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News Article | April 17, 2017
Site: www.materialstoday.com

From an electron's point of view, graphene must be a hair-raising thrill ride. For years, scientists have observed that electrons can blitz through graphene at velocities approaching the speed of light, far faster than they can travel through silicon and other semiconducting materials. Graphene, therefore, has been touted as a promising successor to silicon, potentially leading to faster, more efficient electronic and photonic devices. But manufacturing pristine graphene – a single, perfectly flat, ultrathin sheet of carbon atoms, precisely aligned and linked together like chicken-wire – is extremely difficult. Conventional fabrication processes often generate wrinkles, which can derail an electron's bullet-train journey, significantly limiting graphene's electrical performance. Now engineers at Massachusetts Institute of Technology (MIT) have found a way to make graphene with fewer wrinkles, and to iron out those wrinkles that do still appear. After fabricating and then flattening out the graphene, the researchers tested its electrical conductivity. They found each sheet exhibited uniform performance, meaning that electrons flowed freely across the sheet, at similar speeds, even across previously wrinkled regions. In a paper published in the Proceedings of the National Academy of Sciences, the researchers report that their techniques successfully produce wafer-scale ‘single-domain’ graphene – single layers of graphene that are uniform in both atomic arrangement and electronic performance. "For graphene to play as a main semiconductor material for industry, it has to be single-domain, so that if you make millions of devices on it, the performance of the devices is the same in any location," says Jeehwan Kim, assistant professor in the departments of Mechanical Engineering and Materials Science and Engineering at MIT. "Now we can really produce single-domain graphene at wafer scale." Kim's co-authors include Sanghoon Bae, Samuel Cruz and Yunjo Kim from MIT, along with researchers from IBM, the University of California at Los Angeles and Kyungpook National University in South Korea. The most common way to make graphene involves chemical vapor deposition (CVD), a process in which carbon atoms are deposited onto a crystalline substrate such as copper foil. Once the copper foil is evenly coated with a single layer of carbon atoms, scientists submerge the entire thing in acid to etch away the copper. What remains is a single sheet of graphene, which researchers then pull out from the acid. Unfortunately, the CVD process can result in the formation of relatively large, macroscropic wrinkles in the graphene, due to the roughness of the underlying copper itself and the process of pulling the graphene out from the acid. The alignment of carbon atoms is not uniform across the graphene, creating a ‘polycrystalline’ state in which graphene resembles an uneven, patchwork terrain, preventing electrons from flowing at uniform rates. In 2013, while working at IBM, Kim and his colleagues developed a method for fabricating wafers of single-crystalline graphene, in which the orientation of the carbon atoms is exactly the same throughout a wafer. Rather than copper foil, his team produced single-crystalline graphene on a silicon carbide wafer with an atomically smooth surface, albeit with tiny, step-like wrinkles on the order of several nanometers. They then used a thin sheet of nickel to peel off the top-most graphene from the silicon carbide wafer and place it on a silicon wafer, in a process known as layer-resolved graphene transfer. In their new paper, Kim and his colleagues discovered that, with a slight modification, this layer-resolved graphene transfer process can iron out the steps and tiny wrinkles in silicon carbide-fabricated graphene. Before transferring the layer of graphene onto a silicon wafer, the team oxidized the silicon, creating a layer of silicon dioxide that naturally exhibits electrostatic charges. When the researchers then deposited the graphene, the silicon dioxide effectively pulled graphene's carbon atoms down onto the wafer, flattening out its steps and wrinkles. Kim says this ironing method would not work on CVD-fabricated graphene, as the wrinkles generated through CVD are much larger, on the order of several microns. "The CVD process creates wrinkles that are too high to be ironed out," Kim notes. "For silicon carbide graphene, the wrinkles are just a few nanometers high, short enough to be flattened out." To test whether the flattened, single-crystalline graphene wafers were single-domain, the researchers fabricated tiny transistors on multiple sites on each wafer, including across previously wrinkled regions. "We measured electron mobility throughout the wafers, and their performance was comparable," Kim says. "What's more, this mobility in ironed graphene is two times faster. So now we really have single-domain graphene, and its electrical quality is much higher [than graphene-attached silicon carbide]." Kim says that while there are still challenges to adapting graphene for use in electronics, the group's results give researchers a blueprint for how to reliably manufacture pristine, single-domain, wrinkle-free graphene at wafer scale. "If you want to make any electronic device using graphene, you need to work with single-domain graphene," Kim says. "There's still a long way to go to make an operational transistor out of graphene. But we can now show the community guidelines for how you can make single-crystalline, single-domain graphene." This story is adapted from material from MIT, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.


News Article | April 19, 2017
Site: www.prlog.org

-- Edison International President and CEO Pedro J. Pizarro presented Don Bosco Technical Institute (Bosco Tech) senior Willam Ramos with a 2017 Edison International Scholar award and scholarship on April 10.Ramos, who will begin his studies in chemistry at California Polytechnic State University, San Luis Obispo (SLO) this fall, was one of 1,200 applicants for the scholarship that is annually awarded to 30 high-achieving high school seniors within Edison's broad service area who plan to pursue STEM degrees at four-year colleges and universities."Edison International congratulates this year's outstanding scholars," said Pizarro. "Through their pursuit of science, technology, engineering and math, we believe these students will make important contributions to our communities and society. We are proud to support them."Ramos, who was surprised and excited to receive the Edison award, is studying Materials Science, Engineering & Technology (MSET). He is a member of the school's award-winning band, a Youth Ministry program leader, and a Bosco Tech Ambassador."William truly epitomizes what a Bosco Tech student is," said Bosco Tech President Xavier Jimenez. "He is an intelligent, inquisitive student who wholeheartedly applies himself to his studies and who appreciates the opportunity to learn. He plans to become a teacher in order to instill in other young people a love of science. We're thrilled that Edison International has recognized William's abilities and potential."Celebrating its sixty second year, Bosco Tech is an all-male Catholic high school that combines a rigorous college-preparatory program with a technology-focused education. The innovative STEM curriculum allows students to exceed university admission requirements while completing extensive integrated coursework in one of five applied science and engineering fields. Each year for the past several years, one hundred percent of the graduating class has earned college acceptances. Visit www.boscotech.edu for more information.Edison International, through its subsidiaries, is a generator and distributor of electric power, as well as a provider of energy services and technologies, including renewable energy. Headquartered in Rosemead, Calif., Edison International is the parent company of Southern California Edison, one of the nation's largest electric utilities.Edison International's support of charitable causes, such as the Edison Scholars Program, is funded entirely by Edison International shareholders;SCE customers' utility bill payments do not fund company donations.


CrowdReviews Partnered with Madridge Publishers to Announce: International Conference on Materials Science and Research ICMSR-2017 features highly enlightening and interactive sessions to encourage the exchange of ideas across a wide range of disciplines in the field of Materials Science and Research. They invite contributions related to materials science research. You can submit your work in these broad themes. ICMSR-2017 Themes: Materials Science and Engineering Advanced Materials (Biomaterials, Inorganic-Organic Composites, etc.) Materials Chemistry and Physics Discovery and design of new materials Synthesis & Architecture of Materials Computational Materials Science Nano and Biomaterials Nanotechnology in Materials Science Mining, Metallurgy and Materials Science Materials for Energy and Environment Ceramics, Polymers and Composite Materials Materials in Industry To submit your abstracts please see: http://icmsr.madridge.com/abstract-submission.php ICMSR-2017 Organizing Committee: · Chandrasekar Srinivasakannan, The Petroleum Institute, Abu Dhabi, UAE · R G Faulkner, Loughborough University, UK · Fedor Kusmartsev, Loughborough University , UK · Khalil Abdelrazek Khalil Abdelmawgoud, University of Sharjah,UAE · Han Qingyou, Purdue University, USA · Mohy Saad Mansour, Cairo University, Egypt · Sofian Kanan, American University of Sharjah, UAE · Zeinab Saleh Safar, Cairo University, Egypt · Essam E Khalil, Cairo University, Egypt · Ammar Nayfeh, Masdar Institute of Science and Technology, UAE · Fawzi Banat, The Petroleum Institute, Abu Dhabi, UAE · Genqiang Zhang, University of Science and Technology of China, China · Karam Ramzy Beshay, Cairo University, Egypt · Mohamed Rashad El Hebeary, Cairo University, Egypt · Ahmed Hisham Morshed, Taibah University, KSA · Abdulla Ismail, Rochester Institute of Technology, Dubai, UAE · Jang hi Im, University of Texas, USA · Fatma Ashour, Cairo University, Egypt ICMSR-2017 is organizing an outstanding Scientific Exhibition/Program and anticipates the world’s leading specialists involved in Materials Science Research. They welcome Sponsorship and Exhibitions from the Companies and Organizations who wish to showcase their products at this exciting event. Contact person: Nirosha A icmsr@madridge.com icmsr@madridge.net Naples, FL, April 18, 2017 --( PR.com )-- The International Conference on Materials Science and Research is going to be held during November 16-18, 2017 in Dubai, UAE.ICMSR-2017 features highly enlightening and interactive sessions to encourage the exchange of ideas across a wide range of disciplines in the field of Materials Science and Research.They invite contributions related to materials science research. You can submit your work in these broad themes.ICMSR-2017 Themes:Materials Science and EngineeringAdvanced Materials (Biomaterials, Inorganic-Organic Composites, etc.)Materials Chemistry and PhysicsDiscovery and design of new materialsSynthesis & Architecture of MaterialsComputational Materials ScienceNano and BiomaterialsNanotechnology in Materials ScienceMining, Metallurgy and Materials ScienceMaterials for Energy and EnvironmentCeramics, Polymers and Composite MaterialsMaterials in IndustryTo submit your abstracts please see:ICMSR-2017 Organizing Committee:· Chandrasekar Srinivasakannan, The Petroleum Institute, Abu Dhabi, UAE· R G Faulkner, Loughborough University, UK· Fedor Kusmartsev, Loughborough University , UK· Khalil Abdelrazek Khalil Abdelmawgoud, University of Sharjah,UAE· Han Qingyou, Purdue University, USA· Mohy Saad Mansour, Cairo University, Egypt· Sofian Kanan, American University of Sharjah, UAE· Zeinab Saleh Safar, Cairo University, Egypt· Essam E Khalil, Cairo University, Egypt· Ammar Nayfeh, Masdar Institute of Science and Technology, UAE· Fawzi Banat, The Petroleum Institute, Abu Dhabi, UAE· Genqiang Zhang, University of Science and Technology of China, China· Karam Ramzy Beshay, Cairo University, Egypt· Mohamed Rashad El Hebeary, Cairo University, Egypt· Ahmed Hisham Morshed, Taibah University, KSA· Abdulla Ismail, Rochester Institute of Technology, Dubai, UAE· Jang hi Im, University of Texas, USA· Fatma Ashour, Cairo University, EgyptICMSR-2017 is organizing an outstanding Scientific Exhibition/Program and anticipates the world’s leading specialists involved in Materials Science Research. They welcome Sponsorship and Exhibitions from the Companies and Organizations who wish to showcase their products at this exciting event.Contact person:Nirosha A


News Article | April 17, 2017
Site: www.spie.org

From the SPIE Photonics West Show Daily : 2D tunable materials would allow researchers to "move from still-life daguerreotype nanophotonics to the film and television era." In the world of materials science these days, 2D is all the rage. Over the last decade or so, researchers have discovered that by making certain materials into thin, two-dimensional sheets — sometimes only one or two atoms thick — the materials can acquire new properties and behaviors. In particular, by engineering the nanostructure of these materials in certain ways, researchers can create materials whose properties can be tuned in real-time. Simply by adjusting the voltage, for example, researchers can change the material's basic optical properties, potentially controlling the wave vector, wavelength, amplitude, phase, and polarization of light. The goal is to do it in the context of all optical processes, from scattering and absorption to luminescence and thermal emission. Conventionally, the properties of nanophotonic materials are static, built into the design and structure of the device. But tunability means properties that are dynamic, opening a whole range of new technological applications, from driverless cars to 3D holographic imaging. "This allows one to move from still-life daguerreotype nanophotonics to the film and television era," said Harry Atwater of the California Institute of Technology, who described some of his group's latest advances at Photonics West 2017 on 30 January. Atwater is the Howard Hughes Professor of Applied Physics and Materials Science at Caltech and serves as director of the DOE Energy Center for Artificial Photosynthesis. Of all 2D materials, graphene, a flat lattice of carbon only one-atom thick, is most famous. Recently, Atwater and his colleagues used graphene to make a material with 100% optical absorption, something that theorists first proposed was possible five years ago. To force the graphene to interact strongly with light, the researchers sliced a monolayer of graphene into thin ribbons only 50 or 100 nm wide. These ribbons allow light to efficiently couple with surface plasmons, the collective excitation of electrons, in the graphene. Surrounding the ribbons is gold film that funnels light to the graphene. Underneath is a Salisbury screen, which acts like a mirror that prevents light from escaping through the material, reflecting photons back into the graphene. The researchers designed the structure of this surface so that its impedance matches that of free space, which enables it to absorb all photons that come its way. "That's quite a dramatic result," Atwater said. But by changing the voltage going through the graphene, the researchers can adjust how much it absorbs light. The graphene nanomaterial works in infrared wavelengths, so tunability could lead to all sorts of devices for controlling thermal radiation. In essence, Atwater explained, you could turn a black body into a white body with a flick of a switch. Covering a building with this kind of material could provide a new way to control heating and cooling-by adjusting whether the building absorbs or reflects heat. "It's like a coat of paint I can change the color from black to white in the infrared," Atwater said. The researchers have also used graphene to make a tunable phase modulator, which means that instead of simply reflecting thermal radiation, the surface can steer it toward a particular direction depending on the voltage. This paves the way toward beam-steering devices that can reflect infrared beams in any direction without the need for the slower, mechanically moving mirrors used in conventional beam steerers. These kinds of infrared beam steering devices would be essential for LIDAR systems in driverless cars. To know where it's going, a driverless car needs an infrared beam steering system to quickly scan its surroundings to make a 3D map. Atwater's group has already demonstrated a tunable phased array in the near infrared that scans at megahertz frequencies. Next, Atwater hopes to control polarization of light in graphene. Perhaps farther in the future, when researchers have achieved even greater control and tunability, these kinds of devices could be used for 3D holographic images, he said. Such holograms would require both phase and amplitude modulation across multiple wavelengths. Of course, graphene isn't the only 2D material out there. One of the newest is black phosphorous. Unlike graphene, which is a semimetal, black phosphorous is a semiconductor — and is tunable without the need for any additional engineering or nanopatterning. For example, black phosphorous acts as a natural quantum well. By applying a voltage, you can tune the energy levels in that quantum well. It also has a different bandgap depending on how thick you make the material. In a monolayer, the bandgap is 2 eV, but drops down to 0.3 eV in bulk. But because 2D black phosphorous is still so new, researchers like Atwater are just trying to understand and measure its properties, gauging potential applications. Topological insulators are another class of promising 2D semiconducting materials. The defining characteristic of these materials, Atwater said, is a correlation between spin and charge. Like with black phosphorous, researchers are still exploring the properties of these materials. For both black phosphorous and topological insulators, what may also be needed are discussions with industry experts to see exactly what applications these tunable 2D materials can be used for. Looking in the nearer future, though, Atwater's team is developing new photovoltaic cells with sheets of materials such as MoS2 and WSe2 — as thin as 10 nm. Cells based on these materials are extremely efficient, absorbing nearly 100% of light. Being so thin and light, they could be useful for wearable technologies, vehicles, and other applications where weight is an issue. Whatever the future holds, however, it seems 2D is here to stay. Photonics West 2017, 28 January through 2 February at the Moscone Center in San Francisco, CA (USA), encompassed more than 4700 presentations on light-based technologies across more than 95 conferences. It was also the venue for dozens of technical courses for professional development, the Prism Awards for Photonics Innovation, the SPIE Startup Challenge, a two-day job fair, two major exhibitions, and a diverse business program with more than 25 events. SPIE Photonics West 2018 will be held 27 January through 1 February at Moscone Center.


News Article | April 17, 2017
Site: www.materialstoday.com

A new class of carbon nanotubes could make an effective next-generation clean-up crew for toxic sludge and contaminated water, say researchers at Rochester Institute of Technology (RIT). In a recent study, the researchers found that enhanced single-walled carbon nanotubes offer a more effective and sustainable approach to water treatment and remediation than standard industry materials such as silicon gels and activated carbon. They report their findings in a paper in Environmental Science Water: Research and Technology. In the paper, RIT researchers John-David Rocha and Reginald Rogers demonstrate the potential of this emerging technology for cleaning polluted water. Their work applies carbon nanotubes to environmental problems in a specific new way that builds on a nearly two decades of nanomaterial research. "This aspect is new – taking knowledge of carbon nanotubes and their properties and realizing, with new processing and characterization techniques, the advantages nanotubes can provide for removing contaminants from water," said Rocha, assistant professor in the School of Chemistry and Materials Science in RIT's College of Science. Rocha and Rogers are advancing nanotube technology for environmental remediation and water filtration for home use. "We have shown that we can regenerate these materials," said Rogers, assistant professor of chemical engineering in RIT's Kate Gleason College of Engineering. "In the future, when your water filter finally gets saturated, put it in the microwave for about five minutes and the impurities will get evaporated off." Carbon reduced to the nanoscale defies the rules of physics and operates in a world of quantum mechanics in which small materials become mighty. "We know carbon as graphite for our pencils, as diamonds, as soot," Rocha said. "We can transform that soot or graphite into a nanometer-type material known as graphene." A single-walled carbon nanotube is created when a sheet of graphene is rolled up. The physical change alters the material's chemical structure and determines how it behaves. The result is "one of the most heat conductive and electrically conductive materials in the world", Rocha said. "These are properties that only come into play because they are at the nanometer scale." The RIT researchers created new techniques for manipulating the tiny materials. Rocha developed a method for isolating high-quality, single-walled carbon nanotubes and for sorting them according to their semiconductive or metallic properties. Rogers redistributed the pure carbon nanotubes into thin papers akin to carbon-copy paper. "Once the papers are formed, now we have the adsorbent – what we use to pull the contaminants out of water," Rogers explained. The filtration process works because "carbon nanotubes dislike water”; only the organic contaminants in the water stick to the nanotube, not the water molecules. "This type of application has not been done before," Rogers said. "Nanotubes used in this respect is new." This story is adapted from material from Rochester Institute of Technology, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.


News Article | April 17, 2017
Site: news.mit.edu

Implantable fibers have been an enormous boon to brain research, allowing scientists to stimulate specific targets in the brain and monitor electrical responses. But similar studies in the nerves of the spinal cord, which might ultimately lead to treatments to alleviate spinal cord injuries, have been more difficult to carry out. That’s because the spine flexes and stretches as the body moves, and the relatively stiff, brittle fibers used today could damage the delicate spinal cord tissue. Now, researchers have developed a rubber-like fiber that can flex and stretch while simultaneously delivering both optical impulses, for optoelectronic stimulation, and electrical connections, for stimulation and monitoring. The new fibers are described in a paper in the journal Science Advances, by MIT graduate students Chi (Alice) Lu and Seongjun Park, Professor Polina Anikeeva, and eight others at MIT, the University of Washington, and Oxford University. “I wanted to create a multimodal interface with mechanical properties compatible with tissues, for neural stimulation and recording,” as a tool for better understanding spinal cord functions, says Lu. But it was essential for the device to be stretchable, because “the spinal cord is not only bending but also stretching during movement.” The obvious choice would be some kind of elastomer, a rubber-like compound, but most of these materials are not adaptable to the process of fiber drawing, which turns a relatively large bundle of materials into a thread that can be narrower than a hair. The spinal cord “undergoes stretches of about 12 percent during normal movement,” says Anikeeva, who is the Class of 1942 Career Development Professor in the Department of Materials Science and Engineering. “You don’t even need to get into a ‘downward dog’ [yoga position] to have such changes.” So finding a material that can match that degree of stretchiness could potentially make a big difference to research. “The goal was to mimic the stretchiness and softness and flexibility of the spinal cord,” she says. “You can match the stretchiness with a rubber. But drawing rubber is difficult — most of them just melt,” she says. “Eventually, we’d like to be able to use something like this to combat spinal cord injury. But first, we have to have biocompatibility and to be able to withstand the stresses in the spinal cord without causing any damage,” she says. The fibers are not only stretchable but also very flexible. “They’re so floppy, you could use them to do sutures, and do light delivery at the same time,” professor Polina Anikeeva says. (Video: Chi (Alice) Lu and Seongjun Park) The team combined a newly developed transparent elastomer, which could act as a waveguide for optical signals, and a coating formed of a mesh of silver nanowires, producing a conductive layer for the electrical signals. To process the transparent elastomer, the material was embedded in a polymer cladding that enabled it to be drawn into a fiber that proved to be highly stretchable as well as flexible, Lu says. The cladding is dissolved away after the drawing process. After the entire fabrication process, what’s left is the transparent fiber with electrically conductive, stretchy nanowire coatings. “It’s really just a piece of rubber, but conductive,” Anikeeva says. The fiber can stretch by at least 20 to 30 percent without affecting its properties, she says. The fibers are not only stretchable but also very flexible. “They’re so floppy, you could use them to do sutures and deliver light  at the same time,” she says. “We’re the first to develop something that enables simultaneous electrical recording and optical stimulation in the spinal cords of freely moving mice,” Lu says. “So we hope our work opens up new avenues for neuroscience research.” Scientists doing research on spinal cord injuries or disease usually must use larger animals in their studies, because the larger nerve fibers can withstand the more rigid wires used for stimulus and recording. While mice are generally much easier to study and available in many genetically modified strains, there was previously no technology that allowed them to be used for this type of research, she says. “There are many different types of cells in the spinal cord, and we don’t know how the different types respond to recovery, or lack of recovery, after an injury,” she says. These new fibers, the researchers hope, could help to fill in some of those blanks. The team included Alexander Derry, Chong Hou, Siyuan Rao, Jeewoo Kang, and professor Yoel Fink at MIT; Tom Richner and professor Chet Mortiz at the University of Washington; and Imogen Brown at Oxford University. The research was supported by the National Science Foundation, the National Institute of Neurological Disorders and Stroke, the U.S. Army Research Laboratory, and the U.S. Army Research Office through the Institute for Soldier Nanotechnologies at MIT.


News Article | April 19, 2017
Site: phys.org

A new technique developed by MIT engineers may vastly reduce the overall cost of wafer technology and enable devices made from more exotic, higher-performing semiconductor materials than conventional silicon. The new method, reported today in Nature, uses graphene—single-atom-thin sheets of graphite—as a sort of "copy machine" to transfer intricate crystalline patterns from an underlying semiconductor wafer to a top layer of identical material. The engineers worked out carefully controlled procedures to place single sheets of graphene onto an expensive wafer. They then grew semiconducting material over the graphene layer. They found that graphene is thin enough to appear electrically invisible, allowing the top layer to see through the graphene to the underlying crystalline wafer, imprinting its patterns without being influenced by the graphene. Graphene is also rather "slippery" and does not tend to stick to other materials easily, enabling the engineers to simply peel the top semiconducting layer from the wafer after its structures have been imprinted. Jeehwan Kim, the Class of 1947 Career Development Assistant Professor in the departments of Mechanical Engineering and Materials Science and Engineering, says that in conventional semiconductor manufacturing, the wafer, once its crystalline pattern is transferred, is so strongly bonded to the semiconductor that it is almost impossible to separate without damaging both layers. "You end up having to sacrifice the wafer—it becomes part of the device," Kim says. With the group's new technique, Kim says manufacturers can now use graphene as an intermediate layer, allowing them to copy and paste the wafer, separate a copied film from the wafer, and reuse the wafer many times over. In addition to saving on the cost of wafers, Kim says this opens opportunities for exploring more exotic semiconductor materials. "The industry has been stuck on silicon, and even though we've known about better performing semiconductors, we haven't been able to use them, because of their cost," Kim says. "This gives the industry freedom in choosing semiconductor materials by performance and not cost." Kim's research team discovered this new technique at MIT's Research Laboratory of Electronics. Kim's MIT co-authors are first author and graduate student Yunjo Kim; graduate students Samuel Cruz, Babatunde Alawonde, Chris Heidelberger, Yi Song, and Kuan Qiao; postdocs Kyusang Lee, Shinhyun Choi, and Wei Kong; visiting research scholar Chanyeol Choi; Merton C. Flemings-SMA Professor of Materials Science and Engineering Eugene Fitzgerald; professor of electrical engineering and computer science Jing Kong; and assistant professor of mechanical engineering Alexie Kolpak; along with Jared Johnson and Jinwoo Hwang from Ohio State University, and Ibraheem Almansouri of Masdar Institute of Science and Technology. Since graphene's discovery in 2004, researchers have been investigating its exceptional electrical properties in hopes of improving the performance and cost of electronic devices. Graphene is an extremely good conductor of electricity, as electrons flow through graphene with virtually no friction. Researchers, therefore, have been intent on finding ways to adapt graphene as a cheap, high-performance semiconducting material. "People were so hopeful that we might make really fast electronic devices from graphene," Kim says. "But it turns out it's really hard to make a good graphene transistor." In order for a transistor to work, it must be able to turn a flow of electrons on and off, to generate a pattern of ones and zeros, instructing a device on how to carry out a set of computations. As it happens, it is very hard to stop the flow of electrons through graphene, making it an excellent conductor but a poor semiconductor. Kim's group took an entirely new approach to using graphene in semiconductors. Instead of focusing on graphene's electrical properties, the researchers looked at the material's mechanical features. "We've had a strong belief in graphene, because it is a very robust, ultrathin, material and forms very strong covalent bonding between its atoms in the horizontal direction," Kim says. "Interestingly, it has very weak Van der Waals forces, meaning it doesn't react with anything vertically, which makes graphene's surface very slippery." The team now reports that graphene, with its ultrathin, Teflon-like properties, can be sandwiched between a wafer and its semiconducting layer, providing a barely perceptible, nonstick surface through which the semiconducting material's atoms can still rearrange in the pattern of the wafer's crystals. The material, once imprinted, can simply be peeled off from the graphene surface, allowing manufacturers to reuse the original wafer. The team found that its technique, which they term "remote epitaxy," was successful in copying and peeling off layers of semiconductors from the same semiconductor wafers. The researchers had success in applying their technique to exotic wafer and semiconducting materials, including indium phosphide, gallium arsenenide, and gallium phosphide—materials that are 50 to 100 times more expensive than silicon. Kim says that this new technique makes it possible for manufacturers to reuse wafers—of silicon and higher-performing materials—"conceptually, ad infinitum." The group's graphene-based peel-off technique may also advance the field of flexible electronics. In general, wafers are very rigid, making the devices they are fused to similarly inflexible. Kim says now, semiconductor devices such as LEDs and solar cells can be made to bend and twist. In fact, the group demonstrated this possibility by fabricating a flexible LED display, patterned in the MIT logo, using their technique. "Let's say you want to install solar cells on your car, which is not completely flat—the body has curves," Kim says. "Can you coat your semiconductor on top of it? It's impossible now, because it sticks to the thick wafer. Now, we can peel off, bend, and you can do conformal coating on cars, and even clothing." Going forward, the researchers plan to design a reusable "mother wafer" with regions made from different exotic materials. Using graphene as an intermediary, they hope to create multifunctional, high-performance devices. They are also investigating mixing and matching various semiconductors and stacking them up as a multimaterial structure. "Now, exotic materials can be popular to use," Kim says. "You don't have to worry about the cost of the wafer. Let us give you the copy machine. You can grow your semiconductor device, peel it off, and reuse the wafer."


News Article | April 17, 2017
Site: news.mit.edu

Metal fatigue can lead to abrupt and sometimes catastrophic failures in parts that undergo repeated loading, or stress. It’s a major cause of failure in structural components of everything from aircraft and spacecraft to bridges and powerplants. As a result, such structures are typically built with wide safety margins that add to costs. Now, a team of researchers at MIT and in Japan and Germany has found a way to greatly reduce the effects of fatigue by incorporating a laminated nanostructure into the steel. The layered structuring gives the steel a kind of bone-like resilience, allowing it to deform without allowing the spread of microcracks that can lead to fatigue failure. The findings are described in a paper in the journal Science by C. Cem Tasan, the Thomas B. King Career Development Professor of Metallurgy at MIT; Meimei Wang, a postdoc in his group; and six others at Kyushu University in Japan and the Max Planck Institute in Germany. “Loads on structural components tend to be cyclic,” Tasan says. For example, an airplane goes through repeated pressurization changes during every flight, and components of many devices repeatedly expand and contract due to heating and cooling cycles. While such effects typically are far below the kinds of loads that would cause metals to change shape permanently or fail immediately, they can cause the formation of microcracks, which over repeated cycles of stress spread a bit further and wider, ultimately creating enough of a weak area that the whole piece can fracture suddenly. “A majority of unexpected failures [of structural metal parts] are due to fatigue,” Tasan says. For this reason, large safety factors are used in component design, leading to increased costs during production and component life. Tasan and his team were inspired by the way nature addresses the same kind of problem, making bones lightweight but very resistant to crack propagation. A major factor in bone’s fracture resistance is its hierarchical mechanical structure, so the team investigated microstructures that would mimic this in a metal alloy. The question was, he says, “Can we design a material with a microstructure that makes it most difficult for cracks to propagate, even if they nucleate?” Bone provided a clue to how to do that, through its hierarchical microstructure — that is, the way its internal structures have different patterns of voids and connections at many different length scales, with a lattice-like internal structure — that combines strength with light weight. The team developed a kind of steel that has three key characteristics, which combine to limit the spread of cracks that do form. Besides having a layered structure that tends to keep cracks from spreading beyond the layers where they start, the material has microstructural phases with different degrees of hardness, which complement each other, so when a crack starts to form, “every time it wants to propagate further, it needs to follow an energy-intensive path,” and the result is a great reduction in such spreading. Also, the material has a metastable composition; tiny areas within it are poised between different stable states, some more flexible than others, and their phase transitions can help absorb the energy of spreading cracks and even lead the cracks to close back up. To further understand the relative roles of these three characteristics, the team compared steels each with a combination of two out of the three key properties. None of these worked as well as the three-way combination, he says. “This showed us that our modification has better fatigue resistance than any of these.” The testing of such materials under realistic conditions is difficult to do, Tasan explains, partly because of “the extreme sensitivity of these materials to surface defects. If you scratch it, it’s going to fail much faster.” So meticulous preparation and inspection of test samples is essential. This finding is just a first step, Tasan says, and it remains to be seen what would be needed to scale up the material to quantities that could be commercialized, and what applications would benefit most. “Economics always comes into it,” he says. “I’m a metallurgist, and this is a new material that has interesting properties. Large industries such as automotive or aerospace are very careful about making changes in materials, as it brings extra effort and costs.” But there are likely to be several uses where the material would be a significant advantage. “For critical applications, [the benefits] are so critical that change is worth the extra trouble” about the cost, he says. “This is an alloy that would be more expensive than a basic low-carbon steel, but the property benefits have been shown to be quite exceptional, and it’s with much lower amounts of alloying metals (and hence, costs) than other proposed materials.” The research was supported by the European Research Council and MIT’s Department of Materials Science and Engineering. The team included Motomichi Koyama, Zhao Zhang, Kaneaki Tsuzaki, and Hiroshi Noguchi of Kyushu University in Fukuoka, Japan, and Dirk Ponge, and Dierk Raabe of the Max Planck Institute in Dusseldorf, Germany.


News Article | April 17, 2017
Site: news.mit.edu

One of the key technologies needed to transform world energy supplies away from fossil fuels and toward clean, renewable sources is a cheap and reliable way of storing and releasing energy. That will enable intermittent supplies such as solar and wind power, with their variable and often unpredictable outputs, to store energy that’s produced when it’s not needed and to release it when it’s needed most (or can be sold for the best price). That was a message that came up repeatedly over the two days of talks and panel discussions at the 12th annual MIT Energy Conference, held on March 3 and 4. But while better, cheaper storage is essential, implementing it faces technical, economic, and policy challenges, several speakers noted. Massachusetts, home to a number of leading startup ventures in the energy storage area, has “a huge opportunity to be a leader” in this burgeoning industry, said Judith Judson, the commissioner of the Massachusetts Department of Energy Resources, in one of the conference’s panel discussions. The state is already home to a number of companies working on innovative battery technologies, several of which are based on research from MIT labs. But getting such technologies out into the world is more than just a matter of building a better mousetrap. For one thing, “the role of the utilities to push on this technology is so important,” said Belen Linares, the global research and development director for Spain-based energy company Acciona. “It’s collaborations between schools and industry that are going to give these technologies the real boost they need.” Ravi Manghani, energy storage director for GTM Research, a solar-market analysis firm, who moderated that panel, concluded that what researchers really need to do now is “work on making energy storage less complicated and more boring.” It needs to be the kind of simple technology that can be purchased and then forgotten, he suggested, somewhat like a home water heater. One promising new entry in that sector is Ambri, a company developing grid-scale batteries based on all-liquid active components, a technology developed at MIT in the lab of Donald Sadoway, the John F. Elliott Professor in Materials Science and Engineering. Dana Guernsey, Ambri’s director of corporate development, said that “one of the exciting reasons to be in this industry” is the potential to open up electrification “in places where there is no grid at all. Storage systems will electrify parts of the world that have been dark,” by enabling the construction of small, localized “microgrids” that can serve villages, schools, or small businesses. Consumers can help to bring about that transformation, a number of speakers said. A panel discussion on “the engaged ratepayer” made it clear that utilities are becoming ever more responsive to the needs and wants of their customers, as the business has become more competitive. “The rate of change now in the industry is extraordinary,” said Terry Sobolewski, the chief customer officer of the utility company National Grid. “And it’s almost entirely driven by customers.” In fact, the customer-centric orientation of the companies is now so strong that the formerly universal term “ratepayer” has now been officially discontinued by most of these companies because it implies a one-way relationship, and the companies now really want to stress their responsiveness and engagement, Sobolewski said. Part of that responsiveness includes working with business and industrial customers. “More and more industries are asking for help,” he said, “on ‘how do I integrate renewables into my business?’” The change in attitude, he said, suggests that “we are on the precipice of this transformation.” Accelerating the transformation to non-fossil-fuel energy sources will also require improved analytical tools for gathering data about the performance of buildings and industrial plants using different combinations of energy and efficiency systems, several speakers said. Southern California Edison is making inroads in this area, said Andre Ramirez, a principal advisor to the company. Its 5 million customers, he said, are all now on a “time-of-use” rate system, by default. That kind of rate system allows customers to shift energy-intensive activities, such as running a clothes dryer or charging an electric car, to off-peak periods when the rates may be much lower. Such shifting, if done on a large scale, can greatly reduce the utility’s need to build expensive peak-power generators to handle those loads. “We’re at the leading edge of that change,” Ramirez said. The kind of detailed information that can be gathered over time about residential use can lead to specific, targeted suggestions for energy improvements for a given home or business. But information can also influence other kinds of decisions. For example, “millennials want to work for companies that have a conscience,” including what their energy strategies are and what their values are, said Tim Healy, CEO and chairman of the energy data analysis and management company EnerNOC. Transparency about a company’s business practices, including the details of its actual energy production sources, can be an important part of that, he said. As for the energy systems themselves, innovations in the regulatory system that establishes rates and governs the interactions among power producers, distribution networks, and end-users are a major need at this point. “Regulatory affairs is where the innovation needs to occur,” Healy said. MIT’s Energy Conference is organized annually under the auspices of the MIT Energy Club, which with its 5,000 members, including students, faculty, staff, and alumni, is “the largest energy club anywhere,” said Robert Armstrong, director of the MIT Energy Initiative, in his opening remarks at this year’s event.

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