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  • richardmitnick 1:52 pm on January 5, 2017 Permalink | Reply
    Tags: , Nanotechnology, , , Semiconductor discs could boost night vision   

    From physicsworld.com: “Semiconductor discs could boost night vision” 

    physicsworld
    physicsworld.com.com

    1
    Frequency double: Maria del Rocio Camacho-Morales studies the new optical material.

    A new method of fabricating nanoscale optical crystals capable of converting infrared to visible light has been developed by researchers in Australia, China and Italy. The new technique allows the crystals to be placed onto glass and could lead to improvements in holographic imaging – and even the development of improved night-vision goggles.

    Second-harmonic generation, or frequency doubling, is an optical process whereby two photons with the same frequency are combined within a nonlinear material to form a single photon with twice the frequency (and half the wavelength) of the original photons. The process is commonly used by the laser industry, in which green 532 nm laser light is produced from a 1064 nm infrared source. Recent developments in nanotechnology have opened up the potential for efficient frequency doubling using nanoscale crystals – potentially enabling a variety of novel applications.

    Materials with second-order nonlinear susceptibilities – such as gallium arsenide (GaAs) and aluminium gallium arsenide (AlGaAs) – are of particular interest for these applications because their low-order nonlinearity makes them efficient at conversion.

    Substrate mismatch

    To be able to exploit second-harmonic generation in a practical device, these nanostructures must be fabricated on a substrate with a relatively low refractive index (such as glass), so that light may pass through the optical device. This is challenging, however, because the growth of GaAs-based crystals in a thin film – and type III-V semiconductors in general – requires a crystalline substrate.

    “This is why growing a layer of AlGaAs on top of a low-refractive-index substrate, like glass, leads to unmatched lattice parameters, which causes crystalline defects,” explains Dragomir Neshev, a physicist at the Australian National University (ANU). These defects, he adds, result in unwanted changes in the electronic, mechanical, optical and thermal properties of the films.

    Previous attempts to overcome this issue have led to poor results. One approach, for example, relies on placing a buffer layer under the AlGaAs films, which is then oxidized. However, these buffer layers tend to have higher refractive indices than regular glass substrates. Alternatively, AlGaAs films can be transferred to a glass surface prior to the fabrication of the nanostructures. In this case the result is poor-quality nanocrystals.

    Best of both

    The new study was done by Neshev and colleagues at ANU, Nankai University and the University of Brescia, who combined the advantages of the two different approaches to develop a new fabrication method. First, high-quality disc-shaped nanocrystals about 500 nm in diameter are fabricated using electron-beam lithography on a GaAs wafer, with a layer of AlAs acting as a buffer between the two. The buffer is then dissolved, and the discs are coated in a transparent layer of benzocyclobutene. This can then be attached to the glass substrate, and the GaAs wafer peeled off with minimal damage to the nanostructures.

    The development could have various applications. “The nanocrystals are so small they could be fitted as an ultrathin film to normal eye glasses to enable night vision,” says Neshev, explaining that, by combining frequency doubling with other nonlinear interactions, the film might be used to convert invisible, infrared light to the visible spectrum.

    If they could be made, such modified glasses would be an improvement on conventional night-vision binoculars, which tend to be large and cumbersome. To this end, the team is working to scale up the size of the nanocrystal films to cover the area of typical spectacle lenses, and expects to have a prototype device completed within the next five years.

    Security holograms

    Alongside frequency doubling, the team was also able to tune the nanodiscs to control the direction and polarization of the emitted light, which makes the film more efficient. “Next, maybe we can even engineer the light and make complex shapes such as nonlinear holograms for security markers,” says Neshev, adding: “Engineering of the exact polarization of the emission is also important for other applications such as microscopy, which allows light to be focused to a smaller volume.”

    “Vector beams with spatially arranged polarization distributions have attracted great interest for their applications in a variety of technical areas,” says Qiwen Zhan, an engineer at the University of Dayton in Ohio, who was not involved in this study. The novel fabrication technique, he adds, “opens a new avenue for generating vector fields at different frequencies through nonlinear optical processes”.

    With their initial study complete, Neshev and colleagues are now looking to refine their nanoantennas, both to increase the efficiency of the wavelength conversion process but also to extend the effects to other nonlinear interactions such as down-conversion.

    The research is described in the journal Nano Letters.

    See the full article here .

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    PhysicsWorld is a publication of the Institute of Physics. The Institute of Physics is a leading scientific society. We are a charitable organisation with a worldwide membership of more than 50,000, working together to advance physics education, research and application.

    We engage with policymakers and the general public to develop awareness and understanding of the value of physics and, through IOP Publishing, we are world leaders in professional scientific communications.
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  • richardmitnick 10:07 am on January 4, 2017 Permalink | Reply
    Tags: , Bugs, , Nanotechnology, Seeing Nano   

    From Duke: “Seeing Nano” 

    Duke Bloc
    Duke Crest

    Duke University

    Jan 1, 2017

    The sewer gnat is a common nuisance around kitchen and bathroom drains that’s no bigger than a pea. But magnified thousands of times, its compound eyes and bushy antennae resemble a first place winner in a Movember mustache contest.

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    An image of a sewer gnat’s head taken through a scanning electron microscope. Courtesy of Fred Nijhout.

    Sewer gnats’ larger cousins, horseflies are known for their painful bite. Zoom in and it’s easy to see how they hold onto their furry livestock prey: the tiny hooked hairs on their feet look like Velcro.

    Students in professor Fred Nijhout’s entomology class photograph these and other specimens at more than 300,000 times magnification at Duke’s Shared Materials Instrumentation Facility (SMIF).

    There the insects are dried, coated in gold and palladium, and then bombarded with a beam of electrons from a scanning electron microscope, which can resolve structures tens of thousands of times smaller than the width of a human hair.

    From a ladybug’s leg to a weevil’s suit of armor, the bristly, bumpy, pitted surfaces of insects are surprisingly beautiful when viewed up close.

    “The students have come to treat travels across the surface of an insect as the exploration of a different planet,” Nijhout said.

    2
    The foot of a horsefly is equipped with menacing claws and Velcro-like hairs that help them hang onto fur. Photo by Valerie Tornini.

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    The hard outer skeleton of a weevil looks smooth and shiny from afar, but up close it’s covered with scales and bristles. Courtesy of Fred Nijhout.

    You, too, can gaze at alien worlds too small to see with the naked eye. Students and instructors across campus can use the SMIF’s high-powered microscopes and other state of the art research equipment at no charge with support from the Class-Based Explorations Program.

    Biologist Eric Spana’s experimental genetics class uses the microscopes to study fruit flies that carry genetic mutations that alter the shape of their wings.

    Students in professor Hadley Cocks’ mechanical engineering 415L class take lessons from objects that break. A scanning electron micrograph of a cracked cymbal once used by the Duke pep band reveals grooves and ridges consistent with the wear and tear from repeated banging.

    6
    Magnified 3000 times, the surface of this broken cymbal once used by the Duke Pep Band reveals signs of fatigue cracking. Courtesy of Hadley Cocks.

    These students are among more than 200 undergraduates in eight classes who benefitted from the program last year, thanks to a grant from the Donald Alstadt Foundation.

    You don’t have to be a scientist, either. Historians and art conservators have used scanning electron microscopes to study the surfaces of Bronze Age pottery, the composition of ancient paints and even dust from Egyptian mummies and the Shroud of Turin.

    Instructors and undergraduates are invited to find out how they could use the microscopes and other nanotech equipment in the SMIF in their teaching and research. Queries should be directed to Dr. Mark Walters, Director of SMIF, via email at mark.walters@duke.edu.

    See the full article here .

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    Duke Campus

    Younger than most other prestigious U.S. research universities, Duke University consistently ranks among the very best. Duke’s graduate and professional schools — in business, divinity, engineering, the environment, law, medicine, nursing and public policy — are among the leaders in their fields. Duke’s home campus is situated on nearly 9,000 acres in Durham, N.C, a city of more than 200,000 people. Duke also is active internationally through the Duke-NUS Graduate Medical School in Singapore, Duke Kunshan University in China and numerous research and education programs across the globe. More than 75 percent of Duke students pursue service-learning opportunities in Durham and around the world through DukeEngage and other programs that advance the university’s mission of “knowledge in service to society.”

     
  • richardmitnick 3:08 pm on January 3, 2017 Permalink | Reply
    Tags: , , Center for Functional Nanomaterials (CFN), Nanoscale 'Conversations' Create Complex and Multi-Layered Structures, Nanotechnology   

    From BNL: “Nanoscale ‘Conversations’ Create Complex, Multi-Layered Structures” 

    Brookhaven Lab

    December 22, 2016
    Justin Eure

    1
    Study co-authors Pawel Majewski and Kevin Yager preparing nanoscale films of self-assembling materials.

    Building nanomaterials with features spanning just billionths of a meter requires extraordinary precision. Scaling up that construction while increasing complexity presents a significant hurdle to the widespread use of such nano-engineered materials.

    Now, scientists at the U.S. Department of Energy’s Brookhaven National Laboratory have developed a way to efficiently create scalable, multilayer, multi-patterned nanoscale structures with unprecedented complexity.

    The Brookhaven team exploited self-assembly, where materials spontaneous snap together to form the desired structure. But they introduced a significant leap in material intelligence, because each self-assembled layer now guides the configuration of additional layers.

    The results, published in the journal Nature Communications, offer a new paradigm for nanoscale self-assembly, potentially advancing nanotechnology used for medicine, energy generation, and other applications.

    “There’s something amazing and rewarding about creating structures no one has ever seen before,” said study coauthor Kevin Yager, a scientist at Brookhaven Lab’s Center for Functional Nanomaterials (CFN). “We’re calling this responsive layering—like building a tower, but where each brick is intelligent and contains instructions for subsequent bricks.”

    The technique was pioneered entirely at the CFN, a DOE Office of Science User Facility.

    “The trick was chemically ‘sealing’ each layer to make it robust enough that the additional layers don’t disrupt it,” said lead author Atikur Rahman, a Brookhaven Lab postdoc during the study and now an assistant professor at the Indian Institute of Science Education and Research, Pune. “This granted us unprecedented control. We can now stack any sequence of self-organized layers to create increasingly intricate 3D structures.”

    Guiding nanoscale conversations

    2
    The added color in this scanning electron microscope (SEM) image showcases the discrete, self-assembled layers within these novel nanostructures. The pale blue bars are each roughly 4,000 times thinner than a single human hair. No image credit.

    Other nano-fabrication methods—such as lithography—can create precise nano-structures, but the spontaneous ordering of self-assembly makes it faster and easier. Further, responsive layering pushes that efficiency in new directions, enabling, for example, structures with internal channels or pockets that would be exceedingly difficult to make by any other means.

    “Self-assembly is inexpensive and scalable because it’s driven by intrinsic interactions,” said study coauthor and CFN scientist Gregory Doerk. “We avoid the complex tools that are traditionally used to carve precise nano-structures.”

    The CFN collaboration used thin films of block copolymers (BCP)—chains of two distinct molecules linked together. Through well-established techniques, the scientists spread BCP films across a substrate, applied heat, and watched the material self-assemble into a prescribed configuration. Imagine spreading LEGOs over a baking sheet, sticking it in the oven, and then seeing it emerge with each piece elegantly snapped together in perfect order.

    However, these materials are conventionally two-dimensional, and simply stacking them would yield a disordered mess. So the Brookhaven Lab scientists developed a way to have self-assembled layers discretely “talk” to one another.

    The team infused each layer with a vapor of inorganic molecules to seal the structure—a bit like applying nanoscale shellac to preserve a just-assembled puzzle.

    “We tuned the vapor infiltration step so that each layer’s structure exhibits controlled surface contours,” Rahman said. “Subsequent layers then feel and respond to this subtle topography.”

    Coauthor Pawel Majewski added, “Essentially, we open up a ‘conversation’ between layers. The surface patterns drive a kind of topographic crosstalk, and each layer acts as a template for the next one.”

    Exotic configurations

    4
    An aerial view of a complete, self-assembled, multilayer nanostructure. In this instance, parallel bars of block copolymers with varying thickness were criss-crossed. No image credit.

    As often occurs in fundamental research, this crosstalk was an unexpected phenomenon.

    “We were amazed when we first saw templated ordering from one layer to the next, Rahman said. “We knew immediately that we had to exhaustively test all the possible combinations of film layers and explore the technique’s potential.”

    The collaboration demonstrated the formation of a broad range of nano-structures—including many configurations never before observed. Some contained hollow chambers, round pegs, rods, and winding shapes.

    “This was really a Herculean effort on the part of Atikur,” Yager said. “The multi-layer samples covered a staggering range of combinations.”

    Mapping never-before-seen structures

    5
    This image shows the range of multilayer morphologies achieved through this new technique. The first column shows a cross section of the novel 3D nanostructures as captured by scanning electron microscopy (SEM). The computer renderings in the second column highlight the integrity and diversity of each distinct layer, while the overhead SEM view of the third column reveals the complex patterns achieved through the “intelligent” layering. No image credit.

    See the full article here .

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    BNL Campus

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

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


    SLAC Lab

    December 26, 2016

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

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

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

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

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

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

    The Smaller the Better

    3

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

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

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

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

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

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

    Constructive Attraction

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

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

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

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

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

    A Versatile Toolkit for Creating Novel Materials

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

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

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

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

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

    LBNL ALS interior
    LBNL ALS

    and National Energy Research Scientific Computing Center (NERSC),

    NERSC CRAY Cori supercomputer
    NERSC

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

    See the full article here .

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    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 2:42 pm on December 26, 2016 Permalink | Reply
    Tags: , , , Nanodisc technology, Nanotechnology,   

    From U Michigan via phys.org: “Nanodiscs deliver personalized cancer therapy to immune system” 

    U Michigan bloc

    University of Michigan

    phys.org

    phys.org

    December 26, 2016
    Researchers at the University of Michigan have had initial success in mice using nanodiscs to deliver a customized therapeutic vaccine for the treatment of colon and melanoma cancer tumors.

    “We are basically educating the immune system with these nanodiscs so that immune cells can attack cancer cells in a personalized manner,” said James Moon, the John Gideon Searle assistant professor of pharmaceutical sciences and biomedical engineering.

    Personalized immunotherapy is a fast-growing field of research in the fight against cancer.

    The therapeutic cancer vaccine employs nanodiscs loaded with tumor neoantigens, which are unique mutations found in tumor cells. By generating T-cells that recognize these specific neoantigens, the technology targets cancer mutations and fights to eliminate cancer cells and prevent tumor growth.

    Unlike preventive vaccinations, therapeutic cancer vaccines of this type are meant to kill established cancer cells.

    “The idea is that these vaccine nanodiscs will trigger the immune system to fight the existing cancer cells in a personalized manner,” Moon said.

    The nanodisc technology was tested in mice with established melanoma and colon cancer tumors. After the vaccination, twenty-seven percent of T-cells in the blood of the mice in the study targeted the tumors.

    When combined with immune checkpoint inhibitors, an existing technology that amplifies T-cell tumor-fighting responses, the nanodisc technology killed tumors within 10 days of treatment in the majority of the mice. After waiting 70 days, researchers then injected the same mice with the same tumor cells, and the tumors were rejected by the immune system and did not grow.

    “This suggests the immune system ‘remembered’ the cancer cells for long-term immunity,” said Rui Kuai, U-M doctoral student in pharmaceutical sciences and lead author of the study.

    “The holy grail in cancer immunotherapy is to eradicate tumors and prevent future recurrence without systemic toxicity, and our studies have produced very promising results in mice,” Moon said.

    The technology is made of extremely small, synthetic high density lipoproteins measuring roughly 10 nanometers. By comparison, a human hair is 80,000 to 100,000 nanometers wide.

    “It’s a powerful vaccine technology that efficiently delivers vaccine components to the right cells in the right tissues. Better delivery translates to better T-cell responses and better efficacy,” said study co-senior author Anna Schwendeman, U-M assistant professor of pharmacy.

    The next step is to test the nanodisc technology in a larger group of larger animals, Moon said.

    EVOQ Therapeutics, a new U-M spinoff biotech company, has been founded to translate these results to the clinic. Lukasz Ochyl, a doctoral student in pharmaceutical sciences, is also a co-author.

    The study, Designer vaccine nanodiscs for personalized cancer immunotherapy, is scheduled for advance online publication Dec. 26 on the Nature Materials website.

    See the full article here .

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    U MIchigan Campus

    The University of Michigan (U-M, UM, UMich, or U of M), frequently referred to simply as Michigan, is a public research university located in Ann Arbor, Michigan, United States. Originally, founded in 1817 in Detroit as the Catholepistemiad, or University of Michigania, 20 years before the Michigan Territory officially became a state, the University of Michigan is the state’s oldest university. The university moved to Ann Arbor in 1837 onto 40 acres (16 ha) of what is now known as Central Campus. Since its establishment in Ann Arbor, the university campus has expanded to include more than 584 major buildings with a combined area of more than 34 million gross square feet (781 acres or 3.16 km²), and has two satellite campuses located in Flint and Dearborn. The University was one of the founding members of the Association of American Universities.

    Considered one of the foremost research universities in the United States,[7] the university has very high research activity and its comprehensive graduate program offers doctoral degrees in the humanities, social sciences, and STEM fields (Science, Technology, Engineering and Mathematics) as well as professional degrees in business, medicine, law, pharmacy, nursing, social work and dentistry. Michigan’s body of living alumni (as of 2012) comprises more than 500,000. Besides academic life, Michigan’s athletic teams compete in Division I of the NCAA and are collectively known as the Wolverines. They are members of the Big Ten Conference.

     
  • richardmitnick 2:36 pm on December 6, 2016 Permalink | Reply
    Tags: , , , , , Don DiMarzio, Nanotechnology   

    From BNL: “Q&A with CFN User Don DiMarzio” 

    Brookhaven Lab

    December 6, 2016
    Ariana Tantillo
    atantillo@bnl.gov

    1
    Don DiMarzio. No image credit

    Don DiMarzio is an engineering fellow at Northrop Grumman and a senior scientist within the company’s advanced research, development, design, and demonstration group NG Next, where he studies nanomaterials and radio-frequency metamaterials. He is also an adjunct professor at Stony Brook University, where he teaches a nanotechnology class. Since March 2016, he has been using the advanced characterization labs at the Center for Functional Nanomaterials (CFN)—a U.S. Department of Energy (DOE) Office of Science User Facility at Brookhaven Lab—primarily to investigate nanostructures whose self-assembly is directed through DNA scaffolds. CFN physicist Oleg Gang has been developing this DNA-based technique for several years.

    Northrop Grumman is typically known for building aircraft, such as the U.S. Air Force’s B-2 stealth bomber, as well as unmanned autonomous aircraft and satellites. How does basic research come into play?

    About two years ago, Tom Vice, corporate vice president and president of Northrop Grumman Aerospace Systems, began discussing with his leadership team how to reconstitute the basic research activity that had existed in various forms earlier in the company’s history. NG Next, which includes basic research, applied research and technology development, advanced design, and rapid prototyping, emerged from these discussions. The goal of NG Next is to position Northrop Grumman at the cutting edge of science and technology and to attract the best and brightest young talent.

    NG Next’s basic research group is led by Tom Pieronek, vice president of basic research. The group has eight thrusts or topic areas relevant to the aerospace industry. One of these topics is nanomaterials, which is the focus of the Nanomaterials Group, led by Jesse Tice. I belong to this group. Other thrusts within the basic research group include semiconductor materials, plasmonics, and cognitive autonomy. The charter of our basic research organization is to do real science that is nonproprietary and publishable, in collaboration with the nation’s top universities and government labs. Any fundamental new discoveries that we think are promising may be transferred over to our applied research and prototyping groups within NG Next.

    The Center for Functional Nanomaterials (CFN) is one of five U.S. Department of Energy Nanoscale Science Research Centers and is among the many nanoscale facilities located at universities across the United States. What influenced your decision to submit a user proposal to CFN?

    After I got my PhD in solid-state physics, I did a postdoc at Brookhaven’s National Synchrotron Light Source (NSLS) in the late 1980s and really enjoyed working at Brookhaven.

    BNL NSLS
    BNL NSLS Interior
    BNL/NSLS

    After my postdoc, I became a scientist at the Grumman Corporate Research Center in Bethpage, NY, but continued my collaborations with Brookhaven on and off throughout the years.

    When Northrop Grumman leadership began planning for the new basic research group last year, I got involved. Part of my planning and development work for the group included helping to organize workshops—one in nanomaterials and the other in radio-frequency metamaterials—at our regional headquarters in southern California. For these invite-only workshops, the goal was to learn what was at the cutting edge in research, where we should focus our efforts, and who we could collaborate with.

    Our Nanomaterials Workshop provided a broad perspective on cutting-edge research, from nanomaterials synthesis and structures fabrication through fundamental properties and applications. One area that showed great potential was in nanoparticle self-assembly, and one of the major players in that field is the CFN. Although I had been working with various nanotechnologies before the establishment of NG Next, the CFN was either not established yet or our research was both applied and highly proprietary. But with the establishment of the basic research group within NG Next, it became clear that there was a definite opportunity for collaboration, especially considering that the way CFN is set up aligns with NG Next’s charter to publish, make presentations, and collaborate.

    When I learned about CFN physicist Oleg Gang’s work on exploiting DNA to direct the self-assembly of nanoparticles, I became very intrigued. I was particularly impressed with the strength and flexibility of this DNA origami scaffolding to fabricate a wide range of structures relevant for device and materials applications, and the ability to transition these assemblies from “soft” to “hard” while preserving key functionalities. Northrop Grumman sees this work as a potentially ground-breaking area that may lead to revolutionary new fabrication capability for everything from sensor systems to structural composites.

    While most of NG Next’s basic research group is in California, I am here on Long Island (at our Bethpage facility), so CFN is conveniently located near where I work and live. The group in California is currently building out its own labs that will be separate from our traditional applied laboratories. As an existing facility with state-of-the-art equipment and expertise in nanomaterials synthesis, device fabrication, and advanced characterization, CFN was the perfect complement to our West Coast research operations.

    3
    Gold nanoparticles are coordinated by DNA origami octahedron into the prescribed cluster, as obtained from the 3D transmission electron microscopy reconstruction (based on Y. Tian et al. Nature Nanotechnology 10, 637–644, 2015).

    Are you working on any other projects at CFN besides the directed self-assembly?

    In nanomaterials research, I am supporting principal investigators who are using CFN’s advanced characterization tools, particularly those in microscopy, to look at cutting-edge 2D materials like tin selenide (SnSe) and black phosphorous, in collaboration with our university partners.

    For our nanomaterials work, I am also collaborating with an NG Next group involved in plasmonics research, leveraging our DNA assembly work to fabricate new and unique optical structures.

    What are some of the characterization techniques you use at CFN?

    To probe the composition of the DNA-based nanostructures, we focus on small-angle x-ray scattering (SAXS) and transmission electron microscopy (TEM). To probe the chemical states of 2D materials and devices, we use energy-dispersive x-ray spectroscopy and electron energy-loss spectroscopy. In addition to these traditional microscopy techniques, we employ aberration-corrected low-energy electron microscopy (LEEM) and angle-resolved photoemission spectroscopy (ARPES) for some of our 2D materials. This latter technique is important because the band structure, or electronic energy levels, of 2D materials often has directional dependence.

    Your work at CFN sounds like it could also benefit from the advanced characterization methods at the National Synchrotron Light Source II (NSLS-II). Are you collaborating with NSLS-II or do you have plans to?

    BNL NSLS II
    BNL NSLS Interior
    BNL/NSLS-II

    Plans are in the works for experiments at the NSLS-II, building on our current efforts at the CFN. We will be working with CFN scientists Dario Stacchiola and Jerzy Sadowski on the new LEEM/ARPES system during its commissioning in January, and we are evaluating the use of synchrotron SAXS for large-volume data acquisition from nanomaterials for additive manufacturing.

    Our leadership is very supportive of our interactions with Brookhaven’s DOE Office of Science User Facilities and would like to solidify relationships for the long term.

    How has it been coming back to Brookhaven more than 30 years later?

    Even though I work for Northrop Grumman, I feel like I am part of the family here at CFN. I am working at CFN pretty much every day. From the start, CFN leadership has been very accommodating. They helped us get rapid access while we started negotiations on our CRADA [cooperative research and development agreement] and submitted our long-range user proposals for the directed assembly and 2D materials projects.

    Since I arrived, CFN staff scientists have been very helpful with training on laboratory equipment such as the SAXS, TEM, and scanning TEM (STEM) systems. The CFN group leads have been particularly helpful in facilitating timely sample preparation, such as that with the focused-ion beam, and with scheduling the use of characterization tools.

    You mentioned you are at CFN basically every day. What keeps you coming back?

    I feel like a kid in a candy shop here. Everyone who works here is passionate about what they do, so coming in every day is something I look forward to. I have my own spare office, close to the group leaders who I am working with. Although I primarily work with Oleg, I get to interact with many other staff scientists and postdocs, not only through my research but also through my volunteer work at CFN. I am the elected vice chair of the CFN Users’ Executive Committee and co-chair of the 2017 NSLS-II & CFN Joint Users’ Meeting.

    How did you become interested in nanomaterials?

    Years ago, I was doing applied research in photocatalysis involving the use of titanium dioxide nanoparticles to create self-decontaminating surfaces—a DARPA [Defense Advanced Research Projects Agency] project. Subsequently, I got involved in developing lightweight carbon nanotube based electrical cables for Department of Defense applications. The carbon nanotube work is ongoing at Northrop Grumman, with applications for space systems and air platforms. Although these applications are important, my turn to basic research was rooted in the NG Next vision to investigate fundamental phenomena that will enable new game-changing technologies that will have applications to both Northrop Grumman’s traditional customers and future technology marketplaces.

    See the full article here .

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    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 9:03 am on October 14, 2016 Permalink | Reply
    Tags: Crystal Clear Imaging: Infrared Brings to Light Nanoscale Molecular Arrangement, CU Boulder STROBE for Science and Technology Center on Real-Time Functional Imaging, Infrared imaging, , Nanotechnology, Scattering-type scanning near-field optical microscopy,   

    From LBNL- “Crystal Clear Imaging: Infrared Brings to Light Nanoscale Molecular Arrangement” 

    Berkeley Logo

    Berkeley Lab

    October 13, 2016
    Glenn Roberts Jr.
    geroberts@lbl.gov
    510-486-5582

    1
    Infrared light (pink) produced by Berkeley Lab’s Advanced Light Source synchrotron (upper left) and a conventional laser (middle left) is combined and focused on the tip of an atomic force microscope (gray, lower right), where it is used to measure nanoscale details in a crystal sample (dark red). (Credit: Berkeley Lab, CU-Boulder)

    Detailing the molecular makeup of materials—from solar cells to organic light-emitting diodes (LEDs) and transistors, and medically important proteins—is not always a crystal-clear process.

    To understand how materials work at these microscopic scales, and to better design materials to improve their function, it is necessary to not only know all about their composition but also their molecular arrangement and microscopic imperfections.

    Now, a team of researchers working at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) has demonstrated infrared imaging of an organic semiconductor known for its electronics capabilities, revealing key nanoscale details about the nature of its crystal shapes and orientations, and defects that also affect its performance.

    To achieve this imaging breakthrough, researchers from Berkeley Lab’s Advanced Light Source (ALS) and the University of Colorado-Boulder (CU-Boulder) combined the power of infrared light from the ALS and infrared light from a laser with a tool known as an atomic force microscope.

    LBNL Advanced Light Source
    LBNL Advanced Light Source

    The ALS, a synchrotron, produces light in a range of wavelengths or “colors”—from infrared to X-rays—by accelerating electron beams near the speed of light around bends.

    The researchers focused both sources of infrared light onto the tip of the atomic force microscope, which works a bit like a record-player needle—it moves across the surface of a material and measures the subtlest of surface features as it lifts and dips.

    The technique, detailed in a recent edition of the journal Science Advances, allows researchers to tune the infrared light in on specific chemical bonds and their arrangement in a sample, show detailed crystal features, and explore the nanoscale chemical environment in samples.

    2
    This image shows the crystal shape and height of a material known as PTCDA, with height represented by the shading (white is taller, darker orange is lowest). The scale bar represents 500 nanometers. The illustration at bottom is a representation of the crystal shape. (Credit: Berkeley Lab, CU-Boulder)

    “Our technique is broadly applicable,” said Hans Bechtel an ALS scientist. “You could use this for many types of material—the only limitation is that it has to be relatively flat” so that the tip of the atomic force microscope can move across its peaks and valleys.

    Markus Raschke, a CU-Boulder professor who developed the imaging technique with Eric Muller, a postdoctoral researcher in his group, said, “If you know the molecular composition and orientation in these organic materials then you can optimize their properties in a much more straightforward way.

    “This work is informing materials design. The sensitivity of this technique is going from an average of millions of molecules to a few hundred, and the imaging resolution is going from the micron scale (millionths of an inch) to the nanoscale (billionths of an inch),” he said.

    The infrared light of the synchrotron provided the essential wide band of the infrared spectrum, which makes it sensitive to many different chemicals’ bonds at the same time and also provides the sample’s molecular orientation. The conventional infrared laser, with its high power yet narrow range of infrared light, meanwhile, allowed researchers to zoom in on specific bonds to obtain very detailed imaging.

    “Neither the ALS synchrotron nor the laser alone would have given us this level of microscopic insight,” Raschke said, while the combination of the two provided a powerful probe “greater than the sum of its parts.”

    Raschke a decade ago first explored synchrotron-based infrared nano-spectroscopy using the BESSY synchrotron in Berlin. With his help and that of ALS scientists Michael Martin and Bechtel, the ALS in 2014 became the first synchrotron to offer nanoscale infrared imaging to visiting scientists.

    The technique is particularly useful for the study and understanding of so-called “functional materials” that possess special photonic, electronic, or energy-conversion or energy-storage properties, he noted.

    In principle, he added, the new advance in determining molecular orientation could be adapted to biological studies of proteins. “Molecular orientation is critical in determining biological function,” Raschke said. The orientation of molecules determines how energy and charge flows across from cell membranes to molecular solar energy conversion materials.

    Bechtel said the infrared technique permits imaging resolution down to about 10-20 nanometers, which can resolve features up to 50,000 times smaller than a grain of sand.

    The imaging technique used in these experiments, known as “scattering-type scanning near-field optical microscopy,” or s-SNOM, essentially uses the atomic force microscope tip as an ultrasensitive antenna, which transmits and receives focused infrared light in the region of the tip. Scattered light, captured from the tip as it moves over the sample, is recorded by a detector to produce high-resolution images.

    “It’s non-invasive, and it provides information about molecular vibrations,” as the microscope’s tip moves over the sample, Bechtel said. Researchers used the technique to study the crystalline features of an organic semiconductor material known as PTCDA (perylenetetracarboxylic dianhydride).

    Researchers reported that they observed defects in the orientation of the material’s crystal structure that provide a new understanding of the crystals’ growth mechanism and could aid in the design molecular devices using this material.

    3
    Researchers measured the molecular orientation of crystals (light gray and white) in samples of a semiconductor material known as PTCDA. The scale bar is 500 nanometers. The colored dots correspond to the orientation of the crystals in the color bar to the left. The figures at far left show the tip of the atomic force microscope in relation to different crystal orientations. (Credit: Berkeley Lab, CU-Boulder)

    The new imaging capability sets the stage for a new National Science Foundation Center, announced in late September, that links CU-Boulder with Berkeley Lab, UC Berkeley, Florida International University, UC Irvine, and Fort Lewis College in Durango, Colo. The center will combine a range of microscopic imaging methods, including those that use electrons, X-rays, and light, across a broad range of disciplines.

    This center, dubbed STROBE for Science and Technology Center on Real-Time Functional Imaging, will be led by Margaret Murnane, a distinguished professor at CU-Boulder, with Raschke serving as a co-lead.

    At Berkeley Lab, STROBE will be served by a range of ALS capabilities, including the infrared beamlines managed by Bechtel and Martin and a new beamline dubbed COSMIC (for “coherent scattering and microscopy”). It will also benefit from Berkeley Lab-developed data analysis tools.

    Other contributors to the work include Benjamin Pollard and Peter van Blerkom, both members of Raschke’s group at CU-Boulder.

    The work was supported by the National Science Foundation. The ALS is a DOE Office of Science User Facility.

    See the full article here .

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  • richardmitnick 8:03 pm on October 6, 2016 Permalink | Reply
    Tags: , Nanotechnology, , Smallest. Transistor. Ever.   

    From LBNL: “Smallest. Transistor. Ever.” 

    Berkeley Logo

    Berkeley Lab

    October 6, 2016
    Sarah Yang
    scyang@lbl.gov
    (510) 486-4575

    1
    Schematic of a transistor with a molybdenum disulfide channel and 1-nanometer carbon nanotube gate. (Credit: Sujay Desai/UC Berkeley)

    A research team led by faculty scientist Ali Javey at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) has done just that by creating a transistor with a working 1-nanometer gate. For comparison, a strand of human hair is about 50,000 nanometers thick.

    “We made the smallest transistor reported to date,” said Javey, lead principal investigator of the Electronic Materials program in Berkeley Lab’s Materials Science Division. “The gate length is considered a defining dimension of the transistor. We demonstrated a 1-nanometer-gate transistor, showing that with the choice of proper materials, there is a lot more room to shrink our electronics.”

    The key was to use carbon nanotubes and molybdenum disulfide (MoS2), an engine lubricant commonly sold in auto parts shops. MoS2 is part of a family of materials with immense potential for applications in LEDs, lasers, nanoscale transistors, solar cells, and more.

    The findings were published today in the journal Science. Other investigators on this paper include Jeff Bokor, a faculty senior scientist at Berkeley Lab and a professor at UC Berkeley; Chenming Hu, a professor at UC Berkeley; Moon Kim, a professor at the University of Texas at Dallas; and H.S. Philip Wong, a professor at Stanford University.

    The development could be key to keeping alive Intel co-founder Gordon Moore’s prediction that the density of transistors on integrated circuits would double every two years, enabling the increased performance of our laptops, mobile phones, televisions, and other electronics.

    “The semiconductor industry has long assumed that any gate below 5 nanometers wouldn’t work, so anything below that was not even considered,” said study lead author Sujay Desai, a graduate student in Javey’s lab. “This research shows that sub-5-nanometer gates should not be discounted. Industry has been squeezing every last bit of capability out of silicon. By changing the material from silicon to MoS2, we can make a transistor with a gate that is just 1 nanometer in length, and operate it like a switch.”

    When ‘electrons are out of control’

    2
    Transmission electron microscope image of a cross section of the transistor. It shows the 1-nanometer carbon nanotube gate and the molybdenum disulfide semiconductor separated by zirconium dioxide, an insulator. (Credit: Qingxiao Wang/UT Dallas)

    Transistors consist of three terminals: a source, a drain, and a gate. Current flows from the source to the drain, and that flow is controlled by the gate, which switches on and off in response to the voltage applied.

    Both silicon and MoS2 have a crystalline lattice structure, but electrons flowing through silicon are lighter and encounter less resistance compared with MoS2. That is a boon when the gate is 5 nanometers or longer. But below that length, a quantum mechanical phenomenon called tunneling kicks in, and the gate barrier is no longer able to keep the electrons from barging through from the source to the drain terminals.

    “This means we can’t turn off the transistors,” said Desai. “The electrons are out of control.”

    Because electrons flowing through MoS2 are heavier, their flow can be controlled with smaller gate lengths. MoS2 can also be scaled down to atomically thin sheets, about 0.65 nanometers thick, with a lower dielectric constant, a measure reflecting the ability of a material to store energy in an electric field. Both of these properties, in addition to the mass of the electron, help improve the control of the flow of current inside the transistor when the gate length is reduced to 1 nanometer.

    Once they settled on MoS2 as the semiconductor material, it was time to construct the gate. Making a 1-nanometer structure, it turns out, is no small feat. Conventional lithography techniques don’t work well at that scale, so the researchers turned to carbon nanotubes, hollow cylindrical tubes with diameters as small as 1 nanometer.

    They then measured the electrical properties of the devices to show that the MoS2 transistor with the carbon-nanotube gate effectively controlled the flow of electrons.

    “This work demonstrated the shortest transistor ever,” said Javey, who is also a UC Berkeley professor of electrical engineering and computer sciences. “However, it’s a proof of concept. We have not yet packed these transistors onto a chip, and we haven’t done this billions of times over. We also have not developed self-aligned fabrication schemes for reducing parasitic resistances in the device. But this work is important to show that we are no longer limited to a 5-nanometer gate for our transistors. Moore’s Law can continue a while longer by proper engineering of the semiconductor material and device architecture.”

    The work at Berkeley Lab was primarily funded by the Department of Energy’s Basic Energy Sciences program.

    See the full article here .

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  • richardmitnick 4:59 pm on September 26, 2016 Permalink | Reply
    Tags: , , , Nanotechnology,   

    From BNL: “Crystalline Fault Lines Provide Pathway for Solar Cell Current” 

    Brookhaven Lab

    September 26, 2016
    Karen McNulty Walsh
    kmcnulty@bnl.gov
    (631) 344-8350
    Peter Genzer
    genzer@bnl.gov
    (631) 344-3174

    New tomographic AFM imaging technique reveals that microstructural defects, generally thought to be detrimental, actually improve conductivity in cadmium telluride solar cells.

    1
    CFN staff scientist Lihua Zhang places a sample in the transmission electron microscope.

    A team of scientists studying solar cells made from cadmium telluride, a promising alternative to silicon, has discovered that microscopic “fault lines” within and between crystals of the material act as conductive pathways that ease the flow of electric current. This research—conducted at the University of Connecticut and the U.S. Department of Energy’s Brookhaven National Laboratory, and described in the journal Nature Energy—may help explain how a common processing technique turns cadmium telluride into an excellent material for transforming sunlight into electricity, and suggests a strategy for engineering more efficient solar devices that surpass the performance of silicon.

    “If you look at semiconductors like silicon, defects in the crystals are usually bad,” said co-author Eric Stach, a physicist at Brookhaven Lab’s Center for Functional Nanomaterials (CFN). As Stach explained, misplaced atoms or slight shifts in their alignment often act as traps for the particles that carry electric current—negatively charged electrons or the positively charged “holes” left behind when electrons are knocked loose by photons of sunlight, making them more mobile. The idea behind solar cells is to separate the positive and negative charges and run them through a circuit so the current can be used to power houses, satellites, or even cities. Defects interrupt this flow of charges and keep the solar cell from being as efficient as it could be.

    But in the case of cadmium telluride, the scientists found that boundaries between individual crystals and “planar defects”—fault-like misalignments in the arrangement of atoms—create pathways for conductivity, not traps.

    2
    These CTAFM images show a cadmium telluride solar cell from the top (above) and side profile (bottom) with bright spots representing areas of higher electron conductivity. The images reveal that the conductive pathways coincide with crystal grain boundaries. Credit: University of Connecticut.

    Members of Bryan Huey’s group at the Institute of Materials Science at the University of Connecticut were the first to notice the surprising connection. In an effort to understand the effects of a chloride solution treatment that greatly enhances cadmium telluride’s conductive properties, Justin Luria and Yasemin Kutes studied solar cells before and after treatment. But they did so in a unique way.

    Several groups around the world had looked at the surfaces of such solar cells before, often with a tool known as a conducting atomic force microscope. The microscope has a fine probe many times sharper than the head of a pin that scans across the material’s surface to track the topographic features—the hills and valleys of the surface structure—while simultaneously measuring location-specific conductivity. Scientists use this technique to explore how the surface features relate to solar cell performance at the nanoscale.

    But no one had devised a way to make measurements beneath the surface, the most important part of the solar cell. This is where the UConn team made an important breakthrough. They used an approach developed and perfected by Kutes and Luria over the last two years to acquire hundreds of sequential images, each time intentionally removing a nanoscale layer of the material, so they could scan through the entire thickness of the sample. They then used these layer-by-layer images to build up a three-dimensional, high-resolution ‘tomographic’ map of the solar cell—somewhat like a computed tomography (CT) brain scan.


    Assembling the layer-by-layer CTAFM scans into a side-profile video file reveals the relationship between conductivity and planar defects throughout the entire thickness of the cadmium telluride crystal, including how the defects appear to line up to form continuous pathways of conductivity.Credit: University of Connecticut.

    “Everyone using these microscopes basically takes pictures of the ‘ground,’ and interprets what is beneath,” Huey said. “It may look like there’s a cave, or a rock shelf, or a building foundation down there. But we can only really know once we carefully dig, like archeologists, keeping track of exactly what we find every step of the way—though, of course, at a much, much smaller scale.”

    The resulting CT-AFM maps uniquely revealed current flowing most freely along the crystal boundaries and fault-like defects in the cadmium telluride solar cells. The samples that had been treated with the chloride solution had more defects overall, a higher density of these defects, and what appeared to be a high degree of connectivity among them, while the untreated samples had few defects, no evidence of connectivity, and much lower conductivity.

    Huey’s team suspected that the defects were so-called planar defects, usually caused by shifts in atomic alignments or stacking arrangements within the crystals. But the CTAFM system is not designed to reveal such atomic-scale structural details. To get that information, the UConn team turned to Stach, head of the electron microscopy group at the CFN, a DOE Office of Science User Facility.

    “Having previously shared ideas with Eric, it was a natural extension of our discovery to work with his group,” Huey said.

    Said Stach, “This is the exact type of problem the CFN is set up to handle, providing expertise and equipment that university researchers may not have to help drive science from hypothesis to discovery.”

    CFN staff physicist Lihua Zhang used a transmission electron microscope (TEM) and UConn’s results as a guide to meticulously study how atomic scale features of chloride-treated cadmium telluride related to the conductivity maps. The TEM images revealed the atomic structure of the defects, confirming that they were due to specific changes in the stacking sequence of atoms in the material. The images also showed clearly that these planar defects connected different grains in the crystal, leading to high-conductivity pathways for the movement of electrons and holes.

    “When we looked at the regions with good conductivity, the planar defects linked from one crystal grain to another, forming continuous pathways of conductance through the entire thickness of the material,” said Zhang. “So the regions that had the best conductivity were the ones that had a high degree of connectivity among these defects.”

    3
    These transmission electron microscopy images taken at Brookhaven’s CFN reveals how the stacking pattern of individual atoms (bright spots) shifts. The images confirmed that the bright spots of high conductivity observed with CTAFM imaging at UConn occurred at the interfaces between two different atomic alignments (left) and that these “planar defects” were continuous between individual crystals, creating pathways of conductivity (right). The labels WZ and ZB refer to the two atomic stacking sequences “wurtzite” and “zinc blende,” which are the two types of crystal structures cadmium telluride can form. No image credit.

    The authors say it’s possible that the chloride treatment helps to create the connectivity, not just more defects, but that more research is needed to definitively determine the most significant effects of the chloride solution treatment.

    In any case, Stach says that combining the CTAFM technique and electron microscopy, yields a “clear winner” in the search for more efficient, cost-competitive alternatives to silicon solar cells, which have nearly reached their limit for efficiency.

    “There is already a billion-dollar-a-year industry making cadmium telluride solar cells, and lots of work exploring other alternatives to silicon. But all of these alternatives, because of their crystal structure, have a higher tendency to form defects,” he said. “This work gives us a systematic method we can use to understand if the defects are good or bad in terms of conductivity. It can also be used to explore the effects of different processing methods or chemicals to control how defects form. In the case of cadmium telluride, we may want to find ways to make more of these defects, or look for other materials in which defects improve performance.”

    This research was supported by the DOE Office of Energy Efficiency and Renewable Energy (EERE)—including its Sunshot Program—and the DOE Office of Science. The cadmium telluride samples were provided by Andrew Moore of Colorado State University.

    The University of Connecticut’s Institute of Materials Science serves as the heart of materials science research at the University of Connecticut, with a mission of supporting materials research and industry throughout Connecticut and the Northeast. It houses the research labs of more than 30 core faculty, with an overall membership of 120 UConn faculty whose work benefits from the available facilities and expertise.

    See the full article here .

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    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 8:41 am on September 26, 2016 Permalink | Reply
    Tags: , Controllable light-emitting materials to advance light sensing and nano-medicine, Nanotechnology, ,   

    From Tokyo Tech: “Controllable light-emitting materials to advance light sensing and nano-medicine” 

    tokyo-tech-bloc

    Tokyo Institute of Technology

    September 26, 2016
    No writer credit found

    Luminous bismuth: controllable light-emitting materials having the potential to advance high-intensity, light sensing and nano-medicine

    Scientists at Tokyo Tech have developed an approach to control the photoluminescence and solid-state emission of bismuth complexes by complexation with phenylazomethine dendrimers. This research
    [journal: Angewandte Chemie International Edition] not only sheds light on the structure of a rare, luminescent bismuth complex, but will also be used to advance the potential applications of luminous dendrimers, especially in light harvesting, sensing, electronics, photonics, and nano-medicine.

    Precise control of the photoluminescence, or light emission from matter after the absorption of photons, plays a considerable role in the advancement of various optical materials. Modification of the emission intensity, rather than the wavelength, presents a challenge for materials scientists, and simple strategies that can be used to control the intensity of phosphors are desired.

    The assembly of photoluminescent components within dendrimers, a class of synthetic polymers with branching, tree-like structures, may be a suitable method for controlling the emission intensity. However, the use of dendrimers as nano-capsules suffers from several drawbacks such as quenched luminescence due to high local concentrations of the phosphors, and controlling the number of phosphors within the dendrimer skeleton is difficult.

    To address these challenges, a group of scientists led by Kimihisa Yamamoto from the Laboratory for Chemistry and Life Science at Tokyo Institute of Technology developed luminous dendrimers with finely tunable optical properties using dendritic polyphenylazomethines (DPAs). Due to the electron donating ability of the phenylazomethines, the assembly of the metal ions could be controlled in a radial and stepwise fashion. The semi-rigid structure of the DPAs also allowed for the optical properties of the metal complexes to be maintained by preventing intermolecular electronic interactions. Thus, by careful selection of the ligand, the typical issues encountered with encapsulation of phosphors by dendrimers were overcome, and a new method to control emission intensity was achieved. In addition, the luminescence of the bismuth complexes could be switched on and off by the addition of a Lewis base or by redox control, owing to the reversible coordination bonds within the complexes. As such, Prof. Yamamoto and co-workers showed that the phenylazomethine-bismuth complexes are a new class of stimuli-responsive materials.

    Prof. Yamamoto and co-workers formed rare and functional photoluminescent dendrimers containing specific numbers of bismuth ions. The stimuli-responsive optical properties of the bismuth complexes, including the tunable emission intensity, are expected to be useful for the generation of novel sensors and optical standards. The results not only shed light on the structures of the novel bismuth complexes, but will also facilitate the future design of novel functional phosphors, which may have far-reaching applications in a variety of fields.

    1
    Figure. Luminous phenylazomethine-bismuth complexes were precisely assembled in the dendrimer. The emission intensity of one molecular dendrimer could be controlled by the number of bismuth units. The dendrimer skeleton enabled solid-state emission and optical switching induced by chemical and electronic stimuli. No image credit.

    See the full article here .

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    Tokyo Tech is the top national university for science and technology in Japan with a history spanning more than 130 years. Of the approximately 10,000 students at the Ookayama, Suzukakedai, and Tamachi Campuses, half are in their bachelor’s degree program while the other half are in master’s and doctoral degree programs. International students number 1,200. There are 1,200 faculty and 600 administrative and technical staff members.

    In the 21st century, the role of science and technology universities has become increasingly important. Tokyo Tech continues to develop global leaders in the fields of science and technology, and contributes to the betterment of society through its research, focusing on solutions to global issues. The Institute’s long-term goal is to become the world’s leading science and technology university.

     
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