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  • richardmitnick 5:08 pm on December 17, 2014 Permalink | Reply
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    From LBL: “Switching to Spintronics” 

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    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.

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    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).

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    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.

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    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
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    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).

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    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
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    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.

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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.

    LBL Advanced Light Source
    LBL ALS

    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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  • richardmitnick 4:51 am on July 1, 2014 Permalink | Reply
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    From Berkeley Lab: “News Center Up in Flames: Evidence Confirms Combustion Theory” 

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    Berkeley Lab

    June 30, 2014
    Kate Greene

    Berkeley Lab and University of Hawaii research outlines the story of soot, with implications for cleaner-burning fuels.

    Researchers at the Department of Energy’s Lawrence Berkeley National Lab (Berkeley Lab) and the University of Hawaii have uncovered the first step in the process that transforms gas-phase molecules into solid particles like soot and other carbon-based compounds.

    The finding could help combustion chemists make more-efficient, less-polluting fuels and help materials scientists fine-tune their carbon nanotubes and graphene sheets for faster, smaller electronics. In addition, the results could have implications for the burgeoning field of astrochemistry, potentially establishing the chemical process for how gaseous outflows from stars turn into carbon-based matter in space.

    flame
    Graphical representation of the chemistry in the early stages of soot formation. The mechanism to the right was demonstrated by experiment, while the one on the left was not. Credit: Dorian Parker, University of Hawaii

    “When you burn a flame, you start with a gas-phase reactant and then analyze the products, which include soot,” says Musahid Ahmed, scientist in the Chemical Sciences Division at Berkeley Lab. “But there is no direct evidence for the chemical bonds that break and form in the process.” For more than 30 years, scientists have developed computational models of combustion to explain how gas molecules form soot, but now Ahmed and his colleagues have data to confirm one long-standing theory in particular. “Our paper presents the first direct observation of this process,” he says.

    While the research is relevant to a number of disciplines—combustion science, materials science, and astrochemistry—it’s combustion science that could see the most direct impact the soonest, says Ahmed. Specifically, the fundamental chemistry discovery could be used to find or design fuels that burn cleaner and don’t produce as much soot.

    Think about your car engine. If the combustion process were perfect, only carbon dioxide and water would come out of the tailpipe. Instead, we see fumes and particulates like soot, a visible macromolecule made up of sheets of carbon.

    Theoretically, there are hundreds of different ways molecules can combine to create these dirty emissions. But there has been one popular class of mechanisms that outlines possible early steps for bond making and bond breaking during combustion. Called hydrogen abstraction-acetylene addition, or HACA, it was developed by Michael Frenklach professor of mechanical engineering at the University of California Berkeley in 1991.

    One version of HACA works like this: during the high-temperature, high-pressure environment of combustion, a simple ring of six carbon and six hydrogen atoms, called benzene, would lose one of its hydrogen atoms, allowing another two-carbon molecule called acetylene, to attach to the ring, giving it a kind of tail. Then the acetylene tail would lose one of its hydrogen atoms so another acetylene could link up in, doubling the carbon atoms in the tail to four.

    Next, the tail would curl around and attach to the original ring, creating a double-ring structure called naphthalene. Link by link, ring by ring, these molecules would continue to grow in an unwieldy, crumpled way until they became the macromolecules that we recognize as soot.

    To test the first step of the theoretical HACA mechanism, Ahmed and collaborators from the University of Hawaii used a beamline at the Advanced Light Source (ALS) at Berkeley Lab specifically outfitted to study chemical dynamics. The ALS, a DOE Office of Science user facility, produces numerous photons over a wide range of energies, allowing researchers to probe a variety of molecules produced in this chemical reaction with specialized mass spectrometry analysis.

    two
    Musa Ahmed and Tyler Troy at the Advanced Light Source (ALS) Beamline 9.0.2 where the chemical dynamics experiments on combustion take place. Credit: Roy Kaltschmidt

    Unique to this experimental setup, Ahmed’s team used a so-called hot nozzle, which recreates combustion environment in terms of pressure and temperature. The group started with a gaseous mix of nitrosobenzene (a benzene ring with a molecule of nitrogen and oxygen attached) and acetylene, and pumped it through a heated tube at a pressure of about 300 torr and a temperature of about 750 degrees Celsius. The molecules that came out the other end were immediately skimmed into a mass spectrometer that made use of the synchrotron light for analysis.

    The researchers found two molecules predominantly emerged from the process. The more abundant kind was the carbon ring with a short acetylene tail on it, called phenylacetylene. But they also saw evidence for the double ring, naphthalene. These results, says Ahmed, effectively rule out one HACA mechanism—that a carbon ring would gain two separate tails and those tails would bond to form the double ring—and confirm the most popular HACA mechanism where a long tail curls around to form naphthalene.

    Ahmed’s local team included Tyler Troy, postdoctoral fellow at Berkeley Lab, and this work was performed with long-term collaborator Ralf Kaiser, professor of physical chemistry at the University of Hawaii at Manoa, and Dorian Parker, postdoctoral fellow also at Hawaii. The research was published June 20 online in the journal Angewandte Chemie.

    “Having established the route to naphthalene, the simplest polycyclic aromatic hydrocarbon, the next step will be to unravel the pathways to more complex systems,” says Kaiser.

    Further experiments will investigate these follow-up mechanisms. It’s a tricky feat, explains Ahmed, because the molecular possibilities quickly multiply. The researchers will add infrared spectroscopy to their analysis in order to catch the variety of molecules that form during these next phases of combustion.

    This research was funded by the DOE Office of Science and the National Science Foundation.

    See the full article here.

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

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  • richardmitnick 9:10 am on June 9, 2014 Permalink | Reply
    Tags: , Berkeley ALS, ,   

    From D.O.E Pulse: “Nanoscope to probe chemistry on the molecular scale” 

    pulse

    D.O.E. Pulse

    June 9, 2014
    Kate Greene, 510.486.4404, kgreene@lbl.gov

    For years, scientists have had an itch they couldn’t scratch. Even with the best microscopes and spectrometers, it’s been difficult to study and identify molecules at the so-called mesoscale, a region of matter that ranges from 10 to 1000 nanometers in size. Now, with the help of broadband infrared light from the Advanced Light Source (ALS) synchrotron at DOE’s Lawrence Berkeley National Laboratory (Berkeley Lab), researchers have developed a broadband imaging technique that looks inside this realm with unprecedented sensitivity and range.

    sheet

    This peptoid nanosheet, produced by Gloria Olivier and Ron Zuckerman at Berkeley Lab, is less than 8 nanometers thick at points. SINS makes it possible to acquire spectroscopic images of these ultra-thin nanosheets for the first time.

    By combining atomic force microscopy with infrared synchrotron light, researchers from Berkeley Lab and the University of Colorado have improved the spatial resolution of infrared spectroscopy by orders of magnitude, while simultaneously covering its full spectroscopic range, enabling the investigation of variety of nanoscale, mesoscale, and surface phenomena that were previously difficult to study.

    The new technique, called Synchrotron Infrared Nano-Spectroscopy or SINS, will enable in-depth study of complex molecular systems, including liquid batteries, living cells, novel electronic materials and stardust.

    “The big thing is that we’re getting full broadband infrared spectroscopy at 100 to 1000 times smaller scale,” says Hans Bechtel, principal scientific engineering associate at Berkeley Lab. “This is not an incremental achievement. It’s really revolutionary.”

    In a Proceedings of the National Academy of Sciences paper published May 6 online, titled Ultra-broadband infrared nano-spectroscopic imaging, Berkeley Lab’s Bechtel and Michael Martin, a Berkeley Lab staff scientist, and colleagues from Markus Raschke’s group at the University of Colorado at Boulder describe SINS. They demonstrate the nanoscope’s ability to capture broadband spectroscopic data over a variety of samples, including a semiconductor-insulator system, a mollusk shell, proteins, and a peptoid nanosheet. Martin says these demonstrations just “scratch the surface” of the potential of the new technique.

    Synchronizing Scopes

    SINS combines two pre-existing infrared technologies: a newer technique called infrared scattering-scanning near-field optical microscopy (IR s-SNOM) and an old laboratory standby, known even to college chemistry students, called Fourier Transform Infrared Spectroscopy (FTIR). A clever melding of these two tools, combined with the intense infrared light of the synchrotron at Berkeley Lab gives the researchers the ability to identify clusters of molecules sized as small as 20 to 40 nanometers.

    Experimental setup for SINS that includes the synchrotron light source, an atomic force microscope, a rapid-scan Fourier transform infrared spectrometer, a beamsplitter, mirrors and a detector.

    The new approach overcomes long-standing barriers with pre-existing microscopy techniques that often involve demanding technical and sample preparation requirements. Infrared spectroscopy uses low-energy light, is minimally invasive, and is applicable under ambient conditions, making it an excellent tool for chemical and molecular identifications in systems that are static as well as those that are living and dynamic. The technique works by shining low-energy infrared light onto a molecular sample. Molecules can be thought of as systems of balls (atoms) and springs (bonds between atoms) that vibrate with characteristic wiggles; they absorb infrared radiation at frequencies that correspond to their natural vibrating modes. The output from this absorption is a spectrum, often called a fingerprint, which shows distinctive peaks and dips, depending on the bonds and atoms present in the sample.

    But infrared spectroscopy has its challenges too. While it works well for bulk samples, traditional infrared spectroscopy can’t resolve molecular composition below about 2000 nanometers. The major hurdle is the diffraction limit of light, which is the fundamental barrier that determines the smallest focus spot of light and is particularly troublesome for the large wavelengths of infrared light. In recent years, though, the diffraction limit has been overcome by a technique called scattering-scanning near-field optical microscopy, or s-SNOM, which involves shining light onto a metallic tip. The tip acts as an antenna for the light, directing it to a tiny region at its apex just tens of nanometers wide.

    This trick is what’s used in IR s-SNOM, where infrared light is coupled to a metallic tip. The challenge with IR s-SNOM, however, is that researchers have been relying on infrared light produced by lasers. Lasers emit a large number of photons needed for the technique, but because they operate in a narrow wavelength band, they can only probe a narrow range of molecular vibrations. In other words, laser light simply can’t give you the flexibility to explore a spectrum of mixed molecules.

    A spectral-linescan of a blue mussel shell, which transitions from calcite to aragonite, illustrates the spatial resolution and spectroscopic range capabilities of the SINS technique. The image shows two simultaneously acquired vibrational modes across the transition region.

    Bechtel, Martin and Raschke’s team saw the opportunity to use Berkeley Lab’s ALS to overcome the laser limitation. The lab’s synchrotron produces broadband infrared light with a high-photon count that can be focused to the diffraction limit. The researchers coupled the synchrotron light to a metallic tip with an apex of about 20 nanometers, focusing the infrared beam onto the samples. The resulting spectrum is analyzed with a modified FTIR instrument.

    “This is actually one of very few examples where synchrotron light has been coupled to scanning probe microscopy,” says Raschke. “Moreover, the implementation of the technique at the synchrotron brings chemical nano-spectroscopy and -imaging out of the lab of a few laser science experts and makes it available for a broader scientific community at a user facility.”

    From mollusks to moon rocks

    The team demonstrated the technique by confirming the spectroscopic signature of silicon dioxide on silicon and by illustrating the sharp chemical transition that occurs within the shells of the blue mussel (M. edulis). Additionally, the researchers looked at proteins and a peptoid nanosheet, an engineered, ultra-thin film of proteins with medical and pharmacological applications.

    Martin is excited for the potential of SINS, which is available for researchers from any institution to use. In particular he’s interested in a closer look at battery systems, with the hope that understanding battery chemistry on the mesoscale could provide insight into better performance. Further out, he expects SINS to be useful for a range of biochemistry as well. “This hints at a dream I’ve had in my mind, to look at the surface of a cell, inside the bi-layer membrane, the channels, and receptors,” says Martin. “If we could put a SINS tip on a living cell, we could watch biochemistry happen in real time.”

    Bechtel, for his part, is intrigued by the possibility of using SINS for the study of lunar rocks, meteorites and stardust. These extraterrestrial materials have a molecular diversity that is difficult to resolve on the nanoscale, particularly in a non-destructive manner for these rare samples. A better understanding of the makeup of moon rocks and dust from space could provide clues to the formation of the planets and solar system.

    Raschke is using the technique to study the processes that limit the performance of organic solar cells. He is looking to further improve the flexibility of the technique such that it can be applied under variable and controlled atmospheric and low-temperature conditions. Among other tweaks, he plans to increase the sensitivity of the technique with the ultimate goal of performing singe-molecule chemical spectroscopy.
    This research was supported by the DOE’s Office of Science.

    See the full article here.

    DOE Pulse highlights work being done at the Department of Energy’s national laboratories. DOE’s laboratories house world-class facilities where more than 30,000 scientists and engineers perform cutting-edge research spanning DOE’s science, energy, National security and environmental quality missions. DOE Pulse is distributed twice each month.

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  • richardmitnick 7:38 pm on May 8, 2014 Permalink | Reply
    Tags: , , Berkeley ALS, ,   

    From Berkeley Lab: “Berkeley Lab Develops Nanoscope to Probe Chemistry on the Molecular Scale” 


    Berkeley Lab

    May 07, 2014
    Kate Greene 510-486-4404 kgreene@lbl.gov

    For years, scientists have had an itch they couldn’t scratch. Even with the best microscopes and spectrometers, it’s been difficult to study and identify molecules at the so-called mesoscale, a region of matter that ranges from 10 to 1000 nanometers in size. Now, with the help of broadband infrared light from the Advanced Light Source (ALS) synchrotron at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab), researchers have developed a broadband imaging technique that looks inside this realm with unprecedented sensitivity and range.

    pep
    This peptoid nanosheet, produced by Gloria Olivier and Ron Zuckerman at Berkeley Lab, is less than 8 nanometers thick at points. SINS makes it possible to acquire spectroscopic images of these ultra-thin nanosheets for the first time.

    By combining atomic force microscopy with infrared synchrotron light, researchers from Berkeley Lab and the University of Colorado have improved the spatial resolution of infrared spectroscopy by orders of magnitude, while simultaneously covering its full spectroscopic range, enabling the investigation of variety of nanoscale, mesoscale, and surface phenomena that were previously difficult to study.

    The new technique, called Synchrotron Infrared Nano-Spectroscopy or SINS, will enable in-depth study of complex molecular systems, including liquid batteries, living cells, novel electronic materials and stardust.

    “The big thing is that we’re getting full broadband infrared spectroscopy at 100 to 1000 times smaller scale,” says Hans Bechtel, principal scientific engineering associate at Berkeley Lab. “This is not an incremental achievement. It’s really revolutionary.”

    In a Proceedings of the National Academy of Sciences paper published May 6 online, titled Ultra-broadband infrared nano-spectroscopic imaging, Berkeley Lab’s Bechtel and Michael Martin, a Berkeley Lab staff scientist, and colleagues from Markus Raschke’s group at the University of Colorado at Boulder describe SINS. They demonstrate the nanoscope’s ability to capture broadband spectroscopic data over a variety of samples, including a semiconductor-insulator system, a mollusk shell, proteins, and a peptoid nanosheet. Martin says these demonstrations just “scratch the surface” of the potential of the new technique.

    Synchronizing Scopes

    SINS combines two pre-existing infrared technologies: a newer technique called infrared scattering-scanning near-field optical microscopy (IR s-SNOM) and an old laboratory standby, known even to college chemistry students, called Fourier Transform Infrared Spectroscopy (FTIR). A clever melding of these two tools, combined with the intense infrared light of the synchrotron at Berkeley Lab gives the researchers the ability to identify clusters of molecules sized as small as 20 to 40 nanometers.

    exp
    Experimental setup for SINS that includes the synchrotron light source, an atomic force microscope, a rapid-scan Fourier transform infrared spectrometer, a beamsplitter, mirrors and a detector.

    micro
    Atomic force microscope (AFM/MFM) on the left with controlling computer on the right.

    The new approach overcomes long-standing barriers with pre-existing microscopy techniques that often involve demanding technical and sample preparation requirements. Infrared spectroscopy uses low-energy light, is minimally invasive, and is applicable under ambient conditions, making it an excellent tool for chemical and molecular identifications in systems that are static as well as those that are living and dynamic. The technique works by shining low-energy infrared light onto a molecular sample. Molecules can be thought of as systems of balls (atoms) and springs (bonds between atoms) that vibrate with characteristic wiggles; they absorb infrared radiation at frequencies that correspond to their natural vibrating modes. The output from this absorption is a spectrum, often called a fingerprint, which shows distinctive peaks and dips, depending on the bonds and atoms present in the sample.

    But infrared spectroscopy has its challenges too. While it works well for bulk samples, traditional infrared spectroscopy can’t resolve molecular composition below about 2000 nanometers. The major hurdle is the diffraction limit of light, which is the fundamental barrier that determines the smallest focus spot of light and is particularly troublesome for the large wavelengths of infrared light. In recent years, though, the diffraction limit has been overcome by a technique called scattering-scanning near-field optical microscopy, or s-SNOM, which involves shining light onto a metallic tip. The tip acts as an antenna for the light, directing it to a tiny region at its apex just tens of nanometers wide.

    This trick is what’s used in IR s-SNOM, where infrared light is coupled to a metallic tip. The challenge with IR s-SNOM, however, is that researchers have been relying on infrared light produced by lasers. Lasers emit a large number of photons needed for the technique, but because they operate in a narrow wavelength band, they can only probe a narrow range of molecular vibrations. In other words, laser light simply can’t give you the flexibility to explore a spectrum of mixed molecules.

    spec
    A spectral-linescan of a blue mussel shell, which transitions from calcite to aragonite, illustrates the spatial resolution and spectroscopic range capabilities of the SINS technique. The image shows two simultaneously acquired vibrational modes across the transition region.

    Bechtel, Martin and Raschke’s team saw the opportunity to use Berkeley Lab’s ALS to overcome the laser limitation. The lab’s synchrotron produces broadband infrared light with a high-photon count that can be focused to the diffraction limit. The researchers coupled the synchrotron light to a metallic tip with an apex of about 20 nanometers, focusing the infrared beam onto the samples. The resulting spectrum is analyzed with a modified FTIR instrument.

    “This is actually one of very few examples where synchrotron light has been coupled to scanning probe microscopy,” says Raschke. “Moreover, the implementation of the technique at the synchrotron brings chemical nano-spectroscopy and -imaging out of the lab of a few laser science experts and makes it available for a broader scientific community at a user facility.”

    From mollusks to moon rocks

    The team demonstrated the technique by confirming the spectroscopic signature of silicon dioxide on silicon and by illustrating the sharp chemical transition that occurs within the shells of the blue mussel (M. edulis). Additionally, the researchers looked at proteins and a peptoid nanosheet, an engineered, ultra-thin film of proteins with medical and pharmacological applications.

    Martin is excited for the potential of SINS, which is available for researchers from any institution to use. In particular he’s interested in a closer look at battery systems, with the hope that understanding battery chemistry on the mesoscale could provide insight into better performance. Further out, he expects SINS to be useful for a range of biochemistry as well. “This hints at a dream I’ve had in my mind, to look at the surface of a cell, inside the bi-layer membrane, the channels, and receptors,” says Martin. “If we could put a SINS tip on a living cell, we could watch biochemistry happen in real time.”

    mm
    Berkeley Lab’s Michael Martin

    Bechtel, for his part, is intrigued by the possibility of using SINS for the study of lunar rocks, meteorites and stardust. These extraterrestrial materials have a molecular diversity that is difficult to resolve on the nanoscale, particularly in a non-destructive manner for these rare samples. A better understanding of the makeup of moon rocks and dust from space could provide clues to the formation of the planets and solar system.

    Raschke is using the technique to study the processes that limit the performance of organic solar cells. He is looking to further improve the flexibility of the technique such that it can be applied under variable and controlled atmospheric and low-temperature conditions. Among other tweaks, he plans to increase the sensitivity of the technique with the ultimate goal of performing singe-molecule chemical spectroscopy.

    This research was supported by the DOE Office of Science.

    See the full article here.

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

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  • richardmitnick 7:03 am on February 25, 2014 Permalink | Reply
    Tags: , Berkeley ALS, , , ,   

    From Berkeley Lab: “On the Road to Mottronics…” 


    Berkeley Lab

    Researchers at the Advanced Light Source Find Key to Controlling the Electronic and Magnetic Properties of Mott Thin Films

    February 24, 2014
    Lynn Yarris (510) 486-5375 lcyarris@lbl.gov

    Mottronics” is a term seemingly destined to become familiar to aficionados of electronic gadgets. Named for the Nobel laureate Nevill Francis Mott, Mottronics involve materials – mostly metal oxides – that can be induced to transition between electrically conductive and insulating phases. If these phase transitions can be controlled, Mott materials hold great promise for future transistors and memories that feature higher energy efficiencies and faster switching speeds than today’s devices. A team of researchers working at Berkeley Lab’s Advanced Light Source (ALS) have demonstrated the conducting/insulating phases of ultra-thin films of Mott materials can be controlled by applying an epitaxial strain to the crystal lattice.

    balls
    Epitaxial mismatches in the lattices of nickelate ultra-thin films can be used to tune the energetic landscape of Mott materials and thereby control conductor/insulator transitions. No image credit.

    “Our work shows how an epitaxial mismatch in the lattice can be used as a knot to tune the energetic landscape of Mott materials and thereby control conductor/insulator transitions,” says Jian Liu, a post-doctoral scholar now with Berkeley Lab’s Materials Sciences Division, who is the lead author on a paper describing this work in the journal Nature Communications. “Through epitaxial strain, we forced nickelate films containing only a few atomic layers into different phases with dramatically different electronic and magnetic properties. While some of these phases are not obtainable in conventional ways, we were able to produce them in a form that is ready for device development.”

    The Nature Communications paper is titled Heterointerface engineered electronic and magnetic phases of NdNiO3 thin films. The corresponding author is Jak Chakhalian, a professor of physics at the University of Arkansas. Co-authors are Mehdi Kargarian, Mikhail Kareev, Ben Gray, Phil Ryan, Alejandro Cruz, Nadeem Tahir, Yi-De Chuang, Jinghua Guo, James Rondinelli, John Freeland and Gregory Fiete.

    two
    Jinghua Guo (left) and Yi-De Chuang at Beamline 8.0.1 of the Advanced Light Source were part of a team that discovered a key to controlling the electronic and magnetic properties of Mott materials. (Photo by Roy Kaltschmidt)

    Nickel-based rare-earth perovskite oxides, or “nickelates,” are considered to be an ideal model for the study of Mott materials because they display strongly correlated electron systems that give rise to unique electronic and magnetic properties. Liu and his co-authors studied thin films of neodymium nickel oxide using ALS beamline 8.0.1, a high flux undulator beamline that produces x-ray beams optimized for the study of nanoscale materials and strongly correlated physics.

    “ALS beamline 8.0.1 provides the high photon flux and energy range that are critical when dealing with nanoscale samples,” Liu says. “The state-of-the-art Resonant X-ray Scattering endstation has a high-speed, high-sensitivity CCD camera that makes it feasible to find and track diffraction peaks off a thin film that was only six nanometers thick.”

    The transition between the conducting and insulating phases in nickelates is determined by various microscopic interactions, some of which favor the conducting phase, some which favor the insulating phase. The energetic balance of these interactions determines how easily electricity is conducted by electrons moving between the nickel and oxygen ions. By applying enough epitaxial strain to alter the space between these ions, Liu and his colleagues were able to tune this energetic balance and control the conducting/insulating transition. In addition, they found strain could also be used to control the nickelate’s magnetic properties, again by exploiting the lattice mismatch.

    “Magnetism is another hallmark of Mott materials that often goes hand-in-hand with the insulating state and is used to distinguish Mott insulators,” says Liu. “The challenge is that most Mott insulators, including nickelates, are antiferromagnets that macroscopically behave as non-magnetic materials. “At ALS beamline 8.0.1, we were able to directly track the magnetic evolution of our thin films while tuning the metal-to-insulator transition. Our findings give us a better understanding of the physics behind the magnetic properties of these nickelate films and point to potential applications for this magnetism in novel Mottronics devices.”

    This research was primarily supported the U.S. Department of Energy’s Office of Science.

    See the full article here.

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

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