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  • richardmitnick 7:58 am on April 22, 2015 Permalink | Reply
    Tags: , Material Sciences,   

    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

    1
    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.

    1
    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.

    See the full article here.

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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

    2
    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
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    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
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    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.

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    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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  • 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.

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    coesite

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

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    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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    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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  • richardmitnick 1:27 pm on March 18, 2015 Permalink | Reply
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    From Sandia: “Iron rain fell on early Earth, new Z machine data supports” 


    Sandia Lab

    March 18, 2015
    Neal Singer, nsinger@sandia.gov, (505) 845-7078

    Sandia Z machine
    Sandia National Laboratories Z machine is the most powerful producer of pulses of electrical energy on Earth. Thomas J. Gardner, Sandia Lab

    Researchers at Sandia National Laboratories’ Z machine have helped untangle a long-standing mystery of astrophysics: why iron is found spattered throughout Earth’s mantle, the roughly 2,000-mile thick region between Earth’s core and its crust.

    At first blush, it seemed more reasonable that iron arriving from collisions between Earth and planetesimals — ranging from several meters to hundreds of kilometers in diameter — during Earth’s late formative stages should have powered bullet-like directly to Earth’s core, where so much iron already exists.

    A second, correlative mystery is why the moon proportionately has much less iron in its mantle than does Earth. Since the moon would have undergone the same extraterrestrial bombardment as its larger neighbor, what could explain the relative absence of that element in the moon’s own mantle?

    To answer these questions, scientists led by Professor Stein Jacobsen at Harvard University and Professor Sarah Stewart at the University of California at Davis (UC Davis) wondered whether the accepted theoretical value of the vaporization point of iron under high pressures was correct. If vaporization occurred at lower pressures than assumed, a solid piece of iron after impact might disperse into an iron vapor that would blanket the forming Earth instead of punching through it. A resultant iron-rich rain would create the pockets of the element currently found in the mantle.

    As for the moon, the same dissolution of iron into vapor could occur, but the satellite’s weaker gravity would be unable to capture the bulk of the free-floating iron atoms, explaining the dearth of iron deposits on Earth’s nearest neighbor.

    Looking for experimental rather than theoretical values, researchers turned to Sandia’s Z machine and its Fundamental Science Program, coordinated by Sandia manager Thomas Mattsson. This led to a collaboration among Sandia, Harvard University, UC Davis, and Lawrence Livermore National Laboratory (LLNL) to determine an experimental value for the vaporization threshold of iron that would replace the theoretical value used for decades.

    Rick Kraus at LLNL (formerly at Harvard) and Sandia researchers Ray Lemke and Seth Root used Z to accelerate metals to extreme speeds using high magnetic fields. The researchers created a target that consisted of an iron plate 5 millimeters square and 200 microns thick, against which they launched aluminum flyer plates travelling up to 25 kilometers per second. At this impact pressure, the powerful shock waves created in the iron cause it to compress, heat up and — in the zero pressure resulting from waves reflecting from the iron’s far surface — vaporize.

    The result, published March 2 in Nature Geosciences under the title Impact vaporization of planetesimal cores in the late stages of planet formation, shows the shock pressure experimentally required to vaporize iron is approximately 507 gigapascals (GPa), undercutting by more than 40 percent the previous theoretical estimate of 887 GPa. Astrophysicists say that this lower pressure is readily achieved during the end stages of planetary growth through accretion.

    Principal investigator Kraus said, “Because planetary scientists always thought it was difficult to vaporize iron, they never thought of vaporization as an important process during the formation of the Earth and its core. But with our experiments, we showed that it’s very easy to impact-vaporize iron.”

    He continued, “This changes the way we think of planet formation, in that instead of core formation occurring by iron sinking down to the growing Earth’s core in large blobs (technically called diapirs), that iron was vaporized, spread out in a plume over the surface of the Earth and rained out as small droplets. The small iron droplets mixed easily with the mantle, which changes our interpretation of the geochemical data we use to date the timing of Earth’s core formation.”

    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 1:44 pm on February 14, 2015 Permalink | Reply
    Tags: , Material Sciences, , ,   

    From Rutgers: “Rutgers-Led Research Team Makes Major Stride in Explaining 30-Year-Old ‘Hidden Order’ Physics Mystery” 

    Rutgers University
    Rutgers University

    February 12, 2015

    Findings may lead to new kinds of materials for electronics and superconducting magnets.

    A new explanation for a type of order, or symmetry, in an exotic material made with uranium may lead to enhanced computer displays and data storage systems, and more powerful superconducting magnets for medical imaging and levitating high-speed trains, according to a Rutgers-led team of research physicists.

    The team’s findings are a major step toward explaining a puzzle that physicists worldwide have been struggling with for 30 years, when scientists first noticed a change in the material’s electrical and magnetic properties but were unable to describe it fully. This subtle change occurs when the material is cooled to 17.5 degrees above absolute zero or lower (a bone-chilling minus 428 degrees Fahrenheit).

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    Physicists Hsiang-Hsi Kung and Girsh Blumberg with instrumentation they used to examine hidden order. Photo: Carl Blesch

    “This ‘hidden order’ has been the subject of nearly a thousand scientific papers since it was first reported in 1985 at Leiden University in the Netherlands,” said Girsh Blumberg, professor in the Department of Physics and Astronomy in the School of Arts and Sciences.

    Collaborators from Rutgers University, the Los Alamos National Laboratory in New Mexico, and Leiden University published their findings this week in the web-based journal Science Express, which features selected research papers in advance of their appearance in the journal Science. Blumberg and two Rutgers colleagues, graduate student Hsiang-Hsi Kung and professor Kristjan Haule, led the collaboration.

    Changes in order are what make liquid crystals, magnetic materials and superconductors work and perform useful functions. While the Rutgers-led discovery won’t transform high-tech products overnight, this kind of knowledge is vital to ongoing advances in electronic technology.

    “The Los Alamos collaborators produced a crystalline sample of the uranium, ruthenium and silicon compound with unprecedented purity, a breakthrough we needed to make progress in solving the puzzle of hidden order,” said Blumberg. Uranium is commonly known as an element in nuclear reactor fuel or weapons material, but in this case, physicists value it as a heavy metal with electrons that behave differently than those in common metals.

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    Below the hidden order temperature of 17.5 degrees Kelvin, uranium electron orbital patterns in adjacent crystal layers become mirror images of each other (right side of illustration). Above that temperature, uranium electron orbitals are the same (left side of illustration).Image: Hsiang-Hsi Kung

    Under these cold conditions, the orbital patterns made by electrons in uranium atoms from adjacent crystal layers become mirror images of each other. Above the hidden order temperature, these electron orbitals are the same. The Rutgers researchers discovered this so-called “broken mirror symmetry” using instrumentation they developed – based on a principle known as Raman scattering – to distinguish the pattern of the mirror images in the electron orbitals.

    Blumberg also credits two theoretical physics professors at Rutgers for predicting the phenomenon that his team discovered.

    “In this field, it’s rare to have such predictive power,” he said, noting that Gabriel Kotliar developed a computational technique that led to the prediction of the hidden order symmetry. Haule and Kotliar applied this technique to predict the changes in electron orbitals that Kung and Blumberg detected.

    At still colder temperatures of 1.5 degrees above absolute zero, the material becomes superconducting – losing all resistance to the flow of electricity. While not practical for today’s products and systems that rely on superconductivity, the material provides new insights into ways that materials can become superconducting.

    3
    Kristjan Haule, left, reviews prediction of hidden order symmetry with Hsiang-Hsi Kung and Girsh Blumberg. Photo: Carl Blesch

    The hidden order puzzle has also been a focus of other Rutgers researchers. Two years ago, professors Premala Chandra and Piers Coleman, along with alumna Rebecca Flint, published another theoretical explanation of the phenomenon in the journal Nature.

    The Leiden University collaborator, John Mydosh, is a member of the laboratory that discovered hidden order in 1985.

    “The work of Blumberg and his team is an important and viable step towards the understanding of hidden order,” Mydosh said. “We are well on our way after 30 years towards the final solution.”

    Working with Kung, Blumberg and Haule at Rutgers were Verner Thorsmølle and Weilu Zhang. The Los Alamos National Laboratory collaborators are Ryan Baumbach and Eric Bauer.

    The research was funded by the National Science Foundation and the U.S. Department of Energy’s Office of Basic Energy Sciences, Division of Materials Sciences and Engineering.

    See the full article here.

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    Rutgers, The State University of New Jersey, is a leading national research university and the state’s preeminent, comprehensive public institution of higher education. Rutgers is dedicated to teaching that meets the highest standards of excellence; to conducting research that breaks new ground; and to providing services, solutions, and clinical care that help individuals and the local, national, and global communities where they live.

    Founded in 1766, Rutgers teaches across the full educational spectrum: preschool to precollege; undergraduate to graduate; postdoctoral fellowships to residencies; and continuing education for professional and personal advancement.

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  • richardmitnick 3:19 pm on February 13, 2015 Permalink | Reply
    Tags: , , Iron, Material Sciences   

    From Caltech: “How Iron Feels the Heat” 

    Caltech Logo
    Caltech

    02/13/2015
    Jessica Stoller-Conrad

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    As you heat up a piece of iron, the arrangement of the iron atoms changes several times before melting. This unusual behavior is one reason why steel, in which iron plays a starring role, is so sturdy and ubiquitous in everything from teapots to skyscrapers. But the details of just how and why iron takes on so many different forms have remained a mystery. Recent work at Caltech in the Division of Engineering and Applied Science, however, provides evidence for how iron’s magnetism plays a role in this curious property—an understanding that could help researchers develop better and stronger steel.

    “Humans have been working with regular old iron for thousands of years, but this is a piece about its thermodynamics that no one has ever really understood,” says Brent Fultz, the Barbara and Stanley R. Rawn, Jr., Professor of Materials Science and Applied Physics.

    The laws of thermodynamics govern the natural behavior of materials, such as the temperature at which water boils and the timing of chemical reactions. These same principles also determine how atoms in solids are arranged, and in the case of iron, nature changes its mind several times at high temperatures. At room temperature, the iron atoms are in an unusual loosely packed open arrangement; as iron is heated past 912 degrees Celsius, the atoms become more closely packed before loosening again at 1,394 degrees Celsius and ultimately melting at 1,538 degrees Celsius.

    Iron is magnetic at room temperature, and previous work predicted that iron’s magnetism favors its open structure at low temperatures, but at 770 degrees Celsius iron loses its magnetism. However, iron maintains its open structure for more than a hundred degrees beyond this magnetic transition. This led the researchers to believe that there must be something else contributing to iron’s unusual thermodynamic properties.

    For this missing link, graduate student Lisa Mauger and her colleagues needed to turn up the heat. Solids store heat as small atomic vibrations—vibrations that create disorder, or entropy. At high temperatures, entropy dominates thermodynamics, and atomic vibrations are the largest source of entropy in iron. By studying how these vibrations change as the temperature goes up and magnetism is lost, the researchers hoped to learn more about what is driving these structural rearrangements.

    To do this, the team took its samples of iron to the High Pressure Collaborative Access Team beamline of the Advanced Photon Source [APS] at Argonne National Laboratory [ANL] in Argonne, Illinois. This synchrotron facility produces intense flashes of x-rays that can be tuned to detect the quantum particles of atomic vibration—called phonon excitations—in iron.

    ANL APS
    ANL APS interior
    APS at ANL

    When coupling these vibrational measurements with previously known data about the magnetic behavior of iron at these temperatures, the researchers found that iron’s vibrational entropy was much larger than originally suspected. In fact, the excess was similar to the entropy contribution from magnetism—suggesting that magnetism and atomic vibrations interact synergistically at moderate temperatures. This excess entropy increases the stability of the iron’s open structure even as the sample is heated past the magnetic transition.

    The technique allowed the researchers to conclude, experimentally and for the first time, that magnons—the quantum particles of electron spin (magnetism)—and phonons interact to increase iron’s stability at high temperatures.

    Because the Caltech group’s measurements matched up with the theoretical calculations that were simultaneously being developed by collaborators in the laboratory of Jörg Neugebauer at the Max-Planck-Institut für Eisenforschung GmbH (MPIE), Mauger’s results also contributed to the validation of a new computational model.

    “It has long been speculated that the structural stability of iron is strongly related to an inherent coupling between magnetism and atomic motion,” says Fritz Körmann, postdoctoral fellow at MPIE and the first author on the computational paper. “Actually finding this coupling, and that the data of our experimental colleagues and our own computational results are in such an excellent agreement, was indeed an exciting moment.”

    “Only by combining methods and expertise from various scientific fields such as quantum mechanics, statistical mechanics, and thermodynamics, and by using incredibly powerful supercomputers, it became possible to describe the complex dynamic phenomena taking place inside one of the technologically most used structural materials,” says Neugebauer. “The newly gained insight of how thermodynamic stability is realized in iron will help to make the design of new steels more systematic.”

    For thousands of years, metallurgists have been working to make stronger steels in much the same way that you’d try to develop a recipe for the world’s best cookie: guess and check. Steel begins with a base of standard ingredients—iron and carbon—much like a basic cookie batter begins with flour and butter. And just as you’d customize a cookie recipe by varying the amounts of other ingredients like spices and nuts, the properties of steel can be tuned by adding varying amounts of other elements, such as chromium and nickel.

    With a better computational model for the thermodynamics of iron at different temperatures—one that takes into account the effects of both magnetism and atomic vibrations—metallurgists will now be able to more accurately predict the thermodynamic properties of iron alloys as they alter their recipes.

    The experimental work was published in a paper titled Nonharmonic Phonons in α-Iron at High Temperatures,” in the journal Physical Review B. In addition to Fultz and first author Mauger, other Caltech coauthors include Jorge Alberto Muñoz (PhD ’13) and graduate student Sally June Tracy. The computational paper, Temperature Dependent Magnon-Phonon Coupling in bcc Fe from Theory and Experiment, was coauthored by Fultz and Mauger, led by researchers at the Max Planck Institute, and published in the journal Physical Review Letters. Fultz’s and Mauger’s work was supported by funding from the U.S. Department of Energy.

    See the full article here.

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    The California Institute of Technology (commonly referred to as Caltech) is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering. Its 124-acre (50 ha) primary campus is located approximately 11 mi (18 km) northeast of downtown Los Angeles. “The mission of the California Institute of Technology is to expand human knowledge and benefit society through research integrated with education. We investigate the most challenging, fundamental problems in science and technology in a singularly collegial, interdisciplinary atmosphere, while educating outstanding students to become creative members of society.”
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