Nano research could impact flexible electronic devices

ScienceDaily (Jan. 12, 2012) — A discovery by a research team at North Dakota State University, Fargo, and the National Institute of Standards and Technology (NIST), shows that the flexibility and durability of carbon nanotube films and coatings are intimately linked to their electronic properties. The research could one day impact flexible electronic devices such as solar cells and wearable sensors. The research also provided a promising young high school student the chance to work in the lab with world-class scientists, jumpstarting her potential scientific career.

The NDSU/NIST research team, led by Erik Hobbie, Ph.D., is working to determine why thin films made from metallic single-wall carbon nanotubes are superior for potential applications that demand both electronic performance and mechanical durability. "One simple reason is that the metallic nanotubes tend to transport charge more easily when they touch each other," said Hobbie. "But another less obvious reason has to do with how much the films can flex without changing their structure at very small scales."

Results from the study are published in ACS Nano.

The team includes NDSU graduate student John M. Harris; postdoctoral researcher Ganjigunte R. Swathi Iyer; Anna K. Bernhardt, North Dakota Governor's School attendee; and NIST researchers Ji Yeon Huh, Steven D. Hudson and Jeffrey A. Fagan.

There is great interest in using carbon nanotube films and coatings as flexible transparent electrodes in electronic devices such as solar cells. "Our research demonstrates that the flexibility and durability of these films are intimately linked to their electronic properties," said Hobbie. "This is a very new idea, so hopefully, it will generate a new series of studies and questions focused on the exact origins and consequences of this effect."

Such research could potentially result in material that reduces solar cell costs, and leads to the ability to use them in clothing or foldable electronics. Electronic devices currently on the market that require transparent electrodes, like touch screens and solar cells, typically use indium tin oxide, an increasingly expensive material. "It is also very brittle," said Hobbie, "implying that it cannot be used in devices that require mechanical flexibility like wearable or foldable electronics."

Single-wall carbon nanotubes show significant promise as transparent conductive coatings with outstanding electronic, mechanical and optical properties. "A particularly attractive feature of these films is that the physical properties can be tuned through the addition or subtraction of a relatively small number of nanotubes," said Hobbie. "Thin films made from such materials hold tremendous potential for flexible electronics applications, including the replacement of indium tin oxide in liquid crystal displays and photovoltaic devices."

Thin films made from metallic single-wall carbon nanotubes show better durability as flexible transparent conductive coatings, which the researchers attribute to a combination of superior mechanical performance and higher interfacial conductivity. The research team found significant differences in the electronic manifestations of thin-film wrinkling, depending on the electronic type of the nanotubes, and examined the underlying mechanisms.

The results of this study suggest that the metallic films make better flexible transparent conductive coatings; they have higher conductivity and are more durable. "Our results are relevant to a number of ongoing efforts in transparent conducting films and flexible electronic devices," said Hobbie.

The research was supported by the National Science Foundation through CMMI-0969155 and the U.S. Department of Energy through DE-FB36-08GO88160.

The opportunity to work on such research was new to Anna Bernhardt, a high school junior from a town of 1,000 people in western North Dakota. She was among 66 of the most academically driven high school sophomores and juniors who attended a six-week intensive summer residential program on the NDSU campus for scholastically motivated students in the state.

Students receive concentrated instruction from 40 NDSU faculty through discussion groups, labs, field trips and other activities. The state of North Dakota funds the cost of participation for North Dakota students who are accepted into the program. It's available free to public school students, while private and homeschool students selected for the program can make arrangements to attend for free through their local public school district.

While it is unusual for a young student to be involved in nanotechnology research at this level, it presented an opportunity for everyone involved. Bernhardt prepared single-wall carbon nanotube samples and participated in testing of the samples. "The experience of working in a research setting has helped me to decide that I would love to do more research in the future," said the young scientist. "The biggest benefit of working in the lab was getting a taste of the true research experience. Without North Dakota's Governor's School, I would never have been able to have this experience and surely wouldn't be so certain that I would like to do more research in the future."

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The above story is reprinted from materials provided by North Dakota State University, via Newswise.

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Journal Reference:

John M. Harris, Ganjigunte R. Swathi Iyer, Anna K. Bernhardt, Ji Yeon Huh, Steven D. Hudson, Jeffrey A. Fagan, Erik K. Hobbie. Electronic Durability of Flexible Transparent Films from Type-Specific Single-Wall Carbon Nanotubes. ACS Nano, 2011; 111220100417004 DOI: 10.1021/nn204383t

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Are Android Powered Devices on Pace to Surpass Apple's iOS?

Since the debut of the Apple iPhone in 2007, competition in the smart device market has been dismal at best. That is, until the development and marketing of the Android operating system. Focusing on what Apple did well and aiming to change what the iOS platform is lacking, the Android OS has quickly gained praise from users of its Droid devices. Addressing concerns such as the lack of flash and the proprietary nature of the APP store, the Android operating system has appeared to remove the governor from the iOS platform, and has taken a host of users with it in the process. The following article will address the surge of the Android platform and will compare growth in the top 20 markets worldwide.

A major initial selling point to the Android platform is that unlike iOS, Android powered devices can run flash applications. The lack of flash has proven to be a continual hair-puller for most iPhone and iPad users, with most users anticipating the addition on each software update, only to be fooled. Steve Jobs, made it clear before passing that his intentions were to never allow the software on his devices due to inefficiency. In return he developed HTML5 as a more processor friendly application engine. It remains to be seen if Apple will add Flash to its new ramped iPhone and iPad processor or if they will respect the wishes of their legendary CEO and founder. One thing is clear, sales and demand for the Android platform may be in large driven by this disparity.

With 2011 coming to an end, holiday sales and network usage are an accurate indicator of how each market fared in the smart device war. With the iOS still clearly the worldwide leader in overall usage, it was very interesting to see the percentage gain in market proportion drawn by the Android powered devices. In the nation's top 20 markets, Android powered devices reigned in countries like South Korea (the manufacturing site of the Droid) and Sweden. With a 60% increase in growth vs Apple's 30%, it is clear to see that the Android platform is more than here to stay, it may eventually take the title.

While overall growth numbers are staggeringly high, the more impressive number is the total number of smart phone users worldwide. Increasing 12 times since 2009, the smart phone market is one of the largest growth areas on the planet. Driven largely by Apple and Android, the future of personal portable computing and communication is apparently limitless.

For questions regarding this article or iPhone Screen Repair or iPhone 4S Screen Repair please visit our website.

I have been actively following the development of Apple products since the debut of the iPhone in 2007. Since that time I have expanded my interest to the iPad, iPod and competing devices such. In early 2008 I founded an iPhone repair company that expanded its vision to the eventual repair of all Apple branded devices. Since that time I have continued to actively follow the progression of the smart phone market, while actively writing and blogging about the innovations being made worldwide.

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Benchmark Tests for Android Devices: Explained in Detail

Of late, you would have been hearing about benchmark tests like 'Quadrant', 'Nenamark', 'Linpack', 'Browsermark' etc. being performed on smartphones and tablets and avid tech enthusiasts eagerly comparing how all these latest devices are competing against each other. We'll explore what these benchmark tests are, the reason for them becoming popular and the various benchmark tests in this article.

What are benchmark tests?

In computing, a benchmark is the act of running a set of computer programs for the purpose of assessing the relative performance of an object. So, benchmarking in smartphones and tablets is usually associated with assessing the performance characteristics of the smartphones' and tablets' hardware. But, that doesn't mean there aren't any software benchmark tests. Please understand that these tests are being performed only to compare the relative performance of the devices and in no way can be used to conclude how smooth or how fast the actual user experience will be.

Why have these benchmark tests become popular for smartphones and tablets?

Each and every smartphone and tablet that is being released into the market today has almost the same components: a CPU (Central Processing Unit / Microprocessor / Core), a GPU (Graphics Processing Unit), an Instruction Set, RAM (Random Access Memory), Display containing a particular amount of resolution, Internal Flash Memory etc. Almost all the benchmark tests can run successfully on these devices and gauge the performance of these in-built components. The relevance of some of these tests significantly gains weight when we factor in the 'Operating System' that is run on the devices.

What are the various benchmark tests that are relevant to the smartphones and tablets?

The following tests are relevant

QuadrantLinpackNenamark 1Nenamark 2JavascriptBrowsermarkGL 2.1NeocoreAnTuTuVellamo

Quadrant

'Quadrant' is a product of 'Aurora Softworks'. It is nothing but a series of tests performed on a mobile device which benchmark the CPU, Memory, I/O and 2D/3D graphics. The 'Standard Quadrant' is free for Android Users who can download the application from the 'Android Market' and run it on their devices. The benchmark provides an overall score which can be compared with the benchmark scores from the other devices. If you overclock your CPU, this will obviously get reflected in the benchmark test in a better score. If you want a reference point for your device, the 'Samsung Galaxy Note' has one of the highest, or probably, the highest Quadrant score of 3624 (without overclocking).

Linpack

The Linpack benchmark is a measure of the system's floating point computing power. Introduced by Jack Dongarra, it measures how fast a device can solve a dense N-by-N system of linear equations. This benchmark was originally designed to run on supercomputers in the 1970's. So, you can imagine how advanced the device in your hand is today. You can download this application from the 'Android Market' and check the strength of the CPU in your device. The results are designated in MFLOPS (Millions of Floating Point Operations per Second).

Nenamark 1

The first iteration of the 'Nenamark' benchmark test was designed to test the strength of the GPU (The above two tests, Quadrant and Linpack, measure the strength of the CPU). Nenamark 1, designed to run around 10-15 fps (frames per second), uses programmable shaders for graphical effects such as reflections, dynamic shadows, parametric surfaces, particles and different light models to push the GPU to the limits. Results are designated in FPS.

Nenamark 2

'Nenamark 1' had been released an year ago and since then, the smartphones have become a lot more capable with refresh rates of their screens crossing 60 fps. So, the 'Nenamark 1' was not deemed very effective to test such devices and hence Nenamark 2 had been conceptualized. Results are designated in FPS.

JavaScript

'Sunspider JavaScript' is a benchmark that aims to measure the JavaScript performance on tasks relevant to the current and near future use of JavaScript in the real world, such as encryption and text manipulation. In other words, the test simulates real-world usage of JavaScript on Websites. The results are reported in milliseconds (ms). If you want a reference point for your device, the 'Samsung Galaxy Nexus' has one of the best scores: 1879 ms.

Just remember that the more you score on 'Quadrant', 'Linpack', 'Nenamark 1' and 'Nenamark 2', the better. The lesser you score on 'JavaScript', the better.

Broswermark

Rightware, recently spun off from Futuremark, has introduced the 'Browsermark' benchmark test in order to compare the browsers of various smartphone devices. The test measures a browser's performance in JavaScript and HTML rendering. The test results are reported in numbers. If you want a reference point for your device, currently, among the smartphones, the 'Samsung Galaxy Nexus' has the highest reported browsermark score of 98272.

GL 2.1

The 'GL Benchmark' is a 3D benchmarking program designed to test how well your phone can reproduce 3D scenes and images. So, this benchmark test is actually a test of the strength of the GPU of your smartphone/tablet device. Currently, the Power VR SGX 543 MP2 is the leader in the GPU department and its stamina is reflected in the GL Benchmark tests. Please note that the GL Benchmark test is a combination of several other benchmark tests whose results are reported in 'FPS' (Frames Per Second) and 'mS' (milli Seconds).

Neocore

Neocore is another GPU benchmarking test which benchmarks the Open GL ES-1.1 graphics performance. The results of this benchmark test are reported in FPS.

AnTuTu

AnTuTu can run a full test of a key project, through the "Memory Performance", "CPU Integer Performance", "CPU Floating Point Performance", "2D 3D Graphics Performance", "SD card reading/writing speed", "Database IO" performance. A Total score is reported once you run this benchmark. If you want a reference point for your device, "Asus Eee Pad Transformer Prime" with a score of 12872 has the highest score till date.

Vellamo

Vellamo, a benchmark test originally developed by Qualcomm, is a mobile web-browser benchmark that provides a holistic view into browser performance by measuring each component systematically, providing results for CPU and memory, scrolling, JavaScript, HTML 5, canvas rendering speed and network access. So, it is similar to the 'Rightware Browsermark' test.

For staying updated on the latest developments in the field of technology visit 'The GadgetCrat': http://www.thegadgetcrat.in/

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New method for enhancing thermal conductivity could cool computer chips, lasers and other devices

ScienceDaily (Dec. 14, 2011) — The surprising discovery of a new way to tune and enhance thermal conductivity -- a basic property generally considered to be fixed for a given material -- gives engineers a new tool for managing thermal effects in smart phones and computers, lasers and a number of other powered devices.

The finding was made by a group of engineers headed by Deyu Li, associate professor of mechanical engineering at Vanderbilt University, and published online in the journal Nature Nanotechnology on Dec. 11.

Li and his collaborators discovered that the thermal conductivity of a pair of thin strips of material called boron nanoribbons can be enhanced by up to 45 percent depending on the process that they used to stick the two ribbons together. Although the research was conducted with boron nanoribbons, the results are generally applicable to other thin film materials.

An entirely new way to control thermal effects

"This points at an entirely new way to control thermal effects that is likely to have a significant impact in microelectronics on the design of smart phones and computers, in optoelectronics on the design of lasers and LEDs, and in a number of other fields," said Greg Walker, associate professor of mechanical engineering at Vanderbilt and an expert in thermal transport who was not directly involved in the research.

According to Li, the force that holds the two nanoribbons together is a weak electrostatic attraction called the van der Waals force. (This is the same force that allows the gecko to walk up walls.)

"Traditionally, it is widely believed that the phonons that carry heat are scattered at van der Waals interfaces, which makes the ribbon bundles' thermal conductivity the same as that of each ribbon. What we discovered is in sharp contrast to this classical view. We show that phonons can cross these interfaces without being scattered, which significantly enhances the thermal conductivity," said Li. In addition, the researchers found that they could control the thermal conductivity between a high and a low value by treating the interface of the nanoribbon pairs with different solutions.

The enhancement is completely reversible

One of the remarkable aspects of the effect Li discovered is that it is reversible. For example, when the researchers wetted the interface of a pair of nanoribbons with isopropyl alcohol, pressed them together and let them dry, the thermal conductivity was the same as that of a single nanoribbon. However, when they wetted them with pure alcohol and let them dry, the thermal conductivity was enhanced. Then, when they wetted them with isopropyl alcohol again, the thermal conductivity dropped back to the original low value.

"It is very difficult to tune a fundamental materials property such as thermal conductivity and the demonstrated tunable thermal conductivity makes the research especially interesting," Walker said.

One of the first areas where this new knowledge is likely to be applied is in thermal management of microelectronic devices like computer chips. Today, billions to trillions of transistors are jammed into chips the size of a fingernail. These chips generate so much heat that one of the major factors in their design is to prevent overheating. In fact, heat management is one of the major reasons behind today's multi-core processor designs.

"A better understanding of thermal transport across interfaces is the key to achieving better thermal management of microelectronic devices," Li said.

Discovery may improve design of nanocomposites

Another area where the finding will be important is in the design of "nanocomposites" -- materials made by embedding nanostructure additives such as carbon nanotubes to a host material such as various polymers -- that are being developed for use in flexible electronic devices, structural materials for aerospace vehicles and a variety of other applications.

Collaborators on the study were post-doctoral research associate Juekan Yang, graduate students Yang Yang and Scott Waltermire from Vanderbilt; graduate students Xiaoxia Wu and Youfei Jiang, post-doctoral research associate Timothy Gutu, research assistant professor Haitao Zhang, and Associate Professor Terry T. Xu from the University of North Carolina; Professor Yunfei Chen from the Southeast University in China; Alfred A. Zinn from Lockheed Martin Space Systems Company; and Ravi Prasher from the U.S. Department of Energy.

The research was performed with financial support from the National Science Foundation, Lockheed Martin's Engineering and Technology University Research Initiatives program and the Office of Naval Research.

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The above story is reprinted from materials provided by Vanderbilt University. The original article was written by David Salisbury.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.

Journal Reference:

Juekuan Yang, Yang Yang, Scott W. Waltermire, Xiaoxia Wu, Haitao Zhang, Timothy Gutu, Youfei Jiang, Yunfei Chen, Alfred A. Zinn, Ravi Prasher, Terry T. Xu, Deyu Li. Enhanced and switchable nanoscale thermal conduction due to van der Waals interfaces. Nature Nanotechnology, 2011; DOI: 10.1038/nnano.2011.216

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

New method for enhancing thermal conductivity could cool computer chips, lasers and other devices

ScienceDaily (Dec. 14, 2011) — The surprising discovery of a new way to tune and enhance thermal conductivity -- a basic property generally considered to be fixed for a given material -- gives engineers a new tool for managing thermal effects in smart phones and computers, lasers and a number of other powered devices.

The finding was made by a group of engineers headed by Deyu Li, associate professor of mechanical engineering at Vanderbilt University, and published online in the journal Nature Nanotechnology on Dec. 11.

Li and his collaborators discovered that the thermal conductivity of a pair of thin strips of material called boron nanoribbons can be enhanced by up to 45 percent depending on the process that they used to stick the two ribbons together. Although the research was conducted with boron nanoribbons, the results are generally applicable to other thin film materials.

An entirely new way to control thermal effects

"This points at an entirely new way to control thermal effects that is likely to have a significant impact in microelectronics on the design of smart phones and computers, in optoelectronics on the design of lasers and LEDs, and in a number of other fields," said Greg Walker, associate professor of mechanical engineering at Vanderbilt and an expert in thermal transport who was not directly involved in the research.

According to Li, the force that holds the two nanoribbons together is a weak electrostatic attraction called the van der Waals force. (This is the same force that allows the gecko to walk up walls.)

"Traditionally, it is widely believed that the phonons that carry heat are scattered at van der Waals interfaces, which makes the ribbon bundles' thermal conductivity the same as that of each ribbon. What we discovered is in sharp contrast to this classical view. We show that phonons can cross these interfaces without being scattered, which significantly enhances the thermal conductivity," said Li. In addition, the researchers found that they could control the thermal conductivity between a high and a low value by treating the interface of the nanoribbon pairs with different solutions.

The enhancement is completely reversible

One of the remarkable aspects of the effect Li discovered is that it is reversible. For example, when the researchers wetted the interface of a pair of nanoribbons with isopropyl alcohol, pressed them together and let them dry, the thermal conductivity was the same as that of a single nanoribbon. However, when they wetted them with pure alcohol and let them dry, the thermal conductivity was enhanced. Then, when they wetted them with isopropyl alcohol again, the thermal conductivity dropped back to the original low value.

"It is very difficult to tune a fundamental materials property such as thermal conductivity and the demonstrated tunable thermal conductivity makes the research especially interesting," Walker said.

One of the first areas where this new knowledge is likely to be applied is in thermal management of microelectronic devices like computer chips. Today, billions to trillions of transistors are jammed into chips the size of a fingernail. These chips generate so much heat that one of the major factors in their design is to prevent overheating. In fact, heat management is one of the major reasons behind today's multi-core processor designs.

"A better understanding of thermal transport across interfaces is the key to achieving better thermal management of microelectronic devices," Li said.

Discovery may improve design of nanocomposites

Another area where the finding will be important is in the design of "nanocomposites" -- materials made by embedding nanostructure additives such as carbon nanotubes to a host material such as various polymers -- that are being developed for use in flexible electronic devices, structural materials for aerospace vehicles and a variety of other applications.

Collaborators on the study were post-doctoral research associate Juekan Yang, graduate students Yang Yang and Scott Waltermire from Vanderbilt; graduate students Xiaoxia Wu and Youfei Jiang, post-doctoral research associate Timothy Gutu, research assistant professor Haitao Zhang, and Associate Professor Terry T. Xu from the University of North Carolina; Professor Yunfei Chen from the Southeast University in China; Alfred A. Zinn from Lockheed Martin Space Systems Company; and Ravi Prasher from the U.S. Department of Energy.

The research was performed with financial support from the National Science Foundation, Lockheed Martin's Engineering and Technology University Research Initiatives program and the Office of Naval Research.

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The above story is reprinted from materials provided by Vanderbilt University. The original article was written by David Salisbury.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.

Journal Reference:

Juekuan Yang, Yang Yang, Scott W. Waltermire, Xiaoxia Wu, Haitao Zhang, Timothy Gutu, Youfei Jiang, Yunfei Chen, Alfred A. Zinn, Ravi Prasher, Terry T. Xu, Deyu Li. Enhanced and switchable nanoscale thermal conduction due to van der Waals interfaces. Nature Nanotechnology, 2011; DOI: 10.1038/nnano.2011.216

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Making a light-harvesting antenna from scratch: Biomimetic antenna for gathering sunlight may one day transform solar-powered devices

Sometimes when people talk about solar energy, they tacitly assume that we're stuck with some version of the silicon solar cell and its technical and cost limitations. Not so.

The invention of the solar cell, in 1941, was inspired by a newfound understanding of semiconductors, materials that can use light energy to create mobile electrons -- and ultimately an electrical current.

Silicon solar cells have almost nothing to do with the biological photosystems in tree leaves and pond scum that use light energy to push electrons across a membrane -- and ultimately create sugars and other organic molecules.

At the time, nobody understood these complex assemblages of proteins and pigments well enough to exploit their secrets for the design of solar cells.

But things have changed.

At Washington University in St. Louis's Photosynthetic Antenna Research Center (PARC) scientists are exploring native biological photosystems, building hybrids that combine natural and synthetic parts, and building fully synthetic analogs of natural systems.

One team has just succeeded in making a crucial photosystem component -- a light-harvesting antenna -- from scratch. The new antenna is modeled on the chlorosome found in green bacteria.

Chlorosomes are giant assemblies of pigment molecules. Perhaps Nature's most spectacular light-harvesting antennae, they allow green bacteria to photosynthesize even in the dim light in ocean deeps.

Dewey Holten, PhD, professor of chemistry in Arts & Sciences, ard collaborator Christine Kirmaier, PhD, research professor of chemistry are part of a team that is trying to make synthetic chlorosomes. Holten and Kirmaier use ultra-fast laser spectroscopy and other analytic techniques to follow the rapid-fire energy transfers in photosynthesis.

His team's latest results were described in a recent issue of New Journal of Chemistry.

Chlorosomes

Biological systems that capture the energy in sunlight and convert it to the energy of chemical bonds come in many varieties, but they all have two basic parts: the light harvesting complexes, or antennae, and the reaction center complexes. The antennae consist of many pigment molecules that absorb photons and pass the excitation energy to the reaction centers.

In the reaction centers, the excitation energy sets off a chain of reactions that create ATP, a molecule often called the energy currency of the cell because the energy stored ATP powers most cellular work. Cellular organelles selectively break those bonds in ATP molecules when they need an energy hit for cellular work.

Green bacteria, which live in the lower layers of ponds, lakes and marine environments, and in the surface layers of sediments, have evolved large and efficient light-harvesting antennae very different from those found in plants bathing in sunlight on Earth's surface.

The antennae consist of highly organized three-dimensional systems of as many as 250,000 pigment molecules that absorb light and funnel the light energy through a pigment/protein complex called a baseplate to a reaction center, where it triggers chemical reactions that ultimately produce ATP.

In plants and algae (and in the baseplate in the green bacteria) photo pigments are bound to protein scaffolds, which space and orient the pigment molecules in such a way that energy is efficiently transferred between them.

But chlorosomes don't have a protein scaffold. Instead the pigment molecules self -assemble into a structure that supports the rapid migration of excitation energy.

This is intriguing because it suggests chlorosome mimics might be easier to incorporate in the design of solar devices than biomimetics that are made of proteins as well as pigments.

Synthetic pigments

The goal of the work described in the latest journal article was to see whether synthesized pigment molecules could be induced to self-assemble. The process by which the pigments align and bond is not well understood.

"The structure of the pigment assemblies in chlorosomes is the subject of intense debate," Holten says, "and there are several competing models for it."

Given this uncertainty, the scientists wanted to study many variations of a pigment molecule to see what favored and what blocked assembly.

A chemist wishing to design pigments that mimic those found in photosynthetic organisms first builds one of three molecular frameworks. All three are macrocycles, or giant rings: porphyrin, chlorin and bacteriochlorin.

"One of the members of our team, Jon Lindsey can synthesize analogs of all three pigment types from scratch," says Holten. (Lindsey, PhD, is Glaxo Professor of Chemistry at North Carolina State University.)

In the past, chemists making photo pigments have usually started with porphyrins, which are the easiest of the three types of macrocycles to synthesize. But Lindsey also has developed the means to synthesize chlorins, the basis for the pigments found in the chlorosomes of green bacteria. The chlorins push the absorption to the red end of the visible spectrum, an area of the spectrum scientists would like to be able to harvest for energy.

Key to pigment self-assembly are the metal atoms and hydroxyl (OH) and carbonyl (C=O) groups in the pigment molecules (the groups shown in color in the above illustration).

Doctoral student Olga Mass and coworkers in Lindsey's lab synthesized 30 different chlorins, systematically adding or removing chemical groups thought to be important for self-assembly but also attaching peripheral chemical groups that take up space and might make it harder for the molecules to stack or that shift around the distributions of electrons so that the molecules might stack more easily.

Testing for aggregation

The powdered pigments were carefully packaged and shipped by Fed Ex (because the Post Office won't ship chemicals) to Holten's lab at WUSTL and to David Bocian's lab at the University of California at Riverside.

Scientists in both labs made up green-tinctured solutions of each of the 30 molecules in small test tubes and then poked and prodded the solutions by means of analytical techniques to see whether the pigment had aggregated and, if so, how much had formed the assemblies. Holten's lab studied their absorption of light and their fluorescence (which indicated the presence of monomers, since assemblies don't normally fluoresce) and Bocian's lab studied their vibrational properties, which are determined by the network of bonds in the molecule or pigment aggregate as a whole.

In one crucial test Joseph Springer, a PhD student in Holten's lab, compared the absorption spectrum of a pigment in a polar solvent that would prevent it from self-assembling to the spectrum of the pigment in a nonpolar solvent that would allow the molecules to interact with one another and form assemblies.

"You can see them aggregate," Springer says. "A pigment that is totally in solution is clear, but colored a brilliant green. When it aggregates, the solution becomes a duller green and you can see tiny flecks in the liquid."

The absorption spectra indicated that some pigments formed extensive assemblies and that the steric and electronic properties of the molecules predicted the degree to which they would assemble.

Up next

Although this project focused on self-assembly, the PARC scientists have already taken the next step toward a practical solar device. "With Pratim Biswas, PhD, the Lucy and Stanley Lopata Professor and chair of the Department of Energy, Environmental & Chemical Engineering, we've since demonstrated that we can get the pigments to self-assemble on surfaces, which is the next step in using them to design solar devices," says Holten.

"We're not trying to make a more efficient solar cell in the next six months," Holten cautions. "Our goal instead is to develop fundamental understanding so that we can enable the next generation of more efficient solar powered devices."

Biomimicry hasn't always worked. Engineers often point out early flying machines that attempted to mimic birds didn't work and that flying machines stayed aloft only when nventors abandoned biological models and came up with their own designs.

But there is nothing predestined or inevitable about this. As biological knowledge has exploded in the past 50 years, mimicking nature has become a smarter strategy. Biomimetic or biohybrid designs already have solved significant engineering problems in other areas and promise to greatly improve the design of solar powered devices as well.

After all, Nature has had billions of years to experiment with ways to harness the energy in sunlight for useful work.

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The above story is reprinted from materials provided by Washington University in St. Louis. The original article was written by Diana Lutz.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.

Journal Reference:

Olga Mass, Dinesh R. Pandithavidana, Marcin Ptaszek, Koraliz Santiago, Joseph W. Springer, Jieying Jiao, Qun Tang, Christine Kirmaier, David F. Bocian, Dewey Holten, Jonathan S. Lindsey. De novo synthesis and properties of analogues of the self-assembling chlorosomal bacteriochlorophylls. New Journal of Chemistry, 2011; 35 (11): 2671 DOI: 10.1039/C1NJ20611G

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

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Efficiency metrics for energy storage devices need standardization

Solving the mystery of prematurely dead cell phone and laptop batteries may prove to be a vital step toward creating a sustainable energy grid according to Drexel researcher Dr. Yury Gogotsi. In a piece published in the November 18 edition of Science, Gogotsi, who is the head of the A.J. Drexel Nanotechnology Institute, calls for a new, standardized gauge of performance measurement for energy storage devices that are as small as those used in cell phones to as large as those used in the national energy grid.

Gogotsi is one of the featured experts, along with Bill Gates, tapped by Science to address problems that must be solved en route to the widespread use of renewable energy. His piece, co-authored with Dr. Patrice Simon of the Université Paul Sabatier in Toulouse, France, is entitled "True Performance Metrics in Electrochemical Energy Storage."

"A dramatic expansion of research in the area of electrochemical energy storage has occurred over the past due to an ever increasing variety of handheld electronic devices that we all use," Gogotsi said. "This has expanded use of electrical energy in transportation, and the need to store renewable energy efficiently at the grid level. This process has been accompanied by the chase for glory with the arrival of new materials and technologies that leads to unrealistic expectations for batteries and supercapacitors and may hurt the entire energy storage field."

The main type of energy storage device addressed in the article is the supercapacitor. Supercapacators, which are built from relatively inexpensive natural materials such as carbon, aluminum and polymers, are found in devices, ranging from mobile phones and laptop batteries to trams, buses and solar cells. While supercapacitors tend to store less energy compared to standard lithium-ion batteries, they have the ability to charge and discharge energy more quickly than batteries and can be recharged a near infinite number of times, and operate in a wider temperature range with a high efficiency.

Typically, the performance of both, batteries and supercapacitors, is presented using Ragone plots, graphs that show a relation between the energy density and the power density. For example, a Rangone plot for the battery used in an electric car shows both how far it can travel on a single charge -energy density- and how fast the car can travel -power density. An ideal energy storage device is expected to store plenty of energy and do it quickly.

The issue that Gogotsi and Simon bring to light is the idea that current metrics for grading energy storage devices, including the Ragone plot, may not provide a complete picture of the devices' capability. According to the researchers, other metrics, such as a device's cycle lifetime, energy efficiency, self-discharge, temperature range of operation and cost, must also be reported.

"This paper calls upon the community of scientists and engineers who work on supercapacitors to present data on material performance using metrics beyond the traditional Ragone plot," Simon said. "Although such plots are useful for comparing fully packaged commercial devices, they might predict unrealistic performance for packaged cells from extrapolation of small amounts of materials."

Gogotsi and Simon have a longtime research collaboration, investigating materials for supercapacitors. Their joint work has received global coverage and various awards and distinctions. Funding for the collaboration between Gogotsi and Simon is sponsored by the Partner University Fund (PUF) which supports innovative and sustainable partnerships between French and US institutions of research and higher education.

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Y. Gogotsi, P. Simon. True Performance Metrics in Electrochemical Energy Storage. Science, 2011; 334 (6058): 917 DOI: 10.1126/science.1213003

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Electronic Devices In 3D

There are so many different kinds of electronic devices, it seems like every time you turn around there is something that is a new, must have device. The worst offender of them all are the cell phone manufacturers and cell phone providers. It is like they just want you to have to buy their new model phone every time your contract is up. Nobody just puts all of the good ideas into one phone and then stops; they are always looking for the next thing to cram into the tiny device.

At least the trend of making phones smaller and smaller is over. Grown men can use the devices without fear of dropping them or not being able to use them because they were getting so tiny. They were getting so small, mine kept getting lost in my pocket. But the bigger point is that technology doesn't ever stop and every year there are so many innovations and improvements, it can be difficult for a non technophile to keep up with it all.

One of the newest craze that the providers are trying to push on us is 3D. You see 3D at the movies and on your televisions at home and even on your gaming systems. Now there is 3D on your phone. You read that correctly, 3D on your phone. It may not have seemed necessary, and maybe it isn't, but was 3D on your television really needed? Was a triple-decker cheeseburger really necessary? Are giant tire on a 4x4 so that it can crush other, smaller cars necessary? Of course not, but along with a triple cheeseburger and monster trucks, a 3D phone is just plain awesome.

Why have 3D phones? Because you can, that's why. Not only can you watch certain 3D enabled video, you can take 3D photos as well. Imagine going on your family vacation and being able to whip out your phone and take cool 3D pictures for your digital scrapbook. Imagine being at the beach and getting that perfect shot of the kids playing in the water-IN 3D!

Imagine taking a photo of your girlfriend riding an awesome roller coaster-IN 3D! The point is that it literally adds another dimension to you photos and video that you can watch on your phone without the need for special 3D glasses. The technology is evolving so quickly, and 3D might be a fad, but you have to admit-it is pretty awesome.

If you are looking for for HDMI cables you can find some of the best quality and prices by logging onto Selby acoustic at selbyacoustics.com.au.

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New X-ray technique for electronic structures: Ability to probe deep below material surfaces should be boon for nanoscale devices

ScienceDaily (Aug. 26, 2011) — The expression "beauty's only skin-deep" has often been applied to the chemistry of materials because so much action takes place at the surface. However, for many of the materials in today's high technologies, such as semiconductors and superconductors, once a device is fabricated it is the electronic structures below the surface, in the bulk of the material or in buried layers, that determine its effectiveness. For the past 30 years, one of the most valuable and widely used techniques for studying electronic structures has been ARPES -- Angle-Resolved PhotoEmission Spectroscopy. However, this technique primarily looks at surfaces.

Now, for the first time, bulk electronic structures have been opened to comparable scrutiny through a new variation of this standard called HARPES -- Hard x-ray Angle-Resolved PhotoEmission Spectroscopy -- whose development was led by researchers with the U.S. Department of Energy (DOE)'s Lawrence Berkeley National Laboratory (Berkeley Lab).

"HARPES should enable us to study the electronic structure of any new material in the bulk, with minimum effects of surface reactions or contamination," says physicist Charles Fadley who led the development of HARPES. "Our technique should also allow us to probe the buried layers and interfaces that are ubiquitous in nanoscale devices, and are key to smaller logic elements in electronics, novel memory architectures in spintronics, and more efficient energy conversion in such technologies as photovoltaic cells."

Fadley is a physicist who holds joint appointments with Berkeley Lab's Materials Sciences Division and the University of California (UC) Davis where he is a Distinguished Professor of Physics. He is also one of the world's foremost practitioners of photoelectron spectroscopy, a technique based on the photoelectric effect described in 1905 by Albert Einstein. When a beam of photons -- particles of light such as x-rays -- is flashed on a sample, energy is transferred from the photons to electrons, causing them to be emitted from the sample. By measuring the kinetic energy of these emitted photoelectrons and the angles at which they are ejected, scientists can learn much about the sample's electronic structure.

The successful demonstration of the HARPES technique has been reported in the journal Nature Materials in a paper titled "Probing bulk electronic structure with hard X-ray angle-resolved photoemission." Fadley was the senior author of this paper. The lead and corresponding author was Alexander Gray, a member of Fadley's UC Davis research group and also an affiliate with Berkeley Lab's Materials Sciences Division.

"The key to probing the bulk electronic structure is using hard x-rays, which are x-rays with sufficiently high photon energies to eject photoelectrons from deep beneath the surface of a solid material," Gray says. "High-energy photons impart high kinetic energies to the ejected photoelectrons, enabling them to travel longer distances within the solid. The result is that more of the signal originating from the bulk will be detected by the analyzer."

Whereas the typical ARPES experiment, using low energy or "soft" x-rays (10~100 eV photons), probes to a depth of less than 10 angstroms (a few layers of atoms), with their HARPES technique Fadley and Gray and their colleagues on this project were able to probe as deep as 60 Angstroms into the bulk of single crystals of tungsten and gallium-arsenide. Their achievement was made possible by a combination of third generation light sources capable of producing intense beams of hard x-rays, and an advanced electron spectrometer to measure energies and angles.

"While high-energy photons are needed to penetrate into the bulk, at high energies the photoemission intensity that carries information about the electronic band structure is drastically reduced by various factors, such as phonon effects and small photoelectric cross sections of the valence-band electron orbitals," Gray says. "However, HARPES measurements become possible with the advent of the third-generation synchrotron light sources and the development of hard x-ray monochromators and optics capable of focusing a highly intense x-ray beam into a very small measurement spot."

To demonstrate the capabilities of their HARPES technique, Fadley and Gray used a high intensity undulator beamline at the SPring8 synchrotron radiation facility in Hyogo, Japan, which is operated by the Japanese National Institute for Materials Sciences. The samples they worked with, tungsten and gallium arsenide, contain relatively heavy elements that have relatively small phonon effects (atomic vibrations) but to further reduce these effects the samples were cryo-cooled. By combining room temperature and cryo data, the researchers were able to correct for the influence of indirect transitions and photoelectron diffraction in their results.

"Having sufficient photons from the beamline was critical as was having a high energy resolution that required an undulator source and a special monochromator and a photoelectron spectrometer with both high throughput for intensity and a lens with angle-resolving capability," Fadley says.

Adds Gray, "Our HARPES technique not only provided us with information about the energies of the emitted photoelectrons, but also with information about the crystal momentum of electrons within the bulk solid. This extra dimension carries a vast amount of information regarding electronic, magnetic and structural properties of materials, and can be used for in-depth studies of such novel phenomena as high-temperature superconductivity and so-called Mott transitions from insulating to conducting states that might be used for logic switching in the future."

In the future, Fadley and Gray will be able to carry out HARPES experiments much closer to home. At Berkeley Lab's Advanced Light Source (ALS), the first of the world's third generation synchrotron radiation facilities, a new experimental chamber for beamline 9.3.1 is scheduled to open this fall that will provide unique hard x-ray angle-resolved photoemission capabilities.

Says Zahid Hussain, who manages the ALS Scientific Support group, "An additional hard x-ray photoemission spectroscopy chamber at beamline 9.3.1 will feature an ambient pressure high energy photoemission capability that will allow the study of energy related problems, such as batteries, fuel cells, and catalysis under in-situ and in-operando conditions. It will also enable depth-sensitive studies and make it possible to probe not only solid, but also gas and liquid interfaces. This will be the first such experimental facility in the world."

Co-authoring the Nature Materials paper with Fadley and Gray were Christian Papp, Shigenori Ueda, Benjamin Balke, Yoshiyuki Yamashita, Lukasz Plucinski, Jan Minár, Juergen Braun, Erik Ylvisaker, Claus Schneider, Warren Pickett, Hubert Ebert and Keisuke Kobayashi.

This research was supported in part by the DOE Office of Science.

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by DOE/Lawrence Berkeley National Laboratory.

Journal Reference:

A. X. Gray, C. Papp, S. Ueda, B. Balke, Y. Yamashita, L. Plucinski, J. Minár, J. Braun, E. R. Ylvisaker, C. M. Schneider, W. E. Pickett, H. Ebert, K. Kobayashi, C. S. Fadley. Probing bulk electronic structure with hard X-ray angle-resolved photoemission. Nature Materials, 2011; DOI: 10.1038/nmat3089

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Unexpected adhesion properties of graphene may lead to new nanotechnology devices

ScienceDaily (Aug. 24, 2011) — Graphene, considered the most exciting new material under study in the world of nanotechnology, just got even more interesting, according to a new study by a group of researchers at the University of Colorado Boulder.

The new findings -- that graphene has surprisingly powerful adhesion qualities -- are expected to help guide the development of graphene manufacturing and of graphene-based mechanical devices such as resonators and gas separation membranes, according to the CU-Boulder team. The experiments showed that the extreme flexibility of graphene allows it to conform to the topography of even the smoothest substrates.

Graphene consists of a single layer of carbon atoms chemically bonded in a hexagonal chicken wire lattice. Its unique atomic structure could some day replace silicon as the basis of electronic devices and integrated circuits because of its remarkable electrical, mechanical and thermal properties, said Assistant Professor Scott Bunch of the CU-Boulder mechanical engineering department and lead study author.

A paper on the subject was published online in the Aug. 14 issue of Nature Nanotechnology. Co-authors on the study included CU-Boulder graduate students Steven Koenig and NarasimhaBoddeti and Professor Martin Dunn of the mechanical engineering department.

"The real excitement for me is the possibility of creating new applications that exploit the remarkable flexibility and adhesive characteristics of graphene and devising unique experiments that can teach us more about the nanoscale properties of this amazing material," Bunch said.

Not only does graphene have the highest electrical and thermal conductivity among all materials known, but this "wonder material" has been shown to be the thinnest, stiffest and strongest material in the world, as well as being impermeable to all standard gases. It's newly discovered adhesion properties can now be added to the list of the material's seemingly contradictory qualities, said Bunch.

The CU-Boulder team measured the adhesion energy of graphene sheets, ranging from one to five atomic layers, with a glass substrate, using a pressurized "blister test" to quantify the adhesion between graphene and glass plates.

Adhesion energy describes how "sticky" two things are when placed together. Scotch tape is one example of a material with high adhesion; the gecko lizard, which seemingly defies gravity by scaling up vertical walls using adhesion between its feet and the wall, is another. Adhesion also canplay a detrimental role, as in suspended micromechanical structures where adhesion can cause device failure or prolong the development of a technology, said Bunch.

The CU research, the first direct experimental measurements of the adhesion of graphene nanostructures, showed that so-called "van der Waals forces" -- the sum of the attractive or repulsive forces between molecules -- clamp the graphene samples to the substrates and also hold together the individual graphene sheets in multilayer samples.

The researchers found the adhesion energies between graphene and the glass substrate were several orders of magnitude larger than adhesion energies in typical micromechanical structures, an interaction they described as more liquid-like than solid-like, said Bunch.

The CU-Boulder study was funded primarily by the National Science Foundation and the Defense Advanced Research Projects Agency.

The importance of graphene in the scientific world was illustrated by the 2010 Nobel Prize in physics that honored two scientists at Manchester University in England, Andre K. Geim and Konstantin Novoselov, for producing, isolating, identifying and characterizing graphene.

There is interest in exploiting graphene's incredible mechanical properties to create ultrathin membranes for energy-efficient separations such as those needed for natural gas processing or water purification, while graphene's superior electrical properties promise to revolutionize the microelectronics industry, said Bunch.

In all of these applications, including any large-scale graphene manufacturing, the interaction that graphene has with a surface is of critical importance and a scientific understanding will help push the technology forward, he said.

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by University of Colorado at Boulder.

Journal Reference:

Steven P. Koenig, Narasimha G. Boddeti, Martin L. Dunn, J. Scott Bunch. Ultrastrong adhesion of graphene membranes. Nature Nanotechnology, 2011; DOI: 10.1038/nnano.2011.123

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Sketching with superconductors: Breakthrough in controlling defects could lead to new generation of electronic devices

ScienceDaily (Aug. 22, 2011) — Reporting in the journal Nature Materials, researchers from the London Centre for Nanotechnology and the Physics Department of Sapienza University of Rome have discovered a technique to 'draw' superconducting shapes using an X-ray beam. This ability to create and control tiny superconducting structures has implications for a completely new generation of electronic devices.

Superconductivity is a special state where a material conducts electricity with no resistance, meaning absolutely zero energy is wasted.

The research group has shown that they can manipulate regions of high temperature superconductivity, in a particular material which combines oxygen, copper and a heavier, 'rare earth' element called lanthanum. Illuminating with X-rays causes a small scale re-arrangement of the oxygen atoms in the material, resulting in high temperature superconductivity, of the type originally discovered for such materials 25 years ago by IBM scientists. The X-ray beam is then used like a pen to draw shapes in two dimensions.

A well as being able to write superconductors with dimensions much smaller than the width of a human hair, the group is able to erase those structures by applying heat treatments. They now have the tools to write and erase with high precision, using just a few simple steps and without the chemicals ordinarily used in device fabrication. This ability to re-arrange the underlying structure of a material has wider applications to similar compounds containing metal atoms and oxygen, ranging from fuel cells to catalysts.

Prof. Aeppli, Director of the London Centre for Nanotechnology and the UCL investigator on the project, said: "Our validation of a one-step, chemical-free technique to generate superconductors opens up exciting new possibilities for electronic devices, particularly in re-writing superconducting logic circuits. Of profound importance is the key to solving the notorious 'travelling salesman problem', which underlies many of the world's great computational challenges. We want to create computers on demand to solve this problem, with applications from genetics to logistics. A discovery like this means a paradigm shift in computing technology is one step closer."

Prof Bianconi, the leader of the team from Sapienza, added: "It is amazing that in a few simple steps, we can now add superconducting 'intelligence' directly to a material consisting mainly of the common elements copper and oxygen."

The X-ray experiments were performed at the Elettra (Trieste) synchrotron radiation facility. The work is published in Nature Materials , 21 August 2011 (doi:1038/nmat3088) and follows on from previous discovery of fractal-like structures in superconductors (doi:10.1038/nature09260).

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Nicola Poccia, Michela Fratini, Alessandro Ricci, Gaetano Campi, Luisa Barba, Alessandra Vittorini-Orgeas, Ginestra Bianconi, Gabriel Aeppli, Antonio Bianconi. Evolution and control of oxygen order in a cuprate superconductor. Nature Materials, 2011; DOI: 10.1038/nmat3088Michela Fratini, Nicola Poccia, Alessandro Ricci, Gaetano Campi, Manfred Burghammer, Gabriel Aeppli, Antonio Bianconi. Scale-free structural organization of oxygen interstitials in La2CuO4+y. Nature, 2010; 466 (7308): 841 DOI: 10.1038/nature09260

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Understanding next-generation electronic devices: Smallest atomic displacements ever

ScienceDaily (Sep. 3, 2011) — An international team of scientists has developed a novel X-ray technique for imaging atomic displacements in materials with unprecedented accuracy. They have applied their technique to determine how a recently discovered class of exotic materials -- multiferroics -- can be simultaneously both magnetically and electrically ordered. Multiferroics are also candidate materials for new classes of electronic devices.

The discovery, a major breakthrough in understanding multiferroics, is published in Science dated 2 September 2011.

The authors comprise scientists from the European Synchrotron Radiation Facility (ESRF) in Grenoble (France), the University of Oxford and the University College London (both UK). Helen Walker from the ESRF is the main author of the publication.

Everybody is familiar with the idea that magnets are polarized with a north and a south pole, which is understood to arise from the alignment of magnet moments carried by atoms in magnetic materials. Certain other materials, known as ferroelectrics, exhibit a similar effect for electrical polarisation. The exotic "multiferroic" materials combine both magnetic and ferroelectric polarizations, and can exhibit a strong coupling between the two phenomena.

This leads to the strange effect that a magnetic field can electrically polarise the material, and an electric field magnetise it. A class of strong multiferroics was discovered ten years ago and has since led to a new, rapidly growing field of research, also motivated by the promise of their exotic properties for new electronic devices. One example is a new type of electronic memory, in which an electric field writes data into the memory and a magnetic detector is used to read it. This process is faster, and uses less energy than today's hard disk drives.

However, the origin of the electric polarisation in multiferroics remained mostly elusive to date. The team's work unambiguously shows that the polarization in the multiferroic studied proceeds from the relative displacement of charges of different signs, rather than the transfer of charge from one atom to another.

As the displacement involves a high number of electrons, even small distances can lead to significant polarisation. The actual distance of the displacement still came as a surprise: about 20 femtometres, or about 1/100,000th of the distance between the atoms in the material. Measuring such small displacements was actually believed to be impossible.

"I think that everyone involved was surprised, if not staggered, by the result that we can now image the position of atoms with such accuracy. The work is testament to the fantastic facilities available in Grenoble to the UK science community," says Prof. Des McMorrow, Deputy Director of the London Centre for Nanotechnology, leader of the UCL part of the project.

Walker and her colleagues developed a smart new experimental technique exploiting the interference between two competing processes: charge and magnetic scattering of a powerful, polarized X-ray beam. They studied a single crystal of TbMnO3 which shows a strong multiferroic coupling at temperatures below 30K, and were able to measure the displacements of specific atoms within it with an accuracy approaching one femtometre (10-15m). The atoms themselves are spaced apart 100,000 times this distance.

The new interference scattering technique has set a world record for accuracy in absolute measurements of atomic displacements. (It is also the first measurement of magnetostriction in antiferromagnets.) Most significantly the identification of the origin of ferroelectricty in a multiferroic material is a major step forward in the design of multiferroics for practical applications.

"By revealing the driving mechanism behind multiferroics, which offer so many potential applications, it underlines how experiments designed to understand the fundamental physics of materials can have an impact on the wider world," concludes Dr. Helen Walker who led the work at the ESRF.

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by European Synchrotron Radiation Facility, via EurekAlert!, a service of AAAS.

Journal Reference:

H. C. Walker, F. Fabrizi, L. Paolasini, F. De Bergevin, J. Herrero-Martin, A. T. Boothroyd, D. Prabhakaran, D. F. Mcmorrow. Femtoscale Magnetically Induced Lattice Distortions in Multiferroic TbMnO3. Science, 2 September 2011: Vol. 333 no. 6047 pp. 1273-1276 DOI: 10.1126/science.1208085

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