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  • richardmitnick 1:35 pm on June 23, 2017 Permalink | Reply
    Tags: , , , , Magnetic materials, Magnetocaloric effect, Material Sciences,   

    From Ames Lab- “Scientists’ surprising discovery: making ferromagnets stronger by adding non-magnetic element” 

    Ames Laboratory

    June 23, 2017
    Yaroslav Mudryk
    Division of Materials Science and Engineering
    (515) 294-2728

    Durga Paudyal
    Division of Materials Science and Engineering

    Laura Millsaps
    Ames Laboratory Public Affairs
    (515) 294-3474

    No image caption or credit.

    Researchers at the U.S. Department of Energy’s Ames Laboratory discovered that they could functionalize magnetic materials through a thoroughly unlikely method, by adding amounts of the virtually non-magnetic element scandium to a gadolinium-germanium alloy.

    It was so unlikely they called it a “counterintuitive experimental finding” in their published work on the research.

    “People don’t talk much about scandium when they are talking magnetism, because there has not been much reason to,” said Yaroslav Mudryk, an Associate Scientist at Ames Laboratory. “It’s rare, expensive, and displays virtually no magnetism.”

    “Conventional wisdom says if you take compound A and compound B and combine them together, most commonly you get some combination of the properties of each. In the case of the addition of scandium to gadolinium, however, we observed an abrupt anomaly.”

    Years of research exploring the properties of magnetocaloric materials, relating back to the discovery of the giant magnetocaloric effect in rare earth alloys in 1997 by Vitalij Pecharsky and the late Karl Gschneidner, Jr., laid the groundwork for computational theory to begin “hunting” for hidden properties in magnetic rare-earth compounds that could be discovered by introducing small amounts of other elements, altering the electronic structure of known materials.

    “From computations, we projected that scandium may bring something really unusual to the table: we saw an unexpectedly large magnetic moment developing on its lone 3d electron,” said Ames Laboratory Associate Scientist Durga Paudyal. “It is the hybridization between gadolinium 5d and the scandium 3d states that is the key that strengthens magnetism with the scandium and transforms it to a ferromagnetic state.”

    “Basic research takes time to bear fruit. This is an exemplary case when 20 years ago our team started looking into what are called the 5:4 compounds,” said Ames Laboratory group leader and Iowa State University Distinguished Professor Vitalij Pecharsky. “Only now we have learned enough about these unique rare earth element-containing materials to become not only comfortable but precise in predicting how to manipulate their properties at will.”

    The discovery could greatly change the way scandium and other ‘conventionally’ non-magnetic elements are considered and used in magnetic materials research and development, and possibly creates new tools for controlling, manipulating, and functionalizing useful magnetic rare-earth compounds.

    The research is further discussed in the paper, Enhancing Magnetic Functionality with Scandium: Breaking Stereotypes in the Design of Rare Earth Materials, authored by Yaroslav Mudryk, Durga Paudyal, Jing Liu, and Vitalij K. Pecharsky; and published in the Chemistry of Materials.

    The work was supported by the U.S. Department of Department of Energy’s Office of Science.

    Ames Laboratory is a U.S. Department of Energy Office of Science national laboratory operated by Iowa State University. Ames Laboratory creates innovative materials, technologies and energy solutions. We use our expertise, unique capabilities and interdisciplinary collaborations to solve global problems.

    DOE’s Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit http://science.energy.gov.

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    Ames Laboratory is a government-owned, contractor-operated research facility of the U.S. Department of Energy that is run by Iowa State University.

    For more than 60 years, the Ames Laboratory has sought solutions to energy-related problems through the exploration of chemical, engineering, materials, mathematical and physical sciences. Established in the 1940s with the successful development of the most efficient process to produce high-quality uranium metal for atomic energy, the Lab now pursues a broad range of scientific priorities.

    Ames Laboratory is a U.S. Department of Energy Office of Science national laboratory operated by Iowa State University. Ames Laboratory creates innovative materials, technologies and energy solutions. We use our expertise, unique capabilities and interdisciplinary collaborations to solve global problems.

    Ames Laboratory is supported by the Office of Science of the U.S. Department of Energy. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.
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  • richardmitnick 8:06 am on June 23, 2017 Permalink | Reply
    Tags: A Single Electron’s Tiny Leap Sets Off ‘Molecular Sunscreen’ Response, , , , , Material Sciences, ,   

    From SLAC: “A Single Electron’s Tiny Leap Sets Off ‘Molecular Sunscreen’ Response” 

    SLAC Lab

    June 22, 2017
    Glennda Chui

    Thymine – the molecule illustrated in the foreground – is one of the four basic building blocks that make up the double helix of DNA. It’s such a strong absorber of ultraviolet light that the UV in sunlight should deactivate it, yet this does not happen. Researchers used an X-ray laser at SLAC National Accelerator Laboratory to observe the infinitesimal leap of a single electron that sets off a protective response in thymine molecules, allowing them to shake off UV damage. (Greg Stewart/SLAC National Accelerator Laboratory)

    In experiments at the Department of Energy’s SLAC National Accelerator Laboratory, scientists were able to see the first step of a process that protects a DNA building block called thymine from sun damage: When it’s hit with ultraviolet light, a single electron jumps into a slightly higher orbit around the nucleus of a single oxygen atom.

    This infinitesimal leap sets off a response that stretches one of thymine’s chemical bonds and snaps it back into place, creating vibrations that harmlessly dissipate the energy of incoming ultraviolet light so it doesn’t cause mutations.

    The technique used to observe this tiny switch-flip at SLAC’s Linac Coherent Light Source (LCLS) X-ray free-electron laser can be applied to almost any organic molecule that responds to light – whether that light is a good thing, as in photosynthesis or human vision, or a bad thing, as in skin cancer, the scientists said. They described the study in Nature Communications today.


    “All of these light-sensitive organic molecules tend to absorb light in the ultraviolet. That’s not only why you get sunburn, but it’s also why your plastic eyeglass lenses offer some UV protection,” said Phil Bucksbaum, a professor at SLAC and Stanford University and director of the Stanford PULSE Institute at SLAC. “You can even see these effects in plastic lawn furniture – after a couple of seasons it can become brittle and discolored simply due to the fact that the plastic was absorbing ultraviolet light all the time, and the way it absorbs sun results in damage to its chemical bonds.”

    Catching Electrons in Action

    Thymine and the other three DNA building blocks also strongly absorb ultraviolet light, which can trigger mutations and skin cancer, yet these molecules seem to get by with minimal damage. In 2014, a team led by Markus Guehr ­– then a SLAC senior staff scientist and now on the faculty of the University of Potsdam in Germany – reported that they had found the answer: The stretch-snap of a single bond and resulting energy-dissipating vibrations, which took place within 200 femtoseconds, or millionths of a billionth of a second after UV light exposure.

    But what made the bond stretch? The team knew the answer had to involve electrons, which are responsible for forming, changing and breaking bonds between atoms. So they devised an ingenious way to catch the specific electron movements that trigger the protective response.

    It relied on the fact that electrons don’t orbit an atom’s nucleus in neat concentric circles, like planets orbiting a sun, but rather in fuzzy clouds that take a different shape depending on how far they are from the nucleus. Some of these orbitals are in fact like a fuzzy sphere; others look a little like barbells or the start of a balloon animal. You can see examples here.

    No image caption or credit, but there is a comment,
    “I see the distribution in different orbitals. So if for example I take the S orbitals, they are all just a sphere. So wont the 2S orbital overlap with the 1S overlap, making the electrons in each orbital “meet” at some point? Or have I misunderstood something?”

    Strong Signal Could Solve Long-Standing Debate

    For this new experiment, the scientists hit thymine molecules with a pulse of UV laser light and tuned the energy of the LCLS X-ray laser pulses so they would home in on the response of the oxygen atom that’s at one end of the stretching, snapping bond.

    The energy from the UV light excited one of the atom’s electrons to jump into a higher orbital. This left the atom in a sort of tippy state where just a little more energy would boost a second electron into a higher orbital; and that second jump is what sets off the protective response, changing the shape of the molecule just enough to stretch the bond.

    The first jump, which was previously known to happen, is difficult to detect because the electron winds up in a rather diffuse orbital cloud, Guehr said. But the second, which had never been observed before, was much easier to spot because that electron ended up in an orbital with a distinctive shape that gave off a big signal.

    “Although this was a very tiny electron movement, the signal kind of jumped out at us in the experiment,” Guehr said. “I always had a feeling this would be a strong transition, just intuitively, but when we saw this come in it was a special moment, one of the best moments an experimentalist can have.”

    Settling a Longstanding Debate

    Study lead author Thomas Wolf, an associate staff scientist at SLAC, said the results should settle a longstanding debate about how long after UV exposure the protective response kicks in: It happens 60 femtoseconds after UV light hits. This time span is important, he said, because the longer the atom spends in the tippy state between the first jump and the second, the more likely it is to undergo some sort of reaction that could damage the molecule.

    Henrik Koch, a theorist at NTNU in Norway who was a guest professor at Stanford at the time, led the study with Guehr. He led the effort to model, understand and interpret what happened in the experiment, and he participated in it to an unusual extent, Guehr said.

    “He is extremely experienced in applying theory to methodology development, and he had this curiosity to bring this to our experiment,” Guehr said. “He was so fascinated by this research that he did something completely untypical of a theorist – he came to LCLS, into the control room, and he wanted to see the data coming in. I found that completely amazing and very motivating. It turned out that some of my previous thinking was completely right but other aspects were completely wrong, and Henrik did the right theory at the right level so we could learn from it.”

    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.

  • richardmitnick 6:36 am on June 15, 2017 Permalink | Reply
    Tags: , , , , Material Sciences, , RIXS, SIMES - Stanford Institute for Materials & Energy Sciences,   

    From SLAC: “New Research Finds a Missing Piece to High-Temperature Superconductor Mystery” 

    SLAC Lab

    June 14, 2017
    Mike Ross

    This sketch shows how resonant inelastic X-ray scattering (RIXS) helps scientists understand the electronic behavior of copper oxide materials. An X-ray photon aimed at the sample (blue arrow) is absorbed by a copper atom, which then emits a new, lower-energy photon (red arrow) as it relaxes. The amount of momentum transferred and energy lost in this process can induce changes in the charge density waves thought to be important in high-temperature superconductivity. (Wei-Sheng/SLAC National Accelerator Laboratory)

    An international team led by scientists from the Department of Energy’s SLAC National Accelerator Laboratory and Stanford University has detected new features in the electronic behavior of a copper oxide material that may help explain why it becomes a perfect electrical conductor – a superconductor – at relatively high temperatures.

    Using an ultrahigh-resolution X-ray instrument in France, the researchers for the first time saw dynamic behaviors in the material’s charge density wave (CDW) – a pattern of electrons that resembles a standing wave – that lend support to the idea that these waves may play a role in high-temperature superconductivity.

    Data taken at low (20 kelvins) and high (240 kelvins) temperatures showed that as the temperature increased, the CDW became more aligned with the material’s atomic structure. Remarkably, at the lower temperature, the CDW also induced an unusual increase in the intensity of the oxide’s atomic lattice vibrations, indicating that the dynamic CDW behaviors can propagate through the lattice.

    “Previous research has shown that when the CDW is static, it competes with and diminishes superconductivity,” said co-author Wei-Sheng Lee, a SLAC staff scientist and investigator with the Stanford Institute for Materials and Energy Sciences (SIMES), which led the study published June 12 in Nature Physics. “If, on the other hand, the CDW is not static but fluctuating, theory tells us they may actually help form superconductivity.”

    A Decades-long Search for an Explanation

    The new result is the latest in a decades-long search by researchers worldwide for the factors that enable certain materials to become superconducting at relatively high temperatures.

    Since the 1950s, scientists have known how certain metals and simple alloys become superconducting when chilled to within a few degrees of absolute zero: Their electrons pair up and ride waves of atomic vibrations that act like a virtual glue to hold the pairs together. Above a certain temperature, however, the glue fails as thermal vibrations increase, the electron pairs split up and superconductivity disappears.

    In 1986, complex copper oxide materials were found to become superconducting at much higher – although still quite cold – temperatures. This discovery was so unexpected it caused a worldwide scientific sensation. By understanding and optimizing how these materials work, researchers hope to develop superconductors that work at room temperature and above.

    At first, the most likely glue holding superconducting electron pairs together at higher temperatures seemed to be strong magnetic excitations created by interactions between electron spins. But in 2014, a theoretical simulation and experiments led by SIMES researchers concluded that these high-energy magnetic interactions are not the sole factor in copper oxide’s high-temperature superconductivity. An unanticipated CDW also appeared to be important.

    The latest results continue the SIMES collaboration between experiment and theory. Building upon previous theories of how electron interactions with lattice vibrations can be probed with resonant inelastic X-ray scattering, or RIXS, the signature of CDW dynamics was finally identified, providing additional support for the CDW’s role in determining the electronic structure in superconducting copper oxides.

    The Essential New Tool: RIXS

    The new results are enabled by the development of more capable instruments employing RIXS. Now available at ultrahigh resolution at the European Synchrotron Radiation Facility (ESRF) in France, where the team performed this experiment, RIXS will also be an important feature of SLAC’s upgraded Linac Coherent Light Source X-ray free-electron laser, LCLS-II.

    ESRF. Grenoble, France


    The combination of ultrahigh energy resolution and a high pulse repetition rate at LCLS-II will enable researchers to see more detailed CDW fluctuations and perform experiments aimed at revealing additional details of its behavior and links to high-temperature superconductivity. Most importantly, researchers at LCLS-II will be able to use ultrafast light-matter interactions to control CDW fluctuations and then take femtosecond-timescale snapshots of them.

    RIXS involves illuminating a sample with X-rays that have just enough energy to excite some electrons deep inside the target atoms to jump up into a specific higher orbit. When the electrons relax back down into their previous positions, a tiny fraction of them emit X-rays that carry valuable atomic-scale information about the material’s electronic and magnetic configuration that is thought to be important in high-temperature superconductivity.

    “To date, no other technique has seen evidence of propagating CDW dynamics,” Lee said.

    RIXS was first demonstrated in the mid-1970s [Physical Review Letters], but it could not obtain useful information to address key problems until 2007, when Giacomo Ghiringhelli, Lucio Braicovich at Milan Polytechnic in Italy and colleagues at Swiss Light Source made a fundamental change that improved its energy resolution to a level where significant details became visible – technically speaking to about 120 milli-electronvolts (meV) at the relevant X-ray wavelength, which is called a copper L edge. The new RIXS instrument at ESRF is three times better, routinely attaining an energy resolution down to 40 meV. Since 2014, the Milan group has collaborated with SLAC and Stanford scientists in their RIXS research.

    “The new ultrahigh resolution RIXS makes a huge difference,” Lee said. “It can show us previously invisible details.”

    Other researchers involved in this result were from Milan Polytechnic, European Synchrotron Radiation Facility, Japan’s National Institute of Advanced Industrial Science and Technology and Italy’s National Research Council Institute for Superconductors, Oxides and Other Innovative Materials and Devices (CNR-SPIN). Funding for this research came from the DOE Office of Science.

    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.

  • richardmitnick 3:22 pm on June 9, 2017 Permalink | Reply
    Tags: , , , Dynamic boundary, Liquid crystal study, Material Sciences, , Phononic or optomechanical applications, , Scattering angle, Tracking dynamic molecular features in soft materials including the high-frequency molecular vibrations that transmit waves of heat sound and other forms of energy, Tuning the structure   

    From BNL: “X-ray Study Reveals Way to Control Molecular Vibrations that Transmit Heat” 

    Brookhaven Lab

    June 6, 2017
    Karen McNulty Walsh
    (631) 344-8350

    Peter Genzer
    (631) 344-3174

    Findings open new pathway for “tuning” materials to ease or insulate against the flow of heat, sound, and other forms of energy.

    Brookhaven Lab members of the research team at the IXS beamline of the National Synchrotron Light Source II, left to right: Dima Bolmatov, Alessandro Cunsolo, Mikhail Zhernenkov, Ronald Pindak (sitting), Alexei Suvorov (sitting), and Yong Cai. The circular track accommodates utility cables and allows the arm housing the detectors to move to different locations to select the scattering angle for the measurement.

    Scientists at the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory have developed a new way to track dynamic molecular features in soft materials, including the high-frequency molecular vibrations that transmit waves of heat, sound, and other forms of energy. Controlling these vibrational waves in soft materials such as polymers or liquid crystal compounds could lead to a range of energy-inspired innovations—from thermal and acoustic insulators, to ways to convert waste heat into electricity, or light into mechanical motion.

    In a paper just published in Nano Letters, the scientists describe using the newly constructed inelastic x-ray scattering (IXS) beamline at the National Synchrotron Light Source II (NSLS-II), which has unprecedented energy resolution, to monitor the propagation of vibrations through a liquid crystal compound in three different phases.


    Their findings show that the nanoscale structural changes that occur with increasing temperature—as the liquid crystals become less ordered—dramatically disrupt the flow of vibrational waves. Thus choosing or changing the “phase,” or arrangement of molecules, could control the vibrations and the flow of energy.

    “By tuning the structure, we can change the dynamic properties of this material,” said Brookhaven physicist Dima Bolmatov, the paper’s lead author.

    The technique could also be used to study dynamic processes in other soft systems such as biological membranes or any kind of complex fluid.

    “For example, we could look at how the lipid molecules in a cell membrane cooperate with each other to create tiny porous regions where even smaller molecules, like oxygen or carbon dioxide, can pass through—to see how gas exchange operates in gills and lungs,” Bolmatov said.

    The ability to track such fast dynamic properties would not be possible without the unique capabilities of NSLS-II—a DOE Office of Science User Facility at Brookhaven Lab. NSLS-II produces extremely bright x-rays for studies in a wide range of scientific fields.

    At the IXS beamline, scientists bombard samples with these x-rays and measure the energy they give up or gain with a precision to within two thousandths of an electron volt, as well as the angle at which they scatter off the sample—even at very small angles.

    The energy exchange tells us how much energy it took to make some molecules vibrate in a wave-like motion. The scattering angle probes the vibrations propagating over different length scales inside the sample—from nearly a single molecule to tens of nanometers. The new IXS beamline at NSLS-II can resolve those length scales with unprecedented precision,” said Yong Cai, the lead scientist of the IXS beamline.

    “These two parameters—the scattering angle and the energy—have never before been so well measured in soft materials. So the technical properties of this beamline enable us to precisely locate the vibrations and track their propagation in different directions over different length scales—even in materials that lack a well-ordered solid structure,” he added.

    The colorful scattering pattern at left reveals molecular level structural information about the layered smectic phase of a liquid crystal material. The inner arcs indicate that the molecules are arrayed in ordered layers with regular spacing, while the outer arcs indicate there is still liquid-like mobility within the layers. The graph (top, right) represents inelastic x-ray scattering measurements from this smectic phase. Each peak (pink, orange, purple) represents a unique vibrational motion moving through the material, where the two “bumps” that make up each peak represent the energy gained or lost by the vibration. The purple and orange vibrations match the frequency of sound waves while the third, pink, vibration is linked to the tilt of the molecules (bottom, right). The out-of-phase rocking back-and-forth of these molecules matches the frequency of infrared light (heat).

    In the liquid crystal study, the Brookhaven Lab scientists and their collaborators at Kent State University and the University at Albany made measurements at three different temperatures as the material went from an ordered, crystalline phase through transitions to a less-ordered “smectic” state, and finally an “isotropic” liquid. They easily detected the propagation of vibrational waves through the most ordered phase, and showed that the emergence of disorder “killed” the propagation of low energy “acoustic shear” vibrations. Acoustic shear vibrations are associated with a compression of the molecules in a direction perpendicular to the direction of propagation.

    “Knowing where the dynamic boundary is—between the material behaving like an ordered solid and a disordered soft material—gives us a way to control the transmission of energy at the nanoscale,” Bolmatov said.

    In the “smectic” phase, the scientists also observed a vibration that was associated instead with molecular tilt. This type of vibration can interact with light and absorb it because the terahertz frequency of the vibrations matches the frequency of infrared light or heat waves. So changing the material properties can control the way these forms of energy move through the material. Those changes can be achieved by changing the temperature of the material, as was done in this experiment, but also by applying external electric or magnetic fields, Bolmatov said.

    This paves the way for new so-called phononic or optomechanical applications, where sound or light is coupled with the mechanical vibrations. Such coupling makes it possible to control a material by applying external light and sound or vice versa.

    “We’re all familiar with applications using the optical properties of liquid crystals in display screens,” Bolmatov said. “We’ve found new properties that can be controlled or manipulated for new kinds of applications.”

    The team will continue studies of soft materials at IXS, including planned experiments with block copolymers, nanoparticle assemblies, lipid membranes, and other liquid crystals over the summer.

    “The IXS beamline is also now opened to external users—including scientists interested in these and other soft materials and biological processes,” said Cai.

    The research team included Dima Bolmatov, Mikhail Zhernenkov, Alexey Suvorov, Ronald Pindak, Yong Cai, and Alessandro Cunsolo of NSLS-II, and Lewis Sharpnack, Deña M. Agra-Kooijman of Kent State University, and Satyendra Kumar of the University at Albany .

    This research was supported by the DOE Office of Science.

    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.

  • richardmitnick 8:19 pm on June 7, 2017 Permalink | Reply
    Tags: A more sustainable way to refine metals, , Material Sciences,   

    From McGill: “A more sustainable way to refine metals” 

    McGill University

    McGill University

    Contact Information
    Prof. Jean-Philippe Lumb
    514 398-4201

    Secondary Contact Information
    Chris Chipello

    New method could reduce environmental impact of extracting metals from raw materials and post-consumer electronics.

    Strategy for reducing the environmental impact of a refining process: replace hazardous chemicals with more benign and recyclable compounds. CREDIT: Michael J. Krause (Western University)

    A team of chemists in Canada has developed a way to process metals without using toxic solvents and reagents. The system, which also consumes far less energy than conventional techniques, could greatly shrink the environmental impact of producing metals from raw materials or from post-consumer electronics.

    “At a time when natural deposits of metals are on the decline, there is a great deal of interest in improving the efficiency of metal refinement and recycling, but few disruptive technologies are being put forth,” says Jean-Philip Lumb, an associate professor in McGill University’s Department of Chemistry. “That’s what makes our advance so important.

    The discovery stems from a collaboration between Lumb and Tomislav Friščić at McGill in Montreal, and Kim Baines of Western University in London, Ont. In an article published recently in Science Advances, the researchers outline an approach that uses organic molecules, instead of chlorine and hydrochloric acid, to help purify germanium, a metal used widely in electronic devices. Laboratory experiments by the researchers have shown that the same technique can be used with other metals, including zinc, copper, manganese and cobalt.

    The research could mark an important milestone for the “green chemistry” movement, which seeks to replace toxic reagents used in conventional industrial manufacturing with more environmentally friendly alternatives. Most advances in this area have involved organic chemistry – the synthesis of carbon-based compounds used in pharmaceuticals and plastics, for example.

    “Applications of green chemistry lag far behind in the area of metals,” Lumb says. “Yet metals are just as important for sustainability as any organic compound. For example, electronic devices require numerous metals to function.”

    Taking a page from biology

    There is no single ore rich in germanium, so it is generally obtained from mining operations as a minor component in a mixture with many other materials. Through a series of processes, that blend of matter can be reduced to germanium and zinc.

    “Currently, in order to isolate germanium from zinc, it’s a pretty nasty process,” Baines explains. The new approach developed by the McGill and Western chemists “enables you to get germanium from zinc, without those nasty processes.”

    To accomplish this, the researchers took a page from biology. Lumb’s lab for years has conducted research into the chemistry of melanin, the molecule in human tissue that gives skin and hair their color. Melanin also has the ability to bind to metals. “We asked the question: ‘Here’s this biomaterial with exquisite function, would it be possible to use it as a blueprint for new, more efficient technologies?’”

    The scientists teamed up to synthesize a molecule that mimics some of the qualities of melanin. In particular, this “organic co-factor” acts as a mediator that helps to extract germanium at room temperature, without using solvents.

    Using solvent-free mechanochemical techniques, milling jars containing stainless-steel balls are shaken at high speeds to promote chemical reactions. CREDIT: Michael Brand (University of Cardiff) and Jean-Louis Do (McGill University)

    Next step: industrial scale

    The system also taps into Friščić’s expertise in mechanochemistry, an emerging branch of chemistry that relies on mechanical force – rather than solvents and heat – to promote chemical reactions. Milling jars containing stainless-steel balls are shaken at high speeds to help purify the metal.

    “This shows how collaborations naturally can lead to sustainability-oriented innovation,” Friščić says. “Combining elegant new chemistry with solvent-free mechanochemical techniques led us to a process that is cleaner by virtue of circumventing chlorine-based processing, but also eliminates the generation of toxic solvent waste”

    The next step in developing the technology will be to show that it can be deployed economically on industrial scales, for a range of metals.

    “There’s a tremendous amount of work that needs to be done to get from where we are now to where we need to go,” Lumb says. “But the platform works on many different kinds of metals and metal oxides, and we think that it could become a technology adopted by industry. We are looking for stakeholders with whom we can partner to move this technology forward.”

    Funding for the research was provided by the Natural Sciences and Engineering Research Council of Canada, the National Natural Science Foundation of China, the Soochow University-Western University Center for Synchrotron Radiation Research, and the Collaborative Innovation Center of Suzhou Nano Science and Technology, Soochow University.

    “A chlorine-free protocol for processing germanium,” Martin Glavinović et al., Science Advances, 5 May 2017. DOI: 10.1126/sciadv.1700149 http://advances.sciencemag.org/content/3/5/e1700149

    See the full article here .

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    All about McGill

    With some 300 buildings, more than 38,500 students and 250,000 living alumni, and a reputation for excellence that reaches around the globe, McGill has carved out a spot among the world’s greatest universities.
    Founded in Montreal, Quebec, in 1821, McGill is a leading Canadian post-secondary institution. It has two campuses, 11 faculties, 11 professional schools, 300 programs of study and some 39,000 students, including more than 9,300 graduate students. McGill attracts students from over 150 countries around the world, its 8,200 international students making up 21 per cent of the student body.

  • richardmitnick 8:43 pm on May 21, 2017 Permalink | Reply
    Tags: , , , , Material Sciences, , NanoFab, ,   

    From NIST: “Nanocollaboration Leads to Big Things” 


    May 12, 2017 [Nothing like being timely getting into social media.]

    Ben Stein
    (301) 975-2763

    Entrance to NIST’s Advanced Measurement Laboratory in Gaithersburg, Maryland. Credit: Photo Courtesy HDR Architecture, Inc./Steve Hall Copyright Hedrich Blessing

    Roche Sequencing Solutions engineer Juraj Topolancik was looking for a way to decode DNA from cancer patients in a matter of minutes.

    Rajesh Krishnamurthy, a researcher with the startup company 3i Diagnostics, needed help in fabricating a key component of a device that rapidly identifies infection-causing bacteria.

    Ranbir Singh, an engineer with GeneSiC Semiconductor Inc., in Dulles, Virginia, sought to construct and analyze a semiconductor chip that transmits voltages large enough to power electric cars and spacecraft.

    These researchers all credit the NanoFab, located at the Center for Nanoscale Science and Technology (CNST) on the Gaithersburg, Maryland campus of the National Institute of Standards and Technology (NIST). The NanoFab provides cutting-edge nanotechnology capabilities for NIST scientists that is also accessible to outside users, with supplying the state-of-art tools, know-how and dependability to realize their goals.

    Learn more about the CNST NanoFab, where scientists from government, academia and industry can use commercial, state-of-the-art tools at economical rates, and get help from dedicated, full-time technical support staff. Voices: David Baldwin (Great Ball of Light, Inc.), Elisa Williams (Scientific & Biomedical Microsystems), George Coles (Johns Hopkins Applied Physics Laboratory) and William Osborn (NIST).

    When Krishnamurthy, whose company is based in Germantown, Maryland, needed an infrared filter for the bacteria-identifying chip, proximity was but one factor in reaching out to the NanoFab.

    “Even more important was the level of expertise you have here,” he says. “The attention to detail and the trust we have in the staff is so important—we didn’t have to worry if they would do a good job, which gives us tremendous peace of mind,” Krishnamurthy notes.

    The NanoFab also aided his project in another, unexpected way. Krishnamurthy had initially thought that the design for his company’s device would require a costly, highly customized silicon chip. But in reviewing design plans with engineers at the NanoFab, “they came up with a very creative way” to use a more standard, less expensive silicon wafer that would achieve the same goals, he notes.

    “The impact in the short term is that we didn’t have to pay as much [to build and test] the device at the NanoFab, which matters quite a bit because we’re a start-up company,” says Krishnamurthy. “In the long run, this will be a huge factor in [enabling us to mass produce] the device, keeping our costs low because, thanks to the input from the NanoFab, the source material is not a custom material.”

    Singh came to the NanoFab with a different mission. His company is developing a gallium nitride semiconductor device durable enough to transmit hundreds to thousands of volts without deteriorating. He relies on the NanoFab’s metal deposition tools and high-resolution lithography instruments to finish building and assess the properties of the device.

    Semiconductor device, fabricated with the help of the NanoFab, designed to transmit high voltages.
    Credit: GeneSiC Semiconductor Inc.

    “Not only is there a wide diversity of tools, but within each task there are multiple technologies,” Singh adds.

    For instance, he notes, technologies offered at the NanoFab for depositing exquisitely thin and highly uniform layers of metal—which Singh found crucial for making reliable electrical contacts—include both evaporation and sputtering, he says.

    The wide range of metals available for deposition at the NanoFab, uncommon at other nanotech facilities, was another draw.

    “We needed different metals compared to those commonly used on silicon wafers and the NanoFab provided those materials,” notes Singh.

    Topolancik, the Roche Sequencing Solutions engineer, needed high precision etching and deposition tools to fabricate a device that may ultimately improve cancer treatment. His company‘s plan to rapidly sequence DNA from cancer patients could quickly determine if potential anti-cancer drugs and those already in use are producing the genetic mutations necessary to fight cancer.

    “We want to know if the drug is working, and if not, to stop using it and change the treatment,” says Topolancik.

    In the standard method to sequence the double-stranded DNA molecule, a strand is peeled off and resynthesized, base by base, with each base—cytosine, adenine, guanine and thymine—tagged with a different fluorescent label.

    “It’s a very accurate but slow method,” says Topolancik.

    Instead of peeling apart the molecule, Topolancik is devising a method to read DNA directly, a much faster process. Borrowing a technique from the magnetic recording industry, he sandwiches the DNA between two electrodes separated by a gap just nanometers in width.


    Illustration of experiment to directly identify the base pairs of a DNA strand (denoted by A, C, T, G in graph). Tunneling current flows through DNA placed between two closely spaced electrodes. Different bases allow different amounts of current to flow, revealing the components of the DNA molecule.
    Credit: J. Topolancik/Roche Sequencing Solutions

    According to quantum theory, if the gap is small enough, electrons will spontaneously “tunnel” from one electrode to the other. In Topolancik’s setup, the tunneling electrons must pass through the DNA in order to reach the other electrode.

    The strength of the tunneling current identifies the bases of the DNA trapped between the electrodes. It’s an extremely rapid process, but for the technique to work reliably, the electrodes and the gap between them must be fabricated with extraordinarily high precision.

    That’s where the NanoFab comes in. To deposit layers of different metals just nanometers in thickness on a wafer, Topolancik relies on the NanoFab’s ion beam deposition tool. And to etch a pattern in those ultrathin, supersmooth layers without disturbing them—a final step in fabricating the electrodes—requires the NanoFab’s ion etching instrument.

    “These are specialty tools that are not usually accessible in academic facilities, but here [at the NanoFab] you have full, 24/7 access to them,” says Topolancik. “And if a tool goes down, it gets fixed right away,” he adds. “People here care about you, they want you to succeed because that’s the mission of the NanoFab.” As a result, he notes, “I can get done here in two weeks what would take half a year any place else.”

    Take a 360-degree walking tour of the CNST NanoFab in this video!

    See the full article here.

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  • richardmitnick 9:23 pm on April 11, 2017 Permalink | Reply
    Tags: , Material Sciences, , , , , , Theory Institute for Materials and Energy Spectroscopies (TIMES), ,   

    From SLAC: “New SLAC Theory Institute Aims to Speed Research on Exotic Materials at Light Sources” 

    SLAC Lab

    April 11, 2017
    Glennda Chui

    A new institute at the Department of Energy’s SLAC National Accelerator Laboratory is using the power of theory to search for new types of materials that could revolutionize society – by making it possible, for instance, to transmit electricity over power lines with no loss.

    The Theory Institute for Materials and Energy Spectroscopies (TIMES) focuses on improving experimental techniques and speeding the pace of discovery at West Coast X-ray facilities operated by SLAC and by Lawrence Berkeley National Laboratory, its DOE sister lab across the bay.

    But the institute aims to have a much broader impact on studies aimed at developing new materials for energy and other technological applications by making the tools it develops available to scientists around the world.

    TIMES opened in August 2016 as part of the Stanford Institute for Materials and Energy Sciences (SIMES), a DOE-funded institute operated jointly with Stanford.

    Materials that Surprise

    “We’re interested in materials with remarkable properties that seem to emerge out of nowhere when you arrange them in particular ways or squeeze them down into a single, two-dimensional layer,” says Thomas Devereaux, a SLAC professor of photon science who directs both TIMES and SIMES.

    This general class of materials is known as “quantum materials.” Some of the best-known examples are high-temperature superconductors, which conduct electricity with no loss; topological insulators, which conduct electricity only along their surfaces; and graphene, a form of pure carbon whose superior strength, electrical conductivity and other surprising qualities derive from the fact that it’s just one layer of atoms thick.

    In another research focus, Devereaux says, “We want to see what happens when you push materials far beyond their resting state – out of equilibrium, is the way we put it – by exciting them in various ways with pulses of X-ray light at facilities known as light sources.

    “This tells you how materials will behave under realistic operating conditions, for instance in a lightweight airplane or a new type of battery. Understanding and controlling out-of-equilibrium behavior and learning how novel properties emerge in complex materials are two of the scientific grand challenges in our field, and light sources are ideal places to do this work.”

    Joining Forces With Light Sources

    A key part of the institute’s work is to use theory and computation to improve experimental techniques – especially X-ray spectroscopy, which probes the chemical composition and electronic structure of materials – in order to make research at light sources more productive.

    “We are in a golden age of X-ray spectroscopy, in which many billions of dollars have been invested worldwide to develop new X-ray and neutron sources that allow us to study very small details and very fast processes in materials,” Devereaux says. “In fact, we are on the threshold of being able to control matter at a much deeper level than ever possible before.

    “But while X-ray spectroscopy has a long history of collaboration between experimentalists and theorists, there has not been a companion theory institute anywhere. TIMES fills this gap. It aims to solidify collaboration and development of new methods and tools for theory relevant to this new landscape.”

    Devereaux, a theorist who uses computation to study quantum materials, came to SLAC 10 years ago from the University of Waterloo in Canada to work more closely with researchers at three light sources – SLAC’s Stanford Synchrotron Radiation Lightsource (SSRL), Berkeley Lab’s Advanced Light Source (ALS) and the Linac Coherent Light Source (LCLS), the world’s first X-ray free-electron laser, which at the time was under construction at SLAC. Opened for research in 2009, LCLS gives scientists access to pulses a billion times brighter than any available before and that arrive up to 120 times per second, opening whole new avenues for research.





    With LCLS, Devereaux says, “It became clear that we had an unprecedented opportunity to study materials that have been pushed farther away from equilibrium than was ever possible before.”

    Basic Questions and Practical Answers

    The DOE-funded theory institute has hired two staff scientists, Chunjing Jia and Das Pemmaraju, and works closely with SLAC staff scientists Brian Moritz and Hongchen Jiang and with a number of scientists at the three light sources.

    “We have two main goals,” Jia says. “One is to use X-ray spectroscopy and other techniques to look at practical materials, like the ones in batteries – to study the charging and discharging process and see how the structure of the battery changes, for instance. The second is to understand the fundamental underlying physics principles that govern the behavior of materials.”

    Eventually, she added, theorists want to understand those physics principles so well that they can predict the results of high-priority experiments at facilities that haven’t even been built yet – for instance at LCLS-II, a major upgrade to LCLS that will add a much brighter X-ray laser beam that fires up to a million pulses per second. These predictions have the potential to make experiments at new facilities much more productive and efficient.

    Running Experiments in Supercomputers

    Theoretical work can involve a lot of math and millions of hours of supercomputer time, as theorists struggle to clarify how the fundamental laws of quantum mechanics apply to the materials they are investigating, Pemmaraju says.

    “We use these laws in a form that can be simulated on a computer to make predictions about new materials and their properties,” he says. “The full richness and complexity of the theory are still being discovered, and its equations can only be solved approximately with the aid of supercomputers.”

    Jia adds that you can think of these computer simulations as numerical experiments – working “in silico,” rather than at a lab bench. By simulating what’s going on in a material, scientists can decide which of all the experimental options are the best ones, saving both time and money.

    The institute’s core research team includes theorists Joel Moore of the University of California, Berkeley and John Rehr of the University of Washington. Rehr is the developer of FEFF, an efficient and widely accessible software code that is used by the X-ray light source community worldwide. Devereaux says the plan is to establish a center for FEFF within the institute, which will serve as a home for its further development and for making those advances widely available to theorists and experimentalists at various levels of sophistication.

    TIMES and SIMES are funded by the DOE Office of Science, and the three light sources – ALS, SSRL and LCLS – are DOE Office of Science User Facilities.

    See the full article here .

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  • richardmitnick 9:19 am on April 10, 2017 Permalink | Reply
    Tags: , , Material Sciences, Nanoporous materials, , , , Stanford scientist’s new approach may accelerate design of high-power batteries, Storing electricity, Supercapacitors   

    From Stanford: “Stanford scientist’s new approach may accelerate design of high-power batteries” 

    Stanford University Name
    Stanford University

    April 6, 2017
    Danielle Torrent Tucker

    Electric vehicles plug in to charging stations. New research may accelerate discovery of materials used in electrical storage devices, such as car batteries. (Image credit: Shutterstock)

    In work published this week in Applied Physics Letters, the researchers describe a mathematical model for designing new materials for storing electricity. The model could be a huge benefit to chemists and materials scientists, who traditionally rely on trial and error to create new materials for batteries and capacitors. Advancing new materials for energy storage is an important step toward reducing carbon emissions in the transportation and electricity sectors.

    “The potential here is that you could build batteries that last much longer and make them much smaller,” said study co-author Daniel Tartakovsky, a professor in the School of Earth, Energy & Environmental Sciences. “If you could engineer a material with a far superior storage capacity than what we have today, then you could dramatically improve the performance of batteries.”

    Lowering a barrier

    One of the primary obstacles to transitioning from fossil fuels to renewables is the ability to store energy for later use, such as during hours when the sun is not shining in the case of solar power. Demand for cheap, efficient storage has increased as more companies turn to renewable energy sources, which offer significant public health benefits.

    Tartakovsky hopes the new materials developed through this model will improve supercapacitors, a type of next-generation energy storage that could replace rechargeable batteries in high-tech devices like cellphones and electric vehicles. Supercapacitors combine the best of what is currently available for energy storage – batteries, which hold a lot of energy but charge slowly, and capacitors, which charge quickly but hold little energy. The materials must be able to withstand both high power and high energy to avoid breaking, exploding or catching fire.

    “Current batteries and other storage devices are a major bottleneck for transition to clean energy,” Tartakovsky said. “There are many people working on this, but this is a new approach to looking at the problem.”

    The types of materials widely used to develop energy storage, known as nanoporous materials, look solid to the human eye but contain microscopic holes that give them unique properties. Developing new, possibly better nanoporous materials has, until now, been a matter of trial and error – arranging minuscule grains of silica of different sizes in a mold, filling the mold with a solid substance and then dissolving the grains to create a material containing many small holes. The method requires extensive planning, labor, experimentation and modifications, without guaranteeing the end result will be the best possible option.

    “We developed a model that would allow materials chemists to know what to expect in terms of performance if the grains are arranged in a certain way, without going through these experiments,” Tartakovsky said. “This framework also shows that if you arrange your grains like the model suggests, then you will get the maximum performance.”

    Beyond energy

    Energy is just one industry that makes use of nanoporous materials, and Tartakovsky said he hopes this model will be applicable in other areas, as well.

    “This particular application is for electrical storage, but you could also use it for desalination, or any membrane purification,” he said. “The framework allows you to handle different chemistry, so you could apply it to any porous materials that you design.”

    Tartakovsky’s mathematical modeling research spans neuroscience, urban development, medicine and more. As an Earth scientist and professor of energy resources engineering, he is an expert in the flow and transport of porous media, knowledge that is often underutilized across disciplines, he said. Tartakovsky’s interest in optimizing battery design stemmed from collaboration with a materials engineering team at the University of Nagasaki in Japan.

    “This Japanese collaborator of mine had never thought of talking to hydrologists,” Tartakovsky said. “It’s not obvious unless you do equations – if you do equations, then you understand that these are similar problems.”

    The lead author of the study, “Optimal design of nanoporous materials for electrochemical devices,” is Xuan Zhang, Tartakovsky’s former PhD student at the University of California, San Diego. The research was supported by the Defense Advanced Research Projects Agency and the National Science Foundation.

    See the full article here .

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  • richardmitnick 5:01 pm on February 21, 2017 Permalink | Reply
    Tags: , Material Sciences, , When Rocket Science Meets X-ray Science,   

    From LBNL: “When Rocket Science Meets X-ray Science” 

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    Berkeley Lab

    February 21, 2017
    Glenn Roberts Jr.

    Berkeley Lab and NASA collaborate in X-ray experiments to ensure safety, reliability of spacecraft systems.

    Francesco Panerai of Analytical Mechanical Associates Inc., a materials scientist leading a series of X-ray experiments at Berkeley Lab for NASA Ames Research Center, discusses a 3-D visualization (shown on screens) of a heat shield material’s microscopic structure in simulated spacecraft atmospheric entry conditions. The visualization is based on X-ray imaging at Berkeley Lab’s Advanced Light Source. (Credit: Marilyn Chung/Berkeley Lab)

    Note: This is the first installment in a four-part series that focuses on a partnership between NASA and Berkeley Lab to explore spacecraft materials and meteorites with X-rays in microscale detail.

    It takes rocket science to launch and fly spacecraft to faraway planets and moons, but a deep understanding of how materials perform under extreme conditions is also needed to enter and land on planets with atmospheres.

    X-ray science is playing a key role, too, in ensuring future spacecraft survive in extreme environments as they descend through otherworldly atmospheres and touch down safely on the surface.

    Scientists at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) and NASA are using X-rays to explore, via 3-D visualizations, how the microscopic structures of spacecraft heat shield and parachute materials survive extreme temperatures and pressures, including simulated atmospheric entry conditions on Mars.

    Human exploration of Mars and other large-payload missions may require a new type of heat shield that is flexible and can remain folded up until needed.

    Streaking particles collide with carbon fibers in this direct simulation Monte Carlo (DSMC) calculation based on X-ray microtomography data from Berkeley Lab’s Advanced Light Source. NASA is developing new types of carbon fiber-based heat shield materials for next-gen spacecraft. The slow-motion animation represents 2 thousandths of a second. (Credit: Arnaud Borner, Tim Sandstrom/NASA Ames Research Center)

    Candidate materials for this type of flexible heat shield, in addition to fabrics for Mars-mission parachutes deployed at supersonic speeds, are being tested with X-rays at Berkeley Lab’s Advanced Light Source (ALS) and with other techniques.


    “We are developing a system at the ALS that can simulate all material loads and stresses over the course of the atmospheric entry process,” said Harold Barnard, a scientist at Berkeley Lab’s ALS who is spearheading the Lab’s X-ray work with NASA.

    The success of the initial X-ray studies has also excited interest from the planetary defense scientific community looking to explore the use of X-ray experiments to guide our understanding of meteorite breakup. Data from these experiments will be used in risk analysis and aid in assessing threats posed by large asteroids.

    The ultimate objective of the collaboration is to establish a suite of tools that includes X-ray imaging and small laboratory experiments, computer-based analysis and simulation tools, as well as large-scale high-heat and wind-tunnel tests. These allow for the rapid development of new materials with established performance and reliability.

    NASA has tested a new type of flexible heat shield, developed through the Adaptive Deployable Entry and Placement Technology (ADEPT) Project, with a high-speed blow torch at its Arc Jet Complex at NASA Ames, and has explored the microstructure of its woven carbon-fiber material at Berkeley Lab. (Credit: NASA Ames)

    This system can heat sample materials to thousands of degrees, subject them to a mixture of different gases found in other planets’ atmospheres, and with pistons stretch the material to its breaking point, all while imaging in real time their 3-D behavior at the microstructure level.

    NASA Ames Research Center (NASA ARC) in California’s Silicon Valley has traditionally used extreme heat tests at its Arc Jet Complex to simulate atmospheric entry conditions.

    Researchers at ARC can blast materials with a giant superhot blowtorch that accelerates hot air to velocities topping 11,000 miles per hour, with temperatures exceeding that at the surface of the sun. Scientists there also test parachutes and spacecraft at its wind-tunnel facilities, which can produce supersonic wind speeds faster than 1,900 miles per hour.

    Michael Barnhardt, a senior research scientist at NASA ARC and principal investigator of the Entry Systems Modeling Project, said the X-ray work opens a new window into the structure and strength properties of materials at the microscopic scale, and expands the tools and processes NASA uses to “test drive” spacecraft materials before launch.

    “Before this collaboration, we didn’t understand what was happening at the microscale. We didn’t have a way to test it,” Barnhardt said. “X-rays gave us a way to peak inside the material and get a view we didn’t have before. With this understanding, we will be able to design new materials with properties tailored to a certain mission.”

    He added, “What we’re trying to do is to build the basis for more predictive models. Rather than build and test and see if it works,” the X-ray work could reduce risk and provide more assurance about a new material’s performance even at the drawing-board stage.

    Francesco Panerai holds a sample of parachute material at NASA Ames Research Center. The screen display shows a parachute prototype (left) and a magnified patch of the material at right. (Credit: Marilyn Chung/Berkeley Lab)

    Francesco Panerai, a materials scientist with NASA contractor AMA Inc. and the X-ray experiments test lead for NASA ARC, said that the X-ray experiments at Berkeley Lab were on samples about the size of a postage stamp. The experimental data is used to improve realistic computer simulations of heat shield and parachute systems.

    “We need to use modern measurement techniques to improve our understanding of material response,” Panerai said. The 3-D X-ray imaging technique and simulated planetary conditions that NASA is enlisting at the ALS provide the best pictures yet of the behavior of the internal 3-D microstructure of spacecraft materials.

    The experiments are being conducted at an ALS experimental station that captures a sequence of images as a sample is rotated in front of an X-ray beam. These images, which provide views inside the samples and can resolve details less than 1 micron, or 1 millionth of a meter, can be compiled to form detailed 3-D images and animations of samples.

    This study technique is known as X-ray microtomography. “We have started developing computational tools based on these 3-D images, and we want to try to apply this methodology to other research areas, too,” he said.

    Learn more about the research partnership between NASA and Berkeley Lab in these upcoming articles, to appear at :

    Feb. 22—The Heat is On: X-rays reveal how simulated atmospheric entry conditions impact spacecraft shielding.
    Feb. 23—A New Paradigm in Parachute Design: X-ray studies showing the microscopic structure of spacecraft parachute fabrics can fill in key details about how they perform under extreme conditions.
    Feb. 24—Getting to Know Meteors Better: Experiments at Berkeley Lab may help assess risks posed by falling Space rocks.

    The Advanced Light Source is a DOE Office of Science User Facility.

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  • richardmitnick 12:39 pm on January 30, 2017 Permalink | Reply
    Tags: , , Material Sciences, , , Symmetry in patterns, symmorphic and nonsymmorphic patterns of atoms, Theorists propose new class of topological metals with exotic electronic properties, tungsten telluride (WTe2)   

    From Princeton: “Theorists propose new class of topological metals with exotic electronic properties (Physics Review X)” 

    Princeton University
    Princeton University

    January 30, 2017
    Tien Nguyen, Department of Chemistry

    A new theory explains the behavior of a class of metals with exotic electronic properties. Credit: Muechler et al., Physics Review X

    Researchers at Princeton, Yale, and the University of Zurich have proposed a theory-based approach to characterize a class of metals that possess exotic electronic properties that could help scientists find other, similarly-endowed materials.

    Published in the journal Physical Review X, the study described a new class of metals based on their symmetry and a mathematical classification known as a topological number, which is predictive of special electronic properties. Topological materials have drawn intense research interest since the early 2000s culminating in last year’s Nobel Prize in Physics awarded to three physicists, including F. Duncan Haldane, Princeton’s Eugene Higgins Professor of Physics, for theoretical discoveries in this area.

    “Topological classification is a very general way of looking at the properties of materials,” said Lukas Muechler, a Princeton graduate student in the laboratory of Roberto Car, Princeton’s Ralph W. *31 Dornte Professor in Chemistry and lead author on the article.

    A popular way of explaining this abstract mathematical classification involves breakfast items. In topological classification, donuts and coffee cups are equivalent because they both have one hole and can be smoothly deformed into one another. Meanwhile donuts cannot deform into muffins which makes them inequivalent. The number of holes is an example of a topological invariant that is equal for the donut and coffee cup, but distinguishes between the donut and the muffin.

    “The idea is that you don’t really care about the details. As long as two materials have the same topological invariants, we can say they are topologically equivalent,” he said.

    Muechler and his colleagues’ interest in the topological classification of this new class of metals was sparked by a peculiar discovery in the neighboring laboratory of Robert Cava, Princeton’s Russell Wellman Moore Professor of Chemistry. While searching for superconductivity in a crystal called tungsten telluride (WTe2), the Cava lab instead found that the material could continually increase its resistance in response to ever stronger magnetic fields – a property that might be used to build a sensor of magnetic fields.

    The origin of this property was, however, mysterious. “This material has very interesting properties, but there had been no theory around it,” Muechler said.

    The researchers first considered the arrangement of the atoms in the WTe2 crystal. Patterns in the arrangement of atoms are known as symmetries, and they fall into two fundamentally different classes – symmorphic and nonsymmorphic – which lead to profound differences in electronic properties, such as the transport of current in an electromagnetic field.

    a) Symmorphic symmetry b) Nonsymmorphic symmetry Credit: Lukas Muechler

    While WTe2 is composed of many layers of atoms stacked upon each other, Car’s team found that a single layer of atoms has a particular nonsymmorphic symmetry, where the atomic arrangement is unchanged overall if it is first rotated and then translated by a fraction of the lattice period (see figure).

    Having established the symmetry, the researchers mathematically characterized all possible electronic states having this symmetry, and classified those states that can be smoothly deformed into each other as topologically equivalent, just as a donut can be deformed into a cup. From this classification, they found WTe2 belongs to a new class of metals which they coined nonsymmorphic topological metals. These metals are characterized by a different electron number than the nonsymmorphic metals that have previously been studied.

    In nonsymmorphic topological metals, the current-carrying electrons behave like relativistic particles, in other words, as particles traveling at nearly the speed of light. This property is not as susceptible to impurities and defects as ordinary metals, making them attractive candidates for electronic devices.

    The abstract topological classification also led the researchers to suggest some explanations for some of the outstanding electronic properties of bulk WTe2, most importantly its perfect compensation, meaning that it has an equal number of holes and electrons. Through theoretical simulations, the researchers found that this property could be achieved in the three-dimensional crystalline stacking of the WTe2 monolayers, which was a surprising result, Muechler said.

    “Usually in theory research there isn’t much that’s unexpected, but this just popped out,” he said. “This abstract classification directly led us to explaining this property. In this sense, it’s a very elegant way of looking at this compound and now you can actually understand or design new compounds with similar properties.”

    Recent photoemission experiments have also shown that the electrons in WTe2 absorb right-handed photons differently than they would left-handed photons. The theory formulated by the researchers showed that these photoemission experiments on WTe2 can be understood based on the topological properties of this new class of metals.

    In future studies, the theorists want to test whether these topological properties are also present in atomically-thin layers of these metals, which could be exfoliated from a larger crystal to make electronic devices. “The study of this phenomena has big implications for the electronics industry, but it’s still in its infant years,” Muechler said.

    This work was supported by the U.S. Department of Energy (DE-FG02-05ER46201), the Yale Postdoctoral Prize Fellowship, the National Science Foundation (NSF CAREER DMR-095242 and NSF-MRSEC DMR-0819860), the Office of Naval Research (ONR-N00014-11-1- 0635), the U.S. Department of Defense (MURI-130-6082), the David and Lucile Packard Foundation, the W. M. Keck Foundation, and the Eric and Wendy Schmidt Transformative Technology Fund.

    See the full article here .

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