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  • richardmitnick 9:02 am on October 17, 2014 Permalink | Reply
    Tags: , , , Nanotechnology   

    From MIT: “Nanoparticles get a magnetic handle” 


    MIT News

    October 9, 2014
    David L. Chandler | MIT News Office

    A long-sought goal of creating particles that can emit a colorful fluorescent glow in a biological environment, and that could be precisely manipulated into position within living cells, has been achieved by a team of researchers at MIT and several other institutions. The finding is reported this week in the journal Nature Communications.

    4
    Elemental mapping of the location of iron atoms (blue) in the magnetic nanoparticles and cadmium (red) in the fluorescent quantum dots provide a clear visualization of the way the two kinds of particles naturally separate themselves into a core-and-shell structure. Image courtesy of the researchers

    The new technology could make it possible to track the position of the nanoparticles as they move within the body or inside a cell. At the same time, the nanoparticles could be manipulated precisely by applying a magnetic field to pull them along. And finally, the particles could have a coating of a bioreactive substance that could seek out and bind with particular molecules within the body, such as markers for tumor cells or other disease agents.

    “It’s been a dream of mine for many years to have a nanomaterial that incorporates both fluorescence and magnetism in a single compact object,” says Moungi Bawendi, the Lester Wolfe Professor of Chemistry at MIT and senior author of the new paper. While other groups have achieved some combination of these two properties, Bawendi says that he “was never very satisfied” with results previously achieved by his own team or others.

    For one thing, he says, such particles have been too large to make practical probes of living tissue: “They’ve tended to have a lot of wasted volume,” Bawendi says. “Compactness is critical for biological and a lot of other applications.”

    In addition, previous efforts were unable to produce particles of uniform and predictable size, which could also be an essential property for diagnostic or therapeutic applications.

    Moreover, Bawendi says, “We wanted to be able to manipulate these structures inside the cells with magnetic fields, but also know exactly what it is we’re moving.” All of these goals are achieved by the new nanoparticles, which can be identified with great precision by the wavelength of their fluorescent emissions.

    The new method produces the combination of desired properties “in as small a package as possible,” Bawendi says — which could help pave the way for particles with other useful properties, such as the ability to bind with a specific type of bioreceptor, or another molecule of interest.

    In the technique developed by Bawendi’s team, led by lead author and postdoc Ou Chen, the nanoparticles crystallize such that they self-assemble in exactly the way that leads to the most useful outcome: The magnetic particles cluster at the center, while fluorescent particles form a uniform coating around them. That puts the fluorescent molecules in the most visible location for allowing the nanoparticles to be tracked optically through a microscope.

    “These are beautiful structures, they’re so clean,” Bawendi says. That uniformity arises, in part, because the starting material, fluorescent nanoparticles that Bawendi and his group have been perfecting for years, are themselves perfectly uniform in size. “You have to use very uniform material to produce such a uniform construction,” Chen says.

    Initially, at least, the particles might be used to probe basic biological functions within cells, Bawendi suggests. As the work continues, later experiments may add additional materials to the particles’ coating so that they interact in specific ways with molecules or structures within the cell, either for diagnosis or treatment.

    The ability to manipulate the particles with electromagnets is key to using them in biological research, Bawendi explains: The tiny particles could otherwise get lost in the jumble of molecules circulating within a cell. “Without a magnetic ‘handle,’ it’s like a needle in a haystack,” he says. “But with the magnetism, you can find it easily.”

    A silica coating on the particles allows additional molecules to attach, causing the particles to bind with specific structures within the cell. “Silica makes it completely flexible; it’s a well developed material that can bind to almost anything,” Bawendi says.

    For example, the coating could have a molecule that binds to a specific type of tumor cells; then, “You could use them to enhance the contrast of an MRI, so you could see the spatial macroscopic outlines of a tumor,” he says.

    The next step for the team is to test the new nanoparticles in a variety of biological settings. “We’ve made the material,” Chen says. “Now we’ve got to use it, and we’re working with a number of groups around the world for a variety of applications.”

    Christopher Murray, a professor of chemistry and materials science and engineering at the University of Pennsylvania who was not connected with this research, says, “This work exemplifies the power of using nanocrystals as building blocks for multiscale and multifunctional structures. We often use the term ‘artificial atoms’ in the community to describe how we are exploiting a new periodic table of fundamental building blocks to design materials, and this is a very elegant example.”

    The study included researchers at MIT; Massachusetts General Hospital; Institut Curie in Paris; the Heinrich-Pette Institute and the Bernhard-Nocht Institute for Tropical Medicine in Hamburg, Germany; Children’s Hospital Boston; and Cornell University. The work was supported by the National Institutes of Health, the Army Research Office through MIT’s Institute for Soldier Nanotechnologies, and the Department of Energy.

    See the full article, with video, here.

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  • richardmitnick 6:33 pm on October 13, 2014 Permalink | Reply
    Tags: , , Nanotechnology   

    From MIT: “Solid nanoparticles can deform like a liquid” 


    MIT News

    October 12, 2014
    David L. Chandler | MIT News Office

    Unexpected finding shows tiny particles keep their internal crystal structure while flexing like droplets.

    A surprising phenomenon has been found in metal nanoparticles: They appear, from the outside, to be liquid droplets, wobbling and readily changing shape, while their interiors retain a perfectly stable crystal configuration.

    drops
    Image: Yan Liang

    The research team behind the finding, led by MIT professor Ju Li, says the work could have important implications for the design of components in nanotechnology, such as metal contacts for molecular electronic circuits.

    The results, published in the journal Nature Materials, come from a combination of laboratory analysis and computer modeling, by an international team that included researchers in China, Japan, and Pittsburgh, as well as at MIT.

    The experiments were conducted at room temperature, with particles of pure silver less than 10 nanometers across — less than one-thousandth of the width of a human hair. But the results should apply to many different metals, says Li, senior author of the paper and the BEA Professor of Nuclear Science and Engineering.

    Silver has a relatively high melting point — 962 degrees Celsius, or 1763 degrees Fahrenheit — so observation of any liquidlike behavior in its nanoparticles was “quite unexpected,” Li says. Hints of the new phenomenon had been seen in earlier work with tin, which has a much lower melting point, he says.

    The use of nanoparticles in applications ranging from electronics to pharmaceuticals is a lively area of research; generally, Li says, these researchers “want to form shapes, and they want these shapes to be stable, in many cases over a period of years.” So the discovery of these deformations reveals a potentially serious barrier to many such applications: For example, if gold or silver nanoligaments are used in electronic circuits, these deformations could quickly cause electrical connections to fail.

    Only skin deep

    The researchers’ detailed imaging with a transmission electron microscope and atomistic modeling revealed that while the exterior of the metal nanoparticles appears to move like a liquid, only the outermost layers — one or two atoms thick — actually move at any given time. As these outer layers of atoms move across the surface and redeposit elsewhere, they give the impression of much greater movement — but inside each particle, the atoms stay perfectly lined up, like bricks in a wall.

    “The interior is crystalline, so the only mobile atoms are the first one or two monolayers,” Li says. “Everywhere except the first two layers is crystalline.”

    By contrast, if the droplets were to melt to a liquid state, the orderliness of the crystal structure would be eliminated entirely — like a wall tumbling into a heap of bricks.

    Technically, the particles’ deformation is pseudoelastic, meaning that the material returns to its original shape after the stresses are removed — like a squeezed rubber ball — as opposed to plasticity, as in a deformable lump of clay that retains a new shape.

    The phenomenon of plasticity by interfacial diffusion was first proposed by Robert L. Coble, a professor of ceramic engineering at MIT, and is known as “Coble creep.” “What we saw is aptly called Coble pseudoelasticity,” Li says.

    Now that the phenomenon has been understood, researchers working on nanocircuits or other nanodevices can quite easily compensate for it, Li says. If the nanoparticles are protected by even a vanishingly thin layer of oxide, the liquidlike behavior is almost completely eliminated, making stable circuits possible.

    Possible benefits

    On the other hand, for some applications this phenomenon might be useful: For example, in circuits where electrical contacts need to withstand rotational reconfiguration, particles designed to maximize this effect might prove useful, using noble metals or a reducing atmosphere, where the formation of an oxide layer is destabilized, Li says.

    The new finding flies in the face of expectations — in part, because of a well-understood relationship, in most materials, in which mechanical strength increases as size is reduced.

    “In general, the smaller the size, the higher the strength,” Li says, but “at very small sizes, a material component can get very much weaker. The transition from ‘smaller is stronger’ to ‘smaller is much weaker’ can be very sharp.”

    That crossover, he says, takes place at about 10 nanometers at room temperature — a size that microchip manufacturers are approaching as circuits shrink. When this threshold is reached, Li says, it causes “a very precipitous drop” in a nanocomponent’s strength.

    The findings could also help explain a number of anomalous results seen in other research on small particles, Li says.

    “The … work reported in this paper is first-class,” says Horacio Espinosa, a professor of manufacturing and entrepreneurship at Northwestern University who was not involved in this research. “These are very difficult experiments, which revealed for the first time shape recovery of silver nanocrystals in the absence of dislocation. … Li’s interpretation of the experiments using atomistic modeling illustrates recent progress in comparing experiments and simulations as it relates to spatial and time scales. This has implications to many aspects of mechanics of materials, so I expect this work to be highly cited.”

    The research team included Jun Sun, Longbing He, Tao Xu, Hengchang Bi, and Litao Sun, all of Southeast University in Nanjing, China; Yu-Chieh Lo of MIT and Kyoto University; Ze Zhang of Zhejiang University; and Scott Mao of the University of Pittsburgh. It was supported by the National Basic Research Program of China; the National Natural Science Foundation of China; the Chinese Ministry of Education; the National Science Foundation of Jiangsu Province, China; and the U.S. National Science Foundation.

    See the full article here.

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  • richardmitnick 8:57 pm on October 3, 2014 Permalink | Reply
    Tags: , , , , Nanotechnology   

    From MIT: “Crumpled graphene could provide an unconventional energy storage” 


    MIT News

    October 3, 2014
    David L. Chandler | MIT News Office

    Two-dimensional carbon “paper” can form stretchable supercapacitors to power flexible electronic devices.

    When someone crumples a sheet of paper, that usually means it’s about to be thrown away. But researchers have now found that crumpling a piece of graphene “paper” — a material formed by bonding together layers of the two-dimensional form of carbon — can actually yield new properties that could be useful for creating extremely stretchable supercapacitors to store energy for flexible electronic devices.

    temp
    To form the crumpled graphene, a sheet of polymer material is stretched in both dimensions, then graphene paper is bonded to it. When the polymer is released in one direction, the graphene forms pleats, as shown in the bottom left image, taken with a scanning electron microscope (SEM). Then, when released in the other direction, it forms a chaotic crumpled pattern (top left). At top right, an SEM image shows the material in a partially crumpled state. At bottom right, SEM image of a piece that has been crumpled and then flattened out. Image courtesy of the researchers

    The finding is reported in the journal Scientific Reports by MIT’s Xuanhe Zhao, an assistant professor of mechanical engineering and civil and environmental engineering, and four other authors. The new, flexible supercapacitors should be easy and inexpensive to fabricate, the team says.

    “Many people are exploring graphene paper: It’s a good candidate for making supercapacitors, because of its large surface area per mass,” Zhao says. Now, he says, the development of flexible electronic devices, such as wearable or implantable biomedical sensors or monitoring devices, will require flexible power-storage systems.

    Like batteries, supercapacitors can store electrical energy, but they primarily do so electrostatically, rather than chemically — meaning they can deliver their energy faster than batteries can. Now Zhao and his team have demonstrated that by crumpling a sheet of graphene paper into a chaotic mass of folds, they can make a supercapacitor that can easily be bent, folded, or stretched to as much as 800 percent of its original size. The team has made a simple supercapacitor using this method as a proof of principle.

    The material can be crumpled and flattened up to 1,000 times, the team has demonstrated, without a significant loss of performance. “The graphene paper is pretty robust,” Zhao says, “and we can achieve very large deformations over multiple cycles.” Graphene, a structure of pure carbon just one atom thick with its carbon atoms arranged in a hexagonal array, is one of the strongest materials known.

    To make the crumpled graphene paper, a sheet of the material was placed in a mechanical device that first compressed it in one direction, creating a series of parallel folds or pleats, and then in the other direction, leading to a chaotic, rumpled surface. When stretched, the material’s folds simply smooth themselves out.

    Forming a capacitor requires two conductive layers — in this case, two sheets of crumpled graphene paper — with an insulating layer in between, which in this demonstration was made from a hydrogel material. Like the crumpled graphene, the hydrogel is highly deformable and stretchable, so the three layers remain in contact even while being flexed and pulled.

    Though this initial demonstration was specifically to make a supercapacitor, the same crumpling technique could be applied to other uses, Zhao says. For example, the crumpled graphene material might be used as one electrode in a flexible battery, or could be used to make a stretchable sensor for specific chemical or biological molecules.

    “This work is really exciting and amazing to me,” says Dan Li, a professor of materials engineering at Monash University in Australia who was not involved in this research. He says the team “provides an extremely simple but highly effective concept to make stretchable electrodes for supercapacitors by controlled crumpling of multilayered graphene films.” While other groups have made flexible supercapacitors, he says, “Making supercapacitors stretchable has been a great challenge. This paper provides a very smart way to tackle this challenge, which I believe will bring wearable energy storage devices closer.”

    The research team also included Jianfeng Zang at Huazhong University of Science and Technology and Changyang Cao, Yaying Feng, and Jie Liu at Duke University. The work was supported by the Office of Naval Research, the National Science Foundation, and the National 1000 Talents Program of China.

    See the full article here.

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  • richardmitnick 11:02 am on September 22, 2014 Permalink | Reply
    Tags: , Electron Beam Technology, , Nanotechnology   

    From FNAL- “Feature Breakthrough: nanotube cathode creates more electron beam than large laser system 


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

    Monday, Sept. 22, 2014
    Troy Rummler

    Lasers are cool, except when they’re clunky, expensive and delicate.

    So a collaboration led by RadiaBeam Technologies, a California-based technology firm actively involved in accelerator R&D, is designing an electron beam source that doesn’t need a laser. The team led by Luigi Faillace, a scientist at RadiaBeam, is testing a carbon nanotube cathode — about the size of a nickel — in Fermilab’s High-Brightness Electron Source Lab (HBESL) that completely eliminates the need for a room-sized laser system currently used to generate the electron beam.

    Fermilab was sought out to test the experimental cathode because of its capability and expertise for handling intense electron beams, one of relatively few labs that can support this project.

    Tests have shown that the vastly smaller cathode does a better job than the laser. Philippe Piot, a staff scientist in the Fermilab Accelerator Division and a joint appointee at Northern Illinois University, says tests have produced beam currents a thousand to a million times greater than the one generated with a laser. This remarkable result means that electron beam equipment used in industry may become not only less expensive and more compact, but also more efficient. A laser like the one in HBESL runs close to half a million dollars, Piot said, about hundred times more than RadiaBeam’s cathode.

    The technology has extensive applications in medical equipment and national security, as an electron beam is a critical component in generating X-rays. And while carbon nanotube cathodes have been studied extensively in academia, Fermilab is the first facility to test the technology within a full-scale setting.

    “People have talked about it for years,” said Piot, “but what was missing was a partnership between people that have the know-how at a lab, a university and a company.”

    Piot and Fermilab scientist Charles Thangaraj are partnering with RadiaBeam Technologies staff Luigi Faillace and Josiah Hartzell and Northern Illinois University student Harsha Panuganti and researcher Daniel Mihalcea. A U.S. Department of Energy Small Business Innovation Research grant, a federal endowment designed to bridge the R&D gap between basic research and commercial products, funds the project. The work represents the kind of research that will be enabled in the future at the Illinois Accelerator Research Center — a facility that brings together Fermilab expertise and industry.

    hp
    Harsha Panunganti of Northern Illinois University works on the laser system (turned off here) normally used to create electron beams from a photocathode. Photo: Reidar Hahn

    The new cathode appears at first glance like a smooth black button, but at the nanoscale it resembles, in Piot’s words, “millions of lightning rods.”

    tubre
    The dark carbon-nanotube-coated area of this field emission cathode is made of millions of nanotubes that function like little lightning rods. At Fermilab’s High-Brightness Electron Source Lab, scientists have tested this cathode in the front end of an accelerator, where a strong electric field siphons electrons off the nanotubes to create an intense electron beam. Photo: Reidar Hahn

    “When you apply an electric field, the field lines organize themselves around the rods’ extremities and enhance the field,” Piot said. The electric field at the peaks is so intense that it pulls streams of electrons off the cathode, creating the beam.

    Traditionally, lasers strike cathodes in order to eject electrons through photoemission. Those electrons form a beam by piggybacking onto a radio-frequency wave, synchronized to the laser pulses and formed in a resonance cavity. Powerful magnets focus the beam. The tested nanotube cathode requires no laser as it needs only the electric field already generated by the accelerator to siphon the electrons off, a process dubbed field emission.

    The intense electric field, though, has been a tremendous liability. Piot said critics thought the cathode “was just going to explode and ruin the electron source, and we would be crying because it would be dead.”

    One of the first discoveries Piot’s team made when they began testing in May was that the cathode did not, in fact, explode and ruin everything. The exceptional strength of carbon nanotubes makes the project feasible.

    Still, Piot continues to study ways to optimize the design of the cathode to prevent any smaller, adverse effects that may take place within the beam assembly. Future research also may focus on redesigning an accelerator that natively incorporates the carbon nanotube cathode to avoid any compatibility issues.

    See the full article here.

    Fermilab Campus

    Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a US Department of Energy national laboratory specializing in high-energy particle physics.

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  • richardmitnick 3:31 pm on September 12, 2014 Permalink | Reply
    Tags: , , Nanotechnology   

    From DESY: “Scientists watch nanoparticles grow” 

    DESY
    DESY

    27.03.2014
    No Writer Credit

    Analysis allows tailoring materials for switchable windows and solar cells

    With DESY’s X-ray light source PETRA III, Danish scientists observed the growth of nanoparticles live. The study shows how tungsten oxide nanoparticles are forming from solution. These particles are used for example for smart windows, which become opaque at the flick of a switch, and they are also used in particular solar cells. The team around lead author Dr. Dipankar Saha from Århus University present their observations in the scientific journal Angewandte Chemie – International Edition.
    Zoom (17 KB)

    nano
    Top: Structure of the ammonium metatungstate dissolved in water on atomic length scale. The octahedra consisting of the tungsten ion in the centre and the six surrounding oxygen ions partly share corners and edges. Bottom: Structure of the nanoparticles in the ordered crystalline phase. The octahedra exclusively share corners. Credit: Dipankar Saha/Århus University

    For their investigation, the scientists built a small reaction chamber, which is transparent for X-rays. “We use fine capillaries of sapphire or fused silica which are easily penetrable by X-rays,” said Professor Bo Iversen, head of the research group. In these capillaries, the scientists transformed so-called ammonium metatungstate dissolved in water into nanoparticles at high temperature and high pressure. With the brilliant PETRA III X-ray light, the chemists were able to track the growth of small tungsten trioxide particles (WO3) with a typical size of about ten nanometres from the solution in real time.

    “The X-ray measurements show the building blocks of the material,” said co-author Dr. Ann-Christin Dippel from DESY, scientist at beamline P02.1, where the experiments were carried out. “With our method, we are able to observe the structure of the material at atomic length scale. What is special here is the possibility of following the dynamics of the growth process,” Dippel points out. “The different crystal structures that form in these nanoparticles are already known. But now we can track in real-time the transformation mechanism of molecules to nanocrystals. We do not only see the sequence of the process but also why specific structures form.”

    On the molecular level, the basic units of many metal-oxygen compounds like oxides are octahedra, which consist of eight equal triangles. These octahedra may share corners or edges. Depending on their configuration, the resulting compounds have different characteristics. This is not only true for tungsten trioxide but is basically applicable to other materials.

    The octahedra units in the solutions grow up to nanoparticles, with a ten nanometre small particle including about 25 octahedra. “We were able to determine that at first, both structure elements exist in the original material, the connection by corners and by edges,” said Saha. “In the course of the reaction, the octahedra rearrange: the longer you wait, the more the edge connection disappears and the connection by corners becomes more frequent. The nanoparticles which developed in our investigations have a predominantly ordered crystal structure.”

    In the continuous industrial synthesis, this process occurs so quickly, that it mainly produces nanoparticles with mixed disordered structures. “Ordered structures are produced when nanoparticles get enough time to rearrange,” said Saha. “We can use these observations for example to make available nanoparticles with special features. This method is also applicable to other nanoparticles.”

    See the full article here.

    desi

    DESY is one of the world’s leading accelerator centres. Researchers use the large-scale facilities at DESY to explore the microcosm in all its variety – from the interactions of tiny elementary particles and the behaviour of new types of nanomaterials to biomolecular processes that are essential to life. The accelerators and detectors that DESY develops and builds are unique research tools. The facilities generate the world’s most intense X-ray light, accelerate particles to record energies and open completely new windows onto the universe. 
That makes DESY not only a magnet for more than 3000 guest researchers from over 40 countries every year, but also a coveted partner for national and international cooperations. Committed young researchers find an exciting interdisciplinary setting at DESY. The research centre offers specialized training for a large number of professions. DESY cooperates with industry and business to promote new technologies that will benefit society and encourage innovations. This also benefits the metropolitan regions of the two DESY locations, Hamburg and Zeuthen near Berlin.

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  • richardmitnick 3:27 pm on September 11, 2014 Permalink | Reply
    Tags: , , , Nanotechnology   

    From M.I.T Tech: “A Super-Strong and Lightweight New Material” 

    MIT Technology Review
    M.I.T Technology Review

    September 11, 2014
    Katherine Bourzac

    Nanostructured ceramics could be used to build lighter, stronger airplanes and batteries.

    A new type of material, made up of nanoscale struts crisscrossed like the struts of a tiny Eiffel Tower, is one of the strongest and lightest substances ever made.

    mtl
    Tiny trusses: A scanning electron microscope image of the new material reveals its ceramic nano-lattices

    If researchers can figure out how to make the stuff in large quantities, it could be used as a structural material for making planes and trucks, as well as in battery electrodes.

    Researchers led by Caltech materials scientist Julia Greer found that by carefully designing nanoscale struts and joints, they could make ceramics, metals, and other materials that can recover after being crushed, like a sponge. The materials are very strong and light enough to float through the air like a feather. The work is published today in the journal Science.

    In conventional materials, strength, weight, and density are correlated. Ceramics, for example, are strong but also heavy, so they can’t be used as structural materials where weight is critical—for example, in the bodies of cars. And when ceramics fail, they tend to fail catastrophically, shattering like glass.

    But at the nanoscale the same rules do not apply. In this size range, the structural and mechanical properties of ceramics become less tied to properties such as weight, and they can be altered more precisely.

    “For ceramics, smaller is tougher,” says Greer, who was named one of MIT Technology Review’s 35 Innovators Under 35 in 2008 for her work on nanoscale mechanics. This means that nanoscale trusses made from ceramic materials can be both very light—unsurprising, since they are mostly air—and extremely strong.

    In 2011, working with researchers at HRL Laboratories, a private engineering research company, Greer created one of the lightest materials ever made, a microlattice of hollow metal tubes. She later chose to take on the greater challenge of making ceramics with similar properties. This required fine-tuning structures at the nanoscale, meaning the materials are even more difficult to produce.

    To make the ceramic nano-trusses, Greer’s lab uses a technique called two-photon interference lithography. It’s akin to a very low-yield 3-D laser printer.

    First they use this method to create the desired structure, a lattice, out of a polymer. The polymer lattice is then coated with a ceramic such as alumina. Oxygen plasma etches out the polymer, leaving behind a lattice of hollow ceramic tubes.

    Greer’s lab showed that by changing the thickness of the tube walls, it’s possible to control how the material fails. When the walls are thick, the ceramic shatters under pressure as expected. But trusses with thinner walls, just 10 nanometers thick, buckle when compressed and then recover their shape.

    “You don’t expect these materials to recover—you expect them to be brittle and to fracture,” says Christopher Spadaccini, an engineer who specializes in materials manufacturing at the U.S. Department of Energy’s Lawrence Livermore National Laboratory in California.

    The new materials might be particularly interesting for use in batteries, notes Nicholas Fang, a mechanical engineer at MIT who is also working on nanostructured ceramics. Nanostructures have a very high surface area and are lightweight, a combination that could make for a fast-charging battery that stores a lot of energy in a convenient package. In fact, Greer says she is collaborating with German electronics company Bosch to apply her designs to lithium-ion batteries.

    See the full article here.

    The mission of MIT Technology Review is to equip its audiences with the intelligence to understand a world shaped by technology.

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  • richardmitnick 1:49 pm on September 3, 2014 Permalink | Reply
    Tags: , , , , Nanotechnology, Peptoids   

    From LBL: “Peptoid Nanosheets at the Oil/Water Interface” 

    Berkeley Logo

    Berkeley Lab

    September 3, 2014
    Lynn Yarris (510) 486-5375

    From the people who brought us peptoid nanosheets that form at the interface between air and water, now come peptoid nanosheets that form at the interface between oil and water. Scientists at the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab) have developed peptoid nanosheets – two-dimensional biomimetic materials with customizable properties – that self-assemble at an oil-water interface. This new development opens the door to designing peptoid nanosheets of increasing structural complexity and chemical functionality for a broad range of applications, including improved chemical sensors and separators, and safer, more effective drug delivery vehicles.

    Supramolecular assembly at an oil-water interface is an effective way to produce 2D nanomaterials from peptoids because that interface helps pre-organize the peptoid chains to facilitate their self-interaction,” says Ron Zuckermann, a senior scientist at the Molecular Foundry, a DOE nanoscience center hosted at Berkeley Lab. “This increased understanding of the peptoid assembly mechanism should enable us to scale-up to produce large quantities, or scale- down to screen many different nanosheets for novel functions.”

    nano
    Peptoid nanosheets are among the largest and thinnest free-floating organic crystals ever made, with an area-to-thickness equivalent of a plastic sheet covering a football field. Peptoid nanosheets can be engineered to carry out a wide variety of functions.
    two
    Ron Zuckerman and Geraldine Richmond led the development of peptoid nanosheets that form at the interface between oil and water, opening the door to increased structural complexity and chemical functionality for a broad range of applications.

    Zuckermann, who directs the Molecular Foundry’s Biological Nanostructures Facility, and Geraldine Richmond of the University of Oregon are the corresponding authors of a paper reporting these results in the Proceedings of the National Academy of Sciences (PNAS). The paper is titled Assembly and molecular order of two-dimensional peptoid nanosheets at the oil-water interface. Co-authors are Ellen Robertson, Gloria Olivier, Menglu Qian and Caroline Proulx.

    Peptoids are synthetic versions of proteins. Like their natural counterparts, peptoids fold and twist into distinct conformations that enable them to carry out a wide variety of specific functions. In 2010, Zuckermann and his group at the Molecular Foundry discovered a technique to synthesize peptoids into sheets that were just a few nanometers thick but up to 100 micrometers in length. These were among the largest and thinnest free-floating organic crystals ever made, with an area-to-thickness equivalent of a plastic sheet covering a football field. Just as the properties of peptoids can be chemically customized through robotic synthesis, the properties of peptoid nanosheets can also be engineered for specific functions.

    “Peptoid nanosheet properties can be tailored with great precision,” Zuckermann says, “and since peptoids are less vulnerable to chemical or metabolic breakdown than proteins, they are a highly promising platform for self-assembling bio-inspired nanomaterials.”

    In this latest effort, Zuckermann, Richmond and their co-authors used vibrational sum frequency spectroscopy to probe the molecular interactions between the peptoids as they assembled at the oil-water interface. These measurements revealed that peptoid polymers adsorbed to the interface are highly ordered, and that this order is greatly influenced by interactions between neighboring molecules.

    “We can literally see the polymer chains become more organized the closer they get to one another,” Zuckermann says.

    ft
    Peptoid polymers adsorbed to the oil-water interface are highly ordered thanks to interactions between neighboring molecules.

    The substitution of oil in place of air creates a raft of new opportunities for the engineering and production of peptoid nanosheets. For example, the oil phase could contain chemical reagents, serve to minimize evaporation of the aqueous phase, or enable microfluidic production.

    “The production of peptoid nanosheets in microfluidic devices means that we should soon be able to make combinatorial libraries of different functionalized nanosheets and screen them on a very small scale,” Zuckermann says. “This would be advantageous in the search for peptoid nanosheets with the molecular recognition and catalytic functions of proteins.”

    Zuckermann and his group at the Molecular Foundry are now investigating the addition of chemical reagents or cargo to the oil phase, and exploring their interactions with the peptoid monolayers that form during the nanosheet assembly process.

    “In the future we may be able to produce nanosheets with drugs, dyes, nanoparticles or other solutes trapped in the interior,” he says. “These new nanosheets could have a host of interesting biomedical, mechanical and optical properties.”

    This work was primarily funded by the DOE Office of Science and the Defense Threat Reduction Agency. Part of the research was performed at the Molecular Foundry and the Advanced Light Source, which are DOE Office of Science User Facilities.

    See the full article here.

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  • richardmitnick 1:46 pm on August 26, 2014 Permalink | Reply
    Tags: , , , , Nanotechnology,   

    From Berkeley Lab: “Competition for Graphene” 

    Berkeley Logo

    Berkeley Lab

    August 26, 2014
    Lynn Yarris (510) 486-5375

    A new argument has just been added to the growing case for graphene being bumped off its pedestal as the next big thing in the high-tech world by the two-dimensional semiconductors known as MX2 materials. An international collaboration of researchers led by a scientist with the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab) has reported the first experimental observation of ultrafast charge transfer in photo-excited MX2 materials. The recorded charge transfer time clocked in at under 50 femtoseconds, comparable to the fastest times recorded for organic photovoltaics.

    “We’ve demonstrated, for the first time, efficient charge transfer in MX2 heterostructures through combined photoluminescence mapping and transient absorption measurements,” says Feng Wang, a condensed matter physicist with Berkeley Lab’s Materials Sciences Division and the University of California (UC) Berkeley’s Physics Department. “Having quantitatively determined charge transfer time to be less than 50 femtoseconds, our study suggests that MX2 heterostructures, with their remarkable electrical and optical properties and the rapid development of large-area synthesis, hold great promise for future photonic and optoelectronic applications.”

    fw
    Feng Wang is a condensed matter physicist with Berkeley Lab’s Materials Sciences Division and UC Berkeley’s Physics Department. (Photo by Roy Kaltschmidt)

    Wang is the corresponding author of a paper in Nature Nanotechnology describing this research. The paper is titled Ultrafast charge transfer in atomically thin MoS2/WS2 heterostructures. Co-authors are Xiaoping Hong, Jonghwan Kim, Su-Fei Shi, Yu Zhang, Chenhao Jin, Yinghui Sun, Sefaattin Tongay, Junqiao Wu and Yanfeng Zhang.

    MX2 monolayers consist of a single layer of transition metal atoms, such as molybdenum (Mo) or tungsten (W), sandwiched between two layers of chalcogen atoms, such as sulfur (S). The resulting heterostructure is bound by the relatively weak intermolecular attraction known as the van der Waals force. These 2D semiconductors feature the same hexagonal “honeycombed” structure as graphene and superfast electrical conductance, but, unlike graphene, they have natural energy band-gaps. This facilitates their application in transistors and other electronic devices because, unlike graphene, their electrical conductance can be switched off.

    “Combining different MX2 layers together allows one to control their physical properties,” says Wang, who is also an investigator with the Kavli Energy NanoSciences Institute (Kavli-ENSI). “For example, the combination of MoS2 and WS2 forms a type-II semiconductor that enables fast charge separation. The separation of photoexcited electrons and holes is essential for driving an electrical current in a photodetector or solar cell.”

    In demonstrating the ultrafast charge separation capabilities of atomically thin samples of MoS2/WS2 heterostructures, Wang and his collaborators have opened up potentially rich new avenues, not only for photonics and optoelectronics, but also for photovoltaics.

    photo
    Photoluminescence mapping of a MoS2/WS2 heterostructure with the color scale representing photoluminescence intensity shows strong quenching of the MoS2 photoluminescence. (Image courtesy of Feng Wang group)

    “MX2 semiconductors have extremely strong optical absorption properties and compared with organic photovoltaic materials, have a crystalline structure and better electrical transport properties,” Wang says. “Factor in a femtosecond charge transfer rate and MX2 semiconductors provide an ideal way to spatially separate electrons and holes for electrical collection and utilization.”

    Wang and his colleagues are studying the microscopic origins of charge transfer in MX2 heterostructures and the variation in charge transfer rates between different MX2 materials.

    “We’re also interested in controlling the charge transfer process with external electrical fields as a means of utilizing MX2 heterostructures in photovoltaic devices,” Wang says.

    This research was supported by an Early Career Research Award from the DOE Office of Science through UC Berkeley, and by funding agencies in China through the Peking University in Beijing.

    See the full article here.

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  • richardmitnick 12:30 pm on August 22, 2014 Permalink | Reply
    Tags: , , Nanotechnology,   

    From Berkeley Lab: “Shaping the Future of Nanocrystals” 

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    Berkeley Lab

    August 21, 2014
    Lynn Yarris

    The first direct observations of how facets form and develop on platinum nanocubes point the way towards more sophisticated and effective nanocrystal design and reveal that a nearly 150 year-old scientific law describing crystal growth breaks down at the nanoscale.

    Researchers with the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab) used highly sophisticated transmission electron microscopes and an advanced high-resolution, fast-detection camera to capture the physical mechanisms that control the evolution of facets – flat faces – on the surfaces of platinum nanocubes formed in liquids. Understanding how facets develop on a nanocrystal is critical to controlling the crystal’s geometric shape, which in turn is critical to controlling the crystal’s chemical and electronic properties.

    “For years, predictions of the equilibrium shape of a nanocrystal have been based on the surface energy minimization proposal by Josiah Willard Gibbs in the 1870s to describe the equilibrium shape of a water droplet,” says Haimei Zheng, a staff scientist in Berkeley Lab’s Materials Sciences Division who led this study. “For nanocrystals, the idea is that during crystal growth, high-energy facets will grow at a higher rate than low-energy facets and eventually disappear, resulting in a nanocrystal whose shape is configured to minimize surface energy.”

    The research of Zheng and her collaborators showed that at the molecular level, the geometric shape of nanocrystals during synthesis in solution is actually driven by differences in the mobility of ligands across the surfaces of different facets.

    “By choosing ligands that selectively bind on the facets, we should be able to control the shape of the nanocrystal as it grows,” she says. “This would provide a new way to design nanomaterials for advanced applications, including nanostructures for bio-imaging, catalysts for solar conversion, and energy storage.”

    two
    Haimei Zheng and Hong-Gang Liao used TEMs at the National Center for Electron Microscopy and a K2-IS camera to record the first direct observations facet formation in platinum nanocubes. (Photo by Kelly Owen)

    Zheng is the corresponding author of a paper in Science titled Facet Development During Platinum Nanocube Growth. Hong-Gang Liao is the lead author. Co-authors are Danylo Zherebetskyy, Huolin Xin, Cory Czarnik, Peter Ercius, Hans Elmlund, Ming Pan and Lin-Wang Wang.

    The performance of nanocrystals in such surface-enhanced applications as catalysis, sensing and photo-optics is strongly influenced by shape. While significant advances have been made in the synthesis of nanocrystals featuring a variety of shapes – cube, octahedron, tetrahedron, decahedron, icosahedron, etc., – controlling these shapes is often difficult and unpredictable.

    “A major roadblock has been that the atomic pathways of facet development in nanocrystals are mostly unknown due to the lack of direct observation,” Zheng says. “It has been assumed that commonly used surfactants modify the energy of specific facets through preferential adsorption, thereby influencing the relative growth rate of different facets and the shape of the final nanocrystal. However, this assumption was based on post-reaction characterizations that did not account for how facet dynamics evolve during crystal growth.”

    As a crystal undergoes growth, its constituent atoms or molecules fan out along specific directional planes whose coordinates are denoted by a three-digit system called the Miller Index. Facets form when the surfaces along different planes grow at different rates. Three of the most critical facets for determining a crystal’s geometric shape are the so-called “low index facets,” which are designated under the Miller Index as {100}, {110} and {111}.

    image
    Berkeley Lab researchers found that differences in ligand mobility during crystallization cause the low index facets – {100}, {110} and {111} – to stop growing at different times, resulting in the crystal’s final cubic shape. (Image courtesy of Haimei Zheng group)

    Working with platinum, one of the most effective industrial catalysts in use today, Zheng and her collaborators initiated the growth of nanocubes in a thin layer of liquid sandwiched between two silicon nitride membranes. This microfabricated liquid cell can encapsulate and maintain the liquid inside the high vacuum of a transmission electron microscope (TEM) for an extended period of time, enabling in situ observations of single nanoparticle growth trajectories.

    “With the liquid cells, we’re able to use TEMs to observe the growth of nanocrystals that remarkably resemble nanocrystals synthesized in flasks,” Zheng says. “We found that the growth rates of all low index facets are similar until the {100} facets stop growing. The {110} facets will continue to grow until they reach two neighboring {100} facets, at which point they form the edge of a cube whose corners will be filled in by the continued growth of {111} facets. The arrested growth of the {100} facets that triggers this process is determined by ligand mobility on the {100} facets, which is much lower than on the {110} and {111} facets.”

    For their observations, Zeng and her collaborators were able to use several of the TEMs at Berkeley Lab’s National Center for Electron Microscopy (NCEM), a DOE Office of Science user facility, including the TEAM 0.5 instrument, the world’s most powerful TEM. In addition, they were able to use a K2-IS camera from Gatan, Inc., which can capture electron images directly onto a CMOS sensor at 400 frames per second (fps) with 2K-by-2K pixel resolution.

    “The K2-IS camera can also be configured to capture images at up to 1600 fps with appropriate scaling of the field of view, which is critical for observing particles that are moving dynamically in the field of view,” says lead author Liao, a member of Zheng’s research group. “The elimination of the traditional scintillation process during image detection results in significant improvement in both sensitivity and resolution. High resolution imaging is also facilitated by the thin silicon nitride membranes of our liquid cell window, which is about 10 nanometers thick per membrane.”

    The lower ligand mobility and arrested growth of selected facets experimentally observed by Zheng and Liao, were supported by ab initio calculations carried out under the leadership of co-author Wang, a senior scientist with the Materials Sciences Division who heads the Computational Material Science and Nano Science group.

    “At first, we thought the continued growth in the {111} direction might be a result of higher surface energy on the {111} plane,” says co-author Zherebetskyy, a member of Wang’s group. “The experimental observations forced us to consider alternative mechanisms and our calculations show that the relatively low energy barrier on the {111} plane allow the ligand molecules on that plane to be very mobile.”

    Says Wang, “Our collaboration with Haimei Zheng’s group showcases how ab initio calculations can be combined with experimental observations to shed new light on hidden molecular processes.”

    Zheng and her group are now in the process of determining whether the ligand mobility in platinum that shaped the formation of cube-shaped nanocrystals also applies to ligands in other nanomaterials and the formation of nanocrystals in other geometric shapes.

    This research was supported by the DOE Office of Science.

    See the full article here.

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  • richardmitnick 3:51 pm on August 13, 2014 Permalink | Reply
    Tags: , , Nanotechnology   

    From Livermore Lab: “It’s nanotubular: New material could be used for energy storage and conversion” 


    Lawrence Livermore National Laboratory

    08/13/2014
    Anne M Stark

    Lawrence Livermore researchers have made a material that is 10 times stronger and stiffer than traditional aerogels of the same density.

    This ultralow-density, ultrahigh surface area bulk material with an interconnected nanotubular makeup could be used in catalysis, energy storage and conversion, thermal insulation, shock energy absorption and high energy density physics.

    Ultralow-density porous bulk materials have recently attracted renewed interest due to many promising applications.

    Unlocking the full potential of these materials, however, requires realization of mechanically robust architectures with deterministic control over form, cell size, density and composition, which is difficult to achieve by traditional chemical synthesis methods, according to LLNL’s Monika Biener, lead author of a paper appearing on the cover of the July 23 issue of Advanced Materials.

    mag
    Lawrence Livermore National Laboratory researchers have made a material that is 10 times stronger and stiffer than traditional aerogels of the same density, which is detailed in a featured story appearing on the cover of Advanced Materials.

    Biener and colleagues report on the synthesis of ultralow-density, ultrahigh surface area bulk materials with interconnected nanotubular morphology. The team achieved control over density (5 to 400 mg/cm3), pore size (30 um to 4 um) and composition by atomic layer deposition (ALD) using nanoporous gold as a tunable template.

    “The materials are thermally stable and, by virtue of their narrow unimodal pore size distributions and their thin-walled, interconnected tubular architecture, about 10 times stronger and stiffer than traditional aerogels of the same density,” Biener said.

    The three-dimensional nanotubular network architecture developed by the team opens new opportunities in the fields of energy harvesting, catalysis, sensing and filtration by enabling mass transport through two independent pore systems separated by a nanometer-thick 3D membrane.

    Other Livermore authors include Jianchao Ye, Theodore Baumann, Y. Morris Wang, Swanee Shin, Juergen Biener and Alex Hamza.

    The paper titled Ultra-Strong and Low-Density Nanotubular Bulk Materials with Tunable Feature Size” can be found on the Web.

    See the full article here.

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