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    • 2018-11-13 08:05:15
    • Article ID: 703871

    Detecting Light in a Different Dimension

    Electrically conductive polymer nanostructures that are many times longer than they are wide make graphene--atom-thin sheets of carbon--a better light detector

    • Credit: Brookhaven National Laboratory

      Research associate Mingxing Lin (sitting) and materials scientists Dmytro Nykypanchuck (left, standing) and Mircea Cotlet of Brookhaven Lab's Center for Functional Nanomaterials dramatically improved the light response of electronic devices made out of graphene and an electrically conducting polymer by changing the morphology of the polymer from a thin film to a "nanowire" mesh. An image of this mesh architecture—captured with an atomic force microscope, in which a small mechanical transducer called a cantilever probe scans across a material's surface—is seen on the computer screen.

    • Credit: ACS Photonics, Oct. 12, 2018

      Cartoon of the graphene-P3HT nanowire hybrid field-effect transistor. Placing the nanowire mesh (red) on top of the graphene (purple) improves the device's response to light. The silicon dioxide/silicon (grey) substrate, or "gate" electrode, controls the flow of electrical current between the electron source and drain (in this case, Au, or gold, electrodes). The scientists used electron-beam lithography to pattern the device.

    UPTON, NY—Scientists from the Center for Functional Nanomaterials (CFN)—a U.S. Department of Energy (DOE) Office of Science User Facility at Brookhaven National Laboratory—have dramatically improved the response of graphene to light through self-assembling wire-like nanostructures that conduct electricity. The improvement could pave the way for the development of graphene-based detectors that can quickly sense light at very low levels, such as those found in medical imaging, radiation detection, and surveillance applications.

    Graphene is a two-dimensional (2-D) nanomaterial with unusual and useful mechanical, optical, and electronic properties. It is both extremely thin and incredibly strong, detects light of almost any color, and conducts heat and electricity well. However, because graphene is made of sheets of carbon only one atom thick, it can only absorb a very small amount of incoming light (about two percent).

    One approach to overcoming this problem is to combine graphene with strong light-absorbing materials, such as organic compounds that conduct electricity. Scientists recently demonstrated an improved photoresponse by placing thin films (a few tens of nanometers) of one such conductive polymer, poly(3-hexylthiophene), or P3HT, on top of a single layer of graphene.

    Now, the CFN scientists have improved the photoresponse by an additional 600 percent by changing the morphology (structure) of the polymer. Instead of thin films, they used a mesh of nanowires—nanostructures that are many times longer than they are wide—made of the same polymer and similar thickness. The research is described in an article published online on Oct. 12 in ACS Photonics, a journal of the American Chemical Society (ACS).

    “We used self-assembly, a very simple and reproducible method, to create the nanowire mesh,” said first author Mingxing Li, a research associate in the CFN Soft and Bio Nanomaterials Group. “Placed in an appropriate solution and stirred overnight, the polymer will form into wire-like nanostructures on its own. We then spin-casted the resulting nanowires onto electrical devices called graphene field-effect transistors (FETs).”

    The scientists fabricated FETs made of graphene only, graphene and P3HT thin films, and graphene and P3HT nanowires. After checking the thickness and crystal structure of the FET devices through atomic force microscopy, Raman spectroscopy, and x-ray scattering techniques, they measured their light-induced electrical properties (photoresponsivity). Their measurements of the electric current flowing through the FETs under various light illumination powers revealed that the nanowire FETs improve photoresponse by 600 percent compared to the thin film FETs and 3000 percent compared to graphene-only FETs.  

    “We did not expect to see such a dramatic improvement just by changing the morphology of the polymer,” said co-corresponding author Mircea Cotlet, a materials scientist in the CFN Soft and Bio Nanomaterials Group.

    The scientists believe that there are two explanations behind their observations.

    “At a certain polymer concentration, the nanowires have dimensions comparable to the wavelength of light,” said Li. “This size similarity has the effect of increasing light scattering and absorption. In addition, crystallization of P3HT molecules within the nanowires provides more charge carriers to transfer electricity to the graphene layer.”

    “In contrast to conventional thin films where polymer chains and crystals are mostly randomly oriented, the nanoscale dimension of the wires forces the polymer chains and crystals into a specific orientation, enhancing both light absorption and charge transfer,” said co-author Dmytro Nykyphanchuck, a materials scientist in the CFN Soft and Bio Nanomaterials Group.

    The scientists have filed a U.S. patent for their fabrication process, and they are excited to explore light-matter interactions in other 2-D—as well as 0-D and 1-D—materials.  

    “Plasmonics and nanophotonics—the study of light at the nanometer scale—are emerging research areas,” said Cotlet, who earlier this year co-organized a workshop for user communities of the CFN and the National Synchrotron Light Source II (NSLS-II)—another DOE Office of Science User Facility at Brookhaven—to explore frontiers in these areas. “Nanostructures can manipulate and control light at the nanoscale in very interesting ways. The advanced nanofabrication and nanocharacterization tools at the CFN and NSLS-II are perfectly suited for creating and studying materials with enhanced optoeletronic properties.”

    Brookhaven National Laboratory is supported by the Office of Science of the U.S. Department of Energy. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.

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    The Biermann Battery Effect: Spontaneous Generation of Magnetic Fields and Their Severing

    The mechanism responsible for creating intense magnetic fields in laser-driven plasmas also helps tear the fields apart.

    Compelling Evidence for Small Drops of Perfect Fluid

    Nuclear physicists analyzing data from the PHENIX detector at the Relativistic Heavy Ion Collider (RHIC) have published additional evidence that collisions of miniscule projectiles with gold nuclei create tiny specks of the perfect fluid that filled the early universe.

    Topological Matters: Toward a New Kind of Transistor

    An experiment has demonstrated, for the first time, electronic switching in an exotic, ultrathin material that can carry a charge with nearly zero loss at room temperature. Researchers demonstrated this switching when subjecting the material to a low-current electric field.

    Experiments at PPPL show remarkable agreement with satellite sightings

    Feature describes striking similarity of laboratory research findings with observations of the four-satellite Magnetospheric Multiscale Mission that studies magnetic reconnection in space.

    New X-ray imaging approach could boost nanoscale resolution for Advanced Photon Source Upgrade

    A long-standing problem in optics holds that an improved resolution in imaging is offset by a loss in the depth of focus. Now, scientists are joining computation with X-ray imaging as they develop a new and exciting technique to bypass this limitation.

    Two-dimensional materials skip the energy barrier by growing one row at a time

    News Release RICHLAND, Wash. -- A new collaborative study led by a research team at the Department of Energy's Pacific Northwest National Laboratory and University of California, Los Angeles could provide engineers new design rules for creating microelectronics, membranes, and tissues, and open up better production methods for new materials.

    Blasting Molecules with Extreme X-Rays

    To understand how damage from high-energy X-rays affects imaging studies, scientists supported by the Department of Energy shot the most powerful X-ray laser in the world at a series of atoms and molecules. Surprisingly, the atoms within the molecules acted far differently than the isolated ones.

    Scientists Enter Unexplored Territory in Superconductivity Search

    Scientists mapping out the quantum characteristics of superconductors--materials that conduct electricity with no energy loss--have entered a new regime. Using newly connected tools named OASIS at Brookhaven Lab, they've uncovered previously inaccessible details of the "phase diagram" of one of the most commonly studied "high-temperature" superconductors.

    Human Exposures and Health Effects Associated with Unconventional Oil and Gas Development

    The Health Effects Institute (HEI) convened an Energy Research Committee to help ensure the protection of public health during such development. A symposium at the 2018 Society for Risk Analysis (SRA) Annual Meeting will summarize the Committee's review approach and preliminary findings and provide initial options for future research intended to fill knowledge gaps.

    Reflecting Antiferromagnetic Arrangements

    Scientists have demonstrated an x-ray imaging technique that could enable the development of smaller, faster, and more robust electronics that exploit electron spin.


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    Blast to the future

    A grant from DOE's Technology Commercialization Fund will help researchers at Argonne and industry partners seek improvements to U.S. manufacturing by making discovery and design of new materials more efficient.

    Department of Energy to Provide $24 Million for Computer-Based Materials Design

    The U.S. Department of Energy (DOE) announced plans to provide $24 million in new and renewal research awards to advance the development of sophisticated software for computer-based design of novel materials.

    Argonne scientists recognized for decades of pioneering leadership in research

    Argonne scientists Ali Erdemir and Jack Vaughey were named 2018 Fellows of the American Association for the Advancement of Science (AAAS).

    Kurfess, Smith join ORNL to lead advanced manufacturing initiatives

    Two leaders in US manufacturing innovation, Thomas Kurfess and Scott Smith, are joining the Department of Energy's Oak Ridge National Laboratory to support its pioneering research in advanced manufacturing.

    Four Berkeley Lab Scientists Named AAAS Fellows

    Four Berkeley Lab scientists - Allen Goldstein, Sung-Hou Kim, Susannah Tringe, and Katherine Yelick - have been named Fellows of the American Association for the Advancement of Science, the world's largest general scientific society.

    U.S. Department of Energy to Host Nationwide CyberForce Competition(tm) December 1

    Students from dozens of colleges/universities will participate in the U.S. Department of Energy's CyberForce Competition(tm) this weekend

    Seven ORNL researchers named 2019 INCITE award winners

    Seven researchers from the Department of Energy's Oak Ridge National Laboratory have been chosen by the Innovative and Novel Computational Impact on Theory and Experiment, also known as INCITE, program to lead scientific investigations that require the nation's most powerful computers. The ORNL-based projects span a broad range of the scientific spectrum and represent the potential of high-performance computing in ensuring America's scientific competitiveness and energy security.

    DOE Laboratories Win Gordon Bell Prize

    Two U.S. Department of Energy (DOE) National Laboratories were recently awarded the 2018 Association for Computing Machinery's (ACM's) Gordon Bell Prize.

    Department of Energy Announces 32 R&D 100 Award Winners

    DOE researchers have won 32 of the R&D 100 awards given out this year by R&D Magazine. The annual awards are given in recognition of exceptional new products or processes that were developed and introduced into the marketplace during the previous year.

    Jefferson Lab Shares 2018 R&D 100 Award for Cancer Treatment Monitoring System

    The OARtrac(r) system, built by RadiaDyne and including technologies developed by scientists at the U.S. Department of Energy's Thomas Jefferson National Accelerator Facility, has been awarded a 2018 R&D 100 Award by R&D Magazine.


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    The Biermann Battery Effect: Spontaneous Generation of Magnetic Fields and Their Severing

    The mechanism responsible for creating intense magnetic fields in laser-driven plasmas also helps tear the fields apart.

    Subtlety and the Selective Art of Separating Lanthanides

    Unexpected molecular interactions involving water clusters have a subtle, yet profound, effect on extractants picking their targets.

    Review Examines the Science and Needs of Nitrogen-Based Transformations

    Advances in biochemistry and catalysis could lead to faster, greener nitrogen-rich fertilizer.

    Quickly Capture Tiny Particles Reacting

    New method takes a snapshot every millisecond of groups of light-scattering particles, showing what happens during industrially relevant reactions.

    New Technology Consistently Identifies Proteins from a Dozen Cells

    A new platform melding microfluidics and robotics allows more in-depth bioanalysis with fewer cells than ever before.

    Optimal Foraging: How Soil Microbes Adapt to Nutrient Constraints

    How microbial communities adjust to nutrient-poor soils at the genomic and proteomic level gives scientists insights into land use.

    Microbes Eat the Same in Labs and the Desert

    Analyses of natural communities forming soil crusts agree with laboratory studies of isolated microbe-metabolite relationships.

    Diverse Biofeedstocks Have High Ethanol Yields and Offer Biorefineries Flexibility

    Evidence suggests that biorefineries can accept various feedstocks without negatively impacting the amount of ethanol produced per acre.

    Opening Access to Explore the Synthetic Chemistry of Neptunium

    New, easily prepared starting material opens access to learning more about a difficult-to-control element in nuclear waste.

    Tiny Titanium Barrier Halts Big Problem in Fuel-Producing Solar Cells

    New design coats molecular components and dramatically improves stability under tough, oxidizing conditions.


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