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  • richardmitnick 4:11 pm on September 10, 2015 Permalink | Reply
    Tags: , , , Material Sciences, SLAC UED   

    From SLAC: “SLAC’s Ultrafast ‘Electron Camera’ Visualizes Ripples in 2-D Material” 

    SLAC Lab

    September 10, 2015

    Researchers have used SLAC’s experiment for ultrafast electron diffraction (UED), one of the world’s fastest “electron cameras,” to take snapshots of a three-atom-thick layer of a promising material as it wrinkles in response to a laser pulse. Understanding these dynamic ripples could provide crucial clues for the development of next-generation solar cells, electronics and catalysts. (SLAC National Accelerator Laboratory)

    Illustrations (each showing a top and two side views) of a single layer of molybdenum disulfide (atoms shown as spheres). Top left: In a hypothetical world without motions, the “ideal” monolayer would be flat. Top right: In reality, the monolayer is wrinkled as shown in this room-temperature simulation. Bottom: If a laser pulse heats the monolayer up, it sends ripples through the layer. These wrinkles, which researchers have now observed for the first time, have large amplitudes and develop on ultrafast timescales. (SLAC National Accelerator Laboratory)

    SLAC Electron Camera UED
    SLAC’s electron Camera

    SLAC electron camera schematic
    SLAC’s electron Camera schematic

    New research led by scientists from the Department of Energy’s SLAC National Accelerator Laboratory and Stanford University shows how individual atoms move in trillionths of a second to form wrinkles on a three-atom-thick material. Revealed by a brand new “electron camera,” one of the world’s speediest, this unprecedented level of detail could guide researchers in the development of efficient solar cells, fast and flexible electronics and high-performance chemical catalysts.

    The breakthrough, accepted for publication Aug. 31 in Nano Letters, could take materials science to a whole new level. It was made possible with SLAC’s instrument for ultrafast electron diffraction (UED), which uses energetic electrons to take snapshots of atoms and molecules on timescales as fast as 100 quadrillionths of a second.

    “This is the first published scientific result with our new instrument,” said scientist Xijie Wang, SLAC’s UED team lead. “It showcases the method’s outstanding combination of atomic resolution, speed and sensitivity.”

    SLAC Director Chi-Chang Kao said, “Together with complementary data from SLAC’s X-ray laser Linac Coherent Light Source, UED creates unprecedented opportunities for ultrafast science in a broad range of disciplines, from materials science to chemistry to the biosciences.” LCLS is a DOE Office of Science User Facility.

    SLAC LCLS Inside

    download mp4 here.

    Extraordinary Material Properties in Two Dimensions

    Monolayers, or 2-D materials, contain just a single layer of molecules. In this form they can take on new and exciting properties such as superior mechanical strength and an extraordinary ability to conduct electricity and heat. But how do these monolayers acquire their unique characteristics? Until now, researchers only had a limited view of the underlying mechanisms.

    “The functionality of 2-D materials critically depends on how their atoms move,” said SLAC and Stanford researcher Aaron Lindenberg, who led the research team. “However, no one has ever been able to study these motions on the atomic level and in real time before. Our results are an important step toward engineering next-generation devices from single-layer materials.” The research team looked at molybdenum disulfide, or MoS2, which is widely used as a lubricant but takes on a number of interesting behaviors when in single-layer form – more than 150,000 times thinner than a human hair.

    For example, the monolayer form is normally an insulator, but when stretched, it can become electrically conductive. This switching behavior could be used in thin, flexible electronics and to encode information in data storage devices. Thin films of MoS2 are also under study as possible catalysts that facilitate chemical reactions. In addition, they capture light very efficiently and could be used in future solar cells.

    Because of this strong interaction with light, researchers also think they may be able to manipulate the material’s properties with light pulses.

    “To engineer future devices, control them with light and create new properties through systematic modifications, we first need to understand the structural transformations of monolayers on the atomic level,” said Stanford researcher Ehren Mannebach, the study’s lead author.

    Visualization of laser-induced motions of atoms (black and yellow spheres) in a molybdenum disulfide monolayer: The laser pulse creates wrinkles with large amplitudes – more than 15 percent of the layer’s thickness – that develop in a trillionth of a second. (K.-A. Duerloo/Stanford)

    Electron Camera Reveals Ultrafast Motions

    Previous analyses showed that single layers of molybdenum disulfide have a wrinkled surface. However, these studies only provided a static picture. The new study reveals for the first time how surface ripples form and evolve in response to laser light.

    Researchers at SLAC placed their monolayer samples, which were prepared by Linyou Cao’s group at North Carolina State University, into a beam of very energetic electrons. The electrons, which come bundled in ultrashort pulses, scatter off the sample’s atoms and produce a signal on a detector that scientists use to determine where atoms are located in the monolayer. This technique is called ultrafast electron diffraction.

    The team then used ultrashort laser pulses to excite motions in the material, which cause the scattering pattern to change over time.

    “Combined with theoretical calculations, these data show how the light pulses generate wrinkles that have large amplitudes – more than 15 percent of the layer’s thickness – and develop extremely quickly, in about a trillionth of a second. This is the first time someone has visualized these ultrafast atomic motions,” Lindenberg said.

    Once scientists better understand monolayers of different materials, they could begin putting them together and engineer mixed materials with completely new optical, mechanical, electronic and chemical properties.

    The research was supported by DOE’s Office of Science, the SLAC UED/UEM program development fund, the German National Academy of Sciences, and the U.S. National Science Foundation.


    To study ultrafast atomic motions in a single layer of molybdenum disulfide, researchers followed a pump-probe approach: They excited motions with a laser pulse (pump pulse, red) and probed the laser-induced structural changes with a subsequent electron pulse (probe pulse, blue). The electrons of the probe pulse scatter off the monolayer’s atoms (blue and yellow spheres) and form a scattering pattern on the detector – a signal the team used to determine the monolayer structure. By recording patterns at different time delays between the pump and probe pulses, the scientists were able to determine how the atomic structure of the molybdenum disulfide film changed over time. (SLAC National Accelerator Laboratory)

    Citation: E. M. Mannebach et al., Nano Letters, 31 August 2015 (10.1021/acs.nanolett.5b02805)

    Press Office Contact: Andrew Gordon, agordon@slac.stanford.edu, (650) 926-2282

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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 4:01 pm on September 9, 2015 Permalink | Reply
    Tags: , , Material Sciences, ,   

    From MIT: “How to spawn an ‘exceptional ring'” 

    MIT News

    September 9, 2015
    David L. Chandler

    A schematic drawing of how a ring of exceptional points (shown in white) can be spawned from a Dirac point (a dot), and thus change the dispersion from the normal, widely known conical shape into an exotic lantern-like shape. Courtesy of the researchers

    A schematic picture showing the conical dispersion of a Dirac cone being deformed into a new hour-glass-like shape due to radiation. Courtesy of the researchers

    The Dirac cone, named after British physicist Paul Dirac, started as a concept in particle and high-energy physics and has recently became important in research in condensed matter physics and material science. It has since been found to describe aspects of graphene, a two dimensional form of carbon, suggesting the possibility of applications across various fields.

    Graphene is an atomic-scale honeycomb lattice made of carbon atoms.

    Now physicists at MIT have found another unusual phenomenon produced by the Dirac cone: It can spawn a phenomenon described as a “ring of exceptional points.” This connects two fields of research in physics and may have applications in building powerful lasers, precise optical sensors, and other devices.

    The results are published this week in the journal Nature by MIT postdoc Bo Zhen, Yale University postdoc Chia Wei Hsu, MIT physics professors Marin Soljačić and John Joannopoulos, and five others.

    This work represents “the first experimental demonstration of a ring of exceptional points,” Zhen says, and is the first study that relates research in exceptional points with the physical concepts of parity-time symmetry and Dirac cones.

    Individual exceptional points are a peculiar phenomenon unique to an unusual class of physical systems that can lead to counterintuitive phenomena. For example, around these points, opaque materials may seem more transparent, and light may be transmitted only in one direction. However, the practical usefulness of these properties is limited by absorption loss introduced in the materials.

    The MIT team used a nanoengineered material called a photonic crystal to produce the exceptional ring. This new ring of exceptional points is different from those studied by other groups, making it potentially more practical, the researchers say.

    “Instead of absorption loss, we adopt a different loss mechanism — radiation loss — which does not affect the device performance,” Zhen says. “In fact, radiation loss is useful and is necessary in devices like lasers.”

    This phenomenon could enable creation of new kinds of optical systems with novel features, the MIT team says.

    “One important possible application of this work is in creating a more powerful laser system than existing technologies allow,” Soljačić says. To build a more powerful laser requires a bigger lasing area, but that introduces more unwanted “modes” for light, which compete for power, limiting the final output.

    “Photonic crystal surface-emitting lasers are a very promising candidate for the next generation of high-quality, high-power compact laser systems,” Soljačić says, “and we estimate we can improve the output power limit of such lasers by a factor of at least 10.”

    “Our system could also be used for high-precision detectors for biological or chemical materials, because of its extreme sensitivity,” Hsu says. This improved sensitivity is due to another exotic property of the exceptional points: Their response to perturbations is not linear to the perturbation strength.

    Normally, Hsu says, it becomes very difficult to detect a substance when its concentration is low. When the concentration of the target substance is reduced by a million times, the overall signal also decreases by a million times, which can make it too small to detect.

    “But at an exceptional point, it’s not linear anymore,” Hsu says, “and the signal goes down by only 1,000 times, providing a much bigger response that can now be detected.”

    Demetrios Christodoulides, a professor of optics and photonics at the University of Central Florida who was not involved in this work, says, “This represents the first observation of an exceptional ring in a 2-D crystal associated with a two-dimensional band. The MIT work opens up a number of opportunities … in particular, around exceptional points where systems are known on many occasions to behave in a peculiar fashion.”

    The research team also included Yuichi Igarashi of NEC Corp. in Japan and MIT research scientist Ling Lu, postdoc Ido Kaminer, Harvard University graduate student Adi Pick, and Song-Liang Chua at DSO National Laboratory in Singapore. The work was supported, in part, by the Army Research Office through MIT’s Institute for Soldier Nanotechnologies, the National Science Foundation, and the Department of Energy.

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  • richardmitnick 10:41 am on August 26, 2015 Permalink | Reply
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    From ars technica: “Quantum dots may be key to turning windows into photovoltaics” 

    Ars Technica
    ars technica

    Aug 26, 2015
    John Timmer

    Some day, this might generate electricity. Flickr user Ricardo Wang

    While wind may be one of the most economical power sources out there, photovoltaic solar energy has a big advantage: it can go small. While wind gets cheaper as turbines grow larger, the PV hardware scales down to fit wherever we have infrastructure. In fact, simply throwing solar on our existing building stock could generate a very large amount of carbon-free electricity.

    But that also highlights solar’s weakness: we have to install it after the infrastructure is in place, and that installation adds considerably to its cost. Now, some researchers have come up with some hardware that could allow photovoltaics to be incorporated into a basic building component: windows. The solar windows would filter out a small chunk of the solar spectrum and convert roughly a third of it to electricity.

    As you’re probably aware, photovoltaic hardware has to absorb light in order to work, and a typical silicon panel appears black. So, to put any of that hardware (and its supporting wiring) into a window that doesn’t block the view is rather challenging. One option is to use materials that only capture a part of the solar spectrum, but these tend to leave the light that enters the building with a distinctive tint.

    The new hardware takes a very different approach. The entire window is filled with a diffuse cloud of quantum dots that absorb almost all of the solar spectrum. As a result, the “glass” portion of things simply dims the light passing through the window slightly. (The quantum dots are actually embedded in a transparent polymer, but that could be embedded in or coat glass.) The end result is what optics people call a neutral density filter, something often used in photography. In fact, tests with the glass show that the light it transmits meets the highest standards for indoor lighting.

    Of course, simply absorbing the light doesn’t help generate electricity. And, in fact, the quantum dots aren’t used to generate the electricity. Instead, the authors generated quantum dots made of copper, indium, and selenium, covered in a layer of zinc sulfide. (The authors note that there are no toxic metals involved here.) These dots absorb light across a broad band of spectrum, but re-emit it at a specific wavelength in the infrared. The polymer they’re embedded in acts as a waveguide to take many of the photons to the thin edge of the glass.

    And here’s where things get interesting: the wavelength of infrared the quantum dots emit happens to be very efficiently absorbed by a silicon photovoltaic device. So, if you simply place these devices along the edges of the glass, they’ll be fed a steady diet of photons.

    The authors model the device’s behavior and find that nearly half the infrared photons end up being fed the photovoltaic devices (equal amounts get converted to heat or escape the window entirely). It’s notable that the devices are small, though (about 12cm squares)—larger panes would presumably allow even more photons to escape.

    The authors tested a few of the devices, one that filtered out 20 percent of the sunlight and one that only captured 10 percent. The low-level filter sent about one percent of the incident light to the sides, while the darker one sent over three percent.

    There will be losses in the conversion to electricity as well, so this isn’t going to come close to competing with a dedicated panel on a sunny roof. Which is fine, because it’s simply not meant to. Any visit to a major city will serve as a good reminder that we’re regularly building giant walls of glass that currently reflect vast amounts of sunlight, blinding or baking (or both!) the city’s inhabitants on a sunny day. If we could cheaply harvest a bit of that instead, we’re ahead of the game.

    Nature Nanotechnology, 2015. DOI: 10.1038/NNANO.2015.178 (About DOIs).

    See the full article here.

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    Ars Technica was founded in 1998 when Founder & Editor-in-Chief Ken Fisher announced his plans for starting a publication devoted to technology that would cater to what he called “alpha geeks”: technologists and IT professionals. Ken’s vision was to build a publication with a simple editorial mission: be “technically savvy, up-to-date, and more fun” than what was currently popular in the space. In the ensuing years, with formidable contributions by a unique editorial staff, Ars Technica became a trusted source for technology news, tech policy analysis, breakdowns of the latest scientific advancements, gadget reviews, software, hardware, and nearly everything else found in between layers of silicon.

    Ars Technica innovates by listening to its core readership. Readers have come to demand devotedness to accuracy and integrity, flanked by a willingness to leave each day’s meaningless, click-bait fodder by the wayside. The result is something unique: the unparalleled marriage of breadth and depth in technology journalism. By 2001, Ars Technica was regularly producing news reports, op-eds, and the like, but the company stood out from the competition by regularly providing long thought-pieces and in-depth explainers.

    And thanks to its readership, Ars Technica also accomplished a number of industry leading moves. In 2001, Ars launched a digital subscription service when such things were non-existent for digital media. Ars was also the first IT publication to begin covering the resurgence of Apple, and the first to draw analytical and cultural ties between the world of high technology and gaming. Ars was also first to begin selling its long form content in digitally distributable forms, such as PDFs and eventually eBooks (again, starting in 2001).

  • richardmitnick 10:29 am on August 26, 2015 Permalink | Reply
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    From EMSL: “A new material for transparent electronics” 



    August 17, 2015
    No Writer Credit

    Specialized crystalline films revealed to be highly conductive and transparent

    Scanning transmission electron micrograph of a p-Sr0.12La0.88 CrO3/n-SrTiO3(001) heterojunction.

    Results: The performance of solar cells, flat panel displays, and other electronics are limited by today’s materials. A new material, created by modifying a transparent insulating oxide, replacing up to 25 percent of the lanthanum ions in the host material with strontium ions, offers considerable promise. The new perovskite film, with the formula SrxLa1-xCrO3, (x up to 0.25), conducts electricity more effectively than the unmodified oxide and yet retains much of the transparency to visible light exhibited by the pure material.

    Why It Matters: Materials that are both electrically conductive and optically transparent are needed for more efficient solar cells, light detectors, and several kinds of electronic devices that are by nature transparent to visible light. Of particular importance are new materials that conduct electricity by using missing electrons, otherwise known as “holes.” The new perovskite film falls into this category.

    Methods: The development of high-performance transparent conducting oxides (TCOs) is critical to many technologies ranging from flat panel displays to solar cells. Although electron conducting (n-type) TCOs are presently in use in many devices, their hole-conducting (p-type) counterparts have not been commercialized as candidate materials because they exhibit much lower conductivities. Scientists at Pacific Northwest National Laboratory along with collaborators at Binghamton University and the Paul Drude Institute in Berlin show that La1-xSrxCrO3 (LSCO) is a new p-type TCO with considerable potential. The researchers demonstrate that crystalline LSCO films deposited on SrTiO3(001) by molecular beam epitaxy show figures of merit which are highly competitive with best p-type TCOs reported to date, and yet are more stable and structurally compatible with the workhorse materials of oxide electronics, as seen in the image. Being structurally and chemically compatible with other perovskite oxides, perovksite LSCO offers considerable promise in the design of all-perovskite oxide electronics.

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    EMSL campus

    Welcome to EMSL. EMSL is a national scientific user facility that is funded and sponsored by DOE’s Office of Biological & Environmental Research. As a user facility, our scientific capabilities – people, instruments and facilities – are available for use by the global research community. We support BER’s mission to provide innovative solutions to the nation’s environmental and energy production challenges in areas such as atmospheric aerosols, feedstocks, global carbon cycling, biogeochemistry, subsurface science and energy materials.

    A deep understanding of molecular-level processes is critical to gaining a predictive, systems-level understanding of the impacts of aerosols and terrestrial systems on climate change; making clean, affordable, abundant energy; and cleaning up our legacy wastes. Visit our Science page to learn how EMSL leads in these areas, through our Science Themes.

    Team’s in Our DNA. We approach science differently than many institutions. We believe in – and have proven – the value of drawing together members of the scientific community and assembling the people, resources and facilities to solve problems. It’s in our DNA, since our founder Dr. Wiley’s initial call to create a user facility that would facilitate “synergism between the physical, mathematical, and life sciences.” We integrate experts across disciplines; experiment with theory; and our user program proposal calls with other user facilities.

    We proudly provide an enriched, customized experience that allows users to connect with our people and capabilities in an environment where we focus on solving problems. We collaborate with researchers from academia, government labs and industry, and from nearly all 50 states and from other countries.

  • richardmitnick 4:22 pm on August 23, 2015 Permalink | Reply
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    From Yale: “With Polymer Blend, Researchers Develop More Efficient Solar Cells” 

    Yale University bloc

    Yale University

    No Writer Credit


    Yale researchers have significantly increased the efficiency of a polymer solar cell by using a technique that mimics how plants use solar energy and forcing two otherwise incompatible molecules to work together to cover the full color spectrum.

    The researchers, in Dr. Andre Taylor’s Transformative Materials & Devices Lab, developed a solar cell that performed 22.5 percent better than conventional organic solar cells. Their results were published online this month in the Journal of Materials Chemistry A demonstrating a power conversion efficiency of 8.7 percent.

    Most commercial solar cells today are made from silicon. But polymer cells cost less and weigh less, making them an appealing alternative. The problem is that they’re not very efficient – they fail to convert nearly half their absorbed light energy to electrical power. That’s partly because the polymers used in these cells don’t line up well enough to allow energy to exit the cell easily.

    However, because polymers have a mechanical flexibility that silicon cells don’t, researchers are hopeful that they will find ways around these shortcomings.
    “We are starting to approach the limits for improvements that can done with conventional silicon solar cells,” Taylor said. “But with organic polymers you can tweak and do things to them with significant results.”

    In a 2013 study in Nature, Taylor’s lab was the first to show that this can occur between small molecules and a polymer known as P3HT. It’s now demonstrating some of those same benefits in polymer blends.

    Conventional organic solar cells, known as binary solar cells, have one polymer serving as an electron donor and a fullerene derivative as the electron acceptor. Ternary cells – the kind used in this study – can have either two donors and one acceptor or one donor and two acceptors. In most cases, though, more efficient ternary cells usually have two donors and one acceptor since donors are predominantly responsible for light absorption.

    The most recent study uses two polymers, P3HT and PTB7, which are both light-sensitive molecules known as chromophores. In one sense, the two are complementary: P3HT absorbs the blue-green side of the light spectrum, while PTB7 absorbs primarily at the yellow-red spectrum. Together, the two cover a large portion of the visible-light spectrum. Rather than working independently, the proximity of the two polymers also facilitates what’s known as Förster resonance energy transfer (FRET) to occur. That’s when energy is transferred between two chromophores over long distances.

    The problem is how these two polymers align.

    “We are blending two different types of polymers, so they align in different ways,” said TengHooi Goh, lead author of the paper. “P3HT aligns in a way that it stands like a wall and PTB7 is positioned more like a stack of pancakes.”

    “They work well optically, but the contradicting alignment is bad for electron transport,” added Taylor, senior author of the paper.

    To get around this problem, the researchers used a technique known as solvent vapor annealing (SVA), in which they chemically modify the properties of the polymers to better align. The more commonly used method is thermal annealing, but heat has been found to diminish the performance of the polymers. Goh said that SVA can potentially solve incompatible alignment problems in complex polymer systems and drive the efficiency of organic photovoltaics to a new heights.

    The other authors of the paper, Panchromatic Polymer-polymer Ternary Solar Cells Enhanced by Förster Resonance Energy Transfer and Solvent Vapor Annealing, are Jing-Shun Huang, Benjamin Bartolome,Matthew Y. Sfeir, Michelle Vaisman, and Minjoo Lee.

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    Yale University Campus

    Yale University comprises three major academic components: Yale College (the undergraduate program), the Graduate School of Arts and Sciences, and the professional schools. In addition, Yale encompasses a wide array of centers and programs, libraries, museums, and administrative support offices. Approximately 11,250 students attend Yale.

  • richardmitnick 10:09 am on August 18, 2015 Permalink | Reply
    Tags: , , Material Sciences,   

    From MIT: “Going solid-state could make batteries safer and longer-lasting” 

    MIT News

    August 17, 2015
    David L. Chandler

    llustrations show the crystal structure of a superionic conductor. The backbone of the material is a body-centred cubic-like arrangement of sulphur anions. Lithium atoms are depicted in green, sulfur atoms in yellow, PS4 tetrahedra in purple, and GeS4 tetrahedra in blue. Researchers have revealed the fundamental relationship between anion packing and ionic transport in fast lithium-conducting materials. Image: Yan Wang

    New research paves the way for rechargeable batteries with almost indefinite lifetimes, researchers say.

    If you pry open one of today’s ubiquitous high-tech devices — whether a cellphone, a laptop, or an electric car — you’ll find that batteries take up most of the space inside. Indeed, the recent evolution of batteries has made it possible to pack ample power in small places.

    But people still always want their devices to last even longer, or go further on a charge, so researchers work night and day to boost the power a given size battery can hold. Rare, but widely publicized, incidents of overheating or combustion in lithium-ion batteries have also highlighted the importance of safety in battery technology.

    Now researchers at MIT and Samsung, and in California and Maryland, have developed a new approach to one of the three basic components of batteries, the electrolyte. The new findings are based on the idea that a solid electrolyte, rather than the liquid used in today’s most common rechargeables, could greatly improve both device lifetime and safety — while providing a significant boost in the amount of power stored in a given space.

    The results are reported in the journal Nature Materials in a paper by MIT postdoc Yan Wang, visiting professor of materials science and engineering Gerbrand Ceder, and five others. They describe a new approach to the development of solid-state electrolytes that could simultaneously address the greatest challenges associated with improving lithium-ion batteries, the technology now used in everything from cellphones to electric cars.

    The electrolyte in such batteries — typically a liquid organic solvent whose function is to transport charged particles from one of a battery’s two electrodes to the other during charging and discharging — has been responsible for the overheating and fires that, for example, resulted in a temporary grounding of all of Boeing’s 787 Dreamliner jets, Ceder explains. Others have attempted to find a solid replacement for the liquid electrolyte, but this group is the first to show that this can be done in a formulation that fully meets the needs of battery applications.

    Solid-state electrolytes could be “a real game-changer,” Ceder says, creating “almost a perfect battery, solving most of the remaining issues” in battery lifetime, safety, and cost.

    Costs have already been coming down steadily, he says. But as for safety, replacing the electrolyte would be the key, Ceder adds: “All of the fires you’ve seen, with Boeing, Tesla, and others, they are all electrolyte fires. The lithium itself is not flammable in the state it’s in in these batteries. [With a solid electrolyte] there’s no safety problem — you could throw it against the wall, drive a nail through it — there’s nothing there to burn.”

    The proposed solid electrolyte also holds other advantages, he says: “With a solid-state electrolyte, there’s virtually no degradation reactions left” — meaning such batteries could last through “hundreds of thousands of cycles.”

    The key to making this feasible, Ceder says, was finding solid materials that could conduct ions fast enough to be useful in a battery.

    “There was a view that solids cannot conduct fast enough,” he says. “That paradigm has been overthrown.”

    The research team was able to analyze the factors that make for efficient ion conduction in solids, and home in on compounds that showed the right characteristics. The initial findings focused on a class of materials known as superionic lithium-ion conductors, which are compounds of lithium, germanium, phosphorus, and sulfur, but the principles derived from this research could lead to even more effective materials, the team says.

    The research that led to a workable solid-state electrolyte was part of an ongoing partnership with the Korean electronics company Samsung, through the Samsung Advanced Institute of Technology in Cambridge, Massachusetts, Ceder says. That alliance also has led to important advances in the use of quantum-dot materials to create highly efficient solar cells and sodium batteries, he adds.

    This solid-state electrolyte has other, unexpected side benefits: While conventional lithium-ion batteries do not perform well in extreme cold, and need to be preheated at temperatures below roughly minus 20 degrees Fahrenheit, the solid-electrolyte versions can still function at those frigid temperatures, Ceder says.

    The solid-state electrolyte also allows for greater power density — the amount of power that can be stored in a given amount of space. Such batteries provide a 20 to 30 percent improvement in power density — with a corresponding increase in how long a battery of a given size could power a phone, a computer, or a car.

    The team also included MIT graduate student William Richards and postdoc Jae Chul Kim; Shyue Ping Ong at the University of California at San Diego; Yifei Mo at the University of Maryland; and Lincoln Miara at Samsung. The work is part of an alliance between MIT and the Samsung Advanced Institute of Technology focusing on the development of materials for clean energy.

    See the full article here.

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  • richardmitnick 1:17 pm on August 15, 2015 Permalink | Reply
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    From TUM: Graphene gets competition” 

    Techniche Universitat Munchen

    Techniche Universitat Munchen

    Layered semiconducting black arsenic phosphorus as an alternative to silicon

    Prof. Dr. Tom Nilges
    Technical University of Munich
    Synthesis and Characterization of Innovative Materials
    Lichtenbergstr. 4, 85748 Garching, Germany
    Tel.: +49 89 289 13110 – E-mail – Internet

    Graphene, the only one atom thick carbon network, achieved overnight fame with the 2010 Nobel Prize. But now comes competition: Such layers can also be formed by black phosphorous. Chemists at the Technische Universität München (TUM) have now developed a semiconducting material in which individual phosphorus atoms are replaced by arsenic. In a collaborative international effort, American colleagues have built the first field-effect transistors from the new material.

    For many decades silicon has formed the basis of modern electronics. To date silicon technology could provide ever tinier transistors for smaller and smaller devices. But the size of silicon transistors is reaching its physical limit. Also, consumers would like to have flexible devices, devices that can be incorporated into clothing and the likes. However, silicon is hard and brittle. All this has triggered a race for new materials that might one day replace silicon.

    Black arsenic phosphorus might be such a material. Like graphene, which consists of a single layer of carbon atoms, it forms extremely thin layers. The array of possible applications ranges from transistors and sensors to mechanically flexible semiconductor devices. Unlike graphene, whose electronic properties are similar to those of metals, black arsenic phosphorus behaves like a semiconductor.

    Phosphorene vs. graphene

    A cooperation between the Technical University of Munich and the University of Regensburg on the German side and the University of Southern California (USC) and Yale University in the United States has now, for the first time, produced a field effect transistor made of black arsenic phosphorus. The compounds were synthesized by Marianne Koepf at the laboratory of the research group for Synthesis and Characterization of Innovative Materials at the TUM. The field effect transistors were built and characterized by a group headed by Professor Zhou and Dr. Liu at the Department of Electrical Engineering at USC.

    The new technology developed at TUM allows the synthesis of black arsenic phosphorus without high pressure. This requires less energy and is cheaper. The gap between valence and conduction bands can be precisely controlled by adjusting the arsenic concentration. “This allows us to produce materials with previously unattainable electronic and optical properties in an energy window that was hitherto inaccessible,” says Professor Tom Nilges, head of the research group for Synthesis and Characterization of Innovative Materials.

    Detectors for infrared

    With an arsenic concentration of 83 percent the material exhibits an extremely small band gap of only 0.15 electron volts, making it predestined for sensors which can detect long wavelength infrared radiation. LiDAR (Light Detection and Ranging) sensors operate in this wavelength range, for example. They are used, among other things, as distance sensors in automobiles. Another application is the measurement of dust particles and trace gases in environmental monitoring.

    A further interesting aspect of these new, two-dimensional semiconductors is their anisotropic electronic and optical behavior. The material exhibits different characteristics along the x- and y-axes in the same plane. To produce graphene like films the material can be peeled off in ultra thin layers. The thinnest films reached so far are only two atomic layers thick.

    This work was supported by the Office of Naval Research (ONR), the Air Force Office of Scientific Research (AFOSR), the Center of Excellence for Nanotechnologies (CEGN) of King Abdul-Aziz City for Science and Technology (KACST), the German Research Council (DFG) and the TUM Graduate School.


    Black Arsenic–Phosphorus: Layered Anisotropic Infrared Semiconductors with Highly Tunable Compositions and Properties
    Bilu Liu, Marianne Köpf, Ahmad N. Abbas, Xiaomu Wang, Qiushi Guo, Yichen Jia, Fengnian Xia, Richard Weihrich, Frederik Bachhuber, Florian Pielnhofer, Han Wang, Rohan Dhall, Stephen B. Cronin, Mingyuan Ge, Xin Fang, Tom Nilges, Chongwu Zhou
    Adv. Mater., 2015, Early View – DOI: 10.1002/adma.201501758

    See the full article here.

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    Techniche Universitat Munchin Campus

    Technische Universität München (TUM) is one of Europe’s top universities. It is committed to excellence in research and teaching, interdisciplinary education and the active promotion of promising young scientists. The university also forges strong links with companies and scientific institutions across the world. TUM was one of the first universities in Germany to be named a University of Excellence. Moreover, TUM regularly ranks among the best European universities in international rankings.

  • richardmitnick 4:41 pm on August 2, 2015 Permalink | Reply
    Tags: , Material Sciences,   

    From phys.org: “From cameras to computers, new material could change how we work and play” 


    August 2, 2015
    Northeastern University

    An artistic rendering of novel magnetism in 2D-BNCO sheets, the new material Swastik Kar and Srinivas Sridhar created.

    Serendipity has as much a place in science as in love. That’s what Northeastern physicists Swastik Kar and Srinivas Sridhar found during their four-year project to modify graphene, a stronger-than-steel infinitesimally thin lattice of tightly packed carbon atoms. Primarily funded by the Army Research Laboratory and Defense Advanced Research Projects Agency, or DARPA, the researchers were charged with imbuing the decade-old material with thermal sensitivity for use in infrared imaging devices such as night-vision goggles for the military.

    What they unearthed, published Friday in the journal Science Advances, was so much more: an entirely new material spun out of boron, nitrogen, carbon, and oxygen that shows evidence of magnetic, optical, and electrical properties as well as DARPA’s sought-after thermal ones. Its potential applications run the gamut: from 20-megapixel arrays for cellphone cameras to photo detectors to atomically thin transistors that when multiplied by the billions could fuel computers.

    “We had to start from scratch and build everything,” says Kar, an assistant professor of physics in the College of Science. “We were on a journey, creating a new path, a new direction of research.”

    The pair was familiar with “alloys,” controlled combinations of elements that resulted in materials with properties that surpassed graphene’s—for example, the addition of boron and nitrogen to graphene’s carbon to connote the conductivity necessary to produce an electrical insulator. But no one had ever thought of choosing oxygen to add to the mix.

    What led the Northeastern researchers to do so?

    “Well, we didn’t choose oxygen,” says Kar, smiling broadly. “Oxygen chose us.”

    Oxygen, of course, is everywhere. Indeed, Kar and Sridhar spent a lot of time trying to get rid of the oxygen seeping into their brew, worried that it would contaminate the “pure” material they were seeking to develop.

    “That’s where the Aha! moment happened for us,” says Kar. “We realized we could not ignore the role that oxygen plays in the way these elements mix together.”

    “So instead of trying to remove oxygen, we thought: Let’s control its introduction,” adds Sridhar, the Arts and Sciences Distinguished Professor of Physics and director of Northeastern’s Electronic Materials Research Institute.

    Oxygen, it turned out, was behaving in the reaction chamber in a way the scientists had never anticipated: It was determining how the other elements—the boron, carbon, and nitrogen—combined in a solid, crystal form, while also inserting itself into the lattice. The trace amounts of oxygen were, metaphorically, “etching away” some of the patches of carbon, explains Kar, making room for the boron and nitrogen to fill the gaps.

    “It was as if the oxygen was controlling the geometric structure,” says Sridhar.

    They named the new material, sensibly, 2D-BNCO, representing the four elements in the mix and the two-dimensionality of the super-thin lightweight material, and set about characterizing and manufacturing it, to ensure it was both reproducible and scalable. That meant investigating the myriad permutations of the four ingredients, holding three constant while varying the measurement of the remaining one, and vice versa, multiple times over.

    After each trial, they analyzed the structure and the functional properties of the product— electrical, optical—using electron microscopes and spectroscopic tools, and collaborated with computational physicists, who created models of the structures to see if the configurations would be feasible in the real world.

    Next they will examine the new material’s mechanical properties and begin to experimentally validate the magnetic ones conferred, surprisingly, by the intermingling of these four nonmagnetic elements. “You begin to see very quickly how complicated that process is,” says Kar.

    Helping with that complexity were collaborators from around the globe. In addition to Northeastern associate research scientists, postdoctoral fellows, and graduate students, contributors included researchers in government, industry, and academia from the United States, Mexico, and India.

    “There is still a long way to go but there are clear indications that we can tune the electrical properties of these materials,” says Sridhar. “And if we find the right combination, we will very likely get to that point where we reach the thermal sensitivity that DARPA was initially looking for as well as many as-yet unforeseen applications.”

    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 10:40 am on July 30, 2015 Permalink | Reply
    Tags: , , Material Sciences, ,   

    From MIT: “How to look for a few good catalysts” 

    MIT News

    July 30, 2015
    David L. Chandler

    New research shows non-wetting surfaces promote chemical reaction rates.

    Materials that have good wetting properties, as illustrated on the left, where droplets spread out flat, tend to have hydroxyl groups attached to the surface, which inhibits catalytic activity. Materials that repel water, as shown at right, where droplets form sharp, steep boundaries, are more conducive to catalytic activity, as shown by the reactions among small orange molecules. Illustration: Xiao Renshaw Wang

    Two key physical phenomena take place at the surfaces of materials: catalysis and wetting. A catalyst enhances the rate of chemical reactions; wetting refers to how liquids spread across a surface.

    Now researchers at MIT and other institutions have found that these two processes, which had been considered unrelated, are in fact closely linked. The discovery could make it easier to find new catalysts for particular applications, among other potential benefits.

    “What’s really exciting is that we’ve been able to connect atomic-level interactions of water and oxides on the surface to macroscopic measurements of wetting, whether a surface is hydrophobic or hydrophilic, and connect that directly with catalytic properties,” says Yang Shao-Horn, the W.M. Keck Professor of Energy at MIT and a senior author of a paper describing the findings in the Journal of Physical Chemistry C. The research focused on a class of oxides called perovskites that are of interest for applications such as gas sensing, water purification, batteries, and fuel cells.

    Since determining a surface’s wettability is “trivially easy,” says senior author Kripa Varanasi, an associate professor of mechanical engineering, that determination can now be used to predict a material’s suitability as a catalyst. Since researchers tend to specialize in either wettability or catalysis, this produces a framework for researchers in both fields to work together to advance understanding, says Varanasi, whose research focuses primarily on wettability; Shao-Horn is an expert on catalytic reactions.

    “We show how wetting and catalysis, which are both surface phenomena, are related,” Varanasi says, “and how electronic structure forms a link between both.”

    While both effects are important in a variety of industrial processes and have been the subject of much empirical research, “at the molecular level, we understand very little about what’s happening at the interface,” Shao-Horn says. “This is a step forward, providing a molecular-level understanding.”

    “It’s primarily an experimental technique” that made the new understanding possible, explains Kelsey Stoerzinger, an MIT graduate student and the paper’s lead author. While most attempts to study such surface science use instruments requiring a vacuum, this team used a device that could study the reactions in humid air, at room temperature, and with varying degrees of water vapor present. Experiments using this system, called ambient pressure X-ray photoelectron spectroscopy, revealed that the reactivity with water is key to the whole process, she says.

    The water molecules break apart to form hydroxyl groups — an atom of oxygen bound to an atom of hydrogen — bonded to the material’s surface. These reactive compounds, in turn, are responsible for increasing the wetting properties of the surface, while simultaneously inhibiting its ability to catalyze chemical reactions. Therefore, for applications requiring high catalytic activity, the team found, a key requirement is that the surface be hydrophobic, or non-wetting.

    “Ideally, this understanding helps us design new catalysts,” Stoerzinger says. If a given material “has a lower affinity for water, it has a higher affinity for catalytic activity.”

    Shao-Horn notes that this is an initial finding, and that “extension of these trends to broader classes of materials and ranges of hydroxyl affinity requires further investigation.” The team has already begun further exploration of these areas. This research, she says, “opens up the space of materials and surfaces we might think about” for both catalysis and wetting.

    The research team also included graduate student Wesley Hong, visiting scientist Livia Giordano, and postdocs Yueh-Lin Lee and Gisele Azimi at MIT; Ethan Crumlin and Hendrik Bluhm at Lawrence Berkeley National Laboratory; and Michael Biegalski at Oak Ridge National Laboratory. The work was supported by the National Science Foundation and the U.S. Department of Energy.

    See the full article here.

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  • richardmitnick 3:55 pm on July 27, 2015 Permalink | Reply
    Tags: , , Material Sciences, ,   

    From SLAC: “New ‘Molecular Movie’ Reveals Ultrafast Chemistry in Motion” 

    SLAC Lab

    June 22, 2015

    This video describes how the Linac Coherent Light Source, an X-ray free-electron laser at SLAC National Accelerator Laboratory, provided the first direct measurements of how a ring-shaped gas molecule unravels in the millionths of a billionth of a second after it is split open by light. The measurements were compiled in sequence to form the basis for computer animations showing molecular motion. (SLAC National Accelerator Laboratory)

    Scientists for the first time tracked ultrafast structural changes, captured in quadrillionths-of-a-second steps, as ring-shaped gas molecules burst open and unraveled. Ring-shaped molecules are abundant in biochemistry and also form the basis for many drug compounds. The study points the way to a wide range of real-time X-ray studies of gas-based chemical reactions that are vital to biological processes.

    This illustration shows shape changes that occur in quadrillionths-of-a-second intervals in a ring-shaped molecule that was broken open by light. The molecular motion was measured using SLAC’s Linac Coherent Light Source X-ray laser. The colored chart shows a theoretical model of molecular changes that syncs well with the actual results. The squares in the background represent panels in an LCLS X-ray detector. (SLAC National Accelerator Laboratory)

    Researchers working at the Department of Energy’s SLAC National Accelerator Laboratory compiled the full sequence of steps in this basic ring-opening reaction into computerized animations that provide a “molecular movie” of the structural changes.

    Conducted at SLAC’s Linac Coherent Light Source, a DOE Office of Science User Facility, the pioneering study marks an important milestone in precisely tracking how gas-phase molecules transform during chemical reactions on the scale of femtoseconds. A femtosecond is a millionth of a billionth of a second.

    “This fulfills a promise of LCLS: Before your eyes, a chemical reaction is occurring that has never been seen before in this way,” said Mike Minitti, a SLAC scientist who led the experiment in collaboration with Peter Weber at Brown University. The results are featured in the June 22 edition of Physical Review Letters.

    “LCLS is a game-changer in giving us the ability to probe this and other reactions in record-fast timescales,” Minitti said, “down to the motion of individual atoms.” The same method can be used to study more complex molecules and chemistry.

    The free-floating molecules in a gas, when studied with the uniquely bright X-rays at LCLS, can provide a very clear view of structural changes because gas molecules are less likely to be tangled up with one another or otherwise obstructed, he added. “Until now, learning anything meaningful about such rapid molecular changes in a gas using other X-ray sources was very limited, at best.”

    New Views of Chemistry in Action

    The study focused on the gas form of 1,3-cyclohexadiene (CHD), a small, ring-shaped organic molecule derived from pine oil. Ring-shaped molecules play key roles in many biological and chemical processes that are driven by the formation and breaking of chemical bonds. The experiment tracked how the ringed molecule unfurls after a bond between two of its atoms is broken, transforming into a nearly linear molecule called hexatriene.

    “There had been a long-standing question of how this molecule actually opens up,” Minitti said. “The atoms can take different paths and directions. Tracking this ultimately shows how chemical reactions are truly progressing, and will likely lead to improvements in theories and models.”

    The Making of a Molecular Movie

    In the experiment, researchers excited CHD vapor with ultrafast ultraviolet laser pulses to begin the ring-opening reaction. Then they fired LCLS X-ray laser pulses at different time intervals to measure how the molecules changed their shape.

    Researchers compiled and sorted over 100,000 strobe-like measurements of scattered X-rays. Then, they matched these measurements to computer simulations that show the most likely ways the molecule unravels in the first 200 quadrillionths of a second after it opens. The simulations, performed by team member Adam Kirrander at the University of Edinburgh, show the changing motion and position of its atoms.

    Each interval in the animations represents 25 quadrillionths of a second ­– about 1.3 trillion times faster than the typical 30-frames-per-second rate used to display TV shows.

    “It is a remarkable achievement to watch molecular motions with such incredible time resolution,” Weber said.

    A gas sample was considered ideal for this study because interference from any neighboring CHD molecules would be minimized, making it easier to identify and track the transformation of individual molecules. The LCLS X-ray pulses were like cue balls in a game of billiards, scattering off the electrons of the molecules and onto a position-sensitive detector that projected the locations of the atoms within the molecules.

    A Successful Test Case for More Complex Studies

    “This study can serve as a benchmark and springboard for larger molecules that can help us explore and understand even more complex and important chemistry,” Minitti said.

    Additional contributors included scientists at Brown and Stanford universities in the U.S. and the University of Edinburgh in the U.K. The work was supported by the DOE Office of Basic Energy Sciences.

    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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