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Computer simulations show that metal oxides in water go through many short-lived shapes and structures (see story below). Credit: William Casey, UC Davis.

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Scorpions inspire scientists in making tougher surfaces for machinery

Researchers studied the bumps and grooves on the scorpions’ backs, scanning the creatures with a 3D laser device and developing a computer program that modeled the flow of sand-laden air over the scorpions. The team used the model in computer simulations to develop actual patterned surfaces to test which patterns perform best. At the same time, the erosion tests were conducted in the simple erosion wind tunnel for groove surface bionic samples at various impact conditions. Their results showed that a series of small grooves at a 30-degree angle to the flowing gas or liquid give steel surfaces the best protection from erosion.

US inactivity regarding strategic materials criticized at Washington hearing

At a hearing Jan. 26 before the U.S.-China Economic and Security Review Commission, Jeff Green testified that the US has lost critical supply chain capabilities and significant technological capital to China and that the lack of a deliberately thought-out U.S. policy for strategic and critical materials has resulted in economic and national security vulnerabilities. The hearing on “China’s Global Quest for Resources and Implications for the United States” examined Chinese efforts to acquire and manage various natural resources. Green president of the J.A. Green & Co., assists industrial clients in government relations, business development and strategic planning matters and is the former staff director to the House Armed Services Subcommittee on Readiness.

Imaging ‘invisible’ dopant atoms in semiconductor nanocrystals

In semiconductor nanocrystals, the physical effects of deliberately included impurities, called dopants, may depend on the dopant position with the crystal. To date, there has not been an effective technique to determine the location of individual dopant atoms in nanocrystals. IRG-4 researchers demonstrated that a combination of scanning transmission electron microscopy and electron energy loss spectroscopy can be used to reveal the position of such “invisible” dopants.he physical effects of deliberately included impurities, called dopants, may depend on the dopant position with the crystal. To date, there has not been an effective technique to determine the location of individual dopant atoms in nanocrystals. IRG-4 researchers demonstrated that a combination of scanning transmission electron microscopy and electron energy loss spectroscopy can be used to reveal the position of such “invisible” dopants.

Nano research could impact flexible electronic devices

A discovery by a research team at North Dakota State University, Fargo, and the National Institute of Standards and Technology, shows that the flexibility and durability of carbon nanotube films and coatings are intimately linked to their electronic properties. The research could one day impact flexible electronic devices such as solar cells and wearable sensors.

Metal oxide simulations could help green technology

University of California, Davis, researchers have proposed a radical new way of thinking about the chemical reactions between water and metal oxides, the most common minerals on Earth. Using computer simulations and comparing the resulting animations with lab experiments they found that the behavior of an atom on the surface of the cluster can be affected by an atom some distance away. Instead of moving through a sequence of transitional forms, as had been assumed, metal oxides interacting with water fall into a variety of “metastable states” - short-lived intermediates, the researchers found.

Team develops cheaper way of separating nanotubes

Researchers in London have developed a cheaper way of producing high-quality carbon nanotubes in larger quantities than existing methods. A team from the London Center for Nanotechnology has licensed the process, which separates nanotubes into usable quantities without damaging them, to German-based industrial gases company the Linde Group. LCN’s solution was to charge the nanotubes with electrons so that they naturally repel each other, by reacting them with an alkali metal such as sodium in a solution of ammonia. This solution of separated nanotubes can then be used for manufacturing things such as composites, or the nanotubes can be precipitated out of the solution.

Collaborative learning in networks

“We found that collective exploration improved average success over independent exploration because good solutions could diffuse through the network. In contrast to prior work, however, we found that efficient networks outperformed inefficient networks, even in a problem space with qualitative properties thought to favor inefficient networks. We explain this result in terms of individual-level explore-exploit decisions, which we find were influenced by the network structure as well as by strategic considerations and the relative payoff between maxima. We conclude by discussing implications for real-world problem solving and possible extensions.”

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US firm uses solar power to recover oil reserves

A new technology to increase oil production is being tested on one of US’s oldest oil fields in one of the largest demonstration projects of its kind. The new project was launched by Chevron Technology Ventures at the Coalinga Field in California. More than 7,600 mirrors are being used to focus the sun’s energy onto a solar boiler to produce steam that can then be injected into oil reservoirs to enhance oil recovery.

UC Merced research team demonstrates nontracking solar concentrator technology to power air-conditioning unit

Professor Roland Winston and his team of student researchers have designed and developed a system that gathers and concentrates sunlight onto specially made collector tubes. The heat generated can then be transformed using existing technology for cooling, heating and a number of other potential uses. The key factor in their design is this: The collectors are entirely stationary. Typically, solar collectors must move and track the sun to achieve optimal energy production, necessitating additional equipment that can be costly to install and complex to maintain.

Global greenhouse gas emissions hit an all-time high in 2010

Global greenhouse gas emissions increased by 5.8% in 2010 to hit an all-time high of 33 billion tonnes, as continued growth in developing countries swamped both greater use of renewable power and gains in energy efficiency, according to an analysis by the European Commission’s Joint Research Centre and the PBL Netherlands Environmental Assessment Agency. Emissions in China and India increased by 10% and 9%, respectively, compared with 3% in the United States.

Molecular sudoku

A team of scientists from the Catalan Institute of Nanotechnology, ICREA, and Universitat Autonoma de Barcelona investigated the properties of a special kind of sudoku, made by assembling tiny molecules into a 3×3 square array The result is not a mind-boggling game, but a detailed picture of how each molecule interacts with its neighbors and conducts electricity when squeezed between two metallic electrodes.

Mirage effect from thermally modulated transparent carbon nanotube sheets (pdf)

The single-beam mirage effect, also known as photothermal deflection, is studied using a free-standing, highly aligned carbon nanotube aerogel sheet as the heat source. The extremely low thermal capacitance and high heat transfer ability of these transparent forest-drawn carbon nanotube sheets enables high frequency modulation of sheet emperature over an enormous temperature range, thereby providing a sharp, rapidly changing gradient of refractive index in the surrounding liquid or gas.

How fuel cells can help cell phones in a hurricane

A cleaner alternative is emerging. Wireless service providers increasingly are investing in fuel cell systems for backup power. Fuel cells use hydrogen and oxygen, the molecules that create water, to produce electricity with no pollution. We see it as a green alternative that is on the rise. Clean and energy efficient fuel cells can help reduce CO₂ emissions by 50 percent as well as decrease other toxic emissions and deliver additional environmental and efficiency benefits. They also are very quiet, less costly to maintain and are not targets for theft.

Pump may help materials self repair

Artificial microvascular systems can be integrated into structures and materials to aid in self-repair when there’s damage, such as cracks in a coating applied to a building or bridge. Until now, the systems have relied on capillary force to transport healing agents. The team of researchers at the Beckman Institute of the University of Illinois has developed different methods for self-healing, including microvascular systems for self-repair of polymers. The vascular system works when reactive fluids are released in response to stress, enabling polymerization that restores mechanical integrity.

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Scanning electron microscope photo of hollow carbon nanofiber-encapsulated sulfur tubes, at the heart of a new battery design. Credit: Wesley Guangyuan Zheng; Stanford

Stanford University associate professor of materials science and engineering, Yi Cui, knows his way inside and out of a carbon nanotube, and he’s using his knowledge of that terrain to design new electrodes for lithium-ion batteries and ultracapacitors. Two papers published in recent weeks in Nano Letters describe the details.

The first paper (published Sept. 14, subscription required) describes an approach to cathode design for Li-Ion batteries. Sulfur is an attractive cathode material because of its high storage capacity at relatively low voltage. It is also inexpensive, abundant and nontoxic. According to a Stanford press release, batteries with sulfur cathodes can store four to five times as much energy as existing Li-ion batteries.

Previous cathode designs coated sulfur onto porous carbon structures. However, they fail quickly during the charge-recharge cycle because intermediate lithium polysulfide compounds are in contact with the electrolyte solution and dissolve into it. Cui’s graduate student, Wesley Guangyuan Zheng, describes the problem: “[W]e don’t want a large surface area contacting the sulfur and the electrolyte, and on the other hand we want a large surface area for electrical and ionic conductivities.”

The Cui team separated the sulfur from the electrolyte by simply moving it inside the cathode.

Adapting a commercially available water filtration process, they coated the interior of CNTs with sulfur. The new design prevents polysulfides from leaking into the electrolyte solution, while still allowing easy transport of Li ion through the CNT wall. Tests showed a high specific capacity after 150 charge-discharge cycles. In the same paper, they reported improved coulumbic efficiency gained by adding LiNO₃ to the electrolyte.

Cui’s second paper (published Sept. 26) also investigates electrode efficiency, in this case MnO₂, which is a promising material for supercapacitors (also called ultracapacitors) because of its high theoretical specific capacity, low cost and nontoxicity. Although it is blessed with a high charge storage capacity, it has low electrical and ionic conductivity, so getting the charge in or out quickly is a barrier.

To improve the conductivity of the electrode at its surface, two conductive coatings were investigated: carbon nanotubes and a conductive polymer. Coatings were applied by dipping a graphene-MnO₂ nanostructured composite electrode into a solution of the coatings.

Both coatings increased electrode conductivity, and therefore capacitance. The specific capacitance of the CNT-coated electrode increased by 25 percent and that of the polymer-coated electrode increased by 45 percent. The paper also reports that the coated electrodes, which the authors describe as ternary composites, delivered superior cycling performance, retaining over 95 percent of their capacitance after more than 3000 cycles.

In a Technology Review story, it was pointed out that the energy density of the electrode has yet to be reported.

We first reported on Cui’s simple approaches to using CNTs to make supercapacitors about two years ago.

Coincidentally, Penn State just announced that is has received $5 million from DOE to develop a battery that can provide 600 watt-hours per hour. Included will be research on developing a “nanocomposite sulfur cathode and lithium-rich composite anode material.”

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Rice University researchers, Robert Vajtai, Enrique Barrera and Yao Zhao created a conductive cable from iodine-doped nanotubes capable of carrying household current. Credit: Jeff Fitlow/Rice University

Showing how something works is more effective than telling how it works. With the assistance of a fluorescent lightbulb, Rice University researchers demonstrated successful substitution of standard copper wiring with a carbon nanotube cable.

Using double-walled CNTs spun into a cable several centimeters long, a recent Rice PhD, Yao Zhao, constructed a rig that allowed him to run electricity through a CNT cable to a fluorescent lightbulb. The lightbulb was left “on” for several days without interruption and without any sign of degradation in the CNT cable. Zhao is in Enrique Barrera’s research group. CTT recently interviewed Barrara as part of the MSE football series.

The cable was constructed of billions of double-wall CNTs and fabricated by collaborators at Tsinghua University in China. The cables were doped with iodine to increase their conductivity, and Zhao found they could be tied together without losing conductivity.

In a Rice press release, Barrera says the cables have the potential to be just as effective as metal wiring, at about 1/6 the weight. He also said that the chemical processes used to make lab-scale cables will become part of a larger process that starts with raw materials and produces a steady stream of nanocable. The next step for the team is “to make longer, thicker cables that carry higher current while keeping the wire ligtweight.”

The work was published in the Nature journal, Scientific Reports.

Meanwhile, NIST has been studying the reliability of CNTs for electronic devices with the goal of developing measurement and techniques to test fabrication quality and reliability.

Recession and clumping, in gold electrodes after NIST researchers applied 1.7 volts of electricity to the carbon nanotube wiring for an hour. NIST reliability tests may help determine whether nanotubes can replace copper wiring in next-generation electronics.Credit: M. Strus; NIST

Possibly relevant to the Rice work, NIST researchers have been studying failure in CNT networks, where electrons physically jump from one CNT to another, and found that failure seemed to happen between nanotubes, which is the point of greatest resistance. In a press release, NIST postdoctoral researcher, Mark Strus said that by monitoring the initial starting resistance and stages of degradation, it was possible to predict whether the resistance would degrade gradually or sporadically. Gradual degradation is preferred because it allows for operational limits to be set for devices. NIST has developed some electrical stress tests “that link initial resistance to degradation rate, predictability of failure and total device lifetime. The test can be used to screen for proper fabrication and reliability of nanotube networks.”

Also from NIST, a study of CNT interconnects between gold electrodes found that the CNTs carried very high current densities for awhile, but degraded under constant current. By about 40 hours, the edges of the metal electrodes receded and clumped, leading to device failure. Further NIST research is focusing on the intersections between CNT and metals, as well as between different CNTs. In th press release Strus said, “The common link is that we really need to study the interfaces.”

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A key tenet of the Materials Genome Initiative for Global Competitiveness (pdf) is using computation to reduce the time for materials development by 75%, from 20 years to 5 years. A recent press release from Fujitsu Laboratories in Japan gives an early clue about the feasibility of this approach.

Fujitsu is interested in developing materials for novel nanodevices to replace silicon large scale integration devices. The drive to shrink electronic devices is starting to run up against the physical limits of the material to be miniaturized.

Turning to computational methods, Fujitsu used a first-principles method to calculate the electrical properties of a 1,000-atom device based on carbon nanotubes and graphene electrodes. In the press release the company says the significance of this breakthrough is that “The new technology opens the door to the design of exceptionally high-speed, energy-efficient nanodevices that break totally new ground with their development.”

First-principles computation is based on the quantum mechanics of a material’s electrons and atoms, thus experimental data or empirical parameters are not needed. It is useful for simulating the properties of materials like carbon where small differences in atomic arrangement results in large property differences. Consider, for example, how different the electrical properties of charcoal, graphite and diamond are.

Electrical properties were calculated using software developed by the Japan Advanced Institute for Science and Technology and the computational power of a supercomputer at the Information Technology Center at Nagoya University. First-principles calculations are iterative and tend to need a lot of computing time and memory. Each iteration updates input values and the computation continues until the output values converge. It took about three days to calculate the electrical properties of a 1,000-atom nanodevice using about one-third of the supercomputer’s capacity.

In the press release, Fujitsu explained that they worked with JAIST to tweak the software somewhat, and that they also used a “hybrid parallel processing technique.” As a result, Fujitsu was able to include the modeling of several times more atoms than it had previously be able to do.

The nanodevice modeled is a carbon nanotube with graphene electrodes. Lithium atoms occupied the inner edges of the graphene electrodes and several hydrogen atoms bridge the atomic layer between the electrodes and the nanotube. This is a very simple system, atomically, compared to most commercial engineered materials, which often have complex compositions or atomic structures. However, the company said its success in this instance “significantly paves the way to designing novel nanodevices.”

Because the Materials Genome Initiative is aimed at elevating the United States’ national competitiveness, there is some irony of discussing the efforts of a Japanese enterprise. However, this example illustrates the type of technology—also available in the US—that the MGI intends on leveraging.

And, while Fujitsu’s work shows great promise for designing a type of nanodevice, it also demonstrates that this route to materials design requires sizeable computational investment (hardware and software). Even at the speed attained by Fujitsu, the span of potential materials compositions, crystalline structures, properties and applications make it clear that a lot of computational capacity and agility will be needed in the US.

The Fujitsu work was published in the Aug. 11 online edition of Applied Physics Express.

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