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West Lafayette, IN, United States

Zwanenburg F.A.,MESA Institute for Nanotechnology | Zwanenburg F.A.,University of New South Wales | Dzurak A.S.,University of New South Wales | Morello A.,University of New South Wales | And 6 more authors.
Reviews of Modern Physics | Year: 2013

This review describes recent groundbreaking results in Si, Si/SiGe, and dopant-based quantum dots, and it highlights the remarkable advances in Si-based quantum physics that have occurred in the past few years. This progress has been possible thanks to materials development of Si quantum devices, and the physical understanding of quantum effects in silicon. Recent critical steps include the isolation of single electrons, the observation of spin blockade, and single-shot readout of individual electron spins in both dopants and gated quantum dots in Si. Each of these results has come with physics that was not anticipated from previous work in other material systems. These advances underline the significant progress toward the realization of spin quantum bits in a material with a long spin coherence time, crucial for quantum computation and spintronics. Published by the American Physical Society. Source

News Article
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Abstract: ABSTRACT All-dielectric metamaterials Saman Jahani1 and Zubin Jacob1,2,* 1Department of Electrical and Computer Engineering, University of Alberta 2 Birck Nanotechnology Center, School of Electrical and Computer Engineering, Purdue University E-mail: The ideal material for nanophotonic applications will have a large refractive index at optical frequencies, respond to both the electric and magnetic fields of light, support large optical chirality and anisotropy, confine and guide light at the nanoscale, and be able to modify the phase and amplitude of incoming radiation in a fraction of a wavelength. Artificial electromagnetic media, or metamaterials, based on metallic or polar dielectric nanostructures can provide many of these properties by coupling light to free electrons (plasmons) or phonons (phonon polaritons), respectively, but at the inevitable cost of significant energy dissipation and reduced device efficiency. Recently, however, there has been a shift in the approach to nanophotonics. Lowloss electromagnetic responses covering all four quadrants of possible permittivities and permeabilities have been achieved using completely transparent and high-refractive-index dielectric building blocks. Moreover, an emerging class of all-dielectric metamaterials consisting of anisotropic crystals has been shown to support large refractive index contrast between orthogonal polarizations of light. These advances have revived the exciting prospect of integrating exotic electromagnetic effects in practical photonic devices, to achieve, for example, ultrathin and efficient optical elements, and realize the long-standing goal of subdiffraction confinement and guiding of light without metals. In this Review, we present a broad outline of the whole range of electromagnetic effects observed using all-dielectric metamaterials: high-refractive-index nanoresonators, metasurfaces, zero-index metamaterials and anisotropic metamaterials. Finally, we discuss current challenges and future goals for the field at the intersection with quantum, thermal and silicon photonics, as well as biomimetic metasurfaces. New transparent metamaterials under development could make possible computer chips and interconnecting circuits that use light instead of electrons to process and transmit data, representing a potential leap in performance. Although optical fibers are now used to transmit large amounts of data over great distances, the technology cannot easily be miniaturized because the wavelength of light is too large to fit within the miniscule dimensions of microcircuits. "The role of optical fibers is to guide light from point A to point B, in fact, across continents," said Zubin Jacob, an assistant professor of electrical and computer engineering at Purdue University. "The biggest advantage of doing this compared to copper cables is that it has a very high bandwidth, so large amounts of data can pass through these optical cables as opposed to copper wires. However, on our computers and consumer electronics we still use copper wires between different parts of the chip. The reason is that you can't confine light to the same size as a nanoscale copper wire." Transparent metamaterials, nanostructured artificial media with transparent building blocks, allow unprecedented control of light and may represent a solution. Researchers are making progress in developing metamaterials that shrink the wavelength of light, pointing toward a strategy to use light instead of electrons to process and transmit data in computer chips. "If you have very high bandwidth communication on the chip as well as interconnecting circuits between chips, you can go to faster clock speeds, so faster data processing," Jacob said. Such an advance could make it possible to shrink the bulkiness of a high-performance computer cluster to the size of a standard desktop machine. Unlike some of the metamaterials under development, which rely on the use of noble metals such as gold and silver, the new metamaterials are made entirely of dielectric materials, or insulators and non-metals. This approach could allow researchers to overcome a major limitation encountered thus far in the development of technologies based on metamaterials: using metals results in the loss of too much light to be practical for many applications. A review article about all-dielectric metamaterials appeared online this month in the journal Nature Nanotechnology, highlighting the rapid development in this new field of research. The article was authored by doctoral student Saman Jahani and Jacob. "A key factor is that we don't use metals at all in this metamaterial, because if you use metals a lot of the light goes into heat and is lost," Jacob said. "We want to bring everything to the silicon platform because this is the best material to integrate electronic and photonic devices on the same chip." A critical detail is the material's "anisotropic velocity" – meaning light is transmitted much faster in one direction through the material than in another. Conventional materials transmit light at almost the same speed no matter which direction it is traveling through the material. "The tricky part of this work is that we require the material to be highly anisotropic," he said. "So in one direction light travels almost as fast as it would in a vacuum, and in the other direction it travels as it would in silicon, which is around four times slower." The innovation could make it possible to modify a phenomenon called "total internal reflection," the principle currently used to guide light in fiber optics. The researchers are working to engineer total internal reflection in optical fibers surrounded by the new silicon-based metamaterial. "Our contribution has been basically the fact that we have been able to adapt this total internal reflection phenomenon down to the nanoscale, which was conventionally thought impossible," Jacob said. Because the material is transparent it is suitable for transmitting light, which is a critical issue for practical device applications. The approach could reduce heating in circuits, meaning less power would be required to operate devices. Such an innovation could in the long run bring miniaturized data processing units. "Another fascinating application for these transparent metamaterials is in enhancing light-matter coupling for single quantum light emitters," Jacob said. "The size of light waves inside a fiber are too large to effectively interact with tiny atoms and molecules. The transparent metamaterial cladding can compress the light waves to sub-wavelength values thus allowing light to effectively interact with quantum objects. This can pave the way for light sources at the single photon level." The research is being performed jointly at Purdue's Birck Nanotechnology Center in the university's Discovery Park and at the University of Alberta. The researchers have obtained a U.S. patent on the design. The research was funded by the National Science and Engineering Research Council of Canada and Helmholtz Alberta Initiative. For more information, please click If you have a comment, please us. Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.

News Article | April 21, 2016
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A system that uses a laser and electrical current to precisely position and align carbon nanotubes represents a potential new tool for creating electronic devices out of the tiny fibers. Because carbon nanotubes have unique thermal and electrical properties, they may have future applications in electronic cooling and as devices in microchips, sensors, and circuits. Being able to orient the carbon nanotubes in the same direction and precisely position them could allow these nanostructures to be used in such applications. However, it is difficult to manipulate something so small that thousands of them would fit within the diameter of a single strand of hair, says Steven T. Wereley, a professor of mechanical engineering at Purdue University. "One of the things we can do with this technique is assemble carbon nanotubes, put them where we want and make them into complicated structures," he says. New findings from research led by Purdue doctoral student Avanish Mishra are detailed in a paper that has appeared online in the journal Microsystems and Nanoengineering, published by the Nature Publishing Group. The technique, called rapid electrokinetic patterning (REP), uses two parallel electrodes made of indium tin oxide, a transparent and electrically conductive material. The nanotubes are arranged randomly while suspended in deionized water. Applying an electric field causes them to orient vertically. Then an infrared laser heats the fluid, producing a doughnut-shaped vortex of circulating liquid between the two electrodes. This vortex enables the researchers to move the nanotubes and reposition them. "When we apply the electric field, they are immediately oriented vertically, and then when we apply the laser, it starts a vortex, that sweeps them into little nanotube forests," Wereley says. The research paper was authored by Mishra; Purdue graduate student Katherine Clayton; University of Louisville student Vanessa Velasco; Stuart J. Williams, an assistant professor of mechanical engineering at the University of Louisville and director of the Integrated Microfluidic Systems Laboratory; and Wereley. Williams is a former doctoral student at Purdue. The technique overcomes limitations of other methods for manipulating particles measured on the scale of nanometers, or billionths of a meter. In this study, the procedure was used for multiwalled carbon nanotubes, which are rolled-up ultrathin sheets of carbon called graphene. However, according to the researchers, using this technique other nanoparticles such as nanowires and nanorods can be similarly positioned and fixed in vertical orientation. The researchers have received a U.S. patent on the system. The experimental work was performed at the Birck Nanotechnology Center in Purdue's Discovery Park. Future research will explore using the technique to create devices.

News Article | April 7, 2016
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Carbon fibers derived from a sustainable source, a type of wild mushroom, and modified with nanoparticles have been shown to outperform conventional graphite electrodes for lithium-ion batteries. Researchers at Purdue University have created electrodes from a species of wild fungus called Tyromyces fissilis. "Current state-of-the-art lithium-ion batteries must be improved in both energy density and power output in order to meet the future energy storage demand in electric vehicles and grid energy-storage technologies," says Vilas Pol, an associate professor in the School of Chemical Engineering and the School of Materials Engineering. "So there is a dire need to develop new anode materials with superior performance." Batteries have two electrodes, called an anode and a cathode. The anodes in most of today's lithium-ion batteries are made of graphite. Lithium ions are contained in a liquid called an electrolyte, and these ions are stored in the anode during recharging. Pol and doctoral student Jialiang Tang have found that carbon fibers derived from Tyromyces fissilis and modified by attaching cobalt oxide nanoparticles outperform conventional graphite in the anodes. The hybrid design has a synergistic result, Pol says. "Both the carbon fibers and cobalt oxide particles are electrochemically active, so your capacity number goes higher because they both participate," he says. The hybrid anodes have a stable capacity of 530 milliamp hours per gram, which is one and a half times greater than graphite's capacity. Findings are detailed in a paper appearing online in the American Chemical Society's Sustainable Chemistry & Engineering journal. One approach for improving battery performance is to modify carbon fibers by attaching certain metals, alloys or metal oxides that allow for increased storage of lithium during recharging. Tang got the idea of tapping fungi for raw materials while researching alternative sources for carbon fibers. "The methods now used to produce carbon fibers for batteries are often chemical heavy and expensive," Tang says. He noticed a mushroom growing on a rotting wood stump in his backyard and decided to study its potential as a source for carbon fibers. "I was curious about the structure so I cut it open and found that it has very interesting properties," he says. "It's very rubbery and yet very tough at the same time. Most interestingly, when I cut it open it has a very fibrous network structure." Comparisons with other fungi showed the Tyromyces fissilis was especially abundant in fibers. The fibers are processed under high temperatures in a chamber containing argon gas using a procedure called pyrolysis, yielding pure carbon in the original shape of the fungus fibers. The fibers have a disordered arrangement and intertwine like spaghetti noodles. The interconnected network brings faster electron transport, which could result in faster battery charging. Electron microscopy studies were performed at the Birck Nanotechnology Center in Purdue's Discovery Park. The work was supported by Purdue's School of Chemical Engineering. The electron microscopy studies at Birck were funded by a Kirk exploratory research grant and were conducted by former postdoctoral research associate Vinodkumar Etacheri.

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Pollens, the bane of allergy sufferers, could represent a boon for battery makers: Recent research has suggested their potential use as anodes in lithium-ion batteries. "Our findings have demonstrated that renewable pollens could produce carbon architectures for anode applications in energy storage devices," says Vilas Pol, an associate professor in the School of Chemical Engineering and the School of Materials Engineering at Purdue University. Batteries have two electrodes, called an anode and a cathode. The anodes in most of today's lithium-ion batteries are made of graphite. Lithium ions are contained in a liquid called an electrolyte, and these ions are stored in the anode during recharging. The researchers tested bee pollen- and cattail pollen-derived carbons as anodes. "Both are abundantly available," says Pol, who worked with doctoral student Jialiang Tang. "The bottom line here is we want to learn something from nature that could be useful in creating better batteries with renewable feedstock." Research findings are detailed in a paper that appears today in Nature's Scientific Reports. Whereas bee pollen is a mixture of different pollen types collected by honeybees, the cattail pollens all have the same shape. "I started looking into pollens when my mom told me she had developed pollen allergy symptoms about two years ago," Tang says. "I was fascinated by the beauty and diversity of pollen microstructures. But the idea of using them as battery anodes did not really kick in until I started working on battery research and learned more about carbonization of biomass." The researchers processed the pollen under high temperatures in a chamber containing argon gas using a procedure called pyrolysis, yielding pure carbon in the original shape of the pollen particles. They were further processed, or "activated," by heating at lower temperature — about 300 C — in the presence of oxygen, forming pores in the carbon structures to increase their energy-storage capacity. The research showed the pollen anodes could be charged at various rates. While charging for 10 hours resulted in a full charge, charging them for only one hour resulted in more than half of a full charge, Pol says. "The theoretical capacity of graphite is 372 milliamp hours per gram, and we achieved 200 milliamp hours after one hour of charging," he says. The researchers tested the carbon at 25 C and 50 C to simulate a range of climates. "This is because the weather-based degradation of batteries is totally different in New Mexico compared to Indiana," Pol says. Findings showed the cattail pollens performed better than bee pollen. The work is ongoing. Whereas the current work studied the pollen in only anodes, future research will include work to study them in a full-cell battery with a commercial cathode. "We are just introducing the fascinating concept here," Pol says. "Further work is needed to determine how practical it might be." Electron microscopy studies were performed at the Birck Nanotechnology Center in Purdue's Discovery Park. The work was supported by Purdue's School of Chemical Engineering. The electron microscopy studies at Birck were funded by a Kirk exploratory research grant and were conducted by doctoral students Arthur D. Dysart and Vinodkumar Etacheri. An XPS measurement was conducted by Dmitry Zemlyanov at Birck. Other support came from the Hoosier Heavy Hybrid Center of Excellence (H3CoE) fellowship, funded by U.S. Department of Energy. Release Date: February 5, 2016  Source: Purdue University

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