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  • richardmitnick 2:58 pm on October 30, 2014 Permalink | Reply
    Tags: , , , Material Sciences,   

    From LBL: “Lord of the Microrings” 

    Berkeley Logo

    Berkeley Lab

    October 30, 2014
    Lynn Yarris (510) 486-5375

    A significant breakthrough in laser technology has been reported by the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab) and the University of California (UC) Berkeley. Scientists led by Xiang Zhang, a physicist with joint appointments at Berkeley Lab and UC Berkeley, have developed a unique microring laser cavity that can produce single-mode lasing even from a conventional multi-mode laser cavity. This ability to provide single-mode lasing on demand holds ramifications for a wide range of applications including optical metrology and interferometry, optical data storage, high-resolution spectroscopy and optical communications.

    “Losses are typically undesirable in optics but, by deliberately exploiting the interplay between optical loss and gain based on the concept of parity-time symmetry, we have designed a microring laser cavity that exhibits intrinsic single-mode lasing regardless of the gain spectral bandwidth,” says Zhang, who directs Berkeley Lab’s Materials Sciences Division and is UC Berkeley’s Ernest S. Kuh Endowed Chair Professor. “This approach also provides an experimental platform to study parity-time symmetry and phase transition phenomena that originated from quantum field theory yet have been inaccessible so far in experiments. It can fundamentally broaden optical science at both semi-classical and quantum levels”

    Xiang Zhang, director of Berkeley Lab’s Materials Sciences Division. (Photo by Roy Kaltschmidt)

    Zhang, who also directs the National Science Foundation’s Nano-scale Science and Engineering Center, and is a member of the Kavli Energy NanoSciences Institute at Berkeley, is the corresponding author of a paper in Science that describes this work. The paper is titled Single-Mode Laser by Parity-time Symmetry Breaking. Co-authors are Liang Feng, Zi Jing Wong, Ren-Min Ma and Yuan Wang.

    A laser cavity or resonator is the mirrored component of a laser in which light reflected multiple times yields a standing wave at certain resonance frequencies called modes. Laser cavities typically support multiple modes because their dimensions are much larger than optical wavelengths. Competition between modes limits the optical gain in amplitude and results in random fluctuations and instabilities in the emitted laser beams.

    “For many applications, single-mode lasing is desirable for its stable operation, better beam quality, and easier manipulation,” Zhang says. “Light emission from a single-mode laser is monochromatic with low phase and intensity noises, but creating sufficiently modulated optical gain and loss to obtain single-mode lasing has been a challenge.”
    Scanning electron microscope image of the fabricated PT symmetry microring laser cavity.

    Scanning electron microscope image of the fabricated PT symmetry microring laser cavity.

    While mode manipulation and selection strategies have been developed to achieve single-mode lasing, each of these strategies has only been applicable to specific configurations. The microring laser cavity developed by Zhang’s group is the first successful concept for a general design. The key to their success is using the concept of the breaking of parity-time (PT) symmetry. The law of parity-time symmetry dictates that the properties of a system, like a beam of light, remain the same even if the system’s spatial configuration is reversed, like a mirror image, or the direction of time runs backward. Zhang and his group discovered a phenomenon called “thresholdless parity-time symmetry breaking” that provides them with unprecedented control over the resonant modes of their microring laser cavity, a critical requirement for emission control in laser physics and applications.

    Liang Feng

    “Thresholdless PT symmetry breaking means that our light beam undergoes symmetry breaking once the gain/loss contrast is introduced no matter how large this contrast is,” says Liang Feng, lead author of the Science paper, a recent posdoc in Zhang’s group and now an assistant professor with the University at Buffalo. “In other words, the threshold for PT symmetry breaking is zero gain/loss contrast.”

    Zhang, Feng and the other members of the team were able to exploit the phenomenon of thresholdless PT symmetry breaking through the fabrication of a unique microring laser cavity. This cavity consists of bilayered structures of chromium/germanium arranged periodically in the azimuthal direction on top of a microring resonator made from an indium-gallium-arsenide-phosphide compound on a substrate of indium phosphide. The diameter of the microring is 9 micrometers.

    “The introduced rotational symmetry in our microring resonator is continuous, mimicking an infinite system,” says Feng. “The counterintuitive discovery we made is that PT symmetry does not hold even at an infinitesimal gain/loss modulation when a system is rotationally symmetric. This was not observed in previous one-dimensional PT modulation systems because those finite systems did not support any continuous symmetry operations.”

    Using the continuous rotational symmetry of their microring laser cavity to facilitate thresholdless PT symmetry breaking,

    Zhang, Feng and their collaborators are able to delicately manipulate optical gain and loss in such a manner as to ultimately yield single-mode lasing.

    “PT symmetry breaking means an optical mode can be gain-dominant for lasing, whereas PT symmetry means all the modes remain passive,” says Zi-Jing Wong, co-lead author and a graduate student in Zhang’s group. “With our microring laser cavity, we facilitate a desired mode in PT symmetry breaking, while keeping all other modes PT symmetric. Although PT symmetry breaking by itself cannot guarantee single-mode lasing, when acting together with PT symmetry for all other modes, it facilitates single-mode lasing.”

    In their Science paper, the researchers suggest that single-mode lasing through PT-symmetry breaking could pave the way to next generation optoelectronic devices for communications and computing as it enables the independent manipulation of multiple laser beams without the “crosstalk” problems that plague today’s systems. Their microring laser cavity concept might also be used to engineer optical modes in a typical multi-mode laser cavity to create a desired lasing mode and emission pattern.

    “Our microring laser cavities could also replace the large laser boxes that are routinely used in labs and industry today,” Feng says. “Moreover, the demonstrated single-mode operation regardless of gain spectral bandwidth may create a laser chip carrying trillions of informational signals at different frequencies. This would make it possible to shrink a huge datacenter onto a tiny photonic chip.”

    This research was supported by the Office of Naval Research MURI program.

    See the full article here.

    A U.S. Department of Energy National Laboratory Operated by the University of California

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  • richardmitnick 6:22 am on October 21, 2014 Permalink | Reply
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    From SLAC: “Puzzling New Behavior Found in High-Temperature Superconductors” 

    SLAC Lab

    October 20, 2014

    Ultimate Goal: A Super-efficient Way to Conduct Electricity at Room Temperature

    Research by an international team led by SLAC and Stanford scientists has uncovered a new, unpredicted behavior in a copper oxide material that becomes superconducting – conducting electricity without any loss – at relatively high temperatures.

    This new phenomenon – an unforeseen collective motion of electric charges coursing through the material – presents a challenge to scientists seeking to understand its origin and connection with high-temperature superconductivity. Their ultimate goal is to design a superconducting material that works at room temperature.

    “Making a room-temperature superconductor would save the world enormous amounts of energy,” said Thomas Devereaux, leader of the research team and director of the Stanford Institute for Materials and Energy Sciences (SIMES), which is jointly run with SLAC. “But to do that we must understand what’s happening inside the materials as they become superconducting. This result adds a new piece to this long-standing puzzle.”

    The results are published Oct. 19 in Nature Physics.

    Delving Into Doping Differences

    The researchers used an emerging X-ray technique called resonant inelastic X-ray scattering, or RIXS, to measure how the properties of a copper oxide change as extra electrons are added in a process known as doping. The team used the Swiss Light Source’s RIXS instrument, which currently has the world’s highest resolution and can reveal atomic-scale excitations – rapid changes in magnetism, electrical charge and other properties – as they move through the material.

    Copper oxide, a ceramic that normally doesn’t conduct electricity at all, becomes superconducting only when doped with other elements to add or remove electrons and chilled to low temperatures. Intriguingly, the electron-rich version loses its superconductivity when warmed to about 30 degrees above absolute zero (30 kelvins) while the electron-poor one remains superconducting up to 120 kelvins (minus 244 degrees Fahrenheit). One of the goals of the new research is to understand why they behave so differently.

    The experiments revealed a surprising increase of magnetic energy and the emergence of a new collective excitation in the electron-rich compounds, said Wei-sheng Lee, a SLAC staff scientist and lead author on the Nature Physics paper. “It’s very puzzling that these new electronic phenomena are not seen in the electron-poor material,” he said.

    SLAC Staff Scientist Wei-sheng Lee (SLAC National Accelerator Laboratory)

    Lee added that it’s unclear whether the new collective excitation is related to the ability of electrons to pair up and effortlessly conduct electricity – the hallmark of superconductivity – or whether it promotes or limits high-temperature superconductivity. Further insight can be provided by additional experiments using next-generation RIXS instruments that will become available in a few years at synchrotron light sources worldwide.

    A Long, Tortuous Path

    This discovery is the latest step in the long and tortuous path toward understanding high-temperature superconductivity.

    Scientists have known since the late 1950s why certain metals and simple alloys become superconducting when chilled 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.

    Starting in 1986, researchers discovered a number of materials that are superconducting at higher temperatures. By understanding and optimizing how these materials work, they hope to develop superconductors that work at room temperature and above.

    Until recently, 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 a recent theoretical simulation by SLAC and Stanford researchers concluded that these high-energy magnetic interactions are not the sole factor in copper oxide’s high-temperature superconductivity. The new results confirm that prediction, and also complement a 2012 report on the behavior of electron-poor copper oxides by a team that included Lee, Devereaux and several other SLAC/Stanford scientists.

    “Theorists must now incorporate this new ingredient into their explanations of how high-temperature superconductivity works,” said Thorsten Schmitt, leader of the RIXS team at the Paul Scherrer Institute in Switzerland, who collaborated on the study.

    Other researchers involved in the study were from Columbia University, University of Minnesota, AGH University of Science and Technology in Poland, National Synchrotron Radiation Research Center and National Tsing Hua University in Taiwan, and the Chinese Academy of Sciences. Funding for the research came from the DOE Office of Science, U.S. National Science Foundation and Swiss National Science Foundation.

    See the full article, with animation video, here.

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

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  • richardmitnick 2:41 pm on October 14, 2014 Permalink | Reply
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    From BNL: “Unstoppable Magnetoresistance” 

    Brookhaven Lab

    October 14, 2014
    Tien Nguyen

    Mazhar Ali, a fifth-year graduate student in the laboratory of Bob Cava, the Russell Wellman Moore Professor of Chemistry at Princeton University, has spent his academic career discovering new superconductors, materials coveted for their ability to let electrons flow without resistance. While testing his latest candidate, the semimetal tungsten ditelluride (WTe2), he noticed a peculiar result.

    Ali applied a magnetic field to a sample of WTe2, one way to kill superconductivity if present, and saw that its resistance doubled. Intrigued, Ali worked with Jun Xiong, a student in the laboratory of Nai Phuan Ong, the Eugene Higgins Professor of Physics at Princeton, to re-measure the material’s magnetoresistance, which is the change in resistance as a material is exposed to stronger magnetic fields.

    Mazhar Ali (left) and Steven Flynn (right), co-authors on the Nature article
    Photo credit: C. Todd Reichart

    “They have unique capabilities at Brookhaven. One is that they can measure diffraction at 10 Kelvin (-441 °F).”
    — Bob Cava, Princeton University

    “He noticed the magnetoresistance kept going up and up and up—that never happens.” said Cava. The researchers then exposed WTe2 to a 60-tesla magnetic field, close to the strongest magnetic field mankind can create, and observed a magnetoresistance of 13 million percent. The material’s magnetoresistance displayed unlimited growth, making it the only known material without a saturation point. The results were published on September 14 in the journal Nature.

    Electronic information storage is dependent on the use of magnetic fields to switch between distinct resistivity values that correlate to either a one or a zero. The larger the magnetoresistance, the smaller the magnetic field needed to change from one state to another, Ali said. Today’s devices use layered materials with so-called “giant magnetoresistance,” with changes in resistance of 20,000 to 30,000 percent when a magnetic field is applied. “Colossal magnetoresistance” is close to 100,000 percent, so for a magnetoresistance percentage in the millions, the researchers hoped to coin a new term.

    Crystal Structure of WTe2. Image credit: Nature

    Their original choice was “ludicrous” magnetoresistance, which was inspired by “ludicrous speed,” the fictional form of fast-travel used in the comedy “Spaceballs.” They even included an acknowledgement to director Mel Brooks. After other lab members vetoed “ludicrous,” the researchers considered “titanic” before Nature editors ultimately steered them towards the term “large magnetoresistance.”

    Terminology aside, the fact remained that the magnetoresistance values were extraordinarily high, a phenomenon that might be understood through the structure of WTe2. To look at the structure with an electron microscope, the research team turned to Jing Tao, a researcher at Brookhaven National Laboratory.

    Jing Tao

    “Jing is a great microscopist. They have unique capabilities at Brookhaven,” Cava said. “One is that they can measure diffraction at 10 Kelvin (-441 °F). Not too many people on Earth can do that, but Jing can.”

    Electron microscopy experiments revealed the presence of tungsten dimers, paired tungsten atoms, arranged in chains responsible for the key distortion from the classic octahedral structure type. The research team proposed that WTe2 owes its lack of saturation to the nearly perfect balance of electrons and electron holes, which are empty docks for traveling electrons. Because of its structure, WTe2 only exhibits magnetoresistance when the magnetic field is applied in a certain direction. This could be very useful in scanners, where multiple WTe2 devices could be used to detect the position of magnetic fields, Ali said.

    “Aside from making devices from WTe2, the question to ask yourself as a scientist is: How can it be perfectly balanced, is there something more profound,” Cava said.

    See the full article here.

    BNL Campus

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

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  • richardmitnick 4:42 pm on October 8, 2014 Permalink | Reply
    Tags: , Material Sciences,   

    From JPL at Caltech: “Metal Made Like Plastic May Have Big Impact” 


    Media Contact
    Elizabeth Landau
    NASA’s Jet Propulsion Laboratory, Pasadena, Calif.

    Open a door and watch what happens — the hinge allows it to open and close, but doesn’t permanently bend. This simple concept of mechanical motion is vital for making all kinds of movable structures, including mirrors and antennas on spacecraft. Material scientists at NASA’s Jet Propulsion Laboratory in Pasadena, California, are working on new, innovative methods of creating materials that can be used for motion-based mechanisms.

    This image shows components of a mirror structure that can be rotated very precisely by flexing parts made of a material scientists call “bulk metallic glass.” Credit: NASA/JPL-Caltech

    When a device moves because metal is flexing but isn’t permanently deformed, that’s called a compliant mechanism. Compliant mechanisms are all around us — in springs, surgical instruments, paperclips, clothespins and even micro-devices.

    Researchers at JPL, Brigham Young University in Provo, Utah, and the California Institute of Technology in Pasadena, describe a new methodology for creating complex, low-cost compliant mechanisms using a combination of novel materials and manufacturing techniques in a recent paper featured on the cover of the journal Advanced Engineering Materials. They demonstrate that materials called “bulk metallic glasses” have highly desirable properties for these mechanisms. These “glasses,” as the scientists call them, are metal alloys designed to have a random arrangement of atoms.

    “We’ve demonstrated that these metals not only have desirable properties for applications where flexibility and durability are required, but can also be injection-molded like a plastic and made cheaply,” said Douglas Hofmann, principal investigator of the research at JPL. Hofmann is a researcher in material science and metallurgy at JPL, and visiting associate at Caltech. “It offers an entirely new industry for high-performance metals,” he said.

    “Traditionally, titanium alloys have been used in compliant mechanisms because they were the best materials for the job, but titanium was also difficult to work with,” said Larry Howell, professor at Brigham Young University and study co-author. The new research shows that bulk metallic glasses have twice the strength and conventional flexibility of titanium alloys, while also boasting low melting temperatures.

    “I had been working on flexible mechanisms for a long time, and I said, that’s the perfect material we’ve been looking for all along,” said Brian Trease, a mechanical engineer at JPL who was a co-author on the study.

    Although material scientists have been focusing on the 3-D printing of titanium alloys, the new research shows that complex shapes can be molded at low cost, while maintaining their performance, when using bulk metallic glasses.

    “You could start making robot bearings or artificial limbs out of these if you want,” said Eric Homer, assistant professor of mechanical engineering at Brigham Young and lead author of the study. “These materials are ideal for mechanisms where you’re looking for flexibility and high strength.”

    In the new study, the researchers modeled the performance of a number of compliant mechanisms and predicted that bulk metallic glasses would be the highest performing material in those applications, typically doubling the predicted performance of titanium. To verify the model, a bistable spring, a device that can lock in two different positions, was made out of both titanium and metallic glass and mechanically tested to show the benefits. The researchers then worked with two commercial companies to fabricate more than 30 identical versions of the new mechanism, utilizing a brand new injection-molding technology available in industry.

    “Demonstrating that these complex devices can be designed and prototyped using basic science is one thing. Taking the next step and working with industry to actually fabricate them will, we hope, bridge the gap between what we do in the lab and what we can deliver as actual spacecraft hardware,” said Hofmann.

    The researchers also demonstrated the assembly of various bulk metallic glass components into a larger mount used to rotate a mirror.

    “We hope that using these mechanisms in space will allow us to increase precision in our instruments and decrease their mass,” Hofmann said. “They may also prove useful for storing elastic energy that can be used in space to deploy components without having to use motors.”

    Hofmann and co-authors from JPL and Brigham Young envision applications for aerospace and defense. Sporting goods such as golf clubs could be made of these materials, and so could medical implants that need to flex in the body such as hip replacement components. On spacecraft, metallic glasses could be used for tilting and positioning mirrors, or for structures that open antennas or shoot cube satellites out of spacecraft. If metallic glasses can be made en mass like plastics, but retain robust properties of metals, they could also be used for a wide assortment of consumer devices, from laptops to robots to cars.

    See the full article here.


    Jet Propulsion Laboratory (JPL) is a federally funded research and development center and NASA field center located in the San Gabriel Valley area of Los Angeles County, California, United States. Although the facility has a Pasadena postal address, it is actually headquartered in the city of La Cañada Flintridge [1], on the northwest border of Pasadena. JPL is managed by the nearby California Institute of Technology (Caltech) for the National Aeronautics and Space Administration. The Laboratory’s primary function is the construction and operation of robotic planetary spacecraft, though it also conducts Earth-orbit and astronomy missions. It is also responsible for operating NASA’s Deep Space Network.

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  • richardmitnick 8:57 pm on October 3, 2014 Permalink | Reply
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    From MIT: “Crumpled graphene could provide an unconventional energy storage” 

    MIT News

    October 3, 2014
    David L. Chandler | MIT News Office

    Two-dimensional carbon “paper” can form stretchable supercapacitors to power flexible electronic devices.

    When someone crumples a sheet of paper, that usually means it’s about to be thrown away. But researchers have now found that crumpling a piece of graphene “paper” — a material formed by bonding together layers of the two-dimensional form of carbon — can actually yield new properties that could be useful for creating extremely stretchable supercapacitors to store energy for flexible electronic devices.

    To form the crumpled graphene, a sheet of polymer material is stretched in both dimensions, then graphene paper is bonded to it. When the polymer is released in one direction, the graphene forms pleats, as shown in the bottom left image, taken with a scanning electron microscope (SEM). Then, when released in the other direction, it forms a chaotic crumpled pattern (top left). At top right, an SEM image shows the material in a partially crumpled state. At bottom right, SEM image of a piece that has been crumpled and then flattened out. Image courtesy of the researchers

    The finding is reported in the journal Scientific Reports by MIT’s Xuanhe Zhao, an assistant professor of mechanical engineering and civil and environmental engineering, and four other authors. The new, flexible supercapacitors should be easy and inexpensive to fabricate, the team says.

    “Many people are exploring graphene paper: It’s a good candidate for making supercapacitors, because of its large surface area per mass,” Zhao says. Now, he says, the development of flexible electronic devices, such as wearable or implantable biomedical sensors or monitoring devices, will require flexible power-storage systems.

    Like batteries, supercapacitors can store electrical energy, but they primarily do so electrostatically, rather than chemically — meaning they can deliver their energy faster than batteries can. Now Zhao and his team have demonstrated that by crumpling a sheet of graphene paper into a chaotic mass of folds, they can make a supercapacitor that can easily be bent, folded, or stretched to as much as 800 percent of its original size. The team has made a simple supercapacitor using this method as a proof of principle.

    The material can be crumpled and flattened up to 1,000 times, the team has demonstrated, without a significant loss of performance. “The graphene paper is pretty robust,” Zhao says, “and we can achieve very large deformations over multiple cycles.” Graphene, a structure of pure carbon just one atom thick with its carbon atoms arranged in a hexagonal array, is one of the strongest materials known.

    To make the crumpled graphene paper, a sheet of the material was placed in a mechanical device that first compressed it in one direction, creating a series of parallel folds or pleats, and then in the other direction, leading to a chaotic, rumpled surface. When stretched, the material’s folds simply smooth themselves out.

    Forming a capacitor requires two conductive layers — in this case, two sheets of crumpled graphene paper — with an insulating layer in between, which in this demonstration was made from a hydrogel material. Like the crumpled graphene, the hydrogel is highly deformable and stretchable, so the three layers remain in contact even while being flexed and pulled.

    Though this initial demonstration was specifically to make a supercapacitor, the same crumpling technique could be applied to other uses, Zhao says. For example, the crumpled graphene material might be used as one electrode in a flexible battery, or could be used to make a stretchable sensor for specific chemical or biological molecules.

    “This work is really exciting and amazing to me,” says Dan Li, a professor of materials engineering at Monash University in Australia who was not involved in this research. He says the team “provides an extremely simple but highly effective concept to make stretchable electrodes for supercapacitors by controlled crumpling of multilayered graphene films.” While other groups have made flexible supercapacitors, he says, “Making supercapacitors stretchable has been a great challenge. This paper provides a very smart way to tackle this challenge, which I believe will bring wearable energy storage devices closer.”

    The research team also included Jianfeng Zang at Huazhong University of Science and Technology and Changyang Cao, Yaying Feng, and Jie Liu at Duke University. The work was supported by the Office of Naval Research, the National Science Foundation, and the National 1000 Talents Program of China.

    See the full article here.

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  • richardmitnick 2:23 pm on September 25, 2014 Permalink | Reply
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    From MIT: “How to make stronger, ‘greener’ cement” 

    MIT News

    September 25, 2014
    David L. Chandler | MIT News Office

    Concrete is the world’s most-used construction material, and a leading contributor to global warming, producing as much as one-tenth of industry-generated greenhouse-gas emissions. Now a new study suggests a way in which those emissions could be reduced by more than half — and the result would be a stronger, more durable material.


    The findings come from the most detailed molecular analysis yet of the complex structure of concrete, which is a mixture of sand, gravel, water, and cement. Cement is made by cooking calcium-rich material, usually limestone, with silica-rich material — typically clay — at temperatures of 1,500 degrees Celsius, yielding a hard mass called “clinker.” This is then ground up into a powder. The decarbonation of limestone, and the heating of cement, are responsible for most of the material’s greenhouse-gas output.

    The new analysis suggests that reducing the ratio of calcium to silicate would not only cut those emissions, but would actually produce better, stronger concrete. These findings are described in the journal Nature Communications by MIT senior research scientist Roland Pellenq; professors Krystyn Van Vliet, Franz-Josef Ulm, Sidney Yip, and Markus Buehler; and eight co-authors at MIT and at CNRS in Marseille, France.

    “Cement is the most-used material on the planet,” Pellenq says, noting that its present usage is estimated to be three times that of steel. “There’s no other solution to sheltering mankind in a durable way — turning liquid into stone in 10 hours, easily, at room temperature. That’s the magic of cement.”

    In conventional cements, Pellenq explains, the calcium-to-silica ratio ranges anywhere from about 1.2 to 2.2, with 1.7 accepted as the standard. But the resulting molecular structures have never been compared in detail. Pellenq and his colleagues built a database of all these chemical formulations, finding that the optimum mixture was not the one typically used today, but rather a ratio of about 1.5.

    As the ratio varies, he says, the molecular structure of the hardened material progresses from a tightly ordered crystalline structure to a disordered glassy structure. They found the ratio of 1.5 parts calcium for every one part silica to be “a magical ratio,” Pellenq says, because at that point the material can achieve “two times the resistance of normal cement, in mechanical resistance to fracture, with some molecular-scale design.”

    The findings, Pellenq adds, were “validated against a large body of experimental data.” Since emissions related to concrete production are estimated to represent 5 to 10 percent of industrial greenhouse-gas emissions, he says, “any reduction in calcium content in the cement mix will have an impact on the CO2.” In fact, he says, the reduction in carbon emissions could be as much as 60 percent.

    In addition to the overall improvement in mechanical strength, Pellenq says, because the material would be more glassy and less crystalline, there would be “no residual stresses in the material, so it would be more fracture-resistant.”

    The work is the culmination of five years of research by a collaborative team from MIT and CNRS, where Pellenq is research director. The two institutions have a joint laboratory at MIT called the Multi-Scale Materials Science for Energy and Environment, run by Pellenq and Ulm, who is director of MIT’s Concrete Sustainability Hub, and hosted by the MIT Energy Initiative.

    Because of its improved resistance to mechanical stress, Pellenq says the revised formulation could be of particular interest to the oil and gas industries, where cement around well casings is crucial to preventing leakage and blowouts. “More resistant cement certainly is something they would consider,” Pellenq says.

    So far, the work has remained at the molecular level of analysis, he says. “Next, we have to make sure these nanoscale properties translate to the mesoscale” — that is, to the engineering scale of applications for infrastructure, housing, and other uses.

    Zdeněk Bažant, a professor of civil and environmental engineering, mechanical engineering, and materials science and engineering at Northwestern University who was not involved in this research, says, “Roland Pellenq, with his group at MIT, is doing cutting-edge research, clarifying the nanostructure and properties of cement hydrates.”

    The Concrete Sustainability Hub is supported by the Portland Cement Association and the Ready Mixed Concrete Research and Education Foundation.

    See the full article here.

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  • richardmitnick 5:10 pm on September 22, 2014 Permalink | Reply
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    From BNL:”Growth of an Ultra-thin Layered Structure Offers Surprises” 

    Brookhaven Lab

    September 22, 2014
    Laura Mgrdichian

    Many new technologies are based on ultra-thin layered structures that are “grown” using precise deposition techniques. Understanding and ultimately controlling this growth at the atomic level – particularly at the interfaces between these layers, where key properties arise – is essential to imparting these structures with properties tailored to possible applications.

    Researchers from the University of Vermont recently investigated an example of “heteroepitaxial” growth, in which one material is grown on the surface of a second material that has a similar crystal structure as the first. They studied a system of bismuth ferrite (BiFeO3, or BFO) grown on strontium titanate (SrTiO3, or STO). The research is published in the February 20, 2014, edition of Physical Review Letters.

    Simulated “maps” for growing bismuth ferrite on strontium titanate

    BFO is a target for materials science researchers because of its diverse ferroelectric properties and possible applications in developing technologies such as nonvolatile memory and data storage. At the National Synchrotron Light Source, the researchers discovered that the BFO forms clusters that grow and coalesce into a single layer in an unexpected way. They found that their data agree well with the “interrupted coalescence model” (ICM) of layer growth. This finding was a bit of a surprise, but they propose that the model may be applicable to other layered systems.

    BNL NSLS Interior

    “In this system, we saw compact, two-dimensional islands come together efficiently over a range of length scales,” said the study’s corresponding scientist, University of Vermont physicist Randall Headrick. “However, the kinetics of the growth process behave more like droplets than what we expected to observe, which was single-layer clusters that grow exponentially in time. This growth mode has implications for the structure of interfaces and ferroelectric domains in these materials, which will have an impact on domain switching in devices.”

    Headrick and his colleagues used a technique called sputter deposition to apply the BFO atoms to the STO surface and “watched” the growth of the BFO layer using x-ray diffraction at NSLS beamline X21. They saw the BFO quickly form islands of varying sizes, with an average size of about 20 nanometers. The small clusters retained their compact shape as they coalesced into bigger clusters. But, this coalescence was kinetically “frozen” when the clusters reached a critical size, leading to the formation of large connected irregularly shaped regions. In the spaces between, smaller islands continued to form and dot the area.

    The group confirmed these observations by studying the final layered structure with atomic force microscopy and additional x-ray diffraction measurements.

    Atomic Force Microscope at Rutgers University

    This work was supported by the
    Office of Basic Energy Sciences within the U.S. Department of Energy’s Office of Science.

    See the full article here.

    BNL Campus

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

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  • richardmitnick 8:38 am on September 12, 2014 Permalink | Reply
    Tags: , Material Sciences, ,   

    From Stanford: “Stanford engineers help describe key mechanism in energy and information storage” 

    Stanford University Name
    Stanford University

    September 11, 2014
    Bjorn Carey

    By observing how hydrogen is absorbed into individual palladium nanocubes, Stanford materials scientists have detailed a key step in storing energy and information in nanomaterials. The work could inform research that leads to longer-lasting batteries or higher-capacity memory devices.

    The palladium nanocubes viewed through a transmission electron microscope. Each black dot is a palladium atom.

    The ideal energy or information storage system is one that can charge and discharge quickly, has a high capacity and can last forever. Nanomaterials are promising to achieve these criteria, but scientists are just beginning to understand their challenging mechanisms.

    Now, a team of Stanford materials scientists and engineers has provided new insight into the storage mechanism of nanomaterials that could facilitate development of improved batteries and memory devices.

    The team, led by Jennifer Dionne, assistant professor of materials science and engineering at Stanford, and consisting of Andrea Baldi, Tarun Narayan and Ai Leen Koh, studied how metallic nanoparticles composed of palladium absorbed and released hydrogen atoms.

    Previously, scientists have studied hydrogen absorption in ensembles of metallic nanoparticles, but this approach makes it difficult to infer information about how the individual nanoparticles behave. The new study reveals that behavior by measuring the hydrogen content in individual palladium nanoparticles exposed to increasing pressures of hydrogen gas.

    The group’s experimental findings are consistent with a mechanism recently proposed for energy storage in lithium ion batteries, underscoring the interest for the broader scientific community. The work is detailed online in the journal Nature Materials.

    The finding was made possible by the use of a specialized transmission electron microscope (TEM) that allowed the team to detect, with near atomic-scale resolution, the process by which hydrogen entered the nanomaterial.

    “Electron microscopy must ordinarily be conducted in high vacuum,” said co-author Ai Leen Koh, a research scientist with the Stanford Nano Shared Facilities. “But the unique capabilities of Stanford’s environmental TEM obviates this requirement, enabling the study of individual nanoparticles both in vacuum and while immersed in a reactive gas.”
    Stretching metal

    The researchers synthesized palladium nanocubes and then dispersed them onto a very thin membrane. After placing the membrane in the TEM, the engineers flowed hydrogen gas past the palladium nanoparticles and gradually increased its pressure.

    At sufficiently high pressures of hydrogen, the gas molecules dissociate on the surface of the nanocubes and individual hydrogen atoms enter into the spaces between the palladium crystals. Interestingly, the absorption and desorption processes appear to be quite sudden.

    “You can think of it like popcorn,” said co-lead author Tarun Narayan, a graduate student in Dionne’s group. “It’s a very binary process, and a pretty sharp transition. Either the hydrogen is in the palladium or it’s not, and it enters and leaves at predictable pressures. And that’s quite important for a good energy storage system.”

    As the hydrogen enters the palladium nanostructure, the material’s volume increases by about 10 percent. This expansion significantly alters the way in which the particle interacts with the electron beam; this disruption indicates the amount of hydrogen absorbed. Because the nanocubes are single-crystalline and effectively “unbound” from the membrane, the researchers were able to study and measure the storage mechanism in unprecedented detail.

    “You have to stretch the palladium to put the hydrogen inside, but you have to pay energy to make it stretch,” said Andrea Baldi, a postdoctoral researcher in Dionne’s group. “Knowing that cost is very important for any battery designs, and because our nanostructures are not glued to a substrate, we’re able to quantify that stretch more accurately than ever before.”
    Next up: Palladium spheres

    Despite the stress of repeated expansion and contraction, the nanocrystals of palladium were not damaged by hydrogen absorption and desorption, as usually happens in larger specimens.

    “At the nanoscale, materials behave quite differently than they do in bulk,” said Dionne, the senior author. “Their increased surface area to volume ratio can significantly impact their mechanical flexibility and, consequently, their ability to charge and discharge ions or atoms.”

    In particular, this research indicates that nanoparticles can load more easily and at much lower pressures than bulk materials. Further, because they have a higher resistance to elastic stress, the formation of defects in these materials is suppressed.

    “Our results suggest that particles in this size regime don’t develop defects even if charged and discharged with hydrogen multiple times,” Narayan said. “Other researchers are starting to see this in lithium ion battery research as well, and we think a lot of what we’ve learned can be applied to that research.”

    Because of its fast storage speeds, stability and ease-of-loading, the hydrogenation of palladium is an excellent model system to study general energy and information storage mechanisms. Palladium, however, is not a likely material for widespread energy storage – it is too heavy and expensive. Yet, the researchers believe the results could be replicated with other systems involving storing hydrogen in metals.

    The next steps involve applying the newly developed single-particle method to a wide range of nanostructures – spheres and rods, for example – to study how storage can be affected by the shape, size and crystallinity of a nanoparticle. Furthermore, they plan to use the electron microscope to determine exactly where atoms or ions are preferentially absorbed within a singe nanoparticle.

    Dionne is an affiliate of the Stanford Institute for Materials and Energy Sciences (SIMES) and SLAC National Accelerator Laboratory. The research was supported by funding from the National Science Foundation, the Air Force Office of Scientific Research, the U.S. Department of Energy, a Young Energy Scientist Fellowship and a Hellman Fellowship.

    See the full article here.

    Leland and Jane Stanford founded the University to “promote the public welfare by exercising an influence on behalf of humanity and civilization.” Stanford opened its doors in 1891, and more than a century later, it remains dedicated to finding solutions to the great challenges of the day and to preparing our students for leadership in today’s complex world. Stanford, is an American private research university located in Stanford, California on an 8,180-acre (3,310 ha) campus near Palo Alto. Since 1952, more than 54 Stanford faculty, staff, and alumni have won the Nobel Prize, including 19 current faculty members

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  • richardmitnick 3:27 pm on September 11, 2014 Permalink | Reply
    Tags: , Material Sciences, ,   

    From M.I.T Tech: “A Super-Strong and Lightweight New Material” 

    MIT Technology Review
    M.I.T Technology Review

    September 11, 2014
    Katherine Bourzac

    Nanostructured ceramics could be used to build lighter, stronger airplanes and batteries.

    A new type of material, made up of nanoscale struts crisscrossed like the struts of a tiny Eiffel Tower, is one of the strongest and lightest substances ever made.

    Tiny trusses: A scanning electron microscope image of the new material reveals its ceramic nano-lattices

    If researchers can figure out how to make the stuff in large quantities, it could be used as a structural material for making planes and trucks, as well as in battery electrodes.

    Researchers led by Caltech materials scientist Julia Greer found that by carefully designing nanoscale struts and joints, they could make ceramics, metals, and other materials that can recover after being crushed, like a sponge. The materials are very strong and light enough to float through the air like a feather. The work is published today in the journal Science.

    In conventional materials, strength, weight, and density are correlated. Ceramics, for example, are strong but also heavy, so they can’t be used as structural materials where weight is critical—for example, in the bodies of cars. And when ceramics fail, they tend to fail catastrophically, shattering like glass.

    But at the nanoscale the same rules do not apply. In this size range, the structural and mechanical properties of ceramics become less tied to properties such as weight, and they can be altered more precisely.

    “For ceramics, smaller is tougher,” says Greer, who was named one of MIT Technology Review’s 35 Innovators Under 35 in 2008 for her work on nanoscale mechanics. This means that nanoscale trusses made from ceramic materials can be both very light—unsurprising, since they are mostly air—and extremely strong.

    In 2011, working with researchers at HRL Laboratories, a private engineering research company, Greer created one of the lightest materials ever made, a microlattice of hollow metal tubes. She later chose to take on the greater challenge of making ceramics with similar properties. This required fine-tuning structures at the nanoscale, meaning the materials are even more difficult to produce.

    To make the ceramic nano-trusses, Greer’s lab uses a technique called two-photon interference lithography. It’s akin to a very low-yield 3-D laser printer.

    First they use this method to create the desired structure, a lattice, out of a polymer. The polymer lattice is then coated with a ceramic such as alumina. Oxygen plasma etches out the polymer, leaving behind a lattice of hollow ceramic tubes.

    Greer’s lab showed that by changing the thickness of the tube walls, it’s possible to control how the material fails. When the walls are thick, the ceramic shatters under pressure as expected. But trusses with thinner walls, just 10 nanometers thick, buckle when compressed and then recover their shape.

    “You don’t expect these materials to recover—you expect them to be brittle and to fracture,” says Christopher Spadaccini, an engineer who specializes in materials manufacturing at the U.S. Department of Energy’s Lawrence Livermore National Laboratory in California.

    The new materials might be particularly interesting for use in batteries, notes Nicholas Fang, a mechanical engineer at MIT who is also working on nanostructured ceramics. Nanostructures have a very high surface area and are lightweight, a combination that could make for a fast-charging battery that stores a lot of energy in a convenient package. In fact, Greer says she is collaborating with German electronics company Bosch to apply her designs to lithium-ion batteries.

    See the full article here.

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

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  • richardmitnick 8:56 am on September 11, 2014 Permalink | Reply
    Tags: , , Material Sciences   

    From M.I.T.Tech: “No More Cracked Smartphone Glass” 

    MIT Technology Review
    M.I.T Technology Review

    September 11, 2014
    Kevin Bullis
    Photographs by Ken Richardson

    Ultrathin sapphire laminates could lead to durable but affordable next-generation screen covers.

    Glass touch-screen displays are easily cracked and scratched, making them a weak point in today’s ubiquitous mobile devices. Sapphire—second only to diamond in hardness—could make such damage a thing of the past. Sapphire is already used on a few luxury smartphones and for small parts of recent iPhones, including the cover of the camera lens and thumbprint reader on the iPhone 5S. And some models of Apple’s newly announced watch include a sapphire face. In a sign of the material’s growing importance, Apple recently invested $700 million in a sapphire processing factory in Arizona.

    The problem is that sapphire costs five to 10 times as much as the toughened glass used now in almost all smartphones, limiting its use to small screens or specialized devices. But in Danvers, Massachusetts, engineers at GT Advanced Technologies say they are solving the cost problem with a new manufacturing process that cheaply and efficiently produces sheets of sapphire just a quarter as thick as a piece of paper. These sheets, when laminated to a conventional glass display, can do a lot to prevent damage, since it only takes a very thin layer of sapphire to prevent scratches and to resist cracks when a phone is dropped.

    Top: The process starts with a slab of sapphire more than a millimeter thick.
    Above Left to right: A technician loads circular wafers of sapphire into a template, then loads that into a high-power ion ­accelerator.

    The template glows blue as it’s irradiated by hydrogen ions traveling at nearly 20,000 kilometers per second.

    The ion accelerator (right side of image) shoots ions through metal tubes to a target on the left.

    Top: The accelerator includes three rows of nine generators and power supply modules.

    Left: One of the generators is tested.
    Center: A power supply converts low-voltage electricity to high-voltage.

    A wafer-handling system, like this one for silicon wafers, will allow high-throughput production of sapphire laminate.

    Left: In the high heat of a gold-plated oven, the injected ions form hydrogen bubbles that cause the sapphire wafer (at right side of black platform) to slough off a thin layer of sapphire (at center of platform).
    Above top: The resulting sheet is just 26 micrometers thick.
    Above bottom: A laminating machine affixes sapphire to glass.

    A finished disk of sapphire (inner circle) now covers the glass.

    The company’s process can make about 10 sapphire sheets from the same amount of material that would go into just one solid display. That could help make sapphire ubiquitous in smartphones. Indeed, it would probably only add a few dollars to the cost of a phone. And it could allow sapphire to be used on displays for larger devices, such as tablets.

    GT Advanced Technologies is already a major sapphire supplier, having built the Arizona plant for Apple. The facility in Danvers is devoted to a next-generation manufacturing process. Behind the process is a machine called an ion accelerator, the size of a cement mixing truck. The machine generates two million volts of electricity and flings hydrogen ions at sapphire crystal wafers, embedding the ions at a precise depth in the sapphire. Then the material is heated in an oven, causing hydrogen bubbles to form within it and ultimately forcing a layer of sapphire to pop off. When that layer is polished, it becomes transparent.

    Though ion accelerators are already used to modify the properties of semiconducting materials, GT Advanced Technologies had to develop a machine 10 times more powerful in order to embed ions deeply and precisely enough to produce usable sheets of sapphire. The method is a big improvement over conventional means of making thin sapphire sheets, which involve sawing up a large chunk of sapphire into wafers and then grinding them down. That process wastes a lot of costly sapphire and, at the same time, introduces defects that make the thin sheets easy to break.

    Ted Smick, the company’s vice president of equipment engineering, expects his ion accelerator to be ready for market next year, after he develops an automated system for moving sapphire through the process. Eventually, the technology could help make sapphire-coated displays commonplace, making many of the hundreds of millions of smartphones sold each year far more durable.

    See the full article here.

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

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