lower right, revealing an inhomogeneous distribution of phosphorous atoms. (The dimensions are 50x50x10 nm3). The 'shell' of enhanced doping results from surface reactions during growth of the nanowire. (Credit: Image courtesy of Northwestern University)

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.

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.

The results were published online March 29 in the journal Nature Nanotechnology.

“We simply mapped where all the atoms were in a single nanowire, and from the map we determined where the dopant atoms were,” he says. “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,” he says. “This fundamental scientific understanding establishes a basis for engineering.”

Lauhon and his group performed the research at Northwestern’s Center for Atom Probe Tomography, which uses a Local Electrode Atom ProbeTM 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,” Lauhon says.

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

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Journal reference:

1. Perea et al. Direct measurement of dopant distribution in an individual vapour–liquid–solid nanowire. Nature Nanotechnology, 2009; DOI: 10.1038/nnano.2009.51

Adapted from materials provided by Northwestern University.

Nano Changes Rise To Macro Importance In A Key Electronics Material

ScienceDaily (Apr. 14, 2009) — By combining the results of a number of powerful techniques for studying material structure at the nanoscale, a team of researchers from the National Institute of Standards and Technology (NIST), working with colleagues in other federal labs and abroad, believe they have settled a long-standing debate over the source of the unique electronic properties of a material with potentially great importance for wireless communications.

The new study of silver niobate not only opens the door to engineering improved electronic components for smaller, higher performance wireless devices, but also serves as an example of understanding how subtle nanoscale features of a material can give rise to major changes in its physical properties.

Silver niobate is a ceramic dielectric, a class of materials used to make capacitors, filters and other basic components of wireless communications equipment and other high-frequency electronic devices. A useful dielectric needs to have a large dielectric constant—roughly, a measure of the material’s ability to hold an electric charge—that is stable in the operating temperature range. The material also should have low dielectric losses—which means that it does not waste energy as heat and preserves much of its intended signal strength. In the important gigahertz range of the radio spectrum—used for a wide variety of wireless applications—silver niobate-based ceramics are the only materials known that combine a high, temperature-stable dielectric constant with sufficiently low dielectric losses.

It’s been known for some time that silver niobate’s unique dielectric properties are temperature dependent—the dielectric constant peaks in a broad range near room temperature in these ceramics, which makes them suitable for practical applications. Earlier studies were unable to identify the structural basis of the unusual dielectric response because no accompanying changes in the overall crystal structure could be observed. “The crystal symmetry doesn’t seem to change at those temperatures,” explains NIST materials scientist Igor Levin, “but that’s because people were using standard techniques that tell you the average structure. The important changes happen at the nanoscale and are lost in averages.”

Only in recent years, says Levin, have the specialized instruments and analytic techniques been available to probe nanoscale structural changes in crystals. Even so, he says, “these subtle deviations from the average are so small that any single measurement gives only partial information on the structure. You need to combine several complementary techniques that look at different angles of the problem.” Working at different facilities* the team combined results from several high-resolution probes using X-rays, neutrons and electrons—tools that are sensitive to both the local and average crystal structure— to understand silver niobate’s dielectric properties. The results revealed an intricate interplay between the oxygen atoms, arranged in an octahedral pattern that defines the compound’s crystal structure, and the niobium atoms at the centers of the octahedra.

At high temperatures, the niobium atoms are slightly displaced, but their average position remains in the center—so the shift isn’t seen in averaging measurements. As the compound cools, the oxygen atoms cooperate by moving a little, causing the octahedral structure to rotate slightly. This movement generates strain which “locks” the niobium atoms into off-centered positions—but not completely. The resulting partial disorder of the niobium atoms gives rise to the dielectric properties. The results, the researchers say, point to potential avenues for engineering similar properties in other compounds.

The work was supported in part by the U.S. Department of Energy and the U.K. Science and Technology Facilities Council.

* The study required measurements at the Advanced Photon Source at Argonne National Laboratory, the Lujan Neutron Center at Los Alamos National Laboratory and the ISIS Pulsed Neutron and Muon Source at Rutherford Appleton Laboratory (United Kingdom). In addition to NIST, researchers from Argonne, Los Alamos, ISIS and the University of Sheffield contributed to the paper.

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Journal reference:

1. I. Levin, V. Krayzman, J.C. Woicik, J. Karapetrova, T. Proffen, M.G. Tucker and I.M. Reaney. Structural changes underlying the diffuse dielectric response in AgNbO3. Phys. Rev. B, 79, 104113, online March 26, 2009

Adapted from materials provided by National Institute of Standards and Technology.

New Security And Medical Sensor Devices Made Possible By Fundamental Physics Development In Metallic Nanostructures

ScienceDaily (Apr. 13, 2009) — 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.

An image of the metallic ring and disk. The scale bar shows 200 nanometres. (Credit: Image courtesy of Imperial College London)

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.

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."

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Journal reference:

1. Verellen et al. Fano Resonances in Individual Coherent Plasmonic Nanocavities. Nano Letters, 2009; 090312170407019 DOI: 10.1021/nl9001876

Adapted from materials provided by Imperial College London.

'Powerhouses' From Living Cells -- Mitochondria -- Power New Explosives Detector

ScienceDaily (Nov. 22, 2008) — Researchers in Missouri have borrowed the technology that living cells use to produce energy to develop a tiny, self-powered sensor for rapid detection of hidden explosives. The experimental sensor, about the size of a postage stamp, represents the first of its kind to be powered by mitochondria, the microscopic "powerhouses" that provide energy to living cells, the researchers say.

Scientists have developed a stamp-sized sensor for detecting hidden explosives. The sensor is powered by mitochondria, which provide energy to living cells. (Credit: American Chemical Society)

In the new study, Shelley Minteer, Marguerite Germain, and Robert Arechederra point out that today's explosives detectors are expensive, bulky, and complex. Society needs smaller, cheaper, simpler detection devices, based on technology that perhaps could be incorporated into cell phones and portable digital music players, the researchers suggest.

The scientists describe development of an experimental sensor built from a special biofuel cell, essentially a battery-like device consisting of a thin layer of mitochondria sandwiched between a carbon-based electrode and a gas-permeable electrode. In laboratory studies using nitrobenzene as a test compound, the sensor showed a significant boost in electrical power in the presence of the substance, demonstrating the sensor's potential for detecting TNT and related explosives, the researchers say.

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Journal reference:

1. Germain et al. Nitroaromatic Actuation of Mitochondrial Bioelectrocatalysis for Self-Powered Explosive Sensors. Journal of the American Chemical Society, 2008; 130 (46): 15272 DOI: 10.1021/ja807250b

Adapted from materials provided by American Chemical Society.

Fitter Frames: Nanotubes Boost Structural Integrity Of Composites

ScienceDaily (Apr. 3, 2009) — A new research discovery at Rensselaer Polytechnic Institute could lead to tougher, more durable composite frames for aircraft, watercraft, and automobiles.

Researchers at Rensselaer have discovered a new technique for provoking unusual crazing behavior in epoxy composites. The crazing, which causes the composite to deform into a network of nanoscale pillar-like fibers that bridge together both sides of a crack and slow its growth, could lead to tougher, more durable components for aircraft and automobiles. (Credit: Image courtesy of Rensselaer Polytechnic Institute)

Epoxy composites are increasingly being incorporated into the design of new jets, planes, and other vehicles. Composite material frames are extremely lightweight, which lowers the overall weight of the vehicle and boosts fuel efficiency. The downside is that epoxy composites can be brittle, which is detrimental to its structural integrity.

Professor Nikhil Koratkar, of Rensselaer’s Department of Mechanical, Aerospace, and Nuclear Engineering, has demonstrated that incorporating chemically treated carbon nanotubes into an epoxy composite can significantly improve the overall toughness, fatigue resistance, and durability of a composite frame.

When subjected to repetitive stress, a composite frame infused with treated nanotubes exhibited a five-fold reduction in crack growth rate as compared to a frame infused with untreated nanotubes, and a 20-fold reduction when compared to a composite frame made without nanotubes.

This newfound toughness and crack resistance is due to the treated nanotubes, which enhance the molecular mobility of the epoxy at the interface where the two materials touch. When stressed, this enhanced mobility enables the epoxy to craze – or result in the formation of a network of pillar-like fibers that bridge together both sides of the crack and slow its growth.

“This crazing behavior, and the bridging fibers it produces, dramatically slows the growth rate of a crack,” Koratkar said. “In order for the crack to grow, those fibers have to first stretch, deform plastically, and then break. It takes a lot of energy to stretch and break those fibers, energy that would have otherwise gone toward enlarging the crack.”

Results of the study were just published in the journal Small.

Epoxy composites infused with carbon nanotubes are known to be more resistant to cracks than pure epoxy composites, as the nanotubes stitch, or bridge, the two sides of the crack together. Infusing an epoxy with carbon nanotubes that have been functionalized, or treated, with the chemical group amidoamine, however, results in a completely different bridging phenomenon.

At the interface of the functionalized nanotubes and the epoxy, the epoxy starts to craze, which is a highly unusual behavior for this particular type of composite, Koratkar said. The epoxy deforms, becomes more fluid, and creates connective fibers up to 10 microns in length and with a diameter between 100 nanometers and 1,000 nanometers.

“We didn’t expect this at all. Crazing is common in certain types of thermoplastic polymers, but very unusual in the type of epoxy composite we used,” Koratkar said. “In addition to improved fatigue resistance and toughness, the treated nanotubes also enhanced the stiffness, hardness, and strength of the epoxy composite, which is very important for structural applications.”

Koratkar said the aircraft, boat, and automobile industries are increasingly looking to composites as a building material to make vehicle frames and components lighter. His research group plans to further investigate crazing behavior in epoxy composites, in order to better understand why the chemical treatment of nanotubes initiates crazing.

Co-authors of the paper include Rensselaer Associate Professor Catalin Picu, of the Department of Mechanical, Aerospace, and Nuclear Engineering; Rensselaer doctoral students Wei Zhang and Iti Srivastava; and Yue-Feng Zhu, professor in the Department of Mechanical Engineering at Tsinghua University in China.

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Adapted from materials provided by Rensselaer Polytechnic Institute.

ScienceDaily: Your source for the latest research news and science breakthroughs -- updated daily Science News Share Blog Cite Print Email Bo

ScienceDaily (Oct. 19, 2007) — Researchers in California report development of the world's first working radio system that receives radio waves wirelessly and converts them to sound signals through a nano-sized detector made of carbon nanotubes.

The "carbon nanotube radio" device is thousands of times smaller than the diameter of a human hair. The development marks an important step in the evolution of nano-electronics and could lead to the production of the world's smallest radio, the scientists say.

Peter Burke and Chris Rutherglen developed a carbon nanotube "demodulator" that is capable of translating AM radio waves into sound. In a laboratory demonstration, the researchers incorporated the detector into a complete radio system and used it to successfully transmit classical music wirelessly from an iPod to a speaker several feet away from the music player.

Although other researchers have developed nano-sized radio wave detectors in the past, the current study marks the first time that a nano-sized detector has been demonstrated in an actual working radio system, the scientists say. The study demonstrates the feasibility of making other radio components at the nanoscale in the future and may eventually lead to a "truly integrated nanoscale wireless communications system," they say. Such a device could have numerous industrial, commercial, medical and other applications.

Their findings appeared online October 17 and are scheduled for publication in the Nov. 14 print edition of ACS' Nano Letters.

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Adapted from materials provided by American Chemical Society, via EurekAlert!, a service of AAAS.

Nanotechnology? What's That?! Engineers Create Exhibits on Achievements, Promise

June 1, 2006 — Nanotechnology has already brought advances such as self-cleaning windows and energy-efficient LED lighting, and could soon deliver medical breakthroughs. To educate the public about nanotechnology's promise, the National Science Foundation has slated $20 million to fund a network of interactive exhibits at 100 museums around the country.

MADISON, Wis.--Nanotechnology is the big buzz word in the world of science. It's going to impact just about everything we do, touch and see. And this next big thing is extraordinarily small.

You've heard the word, but do you know what nanotechnology is?

University of Wisconsin-Madison engineer Wendy Crone is on a mission. She and her interns are creating user-friendly exhibits to teach the public about the nanoworld.

"Nanotechnology is already starting to affect our lives, and it's anticipated that over the next 20 years it's going to have major impact on everything around us," Crone tells DBIS.

Nanotechnology means working at the scale of molecules. Crone's exhibits show just how small that scale is. "When you put nano in front of meter that means that's a billionth of a meter. So that means that you can fit 1 billion nanometers in one meter," she says. You'd have to slice one hair into 50,000 distinct strands to get a strand one-nanometer thick.

Nanotechnology is the secret behind how self-cleaning windows work and why LEDs are so energy-efficient.

"I think that nanotechnology, I mean, everyone continues to talk about it, is the next big thing," says intern Anne Vedder.

It might even save your life. Drug-coated nanoparticles will soon precisely deliver therapy to organs and tumors. Crone says it's going to be everywhere, and you probably won't even know that it's inside the products that you're using.

The National Science Foundation is giving $20 million to fund the national Nanoscale Informal Science Education Network (NISE Network), which will develop interactive exhibits to teach the public about nanotechnology. The network's goal is to have these exhibits in 100 museums across the United States in the next five years.

BACKGROUND: The engineering faculty, staff and students at the University of Wisconsin, Madison, are working with some of the nation's top science museums to create hands-on exhibits about nanotechnology. The effort is part of the $20 million Nanoscale Informal Science Education Network, which aims to develop innovative materials and vehicles to increase the public's knowledge and understanding of nanotechnology through exhibits.

ABOUT NANOTECHNOLOGY: Nanotechnology is science at the size of individual atoms and molecules: objects and devices measuring mere billionths of a meter, smaller than a red blood cell. At that size scale, materials have different chemical and physical properties than those of the same materials in bulk, because quantum mechanics is more important. For example, carbon atoms can conduct electricity and are stronger than steel when woven into hollow microscopic threads. Nanoparticles are already widely used in certain commercial consumer products, such as suntan lotions, "age-defying" make-up, and self-cleaning windows that shed dirt when it rains. One company manufactures a nanocrystal wound dressing with built-in antibiotic and anti-inflammatory properties. On the horizon is toothpaste that coats, protects and repairs damaged enamel, as well as self-cleaning shoes that never need polishing. Nanoparticles are also used as additives in building materials to strengthen the walls of any given structure, and to create tough, durable, yet lightweight fabrics.

SIZING THINGS UP: The tiny size scale makes it a challenge to translate nanotech research into something museum visitors can see, touch and comprehend, especially in an interactive format. UW-Madison already has the Nanoworld Discovery Center, which does just that. Among the exhibit's features is a segment about ferrofluids: tiny magnetic particles that flow like a liquid. They are used to damp vibrations and eliminate excess energy in expensive stereo systems. Visitors also learn about such applications as stain-resistant clothing, as well as compare incandescent bulbs to light-emitting diodes to learn how nanomaterials can help conserve energy.

Note: This story and accompanying video were originally produced for the American Institute of Physics series Discoveries and Breakthroughs in Science by Ivanhoe Broadcast News and are protected by copyright law. All rights reserved.

Peering Into Nanowires To Measure Dopant Properties

ScienceDaily (Apr. 1, 2009) — 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 next generation of electronics.

Atom-by-atom mapping of a germanium nanowire by atom probe tomography. Left: 3D reconstruction of an individual Ge nanowire with each green sphere representing an individual Ge atom. The dimensions are 50x50x100 nm3. The region enclosed by the red box is displayed at upper right, with single atomic planes visible in the center of the image. The grey spheres are phosphorous dopant atoms used to control the conductivity. (The dimensions are 5x25x15 nm3). The region enclosed by the blue box is displayed in the lower right, revealing an inhomogeneous distribution of phosphorous atoms. (The dimensions are 50x50x10 nm3). The 'shell' of enhanced doping results from surface reactions during growth of the nanowire. (Credit: Image courtesy of Northwestern University)

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.

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.

The results were published online March 29 in the journal Nature Nanotechnology.

“We simply mapped where all the atoms were in a single nanowire, and from the map we determined where the dopant atoms were,” he says. “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,” he says. “This fundamental scientific understanding establishes a basis for engineering.”

Lauhon and his group performed the research at Northwestern’s Center for Atom Probe Tomography, which uses a Local Electrode Atom ProbeTM 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,” Lauhon says.

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

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Journal reference:

1. Perea et al. Direct measurement of dopant distribution in an individual vapour–liquid–solid nanowire. Nature Nanotechnology, 2009; DOI: 10.1038/nnano.2009.51

Adapted from materials provided by Northwestern University.

First Ever Video Of Dynamics Of Carbon Atoms Makes Spintronic-based Computing Look More Promising

ScienceDaily (Apr. 1, 2009) — Science fiction fans still have another two months of waiting for the new Star Trek movie, but fans of actual science can feast their eyes now on the first movie ever of carbon atoms moving along the edge of a graphene crystal. Given that graphene – single-layered sheets of carbon atoms arranged like chicken wire – may hold the key to the future of the electronics industry, the audience for this new science movie might also reach blockbuster proportions.

This 3D rendering of a graphene hole imaged on TEAM 0.5 shows that the carbon atoms along the edge assume either a zigzag or an armchair configuration. The zigzag is the more stable configuration and shows promise for future spintronic technologies. (Credit: Image courtesy of DOE/Lawrence Berkeley National Laboratory)

Researchers with the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab), working with TEAM 0.5, the world’s most powerful transmission electron microscope, have made a movie that shows in real-time carbon atoms repositioning themselves around the edge of a hole that was punched into a graphene sheet. Viewers can observe how chemical bonds break and form as the suddenly volatile atoms are driven to find a stable configuration. This is the first ever live recording of the dynamics of carbon atoms in graphene.

“The atom-by-atom growth or shrinking of crystals is one of the most fundamental problems of solid state physics, but is especially critical for nanoscale systems where the addition or subtraction of even a single atom can have dramatic consequences for mechanical, optical, electronic, thermal and magnetic properties of the material,” said physicist Alex Zettl who led this research. “The ability to see individual atoms move around in real time and to see how the atomic configuration evolves and influences system properties is somewhat akin to a biologist being able to watch as cells divide and a higher order structure with complex functionality evolves.”

Zettl holds joint appointments with Berkeley Lab’s Materials Sciences Division (MSD) and the Physics Department at the University of California (UC) Berkeley, where he is the director of the Center of Integrated Nanomechanical Systems. He is the principal author of a paper describing this work which appears in the March 27, 2009 issue of the journal Science. The paper is entitled, “Graphene at the Edge: Stability and Dynamics.” Co-authoring this paper with Zettl were Çağlar Girit, Jannik Meyer, Rolf Erni, Marta Rossell, Christian Kisielowski, Li Yang, Cheol-Hwan Park, Michael Crommie, Marvin Cohen and Steven Louie.

In their paper, the authors credit the unique capabilities of TEAM 0.5 for making their movie possible. TEAM stands for Transmission Electron Aberration-corrected Microscope. The newest instrument at Berkeley Lab’s National Center for Electron Microscopy (NCEM) - a DOE national user facility and the country’s premier center for electron microscopy and microcharacterization - TEAM 0.5 is capable of producing images with half angstrom resolution, which is less than the diameter of a single hydrogen atom.

Said NCEM director Ulrich Dahmen of this achievement with TEAM 0.5, “The real-time observation of the movements of edge atoms could lead to a new level of understanding and control of nanomaterials. With further advances in electron-optical correctors and detectors it may become possible to increase the sensitivity and speed of such observations, and begin to see a live view of many other reactions at the atomic scale.”

Rubbing graphene off the end of a pencil tip and suspending the specimen in an observation grid, Zettl and his colleagues used prolonged irradiation from TEAM 0.5’s electron beam (set at 80 kV) to introduce a hole into the graphene’s pristine hexagonal carbon lattice. Focusing the beam to a spot on the sheet blows out the exposed carbon atoms to create the hole. Since atoms at the edge of the hole are continually being ejected from the lattice by electrons from the beam the size of the hole grows. The researchers used the same TEAM 0.5 electron beam to record for analysis a movie showing the growth of the hole and the rearrangement of the carbon atoms.

“Atoms that lose their neighbors become highly volatile, and move around rapidly, continually repositioning themselves from one metastable configuration to the next,” said Zettl. “Although configurations come and go, we found a zigzag configuration to be the most stable. It occurs more often and over longer length scales along the edge than the other most common configuration, which we called the armchair.”

Understanding which of these atomic configurations is the most stable is one of the keys to predicting and controlling the stability of a device that utilizes graphene edges. The discovery of strong stability in the zigzag configuration is particularly promising news for the spintronic dreams of the computer industry.

Two years ago, co-authors Cohen and Louie, theorists who hold joint appointments with Berkeley Lab’s Materials Sciences Division and UC Berkeley, calculated that nanoribbons of graphene can conduct a spin current and could therefore serve as the basis for nanosized spintronic devices. Spin, a quantum mechanical property arising from the magnetic field of a spinning electron, carries a directional value of either “up” or “down” that can be used to encode data in the 0s and 1s of the binary system. Spintronic devices promise to be smaller, faster and far more versatile than today’s devices because – among other advantages – data storage does not disappear when the electric current stops.

Said Cohen, “Our calculations showed that zigzag graphene nanoribbons are magnetic and can carry a spin current in the presence of a sufficiently large electric field. By carefully controlling the electric field, it should be possible to generate, manipulate, and detect electron spins and spin currents in spintronics applications.”

Said Louie, “If electric fields can be made to produce and manipulate a 100-percent spin-polarized carrier system through a chosen geometric structure, it will revolutionize spintronics technology.”

The theorists were enthusiastic about actually being able to see their predictions in action.

Said Cohen, “This work is an excellent example of the power of attacking a fundamental problem through a combination of theory, experiment and cutting edge instrumentation. The instrument is one of the world’s best and allows us to see atoms move, the theory allows us to make realistic models, and the experiment was performed through the magic hands of Alex Zettl to ensure that the right measurement was done in the right way.”

Said Louie, “As the old saying goes - seeing is believing. The visual verification of the formation and stability of zigzag edges in the live atomic images from TEAM 0.5 is very satisfying. Furthermore, the ability to simultaneously see atomic structure and perform physical measurements, using the kind of set-up that the Zettl group has at NCEM, should greatly accelerate the cycle of discovery, theoretical understanding, applications and further discovery.”

For Zettl and his movie-making collaborators, next up they will correlate the atomic dynamics in graphene that they can now observe in real time with such properties as electrical conduction, optical response and magnetism. This will be a major advance towards fully understanding and applying graphene to spintronic technology as well as other electronic and photovoltaic devices.

“While, graphene is particularly exciting, our experimental methods should be applicable to other materials, including other 2-D systems as well,” Zettl said. “We are vigorously pursuing these areas of research in collaboration with the theorists and the staff at NCEM.”

Said NCEM principal investigator and co-author of this paper, Kisielowski, “The ability to observe the dynamics of single carbon atoms is a dream come true that reaches beyond investigations of graphene. In fact it gets us one step closer to understanding artificial photosynthesis, which is considered to be an ultimate energy technology and is being pursued at Berkeley Lab through the Helios Project.”

More on TEAM

TEAM 0.5 features state-of-the-art technical advances including an extremely bright electron source, ultra-stable electronics to reduce drift and, perhaps most importantly, the ability to provide optical corrections for spherical aberration (blurring). By making points of light look like disks, spherical aberrations have been the prime limiting factors in the resolution of transmission electron microscopy. Its ability to correct spherical aberrations makes TEAM 0.5 highly versatile. It can be used for broad-beam “wide-angle” imaging as well as for scanning transmission electron microscopy (STEM), in which the tightly focused electron beam is moved across a sample as a probe. In the STM mode, TEAM 0.5 is capable of performing spectroscopy on one atom at a time — an ideal way to precisely locate impurities in an otherwise homogeneous sample, such as individual dopant atoms in a semiconductor. Aberration correction also enables TEAM 0.5 to produce high resolution images at relatively low electron beam energies. Because of their longer wavelengths, lower energy electrons are more difficult to focus than higher energy electrons. Aberration correction overcomes this problem.

TEAM 0.5 was designed and constructed through a collaboration led by Berkeley Lab and including DOE’s Argonne and Oak Ridge National Laboratories, the Frederick Seitz Materials Laboratory of the University of Illinois, and two private companies specializing in electron microscopy, the FEI Company headquartered in Portland, Oregon, and CEOS of Heidelberg, Germany.

The TEAM project is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences. Zettl’s research was supported by the Director, Office of Energy Research, Office of Basic Energy Sciences, Materials Sciences, and Engineering Division, of the U.S. Department of Energy.

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Journal reference:

1. Çaglar Ö. Girit, Jannik C. Meyer, Rolf Erni, Marta D. Rossell, C. Kisielowski, Li Yang, Cheol-Hwan Park, M. F. Crommie, Marvin L. Cohen, Steven G. Louie, and A. Zettl. Graphene at the Edge: Stability and Dynamics. Science, 2009; 323 (5922): 1705 DOI: 10.1126/science.1166999

Adapted from materials provided by DOE/Lawrence Berkeley National Laboratory.