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  • richardmitnick 5:07 pm on November 25, 2014 Permalink | Reply
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    From LLNL: “Lawrence Livermore researchers develop efficient method to produce nanoporous metals” 

    Lawrence Livermore National Laboratory

    Nov. 25, 2014

    Kenneth K Ma

    Nanoporous metals — foam-like materials that have some degree of air vacuum in their structure — have a wide range of applications because of their superior qualities.

    They posses a high surface area for better electron transfer, which can lead to the improved performance of an electrode in an electric double capacitor or battery. Nanoporous metals offer an increased number of available sites for the adsorption of analytes, a highly desirable feature for sensors.

    Lawrence Livermore National Laboratory (LLNL) and the Swiss Federal Institute of Technology (ETH) researchers have developed a cost-effective and more efficient way to manufacture nanoporous metals over many scales, from nanoscale to macroscale, which is visible to the naked eye.

    The process begins with a four-inch silicon wafer. A coating of metal is added and sputtered across the wafer. Gold, silver and aluminum were used for this research project. However, the manufacturing process is not limited to these metals.

    Next, a mixture of two polymers is added to the metal substrate to create patterns, a process known as diblock copolymer lithography (BCP). The pattern is transformed in a single polymer mask with nanometer-size features. Last, a technique known as anisotropic ion beam milling (IBM) is used to etch through the mask to make an array of holes, creating the nanoporous metal.

    During the fabrication process, the roughness of the metal is continuously examined to ensure that the finished product has good porosity, which is key to creating the unique properties that make nanoporous materials work. The rougher the metal is, the less evenly porous it becomes.

    “During fabrication, our team achieved 92 percent pore coverage with 99 percent uniformity over a 4-in silicon wafer, which means the metal was smooth and evenly porous,” said Tiziana Bond, an LLNL engineer who is a member of the joint research team.

    Tiziana Bond

    The team has defined a metric — based on a parametrized correlation between BCP pore coverage and metal surface roughness — by which the fabrication of nanoporous metals should be stopped when uneven porosity is the known outcome, saving processing time and costs.

    “The real breakthrough is that we created a new technique to manufacture nanoporous metals that is cheap and can be done over many scales avoiding the lift-off technique to remove metals, with real-time quality control,” Bond said. “These metals open the application space to areas such as energy harvesting, sensing and electrochemical studies.”

    The lift-off technique is a method of patterning target materials on the surface of a substrate by using a sacrificial material. One of the biggest problems with this technique is that the metal layer cannot be peeled off uniformly (or at all) at the nanoscale.

    The research team’s findings were reported in an article titled Manufacturing over many scales: High fidelity macroscale coverage of nanoporous metal arrays via lift-off-free nanofrabication. It was the cover story in a recent issue of Advanced Materials Interfaces.


    Other applications of nanoporous metals include supporting the development of new metamaterials (engineered materials) for radiation-enhanced filtering and manipulation, including deep ultraviolet light. These applications are possible because nanoporous materials facilitate anomalous enhancement of transmitted (or reflected) light through the tunneling of surface plasmons, a feature widely usable by light-emitting devices, plasmonic lithography, refractive-index-based sensing and all-optical switching.

    The other team members include ETH researcher Ali Ozhan Altun and professor Hyung Gyu Park.

    See the full article here.

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  • richardmitnick 4:34 pm on November 24, 2014 Permalink | Reply
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    From ORNL: “Materials researchers get first look at atom-thin boundaries” 


    Oak Ridge National Laboratory

    November 24, 2014
    Morgan McCorkle
    Communications and Media Relations

    Scientists at the Department of Energy’s Oak Ridge National Laboratory have made the first direct observations of a one-dimensional boundary separating two different, atom-thin materials, enabling studies of long-theorized phenomena at these interfaces.

    Theorists have predicted the existence of intriguing properties at one-dimensional (1-D) boundaries between two crystalline components, but experimental verification has eluded researchers because atomically precise 1-D interfaces are difficult to construct.

    Theorists have predicted the existence of intriguing properties at one-dimensional (1-D) boundaries between two crystalline components, but experimental verification has eluded researchers because atomically precise 1-D interfaces are difficult to construct.

    “While many theoretical studies of such 1-D interfaces predict striking behaviors, in our work we have provided the first experimental validation of those interface properties,” said ORNL’s An-Ping Li.

    The new Nature Communications study builds on work by ORNL and University of Tennessee scientists published in Science earlier this year that introduced a method to grow different two-dimensional materials – graphene and boron nitride – into a single layer only one atom thick.

    graphene is an atomic-scale honeycomb lattice made of carbon atoms

    The team’s materials growth technique unlocked the ability to study the 1-D boundary and its electronic properties in atomic resolution. Using scanning tunneling microscopy, spectroscopy and density-functional calculations, the researchers first obtained a comprehensive picture of spatial and energetic distributions of the 1-D interface states.

    “In three-dimensional (3-D) systems, the interface is embedded so you cannot get a real-space view of the complete interface – you can only look at a projection of that plane,” said Jewook Park, ORNL postdoctoral researcher and the lead author of the work. “In our case, the 1-D interface is completely accessible to real-space study,”

    “The combination of scanning tunneling microscopy and the first principles theory calculations allows us to distinguish the chemical nature of the boundary and evaluate the effects of orbital hybridization at the junction,” said ORNL’s Mina Yoon, a theorist on the team.

    The researchers’ observations revealed a highly confined electric field at the interface and provided an opportunity to investigate an intriguing phenomenon known as a “polar catastrophe,” which occurs in 3-D oxide interfaces. This effect can cause atomic and electron reorganization at the interface to compensate for the electrostatic field resulting from materials’ different polarities.

    “This is the first time we have been able to study the polar discontinuity effect in a 1-D boundary,” Li said.

    Although the researchers focused on gaining a fundamental understanding of the system, they note their study could culminate in applications that take advantage of the 1-D interface.

    “For instance, the 1-D chain of electrons could be exploited to pass a current along the boundary,” Li said. “It could be useful for electronics, especially for ultra-thin or flexible devices.”

    The team plans to continue examining different aspects of the boundary including its magnetic properties and the effect of its supporting substrate.

    The study is published as Spatially resolved one-dimensional boundary states in graphene–hexagonal boron nitride planar heterostructures. Coauthors are ORNL’s Jewook Park, Jaekwang Lee, Corentin Durand, Changwon Park, Bobby Sumpter, Arthur Baddorf, Mina Yoon and An-Ping Li; the University of Tennessee’s Lei Liu, Ali Mohsin, and Gong Gu; and Central Methodist University’s Kendal Clark.

    This research was conducted in part at the Center for Nanophase Materials Sciences and the National Energy Research Scientific Computing Center, both DOE Office of Science User Facilities. The research was supported by DOE’s Office of Science, ORNL’s Laboratory Directed Research and Development program, the National Science Foundation and DARPA.

    See the full article here.

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    ORNL is managed by UT-Battelle for the Department of Energy’s Office of Science. DOE’s Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time.


  • richardmitnick 4:28 pm on November 20, 2014 Permalink | Reply
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    From MIT: “Controlling a material with voltage” 

    MIT News

    November 20, 2014
    David L. Chandler | MIT News Office

    Technique could let a small electrical signal change materials’ electrical, thermal, and optical characteristics.

    A new way of switching the magnetic properties of a material using just a small applied voltage, developed by researchers at MIT and collaborators elsewhere, could signal the beginning of a new family of materials with a variety of switchable properties, the researchers say.

    This diagram shows the principle behind using voltage to change material properties. In this sandwich of materials, applying a voltage results in movement of ions — electrically charged atoms — from the middle, functional layer of material into the target layer. This modifies some of the properties — magnetic, thermal, or optical — of the target material, and the changes remain after the voltage is removed. Diagram courtesy of the researchers; edited by Jose-Luis Olivares/MIT

    The technique could ultimately be used to control properties other than magnetism, including reflectivity or thermal conductivity, they say. The first application of the new finding is likely to be a new kind of memory chip that requires no power to maintain data once it’s written, drastically lowering its overall power needs. This could be especially useful for mobile devices, where battery life is often a major limitation.

    The findings were published this week in the journal Nature Materials by MIT doctoral student Uwe Bauer, associate professor Geoffrey Beach, and six other co-authors.

    Beach, the Class of ’58 Associate Professor of Materials Science and Engineering, says the work is the culmination of Bauer’s PhD thesis research on voltage-programmable materials. The work could lead to a new kind of nonvolatile, ultralow-power memory chips, Beach says.

    The concept of using an electrical signal to control a magnetic memory element is the subject of much research by chip manufacturers, Beach says. But the MIT-based team has made important strides in making the technique practical, he says.

    The structure of these devices is similar to that of a capacitor, Beach explains, with two thin layers of conductive material separated by an insulating layer. The insulating layer is so thin that under certain conditions, electrons can tunnel right through it.

    But unlike in a capacitor, the conductive layers in these low-power chips are magnetized. In the new device, one conductive layer has fixed magnetization, but the other can be toggled between two magnetic orientations by applying a voltage to it. When the magnetic orientations are aligned, it is easier for electrons to tunnel from one layer to the other; when they have opposite orientations, the device is more insulating. These states can be used to represent “zero” and “one.”

    The work at MIT shows that it takes just a small voltage to flip the state of the device — which then retains its new state even after power is switched off. Conventional memory devices require a continuous source of power to maintain their state.

    The MIT team was able to design a system in which voltage changes the magnetic properties 100 times more powerfully than other groups have been able to achieve; this strong change in magnetism makes possible the long-term stability of the new memory cells.

    They achieved this by using an insulating layer made of an oxide material in which the applied voltage can rearrange the locations of the oxygen ions. They showed that the properties of the magnetic layer could be changed dramatically by moving the oxygen ions back and forth near the interface.

    The team is now working to ramp up the speed at which these changes can be made to the memory elements. They have already reached rates of a megahertz (millions of times per second) in switching, but a fully competitive memory module will require further increase on the order of a hundredfold to a thousandfold, they say.

    The team also found that the magnetic properties could be changed using a pulse of laser light that heats the oxide layer, helping the oxygen ions to move more easily. The laser beam used to alter the state of the material can scan across its surface, making changes as it goes.

    The same techniques could be used to alter other properties of materials, Beach explains, such as reflectivity or thermal conductivity. Such properties can ordinarily be changed only through mechanical or chemical processing. “All these properties could come under electrical control, to be switched on and off, and even ‘written’ using a beam of light,” Beach says. This ability to make such changes on the fly essentially produces “an Etch-a-Sketch for material properties,” he says.The new findings “started as a fluke,” Beach says: Bauer was experimenting with the layered material, expecting to see standard temporary capacitive effects from an applied voltage. “But he turned off the voltage and it stayed that way,” with a reversed magnetic state, Beach says, leading to further investigation.

    “I think this will have broad applications,” Beach says, adding that it uses methods and materials that are already standard in microchip manufacturing.

    In addition to Bauer and Beach, the team included Lide Yao and Sebastiaan van Dijken of Aalto University in Finland and, at MIT, graduate students Aik Jun Tan, Parnika Agrawal, and Satoru Emori and professor of ceramics and electronic materials Harry Tuller. The work was supported by the National Science Foundation and Samsung.

    See the full article here.

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  • richardmitnick 4:12 pm on November 20, 2014 Permalink | Reply
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    From MIT: “New 2-D quantum materials for nanoelectronics” 

    MIT News

    November 20, 2014
    David L. Chandler | MIT News Office

    MIT team provides theoretical roadmap to making 2-D electronics with novel properties.

    Researchers at MIT say they have carried out a theoretical analysis showing that a family of two-dimensional materials exhibits exotic quantum properties that may enable a new type of nanoscale electronics.

    These materials are predicted to show a phenomenon called the quantum spin Hall (QSH) effect, and belong to a class of materials known as transition metal dichalcogenides, with layers a few atoms thick. The findings are detailed in a paper appearing this week in the journal Science, co-authored by MIT postdocs Xiaofeng Qian and Junwei Liu; assistant professor of physics Liang Fu; and Ju Li, a professor of nuclear science and engineering and materials science and engineering.

    This diagram illustrates the concept behind the MIT team’s vision of a new kind of electronic device based on 2-D materials. The 2-D material is at the middle of a layered “sandwich,” with layers of another material, boron nitride, at top and bottom (shown in gray). When an electric field is applied to the material, by way of the rectangular areas at top, it switches the quantum state of the middle layer (yellow areas). The boundaries of these “switched” regions act as perfect quantum wires, potentially leading to new electronic devices with low losses. Illustration: Yan Liang

    QSH materials have the unusual property of being electrical insulators in the bulk of the material, yet highly conductive on their edges. This could potentially make them a suitable material for new kinds of quantum electronic devices, many researchers believe.

    But only two materials with QSH properties have been synthesized, and potential applications of these materials have been hampered by two serious drawbacks: Their bandgap, a property essential for making transistors and other electronic devices, is too small, giving a low signal-to-noise ratio; and they lack the ability to switch rapidly on and off. Now the MIT researchers say they have found ways to potentially circumvent both obstacles using 2-D materials that have been explored for other purposes.

    Existing QSH materials only work at very low temperatures and under difficult conditions, Fu says, adding that “the materials we predicted to exhibit this effect are widely accessible. … The effects could be observed at relatively high temperatures.”

    “What is discovered here is a true 2-D material that has this [QSH] characteristic,” Li says. “The edges are like perfect quantum wires.”

    The MIT researchers say this could lead to new kinds of low-power quantum electronics, as well as spintronics devices — a kind of electronics in which the spin of electrons, rather than their electrical charge, is used to carry information.

    Graphene, a two-dimensional, one-atom-thick form of carbon with unusual electrical and mechanical properties, has been the subject of much research, which has led to further research on similar 2-D materials. But until now, few researchers have examined these materials for possible QSH effects, the MIT team says. “Two-dimensional materials are a very active field for a lot of potential applications,” Qian says — and this team’s theoretical work now shows that at least six such materials do share these QSH properties.

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

    The MIT researchers studied materials known as transition metal dichalcogenides, a family of compounds made from the transition metals molybdenum or tungsten and the nonmetals tellurium, selenium, or sulfur. These compounds naturally form thin sheets, just atoms thick, that can spontaneously develop a dimerization pattern in their crystal structure. It is this lattice dimerization that produces the effects studied by the MIT team.

    While the new work is theoretical, the team produced a design for a new kind of transistor based on the calculated effects. Called a topological field-effect transistor, or TFET, the design is based on a single layer of the 2-D material sandwiched by two layers of 2-D boron nitride. The researchers say such devices could be produced at very high density on a chip and have very low losses, allowing high-efficiency operation.

    By applying an electric field to the material, the QSH state can be switched on and off, making possible a host of electronic and spintronic devices, they say.

    In addition, this is one of the most promising known materials for possible use in quantum computers, the researchers say. Quantum computing is usually susceptible to disruption — technically, a loss of coherence — from even very small perturbations. But, Li says, topological quantum computers “cannot lose coherence from small perturbations. It’s a big advantage for quantum information processing.”

    Because so much research is already under way on these 2-D materials for other purposes, methods of making them efficiently may be developed by other groups and could then be applied to the creation of new QSH electronic devices, Qian says.

    Nai Phuan Ong, a professor of physics at Princeton University who was not connected to this work, says, “Although some of the ideas have been mentioned before, the present system seems especially promising. This exciting result will bridge two very active subfields of condensed matter physics, topological insulators and dichalcogenides.”

    The research was supported by the National Science Foundation, the U.S. Department of Energy, and the STC Center for Integrated Quantum Materials. Qian and Liu contributed equally to the work.

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  • richardmitnick 4:24 pm on November 18, 2014 Permalink | Reply
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    From BNL: “Organic Crystal Film Grown on New Substrate Breaks Performance Record” 

    Brookhaven Lab

    November 18, 2014
    Laura Mgrdichian

    The study is an important step toward realizing mainstream organic electronic devices

    Many future electronic devices may be based not on standard conductors and semiconductors but rather on small organic (carbon-based) molecules and polymers. These organic electronics will have several advantages over conventional electronics, including being cheaper to fabricate, physically bendable and flexible, and, in some cases, can be created using printing methods – perhaps even in your own home.

    The field of organic electronics is still in its infancy, however, and scientists have much to learn before organic electronic devices are part of our everyday lives. One obstacle researchers have faced is how to successfully grow high-quality crystals of an organic molecule on top of a conventional substrate – without using a complex growth process or chemically modifying the substrate first. Solving this problem is the necessary first step to creating organic electronic circuits and devices.

    Organic two-dimensional heterostructure of rubrene/h-BN

    Recently, a research group made some significant headway. Working in part at the National Synchrotron Light Source (NSLS), scientists from Columbia University, Harvard University, Brookhaven Lab, and Japan’s National Institute for Materials Science grew a high-quality, high-performing film of rubrene, an organic semiconductor, onto a substrate of hexagonal boron nitride, a layered crystalline material with hexagonally shaped molecular units (similar to graphite carbon). Their work, which they discuss in the May 14, 2014, edition of the journal Advanced Materials, is notable both due to the high-quality crystalline nature of the film and because the substrate is a new player in the field of organic electronics development.

    “The interface between the substrate and the molecular film is very important. It governs the initial nucleation during the growth of the film and also has a big impact on how the film will carry charge,” says Columbia researcher Phillip Kim, one of the paper’s authors. “Our film/substrate heterostructure yielded the highest mobility observed yet in similar systems. It is comparable to those of free-standing single crystals and represents a record for organic films grown on any substrates.”

    When paired with organic materials, conventional substrates like silicon oxide, glass, and plastic are too disordered at the molecular level and also don’t have molecular structures that are similar enough to the organic compounds. In materials science terms, they lack an “epitaxial” relationship. This discourages proper film growth and results in lower-quality films that lack long-range order. In everyday terms, this is kind of like trying to build a layer of Lego bricks on Lego board that doesn’t have an ordered grid of nubs.

    Kim and his colleagues showed that hexagonal boron nitride (h-BN) has many advantages as a substrate for organic electronics. Using an approach called “van der Waals epitaxy,” a method that takes advantage of the weak van der Waals force between molecules, the group grew rubrene films varying from 5 to 1000 nanometers thick. They studied each sample’s structure and charge-carrying ability using several methods.

    Atomic force microscopy (AFM) and transmission electron microscopy (TEM) images suggested that the film was formed of large single-crystal domains. Selected area electron diffraction (SAED), which can be performed inside a transmission electron microscope, also confirmed this. But because SAED provides only local structural information, the group used grazing x-ray diffraction at NSLS beamline X9 to get a broader “view” of the structure. The x-ray data showed sharp, intense peaks, indicating that the sample contained a high-quality crystal structure.

    To study how the film carries charge, graphene electrical contacts were incorporated into the growth process, resulting in a field-effect transistor structure. Measuring the current across it showed that electrons traveling within it are highly mobile, meaning they don’t run into too many barriers caused by a “choppy” molecular structure.

    “Our study highlights the advantages of h-BN and similar materials over commonly used substrates to achieve high-performance organic electronic devices,” said Kim. “More generally, this approach to film growth – van der Waals epitaxy – could be used to fabricate organic/inorganic structures that can be readily expanded to numerous other organic and layered materials for various electronic applications.”

    This research was supported by: the Center for Redefining Photovoltaic Efficiency Through Molecule Scale Control, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences; the FAME Center, one of six centers of STARnet, a Semiconductor Research Corporation program sponsored by MARCO and DARPA; the Nano Material Technology Development Program through the National Research Foundation of Korea funded by the Ministry of Science, ICT and Future Planning; the Basic Science Research Program through the National Research Foundation of Korea; the U.S. Department of Energy, Office of Basic Energy Sciences, under the Extreme Science and Engineering Discovery Environment, supported by the National Science Foundation.

    See the full article here.

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

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  • richardmitnick 2:25 pm on November 12, 2014 Permalink | Reply
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    From SLAC: “Study at SLAC Explains Atomic Action in High-Temperature Superconductors “ 

    SLAC Lab

    November 12, 2014

    A study at the Department of Energy’s SLAC National Accelerator Laboratory suggests for the first time how scientists might deliberately engineer superconductors that work at higher temperatures.

    In their report, a team led by SLAC and Stanford University researchers explains why a thin layer of iron selenide superconducts — carries electricity with 100 percent efficiency — at much higher temperatures when placed atop another material, which is called STO for its main ingredients strontium, titanium and oxygen.

    In this illustration, a single layer of superconducting iron selenide (balls and sticks) has been placed stop another material known as STO for its main ingredients strontium, titanium and oxygen. The STO is shown as blue pyramids, which represent the arrangement of its atoms. A study at SLAC found that when natural vibrations (green glow) from the STO move up into the iron selenide film, electrons in the film (white spheres) can pair up and conduct electricity with 100 percent efficiency at much higher temperatures than before. The results suggest a way to deliberately engineer superconductors that work at even higher temperatures. (SLAC National Accelerator Laboratory)

    This view from the side makes an important point: Putting iron selenide on top of STO enhances its superconductivity only if it’s applied in a single layer (left). When more than one layer is applied, the natural vibrations coming up from the STO layer don’t give electrons the boost of energy they need to pair up and superconduct (right). (SLAC National Accelerator Laboratory)

    These findings, described today in the journal Nature, open a new chapter in the 30-year quest to develop superconductors that operate at room temperature, which could revolutionize society by making virtually everything that runs on electricity much more efficient. Although today’s high-temperature superconductors operate at much warmer temperatures than conventional superconductors do, they still work only when chilled to minus 135 degrees Celsius or below.

    In the new study, the scientists concluded that natural trillion-times-per-second vibrations in the STO travel up into the iron selenide film in distinct packets, like volleys of water droplets shaken off by a wet dog. These vibrations give electrons the energy they need to pair up and superconduct at higher temperatures than they would on their own.

    “Our simulations indicate that this approach – using natural vibrations in one material to boost superconductivity in another – could be used to raise the operating temperature of iron-based superconductors by at least 50 percent,” said Zhi-Xun Shen, a professor at SLAC and Stanford University and senior author of the study.

    While that’s still nowhere close to room temperature, he added, “We now have the first example of a mechanism that could be used to engineer high-temperature superconductors with atom-by-atom control and make them better.”

    Spying on Electrons

    The study probed a happy combination of materials developed two years ago by scientists in China. They discovered that when a single layer of iron selenide film is placed atop STO, its maximum superconducting temperature shoots up from 8 degrees to nearly 77 degrees above absolute zero (minus 196 degrees Celsius).

    While this was a huge and welcome leap, it would be hard to build on this advance without understanding what, exactly, was going on.

    In the new study, SLAC Staff Scientist Rob Moore and Stanford graduate student J.J. Lee and postdoctoral researcher Felix Schmitt built a system for growing iron selenide films just one layer thick on a base of STO.

    The team examined the combined material at SLAC’s Stanford Synchrotron Radiation Lightsource, a DOE Office of Science User Facility. They used an exquisitely sensitive technique called ARPES to measure the energies and momenta of electrons ejected from samples hit with X-ray light. This tells scientists how the electrons inside the sample are behaving; in superconductors they pair up to conduct electricity without resistance. The researchers also got help from theorists who did simulations to help explain what they were seeing.

    SSRL at SLAC

    A Promising New Direction

    “This is a very impressive experiment, one that would have been very difficult to impossible to do anywhere else,” said Andrew Millis, a theoretical condensed matter physicist at Columbia University, who was not involved in the study. “And it’s clearly telling us something important about why putting one thin layer of iron selenide on this substrate, which everyone thought was inert and boring, changes things so dramatically. It opens lots of interesting questions, and it will definitely stimulate a lot of research.”

    Scientists still don’t know what holds electron pairs together so they can effortlessly carry current in high-temperature superconductors. With no way to deliberately invent new high-temperature superconductors or improve old ones, progress has been slow.

    The new results “point to a new direction that people have not considered before,” Moore said. “They have the potential to really break records in high-temperature superconductivity and give us a new understanding of things we’ve been struggling with for years.”

    He added that SLAC is developing a new X-ray beamline at SSRL with a more advanced ARPES system to create and study these and other exotic materials. “This paper predicts a new pathway to engineering superconductivity in these materials,” Moore said, “and we’re building the tools to do just that.”

    In addition to researchers from SLAC’s Materials Science Division and from Stanford, scientists from the University of British Columbia, the University of Tennessee, Lawrence Berkeley National Laboratory and the University of California, Berkeley contributed to this study. The work was funded by the DOE Office of Science.

    See the full article here.

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

    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
    Tags: , , Material Sciences, ,   

    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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