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  • richardmitnick 1:38 pm on December 8, 2014 Permalink | Reply
    Tags: , , Nanotechnology,   

    From Sandia: “Turning biological cells to stone improves cancer and stem cell research” 

    Sandia Lab

    December 8, 2014
    Neal Singer, nsinger@sandia.gov, (505) 845-7078

    ‘Zombie’ method also hardens biostructures for mass production

    Changing flesh to stone sounds like the work of a witch in a fairy tale.

    Sandia National Laboratories researchers Bryan Kaehr and Kristin Meyer analyze a silicized surface using optical microscopy and multiphoton fluorescence. (Photo by Randy Montoya)

    But a new technique to transmute living cells into more permanent materials that defy decay and can endure high-powered probes is widening research opportunities for biologists who are developing cancer treatments, tracking stem cell evolution or even trying to understand how spiders vary the quality of the silk they spin.

    The simple, silica-based method also offers materials scientists the ability to “fix” small biological entities like red blood cells into more commercially useful shapes. And, at least in theory, the method can transmute naturally grown objects like livers and spleens from livestock into non-organic “zombie” replicas that function simultaneously at a variety of length-scales, from macro to nano, in more sophisticated ways than the most advanced machinery can produce.

    “Why go to the trouble of making objects if nature will do it for you?” asks lead investigator Bryan Kaehr of the Department of Energy’s (DOE) Sandia National Laboratories.

    The unusual method has been the subject of papers in Proceedings of the National Academy of Sciences, the Journal of the American Chemical Society (JACS), and on Dec. 8, Nature Communications.

    The initial insight came when Kaehr and then-University of New Mexico (UNM) postdoctoral student Jason Townson discovered that the silica slurry they were using had an unexpected property: At a reasonably low pH level, the silica molecules, instead of clotting with each other, bound only to surfaces against which they rested, forming the thinnest of coatings.

    Kaehr wondered if a similar coating on biological cells would strengthen cell structures so they could be examined for longer periods with more powerful tools. So the researchers put cultured tissue cells in a silica solution and let the mix harden overnight. Then they raised the temperature to burn off the biomaterial. What remained, astonishingly, were perfectly replicated cells, like little row houses of glass.

    Chicken feet and skin-cells turned to glass by the Sandia and University of New Mexico silicizing process. (Image courtesy of Sandia National Laboratories)

    But the replicated cells were so sturdy that Kaehr surmised that the slurry must have coated the cells inside as well as out. Breaking a row of cells as one would a tiny pane of glass, the team examined their interiors with an electron microscope. They found they had indeed replicated the nanoscopic organelles of the cell as well as its exterior. They had discovered a way to create a near-perfect silica counterfeit of a biological organism, from its overall shape down to its nanostructures.

    This initial result is already being used by biologists in Finland to create three-dimensional models that preserve the different stages of stem cells as they evolve to their final form, said Sandia fellow and paper co-author Jeff Brinker, who is also a UNM professor.

    Townson, now on the faculty at UNM, uses the method to research the movements of cancer-fighting nanoparticles inserted into chicken cells prior to their conversion to silica. “With optical microscopy, it is difficult to form an image of the interactions of nanoparticles with cells while preserving a three-dimensional context,” he said. Bioreplication, where the sample can be mechanically dissected and investigated with electron microscopes, offers better 3-D resolution at the nanoscale.

    The method also is being used in England’s Oxford University to study the internal biological changes by which spiders create different types of silk, adjusting their mechanisms on the fly (so to speak) to create thicker or stickier strands, said Brinker.

    Red blood cells before being distorted into spiky spheres by the Sandia and University of New Mexico technique for possible commercial use. (Image courtesy of Sandia National Laboratories)

    In the JACS article, Kaehr and colleagues showed they could use the silica technique to make permanent alterations in natural objects. They introduced chemicals that transformed red blood cells from life-saver-like objects to spiky spheres. By introducing the silica slurry to the dish containing the altered red blood cells and letting the mixture harden, Kaehr and colleagues made the change permanent. Burning off the protoplasmic original, the team was left with microparticles that might be useful in rubber composites created by tire companies that routinely insert silica spheres in their tire mix for additional strength. Manufacturers would no longer need an energy-consuming factory to make the inserted material which, by bioreplication, would form cheaply and easily, Kaehr said.

    “Our method has good potential over traditional silica additives, and its raw material — blood — is considered a waste product in the meat industry,” he said.

    In addition to food industry waste products, he said, “there’s a huge amount of harmless bacteria out there we could co-opt to create still other shapes.” Bacteria are harder to harvest, he said, because they are protected by a double sheath against silica invasion, but it could be done.

    In the Nature Communications paper, Kaehr and colleagues took the same technique a step further. They took a liver, submerged it in a silica solution and then heated it anaerobically to come up with a hardened, carbonized, exact duplicate of the liver, from centimeter to nanometer scales.

    “We let nature do the work,” he said, “because we don’t yet know how to build an object accurately across six length scales, from centimeter to nanometers.

    An electron microscope shows the heterogeneity of tissue available in a carbonized spleen. (Image courtesy of Sandia National Laboratories)

    “Think about electrodes in batteries,” he said. “That’s a three-dimensional question. Now in livers and spleens, for example, evolution has already optimized absorption and diffusion in a three-dimensional organization. The liver is a marvelously effective organ with tremendous surface area for absorption and an unparalleled ability to release materials in channels ranging from large arteries to capillaries a few micrometers wide.

    “If we transfer the hierarchical structure of a liver to an electrode, rather than having just a passive piece of solid material, we would have greater surface area per volume, greater energy storage, and have a creation that is already optimized to output fluids and small particles to much larger highways like large veins and arteries.”

    The carbonized method also can be used to better examine cancers and other growths without the often tedious and expensive processes normally necessary to “fix,” process and stabilize the organic material for examination to prevent it from falling apart under electron-beam analysis. Carbon, because it conducts electricity instead of absorbing it, is not weakened and destroyed like protoplasm.

    This creative consideration of the possibilities of the natural world in new and dizzying ways is in line with Kaehr’s research sponsor — DOE’s Office of Science, which is interested in “the exploration, discovery and design of biomimetic materials,” he said. Portions of this work were performed at the Center for Intergrated Nanotechnologies, a DOE Office of Science user facility jointly led by Los Alamos and Sandia national laboratories.

    Sandia and UNM have applied for a joint patent on the set of methods.

    See the full article here.

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    Sandia National Laboratories is a multiprogram laboratory operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration. With main facilities in Albuquerque, N.M., and Livermore, Calif., Sandia has major R&D responsibilities in national security, energy and environmental technologies, and economic competitiveness.

  • richardmitnick 7:30 pm on December 4, 2014 Permalink | Reply
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    From ANL: “Atomic ‘mismatch’ creates nano ‘dumbbells'” 

    News APS at Argonne National Laboratory

    December 4, 2014
    Jared Sagoff

    Like snowflakes, nanoparticles come in a wide variety of shapes and sizes. The geometry of a nanoparticle is often as influential as its chemical makeup in determining how it behaves, from its catalytic properties to its potential as a semiconductor component.

    Thanks to a new study from the U.S. Department of Energy’s (DOE) Argonne National Laboratory, researchers are closer to understanding the process by which nanoparticles made of more than one material – called heterostructured nanoparticles – form. This process, known as heterogeneous nucleation, is the same mechanism by which beads of condensation form on a windowpane.

    Heterostructured nanoparticles can be used as catalysts and in advanced energy conversion and storage systems. Typically, these nanoparticles are created from tiny “seeds” of one material, on top of which another material is grown. In this study, the Argonne researchers noticed that the differences in the atomic arrangements of the two materials have a big impact on the shape of the resulting nanoparticle.

    “Before we started this experiment, it wasn’t entirely clear what’s happening at the interface when one material grows on another,” said nanoscientist Elena Shevchenko of Argonne Center for Nanoscale Materials, a DOE Office of Science user facility.

    In this study, the researchers observed the formation of a nanoparticle consisting of platinum and gold. The researchers started with a platinum seed and grew gold around it. Initially, the gold covered the platinum seed’s surface uniformly, creating a type of nanoparticle known as “core-shell.” However, as more gold was deposited, it started to grow unevenly, creating a dumbbell-like structure.

    This picture combines a transmission electron microscope image of a nanodumbbell with a gold domain oriented in direction. The seed and gold domains in the dumbbell in the image on the right are identified by geometric phase analysis. Image credit: Soon Gu Kwon.

    Thanks to state-of-the-art X-ray analysis provided by Argonne’s Advanced Photon Source (APS), a DOE Office of Science user facility, the researchers identified the cause of the dumbbell formation as “lattice mismatch,” in which the spacing between the atoms in the two materials doesn’t align.

    “Essentially, you can think of lattice mismatch as having a row of smaller boxes on the bottom layer and larger boxes on the top layer. When you try to fit the larger boxes into the space for a smaller box, it creates an immense strain,” said Argonne physicist Byeongdu Lee.

    While the lattice mismatch is only fractions of a nanometer, the effect accumulates as layer after layer of gold forms on the platinum. The mismatch can be handled by the first two layers of gold atoms – creating the core-shell effect – but afterwards it proves too much to overcome. “The arrangement of atoms is the same in the two materials, but the distance between atoms is different,” said Argonne postdoctoral researcher Soon Gu Kwon. “Eventually, this becomes unstable, and the growth of the gold becomes unevenly distributed.”

    As the gold continues to accumulate on one side of the seed nanoparticle, small quantities “slide” down the side of the nanoparticle like grains of sand rolling down the side of a sand hill, creating the dumbbell shape.

    The advantage of the Argonne study comes from the researchers’ ability to perform in situ observations of the material in realistic conditions using the APS. “This is the first time anyone has been able to study the kinetics of this heterogeneous nucleation process of nanoparticles in real-time under realistic conditions,” said Argonne physicist Byeongdu Lee. “The combination of two X-ray techniques gave us the ability to observe the material at both the atomic level and the nanoscale, which gave us a good view of how the nanoparticles form and transform.” All conclusions made based on the X-ray studies were further confirmed using atomic-resolution microscopy in the group of Professor Robert Klie of the University of Illinois at Chicago.

    This analysis of nanoparticle formation will help to lay the groundwork for the formation of new materials with different and controllable properties, according to Shevchenko. “In order to design materials, you have to understand how these processes happen at a very basic level,” she said.

    The research was funded in part by the National Science Foundation and the University of Illinois at Chicago Research Resources Center.

    An article based on the research, Heterogeneous nucleation and shape transformation of multicomponent metallic nanostructures,” appeared in the Nov. 2 online issue of Nature Materials.

    Argonne National Laboratory seeks solutions to pressing national problems in science and technology. The nation’s first national laboratory, Argonne conducts leading-edge basic and applied scientific research in virtually every scientific discipline. Argonne researchers work closely with researchers from hundreds of companies, universities, and federal, state and municipal agencies to help them solve their specific problems, advance America’s scientific leadership and prepare the nation for a better future.

    With employees from more than 60 nations, Argonne is managed by UChicago Argonne, LLC for the U.S. Department of Energy’s Office of Science. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time.

    See the full article here.

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    Argonne is managed by UChicago Argonne, LLC for the U.S. Department of Energy’s Office of Science

    The Advanced Photon Source at Argonne National Laboratory is one of five national synchrotron radiation light sources supported by the U.S. Department of Energy’s Office of Science to carry out applied and basic research to understand, predict, and ultimately control matter and energy at the electronic, atomic, and molecular levels, provide the foundations for new energy technologies, and support DOE missions in energy, environment, and national security.

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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.

    See the full article here.

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  • richardmitnick 4:31 pm on November 19, 2014 Permalink | Reply
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    From LBL: “A Cage Made of Proteins, Designed With Help From the Advanced Light Source” 

    Berkeley Logo

    Berkeley Lab

    November 19, 2014
    Dan Krotz 510-486-4019

    With help from Berkeley Lab’s Advanced Light Source, scientists from UCLA recently designed a cage made of proteins.

    The nano-sized cage could lead to new biomaterials and new ways to deliver drugs inside cells. It boasts a record breaking 225-angstrom outside diameter, the largest to date for a designed protein assembly. It also has a 130-angstrom-diameter central cavity, which is large enough to hold molecular cargo. And its high porosity is perfect for packing a lot of chemistry in a small package.


    More research is needed, but perhaps scientists could some day insert a cancer-fighting drug inside the cage, and tweak its exterior proteins so that it targets malignant cells.

    That’s one promise of the new cage. Another is the way in which it was designed. The cage is composed of specially designed “building block” proteins. When the proteins are in a solution with just the right conditions, they assemble into a hollow cube made of 24 proteins. Some of these cubes form crystals.

    The scientists used the Advanced Light Source, a synchrotron located at Berkeley Lab, to quickly visualize the cage in different solutions. This helped the scientists determine how to best get the cage to assemble itself. It also allowed them to see how different solutions yield cages of various geometries.

    LBL Advanced Light Source
    LBL ALS interior

    They used beamline 12.3.1, also known as SIBYLS, which stands for Structurally Integrated Biology for Life Sciences. The SIBYLS beamline is optimized for the joint application of crystallography and SAXS imaging, or small-angle X-ray scattering. SAXS provides information on the shapes of large molecular assemblies in almost any type of solution. And it’s much faster than conventional protein crystallography techniques.

    “SAXS helped us efficiently and quickly understand the assembly processes of these protein cages. We had feedback in a matter of hours, not days” says Greg Hura, a scientist with Berkeley Lab’s Physical Biosciences Division.

    Hura and John Tainer of Berkeley Lab’s Life Sciences Division are co-authors of a Nature Chemistry paper that describes the protein cage. The research was led by Todd Yeates, a UCLA professor of chemistry and biochemistry.

    Greg Hura at the The SYBILS beamline at the Advanced Light Source, which can quickly visualize a protein assembly’s structure in almost any solution, is helping researchers design new biomaterials.

    SAXS made its mark elucidating the structure of proteins critical to human health, such as DNA repair machines. The technique can analyze about 100 samples in four hours. It also analyzes samples in solutions that approximate the biological conditions in which proteins are found. Hura and Tainer are now expanding SAXS’s repertoire to assist in the development of biomaterials.

    “The magic of proteins is they are capable of a tremendous amount of chemistry, which we can harness in advanced materials for medicine, energy, and other applications,” says Hura, who helped optimize SAXS for high-throughput use.

    The technique could be especially useful in helping to integrate the nanoscale properties of individual proteins into large complexes that perform useful functions. For example, Hura envisions using SAXS to develop protein assemblies that act as highly efficient catalysts, complete with millions of points that interact with a substance of choice.

    “We are keenly interested in the rules for assembly at these nanoscales, since many alternative and valuable designs are currently being explored,” says Hura.

    For the UCLA-developed protein cage, SAXS helped the scientists develop an annealing process that yielded crystal structures of the cage in eight hours. Before, it took several months for crystals to form. SAXS also enabled the team to analyze the protein cages under real-world physiological conditions, such as the pH levels found inside cells, and see how these conditions affected the cages’ properties.

    “The technique allows the direct visualization of a structure’s flexibility and variability in solution, which will help improve the design of protein cages and other biomaterials,” says Hura.

    See the full article here.

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  • richardmitnick 10:13 am on November 7, 2014 Permalink | Reply
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    From MIT: “Nanoscale work yields big results” 

    MIT News

    November 6, 2014
    Leda Zimmerman | MIT Spectrum

    An avid amateur astronomer during her childhood in Vukovar, Croatia, Silvija Gradečak, associate professor in materials science and engineering, was not content observing the physical world only from a distance: “I discovered what I really liked about science were experiments, and having the ability to make something with my hands,” she says.

    Silvija Gradečak’s nanoscale work creates big-scale results that could transform energy production, storage, and lighting. Photo illustration: Len Rubenstein

    Today, handling the smallest elements in nature, Gradečak is generating large-scale results that may transform energy production, storage, and lighting. Her enthusiasm for both basic and applied research will help to power MIT.nano, the Institute’s $350 million nanoscale laboratory now under construction. Gradečak looks forward to working “with people from different backgrounds, advanced nanofabrication tools, and the seamless integration of the technologies needed to work on these problems.”

    At the Swiss Federal Institute of Technology, where Gradečak pursued her doctorate, an electron microscope revealed a new terrain ripe for exploration and manipulation. “I saw individual atoms for the first time, and came to realize that having the ability to arrange them on the nanoscale is a powerful tool,” she says. “There were so many new problems available to work on. All kinds of possibilities emerge when you have the capability to develop materials with unique structure and properties not found in nature.”

    Teasing out these properties becomes possible when examining materials at the nanoscale (a nanometer is one-billionth of a meter, and nanoscale materials run one to 100 nanometers in size). During graduate school, Gradečak zeroed in on gallium nitride, GaN, a synthetic compound used by the semiconductor industry that turned out to feature some extraordinary optical properties: If the composition of GaN is altered at the nanoscale, the compound can produce light ranging from the ultraviolet to the infrared.

    As a young researcher investigating nanoscale defects in GaN that changed the compound’s behavior, Gradečak “opened up a new world,” she says. “We all have to find a niche, our passion, and learning that I could design materials, tune their properties and emissions — this ability was amazing to me.”

    Gradečak was especially fascinated by the wealth of potential optical and electrical applications for these nanoscale materials. GaN and similar semiconducting compounds are capable not just of emitting light at a range of wavelengths, but of conducting electricity and heat more efficiently, too.

    Gradečak set about harnessing the power of nanoscale compounds. She developed a unique repertoire of laboratory methods that involve manipulating compounds in their vapor phase in a growth chamber. Inside, atoms take root on substrates in particular configurations based on Gradečak’s desired outcomes.

    In one venture, Gradečak created nanowires, slender, solid fibers composed of nanoscale semiconductor materials that can be grown on varied surfaces such as silicon or flexible polymers. Of infinitesimal diameter, these nanowires are essentially one-dimensional objects, and because they can be millions of times longer than they are wide, they are ideally suited for transmitting energy in the form of electricity, heat, and light.

    One signature application to emerge from this nanowire research is a new and different kind of light-emitting diode (LED). Gradečak’s device more closely approximates sunlight’s red and green wavelengths than current LED technologies. In addition, instead of utilizing expensive materials such as sapphire as a growth medium, as is the typical practice of current manufacturers, Gradečak’s nanowire-based LEDs can be grown on abundant, inexpensive substrates, including flexible plastics. Her invention may prove much more economical for home and industry consumers.

    Another key development from Gradečak’s lab is a solar cell made from zinc oxide nanowires embedded with tiny quantum dots — nanocrystals made from a semiconductor material that are so small they essentially have no dimension. While the device does not yet convert solar energy to electricity as efficiently as today’s silicon-based solar cells, Gradečak notes, “Our devices are transparent and flexible, and in just a few years, we’ve improved efficiency of our cell by two orders of magnitude; this is an amazing accomplishment.”

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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.

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  • richardmitnick 6:29 pm on October 29, 2014 Permalink | Reply
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    From LLNL: “Tiny carbon nanotube pores make big impact “ 

    Lawrence Livermore National Laboratory

    Oct. 29, 2014

    Anne M Stark

    A team led by the Lawrence Livermore scientists has created a new kind of ion channel consisting of short carbon nanotubes, which can be inserted into synthetic bilayers and live cell membranes to form tiny pores that transport water, protons, small ions and DNA.

    These carbon nanotube “porins” have significant implications for future health care and bioengineering applications. Nanotube porins eventually could be used to deliver drugs to the body, serve as a foundation of novel biosensors and DNA sequencing applications, and be used as components of synthetic cells.

    Researchers have long been interested in developing synthetic analogs of biological membrane channels that could replicate high efficiency and extreme selectivity for transporting ions and molecules that are typically found in natural systems. However, these efforts always involved problems working with synthetics and they never matched the capabilities of biological proteins.

    Unlike taking a pill which is absorbed slowly and is delivered to the entire body, carbon nanotubes can pinpoint an exact area to treat without harming surrounding other organs.

    “Many good and efficient drugs that treat diseases of one organ are quite toxic to another,” said Aleksandr Noy, an LLNL biophysicist who led the study and is the senior author on the paper appearing in the Oct. 30 issue of the journal, Nature. “This is why delivery to a particular part of the body and only releasing it there is much better.”

    From left: Lawrence Livermore National Laboratory scientists Aleksandr Noy, Kyunghoon Kim and Jia Geng hold up a model of a carbon nanotube that can be inserted into live cells, which can pinpoint an exact area to treat without harming other organs. Photo by Julie Russell.

    The Lawrence Livermore team, together with colleagues at the Molecular Foundry at the Lawrence Berkeley National Laboratory, University of California Merced and Berkeley campuses, and University of Basque Country in Spain created a much more efficient, biocompatible membrane pore channel out of a carbon nanotube (CNT) — a straw-like molecule that consists of a rolled up graphene sheet.

    This research showed that despite their structural simplicity, CNT porins display many characteristic behaviors of natural ion channels: they spontaneously insert into the membranes, switch between metastable conductance states, and display characteristic macromolecule-induced blockades. The team also found that, just like in the biological channels, local channel and membrane charges could control the ionic conductance and ion selectivity of the CNT porins.

    “We found that these nanopores are a promising biomimetic platform for developing cell interfaces, studying transport in biological channels, and creating biosensors,” Noy said. “We are thinking about CNT porins as a first truly versatile synthetic nanopore that can create a range of applications in biology and materials science.”

    “Taken together, our findings establish CNT porins as a promising prototype of a synthetic membrane channel with inherent robustness toward biological and chemical challenges and exceptional biocompatibility that should prove valuable for bionanofluidic and cellular interface applications,” said Jia Geng, a postdoc who is the first co-author of the paper.

    Kyunghoon Kim, a postdoc and another co-author, added: “We also expect that our CNT porins could be modified with synthetic ‘gates’ to dramatically alter their selectivity, opening up exciting possibilities for their use in synthetic cells, drug delivery and biosensing.”

    Other LLNL researchers include Ramya Tunuguntla, Kang Rae Cho, Dayannara Munoz and Morris Wang. The team members performed some of the work at the Molecular Foundry, a DOE user facility as a part of its user project.

    See the full article here.

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  • richardmitnick 9:02 am on October 17, 2014 Permalink | Reply
    Tags: , , , Nanotechnology   

    From MIT: “Nanoparticles get a magnetic handle” 

    MIT News

    October 9, 2014
    David L. Chandler | MIT News Office

    A long-sought goal of creating particles that can emit a colorful fluorescent glow in a biological environment, and that could be precisely manipulated into position within living cells, has been achieved by a team of researchers at MIT and several other institutions. The finding is reported this week in the journal Nature Communications.

    Elemental mapping of the location of iron atoms (blue) in the magnetic nanoparticles and cadmium (red) in the fluorescent quantum dots provide a clear visualization of the way the two kinds of particles naturally separate themselves into a core-and-shell structure. Image courtesy of the researchers

    The new technology could make it possible to track the position of the nanoparticles as they move within the body or inside a cell. At the same time, the nanoparticles could be manipulated precisely by applying a magnetic field to pull them along. And finally, the particles could have a coating of a bioreactive substance that could seek out and bind with particular molecules within the body, such as markers for tumor cells or other disease agents.

    “It’s been a dream of mine for many years to have a nanomaterial that incorporates both fluorescence and magnetism in a single compact object,” says Moungi Bawendi, the Lester Wolfe Professor of Chemistry at MIT and senior author of the new paper. While other groups have achieved some combination of these two properties, Bawendi says that he “was never very satisfied” with results previously achieved by his own team or others.

    For one thing, he says, such particles have been too large to make practical probes of living tissue: “They’ve tended to have a lot of wasted volume,” Bawendi says. “Compactness is critical for biological and a lot of other applications.”

    In addition, previous efforts were unable to produce particles of uniform and predictable size, which could also be an essential property for diagnostic or therapeutic applications.

    Moreover, Bawendi says, “We wanted to be able to manipulate these structures inside the cells with magnetic fields, but also know exactly what it is we’re moving.” All of these goals are achieved by the new nanoparticles, which can be identified with great precision by the wavelength of their fluorescent emissions.

    The new method produces the combination of desired properties “in as small a package as possible,” Bawendi says — which could help pave the way for particles with other useful properties, such as the ability to bind with a specific type of bioreceptor, or another molecule of interest.

    In the technique developed by Bawendi’s team, led by lead author and postdoc Ou Chen, the nanoparticles crystallize such that they self-assemble in exactly the way that leads to the most useful outcome: The magnetic particles cluster at the center, while fluorescent particles form a uniform coating around them. That puts the fluorescent molecules in the most visible location for allowing the nanoparticles to be tracked optically through a microscope.

    “These are beautiful structures, they’re so clean,” Bawendi says. That uniformity arises, in part, because the starting material, fluorescent nanoparticles that Bawendi and his group have been perfecting for years, are themselves perfectly uniform in size. “You have to use very uniform material to produce such a uniform construction,” Chen says.

    Initially, at least, the particles might be used to probe basic biological functions within cells, Bawendi suggests. As the work continues, later experiments may add additional materials to the particles’ coating so that they interact in specific ways with molecules or structures within the cell, either for diagnosis or treatment.

    The ability to manipulate the particles with electromagnets is key to using them in biological research, Bawendi explains: The tiny particles could otherwise get lost in the jumble of molecules circulating within a cell. “Without a magnetic ‘handle,’ it’s like a needle in a haystack,” he says. “But with the magnetism, you can find it easily.”

    A silica coating on the particles allows additional molecules to attach, causing the particles to bind with specific structures within the cell. “Silica makes it completely flexible; it’s a well developed material that can bind to almost anything,” Bawendi says.

    For example, the coating could have a molecule that binds to a specific type of tumor cells; then, “You could use them to enhance the contrast of an MRI, so you could see the spatial macroscopic outlines of a tumor,” he says.

    The next step for the team is to test the new nanoparticles in a variety of biological settings. “We’ve made the material,” Chen says. “Now we’ve got to use it, and we’re working with a number of groups around the world for a variety of applications.”

    Christopher Murray, a professor of chemistry and materials science and engineering at the University of Pennsylvania who was not connected with this research, says, “This work exemplifies the power of using nanocrystals as building blocks for multiscale and multifunctional structures. We often use the term ‘artificial atoms’ in the community to describe how we are exploiting a new periodic table of fundamental building blocks to design materials, and this is a very elegant example.”

    The study included researchers at MIT; Massachusetts General Hospital; Institut Curie in Paris; the Heinrich-Pette Institute and the Bernhard-Nocht Institute for Tropical Medicine in Hamburg, Germany; Children’s Hospital Boston; and Cornell University. The work was supported by the National Institutes of Health, the Army Research Office through MIT’s Institute for Soldier Nanotechnologies, and the Department of Energy.

    See the full article, with video, here.

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  • richardmitnick 6:33 pm on October 13, 2014 Permalink | Reply
    Tags: , , Nanotechnology   

    From MIT: “Solid nanoparticles can deform like a liquid” 

    MIT News

    October 12, 2014
    David L. Chandler | MIT News Office

    Unexpected finding shows tiny particles keep their internal crystal structure while flexing like droplets.

    A surprising phenomenon has been found in metal nanoparticles: They appear, from the outside, to be liquid droplets, wobbling and readily changing shape, while their interiors retain a perfectly stable crystal configuration.

    Image: Yan Liang

    The research team behind the finding, led by MIT professor Ju Li, says the work could have important implications for the design of components in nanotechnology, such as metal contacts for molecular electronic circuits.

    The results, published in the journal Nature Materials, come from a combination of laboratory analysis and computer modeling, by an international team that included researchers in China, Japan, and Pittsburgh, as well as at MIT.

    The experiments were conducted at room temperature, with particles of pure silver less than 10 nanometers across — less than one-thousandth of the width of a human hair. But the results should apply to many different metals, says Li, senior author of the paper and the BEA Professor of Nuclear Science and Engineering.

    Silver has a relatively high melting point — 962 degrees Celsius, or 1763 degrees Fahrenheit — so observation of any liquidlike behavior in its nanoparticles was “quite unexpected,” Li says. Hints of the new phenomenon had been seen in earlier work with tin, which has a much lower melting point, he says.

    The use of nanoparticles in applications ranging from electronics to pharmaceuticals is a lively area of research; generally, Li says, these researchers “want to form shapes, and they want these shapes to be stable, in many cases over a period of years.” So the discovery of these deformations reveals a potentially serious barrier to many such applications: For example, if gold or silver nanoligaments are used in electronic circuits, these deformations could quickly cause electrical connections to fail.

    Only skin deep

    The researchers’ detailed imaging with a transmission electron microscope and atomistic modeling revealed that while the exterior of the metal nanoparticles appears to move like a liquid, only the outermost layers — one or two atoms thick — actually move at any given time. As these outer layers of atoms move across the surface and redeposit elsewhere, they give the impression of much greater movement — but inside each particle, the atoms stay perfectly lined up, like bricks in a wall.

    “The interior is crystalline, so the only mobile atoms are the first one or two monolayers,” Li says. “Everywhere except the first two layers is crystalline.”

    By contrast, if the droplets were to melt to a liquid state, the orderliness of the crystal structure would be eliminated entirely — like a wall tumbling into a heap of bricks.

    Technically, the particles’ deformation is pseudoelastic, meaning that the material returns to its original shape after the stresses are removed — like a squeezed rubber ball — as opposed to plasticity, as in a deformable lump of clay that retains a new shape.

    The phenomenon of plasticity by interfacial diffusion was first proposed by Robert L. Coble, a professor of ceramic engineering at MIT, and is known as “Coble creep.” “What we saw is aptly called Coble pseudoelasticity,” Li says.

    Now that the phenomenon has been understood, researchers working on nanocircuits or other nanodevices can quite easily compensate for it, Li says. If the nanoparticles are protected by even a vanishingly thin layer of oxide, the liquidlike behavior is almost completely eliminated, making stable circuits possible.

    Possible benefits

    On the other hand, for some applications this phenomenon might be useful: For example, in circuits where electrical contacts need to withstand rotational reconfiguration, particles designed to maximize this effect might prove useful, using noble metals or a reducing atmosphere, where the formation of an oxide layer is destabilized, Li says.

    The new finding flies in the face of expectations — in part, because of a well-understood relationship, in most materials, in which mechanical strength increases as size is reduced.

    “In general, the smaller the size, the higher the strength,” Li says, but “at very small sizes, a material component can get very much weaker. The transition from ‘smaller is stronger’ to ‘smaller is much weaker’ can be very sharp.”

    That crossover, he says, takes place at about 10 nanometers at room temperature — a size that microchip manufacturers are approaching as circuits shrink. When this threshold is reached, Li says, it causes “a very precipitous drop” in a nanocomponent’s strength.

    The findings could also help explain a number of anomalous results seen in other research on small particles, Li says.

    “The … work reported in this paper is first-class,” says Horacio Espinosa, a professor of manufacturing and entrepreneurship at Northwestern University who was not involved in this research. “These are very difficult experiments, which revealed for the first time shape recovery of silver nanocrystals in the absence of dislocation. … Li’s interpretation of the experiments using atomistic modeling illustrates recent progress in comparing experiments and simulations as it relates to spatial and time scales. This has implications to many aspects of mechanics of materials, so I expect this work to be highly cited.”

    The research team included Jun Sun, Longbing He, Tao Xu, Hengchang Bi, and Litao Sun, all of Southeast University in Nanjing, China; Yu-Chieh Lo of MIT and Kyoto University; Ze Zhang of Zhejiang University; and Scott Mao of the University of Pittsburgh. It was supported by the National Basic Research Program of China; the National Natural Science Foundation of China; the Chinese Ministry of Education; the National Science Foundation of Jiangsu Province, China; and the U.S. National Science Foundation.

    See the full article here.

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  • richardmitnick 8:57 pm on October 3, 2014 Permalink | Reply
    Tags: , , , , Nanotechnology   

    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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