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  • richardmitnick 12:03 pm on April 17, 2017 Permalink | Reply
    Tags: Berkeley ALS, How X-rays Pushed Topological Matter Research Over the Top,   

    From LBNL: “How X-rays Pushed Topological Matter Research Over the Top” 

    Berkeley Logo

    Berkeley Lab

    April 14, 2017
    Glenn Roberts Jr.
    geroberts@lbl.gov
    510-486-5582

    1
    Beamline 10.0.1 at Berkeley Lab’s Advanced Light Source is optimized for studies of topological properties in materials. (Credit: Roy Kaltschmidt/Berkeley Lab)

    LBNL/ALS

    While using X-rays generated by the Advanced Light Source (ALS), a synchrotron facility at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab), to study a bismuth-containing thermoelectric material that can convert heat into electricity, physicist M. Zahid Hasan of Princeton University saw that something was interfering with the anticipated view of electrons’ behavior inside the material.

    Knowing how electrons move within this material was sought as a key to decipher how it worked, so this interference—which he and his team observed more than a decade ago during an experiment employing an X-ray-based technique dubbed ARPES (angle-resolved photoemission spectroscopy)—was a problem … at first.

    “Since 2004, I was involved with this research looking for a better understanding of bismuth-based thermoelectric materials, among other things,” said Hasan.

    Around 2007, after completing more X-ray experiments at the ALS and other synchrotrons, and after gaining some understanding of the theory related to his team’s observations, it would become clear to Hasan that this obstruction was actually a discovery: One that would spark a revolution in materials research that continues today, and that could eventually lead to new generations of electronics and quantum technologies.

    Topological matter research is now a flourishing field of research at the ALS, with several staff members devoted to supporting X-ray techniques that largely focus on its properties.

    “Since 2005, something on the surface was annoying me quite a bit,” said Hasan, a Princeton physics professor who in late 2016 became a visiting faculty member at Berkeley Lab’s Materials Sciences Division and a Visiting Miller Professor at UC Berkeley. “I could not get rid of the surface states.”

    Back at Princeton, Hasan struck up a conversation with a fellow physics professor, Duncan Haldane, and he also spoke with Charles Kane, a physics professor at the neighboring University of Pennsylvania, for their collective theoretical insight about the surface effects he was seeing in some bismuth-containing materials. “At that point I was not aware of the theoretical predictions.”

    They discussed theoretical work, some of it dating back several decades, that had explored bizarre and resilient “topological” states in which electrons could move about the surface of a thin material with next to no resistance—like in a traditional superconductor but with a different mechanism.

    The theoretical work provided little clue in how to find the effects in the materials exhibiting this phenomenon, though. So Hasan set out on a path that crossed into the fields of quantum theory, particle physics, and complex mathematics.

    “I had to translate all of the abstract math into these experiments,” he said. “It was like translating from a foreign language.”

    2
    In mathematics, topology is focused on properties that change step-wise, like the number of holes in the objects in the above image. Pioneering theories on topological phenomena in materials were key to the 2016 Nobel Prize in Physics, and were ultimately realized in X-ray experiments at Berkeley Lab’s Advanced Light Source and other similar light sources. Topology explains why electrical conductivity changes in thin-layer materials. (Credit: © Johan Jarnestad/The Royal Swedish Academy of Sciences)

    Flash forward to October 2016, and this time Haldane was describing his early theoretical work during a Nobel Prize press conference. Haldane shared the 2016 Nobel Prize in Physics with David Thouless of the University of Washington (a former postdoctoral researcher at Berkeley Lab), and J. Michael Kosterlitz of Brown University for their work in “theoretical discoveries of topological phase transitions and topological phases of matter.”

    Haldane had said at the time of the Nobel Prize announcement, “I put in the first paper that this is unlikely to be anything anyone could make.” His work, he said, was a “sleeper” that “sat around as an interesting toy model for a very long time—no one quite knew what to do with it.”

    What helped bring that “toy model” to life were later theories by Kane and collaborators, and innovative ARPES studies at the ALS and other synchrotrons that directly probed exotic topological states in some materials.

    Synchrotrons like the ALS have dozens of beamlines that produce focused X-rays and other types of light beams for a variety of experiments that explore the properties of exotic materials and other samples at tiny scales, and ARPES provides a window into materials’ electron properties.

    The Nobel Committee, in its supporting materials for the prize, had cited early experiments by Hasan’s team at the ALS on materials exhibiting topological insulator phases. A topological insulator acts like an electrical conductor on the surface and an insulator (with no electrical flow) inside.

    3
    Band structure of bismuth selenide, a topological insulator. The red areas represent surface states and the vertical space between the yellow areas is the bulk band gap. At lower right, a 3-D schematic of the cone-shaped surface band structure. The spin states (yellow arrows) indicate that electrons on the surface won’t backscatter from disorder and impurities in the material. (Credit: David Hsieh, Yuqi Xia, Andrew Wray/Princeton University)

    Zahid Hussain, division deputy at the ALS said, “Hasan is an exceptional scientist with a deep understanding of both theory and experiment. He is the reason this became experimentally visible. One experiment did that.”

    Hasan’s work provided an early demonstration of a 3-D topological insulator, for example.

    In these materials, the electron motion is relatively robust, and is immune to many types of impurities and deformities. Researchers have found examples of topological properties in materials even at room temperature.

    This is a critical advantage over so-called high-temperature superconductors, which must be chilled to extreme temperatures in order to achieve a nearly resistance-free flow of electrons.

    4
    A 3-D image of the surface band structure of bismuth telluride. (Credit: Yulin Chen, Z.-X. Shen/Stanford University)

    With topological materials, the electrons exhibit unique patterns in a property known as electron spin that is analogous to a compass needle pointing up or down, and this property can change based on the electron’s path and position in a material.

    One potential future application for the spin properties of electrons in topological materials is spintronics, an emerging field that seeks to control the spin on demand to transmit and store information, much like the zeroes and ones in traditional computer memory.

    Spin could also be harnessed as the information carriers in quantum computers, which could conceivably carry out exponentially more calculations of a certain type in a shorter time than conventional supercomputers.

    Jonathan Denlinger, a staff scientist in the Scientific Support Group at the ALS, said the breakthrough studies on materials with topological behavior led to a rapid shift in focus on materials’ surface properties. Researchers had historically been more interested in electrons within the “bulk,” or inside of materials.

    Hasan’s group used three ALS beamlines—MERLIN, 12.0.1, and 10.0.1—in pioneering ARPES studies of topological matter. Hasan was a co-leader on the proposal that led to the construction of MERLIN in the early 2000s.

    Denlinger, and fellow ALS staff scientists Alexei Fedorov and Sung-Kwan Mo, work at these ALS beamlines, which specialize in ARPES and a related variant called spin-resolved photoelectron spectroscopy. The techniques can provide detailed information about how electrons travel in materials and also about the electrons’ spin orientation.

    ARPES beamlines at the ALS remain in high demand for topological matter research. Fedorov said, “These days, almost every proposal submitted to our beamline in one way or another deals with topological matter.”

    The quest for discoveries of new topological matter at the ALS will also be boosted by a beamline known as MAESTRO (Microscopic and Electronic Structure Observatory) that opened to users last year and will help visualize exotic ordered structures formed in some topological materials.

    “ALS-U, a planned upgrade of the ALS, should improve and enhance topological matter studies using the ALS,” Mo said. “It will allow us to focus down to a very small spot,” which could reveal more detail in the electron behavior of topological matter.

    Improved X-ray performance could help identify some topological materials that were previously overlooked, and to better distinguish and classify their properties, Hasan said.

    Hasan’s early work in topological matter, including topological insulators, led him to the detection of a previously theorized massless particle known as the Weyl fermion in topological semimetals, and he is now devising a related experiment that he hopes will mimic the period of the early universe in which particles began to take on mass.

    Denlinger, Fedorov, and Mo are gearing up for more studies of topological matter, and are reaching out to possible collaborators across Berkeley Lab and the global scientific community.

    Nanoscale materials show a lot of promise for topological materials applications, and thermoelectrics—those same materials that can transfer heat to electricity and vice versa, and that led to the first realization of topological matter in X-ray experiments—should see performance gains in the short term thanks to the feverish pace of R&D in the field, Fedorov noted.

    Hasan, too, said he is excited about progress in the field. “We are in the middle of a topological revolution in physics, for sure,” he said.

    The Advanced Light Source (ALS) is a DOE Office of Science User Facility. Operation of ALS and this work is supported by the DOE Office of Science.

    See the full article here .

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

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


    SLAC Lab

    April 11, 2017
    Glennda Chui

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

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

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

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

    Materials that Surprise

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

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

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

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

    Joining Forces With Light Sources

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

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

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

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

    SLAC/SSRL

    LBNL/ALS

    SLAC LCLS

    SLAC/LCLS II

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

    Basic Questions and Practical Answers

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

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

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

    Running Experiments in Supercomputers

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

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

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

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

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

    See the full article here .

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  • richardmitnick 2:16 pm on February 28, 2017 Permalink | Reply
    Tags: ADEPT (Adaptive Deployable Entry and Placement Technology), Berkeley ALS, , PICA (Phenolic Impregnated Carbon Ablator), The Heat is On   

    From LBNL: “The Heat is On” 

    Berkeley Logo

    Berkeley Lab

    February 22, 2017
    Glenn Roberts Jr.
    geroberts@lbl.gov
    510-486-5582

    1
    The saucer-like Mars Science Laboratory, which landed the Curiosity rover on MARS, featured the largest heat shield (pictured here)—at 14 feet 9 inches in diameter—to enter a planet’s atmosphere. NASA is now engaging in R&D for even larger heat shields made of flexible, foldable material that can open up like an umbrella to protect spacecraft during atmospheric entry. (Credit: NASA/JPL-Caltech/Lockheed Martin)

    The Mars Science Laboratory (MSL) spacecraft that landed the Curiosity rover on Mars endured the hottest, most turbulent atmospheric entry ever attempted in a mission to the Red Planet. The saucer-shaped MSL was protected by a thin, lightweight carbon fiber-based heat-shield material that was a bit denser than balsa wood.

    The same material, dubbed PICA (Phenolic Impregnated Carbon Ablator), also protected NASA’s Stardust spacecraft as it returned to Earth after collecting comet and space dust samples in 2006. It is based on a family of materials that was recognized by the space agency as its Invention of the Year in 2007.

    SpaceX, a NASA-contracted private company that delivers cargo to the International Space Station, has since adapted the PICA material for its Dragon space capsule.

    While traditional heat shields form a rigid structure, NASA Ames Research Center (NASA ARC) in Moffett Field, California, which developed the PICA material, is now developing a new family of flexible heat-shield systems that uses a woven carbon-fiber substrate, or base material. This material’s heat-resistance and structural properties can be fine-tuned by adjusting the weaving techniques.

    In addition, the flexible nature of woven materials can accommodate the design of large-profile spacecraft capable of landing heavier payloads, including human crews.

    The new flexible heat-shield system, called ADEPT (Adaptive Deployable Entry and Placement Technology), would be stowed inside the spacecraft and deployed like an umbrella prior to atmospheric entry. Supported by an array of sturdy metallic struts, the ADEPT system could also serve to steer the spacecraft during descent.

    Unlike the reusable ceramic tiles used on NASA’s space shuttles to survive reentry from low-Earth orbit, the lighter PICA and woven carbon materials are designed for single use, protecting their payload while they slowly burn up during the rigors of atmospheric entry.


    Access mp4 video here .
    NASA’s Adaptable, Deployable Entry Placement Technology (ADEPT) Project will test and demonstrate a large, flexible heat shield that can be stored aboard a spacecraft until needed for atmospheric entry. (Credit: NASA)

    That’s why it’s critical to ensure through testing, simulation, and analysis, that heat-shield materials can survive long enough to protect the spacecraft during high-speed entry into a planet’s atmosphere.

    To understand performance of the system at the microscopic scale, NASA research scientists are conducting X-ray experiments at Lawrence Berkeley National Laboratory (Berkeley Lab) to track a material’s response to extreme temperatures and pressures.

    3
    How a sample of woven carbon-fiber material degrades over five minutes during heating in an increasingly dense simulated atmosphere.

    “We’ve been working on studies of various heat-shield materials for the past three years,” said Harold Barnard, a scientist at Berkeley Lab’s Advanced Light Source (ALS), “and we are trying to develop high-speed X-ray imaging techniques so we can actually capture these heat-shield materials reacting and decomposing in real time.”

    During an actual atmospheric entry at Mars, there is substantial heat load on the shielding material, with surface temperatures approaching 4,000 degrees Fahrenheit.

    LBNL/ALS
    LBNL/ALS

    “We are developing methods for recreating those sorts of conditions, and scanning materials in real time as they are experiencing these loads and transitions,” Barnard said. A test platform now in development uses a pneumatic piston to stretch the material, in combination with heat and gas-flow controls, to simulate entry conditions.

    4
    Harold Barnard (from left), Alastair MacDowell and Dula Parkinson are scientists at Berkeley Lab’s Advanced Light Source who are working with NASA to test heat shield and other materials. They use a technique called X-ray micro-tomography to scan objects and produce 3-D renderings of the microstructure of materials. (Credit: Marilyn Chung/Berkeley Lab)

    4
    A small model of NASA’s ADEPT heat shield, on display at NASA Ames Research Center. (Credit: Marilyn Chung/Berkeley Lab)

    Francesco Panerai, a scientist with AMA Inc. at NASA ARC and the lead experimentalist for NASA’s X-ray studies at Berkeley Lab’s ALS, said, “X-rays enable new simulations that we were not able to do before. Before we were using X-rays, we were limited to 2-D images, and we were trying to mimic these with computer simulations. X-ray tomography enables us to digitize the real 3-D microstructure of the material.”

    The work at the ALS has already produced some promising results that show how present-day and next-generation heat-shield materials, including woven carbon fibers for flexible heat shields, gradually decompose in simulated atmospheric entry conditions. More experiments are planned to study different weave arrangements and material types.

    “You can really see a lot of details” in the ALS images, Panerai said, which were produced using a technique called microtomography. “You can see clusters of fibers, and you can see that the fibers are hollow.” The fibers in the studies are less than one-tenth the width of a human hair.

    6
    This image, generated from X-ray micro-tomography scans at Berkeley Lab’s Advanced Light Source, shows the 3-D microscale structure of a carbon-fiber felt material. (Credit: Tim Sandstrom/NASA Ames)

    He added, “It’s very complex to reproduce velocity and temperature at the same time in physical experiments. The ALS allows us to reproduce similar conditions to entry—very high temperatures, and we can watch how flow moves inside materials.” The work could benefit future missions to Mars, Saturn, and Venus, among others.

    Joseph C. Ferguson, a researcher with Science and Technology Corp. at NASA ARC, led the development of a software tool called PuMA (Porous Materials Analysis) that can extract information about a material’s properties from the ALS X-ray imaging data, including details about how porous a material is, how it conducts heat, and how it decomposes under entry conditions.

    All of these characteristics factor into a material’s ability to protect a spacecraft. NASA developers have made this software tool available to other experimenters at the ALS for other applications.

    Barnard said the NASA work has pushed ALS researchers to develop faster microtomography imaging methods that capture how materials respond over time to stress.

    “We have been able to push the imaging speed down to between 2.5 to 3 seconds per scan,” Barnard said. “Normally these scans can take up to 10 minutes. It has been good for us to work on this project. We want better instrumentation and analysis techniques for the experiments here, and we are pushing our instrumentation boundaries while helping NASA to develop heat shields.”

    Dula Parkinson, a research scientist who works with Barnard at the ALS on microtomography experiments, said the faster imaging speeds, which can produce about 2,000 frames per second, are generating a high volume of data.

    “The capabilities of our detectors and other instruments over the past five years have improved orders of magnitude,” Parkinson said. “It has increased our needs for data management and computing power.”

    The ALS draws on resources from Berkeley Lab’s Center for Advanced Mathematics for Energy Research Applications (CAMERA), which assists with image processing and algorithms for visualizing the X-ray data, and also from Berkeley Lab’s National Energy Research Scientific Computing Center (NERSC).

    NASA ARC researchers also tap into ALS-produced data via the Energy Sciences Network (ESnet), a high-bandwidth data network managed by Berkeley Lab that connects research facilities and supercomputer centers. NASA scientists use NASA ARC’s Pleiades, one of the world’s most powerful supercomputers, to perform analysis and simulations on data generated at the ALS.

    “Supercomputing is very important in this effort,” Panerai said. “One of the areas we will explore is to try to predict the properties of a virtual material” based on what is learned from X-ray experiments and computer modeling of existing materials.

    “We would like to know the material’s response before we create it,” Panerai said. “We think this could help in materials design.”

    See the full article here .

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  • richardmitnick 3:21 pm on December 26, 2016 Permalink | Reply
    Tags: , Berkeley ALS, , , Researchers Use World's Smallest Diamonds to Make Wires Three Atoms Wide,   

    From SLAC: “Researchers Use World’s Smallest Diamonds to Make Wires Three Atoms Wide” 


    SLAC Lab

    December 26, 2016

    LEGO-style Building Method Has Potential for Making One-Dimensional Materials with Extraordinary Properties

    1
    Fuzzy white clusters of nanowires on a lab bench, with a penny for scale. Assembled with the help of diamondoids, the microscopic nanowires can be seen with the naked eye because the strong mutual attraction between their diamondoid shells makes them clump together, in this case by the millions. At top right, an image made with a scanning electron microscope shows nanowire clusters magnified 10,000 times. (SEM image by Hao Yan/SIMES; photo by SLAC National Accelerator Laboratory)

    Scientists at Stanford University and the Department of Energy’s SLAC National Accelerator Laboratory have discovered a way to use diamondoids – the smallest possible bits of diamond – to assemble atoms into the thinnest possible electrical wires, just three atoms wide.

    By grabbing various types of atoms and putting them together LEGO-style, the new technique could potentially be used to build tiny wires for a wide range of applications, including fabrics that generate electricity, optoelectronic devices that employ both electricity and light, and superconducting materials that conduct electricity without any loss. The scientists reported their results today in Nature Materials.

    “What we have shown here is that we can make tiny, conductive wires of the smallest possible size that essentially assemble themselves,” said Hao Yan, a Stanford postdoctoral researcher and lead author of the paper. “The process is a simple, one-pot synthesis. You dump the ingredients together and you can get results in half an hour. It’s almost as if the diamondoids know where they want to go.”

    2
    This animation shows molecular building blocks joining the tip of a growing nanowire. Each block consists of a diamondoid – the smallest possible bit of diamond – attached to sulfur and copper atoms (yellow and brown spheres). Like LEGO blocks, they only fit together in certain ways that are determined by their size and shape. The copper and sulfur atoms form a conductive wire in the middle, and the diamondoids form an insulating outer shell. (SLAC National Accelerator Laboratory)

    The Smaller the Better

    3

    Illustration of a cluster of nanowires assembled by diamondoids
    An illustration shows a hexagonal cluster of seven nanowires assembled by diamondoids. Each wire has an electrically conductive core made of copper and sulfur atoms (brown and yellow spheres) surrounded by an insulating diamondoid shell. The natural attraction between diamondoids drives the assembly process. (H. Yan et al., Nature Materials)

    Although there are other ways to get materials to self-assemble, this is the first one shown to make a nanowire with a solid, crystalline core that has good electronic properties, said study co-author Nicholas Melosh, an associate professor at SLAC and Stanford and investigator with SIMES, the Stanford Institute for Materials and Energy Sciences at SLAC.

    The needle-like wires have a semiconducting core – a combination of copper and sulfur known as a chalcogenide – surrounded by the attached diamondoids, which form an insulating shell.

    Their minuscule size is important, Melosh said, because a material that exists in just one or two dimensions – as atomic-scale dots, wires or sheets – can have very different, extraordinary properties compared to the same material made in bulk. The new method allows researchers to assemble those materials with atom-by-atom precision and control.

    The diamondoids they used as assembly tools are tiny, interlocking cages of carbon and hydrogen. Found naturally in petroleum fluids, they are extracted and separated by size and geometry in a SLAC laboratory. Over the past decade, a SIMES research program led by Melosh and SLAC/Stanford Professor Zhi-Xun Shen has found a number of potential uses for the little diamonds, including improving electron microscope images and making tiny electronic gadgets.

    4
    Stanford graduate student Fei Hua Li, left, and postdoctoral researcher Hao Yan in one of the SIMES labs where diamondoids – the tiniest bits of diamond – were used to assemble the thinnest possible nanowires. (SLAC National Accelerator Laboratory)

    Constructive Attraction

    5
    Ball-and-stick models of diamondoid atomic structures in the SIMES lab at SLAC. SIMES researchers used the smallest possible diamondoid – adamantane, a tiny cage made of 10 carbon atoms – to assemble the smallest possible nanowires, with conductive cores just three atoms wide. (SLAC National Accelerator Laboratory)

    For this study, the research team took advantage of the fact that diamondoids are strongly attracted to each other, through what are known as van der Waals forces. (This attraction is what makes the microscopic diamondoids clump together into sugar-like crystals, which is the only reason you can see them with the naked eye.)

    They started with the smallest possible diamondoids – single cages that contain just 10 carbon atoms – and attached a sulfur atom to each. Floating in a solution, each sulfur atom bonded with a single copper ion. This created the basic nanowire building block.

    The building blocks then drifted toward each other, drawn by the van der Waals attraction between the diamondoids, and attached to the growing tip of the nanowire.

    “Much like LEGO blocks, they only fit together in certain ways that are determined by their size and shape,” said Stanford graduate student Fei Hua Li, who played a critical role in synthesizing the tiny wires and figuring out how they grew. “The copper and sulfur atoms of each building block wound up in the middle, forming the conductive core of the wire, and the bulkier diamondoids wound up on the outside, forming the insulating shell.”

    A Versatile Toolkit for Creating Novel Materials

    The team has already used diamondoids to make one-dimensional nanowires based on cadmium, zinc, iron and silver, including some that grew long enough to see without a microscope, and they have experimented with carrying out the reactions in different solvents and with other types of rigid, cage-like molecules, such as carboranes.

    The cadmium-based wires are similar to materials used in optoelectronics, such as light-emitting diodes (LEDs), and the zinc-based ones are like those used in solar applications and in piezoelectric energy generators, which convert motion into electricity.

    “You can imagine weaving those into fabrics to generate energy,” Melosh said. “This method gives us a versatile toolkit where we can tinker with a number of ingredients and experimental conditions to create new materials with finely tuned electronic properties and interesting physics.”

    Theorists led by SIMES Director Thomas Devereaux modeled and predicted the electronic properties of the nanowires, which were examined with X-rays at SLAC’s Stanford Synchrotron Radiation Lightsource, a DOE Office of Science User Facility, to determine their structure and other characteristics.

    The team also included researchers from the Stanford Department of Materials Science and Engineering, Lawrence Berkeley National Laboratory, the National Autonomous University of Mexico (UNAM) and Justus-Liebig University in Germany. Parts of the research were carried out at Berkeley Lab’s Advanced Light Source (ALS)

    LBNL ALS interior
    LBNL ALS

    and National Energy Research Scientific Computing Center (NERSC),

    NERSC CRAY Cori supercomputer
    NERSC

    both DOE Office of Science User Facilities. The work was funded by the DOE Office of Science and the German Research Foundation.

    See the full article here .

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  • richardmitnick 5:08 pm on December 17, 2014 Permalink | Reply
    Tags: Berkeley ALS, , , ,   

    From LBL: “Switching to Spintronics” 

    Berkeley Logo

    Berkeley Lab

    December 17, 2014
    Lynn Yarris (510) 486-5375

    In a development that holds promise for future magnetic memory and logic devices, researchers with the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab) and Cornell University successfully used an electric field to reverse the magnetization direction in a multiferroic spintronic device at room temperature. This demonstration, which runs counter to conventional scientific wisdom, points a new way towards spintronics. and smaller, faster and cheaper ways of storing and processing data.

    s
    Conceptual illustration of how magnetism is reversed (see compass) by the application of an electric field (blue dots) applied across gold capacitors. Blurring of compass needles under electric field represents two-step process. (Image courtesy of John Heron, Cornell)

    “Our work shows that 180-degree magnetization switching in the multiferroic bismuth ferrite can be achieved at room temperature with an external electric field when the kinetics of the switching involves a two-step process,” says Ramamoorthy Ramesh, Berkeley Lab’s Associate Laboratory Director for Energy Technologies, who led this research. “We exploited this multi-step switching process to demonstrate energy-efficient control of a spintronic device.”

    Ramesh, who also holds the Purnendu Chatterjee Endowed Chair in Energy Technologies at the University of California (UC) Berkeley, is the senior author of a paper describing this research in Nature. The paper is titled Deterministic switching of ferromagnetism at room temperature using an electric field. John Heron, now with Cornell University, is the lead and corresponding author. (See below for full list of co-authors).

    r
    Ramamoorthy Ramesh is Berkeley Lab’s Associate Laboratory Director for Energy Technologies, a UC Berkeley professor, and a leading authority on multiferroics. (Photo by Roy Kaltschmidt)

    Multiferroics are materials in which unique combinations of electric and magnetic properties can simultaneously coexist. They are viewed as potential cornerstones in future data storage and processing devices because their magnetism can be controlled by an electric field rather than an electric current, a distinct advantage as Heron explains.

    “The electrical currents that today’s memory and logic devices rely on to generate a magnetic field are the primary source of power consumption and heating in these devices,” he says. “This has triggered significant interest in multiferroics for their potential to reduce energy consumption while also adding functionality to devices.”

    Nature, however, has imposed thermodynamic barriers and material symmetry constrains that theorists believed would prevent the reversal of magnetization in a multiferroic by an applied electric field. Earlier work by Ramesh and his group with bismuth ferrite, the only known thermodynamically stable room-temperature multiferroic, in which an electric field was used as on/off switch for magnetism, suggested that the kinetics of the switching process might be a way to overcome these barriers, something not considered in prior theoretical work.

    “Having made devices and done on/off switching with in-plane electric fields in the past, it was a natural extension to study what happens when an out-of-plane electric field is applied,” Ramesh says.

    Ramesh, Heron and their co-authors set up a theoretical study in which an out-of-plane electric field – meaning it ran perpendicular to the orientation of the sample – was applied to bismuth ferrite films. They discovered a two-step switching process that relies on ferroelectric polarization and the rotation of the oxygen octahedral.

    j
    John Heron is the lead author of a Nature paper describing the switching of ferromagnetism at room temperature using an electric field.

    “The two-step switching process is key as it allows the octahedral rotation to couple to the polarization,” Heron says. “The oxygen octahedral rotation is also critical because it is the mechanism responsible for the ferromagnetism in bismuth ferrite. Rotation of the oxygen octahedral also allows us to couple bismuth ferrite to a good ferromagnet such as cobalt-iron for use in a spintronic device.”

    To demonstrate the potential technological applicability of their technique, Ramesh, Heron and their co-authors used heterostructures of bismuth ferrite and cobalt iron to fabricate a spin-valve, a spintronic device consisting of a non-magnetic material sandwiched between two ferromagnets whose electrical resistance can be readily changed. X-ray magnetic circular dichroism photoemission electron microscopy (XMCD-PEEM) images showed a clear correlation between magnetization switching and the switching from high-to-low electrical resistance in the spin-valve. The XMCD-PEEM measurements were completed at PEEM-3, an aberration corrected photoemission electron microscope at beamline 11.0.1 of Berkeley Lab’s Advanced Light Source.

    LBL Advanced Light Source
    LBL ALS interior
    LBL ALS

    “We also demonstrated that using an out-of-plane electric field to control the spin-valve consumed energy at a rate of about one order of magnitude lower than switching the device using a spin-polarized current,” Ramesh says.

    In addition to Ramesh and Heron, other co-authors of the Nature paper were James Bosse, Qing He, Ya Gao, Morgan Trassin, Linghan Ye, James Clarkson, Chen Wang, Jian Liu, Sayeef Salahuddin, Dan Ralph, Darrell Schlom, Jorge Iniguez and Bryan Huey.

    See the full article here.

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  • richardmitnick 7:35 pm on December 15, 2014 Permalink | Reply
    Tags: Berkeley ALS, Concrete,   

    From LBL: “News Center Back to the Future with Roman Architectural Concrete” 

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    Berkeley Lab

    December 15, 2014
    Lynn Yarris (510) 486-5375

    No visit to Rome is complete without a visit to the Pantheon, Trajan’s Markets, the Colosseum, or the other spectacular examples of ancient Roman concrete monuments that have stood the test of time and the elements for nearly two thousand years. A key discovery to understanding the longevity and endurance of Roman architectural concrete has been made by an international and interdisciplinary collaboration of researchers using beams of X-rays at the Advanced Light Source (ALS) of the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab).

    LBL Advanced Light Source
    LBL ALS interior
    ALS at LBL

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    The concrete walls of Trajan’s Markets in Rome have stood the test of time and the elements for nearly 2,000 years. They have even survived a major earthquake in 1349. (Photo courtesy of Marie Jackson)

    Working at ALS beamline 12.3.2, a superconducting bending magnet X-ray micro-diffraction beamline, the research team studied a reproduction of Roman volcanic ash-lime mortar that had been previously subjected to fracture testing experiments at Cornell University. In the concrete walls of Trajan’s Markets, constructed around 110 CE, this mortar binds cobble-sized fragments of tuff and brick. Through observing the mineralogical changes that took place in the curing of the mortar over a period of 180 days and comparing the results to 1,900 year old samples of the original, the team discovered that a crystalline binding hydrate prevents microcracks from propagating.

    “The mortar resists microcracking through in situ crystallization of platy strätlingite, a durable calcium-alumino-silicate mineral that reinforces interfacial zones and the cementitious matrix,” says Marie Jackson, a faculty scientist with the University of California (UC) Berkeley’s Department of Civil and Environmental Engineering who led this study. “The dense intergrowths of the platy crystals obstruct crack propagation and preserve cohesion at the micron scale, which in turn enables the concrete to maintain its chemical resilience and structural integrity in a seismically active environment at the millennial scale.”

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    (From left) Marie Jackson, Qinfei Li, Martin Kunz and Paulo Monteiro at ALS Beamline 12.3.2 where they conducted a study on ancient Roman concrete. (Photo by Roy Kaltschmidt)

    Jackson, a volcanologist by training who led an earlier study at the ALS on Roman seawater concrete, is the lead author of a paper describing this study in the Proceedings of the National Academy of Sciences (PNAS) titled Mechanical Resilience and Cementitious Processes in Imperial Roman Architectural Mortar. Co-authors of the paper are Eric Landis, Philip Brune, Massimo Vitti, Heng Chen, Qinfei Li, Martin Kunz, Hans-Rudolf Wenk, Paulo Monteiro and Anthony Ingraffea.

    The mortars that bind the concrete composites used to construct the structures of Imperial Rome are of keen scientific interest not just because of their unmatched resilience and durability, but also for the environmental advantages they offer. Most modern concretes are bound by limestone-based Portland cement. Manufacturing Portland cement requires heating a mix of limestone and clay to 1,450 degrees Celsius (2,642 degrees Fahrenheit), a process that releases enough carbon – given the 19 billion tons of Portland cement used annually – to account for about seven-percent of the total amount of carbon emitted into the atmosphere each year.

    Roman architectural mortar, by contrast, is a mixture of about 85-percent (by volume) volcanic ash, fresh water, and lime, which is calcined at much lower temperature than Portland cement. Coarse chunks of volcanic tuff and brick compose about 45-to-55-percent (by volume) of the concrete. The result is a significant reduction in carbon emissions.

    “If we can find ways to incorporate a substantial volumetric component of volcanic rock in the production of specialty concretes, we could greatly reduce the carbon emissions associated with their production also improve their durability and mechanical resistance over time,” Jackson says.

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    Ancient Roman concrete consists of coarse chunks of volcanic tuff and brick bound together by a volcanic ash-lime mortar that resists microcracking, a key to its longevity and endurance. (Photo by Roy Kaltschmidt, Berkeley Lab)

    As part of their study, Jackson and her collaborators at UC Berkeley used ALS beamline 12.3.2 to make X-ray micro-diffraction measurements of slices of the Roman mortar that were only about 0.3 millimeters thick.

    “We obtained X-ray diffractograms for many different points within a given cementitious microstructure,” Jackson says. “This enabled us to detect changes in mineral assemblages that gave precise indications of chemical processes active over very small areas.”

    The mineralogical changes that Jackson and her collaborators observed showed the mortar reproduction gaining strength and toughness over 180 days as calcium-aluminum-silicate-hydrate (C-A-S-H) cementing binder coalesced and strätlingite crystals grew in interfacial zones between volcanic scoria and the mortar matrix. The toughening of these interfacial zones is reflected in the bridging crack morphology, which was measured by co-author Landis at the University of Maine, using computed tomography scans of the fractured mortar specimens. These experimental results correlate well with computations of increasing fracture energy determined by co-author Brune, now at Dupont Technologies. The strätlingite crystals show no corrosion and their smooth surfaces suggest long-term stability, similar to geological strätlingite that persists for hundreds of thousands of years.

    “The in situ crystallization of the strätlingite crystals produces interfacial zones that are very different from any interfacial microstructure observed in Portland cement concretes,” Jackson says. “High porosity along the interfacial zones of inert aggregates in Portland cement concrete creates the sites where crack paths first nucleate and propagate.”

    A future challenge for researchers, Jackson says, will be to “find ways to activate aggregates, as slag or as volcanic ash for example, in innovative concretes so that these can develop strätlingite reinforcements in interfacial zones like the Roman architectural mortars.”

    The fracture testing experiments at Cornell University were led by co-author Ingraffea. The samples of mortar from Trajan’s Markets were provided by co-author Vitti and the Sovrintendenza Capitolina di Roma Capitale. Co-author Kunz is the principal scientist at ALS beamline 12.3.2.

    This research was supported by the National Science Foundation and the Loeb Library at Harvard University. The Advanced Light Source is a DOE Office of Science User Facility.

    See the full article here.

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  • richardmitnick 2:29 pm on December 2, 2014 Permalink | Reply
    Tags: , Berkeley ALS, ,   

    From LBL: “A Better Look at the Chemistry of Interfaces” 

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    Berkeley Lab

    December 2, 2014
    Lynn Yarris (510) 486-5375

    Researchers working at the Advanced Light Source (ALS) of the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab) have combined key features of two highly acclaimed X-ray spectroscopy techniques into a new technique that offers sub-nanometer resolution of every chemical element to be found at heterogeneous interfaces, such as those in batteries and fuel cells. This new technique is called SWAPPS for Standing Wave Ambient Pressure Photoelectron Spectroscopy, and it combines standing-wave photoelectron spectroscopy (SWPS) with high ambient pressure photoelectron spectroscopy (APPS).

    i
    By utilizing X-ray standing waves to excite photoelectrons, SWAPPS delivers vital information about all the chemical elements at the heterogeneous interfaces found in batteries, fuel cells and other devices.

    “SWAPPS enables us to study a host of surface chemical processes under realistic pressure conditions and for systems related to energy production, such as electrochemical cells, batteries, fuel cells and photovoltaic cells, as well as in catalysis and environmental science,” says Charles Fadley, a physicist who holds joint appointments with Berkeley Lab’s Materials Sciences Division and the University of California Davis, where he is a Distinguished Professor of Physics. “SWAPPS provides all the advantages of the widely used technique of X-ray photoelectron spectroscopy, including element and chemical-state sensitivity, and quantitative analysis of relative concentrations of all species present. However with SWAPPS we don’t require the usual ultrahigh vacuum, which means we can measure the interfaces between volatile liquids and solids.”

    Fadley is one of three corresponding authors of a paper describing SWAPPS in Nature Communications. The paper is titled Concentration and chemical-state profiles at heterogeneous interfaces with sub-nm accuracy from standing-wave ambient-pressure photoemission. The other two corresponding authors are Hendrik Bluhm, with Berkeley Lab’s Chemical Sciences Division, a pioneer in the development of APPS, and Slavomír Nemšák, now with Germany’s Jülich Peter Grünberg Institute. (See below for the complete list of authors).

    team
    (From left) Chuck Fadley, Ioannis Zegkinoglou, Slavomir Nemsak, Osman Karslioglu, Andrey Shavorskiy and Hendrik Bluhm at Beamline 11.0.2 of the Advanced Light Source (photo by Roy Kaltschmidt)

    In terms of energies and wavelengths, X-rays serve as excellent probes of chemical processes. In the alphabet soup of X-ray analytical techniques, two in particular stand out for the study of chemistry at the interface where layers of two different materials or phases of matter meet. The first is SWPS, developed at the ALS by Fadley and his research group, which made it possible for the first time to selectively study buried interfaces in a sample with either soft or hard X-rays. The second is APPS, also developed at the ALS by a team that included Bluhm, which made it possible for the first time to use X-ray photoelectron spectroscopy under pressures and humidities similar to those encountered in natural or practical environments.

    “Heterogeneous processes at solid/gas, liquid/gas and solid/liquid interfaces are ubiquitous in modern devices and technologies but often difficult to study quantitatively,” Bluhm says. “Full characterization requires measuring the depth profiles of chemical composition and state with enhanced sensitivity in narrow interfacial regions at the nanometer scale. By combining features of SWPS and APPS techniques, we can use SWAPPS to measure the elemental and chemical composition of heterogeneous interfaces with sub-nanometer resolution in the direction perpendicular to the interface.”

    Says Fadley, “We believe SWAPPS will deliver vital information about the structure and chemistry of liquid/vapor and liquid/solid interfaces, in particular the electrical double layer whose structure is critical to the operation of batteries, fuel cells and all of electrochemistry, but which is still not understood at a microscopic level.”

    Fadley, Bluhm, Nemšák and their collaborators used their SWAPPS technique to study a model system in which a nanometer layer of an aqueous electrolyte of sodium hydroxide and cesium hydroxide was grown on an iron oxide (hematite) solid. The spatial distributions of the electrolyte ions and the carbon contaminants across the solid/liquid and liquid/gas interfaces were directly probed and absolute concentrations of the chemical species were determined. The observation of binding-energy shifts with depth provided additional information on the bonding and/or depth-dependent potentials in the system.

    “We determined that the sodium ions are located close to the iron oxide/solution interface, while cesium ions are on average not in direct contact with the solid/liquid interface,” Bluhm says. “We also discovered that there are two different kinds of carbon species, one hydrophobic, which is located exclusively in a thin film at the liquid/vapor interface, and a hydrophilic carbonate or carboxyl that is evenly distributed throughout the liquid film.”

    SWAPPS measures the depth profiles of chemical elements with sub-nanometer resolution in the direction perpendicular to the interface, utilizing an X-ray standing wave field that can be tailored to focus on specific depths, i.e., near the surface or near the iron oxide interface.

    SWAPPS measures the depth profiles of chemical elements with sub-nanometer resolution in the direction perpendicular to the interface utilizing an X-ray standing wave field that can be tailored to focus on specific depths, i.e., near the surface or near the iron oxide interface.

    A key to the success of this study was the use of X-ray standing waves to excite the photoelectrons. A standing wave is a vibrational pattern created when two waves of identical wavelength interfere with one another: one is the incident X-ray and the other is the X-ray reflected by a mirror. Interactions between standing waves and core-level electrons reveal much about the depth distributions of each chemical species in a sample.

    “Tailoring the X-ray wave field into a standing wave can be used to achieve greater depth sensitivity in photoelectron spectroscopy,” Fadley says. “Our combination of an oscillatory standing-wave field and the exponential decay of the photoelectron signal at each interface gives us unprecedented depth resolution.”

    In their Nature Communications paper, the authors say that future time-resolved SWAPPS studies using free-electron laser or high-harmonic generation light sources would also permit, via pump-probe methods, looking at the timescales of processes at interfaces on the femtosecond time scale.

    “The range of future applications and measurement scenarios for SWAPPS is enormous,” Fadley says.

    This work was carried out at ALS Beamline 11.0.2, which is operated by Berkeley Lab’s Chemical Sciences Division and hosts two ambient-pressure photoemission spectroscopy endstations.

    In addition to Fadley, Bluhm and Nemšák, other authors of the Nature Communications paper describing SWAPPS were Andrey Shavorskiy, Osman Karslioglu, Ioannis Zegkinoglou, Peter Greene, Edward Burks, Arunothai Rattanachata, Catherine Conlon, Armela Keqi, Farhad Salmassi, Eric Gullikson, See-Hun Yang and Kai Liu.

    This research was primarily funded by the DOE Office of Science. The Advanced Light Source is a DOE Office of Science User Facility.

    See the full article here.

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  • richardmitnick 4:31 pm on November 19, 2014 Permalink | Reply
    Tags: , Berkeley ALS, ,   

    From LBL: “A Cage Made of Proteins, Designed With Help From the Advanced Light Source” 

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    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.

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    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
    LBL ALS

    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.

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    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 5:03 pm on September 10, 2014 Permalink | Reply
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    From LBL: “Advanced Light Source Sets Microscopy Record” 

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    Berkeley Lab

    September 10, 2014
    Lynn Yarris (510) 486-5375

    A record-setting X-ray microscopy experiment may have ushered in a new era for nanoscale imaging. Working at the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab), a collaboration of researchers used low energy or “soft” X-rays to image structures only five nanometers in size. This resolution, obtained at Berkeley Lab’s Advanced Light Source (ALS), a DOE Office of Science User Facility, is the highest ever achieved with X-ray microscopy.

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    image
    Ptychographic image using soft X-rays of lithium iron phosphate nanocrystal after partial dilithiation. The delithiated region is shown in red.

    Using ptychography, a coherent diffractive imaging technique based on high-performance scanning transmission X-ray microscopy (STXM), the collaboration was able to map the chemical composition of lithium iron phosphate nanocrystals after partial dilithiation. The results yielded important new insights into a material of high interest for electrochemical energy storage.

    “We have developed diffractive imaging methods capable of achieving a spatial resolution that cannot be matched by conventional imaging schemes,” says David Shapiro, a physicist with the ALS. “We are now entering a stage in which our X-ray microscopes are no longer limited by our optics and we can image at nearly the wavelength of our X-ray light.”

    Shapiro is the lead and corresponding author of a paper reporting this research in Nature Photonics. The paper is titled “Chemical composition mapping with nanometer resolution by soft X-ray microscopy.” (See below for a full list of co-authors and their affiliations.)

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    David Shapiro with the STXM instruments at ALS beamline 5.3.2.1. (Photo by Roy Kaltschmidt)

    In ptychography (pronounced tie-cog-raphee), a combination of multiple coherent diffraction measurements is used to obtain 2D or 3D maps of micron-sized objects with high resolution and sensitivity. Because of the sensitivity of soft x-rays to electronic states, ptychography can be used to image chemical phase transformations and the mechanical consequences of those transformations that a material undergoes.

    “Until this work, however, the spatial resolution of ptychographic microscopes did not surpass that of the best conventional systems using X-ray zone plate lenses,” says Howard Padmore, leader of the Experimental Systems Group at the ALS and a co-author of the Nature Photonics paper. “The problem stemmed from the fact that ptychography was primarily developed on hard X-ray sources using simple pinhole optics for illumination. This resulted in a low scattering cross-section and low coherent intensity at the sample, which meant that exposure times had to be extremely long, and that mechanical and illumination stabilities were not good enough for high resolution.”

    Key to the success of Shapiro, and his collaborators were the use of soft X-rays which have wavelengths ranging between 1 to 10 nanometers, and a special algorithm that eliminated the effect of all incoherent background signals. Ptychography measurements were recorded with the STXM instruments at ALS beamline 11.0.2, which uses an undulator x-ray source, and ALS beamline 5.3.2.1, which uses a bending magnet source. A coherent soft X-ray beam would be focused onto a sample and scanned in 40 nanometer increments. Diffraction data would then be recorded on an X-ray CCD (charge-coupled device) that allowed reconstruction of the sample to very high spatial resolution.

    “Throughout the ptychography scans, we maintained the sample and focusing optic in relative alignment using an interferometric feedback system with a precision comparable to the wavelength of the X-ray illumination,” Shapiro says.

    Lithium iron phosphate is widely studied for its use as a cathode material in rechargeable lithium-ion batteries. In using their ptychography technique to map the chemical composition of lithium iron phosphate crystals, Shapiro and his collaborators found a strong correlation between structural defects and chemical phase propagation.

    “Surface cracking in these crystals was expected,” Shapiro says, “but there is no other means of visualizing the correlation of those cracks with chemical composition at these scales. The ability to visualize the coupling of the kinetics of a phase transformation with the mechanical consequences is critical to designing materials with ultimate durability.”

    Shapiro and his colleagues have already begun applying their ptychography technique to the study of catalytic and magnetic films, magnetotactic bacteria, polymer blends and green cements.
    In this soft X-ray ptychography set-up, a 60 nm width outer-zone-plate focuses a coherent soft X-ray beam onto the sample, which is scanned in 40 nm increments to ensure overlap of the probed areas.

    In this soft X-ray ptychography set-up, a 60 nm width outer-zone-plate focuses a coherent soft X-ray beam onto the sample, which is scanned in 40 nm increments to ensure overlap of the probed areas.

    For the chemical mapping of lithium iron phosphate they used the STXM instrument at ALS beamline 5.3.2.1 which required up to 800 milliseconds of exposure to the X-ray beam for each scan. Next year, they anticipate using a new ALS beamline called COSMIC (COherent Scattering and MICroscopy), which will feature a high brightness undulator x-ray source coupled to new high-frame-rate CCD sensors that will cut beam exposure times to only a few milliseconds and provide spatial resolution at the wavelength of the radiation.

    image2
    In this soft X-ray ptychography set-up, a 60 nm width outer-zone-plate focuses a coherent soft X-ray beam onto the sample, which is scanned in 40 nm increments to ensure overlap of the probed areas. – See more at: http://newscenter.lbl.gov/2014/09/10/advanced-light-source-sets-microscopy-record/#sthash.6DLMbCxp.dpuf

    “If visible light microscopes could only achieve a resolution that was 50 times the wavelength of visible light, we would not be able to see most single celled organisms,” Shapiro says. “Where would the life sciences be with such a limitation? We are now approaching the point where we will have X-ray microscopes of comparable quality to today’s visible light instruments for the study of nanomaterials.”

    Co-authoring the Nature Photonics paper in addition to Shapiro and Padmore were Young-Sang Yu, Tolek Tyliszczak, Jordi Cabana, Rich Celestre, Weilun Chao, David Kilcoyne, Stefano Marchesini, Tony Warwick and Lee Yang of Berkeley Lab; Konstantin Kaznatcheev of Brookhaven National Laboratory; Shirley Meng of the University of San Diego; and Filipe Maia of Uppsala University in Sweden.

    This research was primarily supported by the DOE Office of Science.

    See the full article here.

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  • richardmitnick 11:15 am on September 3, 2014 Permalink | Reply
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    From Berleley ALS “For the Birds: The Magic of Color in Feathers” 

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    Berkeley Lab

    Berkeley Advanced Light Source
    Advanced Light Source at LBL.

    29 August 2014
    No Writer Credit

    Who hasn’t been amazed by the beauty and wild colors of bird feathers? Yet the diverse range of colors seen across the animal kingdom is made possible by surprisingly few molecular building blocks. It is these molecules, referred to collectively as melanins, that are understood to provide the pigmentation that confers color to animal skin, hair, and feathers. So, how is nature able to achieve such a wide variety of colors with so few components? Recent work at the ALS by Musahid Ahmed, Shirley Liu, Tyler Troy, and Dula Parkinson in collaboration with Matt Shawkey (University of Akron), have found that is the proportions in which these molecular components come together that makes all the difference.

    In their experiments, melanin samples extracted from a variety of bird plumage were gently vaporized by a laser under high-vacuum conditions. The sample vapor is then exposed to synchrotron radiation, causing the molecules to lose an electron to form a charged ion which is then detected by the beamline’s mass spectrometer.

    During this process however, some ions fall apart to form many smaller pieces which are also detected, making it difficult to determine what each mass peak represents. As a result, a computer algorithm was developed to interpret and categorize the mass spectra matching specific patterns to the color of the sampled bird feather. The algorithm can now be applied to samples for which the plumage color is unknown.

    map
    Peak probability contrasts (PPC) analysis projected onto three dimensions for black, brown, grey, and peacock (green) feathers. Where relevant, red arrows indicate the pigment extraction location.
    In addition to deciphering the chemical structures of melanin, this work will help paleontologists to derive the colors and patterns of furs, feathers, and skins of ancient beasts using only their fossil remains.

    See the full article here.

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