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  • richardmitnick 12:21 pm on May 28, 2015 Permalink | Reply
    Tags: , , Material Sciences,   

    From Carnegie: “Linking superconductivity and structure” 

    Carnegie Institution for Science
    Carnegie Institution for Science

    May 26, 2015

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    The collapsed tetragonal crystal structure of , with arsenic (As) atoms in a 5-fold coordination, courtesy of Alexander Goncharov.

    Superconductivity is a rare physical state in which matter is able to conduct electricity—maintain a flow of electrons—without any resistance. It can only be found in certain materials, and even then it can only be achieved under controlled conditions of low temperatures and high pressures. New research from a team including Carnegie’s Elissaios Stavrou, Xiao-Jia Chen, and Alexander Goncharov hones in on the structural changes underlying superconductivity in iron arsenide compounds—those containing iron and arsenic. It is published by Scientific Reports.

    Although superconductivity has many practical applications for electronics (including scientific research instruments), medical engineering (MRI machines), and potential future applications including high-performance power transmission and storage, and very fast train travel, the difficulty of creating superconducting materials prevents it from being used to its full potential. As such, any newly discovered superconducting ability is of great interest to scientists and engineers.

    Iron arsenides are relatively recently discovered superconductors. The nature of superconductivity in these particular materials remains a challenge for modern solid state physics. If the complex links between superconductivity, structure, and magnetism in these materials are unlocked, then iron arsenides could potentially be used to reveal superconductivity at much higher temperatures than previously seen, which would vastly increase the ease of practical applications.

    When iron arsenide is combined with a metal—such as in the sodium-containing NaFe2As2 compound studied here—it was known that the ensuing compound is crystallized in a tetrahedral structure. But until now, a detailed structure of the atomic positions involved and how they change under pressure had not been determined.

    The layering of arsenic and iron (As-Fe-As) in this structure is believed to be key to the compound’s superconductivity. However, under pressure, this structure is thought to be partially misshapen into a so-called collapsed tetragonal lattice, which is no longer capable of superconducting, or has diminished superconducting ability.

    The team used experimental evidence and modeling under pressure to actually demonstrate these previously theorized structural changes—tetragonal to collapsed tetragonal—on the atomic level. This is just the first step toward definitively determining the link between structure and superconductivity, which could potentially make higher-temperature superconductivity a real possibility.

    They showed that at about 40,000 times normal atmospheric pressure (4 gigapascals), NaFe2As2 takes on the collapsed tetragonal structure. This changes the angles in the arsenic-iron-arsenic layers and is coincident with the loss in superconductivity. Moreover, they found that this transition is accompanied by a major change in bonding coordination in the formation of the interlayer arsenic-arsenic bonds. A direct consequence of this new coordination is that the system loses its two-dimensionality, and with it, superconductivity.

    “Our findings are an important step in identifying the hypothesized connection between structure and superconductivity in iron-containing compounds,” Goncharov said. “Understanding the loss of superconductivity on an atomic level could enhance our ease of manufacturing such compounds for practical applications, as well as improving our understanding of condensed matter physics.”

    The paper’s other co-authors are: Artem Oganov of Stony Brook University, the Moscow Institute of Physics and Technology, and Northwestern Polytechnical University Xi’an; and Ai-Feng Wang, Ya-Jun Yan, Xi-Gang Luo, and Xian-Hui Chen of the University of Science and Technology of China, Hefei, Anhui.

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    The tetragonal crystal structure of NaFe2As2, courtesy of Alexander Goncharov.

    This work was supported by DARPA, the Carnegie Institution of Canada, EFree (the DOE EFRC center at the Carnegie Institution for Science), the government of the Russian Federation, the Ministry of Education and Science of the Russian Federation.

    GSECARS is supported by the U.S. NSF and DOE Geosciences. Use of the APS was supported by the DOE-BES. Calculations were performed on XSEDE facilities and on the cluster of the Center for Functional Nanomaterials, BNL, which is supported by the DOE-BES. Sample growth was supported by the Natural Science Foundation of China, the ‘‘Strategic Priority Research Program (B)’’ of the Chinese Academy of Sciences, and the National Basic Research Program of China.

    See the full article here.

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    Carnegie Institution of Washington Bldg

    Andrew Carnegie established a unique organization dedicated to scientific discovery “to encourage, in the broadest and most liberal manner, investigation, research, and discovery and the application of knowledge to the improvement of mankind…” The philosophy was and is to devote the institution’s resources to “exceptional” individuals so that they can explore the most intriguing scientific questions in an atmosphere of complete freedom. Carnegie and his trustees realized that flexibility and freedom were essential to the institution’s success and that tradition is the foundation of the institution today as it supports research in the Earth, space, and life sciences.

     
  • richardmitnick 8:29 am on May 28, 2015 Permalink | Reply
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    From MIT: “Spinning a new version of silk” 


    MIT News

    May 28, 2015
    David L. Chandler | MIT News Office

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    Microscope images of lab-produced fibers confirm the results of the MIT researchers’ simulations of spider silk. At top are optical microscope images, and, at bottom, are scanning electron microscope images. At left are fibers 8 micrometers across, and, at right, are thinner, 3 micrometer fibers.
    Courtesy of the researchers

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    Molecular-level simulations of different lengths of silk molecules called fibroins, after being exposed to flow to simulate a spider’s spinning process, reveal the key importance of the length of the molecular chains in achieving well-bonded fibers. At left, the fibroins have a length of 4 units, and, at right, 12 units. Below each “snapshot” of the simulation is a diagram showing the connections between units. The longer chains produce a much stronger fiber. Courtesy of the researchers

    After years of research decoding the complex structure and production of spider silk, researchers have now succeeded in producing samples of this exceptionally strong and resilient material in the laboratory. The new development could lead to a variety of biomedical materials — from sutures to scaffolding for organ replacements — made from synthesized silk with properties specifically tuned for their intended uses.

    The findings are published this week in the journal Nature Communications by MIT professor of civil and environmental engineering (CEE) Markus Buehler, postdocs Shangchao Lin and Seunghwa Ryu, and others at MIT, Tufts University, Boston University, and in Germany, Italy, and the U.K.

    The research, which involved a combination of simulations and experiments, paves the way for “creating new fibers with improved characteristics” beyond those of natural silk, says Buehler, who is also the department head in CEE. The work, he says, should make it possible to design fibers with specific characteristics of strength, elasticity, and toughness.

    The new synthetic fibers’ proteins — the basic building blocks of the material — were created by genetically modifying bacteria to make the proteins normally produced by spiders. These proteins were then extruded through microfluidic channels designed to mimic the effect of an organ, called a spinneret, that spiders use to produce natural silk fibers.

    No spiders needed

    While spider silk has long been recognized as among the strongest known materials, spiders cannot practically be bred to produce harvestable fibers — so this new approach to producing a synthetic, yet spider-like, silk could make such strong and flexible fibers available for biomedical applications. By their nature, spider silks are fully biocompatible and can be used in the body without risk of adverse reactions; they are ultimately simply absorbed by the body.

    The researchers’ “spinning” process, in which the constituent proteins dissolved in water are extruded through a tiny opening at a controlled rate, causes the molecules to line up in a way that produces strong fibers. The molecules themselves are a mixture of hydrophobic and hydrophilic compounds, blended so as to naturally align to form fibers much stronger than their constituent parts. “When you spin it, you create very strong bonds in one direction,” Buehler says.

    The team found that getting the blend of proteins right was crucial. “We found out that when there was a high proportion of hydrophobic proteins, it would not spin any fibers, it would just make an ugly mass,” says Ryu, who worked on the project as a postdoc at MIT and is now an assistant professor at the Korea Advanced Institute of Science and Technology. “We had to find the right mix” in order to produce strong fibers, he says.

    Closing the loop

    This project represents the first use of simulations to understand silk production at the molecular level. “Simulation is critical,” Buehler explains: Actually synthesizing a protein can take several months; if that protein doesn’t turn out to have exactly the right properties, the process would have to start all over.

    Using simulations makes it possible to “scan through a large range of proteins until we see changes in the fiber stiffness,” and then home in on those compounds, says Lin, who worked on the project as a postdoc at MIT and is now an assistant professor at Florida State University.

    Controlling the properties directly could ultimately make it possible to create fibers that are even stronger than natural ones, because engineers can choose characteristics for a particular use. For example, while spiders may need elasticity so their webs can capture insects without breaking, those designing fibers for use as surgical sutures would need more strength and less stretchiness. “Silk doesn’t give us that choice,” Buehler says.

    The processing of the material can be done at room temperature using water-based solutions, so scaling up manufacturing should be relatively easy, team members say. So far, the fibers they have made in the lab are not as strong as natural spider silk, but now that the basic process has been established, it should be possible to fine-tune the materials and improve its strength, they say.

    “Our goal is to improve the strength, elasticity, and toughness of artificially spun fibers by borrowing bright ideas from nature,” Lin says. This study could inspire the development of new synthetic fibers — or any materials requiring enhanced properties, such as in electrical and thermal transport, in a certain direction.

    “This is an amazing piece of work,” says Huajian Gao, a professor of engineering at Brown University who was not involved in this research. “This could lead to a breakthrough that may allow us to directly explore engineering applications of silk-like materials.”

    Gao adds that the team’s exploration of variations in web structure “may have practical impacts in improving the design of fiber-reinforced composites by significantly increasing their strength and robustness without increasing the weight. The impact on material innovation could be particularly important for aerospace and industrial applications, where light weight is essential.”

    The research was supported by the National Institutes of Health, the National Science Foundation, the Office of Naval Research, the National Research Foundation of Korea, and the European Research Council.

    See the full article here.

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  • richardmitnick 7:16 am on May 8, 2015 Permalink | Reply
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    From MIT: “Plugging up leaky graphene” 


    MIT News

    May 8, 2015
    Jennifer Chu

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    In a two-step process, engineers have successfully sealed leaks in graphene. First, the team fabricated graphene on a copper surface (top left) — a process that can create intrinsic defects in graphene, shown as cracks on the surface. After lifting the graphene and depositing it on a porous surface (top right), the transfer creates further holes and tears. In a first step (bottom left), the team used atomic layer deposition to deposit hafnium (in gray) to seal intrinsic cracks, then plugged the remaining holes (bottom left) with nylon (in red), via interfacial polymerization.
    Courtesy of the researchers.

    For faster, longer-lasting water filters, some scientists are looking to graphene —thin, strong sheets of carbon — to serve as ultrathin membranes, filtering out contaminants to quickly purify high volumes of water.

    Graphene’s unique properties make it a potentially ideal membrane for water filtration or desalination. But there’s been one main drawback to its wider use: Making membranes in one-atom-thick layers of graphene is a meticulous process that can tear the thin material — creating defects through which contaminants can leak.

    Now engineers at MIT, Oak Ridge National Laboratory, and King Fahd University of Petroleum and Minerals (KFUPM) have devised a process to repair these leaks, filling cracks and plugging holes using a combination of chemical deposition and polymerization techniques. The team then used a process it developed previously to create tiny, uniform pores in the material, small enough to allow only water to pass through.

    Combining these two techniques, the researchers were able to engineer a relatively large defect-free graphene membrane — about the size of a penny. The membrane’s size is significant: To be exploited as a filtration membrane, graphene would have to be manufactured at a scale of centimeters, or larger.

    In experiments, the researchers pumped water through a graphene membrane treated with both defect-sealing and pore-producing processes, and found that water flowed through at rates comparable to current desalination membranes. The graphene was able to filter out most large-molecule contaminants, such as magnesium sulfate and dextran.

    Rohit Karnik, an associate professor of mechanical engineering at MIT, says the group’s results, published in the journal Nano Letters, represent the first success in plugging graphene’s leaks.

    “We’ve been able to seal defects, at least on the lab scale, to realize molecular filtration across a macroscopic area of graphene, which has not been possible before,” Karnik says. “If we have better process control, maybe in the future we don’t even need defect sealing. But I think it’s very unlikely that we’ll ever have perfect graphene — there will always be some need to control leakages. These two [techniques] are examples which enable filtration.”

    Sean O’Hern, a former graduate research assistant at MIT, is the paper’s first author. Other contributors include MIT graduate student Doojoon Jang, former graduate student Suman Bose, and Professor Jing Kong.

    A delicate transfer

    “The current types of membranes that can produce freshwater from saltwater are fairly thick, on the order of 200 nanometers,” O’Hern says. “The benefit of a graphene membrane is, instead of being hundreds of nanometers thick, we’re on the order of three angstroms — 600 times thinner than existing membranes. This enables you to have a higher flow rate over the same area.”

    O’Hern and Karnik have been investigating graphene’s potential as a filtration membrane for the past several years. In 2009, the group began fabricating membranes from graphene grown on copper — a metal that supports the growth of graphene across relatively large areas. However, copper is impermeable, requiring the group to transfer the graphene to a porous substrate following fabrication.

    However, O’Hern noticed that this transfer process would create tears in graphene. What’s more, he observed intrinsic defects created during the growth process, resulting perhaps from impurities in the original material.

    Plugging graphene’s leaks

    To plug graphene’s leaks, the team came up with a technique to first tackle the smaller intrinsic defects, then the larger transfer-induced defects. For the intrinsic defects, the researchers used a process called “atomic layer deposition,” placing the graphene membrane in a vacuum chamber, then pulsing in a hafnium-containing chemical that does not normally interact with graphene. However, if the chemical comes in contact with a small opening in graphene, it will tend to stick to that opening, attracted by the area’s higher surface energy.

    The team applied several rounds of atomic layer deposition, finding that the deposited hafnium oxide successfully filled in graphene’s nanometer-scale intrinsic defects. However, O’Hern realized that using the same process to fill in much larger holes and tears — on the order of hundreds of nanometers — would require too much time.

    Instead, he and his colleagues came up with a second technique to fill in larger defects, using a process called “interfacial polymerization” that is often employed in membrane synthesis. After they filled in graphene’s intrinsic defects, the researchers submerged the membrane at the interface of two solutions: a water bath and an organic solvent that, like oil, does not mix with water.

    In the two solutions, the researchers dissolved two different molecules that can react to form nylon. Once O’Hern placed the graphene membrane at the interface of the two solutions, he observed that nylon plugs formed only in tears and holes — regions where the two molecules could come in contact because of tears in the otherwise impermeable graphene — effectively sealing the remaining defects.

    Using a technique they developed last year, the researchers then etched tiny, uniform holes in graphene — small enough to let water molecules through, but not larger contaminants. In experiments, the group tested the membrane with water containing several different molecules, including salt, and found that the membrane rejected up to 90 percent of larger molecules. However, it let salt through at a faster rate than water.

    The preliminary tests suggest that graphene may be a viable alternative to existing filtration membranes, although Karnik says techniques to seal its defects and control its permeability will need further improvements.

    “Water desalination and nanofiltration are big applications where, if things work out and this technology withstands the different demands of real-world tests, it would have a large impact,” Karnik says. “But one could also imagine applications for fine chemical- or biological-sample processing, where these membranes could be useful. And this is the first report of a centimeter-scale graphene membrane that does any kind of molecular filtration. That’s exciting.”

    De-en Jiang, an assistant professor of chemistry at the University of California at Riverside, sees the defect-sealing technique as “a great advance toward making graphene filtration a reality.”

    “The two-step technique is very smart: sealing the defects while preserving the desired pores for filtration,” says Jiang, who did not contribute to the research. “This would make the scale-up much easier. One can produce a large graphene membrane first, not worrying about the defects, which can be sealed later.”

    This research was supported in part by the Center for Clean Water and Clean Energy at MIT and KFUPM, the U.S. Department of Energy, and the National Science Foundation.

    See the full article here.

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  • richardmitnick 7:58 am on April 22, 2015 Permalink | Reply
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    From Sandia: “Phonons, arise!” 


    Sandia Lab

    April 22, 2015
    Neal Singer, nsinger@sandia.gov, (505) 845-7078

    Small electric voltage alters conductivity in key materials

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    Sandia National Laboratories researchers Jon Ihlefeld, left, and David Scrymgeour use an atomic-force microscope to examine changes in a material’s phonon-scattering internal walls, before and after applying a voltage. The material scrutinized, PZT, has wide commercial uses.

    Modern research has found no simple, inexpensive way to alter a material’s thermal conductivity at room temperature.

    That lack of control has made it hard to create new classes of devices that use phonons — the agents of thermal conductivity — rather than electrons or photons to harvest energy or transmit information. Phonons — atomic vibrations that transport heat energy in solids at speeds up to the speed of sound — have proved hard to harness.

    Now, using only a 9-volt battery at room temperature, a team led by Sandia National Laboratories researcher Jon Ihlefeld has altered the thermal conductivity of the widely used material PZT (lead zirconate titanate) by as much as 11 percent at subsecond time scales. They did it without resorting to expensive surgeries like changing the material’s composition or forcing phase transitions to other states of matter.

    PZT, either as a ceramic or a thin film, is used in a wide range of devices ranging from computer hard drives, push-button sparkers for barbecue grills, speed-pass transponders at highway toll booths and many microelectromechanical designs.

    “We can alter PZT’s thermal conductivity over a broad temperature range, rather than only at the cryogenic temperatures achieved by other research groups,” said Ihlefeld. “And we can do it reversibly: When we release our voltage, the thermal conductivity returns to its original value.”

    The work was performed on materials with closely spaced internal interfaces — so-called domain walls — unavailable in earlier decades. The close spacing allows better control of phonon passage.

    “We showed that we can prepare crystalline materials with interfaces that can be altered with an electric field. Because these interfaces scatter phonons,” said Ihlefeld, “we can actively change a material’s thermal conductivity by simply changing their concentration. We feel this groundbreaking work will advance the field of phononics.”

    The researchers, supported by Sandia’s Laboratory Directed Research and Development office, the Air Force Office of Scientific Research, and the National Science Foundation, used a scanning electron microscope and an atomic force microscope. to observe how the domain walls of subsections of the material changed in length and shape under the influence of an electrical voltage. It is this change that controllably altered the transport of phonons within the material.

    “The real achievement in our work,” said Ihlefeld, “is that we’ve demonstrated a means to control the amount of heat passing through a material at room temperature by simply applying a voltage across it. We’ve shown that we can actively regulate how well heat — phonons — conducts through the material.”

    Ihlefeld points out that active control of electron and photon transport has led to technologies that are taken for granted today in computing, global communications and other fields.

    “Before the ability to control these particles and waves existed, it was probably difficult even to dream of technologies involving electronic computers and lasers. And prior to our demonstration of a solid-state, fast, room-temperature means to alter thermal conductivity, analogous means to control the transport of phonons have not existed. We believe that our result will enable new technologies where controlling phonons is necessary,” he said.

    The work, published last month in Nano Letters, was co-authored by Sandia researchers David A. Scrymgeour, Joseph R. Michael, Bonnie B. McKenzie and Douglas L. Medlin; Brian M. Foley and Patrick E. Hopkins from the University of Virginia; and Margeaux Wallace and Susan Trolier-McKinstry from Penn State University.

    The goal of future work is to reach a better understanding of “what caused this effect to happen so efficiently,” Ihlefeld said.

    See the full article here.

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    Sandia National Laboratory

    Sandia National Laboratories is a multiprogram laboratory operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration. With main facilities in Albuquerque, N.M., and Livermore, Calif., Sandia has major R&D responsibilities in national security, energy and environmental technologies, and economic competitiveness.
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  • richardmitnick 1:02 pm on April 6, 2015 Permalink | Reply
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    From LBL: “Accelerating Materials Discovery With World’s Largest Database of Elastic Properties” 

    Berkeley Logo

    Berkeley Lab

    April 6, 2015
    Julie Chao (510) 486-6491

    Scientists at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) have published the world’s largest set of data on the complete elastic properties of inorganic compounds, increasing by an order of magnitude the number of compounds for which such data exists.

    This new data set is expected to be a boon to materials scientists working on developing new materials where mechanical properties are important, such as for hard coatings, or stiff materials for cars and airplanes. While there is previously published experimental data for approximately a few hundred inorganic compounds, Berkeley Lab scientists, using the infrastructure of the Materials Project, have calculated the complete elastic properties for 1,181 inorganic compounds, with dozens more being added every week.

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    Berkeley Lab scientists Wei Chen, Maarten de Jong, and Mark Asta (from left) have published the world’s largest set of data on the complete elastic properties of inorganic compounds. (Photo by Roy Kaltschmidt/Berkeley Lab)

    Their research was recently published in the open-access Nature Publishing Group journal Scientific Data, in a paper titled, Charting the complete elastic properties of inorganic crystalline compounds. The two lead authors are Berkeley Lab scientists Maarten de Jong and Wei Chen. Co-authors include Kristin Persson, Mark Asta, Thomas Angsten, and Anubhav Jain of Berkeley Lab as well as collaborators from UC San Diego, Delft University of Technology, Eindhoven University of Technology, Duke University, and MIT.

    The calculated elastic constants “show an excellent correlation with experimental values,” their paper reports.

    Harnessing the power of the Materials Project

    The Materials Project is a Google-like database of material properties aimed at accelerating innovation; it uses supercomputers to calculate the properties of all known materials based on first-principles quantum-mechanical frameworks. Co-founded and co-led by Persson and MIT’s Gerbrand Ceder, the Materials Project has attracted more than 10,000 users since launching in 2011.

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    This is a graphical representation of the dataset, showing volume per atom (represented by arrow direction), shear modulus (x-axis), bulk modulus (y-axis), and Poisson’s ratio (color) for all the compounds calculated. For comparison, the actual values for diamond, the hardest known material, as well as other compounds, are also plotted.

    The elastic properties of a material are important for material design but quite difficult and tedious to measure experimentally, according to Asta, a Berkeley Lab materials scientist who is also chair of the Department of Materials Science and Engineering at UC Berkeley. A compound’s elastic constant is not just one number but a whole tensor, or array of numbers, because the direction in which a material is being pulled or sheared matters.

    “In a crystal, the atoms are stacked in certain ways,” he explained. “If one pulls in one direction, they will measure the stiffness of bonds between a certain arrangements of atoms, but if one pulls in a different direction, the stiffness of different combinations of bonds are measured. So the relationship between force and displacement depends on the direction of the force relative to the arrangement of atoms that make a crystal structure. And in addition to pulling there’s also shearing. So the elastic constant tensor can have up to 21 independent numbers.”

    Being able to measure all this in the lab requires high-quality materials and equipment, which is one reason for the dearth of experimental data. The Berkeley Lab researchers estimated that no more than 200 materials have been characterized experimentally for their full elastic constant tensor.

    Another reason the elastic tensor data has been lacking is that methods for performing calculations of this property in a high-throughput manner have become available only recently. “The computational methods have been available for quite some time, probably at least 20 years, but it’s the infrastructure of the Materials Project that has enabled us to automate the whole process,” said Chen, one of the lead co-authors. “These calculations are tricky to do. Even this year, you can find papers where they have run a calculation for just one elastic constant.”

    Asta explained that the Materials Project infrastructure allows the development of custom workflows, and efficient interfacing to the supercomputers, such as those at Berkeley Lab’s National Energy Research Scientific Computing Center (NERSC), which were used in the calculations. “The Materials Project infrastructure enables a calculation to recover when something’s not happening right,” he said.

    Study yields big surprise: new thermoelectric material discovered

    What makes this data even more useful is that the elastic constant can be used to predict some other useful material properties, including thermal conductivity, which is very difficult to calculate. “From a materials design standpoint, what’s really intriguing about the elastic constant is that it correlates with much more complex properties of a material, so it can be used as a way of screening for other properties,” said Asta.

    In fact, in running a large-scale screening of materials, the Berkeley Lab scientists have discovered a new thermoelectric material, which will be described in a forthcoming paper. Thermoelectrics convert heat to energy and should have low thermal conductivity; finding a new thermoelectric material that is significantly cheaper or more efficient could lead to a breakthrough energy technology to convert waste heat to electricity.

    “We had our experimental collaborators successfully synthesize the material, and they validated our prediction,” Chen said. “So it is very promising. We are now doing more work to further enhance its properties while also doing a larger-scale screening to look for even better thermoelectric materials.”

    The compound they found belongs to a new class of compounds that was not being explored for thermoelectrics.

    Future work: let the machine do the learning

    There are an estimated 50,000 inorganic compounds; given enough time, the Materials Project could eventually calculate the elastic tensor for all of them. But the scientists are now looking at how the process can be accelerated even more. “We want to use statistical learning to extract information to build predictive models in order to predict the elastic constants,” Chen said.

    For example, machine-learning algorithms have identified the volume per atom of a material as a key descriptor of the material’s bulk modulus, which is a measure of the pressure required to change the volume of a material.

    “If we can come up with a trained algorithm that can relate elastic properties to very simply computed properties that we already have from the Materials Project or from experiments, then we can make predictions across a much broader range of materials,” Asta said.

    The Materials Project is funded by the Department of Energy’s Office of Science. This study made extensive use of the resources at NERSC.

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  • richardmitnick 1:11 pm on March 27, 2015 Permalink | Reply
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    From BNL: “Physicists Solve Low-Temperature Magnetic Mystery” 

    Brookhaven Lab

    March 27, 2015
    Chelsea Whyte, (631) 344-8671 or Peter Genzer, (631) 344-3174

    1
    Ignace Jarrige shown with the sample used in the experiment.

    Researchers have made an experimental breakthrough in explaining a rare property of an exotic magnetic material, potentially opening a path to a host of new technologies. From information storage to magnetic refrigeration, many of tomorrow’s most promising innovations rely on sophisticated magnetic materials, and this discovery opens the door to harnessing the physics that governs those materials.

    The work, led by Brookhaven National Laboratory physicist Ignace Jarrige, and University of Connecticut professor Jason Hancock, together with collaborators from Japan and Argonne National Laboratory, marks a major advance in the search for practical materials that will enable several types of next-generation technology. A paper describing the team’s results was published this week in the journal Physical Review Letters.

    The work is related to the Kondo Effect, a physical phenomenon that explains how magnetic impurities affect the electrical resistance of materials. The researchers were looking at a material called ytterbium-indium-copper-four (usually written using its chemical formula: YbInCu4).

    YbInCu4 has long been known to undergo a unique transition as a result of changing temperature. Below a certain temperature, the material’s magnetism disappears, while above that temperature, it is strongly magnetic. This transition, which has puzzled physicists for decades, has recently revealed its secret. “We detected a gap in the electronic spectrum, similar to that found in semiconductors like silicon, whose energy shift at the transition causes the Kondo Effect to strengthen sharply,” said Jarrige

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    From Left to Right: Jason Hancock, Diego Casa, and Jung-ho Kim, shown with one of the instruments used in the experiment.

    Electronic energy gaps define how electrons move (or don’t move) within the material, and are the critical component in understanding the electrical and magnetic properties of materials. “Our discovery goes to show that tailored semiconductor gaps can be used as a convenient knob to finely control the Kondo Effect and hence magnetism in technological materials,” said Jarrige.

    To uncover the energy gap, the team used a process called Resonant Inelastic X-Ray Scattering (RIXS), a new experimental technique that is made possible by an intense X-ray beam produced at a synchrotron operated by the Department of Energy and located at Argonne National Laboratory outside of Chicago. By placing materials in the focused X-ray beam and sensitively measuring and analyzing how the X-rays are scattered, the team was able to uncover elusive properties such as the energy gap and connect them to the enigmatic magnetic behavior.

    The new physics identified through this work suggest a roadmap to the development of materials with strong “magnetocaloric” properties, the tendency of a material to change temperature in the presence of a magnetic field. “The Kondo Effect in YbInCu4 turns on at a very low temperature of 42 Kelvin (-384F),” said Hancock, “but we now understand why it happens, which suggests that it could happen in other materials near room temperature.” If that material is discovered, according to Hancock, it would revolutionize cooling technology.

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    During the RIXS experiment, an X-ray beam is used to excite electrons inside the sample. The X-ray loses energy during the process and then is scattered out of the sample. A fine analysis of the scattered X-rays yields insight into the mechanism that controls the strength of the Kondo Effect.

    Household use of air conditioners in the US accounts for over $11 billion in energy costs and releases 100 million tons of carbon dioxide annually. Use of the magnetocaloric effect for magnetic refrigeration as an alternative to the mechanical fans and pumps in widespread use today could significantly reduce those numbers.

    In addition to its potential applications to technology, the work has advanced the state of the art in research. “The RIXS technique we have developed can be applied in other areas of basic energy science,” said Hancock, noting that the development is very timely, and that it may be useful in the search for “topological Kondo insulators,” materials which have been predicted in theory, but have yet to be discovered.

    See the full article here.

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    One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. The Laboratory’s almost 3,000 scientists, engineers, and support staff are joined each year by more than 5,000 visiting researchers from around the world.Brookhaven is operated and managed for DOE’s Office of Science by Brookhaven Science Associates, a limited-liability company founded by Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit, applied science and technology organization.
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  • richardmitnick 12:56 pm on March 25, 2015 Permalink | Reply
    Tags: , Material Sciences,   

    From phys.org: “Research team develops acoustic topological insulator idea to allow for hiding from sonar” 

    physdotorg
    phys.org

    March 25, 2015
    Bob Yirka

    1
    Around the bend. An acoustic topological insulator would guide sound waves around its edges, as shown in this simulation. Credit: Z. Yang et al., Phys. Rev. Lett. (2015)

    A team of researchers working in Singapore has come up with what they believe is a way to apply a topologic[al] insulator to an object to prevent sound waves from being bounced back and detected by a source. They have published their work in the journal Physical Review Letters.

    Scientists have developed ways to coat materials with other materials to causes electric current to remain on the surface, preventing damage to sensitive parts inside—such coatings are called topological insulators and are generally based on causing less scattering and creating a band gap. In this new effort, the research team has expanded on that idea to bring a similar result for insulating objects from sound waves.

    To make a topological insulator work against sonar would involve creating a coating or cover that could cause sound waves to propagate around an object (instead of scattering) rather than allowing them to be bounced back to a receiver. To make that happen, the researchers envision a cover made up of a lattice of spinning metal cylinders, each of which would be surrounded by a bit of fluid which would itself be contained within an acoustically transparent shell. The same fluid would be used to fill the spaces between the cylinders, but it would not move. Because of the spinning movement inside, a vortex would be created in the fluid that surrounds the cylinders. In this setup, sound waves would not be able to move through the center of the structure due to a periodic pattern that would produce a sonic band gap—but the rotating fluid around the center would allow for causing propagation to occur in a predefined direction—the edge states, the team notes, could guide sound waves with high precision. A submarine covered with such an insulator would be invisible to sonar because sound waves sent in its direction would be routed in a direction away from where they came from, preventing them from bouncing back to the source.

    The work thus far by the team is purely theoretical, but they suggest there is no reason to believe it would not work in practice. The most difficult part they note, would be dealing with irregular “bumps” on a surface, which could throw off the propagation if not handled properly.

    See the full article here.

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    About Phys.org in 100 Words

    Phys.org™ (formerly Physorg.com) is a leading web-based science, research and technology news service which covers a full range of topics. These include physics, earth science, medicine, nanotechnology, electronics, space, biology, chemistry, computer sciences, engineering, mathematics and other sciences and technologies. Launched in 2004, Phys.org’s readership has grown steadily to include 1.75 million scientists, researchers, and engineers every month. Phys.org publishes approximately 100 quality articles every day, offering some of the most comprehensive coverage of sci-tech developments world-wide. Quancast 2009 includes Phys.org in its list of the Global Top 2,000 Websites. Phys.org community members enjoy access to many personalized features such as social networking, a personal home page set-up, RSS/XML feeds, article comments and ranking, the ability to save favorite articles, a daily newsletter, and other options.

     
  • richardmitnick 5:47 am on March 21, 2015 Permalink | Reply
    Tags: , Material Sciences,   

    From MIT Tech Review: “Nanosheet Handler Heralds New Era of Diamond Age Devices” 

    MIT Technology Review
    M.I.T Technology Review

    March 20, 2015
    No Writer Credit

    A simple way to pick up and place diamond nanosheets finally makes it possible to test this wonder material in a wide range of devices, say materials scientists.

    1

    Diamond films are among the most extraordinary materials on the planet. They are strong, transparent and they conduct heat well. They are biologically inert but can also be chemically functionalised by attaching molecules to their surface. What’s more, when doped, they become semiconductors and so can be used in electronic circuits.

    So it’s no wonder that materials scientists are licking their lips at the prospect of incorporating this wonder material into more or less any device they can think of.

    But there’s a problem. Diamond films have to be grown at high temperatures in an atmosphere of pure hydrogen, which is not compatible with the way other microdevices are made, such as silicon chips.

    So a useful trick would be to have a way to make diamonds films in one place and then transfer them to another so that they can be placed onto chips and other devices.

    Today, Venkatesh Seshan at the Kavli Institute of Nanoscience in The Netherlands and a few pals, say they have perfected a way to grow diamond films on a quartz substrate, separate the films and then pick them up and place them somewhere else.

    The team begin by placing nanodiamond seed crystals on the quartz surface and heating it to over 500 degrees C in a hydrogen plasma atmosphere. The seeds then grow, creating a crystalline diamond surface up to 180 nanometres thick.

    The team have perfected a novel technique for releasing the diamond film from this substrate. During the growth, these materials expand at different rates creating stresses that split one layer from the other. “The conditions were purposefully chosen so that at a thickness of ~180 nm, this stress is sufficient to crack the film and to delaminate it from the quartz surface, forming numerous nanosheets,” say Seshan and co.

    The team use an optical microscope to identify the nanosheets and then lift them off using a sticky film, rather like picking up graphene sheets with Scotch tape. The sticky film is then positioned over the device, such as an electornic circuit, and then pressed into position. The team remove the sticky film by slowly peeling it off the nanosheet, a process that takes up to 10 minutes.

    Seshan and co have tested their technique by creating a number of diamond nanosheet–based devices. These include drum-like resonators, an electronic circuit and even place the diamond sheets on top of other material sheets to show how it should be possible to create entirely new materials made of alternating material layers.

    That’s handy because the team can then characterise the way nanodiamond films behave in a range of new situations. It also opens the way for its use in a wide range of other applications.

    There is a caveat, of course. Identifying the nanosheets and positioning them is a time consuming process. So this technique will never be useful for mass producing diamond-based devices.

    That will have to wait for the development of a technique to do the positioning automatically and in parallel on a massive scale.

    But with machine vision techniques developing rapidly, it may be possible to take humans out of the loop in the near future. The massive parallelisation of this kind of manufacturing technique will take more work, however.

    The potential is clear. This kind of work could usher in a new kind of technology to complement the silicon and graphene ages we are currently experience. In other words, start looking forward to the diamond age.

    Ref: arxiv.org/abs/1503.02844 Pick-Up and Drop Transfer of Diamond Nanosheets

    See the full article here.

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    The mission of MIT Technology Review is to equip its audiences with the intelligence to understand a world shaped by technology.

     
  • richardmitnick 1:18 pm on March 20, 2015 Permalink | Reply
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    From Carnegie: “New transitory form of silica observed” 

    Carnegie Institution of Washington bloc

    Carnegie Institution of Washington

    Friday, March 20, 2015

    1
    A simulated visual representation of the structural transition from coesite to post-stishovite. The silicon atoms (blue spheres) surrounded by four oxygen atoms (red spheres) are shown as blue tetrahedrons. The silicon atoms surrounded by six oxygen atoms are shown as green octahedrons. The intermediate phases are not filled in with color, showing the four stages that are neither all-blue like nor all-green like post-stishovite.

    A Carnegie-led team was able to discover five new forms of silica under extreme pressures at room temperature. Their findings are published by Nature Communications.

    Silicon dioxide, commonly called silica, is one of the most-abundant natural compounds and a major component of the Earth’s crust and mantle. It is well-known even to non-scientists in its quartz crystalline form, which is a major component of sand in many places. It is used in the manufacture of microchips, cement, glass, and even some toothpaste.

    Silica’s various high-pressure forms make it an often-used study subject for scientists interested in the transition between different chemical phases under extreme conditions, such as those mimicking the deep Earth.

    The first-discovered high-pressure, high-temperature denser form, or phase, of silica is called coesite, which, like quartz, consists of building blocks of silicon atoms surrounded by four oxygen atoms.

    1
    coesite

    Under greater pressures and temperatures, it transforms into an even denser form called stishovite, with silicon atoms surrounded by six oxygen atoms.

    2
    stishovite

    The transition between these phases was crucial for learning about the pressure gradient of the deep Earth and the four-to-six configuration shift has been of great interest to geoscientists. Experiments have revealed even higher-pressure phases of silica beyond these two, sometimes called post-stishovite.

    A chemical phase is a distinctive and uniform configuration of the molecules that make up a substance. Changes in external conditions, such as temperature and pressure, can induce a transition from one phase to another, not unlike water freezing into ice or boiling into steam.

    The team, including Carnegie’s Qingyang Hu, Jinfu Shu, Yue Meng, Wenge Yang, and Ho-Kwang, “Dave” Mao, demonstrated that under a range from 257,000 to 523,000 times normal atmospheric pressure (26 to 53 gigapascals), a single crystal of coesite transforms into four new, co-existing crystalline phases before finally recombining into a single phase that is denser than stishovite, sometimes called post-stishovite, which is the team’s fifth newly discovered phase. This transition takes place at room temperature, rather than the extreme temperatures found deep in the earth.

    Scientists previously thought that this intermediate was amorphous, meaning that it lacked the long-range order of a crystalline structure. This new study uses superior x-ray analytical probes to show otherwise—they are four, distinct, well-crystalized phases of silica without amorphization. Advanced theoretical calculations performed by the team provided detailed explanations of the transition paths from coesite to the four crystalline phases to post-stishovite.

    “Scientists have long debated whether a phase exists between the four- and six-oxygen phases,” Mao said. “These newly discovered four transition phases and the new phase of post-stishovite we discovered show the missing link for which we’ve been searching.”

    The paper’s other co-authors are Adam Cadien of George Mason University and Howard Sheng of both the Center for High Pressure Science and Technology Advanced Research in Shanghai, China, and George Mason University.

    See the full article here.

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    Carnegie Institution of Washington Bldg

    Andrew Carnegie established a unique organization dedicated to scientific discovery “to encourage, in the broadest and most liberal manner, investigation, research, and discovery and the application of knowledge to the improvement of mankind…” The philosophy was and is to devote the institution’s resources to “exceptional” individuals so that they can explore the most intriguing scientific questions in an atmosphere of complete freedom. Carnegie and his trustees realized that flexibility and freedom were essential to the institution’s success and that tradition is the foundation of the institution today as it supports research in the Earth, space, and life sciences.

     
  • richardmitnick 8:41 am on March 19, 2015 Permalink | Reply
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    From SLAC: “Scientists Watch Quantum Dots ‘Breathe’ in Response to Stress” 


    SLAC Lab

    March 18, 2015

    Nanocrystal Study at SLAC’s X-ray Laser Could Aid in the Design of New Materials

    1
    In this illustration, intense X-rays produced at SLAC’s Linac Coherent Light Source strike nanocrystals of a semiconductor material. Scientists used the X-rays to study an ultrafast “breathing” response in the crystals induced quadrillionths of a second earlier by laser light. (SLAC National Accelerator Laboratory)

    Researchers at the Department of Energy’s SLAC National Accelerator Laboratory watched nanoscale semiconductor crystals expand and shrink in response to powerful pulses of laser light. This ultrafast “breathing” provides new insight about how such tiny structures change shape as they start to melt – information that can help guide researchers in tailoring their use for a range of applications.

    In the experiment using SLAC’s Linac Coherent Light Source (LCLS) X-ray laser, a DOE Office of Science User Facility, researchers first exposed the nanocrystals to a burst of laser light, followed closely by an ultrabright X-ray pulse that recorded the resulting structural changes in atomic-scale detail at the onset of melting.

    SLAC LCLS Inside
    LCLS

    “This is the first time we could measure the details of how these ultrasmall materials react when strained to their limits,” said Aaron Lindenberg, an assistant professor at SLAC and Stanford who led the experiment. The results were published March 12 in Nature Communications.

    Getting to Know Quantum Dots

    The crystals studied at SLAC are known as “quantum dots” because they display unique traits at the nanoscale that defy the classical physics governing their properties at larger scales. The crystals can be tuned by changing their size and shape to emit specific colors of light, for example.

    So scientists have worked to incorporate them in solar panels to make them more efficient and in computer displays to improve resolution while consuming less battery power. These materials have also been studied for potential use in batteries and fuel cells and for targeted drug delivery.

    Scientists have also discovered that these and other nanomaterials, which may contain just tens or hundreds of atoms, can be far more damage-resistant than larger bits of the same materials because they exhibit a more perfect crystal structure at the tiniest scales. This property could prove useful in battery components, for example, as smaller particles may be able to withstand more charging cycles than larger ones before degrading.

    A Surprise in the ‘Breathing’ of Tiny Spheres and Nanowires

    In the LCLS experiment, researchers studied spheres and nanowires made of cadmium sulfide and cadmium selenide that were just 3 to 5 nanometers, or billionths of a meter, across. The nanowires were up to 25 nanometers long. By comparison, amino acids – the building blocks of proteins – are about 1 nanometer in length, and individual atoms are measured in tenths of nanometers.

    By examining the nanocrystals from many different angles with X-ray pulses, researchers reconstructed how they change shape when hit with an optical laser pulse. They were surprised to see the spheres and nanowires expand in width by about 1 percent and then quickly contract within femtoseconds, or quadrillionths of a second. They also found that the nanowires don’t expand in length, and showed that the way the crystals respond to strain was coupled to how their structure melts.

    In an earlier, separate study, another team of researchers had used LCLS to explore the response of larger gold particles on longer timescales.

    “In the future, we want to extend these experiments to more complex and technologically relevant nanostructures, and also to enable X-ray exploration of nanoscale devices while they are operating,” Lindenberg said. “Knowing how materials change under strain can be used together with simulations to design new materials with novel properties.”

    Participating researchers were from SLAC, Stanford and two of their joint institutes, the Stanford Institute for Materials and Energy Sciences (SIMES) and Stanford PULSE Institute; University of California, Berkeley; University of Duisburg-Essen in Germany; and Argonne National Laboratory. The work was supported by the DOE Office of Science and the German Research Council.

    See the full article here.

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    SLAC Campus
    SLAC is a multi-program laboratory exploring frontier questions in photon science, astrophysics, particle physics and accelerator research. Located in Menlo Park, California, SLAC is operated by Stanford University for the DOE’s Office of Science.
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