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  • richardmitnick 9:48 am on November 16, 2015 Permalink | Reply
    Tags: Argonne, , , Q Continuum,   

    From ANL: “Researchers model birth of universe in one of largest cosmological simulations ever run” 

    News from Argonne National Laboratory

    October 29, 2015
    Louise Lerner

    Temp 1
    This series shows the evolution of the universe as simulated by a run called the Q Continuum, performed on the Titan supercomputer and led by Argonne physicist Katrin Heitmann. These images give an impression of the detail in the matter distribution in the simulation. At first the matter is very uniform, but over time gravity acts on the dark matter, which begins to clump more and more, and in the clumps, galaxies form. Image by Heitmann et. al.

    Researchers are sifting through an avalanche of data produced by one of the largest cosmological simulations ever performed, led by scientists at the U.S. Department of Energy’s (DOE’s) Argonne National Laboratory.

    The simulation, run on the Titan supercomputer at DOE’s Oak Ridge National Laboratory, modeled the evolution of the universe from just 50 million years after the Big Bang to the present day — from its earliest infancy to its current adulthood. Over the course of 13.8 billion years, the matter in the universe clumped together to form galaxies, stars, and planets; but we’re not sure precisely how.

    2
    Cray/Titan

    These kinds of simulations help scientists understand dark energy, a form of energy that affects the expansion rate of the universe, including the distribution of galaxies, composed of ordinary matter, as well as dark matter, a mysterious kind of matter that no instrument has directly measured so far.

    Temp 1
    Galaxies have halos surrounding them, which may be composed of both dark and regular matter. This image shows a substructure within a halo in the Q Continuum simulation, with “subhalos” marked in different colors. Image by Heitmann et al.

    Intensive sky surveys with powerful telescopes, like the Sloan Digital Sky Survey and the new, more detailed Dark Energy Survey, show scientists where galaxies and stars were when their light was first emitted.

    SDSS Telescope
    SDSS telescope at Apache Point, NM, USA

    Dark Energy Camera
    CTIO Victor M Blanco 4m Telescope
    DECam and the Blanco telecope in CHile where it is housed

    And surveys of the Cosmic Microwave Background [CMB], light remaining from when the universe was only 300,000 years old, show us how the universe began — “very uniform, with matter clumping together over time,” said Katrin Heitmann, an Argonne physicist who led the simulation.

    Cosmic Microwave Background  Planck
    CMB

    The simulation fills in the temporal gap to show how the universe might have evolved in between: “Gravity acts on the dark matter, which begins to clump more and more, and in the clumps, galaxies form,” said Heitmann.

    Called the Q Continuum, the simulation involved half a trillion particles — dividing the universe up into cubes with sides 100,000 kilometers long. This makes it one of the largest cosmology simulations at such high resolution. It ran using more than 90 percent of the supercomputer. For perspective, typically less than one percent of jobs use 90 percent of the Mira supercomputer at Argonne, said officials at the Argonne Leadership Computing Facility, a DOE Office of Science User Facility. Staff at both the Argonne and Oak Ridge computing facilities helped adapt the code for its run on Titan.

    “This is a very rich simulation,” Heitmann said. “We can use this data to look at why galaxies clump this way, as well as the fundamental physics of structure formation itself.”

    Analysis has already begun on the two and a half petabytes of data that were generated, and will continue for several years, she said. Scientists can pull information on such astrophysical phenomena as strong lensing, weak lensing shear, cluster lensing and galaxy-galaxy lensing.

    The code to run the simulation is called Hardware/Hybrid Accelerated Cosmology Code (HACC), which was first written in 2008, around the time scientific supercomputers broke the petaflop barrier (a quadrillion operations per second). HACC is designed with an inherent flexibility that enables it to run on supercomputers with different architectures.

    Details of the work are included in the study, The Q continuum simulation: harnessing the power of GPU accelerated supercomputers, published in August in the Astrophysical Journal Supplement Series by the American Astronomical Society. Other Argonne scientists on the study included Nicholas Frontiere, Salman Habib, Adrian Pope, Hal Finkel, Silvio Rizzi, Joe Insley and Suman Bhattacharya, as well as Chris Sewell at DOE’s Los Alamos National Laboratory.

    This work was supported by the DOE Office of Science (Scientific Discovery through Advanced Computing (SciDAC) jointly by High Energy Physics and Advanced Scientific Computing Research ) and used resources of the Oak Ridge Leadership Computing Facility (OLCF) at Oak Ridge National Laboratory, a DOE Office of Science User Facility. The work presented here results from an award of computer time provided by the Innovative and Novel Computational Impact on Theory and Experiment (INCITE) program at the OLCF.

    See the full article here .

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    Argonne National Laboratory seeks solutions to pressing national problems in science and technology. The nation’s first national laboratory, Argonne conducts leading-edge basic and applied scientific research in virtually every scientific discipline. Argonne researchers work closely with researchers from hundreds of companies, universities, and federal, state and municipal agencies to help them solve their specific problems, advance America’s scientific leadership and prepare the nation for a better future. With employees from more than 60 nations, Argonne is managed by UChicago Argonne, LLC for the U.S. Department of Energy’s Office of Science. For more visit http://www.anl.gov.

    The Advanced Photon Source at Argonne National Laboratory is one of five national synchrotron radiation light sources supported by the U.S. Department of Energy’s Office of Science to carry out applied and basic research to understand, predict, and ultimately control matter and energy at the electronic, atomic, and molecular levels, provide the foundations for new energy technologies, and support DOE missions in energy, environment, and national security. To learn more about the Office of Science X-ray user facilities, visit http://science.energy.gov/user-facilities/basic-energy-sciences/.

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

    Argonne Lab Campus

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  • richardmitnick 10:24 pm on September 14, 2015 Permalink | Reply
    Tags: , Argonne, Synthetic Photosynthesis   

    From Argonne: “Making fuel from light: Argonne research sheds light on photosynthesis and creation of solar fuel” 

    News from Argonne National Laboratory

    September 1, 2015
    Jo Napolitano

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    Photo: Shutterstock.

    Refined by nature over a billion years, photosynthesis has given life to the planet, providing an environment suitable for the smallest, most primitive organism all the way to our own species.

    While scientists have been studying and mimicking the natural phenomenon in the laboratory for years, understanding how to replicate the chemical process behind it has largely remained a mystery — until now.

    Recent experiments at the U.S. Department of Energy’s Argonne National Laboratory have afforded researchers a greater understanding of how to manipulate photosynthesis, putting humankind one step closer to harvesting “solar fuel,” a clean energy source that could one day help replace coal and natural gas.

    Lisa M. Utschig, a bioinorganic chemist at Argonne for 20 years, said storing solar energy in chemical bonds such as those found in hydrogen can provide a robust and renewable energy source. Burning hydrogen as fuel creates no pollutants, making it much less harmful to the environment than common fossil fuel sources.

    “We are taking sunlight, which is abundant, and we are using water to make a fuel,” said Utschig, who oversaw the project. “It’s pretty remarkable.” Unlike the energy derived from solar panels, which must be used quickly, hydrogen, a solar fuel, can be stored.

    Sarah Soltau, a postdoctoral fellow at Argonne who conducted much of the research, said “the key finding of Argonne’s most recent research is that we were able to actually watch the processes of electrons going from a light-absorbing molecule to a catalyst that produces solar fuel. This piece of knowledge will help us develop a system to work more efficiently than the one we can create now, and, years on, may allow us to replace oil and gas.”

    Argonne researchers attached a protein from spinach to both a light-absorbing molecule (called a photosensitizer) and to a hydrogen-producing catalyst. The protein helped stabilize both the catalyst and photosensitizer, allowing scientists to observe direct electron flow between the two for the first time.

    Researchers used transient optical spectroscopy, a method for detecting very fast changes in the light absorption of a molecule when illuminated with a laser pulse, to observe changes in the color of a compound as it undergoes chemical reactions. They also employed electron paramagnetic resonance, another form of spectroscopy, to study where electrons move inside a molecule.

    “We don’t just see the result, the hydrogen,” Utschig said. “We are peering into this system. We are able to really see how it works and what the essential parts are. Once you know that, the next time you try and design something, you can make it better because you understand it.”

    Argonne has been studying photosynthesis since the 1960s but this particular experiment has been pursued for about a year. Soltau said scientists may be several years from using these techniques to generate storable solar fuels to power cars or households, but that this could be made possible once researchers learn ways to make the process more efficient.

    “We need to look at ways to make solar fuel production last longer,” she said. “Right now, the systems don’t have the stability necessary to last weeks or months.”

    The scientists’ findings were published in a paper titled Aqueous light driven hydrogen production by a Ru–ferredoxin–Co biohybrid in the journal Chemical Communications.

    This research was funded by the U.S. Department of Energy’s Office of Science, Basic Energy Sciences.

    See the full article here .

    Please help promote STEM in your local schools.
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    Stem Education Coalition
    Argonne National Laboratory seeks solutions to pressing national problems in science and technology. The nation’s first national laboratory, Argonne conducts leading-edge basic and applied scientific research in virtually every scientific discipline. Argonne researchers work closely with researchers from hundreds of companies, universities, and federal, state and municipal agencies to help them solve their specific problems, advance America’s scientific leadership and prepare the nation for a better future. With employees from more than 60 nations, Argonne is managed by UChicago Argonne, LLC for the U.S. Department of Energy’s Office of Science. For more visit http://www.anl.gov.

    The Advanced Photon Source at Argonne National Laboratory is one of five national synchrotron radiation light sources supported by the U.S. Department of Energy’s Office of Science to carry out applied and basic research to understand, predict, and ultimately control matter and energy at the electronic, atomic, and molecular levels, provide the foundations for new energy technologies, and support DOE missions in energy, environment, and national security. To learn more about the Office of Science X-ray user facilities, visit http://science.energy.gov/user-facilities/basic-energy-sciences/.

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

    Argonne Lab Campus

     
  • richardmitnick 11:09 am on July 24, 2015 Permalink | Reply
    Tags: Argonne, , ,   

    From FNAL: “Fermilab magnet team helps bring brighter beams to APS Upgrade Project at Argonne” 

    FNAL Home

    Fermilab is an enduring source of strength for the US contribution to scientific research world wide.

    July 24, 2015
    Ali Sundermier

    Temp 1
    Argonne National Laboratory was attracted to the expertise of this Fermilab magnet team. The team recently developed a pre-prototype magnet for Argonne’s APS Upgrade Project. Photo: Doug Howard, TD

    A magnet two meters long sits in the Experiment Assembly Area of the Advanced Photon Source [APS] at Argonne National Laboratory.

    ANL APS interior
    APS

    The magnet, built by Fermilab’s Technical Division, is fire engine red and has on its back a copper coil that doesn’t quite reach from one end to the other. An opening on one end of the magnet’s steel casing gives it the appearance of a rectangular alligator with its mouth slightly ajar.

    “It’s a very pretty magnet,” said Argonne’s Glenn Decker, associate project manager for the accelerator. “It’s simple and it’s easy to understand conceptually. It’s been a very big first step in the APS Upgrade.”

    The APS is a synchrotron light source that accelerates electrons nearly to the speed of light and then uses magnets to steer them around a circular storage ring the size of a major-league baseball stadium. As the electrons bend, they release energy in the form of synchrotron radiation — light that spans the energy range from visible to x-rays. This radiation can be used for a number of applications, such as microscopy and spectroscopy.

    In 2013, the federal Basic Energy Sciences Advisory Committee, which advises the Director of the Department of Energy’s Office of Science, recommended a more ambitious approach to upgrades of U.S. light sources. The APS Upgrade will create a world-leading facility by using new state-of-the-art magnets to tighten the focus of the APS electron beam and dramatically increase the brightness of its X-rays, expanding its experimental capabilities by orders of magnitude.

    Instead of the APS’ present magnet configuration, which uses two bending magnets in each of 40 identical sectors, the upgraded ring will deploy seven bending magnets per sector to produce a brighter, highly focused beam.

    Because the APS Upgrade requires hundreds of magnets — many of them quite unusual — Argonne called on experts at Fermilab and Brookhaven National Laboratory for assistance in magnet design and development.

    Fermilab took on the task of designing, building and testing a pre-prototype for a groundbreaking M1 magnet — the first in the string of bending magnets that makes up the new APS arrangement.

    “At Fermilab we have the whole cycle,” said Fermilab’s Vladimir Kashikhin, who is in charge of magnet designs and simulations. “Because of our experience in magnet technology and the people who can simulate and fabricate magnets and make magnetic measurements, we are capable of making any type of accelerator magnet.”

    The M1’s magnetic field is strong at one end and tapers off at the other end, reducing the impact of processes that increase the beam size, producing a brighter beam. Because of this change in field, this magnet is different from anything Fermilab had ever built. But by May, Fermilab’s team had completed and tested the magnet and shipped it to Argonne, where it charged triumphantly through a series of tests.

    “The magnetic field shape they were asking for was a little bit challenging,” said Dave Harding, the principal investigator leading the project at Fermilab. “Getting the shape of the steel to produce that distribution and magnetic field required some tinkering. But we did it.”

    Although this pre-prototype magnet is unlikely to be installed in the complete storage ring, scientists working in this collaboration view the M1 development as an opportunity to learn about technical difficulties, validate their designs and strengthen their skills.

    “Getting our hands on some real hardware injected a dose of reality into our process,” Decker said. “We’re going to take the lessons we learned from this M1 magnet and fold them into the next iteration of the magnet. We’re looking forward to a continuing collaboration with Fermilab’s Technical Division on magnetic measurements and refinement of our magnet designs, working toward the next world-leading hard X-ray synchrotron light source.”

    See the full article here.

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    Fermilab Campus

    Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a US Department of Energy national laboratory specializing in high-energy particle physics. Fermilab is America’s premier laboratory for particle physics and accelerator research, funded by the U.S. Department of Energy. Thousands of scientists from universities and laboratories around the world
    collaborate at Fermilab on experiments at the frontiers of discovery.

     
  • richardmitnick 8:55 am on March 13, 2015 Permalink | Reply
    Tags: , Argonne,   

    From Argonne: “Study proposes new way to measure superconducting fluctuations” 

    News from Argonne National Laboratory

    March 10, 2015
    Louise Lerner

    1
    Scientists at Argonne proposed theoretical evidence for a new superconducting fluctuation, which may lead to a way of measuring the exact temperature at which superconductivity kicks in and shed light on the poorly understood properties of superconducting materials above this temperature. Above: Sharp peaks are visible as the temperature nears Tc, the temperature at which superconductivity kicks in. Credit: Alexey Galda

    A study published last month by researchers at the U.S. Department of Energy’s Argonne National Laboratory provides theoretical evidence for a new effect that may lead to a way of measuring the exact temperature at which superconductivity kicks in and shed light on the poorly understood properties of superconducting materials above this temperature.

    Superconductors are an old puzzle in physics, made all the more tantalizing because their technological applications are so valuable. Electricity is being lost all around you; very few electric systems use power completely efficiently, and some is always lost—generally as heat, which you can feel as your laptop or phone gets warm. That’s because even our best conductors, like copper, are always losing a little bit of electricity to resistance. Superconductors don’t. When cooled down to operating temperature, they never lose any electricity.

    This is the kind of unique property that can spur entire new fields of invention, and they have—MRIs, cell phone towers and Maglev trains all use superconductors. But they’re not in every engine or transmission line because of a serious logistical issue: their operating temperature is -270°F or lower, so they have to be cooled with liquid helium or nitrogen.

    Superconducting materials have a number of other fascinating properties. For example, scientists found that the electricity flow between two superconductors separated by a thin non-conducting material (called a Josephson junction) can be extremely sensitive to external microwave radiation. As little as a single photon can trigger electricity to flow through such a device when just the right voltage is applied. This unique effect, called resonant tunneling, allows such a high precision of measurement that it is used for DNA sequencing and quantum encryption. The same phenomenon has determined the international standard of voltage for decades.

    The problem is that we still don’t fully understand how superconductors work, and if we want to realize their full potential, we need to.

    To explore superconductors, one of the things scientists do is rearrange them in all sorts of new ways—stacking them in layers, punching holes in them and trimming them down to wires just 50 nanometers across, for example.

    These new arrangements change the way materials behave, including essential properties like the exact temperature at which they become superconducting—called the “critical temperature” or Tc .

    “Until now,” said Valerii Vinokur, Argonne Distinguished Fellow and a coauthor on the paper, “the field hasn’t had a standard, precise way to measure Tc.”

    One of the things we do know is that short-lived islands of superconductivity can form in a material just above Tc. These sporadically emerging and rapidly vanishing regions, called superconducting fluctuations, mirror in one way or another most of the superconducting properties of the material at temperatures below Tc. Despite this, superconducting fluctuations remain poorly understood—so much so that even measuring their lifetime has been a challenge. In the paper, Vinokur and Argonne postdoctoral fellow Alexey Galda proposed an effect that mirrors resonant tunneling above Tc that is strong enough to measure, and—most importantly—gets sharper as the temperature approaches Tc.

    If verified by experiment, this would be a new high-precision tool for measuring fundamental properties of superconducting fluctuations, such as their lifetime, and provide a way to measure more precisely where Tc lies for each material.

    “Every new tool in studying superconductivity is absolutely invaluable—it brings more precision to the field,” Galda said.

    “This would also let us study fluctuations more widely,” he said.

    The fluctuations, Galda said, are interesting because they can help researchers map the microscopic behaviors of materials, which are likely key to why and how materials act the way they do. Fluctuations are influenced by a number of different phenomena; a tool to untangle at least one variable from the set would help researchers tease out the contributions of others.

    “To know how long fluctuations live is very important and has been difficult to determine experimentally,” Vinokur said.

    Researchers in Argonne’s Materials Science division, led by Argonne physicist Wai Kwok, are planning to verify the results experimentally.

    The paper, “Resonant tunneling of fluctuation Cooper pairs,” was published by Nature’s Scientific Reports. The other author on the paper was A. S. Mel’nikov of the Russian Academy of Sciences.

    The study was supported by the U.S. Department of Energy’s Office of Science, as well as the Russian Foundation for Basic Research and the Russian Ministry of Science and Education.

    See the full article here.

    Please help promote STEM in your local schools.
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    Stem Education Coalition
    Argonne National Laboratory seeks solutions to pressing national problems in science and technology. The nation’s first national laboratory, Argonne conducts leading-edge basic and applied scientific research in virtually every scientific discipline. Argonne researchers work closely with researchers from hundreds of companies, universities, and federal, state and municipal agencies to help them solve their specific problems, advance America’s scientific leadership and prepare the nation for a better future. With employees from more than 60 nations, Argonne is managed by UChicago Argonne, LLC for the U.S. Department of Energy’s Office of Science. For more visit http://www.anl.gov.

    The Advanced Photon Source at Argonne National Laboratory is one of five national synchrotron radiation light sources supported by the U.S. Department of Energy’s Office of Science to carry out applied and basic research to understand, predict, and ultimately control matter and energy at the electronic, atomic, and molecular levels, provide the foundations for new energy technologies, and support DOE missions in energy, environment, and national security. To learn more about the Office of Science X-ray user facilities, visit http://science.energy.gov/user-facilities/basic-energy-sciences/.

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

    Argonne Lab Campus

     
  • richardmitnick 11:38 am on December 23, 2014 Permalink | Reply
    Tags: , Argonne,   

    From Sandia: “Breakthrough in predictions of pressure-dependent combustion chemical reactions” 


    Sandia Lab

    December 23, 2014
    Mike Janes, mejanes@sandia.gov, (925) 294-2447

    Researchers at Sandia and Argonne national laboratories have demonstrated, for the first time, a method to successfully predict pressure-dependent chemical reaction rates. It’s an important breakthrough in combustion and atmospheric chemistry that is expected to benefit auto and engine manufacturers, oil and gas utilities and other industries that employ combustion models.

    A paper describing the work, performed by researchers at Sandia’s Combustion Research Facility and Argonne’s Chemical Sciences and Engineering Division, is featured in the Dec. 5 edition of Science.

    Combustion scientists have worked for years to better understand the thousands of chemical reactions that take place during the combustion process, said Sandia’s Ahren Jasper, the study’s lead author.

    As scientists determine and understand the speeds and outcomes of more and more of these reactions, he said, they can use models to more fully characterize what’s occurring inside an engine, and thus better predict combustion efficiency and the emissions formed during combustion.

    A more detailed, fundamental understanding of the chemistry of combustion, in turn, may lead to cleaner and more efficient strategies in automotive vehicle and fuel design.

    Argonne chemist Stephen Klippenstein, a corresponding author of the study, said this method should aid development of global models for all gas phase chemical environments, including the Earth’s atmosphere. Better models will improve understanding of climate change and boost efforts to address it.

    Pressure-dependent reactions historically a vexing problem

    Many of the key steps underlying gas-phase combustion involve elementary chemical reactions that are strongly pressure-dependent, and researchers who develop combustion models require detailed descriptions of these reactions.

    While significant progress has been made over the years in understanding combustion chemistry, the outcome and rates of pressure-dependent chemical reactions — those that depend on the pressure of the gas in the engine — have been very difficult to predict. These reactions depend on the pressure because the redistribution of energy and angular momentum that occurs when the reacting molecules collide with other gas molecules changes the speed and outcome of the reactions.

    Previous qualitative research focused on how various molecular properties influence energy transfer rates, but no accurate method could make a priori predictions of the rate constants, that is, predictions based on theoretical deduction, not observation.

    “We’ve desperately needed the ability to compute and calculate precisely how chemical reactions depend on temperature and pressure, and now we have that,” said Jasper.

    Focus on energy transfer leads to technical solution

    The team focused on modeling the collisions of molecules in atomistic detail and characterizing the transfer of energy and angular momentum that takes place as a result of those collisions.

    “We succeeded by using more accurate models for describing the interaction of the colliding species and by focusing on only those aspects of energy transfer that are most relevant in determining the reaction rate,” Jasper said. This allowed the researchers to develop a detailed description of collision outcomes.

    Jasper and his colleagues then were able to obtain that collision outcome information using direct “classical trajectories” that explicitly describe the motion of the atoms in the molecules, and to use this information in calculating chemical reaction rates.

    A key step, Jasper said, was the development of a model for the collisional energy and angular momentum transfer function that reproduced detailed features predicted by the trajectories and was simple enough to be used in practical reaction rate calculations.

    “Finding a way to accurately compute and represent the energy and angular momentum transfer from these vibrationally-excited molecules proved to be the final piece needed to solve the problem,” said Jasper.

    “The overall theoretical model is rather complex, involving many separate unrelated calculations, and it is remarkable how accurately one can now treat all aspects of the problem in developing such completely a priori predictions,” Klippenstein said.

    The study was also co-authored by Klippenstein and Larry Harding, both distinguished fellows at Argonne, and the influential combustion modeler Jim Miller, a former Sandia staff member now at Argonne. The work continues the team’s longstanding development of master equation and elementary reaction rate theories.

    “This effort was a true collaboration with both labs playing key roles in the intellectual foundations of the work as well as in the actual computations,” Klippenstein noted. “The combined expertise in energy transfer calculations and in reaction rate theories was central to the success of the project.”

    Miller added: “A close but loose-knit working group was developed with these combustion modeling experts over the years, and we’ve developed excellent professional relationships that have led to this technical achievement.”

    The work was supported by the Department of Energy’s Office of Science.

    See the full article here.

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    Sandia National Laboratory

    Sandia National Laboratories is a multiprogram laboratory operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration. With main facilities in Albuquerque, N.M., and Livermore, Calif., Sandia has major R&D responsibilities in national security, energy and environmental technologies, and economic competitiveness.
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  • richardmitnick 6:44 pm on December 6, 2014 Permalink | Reply
    Tags: , Argonne,   

    From ANL: “Underground helium travels to the Earth’s surface via aquifers, new study says” 

    News from Argonne National Laboratory

    December 5, 2014
    Louise Lerner

    Before it can put the party in party balloons, helium is carried from deep within the Earth’s crust to the surface via aquifers, according to new research published this week in Nature Geosciences.

    Aquifers, underground water formations that provide water to millions of people around the world, contain water that has filtered there over hundreds of millennia. Using an atom trap built at the U.S. Department of Energy’s Argonne National Laboratory to date the water in a deep South American aquifer, scientists tracked the rate at which helium pooled in the aquifers. The results suggest that helium is trickling into the aquifer from deeper underground, where it is carried to the surface with the flow of water.

    The only place where helium is made on Earth is underground, where deep veins of uranium and thorium give off atoms of helium as they decay. This helium eventually makes its way to the surface, where it escapes into the atmosphere and ultimately into outer space.

    Geoscientists did not know, however, exactly how this helium gets to the surface. It can filter through rock, but extremely slowly, and the amount of helium in the atmosphere doesn’t match our estimates of how long that would take.

    Some scientists have suggested that helium is released from deeper underground during violent tectonic events like earthquakes or even from underwater volcanoes; but others thought groundwater might be a more likely route.

    Scientists knew the rate at which helium is naturally produced in the aquifer. They just needed to know how old the water was to calculate how much helium would be naturally created during that time span. If the groundwater carried more helium than the aquifers produced themselves, the source for the extra helium would be further beneath the surface.

    Luckily, a group of Argonne researchers led by physicist Zheng-Tian Lu have pioneered a dating technique that uses a very rare isotope called krypton-81. Water picks up this isotope while above ground, but not while below ground; if you know how many atoms of krypton-81 remain in a sample of water, you can tell how long it’s been in the aquifer. And krypton-81 can date much further back than carbon dating—up to a million years or more.

    The atom trap uses lasers that vibrate at the exact same frequency as krypton-81 atoms to count individual atoms. (The team has already used it to track how fast aquifers refill and to date ice in glaciers, among other uses).

    Hydrologists from the International Atomic Energy Agency and their collaborators collected samples of water from various spots around the Guarani aquifer in South America, a massive reservoir that stretches beneath Argentina, Brazil, Paraguay and Uruguay, and extracted all the dissolved gases. Then the krypton was separated out, and finally the samples came to Argonne to have their krypton-81 atoms counted.

    m
    International Atomic Energy Agency hydrologist Luis Araguas-Araguas records data as a machine extracts gases from water samples taken from the Guarani aquifer in South America. The green LED on the front panel indicates the temperature of the water (in this case, 40.9°C, or 106°F). “Generally, the deeper the groundwater, the hotter it is,” said Argonne scientist Wei Jiang, who coauthored a study to track helium as it moves from underground to the surface. Photo by Wei Jiang, Argonne National Laboratory.

    a
    The Guarani aquifer underlays large parts of South America; it supplies water to more than 15 million people. Scientists found helium pools in this aquifer and is released to the atmosphere when the water reaches the surface. Image by Marko Perendija

    The researchers found much more helium than should have been produced in the aquifer itself during the time the water spent there, which indicates that the helium has been filtering up from below and pooling in the aquifer.

    “The difference in helium was a factor of 10—quite significant,” said Argonne physicist Wei Jiang, who coauthored the paper. “This gives us the first solid data for the groundwater scenario.”

    According to the paper’s rough estimate, about half of the helium produced in the crust makes its way to the surface via aquifer.

    “So the helium in your party balloon has very likely been carried around in groundwater,” Lu said.

    Scientists are interested in the global helium cycle because it and other gases are clues to the unseen and mostly mysterious goings-on underneath the Earth’s crust.

    The study’s findings are also helpful to understand aquifers, which provide drinking water and irrigation to millions of people around the world, including half the population of the United States.

    “The International Atomic Energy Agency works with its international partners to improve our understanding of ground water systems so that we can better protect and manage this vital freshwater resource,” said Pradeep Aggarwal, who led the study.

    The work was supported by the Department of Energy’s Office of Science; the development of the krypton-81 dating instrument was supported in part by the National Science Foundation.

    The paper, Continental degassing of helium-4 by surficial discharge of deep groundwater, appears in the Dec. 1 online edition of Nature Geosciences. The lead author was Pradeep Aggarwal of the International Atomic Energy Agency, as well as IAEA scientists Takuya Matsumoto and Luis J. Araguas-Araguas. Other authors included Argonne physicist Peter Mueller, Reika Yokochi of the University of Chicago, Neil Sturchio of the University of Illinois-Chicago, Hung Chang and Didier Gastmans of the Universidade Estadual Paulista, Roland Purtschert of the University of Bern, and Thomas Torgersen of the National Science Foundation.

    See the full article here.

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    Stem Education Coalition
    Argonne National Laboratory seeks solutions to pressing national problems in science and technology. The nation’s first national laboratory, Argonne conducts leading-edge basic and applied scientific research in virtually every scientific discipline. Argonne researchers work closely with researchers from hundreds of companies, universities, and federal, state and municipal agencies to help them solve their specific problems, advance America’s scientific leadership and prepare the nation for a better future. With employees from more than 60 nations, Argonne is managed by UChicago Argonne, LLC for the U.S. Department of Energy’s Office of Science. For more visit http://www.anl.gov.

    The Advanced Photon Source at Argonne National Laboratory is one of five national synchrotron radiation light sources supported by the U.S. Department of Energy’s Office of Science to carry out applied and basic research to understand, predict, and ultimately control matter and energy at the electronic, atomic, and molecular levels, provide the foundations for new energy technologies, and support DOE missions in energy, environment, and national security. To learn more about the Office of Science X-ray user facilities, visit http://science.energy.gov/user-facilities/basic-energy-sciences/.

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

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  • richardmitnick 3:49 pm on October 17, 2014 Permalink | Reply
    Tags: Argonne, , ,   

    From ANL: “Protons hog the momentum in neutron-rich nuclei” 

    News from Argonne National Laboratory

    October 17, 2014
    Kandice Carter, Jefferson Lab Public Affairs, 757-269-7263, kcarter@jlab.org
    or Jared Sagoff, Argonne National Laboratory communications office, 630-252-5549, media@anl.gov.

    Like dancers swirling on the dance floor with bystanders looking on, protons and neutrons that have briefly paired up in the nucleus have higher-average momentum, leaving less for non-paired nucleons. Using data from nuclear physics experiments carried out at the Department of Energy’s Thomas Jefferson National Accelerator Facility, researchers have now shown for the first time that this phenomenon exists in nuclei heavier than carbon, including aluminum, iron and lead.

    nucleons
    Research has shown that protons and neutrons that have briefly paired up in the nucleus have higher-average momentum, which allows a greater fraction of the protons than neutrons to have high momentum in relatively neutron-rich nuclei, such as carbon, aluminum, iron and lead. This result is contrary to long-accepted theories large nuclei and has implications for ultra-cold atomic gas systems and neutron stars.

    The phenomenon also surprisingly allows a greater fraction of the protons than neutrons to have high momentum in these relatively neutron-rich nuclei, which is contrary to long-accepted theories of the nucleus and has implications for ultra-cold atomic gas systems and neutron stars. The results were published online by the journal Science, on the Science Express website.

    The research builds on earlier work featured in Science that found that protons and neutrons in light nuclei pair up briefly in the nucleus, a phenomenon called a short-range correlation. Nucleons prefer pairing up with nucleons of a different type (proton preferred neutrons to other protons) by 20 to 1, and nucleons involved in a short-range correlation carry higher momentum than unpaired ones.

    Using data from an experiment conducted in 2004, the researchers were able to identify high-momentum nucleons involved in short-range correlations in heavier nuclei. In that experiment, led by Argonne physicist Kawtar Hafidi, the Jefferson Lab Continuous Electron Beam Accelerator Facility produced a 5.01 GeV beam of electrons to probe the nuclei of carbon, aluminum, iron and lead. The outgoing electrons and high-momentum protons were measured.

    “We found this dominance of proton-neutron pairs in the nuclei we studied. What’s striking is this pair-dominance all the way to lead,” says Doug Higinbotham, a staff scientist at Jefferson Lab and a lead coauthor on the paper.

    Then the researchers compared the momenta of protons versus neutrons in these nuclei. According to the Pauli exclusion principle, certain like particles can’t have the same momentum state. So, if you have a bunch of neutrons together, some will have low momentum, and others will have high momentum; the more neutrons you have, the more high-momentum neutrons you would see, as they fill up higher and higher momentum states.

    But according to Higinbotham, that expected picture is not what the researchers found when they measured high-momentum protons in neutron-rich nuclei.

    “What this paper is saying is the reverse, that the protons actually have the higher-average momentum. And it’s because they’ve all paired up with neutrons,” Higinbotham says. “It’s like a dance with too many girls (neutrons) and only a few boys (protons). Those boys are dancing their little hearts out, because there aren’t very many of them. So the average proton momentum is going to be higher than the average neutron momentum, because it’s mostly the neutrons that are sitting there, doing nothing, with nothing to pair up with, except themselves.”

    Higinbotham notes that the neutrons may also pair up briefly with other neutrons in short-range correlations and protons with other protons. However, these like-particle brief pairings occur once for roughly every 20 unlike-particle brief pairings.

    Now, the researchers hope to extend these new findings to other, similar systems, such as the quarks in nucleons and atoms in cold gases. According to Or Hen, a graduate student at Tel Aviv University in Israel and the paper’s lead author, he and his colleagues are already reaching out to other researchers.

    “We expect that this will also happen in ultra-cold atomic gas systems. And we’re having meetings with those researchers. If they find the same phenomenon, then we can use the flexibility of their experimental systems to go to extreme cases of very hard-to-study nuclear systems, such as the large imbalances of protons and neutrons that you can find in neutron stars,” Or said.

    To further that goal, Misak Sargsian, a lead coauthor and professor at Florida International University, said he’s extending this work into his own theoretical calculations of neutron stars.

    “Think of a neutron star like it’s a huge nucleus, where you have ten times more neutrons than protons. The effect should be very, very profound for neutron stars. So this opens up a new direction for research,” Sargsian said.

    According to Lawrence Weinstein, a lead coauthor and eminent scholar and professor at Old Dominion University in Norfolk, Va., the scientists would also like to continue their studies of the pairs.

    “We’d like to measure a lot more aspects of how protons and neutrons pair up in nuclei. So we know not just protons prefer neutrons, but how are the pairs behaving, in detail,” he said.

    This new result was made possible by an initiative funded by a grant from the U.S. Department of Energy and led by Weinstein and Sargsian, as well as Mark Strikman, a distinguished professor at Penn State, and Sebastian Kuhn, a professor and eminent scholar at Old Dominion University. The data-mining initiative consisted of re-analyzing experimental data from completed experiments in an attempt to glean new information that previously had not been considered or was missed. A collaboration of more than 140 researchers from more than 40 institutions and nine countries contributed to the result. Researchers at two U.S. Department of Energy national labs, Jefferson Lab and Argonne National Lab, participated in the research.

    Argonne physicist Kawtar Hafidi led the experiment that first collected the data back in 2003. “That data was so unique that we’ve been able to extract all kinds of information on several different areas of nuclear physics since then,” she said. She chairs the group, the CEBAF Large Acceptance Spectrometer collaboration nuclear physics working group, that oversees the review and release of scientific results from the data taken by that experiment.

    “This is excellent work that helps validate our theoretical picture of nuclear structure,” said Robert Wiringa, an Argonne physicist whose theoretical work is cited in the paper.

    The paper was published online by the journal Science, at the Science Express web site, on Thursday, 16 October, 2014. See http://www.sciencexpress.org, and also http://www.aaas.org. Science and Science Express are published by the AAAS, the science society, the world’s largest general scientific organization.

    This work was supported by the U.S. Department of Energy’s Office of Science (Office of Nuclear Physics), the U.S. National Science Foundation, Israel Science Foundation, Chilean Comisión Nacional de Investigación Científica y Technológica, French Centre National de la Recherche Scientifique and Commissariat a l’Energie Atomique, French-American Cultural Exchange, Italian Istituto Nazionale di Fisica Nucleare, National Research Foundation of Korea and the U.K.’s Science and Technology Facilities Council. CEBAF is a DOE Office of Science User Facility.

    See the full article here.

    Argonne National Laboratory seeks solutions to pressing national problems in science and technology. The nation’s first national laboratory, Argonne conducts leading-edge basic and applied scientific research in virtually every scientific discipline. Argonne researchers work closely with researchers from hundreds of companies, universities, and federal, state and municipal agencies to help them solve their specific problems, advance America’s scientific leadership and prepare the nation for a better future. With employees from more than 60 nations, Argonne is managed by UChicago Argonne, LLC for the U.S. Department of Energy’s Office of Science. For more visit http://www.anl.gov.

    The Advanced Photon Source at Argonne National Laboratory is one of five national synchrotron radiation light sources supported by the U.S. Department of Energy’s Office of Science to carry out applied and basic research to understand, predict, and ultimately control matter and energy at the electronic, atomic, and molecular levels, provide the foundations for new energy technologies, and support DOE missions in energy, environment, and national security. To learn more about the Office of Science X-ray user facilities, visit http://science.energy.gov/user-facilities/basic-energy-sciences/.

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

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  • richardmitnick 5:26 pm on August 25, 2014 Permalink | Reply
    Tags: , Argonne,   

    From Argonne Lab: “Argonne, KAERI to develop prototype nuclear reactor “ 

    News from Argonne National Laboratory

    August 25, 2014
    No Writer Credit

    The U.S. Department of Energy’s Argonne National Laboratory has teamed up with the Korea Atomic Energy Research Institute (KAERI) to develop the Prototype Generation-IV Sodium-cooled Fast Reactor (PGSFR). KAERI’s Sodium-cooled Fast Reactor Development Agency has provided $6.78 million funding to date for Argonne’s contributions through a Work-for-Others contract.

    lkaeri
    Argonne will support the Korean Atomic Energy Research Institute’s development of a Prototype Generation-IV Sodium-cooled Fast Reactor that incorporates an innovative metal fuel developed at Argonne. The fuel’s inherent safety potential was demonstrated in landmark tests conducted on the Experimental Breeder Reactor-II. Image credit: KAER I.

    Jong Kyung Kim, President of KAERI, visited Argonne today to execute the memorandum of understanding between KAERI and Argonne for a broad field of technical cooperation on nuclear science and technology, including the PGSFR project. “The technical cooperation between KAERI and Argonne plays a critical role in advancing cutting-edge technologies in nuclear energy,” said Argonne Director Peter Littlewood.

    The PGSFR is a 400 MWth, 150 MWe advanced sodium-cooled fast reactor that incorporates many innovative design features; in particular, metal fuel, which enables inherent safety characteristics. With Argonne support, KAERI is developing the reactor system while the Korean engineering and construction firm KEPCO E&C is designing the balance of the plant. The PGSFR Project aims to secure the Korean licensing authority’s design approval by the end of 2020, and the schedule calls for PGSFR to be commissioned by the end of 2028.

    The metal fuel technology base was developed at Argonne in the 1980s and ‘90s; its inherent safety potential was demonstrated in the landmark tests conducted on the Experimental Breeder Reactor-II in April 1986. They demonstrated the safe shutdown and cooling of the reactor without operator action following a simulated loss-of-cooling accident.

    “We are very excited about our collaboration on the PGSFR,” said Mark Peters, Argonne’s Associate Laboratory Director for Energy Engineering and Systems Analysis. “PGSFR is the world’s first new fast reactor that will use the technology developed at Argonne, and also the world’s first fast reactor that exploits inherent safety characteristics to prevent severe accidents.”

    The Argonne-KAERI collaboration on PGSFR was established following the U.S. Government authorization of the 10 CFR Part 810 request to transfer sodium-cooled fast reactor and low-enriched uranium fuel technology to the Republic of Korea.

    See the full article here.

    Argonne National Laboratory seeks solutions to pressing national problems in science and technology. The nation’s first national laboratory, Argonne conducts leading-edge basic and applied scientific research in virtually every scientific discipline. Argonne researchers work closely with researchers from hundreds of companies, universities, and federal, state and municipal agencies to help them solve their specific problems, advance America’s scientific leadership and prepare the nation for a better future. With employees from more than 60 nations, Argonne is managed by UChicago Argonne, LLC for the U.S. Department of Energy’s Office of Science. For more visit http://www.anl.gov.

    The Advanced Photon Source at Argonne National Laboratory is one of five national synchrotron radiation light sources supported by the U.S. Department of Energy’s Office of Science to carry out applied and basic research to understand, predict, and ultimately control matter and energy at the electronic, atomic, and molecular levels, provide the foundations for new energy technologies, and support DOE missions in energy, environment, and national security. To learn more about the Office of Science X-ray user facilities, visit http://science.energy.gov/user-facilities/basic-energy-sciences/.

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

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  • richardmitnick 4:07 pm on August 25, 2014 Permalink | Reply
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    From Argonne Lab: “Gut bacteria that protect against food allergies identified” 

    News from Argonne National Laboratory

    August 25, 2014
    This story was first reported by the University of Chicago Medicine and Biological Sciences.

    The presence of Clostridia, a common class of gut bacteria, protects against food allergies, a new study in mice finds. By inducing immune responses that prevent food allergens from entering the bloodstream, Clostridia minimize allergen exposure and prevent sensitization – a key step in the development of food allergies. The discovery points toward probiotic therapies for this so-far untreatable condition, report scientists from the University of Chicago, Aug. 25 in the Proceedings of the National Academy of Sciences.

    clos
    One variety of many of Clostridia

    “From a basic science perspective, what is fascinating with this research is the fine-scale machinations that the host microbiome exhibits with its host,” said Dionysios Antonopoulos of the Institute for Genomics and Systems Biology at Argonne National Laboratory and a co-author for the study. “Specific populations of microorganisms serve specific functions in mediating how the host’s immune system senses and interacts with its environment. As with this study, understanding how specific populations of the microbial community are impacted by antibiotics or diet provides a guide on what therapeutic strategies need to be developed to restore a healthy state.”

    Although the causes of food allergy – a sometimes deadly immune response to certain foods – are unknown, studies have hinted that modern hygienic or dietary practices may play a role by disturbing the body’s natural bacterial composition. In recent years, food allergy rates among children have risen sharply – increasing approximately 50 percent between 1997 and 2011 – and studies have shown a correlation to antibiotic and antimicrobial use.

    “Environmental stimuli such as antibiotic overuse, high fat diets, caesarean birth, removal of common pathogens and even formula feeding have affected the microbiota with which we’ve co-evolved,” said study senior author Cathryn Nagler, PhD, Bunning Food Allergy Professor at the University of Chicago. “Our results suggest this could contribute to the increasing susceptibility to food allergies.”

    To test how gut bacteria affect food allergies, Nagler and her team investigated the response to food allergens in mice. They exposed germ-free mice (born and raised in sterile conditions to have no resident microorganisms) and mice treated with antibiotics as newborns (which significantly reduces gut bacteria) to peanut allergens. Both groups of mice displayed a strong immunological response, producing significantly higher levels of antibodies against peanut allergens than mice with normal gut bacteria.

    This sensitization to food allergens could be reversed, however, by reintroducing a mix of Clostridia bacteria back into the mice. Reintroduction of another major group of intestinal bacteria, Bacteroides, failed to alleviate sensitization, indicating that Clostridia have a unique, protective role against food allergens.

    Closing the door

    To identify this protective mechanism, Nagler and her team studied cellular and molecular immune responses to bacteria in the gut. Genetic analysis revealed that Clostridia caused innate immune cells to produce high levels of interleukin-22 (IL-22), a signaling molecule known to decrease the permeability of the intestinal lining.

    Antibiotic-treated mice were either given IL-22 or were colonized with Clostridia. When exposed to peanut allergens, mice in both conditions showed reduced allergen levels in their blood, compared to controls. Allergen levels significantly increased, however, after the mice were given antibodies that neutralized IL-22, indicating that Clostridia-induced IL-22 prevents allergens from entering the bloodstream.

    “We’ve identified a bacterial population that protects against food allergen sensitization,” Nagler said. “The first step in getting sensitized to a food allergen is for it to get into your blood and be presented to your immune system. The presence of these bacteria regulates that process.” She cautions, however, that these findings likely apply at a population level, and that the cause-and-effect relationship in individuals requires further study.

    While complex and largely undetermined factors such as genetics greatly affect whether individuals develop food allergies and how they manifest, the identification of a bacteria-induced barrier-protective response represents a new paradigm for preventing sensitization to food. Clostridia bacteria are common in humans and represent a clear target for potential therapeutics that prevent or treat food allergies. Nagler and her team are working to develop and test compositions that could be used for probiotic therapy and have filed a provisional patent.

    “It’s exciting because we know what the bacteria are; we have a way to intervene,” Nagler said. “There are of course no guarantees, but this is absolutely testable as a therapeutic against a disease for which there’s nothing. As a mom, I can imagine how frightening it must be to worry every time your child takes a bite of food.”

    “Food allergies affect 15 million Americans, including one in 13 children, who live with this potentially life-threatening disease that currently has no cure,” said Mary Jane Marchisotto, senior vice president of research at Food Allergy Research & Education. “We have been pleased to support the research that has been conducted by Dr. Nagler and her colleagues at the University of Chicago.”

    The study, Commensal bacteria protect against food allergen sensitization, was supported by Food Allergy Research & Education (FARE) and the University of Chicago Digestive Diseases Research Core Center. Gene sequencing was conducted at the Next-Generation Sequencing Core at Argonne National Labortory. Additional authors include Andrew T. Stefka, Taylor Feehley, Prabhanshu Tripathi, Ju Qiu, Kathy D. McCoy, Sarkis K. Mazmanian, Melissa Y. Tjota, Goo-Young Seo, Severine Cao, Betty R. Theriault, Dionysios A. Antonopoulos, Liang Zhou, Eugene B. Chang and Yang-Xin Fu.

    Food Allergy Research & Education (FARE) is a 501(c)(3) nonprofit organization that seeks to find a cure for food allergies while keeping affected individuals safe and included. FARE does this by investing in world-class research that advances the treatment and understanding of the disease, providing evidence-based education and resources, undertaking advocacy at all levels of government and increasing awareness of food allergy as a serious public health issue.

    The University of Chicago Medicine and Biological Sciences is one of the nation’s leading academic medical institutions. It comprises the Pritzker School of Medicine, a top medical school in the nation; the University of Chicago Biological Sciences Division; and the University of Chicago Medical Center, which recently opened the Center for Care and Discovery, a $700 million specialty medical facility. Twelve Nobel Prize winners in physiology or medicine have been affiliated with the University of Chicago Medicine.

    See the full article here.

    Argonne National Laboratory seeks solutions to pressing national problems in science and technology. The nation’s first national laboratory, Argonne conducts leading-edge basic and applied scientific research in virtually every scientific discipline. Argonne researchers work closely with researchers from hundreds of companies, universities, and federal, state and municipal agencies to help them solve their specific problems, advance America’s scientific leadership and prepare the nation for a better future. With employees from more than 60 nations, Argonne is managed by UChicago Argonne, LLC for the U.S. Department of Energy’s Office of Science. For more visit http://www.anl.gov.

    The Advanced Photon Source at Argonne National Laboratory is one of five national synchrotron radiation light sources supported by the U.S. Department of Energy’s Office of Science to carry out applied and basic research to understand, predict, and ultimately control matter and energy at the electronic, atomic, and molecular levels, provide the foundations for new energy technologies, and support DOE missions in energy, environment, and national security. To learn more about the Office of Science X-ray user facilities, visit http://science.energy.gov/user-facilities/basic-energy-sciences/.

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

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  • richardmitnick 9:32 am on July 26, 2014 Permalink | Reply
    Tags: , Argonne,   

    From Argonne Lab: “Silicene: To be or not to be?” 

    News from Argonne National Laboratory

    July 24, 2014
    Justin H.S. Breaux

    Sometimes, scientific findings can shake the foundations of what was once held to be true, causing us to step back and re-examine our basic assumptions.

    A recent study at the U.S. Department of Energy’s Argonne National Laboratory has called into question the existence of silicene, thought to be one of the world’s newest and hottest two-dimensional nanomaterials. The study may have great implications to a multi-billion dollar electronics industry that seeks to revolutionize technology at scales 80,000 times smaller than the human hair.

    sil
    The Structure of a typical silicene cluster showing the ordered ripples across the surface. The valencies for the side atoms are satisfied by hydrogens.

    Silicene was proposed as a two-dimensional sheet of silicon atoms that can be created experimentally by super-heating silicon and evaporating atoms onto a silver platform. Silver is the platform of choice because it will not affect the silicon via chemical bonding nor should alloying occur due to its low solubility. During the heating process, as the silicon atoms fall onto the platform, researchers believed that they were arranging themselves in certain ways to create a single sheet of interlocking atoms.

    Silicon, on the other hand, exists in three dimensions and is one of the most common elements on Earth. A metal, semiconductor and insulator, purified silicon is extremely stable and has become essential to the integrated circuits and transistors that run most of our computers.

    Both silicene and silicon should react immediately with oxygen, but they react slightly differently. In the case of silicon, oxygen breaks some of the silicon bonds of the first one or two atomic layers to form a layer of silicon-oxygen. This, surprisingly, acts a chemical barrier to prevent the decay of the lower layers.

    Because it consists of only one layer of silicon atoms, silicene must be handled in a vacuum. Exposure to any amount of oxygen would completely destroy the sample.

    This difference is one of the keys to the researchers’ discovery. After depositing the atoms onto the silver platform, initial tests identified that alloy-like surface phases would form until bulk silicon layers, or “platelets” would precipitate out, which has been mistaken as two-dimensional silicene.

    “Some of the bulk silicon platelets were more than one layer thick,” said Argonne scientist Nathan Guisinger of Argonne’s Center for Nanoscale Materials. “We determined that if we were dealing with multiple layers of silicon atoms, we could bring it out of our ultra-high vacuum chamber and bring it into air and do some other tests.”

    image
    Argonne researchers use an e-beam evaporator to deposit atomic silicon onto a silver platform in a vacuum. The silver is heated to ~400 C allowing the deposits to rearrange into a sheet of interlocking silicon atoms. The B&W cross-sectional transmission electron microscope image to the right shows the growth of bulk-like silicon nanosheets, rather than atomically thin silicene layers.

    “Everybody assumed the sample would immediately decay as soon as they pulled it out of the chamber,” added Northwestern University graduate student Brian Kiraly, one of the principal authors of the study. “We were the first to actually bring it out and perform major experiments outside of the vacuum.”

    four
    A recent Argonne study has called into question the existence of silicene, thought to be one of the world’s newest and hottest two-dimensional nanomaterials. Pictured are researchers (clockwise from bottom left) Nathan Guisinger, Andrew J. Mannix, Brian Kiraly and Brandon L. Fisher. Photo credit: Wes Agresta, Argonne National Laboratory

    Each new series of experiments presented a new set of clues that this was, in fact, not silicene.

    By examining and categorizing the top layers of the material, the researchers discovered silicon oxide, a sign of oxidation in the top layers. They were also surprised to find that particles from the silver platform alloyed with the silicon at significant depths.

    tunnel
    Researchers at Argonne find that silicene, a one-atom thick sheet of silicon, has not been experimentally realized on silver, and that silver is unlikely to be a good substrate for silicene. (a) This three-dimensional scanning tunneling microscopy image shows the growth of seven ultra-thin layers of silicon nanosheets atop a silver crystal. The atomic structures of the nanosheets are illustrated for layers 4, 5 and 6. (b) Step heights for silicon nanosheets are plotted at the bottom.

    “We found out that what previous researchers identified as silicene is really just a combination of the silicon and the silver,” said Northwestern graduate student Andrew Mannix.

    For their final test, the researchers decided to probe the atomic signature of the material.

    Materials are made up of systems of atoms that bond and vibrate in unique ways. Raman spectroscopy allows researchers to measure these bonds and vibrations. Housed within the Center for Nanoscale Materials, a DOE Office of Science User Facility, the spectroscope allows researchers to use light to “shift” the position of one atom in a crystal lattice, which in turn causes a shift in the position of its neighbors. Scientists define a material by measuring how strong or weak these bonds are in relation to the frequency at which the atoms vibrate.

    The researchers noticed something oddly familiar when looking at the vibrational signatures and frequencies of their sample. Their sample did not exhibit characteristic vibrations of silicene, but it did match those of silicon.

    “Having this many research groups and papers potentially be wrong does not happen often,” says Guisinger. “I hope our research helps guide future studies and convincingly demonstrates that silver is not a good platform if you are trying to grow silicene.”

    This material is based upon work supported by the U.S. Department of Energy’s Office of Science.

    See the full article here.

    Argonne National Laboratory seeks solutions to pressing national problems in science and technology. The nation’s first national laboratory, Argonne conducts leading-edge basic and applied scientific research in virtually every scientific discipline. Argonne researchers work closely with researchers from hundreds of companies, universities, and federal, state and municipal agencies to help them solve their specific problems, advance America’s scientific leadership and prepare the nation for a better future. With employees from more than 60 nations, Argonne is managed by UChicago Argonne, LLC for the U.S. Department of Energy’s Office of Science. For more visit http://www.anl.gov.

    The Advanced Photon Source at Argonne National Laboratory is one of five national synchrotron radiation light sources supported by the U.S. Department of Energy’s Office of Science to carry out applied and basic research to understand, predict, and ultimately control matter and energy at the electronic, atomic, and molecular levels, provide the foundations for new energy technologies, and support DOE missions in energy, environment, and national security. To learn more about the Office of Science X-ray user facilities, visit http://science.energy.gov/user-facilities/basic-energy-sciences/.

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

    Argonne Lab Campus


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