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  • richardmitnick 5:03 pm on September 10, 2014 Permalink | Reply
    Tags: , , , Photon Sciences,   

    From LBL: “Advanced Light Source Sets Microscopy Record” 

    Berkeley Logo

    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.)

    ds
    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.

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

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  • richardmitnick 12:59 pm on September 9, 2014 Permalink | Reply
    Tags: , , Photon Sciences, ,   

    From SLAC: “Buckyballs and Diamondoids Join Forces in Tiny Electronic Gadget” 


    SLAC Lab

    September 9, 2014
    Press Office Contact: Andrew Gordon, agordon@slac.stanford.edu, (650) 926-2282

    Scientists Craft Two Exotic Forms of Carbon into a Molecule for Steering Electron Flow

    Scientists have married two unconventional forms of carbon – one shaped like a soccer ball, the other a tiny diamond – to make a molecule that conducts electricity in only one direction. This tiny electronic component, known as a rectifier, could play a key role in shrinking chip components down to the size of molecules to enable faster, more powerful devices.

    dd
    An international team led by researchers at SLAC National Accelerator Laboratory and Stanford University joined two offbeat carbon molecules – diamondoids, the square cages at left, and buckyballs, the soccer-ball shapes at right – to create “buckydiamondoids,” center. These hybrid molecules function as rectifiers, conducting electrons in only one direction, and could help pave the way to molecular electronic devices. (Manoharan Lab/Stanford University)

    “We wanted to see what new, emergent properties might come out when you put these two ingredients together to create a ‘buckydiamondoid,’” said Hari Manoharan of the Stanford Institute for Materials and Energy Sciences (SIMES) at the Department of Energy’s SLAC National Accelerator Laboratory. “What we got was a basically a one-way valve for conducting electricity – clearly more than the sum of its parts.”

    The research team, which included scientists from Stanford University, Belgium, Germany and Ukraine, reported its results September 9, 2014, in Nature Communications.

    Two Offbeat Carbon Characters Meet Up

    Many electronic circuits have three basic components: a material that conducts electrons; rectifiers, which commonly take the form of diodes, to steer that flow in a single direction; and transistors to switch the flow on and off. Scientists combined two offbeat ingredients – buckyballs and diamondoids – to create the new diode-like component.

    Buckyballs – short for buckminsterfullerenes – are hollow carbon spheres whose 1985 discovery earned three scientists a Nobel Prize in chemistry. Diamondoids are tiny carbon cages bonded together as they are in diamonds, but weighing less than a billionth of a billionth of a carat. Both are subjects of a lot of research aimed at understanding their properties and finding ways to use them.

    In 2007, a team led by researchers from SLAC and Stanford discovered that a single layer of diamondoids on a metal surface can efficiently emit a beam of electrons. Manoharan and his colleagues wondered: What would happen if they paired an electron-emitting diamondoid with another molecule that likes to grab electrons? Buckyballs are just that sort of electron-grabbing molecule.

    A Very Small Valve for Channeling Electron Flow

    For this study, diamondoids were produced in the SLAC laboratory of SIMES researchers Jeremy Dahl and Robert Carlson, who are world experts in extracting the tiny diamonds from petroleum. They were then shipped to Germany, where chemists at Justus-Liebig University figured out how to attach them to buckyballs.

    The resulting buckydiamondoids, which are just a few nanometers long, were tested in SIMES laboratories at Stanford. A team led by graduate student Jason Randel and postdoctoral researcher Francis Niestemski used a scanning tunneling microscope to make images of the hybrid molecules and measure their electronic behavior. They discovered the hybrid is an excellent rectifier: The electrical current flowing through the molecule was up to 50 times stronger in one direction, from electron-spitting diamondoid to electron-catching buckyball, than in the opposite direction. This is something neither component can do on its own.

    ball
    An image made with a scanning tunneling microscope shows hybrid buckydiamondoid molecules on a gold surface. The buckyball end of each molecule is attached to the surface, with the diamondoid end sticking up; both are clearly visible. The area shown here is 5 nanometers on a side. (H. Manoharan et al, Nature Communications)

    image
    Illustration of a buckydiamondoid molecule under a scanning tunneling microscope (STM). The sharp metallic tip of the STM ends in a single atom; as it scans over a sample, electrons tunnel from the tip into the sample. In this study the STM made images of the buckydiamondoids and probed their electronic properties. (SLAC National Accelerator Laboratory)

    While this is not the first molecular rectifier ever invented, it’s the first one made from just carbon and hydrogen, a simplicity researchers find appealing, said Manoharan, who is an associate professor of physics at Stanford. The next step, he said, is to see if transistors can be constructed from the same basic ingredients.

    “Buckyballs are easy to make – they can be isolated from soot – and the type of diamondoid we used here, which consists of two tiny cages, can be purchased commercially,” he said. “And now that our colleagues in Germany have figured out how to bind them together, others can follow the recipe. So while our research was aimed at gaining fundamental insights about a novel hybrid molecule, it could lead to advances that help make molecular electronics a reality.”

    Other research collaborators came from the Catholic University of Louvain in Belgium and Kiev Polytechnic Institute in Ukraine. The primary funding for the work came from the U.S. Department of Energy Office of Science.

    See the full article here.

    SLAC Campus
    SLAC is a multi-program laboratory exploring frontier questions in photon science, astrophysics, particle physics and accelerator research. Located in Menlo Park, California, SLAC is operated by Stanford University for the DOE’s Office of Science.
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  • richardmitnick 5:33 am on August 16, 2014 Permalink | Reply
    Tags: , , , , Photon Sciences,   

    From Brookhaven Lab: “Harnessing the Power of Bacteria’s Sophisticated Immune System” 

    Brookhaven Lab

    August 15, 2014
    Karen McNulty Walsh, (631) 344-8350 or Peter Genzer, (631) 344-3174

    Researchers Now Better Understand How Bacteria Can So Quickly Protect Itself From Harm, Could Help Unlock Clues About Antibiotic Resistance

    Bacteria’s ability to destroy viruses has long puzzled scientists, but researchers at the Johns Hopkins Bloomberg School of Public Health say they now have a clear picture of the bacterial immune system and say its unique shape is likely why bacteria can so quickly recognize and destroy their assailants.

    The researchers drew what they say is the first-ever picture of the molecular machinery, known as Cascade, which stands guard inside bacterial cells. To their surprise, they found it contains a two-strand, unencumbered structure that resembles a ladder, freeing it to do its work faster than a standard double-helix would allow.

    The findings, published online Aug. 14 in the journal Science, may also provide clues about the spread of antibiotic resistance, which occurs when bacteria adapt to the point where antibiotics no longer work in people who need them to treat infections, since similar processes are in play. The World Health Organization (WHO) considers antibiotic resistance a major threat to public health around the world.

    “If you understand what something looks like, you can figure out what it does,” says study leader Scott Bailey, PhD, an associate professor in the Bloomberg School’s Department of Biochemistry and Molecular Biology. “And here we found a structure that nobody’s ever seen before, a structure that could explain why Cascade is so good at what it does.”

    For their study, Bailey and his colleagues used something called X-ray crystallography to draw the picture of Cascade, a key component of bacteria’s sophisticated immune system known as CRISPR, an acronym for Clustered Regularly Interspaced Short Palindromic Repeats. Cascade uses the information housed in sequences of RNA as shorthand to identify foreign invaders and kill them.

    crispr
    Diagram of the possible mechanism for CRISPR

    Much of the human immune system is well understood, but until recently scientists didn’t realize the level of complexity associated with the immune system of single-cell life forms, including bacteria. Scientists first identified CRISPR several years ago when trying to understand why bacterial cultures used to make yogurt succumbed to viral infections. Researchers subsequently discovered they could harness the CRISPR bacterial immune system to edit DNA and repair damaged genes. One group, for example, was able to remove viral DNA from human cells infected with HIV.

    Bailey’s work is focused on how Cascade is able to help bacteria fight off viruses called bacteriophages. The Cascade system uses short strands of bacterial RNA to scan the bacteriophage DNA to see if it is foreign or self. If foreign, the cell launches an attack that chews up the invading bacteriophage.

    bac
    The structure of a typical myovirus bacteriophage

    To “see” how this happens, Bailey and his team converted Cascade into a crystalized form. Technicians at the National Synchrotron Light Source at Brookhaven National Laboratory in Upton, New York, and the Stanford Synchrotron Radiation Lightsource then trained high-powered X-rays on the crystals. The X-rays provided computational data to the Bloomberg School scientists allowing them to draw Cascade, an 11-protein machine that only operates if each part is in perfect working order.

    Brookhaven NSLS
    Brookhaven NSLS

    SLAC SSRL
    SLAC SSRL

    What they saw was unexpected. Instead of the RNA and DNA wrapping around each other to form what is known as a double-helix structure, in Cascade the DNA and RNA are more like parallel lines, forming something of a ladder. Bailey says that if RNA had to wrap itself around DNA to recognize an invader – and then unwrap itself to look at the next strand – the process would take too much time to ward off infection. With a ladder structure, RNA can quickly scan DNA.

    ah
    Annie Heroux at NSLS

    In the new study, Bailey says his team determined that the RNA scans the DNA in a manner similar to how humans scan text for a key word. They break long stretches of characters into smaller bite-sized segments, much like words themselves, so they can be spotted more easily.

    Since the CRISPR-Cas system naturally acts as a barrier to the exchange of genetic information between bacteria and bacteriophages, its function can offer clues to how antibiotic resistance develops and ideas for how to keep it from happening.

    “We’re finding more pieces to the puzzle,” Bailey says. “This gives us a better understanding of how these machines find their targets, which may help us harness the CRISPR system as a tool for therapy or manipulation of DNA in a lab setting. And it all started when someone wanted to make yogurt more cheaply.”

    “Crystal structure of a CRISPR RNA-guided surveillance complex bound to a ssDNA target” was written by Sabin Mulepati, Annie Heroux and Scott Bailey.

    This work was funded by a grant from the National Institute of Health’s National Institute of General Medical Sciences (GM097330).

    See the full article here.

    One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. The Laboratory’s almost 3,000 scientists, engineers, and support staff are joined each year by more than 5,000 visiting researchers from around the world.Brookhaven is operated and managed for DOE’s Office of Science by Brookhaven Science Associates, a limited-liability company founded by Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit, applied science and technology organization.
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  • richardmitnick 11:44 am on August 1, 2014 Permalink | Reply
    Tags: , , , , Photon Sciences,   

    From M.I.T.: “Light pulses control graphene’s electrical behavior” 


    M.I.T.

    July 31, 2014
    David L. Chandler | MIT News Office

    Graphene, an ultrathin form of carbon with exceptional electrical, optical, and mechanical properties, has become a focus of research on a variety of potential uses. Now researchers at MIT have found a way to control how the material conducts electricity by using extremely short light pulses, which could enable its use as a broadband light detector.

    graphene
    Researchers at MIT have found a way to control how graphene conducts electricity by using extremely short light pulses. In this illustration, a lattice of graphene is shown with its bonds (bars) connecting carbon atoms (balls). When the light pulse hits the atoms, electrons can accumulate or diminish in number. By controlling the concentration of electrons in a graphene sheet, researchers can change the material’s electrical conductivity.

    Illustration: Jose-Luis Olivares/MIT

    The new findings are published in the journal Physical Review Letters, in a paper by graduate student Alex Frenzel, Nuh Gedik, and three others.

    The researchers found that by controlling the concentration of electrons in a graphene sheet, they could change the way the material responds to a short but intense light pulse. If the graphene sheet starts out with low electron concentration, the pulse increases the material’s electrical conductivity. This behavior is similar to that of traditional semiconductors, such as silicon and germanium.

    But if the graphene starts out with high electron concentration, the pulse decreases its conductivity — the same way that a metal usually behaves. Therefore, by modulating graphene’s electron concentration, the researchers found that they could effectively alter graphene’s photoconductive properties from semiconductorlike to metallike.

    The finding also explains the photoresponse of graphene reported previously by different research groups, which studied graphene samples with differing concentration of electrons. “We were able to tune the number of electrons in graphene, and get either response,” Frenzel says.

    To perform this study, the team deposited graphene on top of an insulating layer with a thin metallic film beneath it; by applying a voltage between graphene and the bottom electrode, the electron concentration of graphene could be tuned. The researchers then illuminated graphene with a strong light pulse and measured the change of electrical conduction by assessing the transmission of a second, low-frequency light pulse.

    In this case, the laser performs dual functions. “We use two different light pulses: one to modify the material, and one to measure the electrical conduction,” Gedik says, adding that the pulses used to measure the conduction are much lower frequency than the pulses used to modify the material behavior. To accomplish this, the researchers developed a device that was transparent, Frenzel explains, to allow laser pulses to pass through it.

    This all-optical method avoids the need for adding extra electrical contacts to the graphene. Gedik, the Lawrence C. and Sarah W. Biedenharn Associate Professor of Physics, says the measurement method that Frenzel implemented is a “cool technique. Normally, to measure conductivity you have to put leads on it,” he says. This approach, by contrast, “has no contact at all.”

    Additionally, the short light pulses allow the researchers to change and reveal graphene’s electrical response in only a trillionth of a second.

    In a surprising finding, the team discovered that part of the conductivity reduction at high electron concentration stems from a unique characteristic of graphene: Its electrons travel at a constant speed, similar to photons, which causes the conductivity to decrease when the electron temperature increases under the illumination of the laser pulse. “Our experiment reveals that the cause of photoconductivity in graphene is very different from that in a normal metal or semiconductor,” Frenzel says.

    The researchers say the work could aid the development of new light detectors with ultrafast response times and high sensitivity across a wide range of light frequencies, from the infrared to ultraviolet. While the material is sensitive to a broad range of frequencies, the actual percentage of light absorbed is small. Practical application of such a detector would therefore require increasing absorption efficiency, such as by using multiple layers of graphene, Gedik says.

    Isabella Gierz, a professor at the Max Planck Institute for the Structure and Dynamics of Matter in Hamburg, Germany, who was not involved in this research, says, “The work is interesting because it presents a systematic study of the doping dependence of the low-energy dynamics, which has not received much attention so far.” She says the new research “certainly helps to reconcile previous apparently contradicting results,” and adds that these findings represent “a solid experiment, analysis, and interpretation.”

    The research team also included Jing Kong, the ITT Career Development Associate Professor of Electrical Engineering at MIT, who provided the graphene samples used for the experiments; physics postdoc Chun Hung Lui; and Yong Cheol Shin, a graduate student in materials science and engineering. The work received support from the U.S. Department of Energy and the National Science Foundation.

    See the full article here.


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  • richardmitnick 11:28 am on July 28, 2014 Permalink | Reply
    Tags: , , , Photon Sciences   

    From Brookhaven Lab: “Understanding the Source of Extra-large Capacities in Promising Li-ion Battery Electrodes” 

    Brookhaven Lab

    July 28, 2014
    Laura Mgrdichian

    Lithium (Li) ion batteries power almost all of the portable electronic devices that we use everyday, including smart phones, cameras, toys, and even electric cars. Researchers across the globe are working to find materials that will lead to safe, cheap, long-lasting, and powerful Li-ion batteries.

    Working at various U.S. Department of Energy light source facilities and at Cambridge and Stony Brook universities, a group of researchers recently studied a class of Li-ion battery electrodes that have capacities much greater than those of the materials used in today’s batteries. The researchers wanted to determine why these materials can often store more charge than theory predicts.

    path
    A summary of the three-stage reaction pathway of the ruthenium-oxide-lithium battery system.

    The authors chose ruthenium oxide (RuO2) as a model system to study these so-called “conversion materials,” named because they undergo large structural changes when reacting with lithium ions, reversibly forming metal nanoparticles and salts (here Ru and Li2O). These reactions are very different from those that occur in conventional electrodes, which store charge by allowing Li ions to nestle into spaces within the crystal lattice.

    “Our investigation identified the source of the additional capacity found for RuO2, and has also yielded a protocol for studying the ‘passivation layer’ that forms on battery electrodes, which protects the electrolyte from undergoing further decomposition reactions in subsequent charge-discharge cycles,” said the study’s corresponding researcher, Clare Grey, a professor in the chemistry departments at Cambridge and Stony Brook universities. “Understanding the structures of these passivation layers is key to making batteries that last long enough for use in applications such as transportation and power-grid storage.”

    At Brookhaven National Laboratory’s National Synchrotron Light Source, the team studied their samples using x-ray absorption near-edge structure (XANES) and extended x-ray absorption fine structure (EXAFS). At the Advanced Photon Source at Argonne National Laboratory, they used two additional techniques, high-resolution x-ray diffraction (XRD) and scattering pair distribution function (PDF) analysis, to extract information on the electronic and long/short-range structural changes of the RuO2 electrode in real time as the battery was discharged and charged. Using these methods, the team showed that RuO2 was reduced to Ru nanoparticles and Li2O via the formation of intermediate phases, LixRuO2.

    Since this did not explain the source of the additional charge-storage mechanism, the group used another technique, high-resolution solid-state nuclear magnetic resonance (NMR). This method involves subjecting a sample to a magnetic field and measuring the response of the nuclei within the sample. It can yield specific information on the chemical compositions and local structures, and is particularly useful for studying compounds that contain only “light” elements, such as hydrogen (H), Li, and oxygen (O), which are difficult to detect using XRD. The NMR data showed that the major contributor to the capacity is the formation of LiOH, which reversibly converts to Li2O and LiH. Minor contributors to the capacity come from Li storage on the Ru nanoparticle surfaces, forming a LixRu alloy, and the decomposition of the electrolyte. The latter, however, ultimately causes the capacity to diminish and will result in the death of the battery following multiple charge cycles.

    Scientists from the University of Cambridge, Brookhaven National Laboratory, Argonne National Laboratory, and Stony Brook University conducted this research. It was published in the December 2013 issue of Nature Materials, 12, 1130-1136. The paper is titled Origin of additional capacities in metal oxide lithium-ion battery electrodes, and the authors are Yan-Yan Hu, Zigeng Liu, Kyung-Wan Nam, Olaf J. Borkiewicz, Jun Cheng, Xiao Hua, Matthew T. Dunstan, Xiqian Yu, Kamila M. Wiaderek, Lin-Shu Du, Karena W. Chapman, Peter J. Chupas, Xiao-Qing Yang and Clare P. Grey.

    See the full article here.

    One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. The Laboratory’s almost 3,000 scientists, engineers, and support staff are joined each year by more than 5,000 visiting researchers from around the world.Brookhaven is operated and managed for DOE’s Office of Science by Brookhaven Science Associates, a limited-liability company founded by Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit, applied science and technology organization.
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  • richardmitnick 10:57 am on July 9, 2014 Permalink | Reply
    Tags: , , , Photon Sciences   

    From Brookhaven Lab: “NSLS-II Reaches 25 Milliamps of Current with New Superconducting RF Cavity” 

    Brookhaven Lab

    July 9, 2014
    Chelsea Whyte

    In the early evening of July 2, 2014, the National Synchrotron Light Source II (NSLS-II) at the U.S. Department of Energy’s Brookhaven National Laboratory reached 25 milliamps of current at 3 GeV (3 billion electron volts) using a new superconducting radio-frequency (SRF) cavity.

    Brookhaven NSLS II Photo
    NSLS II campus

    The milestone was reached “thanks to enormous efforts by everybody in the last two months,” according to Accelerator Division Director Ferdinand Willeke in the Photon Sciences Directorate.

    The accelerator commissioning team achieved this significant milestone by completing several major tasks, which included installing a superconducting RF cavity in the storage ring and making it serviceable by operating a new cryogenic plant.

    In addition, the team installed several other important components, including two in-vacuum undulators in the storage ring; collimators mounted on the ratchet wall; and personal protection systems at beamline front-ends, where x-rays will exit the ring and enter the beam lines.

    25
    25 milliamps of current at 3GeV Just before 5:30 p.m. on July 2, 2014, the storage ring at the National Synchrotron Light Source II — outfitted with new a superconducting radio-frequency cavity — held 25 milliamps of current at 3GeV, a major milestone in the commissioning of the state-of-the-art facility.

    Radio-frequency (RF) group leader Jim Rose added, “With the help of the riggers and the support of the vacuum and cryogenics group, we installed the cavity into the NSLS-II tunnel. Then we cooled it down to 4.5 degrees Kelvin, where it becomes superconducting. After conditioning the cavity to 1.2 megavolts, we turned it over to operations, and the accelerator physicists quickly achieved the 25-milliamp objective of this commissioning run.”

    Advanced Energy Systems in Medford, NY, built the SRF cavity, their first of two superconducting cavities for NSLS-II.

    The second cavity and other hardware are still to be installed before the accelerator reaches full design current of 500 milliamps, according to deputy division director Timur Shaftan.

    “The intensity will come up little by little over the next few years,” Shaftan said. The next step is commissioning of insertion devices and front-ends, he said.

    When completed, NSLS-II will be a state-of-the-art, medium-energy electron storage ring that produces x-rays up to 10,000 times brighter than the original NSLS, which started operating at Brookhaven National Lab in 1982 and is shutting down at the end of September 2014.

    NSLS-II construction began in 2009, with a $912-million budget from the U.S. Department of Energy Office of Science. Construction has passed through distinct phases, starting with conventional construction of the ring building and laboratory-office buildings, and later installation of the accelerator and beamlines. Back in April 2014, accelerator physicists and operators achieved 25 milliamps of current at 3 GeV in the storage ring using a non-superconducting cavity. The final NSLS-II design calls for SRF cavities, however, and so the current milestone was key to final commissioning of the storage ring.

    Progress on the facility continues, with an initial suite of beamlines for early science expected to be commissioned in the coming months.

    DOE’s Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.

    See the full article here.

    One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. The Laboratory’s almost 3,000 scientists, engineers, and support staff are joined each year by more than 5,000 visiting researchers from around the world.Brookhaven is operated and managed for DOE’s Office of Science by Brookhaven Science Associates, a limited-liability company founded by Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit, applied science and technology organization.
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  • richardmitnick 9:18 am on June 27, 2014 Permalink | Reply
    Tags: Atomic Physics, , , , Photon Sciences,   

    From Berkeley Lab: “Not Much Force: Berkeley Researchers Detect Smallest Force Ever Measured” 


    Berkeley Lab

    June 26, 2014
    Lynn Yarris

    What is believed to be the smallest force ever measured has been detected by researchers with the Lawrence Berkeley National Laboratory (Berkeley Lab) and the University of California (UC) Berkeley. Using a combination of lasers and a unique optical trapping system that provides a cloud of ultracold atoms, the researchers measured a force of approximately 42 yoctonewtons. A yoctonewton is one septillionth of a newton and there are approximately 3 x 1023 yoctonewtons in one ounce of force.

    plumb
    Mechanical oscillators translate an applied force into measureable mechanical motion. The Standard Quantum Limit is imposed by the Heisenberg uncertainty principle, in which the measurement itself perturbs the motion of the oscillator, a phenomenon known as “quantum back-action.” (Image by Kevin Gutowski)

    “We applied an external force to the center-of-mass motion of an ultracold atom cloud in a high-finesse optical cavity and measured the resulting motion optically,” says Dan Stamper-Kurn, a physicist who holds joint appointments with Berkeley Lab’s Materials Sciences Division and the UC Berkeley Physics Department. “When the driving force was resonant with the cloud’s oscillation frequency, we achieved a sensitivity that is consistent with theoretical predictions and only a factor of four above the Standard Quantum Limit, the most sensitive measurement that can be made.”

    Stamper-Kurn is the corresponding author of a paper in Science that describes these results. The paper is titled Optically measuring force near the standard quantum limit. Co-authors are Sydney Schreppler, Nicolas Spethmann, Nathan Brahms, Thierry Botter and Maryrose Barrios.

    If you want to confirm the existence of gravitational waves, space-time ripples predicted by Albert Einstein in his theory of general relativity, or want to determine to what extent the law of gravity on the macroscopic scale, as described by Sir Isaac Newton, continues to apply at the microscopic scale, you need to detect and measure forces and motions that are almost incomprehensively tiny. For example, at the Laser Interferometer Gravitational-Wave Observatory (LIGO), scientists are attempting to record motions as small as one thousandth the diameter of a proton.

    sk
    From left, Sydney Schreppler, Dan Stamper-Kurn and Nicolas Spethmann were part of a team that detected the smallest force ever measured using a unique optical trapping system that provides ultracold atoms. (Photo by Roy Kaltschmidt)

    At the heart of all ultrasensitive detectors of force are mechanical oscillators, systems for translating an applied force into measureable mechanical motion. As measurements of force and motion reach quantum levels in sensitivity, however, they bump up against a barrier imposed by the Heisenberg uncertainty principle, in which the measurement itself perturbs the motion of the oscillator, a phenomenon known as “quantum back-action.” This barrier is called the Standard Quantum Limit (SQL). Over the past couple of decades, a wide array of strategies have been deployed to minimize quantum back-action and get ever closer to the SQL, but the best of these techniques fell short by six to eight orders of magnitude.

    “We measured force with a sensitivity that is the closest ever to the SQL,” says Sydney Schreppler, a member of the Stamper-Kurn research group and lead author of the Science paper. “We were able to achieve this sensitivity because our mechanical oscillator is composed of only 1,200 atoms.”

    In the experimental set-up used by Schreppler, Stamper-Kurn and their colleagues, the mechanical oscillator element is a gas of rubidium atoms optically trapped and chilled to nearly absolute zero. The optical trap consists of two standing-wave light fields with wavelengths of 860 and 840 nanometers that produce equal and opposite axial forces on the atoms. Center-of-mass motion is induced in the gas by modulating the amplitude of the 840 nanometer light field. The response is measured using a probe beam with a wavelength of 780 nanometers.

    graph
    To measure force, a cloud of atoms (gray oval) are trapped in an optical cavity created by two standing-wave light fields, ODT A and ODT B. The amplitude of ODT B is varied to create a force that is optomechanically transduced onto the phase of a probe light for measurement. No image credit.

    “When we apply an external force to our oscillator it is like hitting a pendulum with a bat then measuring the reaction,” says Schreppler. “A key to our sensitivity and approaching the SQL is our ability to decouple the rubidium atoms from their environment and maintain their cold temperature. The laser light we use to trap our atoms isolates them from external environmental noise but does not heat them, so they can remain cold and still enough to allow us to approach the limits of sensitivity when we apply a force.”

    Schreppler says it should be possible to get even closer to the SQL for force sensitivity through a combination of colder atoms and improved optical detection efficiency. She also says there are back-action evading techniques that can be taken by performing non-standard measurements. For now, the experimental approach demonstrated in this study provides a means by which scientists trying to detect gravitational waves can compare the limits of their detection abilities to the predicted amplitude and frequency of gravitational waves. For those seeking to determine whether Newtonian gravity applies to the quantum world, they now have a way to test their theories. The enhanced force-sensitivity in this experiment could also point the way to improved atomic force microscopy.

    “A scientific paper in 1980 predicted that the SQL might be reached within five years,” Schreppler says. “It took about 30 years longer than predicted, but we now have an experimental set-up capable both of reaching very close to the SQL and of showing the onset of different kinds of obscuring noise away from that SQL.”

    This research was supported by the Air Force Office of Scientific Research 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 8:43 pm on June 17, 2014 Permalink | Reply
    Tags: , , , , , Photon Sciences   

    From Berkeley Lab: “Dynamic Spectroscopy Duo” 

    Berkeley Logo

    Berkeley Lab

    June 17, 2014
    Lynn Yarris

    From allowing our eyes to see, to enabling green plants to harvest energy from the sun, photochemical reactions – reactions triggered by light – are both ubiquitous and critical to nature. Photochemical reactions also play essential roles in high technology, from the creation of new nanomaterials to the development of more efficient solar energy systems. Using photochemical reactions to our best advantage requires a deep understanding of the interplay between the electrons and atomic nuclei within a molecular system after that system has been excited by light. A major advance towards acquiring this knowledge has been reported by a team of researchers with the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab) and the University of California (UC) Berkeley.

    Graham Fleming, UC Berkeley’s Vice Chancellor for Research and a faculty senior scientist with Berkeley Lab’s Physical Biosciences Division, led the development of a new experimental technique called two-dimensional electronic-vibrational spectroscopy (2D-EV) . By combining the advantages of two well-established spectroscopy technologies – 2D-electronic and 2D-infrared – this technique is the first that can be used to simultaneously monitor electronic and molecular dynamics on a femtosecond (millionth of a billionth of a second) time-scale. The results show how the coupling of electronic states and nuclear vibrations affect the outcome of photochemical reactions.

    “We think that 2D-EV, by providing unprecedented details about photochemical reaction dynamics, has the potential to answer many currently inaccessible questions about photochemical and photobiological systems,” says Fleming, a physical chemist and internationally acclaimed leader in spectroscopic studies of events that take place on the femtosecond time-scale. “We anticipate its adoption by leading laboratories across the globe,”

    three
    From left, Nicholas Lewis, Graham Fleming and Tom Oliver developed 2D-EV, a spectroscopy technique that enables electronic and molecular dynamics during a photochemical reaction to be simultaneously monitored on a femtosecond time-scale. (Photo by Roy Kaltschmidt)

    [Graham] Fleming is the corresponding author of a paper in the Proceedings of the National Academy of Sciences (PNAS) titled Correlating the motion of electrons and nuclei with two-dimensional electronic–vibrational spectroscopy. Co-authors are Thomas Oliver and Nicholas Lewis, both members of Fleming’s research group.

    Fleming and his research group were one of the key developers of 2D electronic spectroscopy (2D-ES), which enables scientists to follow the flow of light-induced excitation energy through molecular systems with femtosecond temporal resolution. Since its introduction in 2007, 2D-ES has become an essential tool for investigating the electronic relaxation and energy transfer dynamics of molecules, molecular systems and nanomaterials following photoexcitation. 2D infrared spectroscopy is the go-to tool for studying nuclear vibrational couplings and ground-state structures of chemical and complex biological systems.

    “Combining these two techniques into 2D-EV tells us how photoexcitation affects the coupling of electronic and vibrational degrees of freedom,” says Oliver. “This coupling is essential to understanding how all molecules, molecular systems and nanomaterials function.”

    In 2D-EV, a sample is sequentially flashed with three femtosecond pulses of laser light. The first two pulses are visible light that create excited electronic states in the sample. The third pulse is mid-infrared light that probes the vibrational quantum state of the excited system. This unique combination of visible excitation and mid-infrared probe pulses enables researchers to correlate the initial electronic absorption of light with the subsequent evolution of nuclear vibrations.

    “2D-EV’s ability to correlate the initial excitation of the electronic–vibrational manifold with the subsequent evolution of high-frequency vibrational modes, which until now have not been explored, opens many potential avenues of fruitful study, especially in systems where electronic–vibrational coupling is important to the functionality of a system,” Fleming says.

    plants
    Photochemical reactions during photosynthesis enable plants to convert solar energy into chemical energy that is stored as sugars in the plants’ biomass. (Photo by Roy Kaltschmidt)

    As a demonstration, Oliver, Lewis and Fleming used their 2D-EV spectroscopy technique to study the excited-state relaxation dynamics of DCM dye dissolved in a deuterated solvent. DCM is considered a model “push-pull” emitter – meaning it contains both electron donor and acceptor groups – but with a long-standing question as to how it fluoresces back to the ground energy state.

    “From 2D-EV spectra, we elucidate a ballistic mechanism on the excited state potential energy surface whereby molecules are almost instantaneously projected uphill in energy toward a transition state between locally excited and charge-transfer states before emission,” Oliver says. “The underlying electronic dynamics, which occur on the hundreds of femtoseconds time-scale, drive the far slower ensuing nuclear motions on the excited state potential surface, and serve as an excellent illustration for the unprecedented detail that 2D-EV will afford to photochemical reaction dynamics.”

    One example of how 2D-EV might be applied is in the study of rhodopsin, the pigment protein in the retina of the eye that is the primary light detector for vision, and carotenoids, the family of pigment proteins, such as chlorophyll, found in green plants and certain bacteria that absorb light for photosynthesis.

    panels
    Photochemical reactions enable solar panels to convert the energy in sunlight into electrical energy.

    “The nonradiative energy transfer in rhodopsin and carotenoids is thought to involve the breakdown of one of the most widely used approximations of quantum mechanics, the Born-Oppenheimer approximation, which states that since motion of electrons are far faster than nuclei, as represented by vibrational motion, the nuclei respond to changes in electronic states,” Oliver says. “With 2D-EV, we will be able to directly correlate the degrees of electronic and vibrational freedom and track their evolution as a function of time. It’s a chicken and egg kind of problem: Do the electrons or nuclei move first? 2D-EV will give us insight into whether or not the Born-Oppenheimer approximation is still valid in these cases.”

    For nanomaterials, 2D-EV should be able to shed much needed light on how the coupling of phonons – atomic soundwaves – with electrons impacts the properties of carbon nanotubes and other nanosystems. 2D-EV can also be used to investigate the barriers to electron transfer between donor and acceptor states in photovoltaic systems.

    “We are continuing to refine the 2D-EV technology and make it more widely applicable so that it can be used to study lower frequency motions that are of great scientific interest,” Oliver says.

    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 3:45 pm on June 16, 2014 Permalink | Reply
    Tags: , , , Photon Sciences   

    Fro Brookhaven Lab: “New Evidence for Oceans of Water Deep in the Earth” 

    Brookhaven Lab

    June 13, 2014
    Karen McNulty Walsh, (631) 344-8350 or Peter Genzer, (631) 344-3174printer iconPrint

    Water bound in mantle rock alters our view of the Earth’s composition

    Researchers from Northwestern University and the University of New Mexico report evidence for potentially oceans worth of water deep beneath the United States. Though not in the familiar liquid form — the ingredients for water are bound up in rock deep in the Earth’s mantle — the discovery may represent the planet’s largest water reservoir.

    earth
    Structure of the Earth

    The presence of liquid water on the surface is what makes our “blue planet” habitable, and scientists have long been trying to figure out just how much water may be cycling between Earth’s surface and interior reservoirs through plate tectonics.

    Northwestern geophysicist Steve Jacobsen and University of New Mexico seismologist Brandon Schmandt have found deep pockets of magma located about 400 miles beneath North America, a likely signature of the presence of water at these depths. The discovery suggests water from the Earth’s surface can be driven to such great depths by plate tectonics, eventually causing partial melting of the rocks found deep in the mantle.

    The findings, to be published June 13 in the journal Science, will aid scientists in understanding how the Earth formed, what its current composition and inner workings are and how much water is trapped in mantle rock.

    “Geological processes on the Earth’s surface, such as earthquakes or erupting volcanoes, are an expression of what is going on inside the Earth, out of our sight,” said Jacobsen, a co-author of the paper. “I think we are finally seeing evidence for a whole-Earth water cycle, which may help explain the vast amount of liquid water on the surface of our habitable planet. Scientists have been looking for this missing deep water for decades.”

    mntle
    A blue crystal of ringwoodite containing around one percent of H2O in its crystal structure is compressed to conditions of 700 km depth inside a diamond-anvil cell. Using a laser to heat the sample to temperatures over 1500C (orange spots), the ringwoodite transformed to minerals found in the lowermost mantle. Synchrotron-infrared spectra collected on beamline U2A at the NSLS reveal changes in the OH-absorption spectra that correspond to melt generation, which was also detected by seismic waves underneath most of North America.

    Scientists have long speculated that water is trapped in a rocky layer of the Earth’s mantle located between the lower mantle and upper mantle, at depths between 250 miles and 410 miles. Jacobsen and Schmandt are the first to provide direct evidence that there may be water in this area of the mantle, known as the “transition zone,” on a regional scale. The region extends across most of the interior of the United States.

    Schmandt, an assistant professor of geophysics at the University of New Mexico, uses seismic waves from earthquakes to investigate the structure of the deep crust and mantle. Jacobsen, an associate professor of Earth and planetary sciences at Northwestern’s Weinberg College of Arts and Sciences, uses observations in the laboratory to make predictions about geophysical processes occurring far beyond our direct observation.

    The study combined Jacobsen’s lab experiments in which he studies mantle rock under the simulated high pressures of 400 miles below the Earth’s surface with Schmandt’s observations using vast amounts of seismic data from the USArray, a dense network of more than 2,000 seismometers across the United States.

    Jacobsen’s and Schmandt’s findings converged to produce evidence that melting may occur about 400 miles deep in the Earth. H2O stored in mantle rocks, such as those containing the mineral ringwoodite, likely is the key to the process, the researchers said.

    “Melting of rock at this depth is remarkable because most melting in the mantle occurs much shallower, in the upper 50 miles,” said Schmandt, a co-author of the paper. “If there is a substantial amount of H2O in the transition zone, then some melting should take place in areas where there is flow into the lower mantle, and that is consistent with what we found.”

    If just one percent of the weight of mantle rock located in the transition zone is H2O, that would be equivalent to nearly three times the amount of water in our oceans, the researchers said.

    This water is not in a form familiar to us — it is not liquid, ice or vapor. This fourth form is water trapped inside the molecular structure of the minerals in the mantle rock. The weight of 250 miles of solid rock creates such high pressure, along with temperatures above 2,000 degrees Fahrenheit, that a water molecule splits to form a hydroxyl radical (OH), which can be bound into a mineral’s crystal structure.

    Schmandt and Jacobsen’s findings build on a discovery reported in March in the journal Nature in which scientists discovered a piece of the mineral ringwoodite inside a diamond brought up from a depth of 400 miles by a volcano in Brazil. That tiny piece of ringwoodite — the only sample in existence from within the Earth — contained a surprising amount of water bound in solid form in the mineral.

    “Whether or not this unique sample is representative of the Earth’s interior composition is not known, however,” Jacobsen said. “Now we have found evidence for extensive melting beneath North America at the same depths corresponding to the dehydration of ringwoodite, which is exactly what has been happening in my experiments.”

    For years, Jacobsen has been synthesizing ringwoodite, colored sapphire-like blue, in his Northwestern lab by reacting the green mineral olivine with water at high-pressure conditions. (The Earth’s upper mantle is rich in olivine.) He found that more than one percent of the weight of the ringwoodite’s crystal structure can consist of water — roughly the same amount of water as was found in the sample reported in the Nature paper.

    “The ringwoodite is like a sponge, soaking up water,” Jacobsen said. “There is something very special about the crystal structure of ringwoodite that allows it to attract hydrogen and trap water. This mineral can contain a lot of water under conditions of the deep mantle.”

    For the study reported in Science, Jacobsen subjected his synthesized ringwoodite to conditions around 400 miles below the Earth’s surface and found it forms small amounts of partial melt when pushed to these conditions. He detected the melt in experiments conducted at the Advanced Photon Source of Argonne National Laboratory and at the National Synchrotron Light Source of Brookhaven National Laboratory.

    Jacobsen uses small gem diamonds as hard anvils to compress minerals to deep-Earth conditions. “Because the diamond windows are transparent, we can look into the high-pressure device and watch reactions occurring at conditions of the deep mantle,” he said. “We used intense beams of X-rays, electrons and infrared light to study the chemical reactions taking place in the diamond cell.”

    Jacobsen’s findings produced the same evidence of partial melt, or magma, that Schmandt detected beneath North America using seismic waves. Because the deep mantle is beyond the direct observation of scientists, they use seismic waves — sound waves at different speeds — to image the interior of the Earth.

    “Seismic data from the USArray are giving us a clearer picture than ever before of the Earth’s internal structure beneath North America,” Schmandt said. “The melting we see appears to be driven by subduction — the downwelling of mantle material from the surface.”

    The melting the researchers have detected is called dehydration melting. Rocks in the transition zone can hold a lot of H2O, but rocks in the top of the lower mantle can hold almost none. The water contained within ringwoodite in the transition zone is forced out when it goes deeper (into the lower mantle) and forms a higher-pressure mineral called silicate perovskite, which cannot absorb the water. This causes the rock at the boundary between the transition zone and lower mantle to partially melt.

    “When a rock with a lot of H2O moves from the transition zone to the lower mantle it needs to get rid of the H2O somehow, so it melts a little bit,” Schmandt said. “This is called dehydration melting.”

    “Once the water is released, much of it may become trapped there in the transition zone,” Jacobsen added.

    Just a little bit of melt, about one percent, is detectible with the new array of seismometers aimed at this region of the mantle because the melt slows the speed of seismic waves, Schmandt said.

    The USArray is part of EarthScope, a program of the National Science Foundation that deploys thousands of seismic, GPS and other geophysical instruments to study the structure and evolution of the North American continent and the processes the cause earthquakes and volcanic eruptions.

    The National Science Foundation (grants EAR-0748797 and EAR-1215720) and the David and Lucile Packard Foundation supported the research.

    The paper is titled Dehydration melting at the top of the lower mantle. In addition to Jacobsen and Schmandt, other authors of the paper are Thorsten W. Becker, University of California, Los Angeles; Zhenxian Liu, Carnegie Institution of Washington; and Kenneth G. Dueker, the University of Wyoming

    See the full article here.

    One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. The Laboratory’s almost 3,000 scientists, engineers, and support staff are joined each year by more than 5,000 visiting researchers from around the world.Brookhaven is operated and managed for DOE’s Office of Science by Brookhaven Science Associates, a limited-liability company founded by Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit, applied science and technology organization.
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  • richardmitnick 8:56 am on June 11, 2014 Permalink | Reply
    Tags: , , , , Photon Sciences   

    From Brookhaven Lab: “DNA-Linked Nanoparticles Form Switchable “Thin Films” on a Liquid Surface” 

    Brookhaven Lab

    June 11, 2014
    Karen McNulty Walsh

    Possible pathway to adjustable filters, surfaces with variable mechanical response, or even new ways to deliver genes for biomedical applications

    Scientists seeking ways to engineer the assembly of tiny particles measuring just billionths of a meter have achieved a new first—the formation of a single layer of nanoparticles on a liquid surface where the properties of the layer can be easily switched. Understanding the assembly of such nanostructured thin films could lead to the design of new kinds of filters or membranes with a variable mechanical response for a wide range of applications. In addition, because the scientists used tiny synthetic strands of DNA to hold the nanoparticles together, the study also offers insight into the mechanism of interactions of nanoparticles and DNA molecules near a lipid membrane. This understanding could inform the emerging use of nanoparticles as vehicles for delivering genes across cellular membranes.

    “Many of the applications we envision for nano particles … require planar geometry. Using DNA linker molecules gives us a way to control the interactions between the nanoparticles.”
    — Sunita Srivastava

    two
    Brookhaven physicist Oleg Gang and Stony Brook University postdoctoral researcher Sunita Srivastava

    “Our work reveals how DNA-coated nanoparticles interact and re-organize at a lipid interface, and how that process affects the properties of a “thin film” made of DNA-linked nanoparticles,” said physicist Oleg Gang who led the study at the Center for Functional Nanomaterials (CFN) at the U.S. Department of Energy’s Brookhaven National Laboratory. The results will be published in the June 11, 2014 print edition of the Journal of the American Chemical Society.

    Like the molecule that carries genetic information in living things, the synthetic DNA strands used as “glue” to bind nanoparticles in this study have a natural tendency to pair up when the bases that make up the rungs of the twisted-ladder shaped molecule match up in a particular way. Scientists at Brookhaven have made great use of the specificity of this attractive force to get nanoparticles coated with single synthetic DNA strands to pair up and assemble in a variety of three-dimensional architectures. The goal of the present study was to see if the same approach could be used to achieve designs of two-dimensional, one-particle-thick films.

    “Many of the applications we envision for nanoparticles, such as optical coatings and photovoltaic and magnetic storage devices, require planar geometry,” said Sunita Srivastava, a Stony Brook University postdoctoral researcher and the lead author on the paper. Other groups of scientists have assembled such planes of nanoparticles, essentially floating them on a liquid surface, but these single-layer arrays have all been static, she explained. “Using DNA linker molecules gives us a way to control the interactions between the nanoparticles.”

    As described in the paper, the scientists demonstrated their ability to achieve differently structured monolayers, from a viscous fluid-like array to a more tightly woven cross-linked elastic mesh—and switch between those different states—by varying the strength of the pairing between complementary DNA strands and adjusting other variables, including the electrostatic charge on the liquid assembly surface and the concentration of salt.

    dna
    Schematic illustration of the assembly of DNA-functionalized nanoparticles (NPs) at positively charged interfaces. (a) In the absence of salt, interactions are dominated by the electrostatic repulsion between DNA chains. (b) The 2D assemblies can be altered by programming the interactions between the NPs. By introducing monovalent salt, an attractive interaction between the NPs is switched ON, due to DNA hybridization. Change in interaction between NPs provides the path to tune the structure of the 2D assemblies at the interface.

    When the surface they used, a lipid, has a strong positive charge it attracts the negatively charged DNA strands that coat the nanoparticles. That electrostatic attraction and the repulsion between the negatively charged DNA molecules surrounding adjacent nanoparticles overpower the attractive force between complementary DNA bases. As a result, the particles form a rather loosely arrayed free-floating viscous monolayer. Adding salt changes the interactions and overcomes the repulsion between like-charged DNA strands, allowing the base pairs to match up and link the nanoparticles together more closely, first forming string-like arrays, and with more salt, a more solid yet elastic mesh-like layer.

    “The mechanism of this phase transition is not obvious,” said Gang. “It cannot be understood from the repulsion-attraction interactions alone. With the help of theory, we reveal that there are collective effects of the flexible DNA chains that drive the system in the particular states. And it is only possible when the particle sizes and the DNA chain sizes are comparable—on the order of 20-50 nanometers,” he said.

    As part of the study, the scientists examined the different configurations of the nanoparticles on top of the liquid layer using x-ray scattering at Brookhaven’s National Synchrotron Light Source (NSLS). They also transferred the monolayer produced at each salt concentration to a solid surface so they could visualize it using electron microscopy at the CFN.

    “Creating these particle monolayers at a liquid interface is very convenient and effective because the particles’ two-dimensional structure is very ‘fluid’ and can be easily manipulated—unlike on a solid substrate, where the particles can easily get stuck to the surface,” Gang said. “But in some applications, we may need to transfer the assembled layer to such a solid surface. By combining the synchrotron scattering and electron microscopy imaging we could confirm that the transfer can be done with minimal disruption to the monolayer.”

    The switchable nature of the monolayers might be particularly attractive for applications such as membranes used for purification and separations, or to control the transport of molecular or nano-scale objects through liquid interfaces. For example, said Gang, when particles are linked but move freely at the interface, they may allow an object—a molecule—to pass through the interface. “However, when we induce linkages between particles to form a mesh-like network, any object larger than the mesh-size of the network cannot penetrate through this very thin film. ”

    “In principle, we can even think about such on-demand regulated networks to adjust the mesh size dynamically. Because, of the nanoscale size-regime, we might envision using such membranes for filtering proteins or other nanoparticles,” he said.

    Understanding how synthetic DNA-coated nanoparticles interact with a lipid surface may also offer insight into how such particles coated with actual genes might interact with cell membranes—which are largely composed of lipids—and with one another in a lipid environment.

    “Other groups have considered using DNA-coated nanoparticles to detect genes within cells, or even for delivering genes to cells for gene therapy and such approaches,” said Gang. “Our study is the first of its kind to look at the structural aspects of DNA-particle/lipid interface directly using x-ray scattering. I believe this approach has significant value as a platform for more detailed investigations of realistic systems important for these new biomedical applications of DNA-nanoparticle pairings,” Gang said.

    This research was sponsored by the DOE Office of Science.

    See the full article here.

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


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