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  • richardmitnick 2:28 pm on February 15, 2018 Permalink | Reply
    Tags: , Cheaper, , Nano-Based Manufacturing, Nanotechnology, , Rutgers-Led Innovation Could Spur Faster   

    From Rutgers: “Rutgers-Led Innovation Could Spur Faster, Cheaper, Nano-Based Manufacturing” 

    Rutgers University
    Rutgers University

    February 13, 2018

    Todd B. Bates
    848-932-0550
    todd.bates@rutgers.edu

    1

    Spherical silver nanoparticles and nanowires after being fused by intense pulses of light.
    Image: Rajiv Malhotra/Rutgers University-New Brunswick

    Engineers at Rutgers University–New Brunswick and Oregon State University are developing a new method of processing nanomaterials that could lead to faster and cheaper manufacturing of flexible thin film devices – from touch screens to window coatings, according to a new study.

    The “intense pulsed light sintering” method uses high-energy light over an area nearly 7,000 times larger than a laser to fuse nanomaterials in seconds. Nanomaterials are materials characterized by their tiny size, measured in nanometers. A nanometer is one millionth of a millimeter, or about 100,000 times smaller than the diameter of a human hair.

    The existing method of pulsed light fusion uses temperatures of around 250 degrees Celsius (482 degrees Fahrenheit) to fuse silver nanospheres into structures that conduct electricity. But the new study, published in RSC Advances and led by Rutgers School of Engineering doctoral student Michael Dexter, showed that fusion at 150 degrees Celsius (302 degrees Fahrenheit) works well while retaining the conductivity of the fused silver nanomaterials.

    The engineers’ achievement started with silver nanomaterials of different shapes: long, thin rods called nanowires in addition to nanospheres. The sharp reduction in temperature needed for fusion makes it possible to use low-cost, temperature-sensitive plastic substrates like polyethylene terephthalate (PET) and polycarbonate in flexible devices, without damaging them.

    “Pulsed light sintering of nanomaterials enables really fast manufacturing of flexible devices for economies of scale,” said Rajiv Malhotra, the study’s senior author and assistant professor in the Department of Mechanical and Aerospace Engineering at Rutgers–New Brunswick. “Our innovation extends this capability by allowing cheaper temperature-sensitive substrates to be used.”

    2
    Fusing, or sintering, nanoparticles by exposing them to pulses of intense light from a xenon lamp.
    Image: Rajiv Malhotra/Rutgers University-New Brunswick

    Fused silver nanomaterials are used to conduct electricity in devices such as radio-frequency identification (RFID) tags, display devices and solar cells. Flexible forms of these products rely on fusion of conductive nanomaterials on flexible substrates, or platforms, such as plastics and other polymers.

    “The next step is to see whether other nanomaterial shapes, including flat flakes and triangles, will drive fusion temperatures even lower,” Malhotra said.

    In another study, published in Scientific Reports, the Rutgers and Oregon State engineers demonstrated pulsed light sintering of copper sulfide nanoparticles, a semiconductor, to make films less than 100 nanometers thick.

    “We were able to perform this fusion in two to seven seconds compared with the minutes to hours it normally takes now,” said Malhotra, the study’s senior author. “We also showed how to use the pulsed light fusion process to control the electrical and optical properties of the film.”

    Their discovery could speed up the manufacturing of copper sulfide thin films used in window coatings that control solar infrared light, transistors and switches, according to the study. This work was funded by the National Science Foundation and The Walmart Manufacturing Innovation Foundation.

    See the full article here .

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  • richardmitnick 2:34 pm on February 14, 2018 Permalink | Reply
    Tags: , Getting to the heart of carbon nanotube clusters, , Nanotechnology   

    From MIT: “Getting to the heart of carbon nanotube clusters” 

    MIT News

    MIT Widget

    MIT News

    February 14, 2018
    Denis Paiste

    1
    A recolored optical image obtained by MIT researchers shows a heart-shaped carbon nanotube cell. A version of the image is featured on the cover of the Feb. 14 print edition of Physical Chemistry Chemical Physics. Image: Ashley Kaiser and Itai Stein/MIT

    2
    Aligned carbon nanotubes (CNTs) grown by chemical vapor deposition are typically wavy, as seen in side view at center of illustration, rather than straight, as illustrated in a single nanotube at right. They also settle into somewhat random patterns, as shown in box at upper left. Waviness reduces the stiffness of CNT arrays by up to 100,000 times, but their stiffness can be increased by densifying, or compressing, the nanotube clusters from two different directions. Image: Itai Stein/MIT

    3
    A scanning electron microscope image shows that heat-treated aligned carbon nanotubes self-assemble into cells with clearly defined cell walls when they are densified by applying and evaporating a few drops of liquid acetone or ethanol. MIT researchers have developed a systematic method to predict the geometry of the two-dimensional cellular patterns that these nanotubes will form. Bright lines represent top edges of cell walls, while darker portions represent nanotubes closer to the silicon substrate base, which is seen in the flat spaces between cell walls. Image: Ashley Kaiser/MIT

    February 14, 2018
    Denis Paiste

    Integrating nanoscale fibers such as carbon nanotubes (CNTs) into commercial applications, from coatings for aircraft wings to heat sinks for mobile computing, requires them to be produced in large scale and at low cost. Chemical vapor deposition (CVD) is a promising approach to manufacture CNTs in the needed scales, but it produces CNTs that are too sparse and compliant for most applications.

    Applying and evaporating a few drops of a liquid such as acetone to the CNTs is an easy, cost-effective method to more tightly pack them together and increase their stiffness, but until now, there was no way to forecast the geometry of these CNT cells.

    MIT researchers have now developed a systematic method to predict the two-dimensional patterns CNT arrays form after they are packed together, or densified, by evaporating drops of either acetone or ethanol. CNT cell size and wall stiffness grow proportionally with cell height, they report in the Feb. 14 issue of Physical Chemistry Chemical Physics.

    One way to think of this CNT behavior is to imagine how entangled fibers such as wet hair or spaghetti collectively reinforce each other. The larger this entangled region is, the higher its resistance to bending will be. Similarly, longer CNTs can better reinforce one another in a cell wall. The researchers also find that CNT binding strength to the base on which they are produced, in this case, silicon, makes an important contribution to predicting the cellular patterns that these CNTs will form.

    “These findings are directly applicable to industry because when you use CVD, you get nanotubes that have curvature, randomness, and are wavy, and there is a great need for a method that can easily mitigate these defects without breaking the bank,” says Itai Stein SM ’13, PhD ’16, who is a postdoc in the Department of Aeronautics and Astronautics. Co-authors include materials science and engineering graduate student Ashley Kaiser, mechanical engineering postdoc Kehang Cui, and senior author Brian Wardle, professor of aeronautics and astronautics.

    “From our previous work on aligned carbon nanotubes and their composites, we learned that more tightly packing the CNTs is a highly effective way to engineer their properties,” says Wardle. “The challenging part is to develop a facile way of doing this at scales that are relevant to commercial aircraft (hundreds of meters), and the predictive capabilities that we developed here are a large step in that direction.”

    Detailed measurements

    Carbon nanotubes are highly desirable because of their thermal, electrical, and mechanical properties, which are directionally dependent. Earlier work in Wardle’s lab demonstrated that waviness reduces the stiffness of CNT arrays by as little as 100 times, and up to 100,000 times. The technical term for this stiffness, or ability to bend without breaking, is elastic modulus. Carbon nanotubes are from 1,000 to 10,000 times longer than they are thick, so they deform principally along their length.

    For an earlier paper published in the journal Applied Physics Letters, Stein and colleagues used nanoindentation techniques to measure stiffness of aligned carbon nanotube arrays and found their stiffness to be 1/1,000 to 1/10,000 times less than the theoretical stiffness of individual carbon nanotubes. Stein, Wardle, and former visiting MIT graduate student Hülya Cebeci also developed a theoretical model explaining changes at different packing densities of the nanofibers.

    The new work shows that CNTs compacted by the capillary forces from first wetting them with acetone or ethanol and then evaporating the liquid also produces CNTs that are hundreds to thousands of times less stiff than expected by theoretical values. This capillary effect, known as elastocapillarity, is similar to a how a sponge often dries into a more compact shape after being wetted and then dried.

    “Our findings all point to the fact that the CNT wall modulus is much lower than the normally assumed value for perfect CNTs because the underlying CNTs are not straight,” says Stein. “Our calculations show that the CNT wall is at least two orders of magnitude less stiff than we expect for straight CNTs, so we can conclude that the CNTs must be wavy.”

    Heat adds strength

    The researchers used a heating technique to increase the adhesion of their original, undensified CNT arrays to their silicon wafer substrate. CNTs densified after heat treatment were about four times harder to separate from the silicon base than untreated CNTs. Kaiser and Stein, who share first authorship of the paper, are currently developing an analytical model to describe this phenomenon and tune the adhesion force, which would further enable prediction and control of such structures.

    “Many applications of vertically aligned carbon nanotubes [VACNTs], such as electrical interconnects, require much denser arrays of nanotubes than what is typically obtained for as-grown VACNTs synthesized by chemical vapor deposition,” says Mostafa Bedewy, assistant professor at the University of Pittsburgh, who was not involved in this work. “Hence, methods for postgrowth densification, such as those based on leveraging elastocapillarity have previously been shown to create interesting densified CNT structures. However, there is still a need for a better quantitative understanding of the factors that govern cell formation in densified large-area arrays of VACNTs. The new study by the authors contributes to addressing this need by providing experimental results, coupled with modeling insights, correlating parameters such as VACNT height and VACNT-substrate adhesion to the resulting cellular morphology after densification.

    “There are still remaining questions about how the spatial variation of CNT density, tortuosity [twist], and diameter distribution across the VACNT height affects the capillary densification process, especially since vertical gradients of these features can be different when comparing two VACNT arrays having different heights,” says Bedewy. “Further work incorporating spatial mapping of internal VACNT morphology would be illuminating, although it will be challenging as it requires combining a suite of characterization techniques.”

    Picturesque patterns

    Kaiser, who was a 2016 MIT Summer Scholar, analyzed the densified CNT arrays with scanning electron microscopy (SEM) in the MIT Materials Research Laboratory’s NSF-MRSEC-supported Shared Experimental Facilities. While gently applying liquid to the CNT arrays in this study caused them to densify into predictable cells, vigorously immersing the CNTs in liquid imparts much stronger forces to them, forming randomly shaped CNT networks. “When we first started exploring densification methods, I found that this forceful technique densified our CNT arrays into highly unpredictable and interesting patterns,” says Kaiser. “As seen optically and via SEM, these patterns often resembled animals, faces, and even a heart — it was a bit like searching for shapes in the clouds.” A colorized version of her optical image showing a CNT heart is featured on the cover of the Feb. 14 print edition of Physical Chemistry Chemical Physics.

    “I think there is an underlying beauty in this nanofiber self-assembly and densification process, in addition to its practical applications,” Kaiser adds. “The CNTs densify so easily and quickly into patterns after simply being wet by a liquid. Being able to accurately quantify this behavior is exciting, as it may enable the design and manufacture of scalable nanomaterials.”

    This work made use of the MIT Materials Research Laboratory Shared Experimental Facilities, which are supported in part by the MRSEC Program of the National Science Foundation, and MIT Microsystems Technology Laboratories. This research was supported in part by Airbus, ANSYS, Embraer, Lockheed Martin, Saab AB, Saertex, and Toho Tenax through MIT’s Nano-Engineered Composite Aerospace Structures Consortium and by NASA through the Institute for Ultra-Strong Composites by Computational Design.

    See the full article here .

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  • richardmitnick 8:42 am on February 13, 2018 Permalink | Reply
    Tags: , Hybrid optics bring color imaging using ultrathin metalenses into focus, Nanotechnology, ,   

    From University of Washington: “Hybrid optics bring color imaging using ultrathin metalenses into focus” 

    U Washington

    University of Washington

    February 12, 2018
    James Urton

    1
    Alan Zhan (left), Arka Majumdar (center) and Shane Colburn (right).Mark Stone/University of Washington

    For photographers and scientists, lenses are lifesavers. They reflect and refract light, making possible the imaging systems that drive discovery through the microscope and preserve history through cameras.

    But today’s glass-based lenses are bulky and resist miniaturization. Next-generation technologies, such as ultrathin cameras or tiny microscopes, require lenses made of a new array of materials.

    2
    A portion of the team’s experimental setup for capturing an image using a metalens. The researchers capture an image of flowers through a metalens (mounted on a microscope slide) and visualize it through a microscope.Matt Hagen/UW Clean Energy Institute.

    In a paper published Feb. 9 in Science Advances, scientists at the University of Washington announced that they have successfully combined two different imaging methods — a type of lens designed for nanoscale interaction with lightwaves, along with robust computational processing — to create full-color images.

    The team’s ultrathin lens is part of a class of engineered objects known as metasurfaces. Metasurfaces are 2-D analogs of metamaterials, which are manufactured materials with physical and chemical properties not normally found in nature. A metasurface-based lens — or metalens — consists of flat microscopically patterned material surfaces designed to interact with lightwaves. To date, images taken with metalenses yield clear images — at best — for only small slices of the visual spectrum. But the UW team’s metalens — in conjunction with computational filtering — yields full-color images with very low levels of aberrations across the visual spectrum.

    “Our approach combines the best aspects of metalenses with computational imaging — enabling us, for the first time, to produce full-color images with high efficiency,” said senior author Arka Majumdar, a UW assistant professor of physics and electrical engineering.

    3
    The UW team’s metalens consists of arrays of tiny pillars of silicon nitride on glass which affect how light interacts with the surface. Depending on the size and arrangement of these pillars, microscopic lenses with different properties can be designed. A traditional metalens (top) exhibits shifts in focal length for different wavelengths of light, producing images with severe color blur. The UW team’s modified metalens design (bottom), however, interacts with different wavelengths in the same manner, generating uniformly blurry images which enable simple and fast software correction to recover sharp and in-focus images.Shane Colburn/Alan Zhan/Arka Majumdar

    Instead of manufactured glass or silicone, metalenses consist of repeated arrays of nanometer-scale structures, such as columns or fins. If properly laid out at these minuscule scales, these structures can interact with individual lightwaves with precision that traditional lenses cannot. Since metalenses are also so small and thin, they take up much less room than the bulky lenses of cameras and high-resolution microscopes. Metalenses are manufactured by the same type of semiconductor fabrication process that is used to make computer chips.

    “Metalenses are potentially valuable tools in optical imaging since they can be designed and constructed to perform well for a given wavelength of light,” said lead author Shane Colburn, a UW doctoral student in electrical engineering. “But that has also been their drawback: Each type of metalens only works best within a narrow wavelength range.”

    In experiments producing images with metalenses, the optimal wavelength range so far has been very narrow: at best around 60 nanometers wide with high efficiency. But the visual spectrum is 300 nanometers wide.

    Today’s metalenses typically produce accurate images within their narrow optimal range — such as an all-green image or an all-red image. For scenes that include colors outside of that optimal range, the images appear blurry, with poor resolution and other defects known as “chromatic aberrations.” For a rose in a blue vase, a red-optimized metalens might pick up the rose’s red petals with few aberrations, but the green stem and blue vase would be unresolved blotches — with high levels of chromatic aberrations.

    4
    The UW team’s metalens, coupled with computational processing, can capture images for a variety of light wavelengths with very low levels of chromatic aberrations. For this black-and-white image of the Mona Lisa (at top), the first row shows how well a green-optimized metalens captures the image for green light, but causes severe blurring for blue and red wavelengths. The UW team’s improved metalens (second row) captures images with similar types of aberrations for blue, green and red wavelengths, showing uniform blurring across wavelengths. But computational filtering removes most of these aberrations, as shown in the bottom row, which is a substantial improvement over a traditional metalens (first row), which is only in focus for green light and is unintelligible for blue and red.Shane Colburn/Alan Zhan/Arka Majumdar

    Majumdar and his team hypothesized that, if a single metalens could produce a consistent type of visual aberration in an image across all visible wavelengths, then they could resolve the aberrations for all wavelengths afterward using computational filtering algorithms. For the rose in the blue vase, this type of metalens would capture an image of the red rose, blue vase and green stem all with similar types of chromatic aberrations, which could be tackled later using computational filtering.

    They engineered and constructed a metalens whose surface was covered by tiny, nanometers-wide columns of silicon nitride. These columns were small enough to diffract light across the entire visual spectrum, which encompasses wavelengths ranging from 400 to 700 nanometers.

    Critically, the researchers designed the arrangement and size of the silicon nitride columns in the metalens so that it would exhibit a “spectrally invariant point spread function.” Essentially, this feature ensures that — for the entire visual spectrum — the image would contain aberrations that can be described by the same type of mathematical formula. Since this formula would be the same regardless of the wavelength of light, the researchers could apply the same type of computational processing to “correct” the aberrations.

    They then built a prototype metalens based on their design and tested how well the metalens performed when coupled with computational processing. One standard measure of image quality is “structural similarity” — a metric that describes how well two images of the same scene share luminosity, structure and contrast. The higher the chromatic aberrations in one image, the lower the structural similarity it will have with the other image. The UW team found that when they used a conventional metalens, they achieved a structural similarity of 74.8 percent when comparing red and blue images of the same pattern; however, when using their new metalens design and computational processing, the structural similarity rose to 95.6 percent. Yet the total thickness of their imaging system is 200 micrometers, which is about 2,000 times thinner than current cellphone cameras.

    “This is a substantial improvement in metalens performance for full-color imaging — particularly for eliminating chromatic aberrations,” said co-author Alan Zhan, a UW doctoral student in physics.

    5
    For the color image of flower buds at the far-left, a traditional metalens (second from left) captures images with strong chromatic aberrations and blurring. The UW team’s modified metalens (third from left) yields an image with similar levels of blurring for all colors. But the team removes most of these aberrations using computational filtering, producing an image (right) with high structural similarity to the original.Shane Colburn/Alan Zhan/Arka Majumdar

    In addition, unlike many other metasurface-based imaging systems, the UW team’s approach isn’t affected by the polarization state of light — which refers to the orientation of the electric field in the 3-D space that lightwaves are traveling in.

    The team said that its method should serve as a road map toward making a metalens — and designing additional computational processing steps — that can capture light more effectively, as well as sharpen contrast and improve resolution. That may bring tiny, next-generation imaging systems within reach.

    The research was funded by the UW, an Intel Early Career Faculty Award and an Amazon Catalyst Award.

    For more information, contact Majumdar at arka@uw.edu or 206-616-5558.

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  • richardmitnick 2:02 pm on February 6, 2018 Permalink | Reply
    Tags: , Atomic Flaws Create Surprising, , , , High-Efficiency UV LED Materials, Nanotechnology   

    From BNL: “Atomic Flaws Create Surprising, High-Efficiency UV LED Materials” 

    Brookhaven Lab

    February 6, 2018
    Peter Genzer
    genzer@bnl.gov
    (631) 344-3174

    Written by Justin Eure

    1
    The research team, front to back and left to right: Danhua Yan, Mingzhao Liu, Klaus Attenkoffer, Jiajie Cen, Dario Stacciola, Wenrui Zhang, Jerzy Sadowski, Eli Stavitski

    Light-emitting diodes (LEDs) traditionally demand atomic perfection to optimize efficiency. On the nanoscale, where structures span just billionths of a meter, defects should be avoided at all costs—until now.

    A team of scientists from the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory and Stony Brook University has discovered that subtle imperfections can dramatically increase the efficiency and ultraviolet (UV) light output of certain LED materials.

    “The results are surprising and completely counterintuitive,” said Brookhaven Lab scientist Mingzhao Liu, the senior author on the study. “These almost imperceptible flaws, which turned out to be missing oxygen in the surface of zinc oxide nanowires, actually enhance performance. This revelation may inspire new nanomaterial designs far beyond LEDs that would otherwise have been reflexively dismissed.”

    The results, published online Dec. 5, 2017, in Applied Physics Letters, help bring these zinc oxide structures one step closer to use as a UV source in practical applications, including medical sensors, catalysts, and even household lighting.

    “The current LED standard for UV light is gallium nitride, which functions beautifully but is both expensive and is far from being environmentally friendly,” said Brookhaven scientist and study coauthor Dario Stacchiola. “This ‘imperfect’ zinc oxide overcomes those issues.”

    The scientists leveraged the singular instrumentation and expertise available at Brookhaven Lab’s Center for Functional Nanomaterials (CFN) and National Synchrotron Light Source II (NSLS-II), both DOE Office of Science User Facilities.

    BNL Center for Functional Nanomaterials interior

    BNL NSLS-II

    “Having the capability of exploring materials from synthesis to complex characterization is a unique advantage of Brookhaven Lab,” Stacchiola said. “In fact, the puzzle of zinc-oxide nanowire emission efficiency could only be solved when new instruments came online at NSLS-II.”

    2
    The scientists used a low-temperature approach to grow this nanowire array composed of zinc-oxide crystals. On average, the nanowires have a diameter of 40–50 nanometers (nm) and a length of 500 nm. No image credit.

    Light born on the edge

    The high-performing LEDs exploit a phenomenon called near band edge (NBE) photoluminescence found in semiconducting materials.

    “When electrons in the conduction band recombine with holes in the valence band—crossing the edge of the so-called band gap—they can emit light,” Liu said. “Optimizing that effect, specifically for UV radiation, was our primary goal.”

    The scientists used a relatively simple low-temperature solution-based approach to grow nanowires composed of zinc-oxide crystals. They then applied oxygen plasma to clean the final nanowire structures.

    “By chance, during one test, we executed this plasma step under much lower pressure than usual—and the results were serendipitous and shocking,” Liu said. “That low-pressure plasma treatment is the real game changer here.”

    The unexpected NBE emissions have puzzled scientists for years, but the investigative tools finally advanced enough to shed light on the mystery.

    Bright lights and next-gen nanotechnology

    The key for the breakthrough came through strong synergy between two beamlines at NSLS-II. Data from beamline 8-ID—one of the most intense x-ray absorption sources in the world—combined with the first set of results from a new, state-of-the-art x-ray photoemission electron microscopy (XPEEM) endstation at beamline 21-ID-2. The XPEEM endstation is run as a partnership between CFN and NSLS-II.

    Beamline 8-ID revealed the amount of x-ray absorption, which was then used to deduce the oxidative state of the samples. The measurements at beamline 21-ID-2 complemented that work, bombarding the sample with x-rays to excite electrons and emit photons according to the band levels of the sample. By analyzing that energy, the band positions—and their role in light emission—could be determined with high precision.

    “We found that surface oxygen vacancies create dipoles that confine charge carriers to the core of the nanowire,” said study coauthor and NSLS-II scientist Klaus Attenkofer. “These vacancies appear to drive the highly efficient and pure light emission. And because we know exactly what distinguishes this zinc-oxide structure, we know how to build on it and explore similar materials.”

    The new synthesis technique enables additional structures, such as high-quality, titanium oxide layers, which could be ideal for photocatalysts. Such a material could efficiently act as a water-splitter, providing hydrogen fuel for a host of renewable energy technologies. Future experiments will explore this possibility and even watch the catalytic reactions unfold in real time.

    “The strong synergy between CFN and NSLS-II makes Brookhaven Lab a unique place to do nanomaterials research,” said Chuck Black, the director of the CFN. “Working closely together, the two facilities are developing and offering new research capabilities for the benefit of researchers worldwide. These forefront tools are critical for accelerating nanoscience research, which will enable the advanced materials of tomorrow.”

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  • richardmitnick 10:30 am on January 11, 2018 Permalink | Reply
    Tags: , , , Extremely bright and fast light emission, , Nanotechnology,   

    From ETH: “Extremely bright and fast light emission” 

    ETH Zürich bloc

    ETH Zürich

    11.01.2018
    Fabio Bergamin

    A type of quantum dot that has been intensively studied in recent years can reproduce light in every colour and is very bright. An international research team that includes scientists from ETH Zürich has now discovered why this is the case. The quantum dots could someday be used in light-emitting diodes.

    1
    A caesium lead bromide nanocrystal under the electron microscope (crystal width: 14 nanometres). Individual atoms are visible as points. (Photograph: ETH Zürich / Empa / Maksym Kovalenko)

    An international team of researchers from ETH Zürich, IBM Research Zürich, Empa and four American research institutions have found the explanation for why a class of nanocrystals that has been intensively studied in recent years shines in such incredibly bright colours. The nanocrystals contain caesium lead halide compounds that are arranged in a perovskite lattice structure.

    Three years ago, Maksym Kovalenko, a professor at ETH Zürich and Empa, succeeded in creating nanocrystals – or quantum dots, as they are also known – from this semiconductor material. “These tiny crystals have proved to be extremely bright and fast emitting light sources, brighter and faster than any other type of quantum dot studied so far,” says Kovalenko. By varying the composition of the chemical elements and the size of the nanoparticles, he also succeeded in producing a variety of nanocrystals that light up in the colours of the whole visible spectrum. These quantum dots are thus also being treated as components for future light-emitting diodes and displays.

    In a study published in the most recent edition of the scientific journal Nature, the international research team examined these nanocrystals individually and in great detail. The scientists were able to confirm that the nanocrystals emit light extremely quickly. Previously-studied quantum dots typically emit light around 20 nanoseconds after being excited when at room temperature, which is already very quick. “However, caesium lead halide quantum dots emit light at room temperature after just one nanosecond,” explains Michael Becker, first author of the study. He is a doctoral student at ETH Zürich and is carrying out his doctoral project at IBM Research.

    2
    A sample with several green glowing perovskite quantum dots excited by a blue laser. (Photograph: IBM Research / Thilo Stöferle)

    Electron-hole pair in an excited energy state

    Understanding why caesium lead halide quantum dots are not only fast but also very bright entails diving into the world of individual atoms, light particles (photons) and electrons. “You can use a photon to excite semiconductor nanocrystals so that an electron leaves its original place in the crystal lattice, leaving behind a hole,” explains David Norris, Professor of Materials Engineering at ETH Zürich. The result is an electron-hole pair in an excited energy state. If the electron-hole pair reverts to its energy ground state, light is emitted.

    Under certain conditions, different excited energy states are possible; in many materials, the most likely of these states is called a dark one. “In such a dark state, the electron hole pair cannot revert to its energy ground state immediately and therefore the light emission is suppressed and occurs delayed. This limits the brightness”, says Rainer Mahrt, a scientist at IBM Research.

    No dark state

    The researchers were able to show that the caesium lead halide quantum dots differ from other quantum dots: their most likely excited energy state is not a dark state. Excited electron-hole pairs are much more likely to find themselves in a state in which they can emit light immediately. “This is the reason that they shine so brightly,” says Norris.

    The researchers came to this conclusion using their new experimental data and with the help of theoretical work led by Alexander Efros, a theoretical physicist at the Naval Research Laboratory in Washington. He is a pioneer in quantum dot research and, 35 years ago, was among the first scientists to explain how traditional semiconductor quantum dots function.

    Great news for data transmission

    As the examined caesium lead halide quantum dots are not only bright but also inexpensive to produce they could be applied in television displays, with efforts being undertaken by several companies, in Switzerland and world-wide. “Also, as these quantum dots can rapidly emit photons, they are of particular interest for use in optical communication within data centres and supercomputers, where fast, small and efficient components are central,” says Mahrt. Another future application could be the optical simulation of quantum systems which is of great importance to fundamental research and materials science.

    ETH professor Norris is also interested in using the new knowledge for the development of new materials. “As we now understand why these quantum dots are so bright, we can also think about engineering other materials with similar or even better properties,” he says.

    Science team:
    Becker MA, Vaxenburg R, Nedelcu G, Sercel PC, Shabaev A, Mehl MJ, Michopoulos JG, Lambrakos SG, Bernstein N, Lyons JL, Stöferle T, Mahrt RF, Kovalenko MV, Norris DJ, Rainò G, Efros AL.

    See the full article here .

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    ETH Zürich campus
    ETH Zürich is one of the leading international universities for technology and the natural sciences. It is well known for its excellent education, ground-breaking fundamental research and for implementing its results directly into practice.

    Founded in 1855, ETH Zürich today has more than 18,500 students from over 110 countries, including 4,000 doctoral students. To researchers, it offers an inspiring working environment, to students, a comprehensive education.

    Twenty-one Nobel Laureates have studied, taught or conducted research at ETH Zürich, underlining the excellent reputation of the university.

     
  • richardmitnick 11:59 am on January 7, 2018 Permalink | Reply
    Tags: , , Nanoscale silicon posts can reflect light differently depending on the angle of incoming light, Nanotechnology, , Two Holograms in One Surface   

    From Caltech: “Two Holograms in One Surface” 

    Caltech Logo

    Caltech

    12/11/2017

    Robert Perkins
    (626) 395-1862
    rperkins@caltech.edu

    1
    (Artist’s rendering) In a proof-of-concept, Faraon’s team encoded two holograms (of the Caltech logo and the LMI logo) on a single silicon oxide and aluminum surface. Credit: Andrei Faraon/Caltech

    2
    Nanoposts of varying shapes can act as pixels in two different holograms.
    Credit: Andrei Faraon/Caltech

    Nanoscale silicon posts can reflect light differently depending on the angle of incoming light.

    A team at Caltech has figured out a way to encode more than one holographic image in a single surface without any loss of resolution. The engineering feat overturns a long-held assumption that a single surface could only project a single image regardless of the angle of illumination.

    The technology hinges on the ability of a carefully engineered surface to reflect light differently depending on the angle at which incoming light strikes that surface.

    Holograms are three-dimensional images encoded in two-dimensional surfaces. When the surface is illuminated with a laser, the image seems to pop off the surface and becomes visible. Traditionally, the angle at which laser light strikes the surface has been irrelevant—the same image will be visible regardless. That means that no matter how you illuminate the surface, you will only create one hologram.

    Led by Andrei Faraon, assistant professor of applied physics and materials science in the Division of Engineering and Applied Science, the team developed silicon oxide and aluminum surfaces studded with tens of millions of tiny silicon posts, each just hundreds of nanometers tall. (For scale, a strand of human hair is 100,000 nanometers wide.) Each nanopost reflects light differently due to variations in its shape and size, and based on the angle of incoming light.

    That last property allows each post to act as a pixel in more than one image: for example, acting as a black pixel if incoming light strikes the surface at 0 degrees and a white pixel if incoming light strikes the surface at 30 degrees.

    “Each post can do double duty. This is how we’re able to have more than one image encoded in the same surface with no loss of resolution,” says Faraon (BS ’04), senior author of a paper on the new material published by Physical Review X on December 7.

    “Previous attempts to encode two images on a single surface meant arranging pixels for one image side by side with pixels for another image. This is the first time that we’re aware of that all of the pixels on a surface have been available for each image,” he says.

    As a proof of concept, Faraon and Caltech graduate student Seyedeh Mahsa Kamali (MS ’17) designed and built a surface that when illuminated with a laser straight on (thus, at 0 degrees) projects a hologram of the Caltech logo but when illuminated from an angle of 30 degrees projects a hologram of the logo of the Department of Energy-funded Light-Material Interactions in Energy Conversion Energy Frontier Research Center, of which Faraon is a principal investigator.

    The process was labor intensive. “We created a library of nanoposts with information about how each shape reflects light at different angles. Based on that, we assembled the two images simultaneously, pixel by pixel,” says Kamali, the first author of the Physical Review X paper.

    Theoretically, it would even be possible to encode three or more images on a single surface—though there will be fundamental and practical limits at a certain point. For example, Kamali says that a single degree of difference in the angle of incident light probably cannot be enough to create a new high-quality image. “We are still exploring just how far this technology can go,” she says.

    Practical applications for the technology include improvements to virtual-reality and augmented-reality headsets. “We’re still a long way from seeing this on the market, but it is an important demonstration of what is possible,” Faraon says.

    See the full article here .

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    The California Institute of Technology (commonly referred to as Caltech) is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering. Its 124-acre (50 ha) primary campus is located approximately 11 mi (18 km) northeast of downtown Los Angeles. “The mission of the California Institute of Technology is to expand human knowledge and benefit society through research integrated with education. We investigate the most challenging, fundamental problems in science and technology in a singularly collegial, interdisciplinary atmosphere, while educating outstanding students to become creative members of society.”

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  • richardmitnick 5:00 pm on January 3, 2018 Permalink | Reply
    Tags: , Bottom-up nanofabrication or molecular self-assembly, Center for Functional Nanomaterials(CFN), Directed self-assembly - combining the two approaches, Gregory Doerk at CFN, Lithography is generally faster–and more reliably produces the designed structures–but requires expensive complex tools, , Nanotechnology, , , Self-assembly is often slower and less predictive but it is inexpensive and can be easier, Top-down nanofabrication, X-ray scattering experiments,   

    From BNL- “CFN Scientist Spotlight: Gregory Doerk Guides the Self-Assembly of Materials to Make Diverse Nanoscale Patterns” 

    Brookhaven Lab

    December 7, 2017 [They just now put this up n social media.]
    Interview with a CFN scientist

    1
    Materials scientist Gregory Doerk in the materials processing lab at CFN.

    Some materials have the unique ability to self-assemble into organized molecular patterns and structures. Materials scientist Gregory Doerk of the Electronic Nanomaterials Group at the Center for Functional Nanomaterials (CFN)—a U.S. Department of Energy (DOE) Office of Science User Facility at Brookhaven National Laboratory—takes advantage of this ability in materials called block copolymers. Using these self-assembling materials, which have chains of two or more distinct molecules linked together by chemical bonds, Doerk directs the formation of such patterns and structures at the nanoscale. The ultimate goal is to leverage these nanoscale architectures to control the properties of materials for applications including solar energy conversion and storage, catalysis, and optics.

    Self-assembly has gained a lot of attention recently as a nanofabrication approach. How does it differ from the approach that has been traditionally used?

    Broadly speaking, there are two platforms for nanofabrication. One platform is top-down nanofabrication, which is the traditional approach used to make computer chips and other microelectronics. Light is used to create patterns that are then carved into silicon wafers. The patterning technique using light is called optical lithography. The other approach is bottom-up nanofabrication, or molecular self-assembly. The properties of the materials are encoded in their weak interactions, which drive certain materials to come together and form specific configurations—kind of like Lego bricks but the bricks all build up on their own to form some structure.

    Lithography is generally faster–and more reliably produces the designed structures–but requires expensive, complex tools. Self-assembly is often slower and less predictive but it is inexpensive and can be easier. There are ways of combining the two approaches, and that combination is known as directed self-assembly. Self-assembling materials such as thin films of block copolymers are ordered using templates patterned by standard lithography. Directed self-assembly enhances current manufacturing processes, expanding the spectrum of pattern geometries that are possible, and lowers the cost of nanofabrication.

    Your self-assembly research is focused on block copolymers. What makes these materials so special?

    3
    The length of the polymer blocks (red and blue squiggly lines) and the strength of their interaction determine the shape of the resulting patterns in block copolymer self-assembly: (from left to right) spheres, cylinders, and lamellae (sheets).

    Since the 1950s, people have been using triblock copolymers (three polymers joined together) in materials like synthetic rubber. Most polymers will not mix. Trying to mix polymers is kind of like trying to mix oil and water.

    But in block copolymers, the polymer chains are chemically bound to each other. For example, diblock (two) copolymer chains are joined through a covalent bond. This bonding frustrates their drive to “demix.” Instead, if block copolymers are given energy to mobilize their chains—for example by annealing (heating) the polymer film on a hot plate to above its glass transition temperature (when a polymer transitions from a hard, glassy material to a soft, rubbery one)—the chains will reconfigure and assemble into nanoscale phase-separated domains. These domains are ordered into nanoscale patterns based on inherent traits of the block copolymer. For example, let us say we have two polymers, A and B, joined together (diblock copolymer). The length of block A relative to the length of both blocks, the overall length of the polymer chains, and the properties of the polymers and the strength of their interaction (how much the polymers want to pull apart) govern the size and morphology, or shape, of the resulting structures. If the chains are too short or their repulsive interactions are too weak, the polymers will mix, causing the ordered state to become a disordered state and thus no pattern will form.

    At CFN, a major part of our work is to transfer the patterns and structures made through self-assembly, electron-beam lithography, or optical lithography at our Nanofabrication Facility into other materials to control material properties. A great example of this is CFN Director Chuck Black’s work using block copolymers to create a self-assembled pattern that serves as a template for etching nanosized cones onto silicon surfaces. With these nanotextures, the silicon surfaces transformed from reflective mirrors to entirely black. That is one way we can use block copolymers.

    But we want to expand the range of things we can do with self-assembly—and thus the range of applications. Diversifying the patterns possible with block copolymer self-assembly is a big part of my research.

    Have you been able to expand this range?

    One way I am interested in expanding what we can do through self-assembly is by creating inorganic replicas of the self-assembled structures. We can accomplish this replication through a process called infiltration synthesis.

    4
    Plan view (top) and cross-sectional (bottom) scanning electron microscope images of an inorganic nanomesh created through iterative self-assembly and infiltration synthesis.

    For example, say you have a block copolymer that forms lamellae (stripes) perpendicular to a substrate. Using an atomic-layer-deposition tool, it is possible to infiltrate those lamellae with a metal oxide and then remove the polymer, leaving behind metal oxide lines in a pattern determined by the polymer self-assembly. It is even possible to perform self-assembly and replica formation on top of previous replicas in an iterative way. What is really interesting is that the topography from the initial layer actually acts as a template dictating how polymer domains in the next layer line up. In the case of a second layer of lamellae perpendicular with the substrate, a self-assembled nanomesh is naturally created.

    What other ways can you expand the range of self-assembled patterns?

    One area in which I have collaborated with other members of the Electronic Nanomaterials Group is to study the blending of block copolymers that form lamellae with block copolymers that form cylinders. The really cool thing we learned is that you can precisely control which of these two patterns emerge in different areas of a substrate through an approach we call selective directed self-assembly. In a diblock copolymer, one of the blocks may be relatively more hydrophobic (water repelling) and the other may be relatively more hydrophilic (water attracting). So if a chemical pattern was made up of alternating hydrophobic and hydrophilic lines, the block copolymer molecules would self-assemble accordingly. By changing the spacing and width of the chemical line gratings (patterns) on the substrate, we were able to direct the self-assembling blocks into specific arrangements—either forming striped patterns (lamellae) or hexagonal dot arrays (cylinders). We can locally adjust the spacing and linewidth of the underlying chemical template to precisely control exactly where these line or dot patterns form on the same substrate, too.

    How big are the features of these self-assembled nanoscale patterns?

    Block copolymers typically self-assemble into ordered periodic structures with a tunable repeat spacing between around 25 to 50 nanometers. Actually, one of the projects I am currently working on is to increase the size range over which block copolymers form patterns. There is a lot of work in the scientific community to go to smaller and smaller sizes (approaching a few nanometers) for lithographic applications such as making computer chips. But for certain applications, you need larger sizes.

    For example, the wavelength range of visible light is about 400 (purple) to 700 (red) nanometers. Even 400 nanometers is still about 10 times larger than the approximately 40-nanometer length scale possible with most block copolymers. As a result, light does not “see” the individual features of block copolymers.

    However, patterns with features closer to 200 nanometers in size can influence light in new ways, and I am working to scale block copolymer assembly to these sizes. One exciting application is using this approach to make “structural colors.” Colors are typically made using dyes or pigments. However, structural colors emerge from the way the light interacts with the nanomaterial—and so potentially one could make new types of lower-power displays through structural color.

    Unfortunately, the process of forming patterns from block copolymers slows drastically, and even stops altogether, for these larger sizes. The development of self-assembled patterns is impeded by defective structures that form at the start of self-assembly. For these defects to “heal,” the block polymer must reconfigure, which involves pulling one chain through the domain of the other polymer, overcoming a large energy barrier to do so. As the size of the polymers increases, the energy barrier goes up exponentially—so exponentially slower healing!

    Have you come up with any solutions to overcome this challenge?

    My colleagues and I found that blending small-molecular-weight homopolymers (polymers made up of the same type of molecules) with the block copolymers makes it easier for the block copolymer chains to move around. Adding homopolymers promotes dramatic increases in the size of well-ordered pattern areas, or “grains.” However, this addition alone does not let us form patterns with larger-size features from block copolymers. We also need to anneal the materials in a solvent vapor. Solvent vapor annealing involves putting a volatile solvent in the region of the diblock copolymer, causing the polymer film to swell. As the polymer film swells, the solvent molecules intersperse between polymer chains. This process has a plasticizing effect, making it easier for the polymer to move. So both mixing the block copolymer with a homopolymer and swelling it with a solvent are needed to speed the formation of large-scale patterns.

    5
    Without blending, the size of grains (single-color regions) of a diblock copolymer with a molecular weight of 36 kilograms/mole barely changes with thermal annealing over time (top row). Blending the block copolymer with homopolymers increases the grain size and speeds up the ordering process (bottom row).

    After annealing, we image the resulting patterns with scanning electron microscopes at CFN. We also perform x-ray scattering experiments at the Complex Materials Scattering beamline at Brookhaven Lab’s National Synchrotron Light Source II [also a DOE Office of Science User Facility] to get a measure of the periodicity during the annealing process so we can determine how quickly the material self-assembles into an ordered pattern.

    BNL NSLS-II

    BNL NSLS-II

    How do all of the different self-assembled patterns you generate translate to possible applications?

    6
    A comparison of scanning electron microscope images after solvent vapor annealing of a large block copolymer (top left) and the same copolymer with added homopolymer (top right) shows that the homopolymer can significantly improve pattern quality. The bottom image is a cross-sectional image of the top right sample.

    The work we do at CFN establishes the basis for producing new materials. For example, consider the mesh pattern I described. My colleague Chang-Yong Nam and I are working on making a mesh of zinc oxide nanowires through infiltration synthesis of block copolymers. Zinc oxide is a versatile semiconducting material, and these nanowires have a lot of surface area, making them attractive for a number of applications—including photoelectrochemical water splitting (a way of converting sunlight into fuel by splitting water into hydrogen and oxygen). These semiconducting nanowires are also very responsive to environmental cues like light or chemicals. Given their large area uniformity, the meshes could be easily integrated into widely deployable gas sensors.

    How did you come to join CFN?

    After graduate school, I completed a postdoctoral appointment working at IBM in California. It was there that I learned about block copolymers, using them to make patterns for microelectronics. I did that for three years, and then in 2013 I joined a research group at HGST, a subsidiary of Western Digital that sells hard disk and solid-state drives. At first, I worked on a project to create patterned nanoscale magnetic media onto which data is written to and read from, in order to enhance data density and stability.

    Following that project, I moved into another area that was not very research oriented. At about this time, the current CFN Director, Chuck Black, gave a talk at HGST. Chuck’s talk piqued my interest in CFN, and soon thereafter a position that very well fit my skills opened up. I applied, and joined CFN in 2015.

    What was it like coming from industry to a national lab setting?

    It definitely takes some getting used to. There is a lot less pressure in some ways but more pressure in other ways. At CFN, you are expected to develop a lot more on your own as far as what direction you need to pursue on the basis of what is valuable to the lab. In industry, the goals of the project are clear, and there are deliverables to keep you on the narrow path to achieving those goals. This is not to say that I did not do exploratory research for a portion of my time in industry.

    The other difference at CFN is that I am more involved with the academic and industrial community at large. I have to manage my time so that I can perform my own research and help users with their research. I find it really cool that researchers from all over the world come to CFN. The talent and expertise of the staff are what make the CFN so great. The staff know backwards and forwards what they are doing in the areas they specialize in, and they are dedicated to helping others.

    What are some of the ways you have helped users?

    I regularly show users how to do block copolymer self-assembly and the etching process to transfer patterns into a substrate. Some users have employed these patterns as superhydrophobic textures to manipulate the flow of liquids in microfluidic devices, for example. In many cases, I help users develop a process when they need self-assembled patterns of varying sizes or shapes, to be applied to different substrates.

    I also help with the lithographic patterning of unusual materials. For example, one user I am working with is trying to pattern protein hydrogels, looking at how they mechanically respond to swelling and de-swelling to understand how they might operate if injected into the body. Such protein hydrogels could have applications in biosensing, drug delivery, and wound healing.

    Some users are interested in solvent vapor annealing, which is a very tricky process to control. So I am building a system with feedback control that can be set to maintain a solvent fraction of any given solvent. Otherwise, if the amount of solvent varies over time, the self-assembly might not work at all (too little solvent) or result in a disordered state (too much solvent).

    How did you become interested in research?

    As an undergraduate at Case Western Reserve University, I majored in chemical engineering. One of my summer internships involved doing fuel cell work at a research lab. This internship led to another one at a fuel cell start-up, where I worked on sensors and solar cells. These internships gave me the opportunity to come up with ideas of my own and try different things. This exploration spurred me to pursue a doctoral degree at the University of California, Berkeley, where I continued my studies in chemical engineering.

    I also think my undergraduate studies in philosophy, which I minored in, gave me a new understanding of the way science works. I really enjoyed reading about the philosophy of science, including books like Kuhn’s The Structure of Scientific Revolutions. I learned how the views we often have are naïve or not accurate. There are lots of things people get wrong for a long time. But that does not mean they were not learning. Science is not perfect—but that is okay.

    I was not the kid who grew up knowing he wanted to be a scientist. I liked philosophy and delving into critical thought. But I began to realize there is a lot of commonality between philosophy and science—in both fields, the aim is to gain knowledge about the world around us. But science is better because you can actually test things!

    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 4:27 pm on January 3, 2018 Permalink | Reply
    Tags: , , , Nanotechnology, , TPL-two-photon lithography,   

    From LLNL: “Lab unlocks secrets of nanoscale 3D printing” 


    Lawrence Livermore National Laboratory

    Jan. 3, 2018
    Jeremy Thomas
    thomas244@llnl.gov
    925-422-5539

    1
    Through the two-photon lithography (TPL) 3D printing process, researchers can print woodpile lattices with submicron features a fraction of the width of a human hair. Image by Jacob Long and Adam Connell/LLNL.

    Lawrence Livermore National Laboratory (LLNL) researchers have discovered novel ways to extend the capabilities of two-photon lithography (TPL), a high-resolution 3D printing technique capable of producing nanoscale features smaller than one-hundredth the width of a human hair.

    The findings, recently published on the cover of the journal ACS Applied Materials & Interfaces , also unleashes the potential for X-ray computed tomography (CT) to analyze stress or defects noninvasively in embedded 3D-printed medical devices or implants.

    Two-photon lithography typically requires a thin glass slide, a lens and an immersion oil to help the laser light focus to a fine point where curing and printing occurs. It differs from other 3D-printing methods in resolution, because it can produce features smaller than the laser light spot, a scale no other printing process can match. The technique bypasses the usual diffraction limit of other methods because the photoresist material that cures and hardens to create structures — previously a trade secret — simultaneously absorbs two photons instead of one.

    2
    LLNL researchers printed octet truss structures with submicron features on top of a solid base with a diameter similar to human hair. Photo by James Oakdale/LLNL.

    In the paper, LLNL researchers describe cracking the code on resist materials optimized for two-photon lithography and forming 3D microstructures with features less than 150 nanometers. Previous techniques built structures from the ground up, limiting the height of objects because the distance between the glass slide and lens is usually 200 microns or less. By turning the process on its head — putting the resist material directly on the lens and focusing the laser through the resist — researchers can now print objects multiple millimeters in height. Furthermore, researchers were able to tune and increase the amount of X-rays the photopolymer resists could absorb, improving attenuation by more than 10 times over the photoresists commonly used for the technique.

    “In this paper, we have unlocked the secrets to making custom materials on two-photon lithography systems without losing resolution,” said LLNL researcher James Oakdale, a co-author on the paper.

    Because the laser light refracts as it passes through the photoresist material, the linchpin to solving the puzzle, the researchers said, was “index matching” – discovering how to match the refractive index of the resist material to the immersion medium of the lens so the laser could pass through unimpeded. Index matching opens the possibility of printing larger parts, they said, with features as small as 100 nanometers.

    “Most researchers who want to use two-photon lithography for printing functional 3D structures want parts taller than 100 microns,” said Sourabh Saha, the paper’s lead author. “With these index-matched resists, you can print structures as tall as you want. The only limitation is the speed. It’s a tradeoff, but now that we know how to do this, we can diagnose and improve the process.”

    3
    Through the two-photon lithography (TPL) 3D printing process, researchers can print woodpile lattices with submicron features a fraction of the width of a human hair. Photo by James Oakdale/LLNL.

    By tuning the material’s X-ray absorption, researchers can now use X-ray-computed tomography as a diagnostic tool to image the inside of parts without cutting them open or to investigate 3D-printed objects embedded inside the body, such as stents, joint replacements or bone scaffolds. These techniques also could be used to produce and probe the internal structure of targets for the National Ignition Facility, as well as optical and mechanical metamaterials and 3D-printed electrochemical batteries.

    The only limiting factor is the time it takes to build, so researchers will next look to parallelize and speed up the process. They intend to move into even smaller features and add more functionality in the future, using the technique to build real, mission-critical parts.

    “It’s a very small piece of the puzzle that we solved, but we are much more confident in our abilities to start playing in this field now,” Saha said. “We’re on a path where we know we have a potential solution for different types of applications. Our push for smaller and smaller features in larger and larger structures is bringing us closer to the forefront of scientific research that the rest of the world is doing. And on the application side, we’re developing new practical ways of printing things.”

    The work was funded through the Laboratory Directed Research and Development (LDRD) program. Other LLNL researchers who contributed to the project include Jefferson Cuadra, Chuck Divin, Jianchao Ye, Jean-Baptiste Forien, Leonardus Bayu Aji, Juergen Biener and Will Smith.

    See the full article here .

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  • richardmitnick 2:53 pm on December 29, 2017 Permalink | Reply
    Tags: , , EBL-electron-beam lithography, Nanotechnology, , STEM-scanning transmission electron microscope   

    From BNL: “Scientists Set Record Resolution for Drawing at the One-Nanometer Length Scale” 2017 

    Brookhaven Lab

    April 28, 2017
    Ariana Tantillo
    atantillo@bnl.gov
    (631) 344-2347

    Peter Genzer
    genzer@bnl.gov
    (631) 344-3174

    An electron microscope–based lithography system for patterning materials at sizes as small as a single nanometer could be used to create and study materials with new properties.

    1
    (Left to right) Lihua Zhang, Vitor Manfrinato, and Aaron Stein are part of the team at Brookhaven Lab’s Center for Functional Nanomaterials that pushed the resolution limits of electron-beam lithography—a technique for creating nanoscale patterns—to the one-nanometer length scale. Team members not pictured are Chang-Yong Nam, Kevin Yager, Eric Stach, and Charles Black.

    The ability to pattern materials at ever-smaller sizes—using electron-beam lithography (EBL), in which an electron-sensitive material is exposed to a focused beam of electrons, as a primary method—is driving advances in nanotechnology. When the feature size of materials is reduced from the macroscale to the nanoscale, individual atoms and molecules can be manipulated to dramatically alter material properties, such as color, chemical reactivity, electrical conductivity, and light interactions.

    In the ongoing quest to pattern materials with ever-smaller feature sizes, scientists at the Center for Functional Nanomaterials (CFN)—a U.S. Department of Energy (DOE) Office of Science User Facility at Brookhaven National Laboratory—have recently set a new record. Performing EBL with a scanning transmission electron microscope (STEM), they have patterned thin films of the polymer poly(methyl methacrylate), or PMMA, with individual features as small as one nanometer (nm), and with a spacing between features of 11 nm, yielding an areal density of nearly one trillion features per square centimeter. These record achievements are published in the April 18 online edition of Nano Letters.

    “Our goal at CFN is to study how the optical, electrical, thermal, and other properties of materials change as their feature sizes get smaller,” said lead author Vitor Manfrinato, a research associate in CFN’s electron microscopy group who began the project as a CFN user while completing his doctoral work at MIT. “Until now, patterning materials at a single nanometer has not been possible in a controllable and efficient way.”

    Commercial EBL instruments typically pattern materials at sizes between 10 and 20 nanometers. Techniques that can produce higher-resolution patterns require special conditions that either limit their practical utility or dramatically slow down the patterning process. Here, the scientists pushed the resolution limits of EBL by installing a pattern generator—an electronic system that precisely moves the electron beam over a sample to draw patterns designed with computer software—in one of CFN’s aberration-corrected STEMs, a specialized microscope that provides a focused electron beam at the atomic scale.

    “We converted an imaging tool into a drawing tool that is capable of not only taking atomic-resolution images but also making atomic-resolution structures,” said coauthor Aaron Stein, a senior scientist in the electronic nanomaterials group at CFN.

    2
    A schematic showing a focused electron beam (green) shining through a polymeric film (grey: carbon atoms; red: oxygen atoms; white: hydrogen atoms). The glowing area (yellow) indicates the molecular volume chemically modified by the focused electron beam.

    Their measurements with this instrument show a nearly 200 percent reduction in feature size (from 5 to 1.7 nm) and 100 percent increase in areal pattern density (from 0.4 to 0.8 trillion dots per square centimeter, or from 16 to 11 nm spacing between features) over previous scientific reports.

    The team’s patterned PMMA films can be used as stencils for transferring the drawn single-digit nanometer feature into any other material. In this work, the scientists created structures smaller than 5 nm in both metallic (gold palladium) and semiconducting (zinc oxide) materials. Their fabricated gold palladium features were as small as six atoms wide.

    Despite this record-setting demonstration, the team remains interested in understanding the factors that still limit resolution, and ultimately pushing EBL to its fundamental limit.

    “The resolution of EBL can be impacted by many parameters, including instrument limitations, interactions between the electron beam and the polymer material, molecular dimensions associated with the polymer structure, and chemical processes of lithography,” explained Manfrinato.

    An exciting result of this study was the realization that polymer films can be patterned at sizes much smaller than the 26 nm effective radius of the PMMA macromolecule. “The polymer chains that make up a PMMA macromolecule are a million repeating monomers (molecules) long—in a film, these macromolecules are all entangled and balled up,” said Stein. “We were surprised to find that the smallest size we could pattern is well below the size of the macromolecule and nears the size of one of the monomer repeating units, as small as a single nanometer.”

    Next, the team plans to use their technique to study the properties of materials patterned at one-nanometer dimensions. One early target will be the semiconducting material silicon, whose electronic and optical properties are predicted to change at the single-digit nanometer scale.

    “This technique opens up many exciting materials engineering possibilities, tailoring properties if not atom by atom, then closer than ever before,” said Stein. “Because the CFN is a national user facility, we will soon be offering our first-of-a-kind nanoscience tool to users from around the world. It will be really interesting to see how other scientists make use of this new capability.”

    This work is supported by DOE’s Office of Science.

    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 1:34 pm on December 21, 2017 Permalink | Reply
    Tags: , , , Magnetic fields of bacterial cells and magnetic nano-objects in liquid can be studied at high resolution using electron microscopy, Nanotechnology   

    From Ames National Lab: “Ames Laboratory-led research team maps magnetic fields of bacterial cells and nano-objects for the first time” 

    Ames Laboratory

    Dec. 21, 2017
    Contacts:
    Tanya Prozorov, Division of Materials Sciences and Engineering
    tprozor@ameslab.gov
    (515) 294-3376

    Laura Millsaps, Ames Laboratory Public Affairs
    millsaps@ameslab.gov
    (515) 294-3474

    A research team led by a scientist from the U.S. Department of Energy’s Ames Laboratory has demonstrated for the first time that the magnetic fields of bacterial cells and magnetic nano-objects in liquid can be studied at high resolution using electron microscopy. This proof-of-principle capability allows first-hand observation of liquid environment phenomena, and has the potential to vastly increase knowledge in a number of scientific fields, including many areas of physics, nanotechnology, biofuels conversion, biomedical engineering, catalysis, batteries and pharmacology.

    1
    Left: Schematic of the off-axis electron holography using a fluid cell. Right: (A)
    Hologram of a magnetite nanocrystal chain released from a magnetotactic
    bacterium, and (B) corresponding magnetic induction map.

    “It is much like being able to travel to a Jurassic Park and witness dinosaurs walking around, instead of trying to guess how they walked by examining a fossilized skeleton,” said Tanya Prozorov, an associate scientist in Ames Laboratory’s Division of Materials Sciences and Engineering.

    Prozorov works with biological and bioinspired magnetic nanomaterials, and faced what initially seemed to be an insurmountable challenge of observing them in their native liquid environment. She studies a model system, magnetotactic bacteria, which form perfect nanocrystals of magnetite. In order to best learn how bacteria do this, she needed an alternative to the typical electron microscopy process of handling solid samples in vacuum, where soft matter is studied in prepared, dried, or vitrified form.

    For this work, Prozorov received DOE recognition through an Office of Science Early Career Research Program grant to use cutting-edge electron microscopy techniques with a liquid cell insert to learn how the individual magnetic nanocrystals form and grow with the help of biological molecules, which is critical for making artificial magnetic nanomaterials with useful properties.

    To study magnetism in bacteria, she applied off-axis electron holography, a specialized technique that is used for the characterization of magnetic nanostructures in the transmission electron microscope, in combination with the liquid cell.

    “When we look at samples prepared in the conventional way, we have to make many assumptions about their properties based on their final state, but with the new technique, we can now observe these processes first-hand,” said Prozorov. “It can help us understand the dynamics of macromolecule aggregation, nanoparticle self-assembly, and the effects of electric and magnetic fields on that process.”

    “This method allows us to obtain large amounts of new information,” said Prozorov. “It is a first step, proving that the mapping of magnetic fields in liquid at the nanometer scale with electron microscopy could be done; I am eager to see the discoveries it could foster in other areas of science.”

    The work was done in collaboration with the Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons and Peter Grünberg Institute, Forschungszentrum Jülich, Germany.

    The research is detailed in the paper, Off-axis electron holography of bacterial cells and magnetic nanoparticles in liquid, by T. Prozorov, T.P. Almeida, A. Kovács, and R.E. Dunin-Borkowski: and published in the Journal of the Royal Society Interface.

    See the full article here .

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    Ames Laboratory is a government-owned, contractor-operated research facility of the U.S. Department of Energy that is run by Iowa State University.

    For more than 60 years, the Ames Laboratory has sought solutions to energy-related problems through the exploration of chemical, engineering, materials, mathematical and physical sciences. Established in the 1940s with the successful development of the most efficient process to produce high-quality uranium metal for atomic energy, the Lab now pursues a broad range of scientific priorities.

    Ames Laboratory is a U.S. Department of Energy Office of Science national laboratory operated by Iowa State University. Ames Laboratory creates innovative materials, technologies and energy solutions. We use our expertise, unique capabilities and interdisciplinary collaborations to solve global problems.

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