Sharing Materials Engineering Technology

NEWS FROM THE WORLD OF MATERIALS

noreply@blogger.com (Madhawa Habarakada) — Wed, 09 Nov 2011 15:18:00 +0000

Materials Scientist Dan Shechtman Wins 2011 Nobel Prize in Chemistry

On October 5, 2011, the Nobel Prize Committee honored materials scientist Dan Shechtman of Technion in Haifa, Israel, with the 2011 Nobel Prize in Chemistry "for the discovery of quasicrystals." But those five official words describing his discovery in 1982 do not even hint at the years of scientific turmoil from which Shechtman emerged triumphant only after a long battle with prominent dissenters in the scientific community. Shechtman spoke as a plenary lecturer at the XX International Materials Research Congress in Cancun, Mexico, on August 17 this year, and the Materials Research Society filed a version of the following story (with some augmentation here) on his talk.

Quasi-periodic Materials—Crystal Redefined
Plenary Lecture by Dan Shechtman

In a fascinating, funny, and heartfelt exploration of the nature of scientific discovery and the complications that come from being right when most of your colleagues think you are wrong, Dan Shechtman of Technion (Israel) and Iowa State University (United States) told the story surrounding his discovery of quasi-periodic crystals in 1982. Along the way he outlined the history of crystallography and provided a great brush-up tutorial on the subject for those of us who studied it a long time ago.

Shechtman showed the page of his TEM logbook from April 8, 1982, when he performed a selected area diffraction on a pitch black grain of an Al-25%Mg sample and saw a diffraction pattern of 10 spots around a central spot. “Ten spots—that cannot be,” he said to himself, as he carefully counted again. He knew that according to the rules of crystallography, 10-fold symmetry was a forbidden crystallographic symmetry state. He wrote “(10-fold???)” in the logbook and went out into the hall looking for someone to show his discovery, but no one was there. When he started telling colleagues about it, no one believed him, beginning what he called the “the years of rejection,” which lasted from 1982 to 1987. At one point during these years he was called a “disgrace to his research group” and was asked to leave. His attempt to publish his results was rejected by the Journal of Applied Physics in 1984, and finally found a publisher in Metallurgical Transactions in 1985.

“Immediately after publication,” Shechtman said, “all hell broke loose. A lot of people said it was nonsense.” He noted that “at the frontier of science, there is not much difference between science and religion. They [scientists] have their prophets and their beliefs.” Linus Pauling, a two-time Nobel Laureate, was his biggest opponent. Pauling insisted that Shechtman was observing the effects of twinning, not a diffraction pattern from a single crystal. But he persevered in his investigations of this forbidden symmetry, using smaller and smaller electron spot sizes, until it became evident that if there was twinning, the twinned particles would have to be smaller than the 400-angstrom electron spot size he was using. He was eventually vindicated when x-ray diffraction data—the gold standard in deciding crystallographic arguments at the time—showed 5-fold rotational symmetry in 1987.

These crystals were not strictly periodic, so they defied the definition of crystallinity that had been accepted for 70 years. Shechtman had discovered quasi-periodic crystalline materials. Instead of a constant distance between each atom in the lattice, the ratio of distances varied in accordance with the Fibonacci series, hence the term “quasi-periodic.” This paradigm shift led to a formal redefinition of the word crystal by the International Society of Crystallographers: “By crystal we mean any solid having an essentially discrete diffraction diagram, and by aperiodic crystal we mean any crystal in which three-dimensional lattice periodicity can be considered to be absent.” Shechtman noted the “soft” wording of this definition, and said “suddenly the Society of Crystallographers became modest. And a good scientist is a modest scientist.”

In the question and answer session following his plenary lecture, Shechtman was asked what he learned from his scientific struggles. “Tenacity,” he answered. “If you get a result that you believe in, then fight for it.”

Materials in Focus

Special World Materials Summit Coverage

The World Materials Summit, sponsored jointly by the MRS, the European MRS (E-MRS), and the Chinese MRS (C-MRS), took place in Washington, D.C., from October 9-12, 2011. This invitation-only event featured approximately 100 of the world's top experts in materials and energy, along with prominent officials from government energy departments around the world. This summit also included, for the first time, a Student Congress comprising 45 of the most promising graduate students and post-docs from across the globe, who met to learn from the experts, to discuss in detail how materials and energy challenges vary from country to country, and to propose a path forward to a sustainable planet. In the end, the summit issued a formal declaration combining recommendations from both the panels of experts and from the Student Congress regarding the most important steps to be taken to achieve global sustainability. The 2011 World Materials Summit was funded in part by the National Science Foundation, the Department of Energy's Office of Basic Energy Sciences, the Office of Naval Research, Aldrich® Materials Science, American Elements®, Dow®, and the European Science Foundation's Materials Committee.

Here we present the highlights of three talks given by speakers from the three regions sponsoring the World Materials Summit.

European Union

Bernard Frois of the CEA--the French Alternative Energies and Atomic Energy Commission (Commissariat à l'énergie atomique et aux énergies alternatives)--sees the de-carbonization of transportation technologies through the use of batteries and fuel cells as one key to a sustainable energy future. The CEA proposes to achieve this goal by controlling the whole process chain, including electrode materials, electrochemical cells, battery packs, battery management systems, and intelligent charging technologies. These individual components and combined systems will be tested at every step of the way from laboratory bench tops to vehicle fleets.

Nanomaterials will play a major role in this process, according to Frois, by taking advantage of quantum effects to enable chemical reactions that are not possible with bulk materials. They increase the electrode/electrolyte contact area, thereby increasing the charge/discharge rates. The shorter path lengths available at the nanoscale will lead to increased power generation.

“We have the battery,” Frois said, referring to the iron-phosphate-based LiFePO₄/Li₄Ti₅O₁₂ cell that he called “the best material ever for a battery.” It is safe and stable, he said, and a car powered by it can be can be fully recharged in 10 minutes. Its performance will be enhanced by a battery management system consisting of sensors and actuators in communication with a CPU.

On the fuel cell side, Frois said that “one of these days hydrogen will be everywhere.” He pointed to the very expensive Opel Hydrogen 4 already being sold in Europe by GM as a first step in this direction. This automobile uses compressed hydrogen in a storage tank at 700 bars pressure to reach speeds of 100 mph and distances of 220 mi. The proton exchange membrane systems that fuel cells currently rely on use a Pt catalyst that is too expensive, so much research is taking place to find a substitute for Pt. “Everybody is working on it,” Frois said.

In the future, Frois envisions an electric vehicle as an energy storage device that will become part of the smart grid, downloading energy from it when needed and uploading unused energy to it at favorable times.

China

Duan Weng of Tsinghua University in China spoke about “Life Cycle Assessment as a Component of Materials Science and Engineering for a Sustainable World.” He started by trying to distinguish green chemistry from environmentally conscious materials (ecomaterials). “Both have a lot in common,” Weng said, “but they are recognized very differently.” While Weng did not propose a definition of ecomaterials in his talk, the CAP' EM (Cycle Assessment Procedure for Eco-materials) group (http://www.capem.eu/capem/en/6939-capem.html) of five European countries have developed this definition: “An ecological building material/product [ecomaterial] is a material/product with no heavy negative environmental impact and with no negative health impact.”

But Weng’s statements suggested that he would disagree with such a definition. “The perception that ecomaterials are materials for environmental protection is misleading,” Weng said. “In fact, all materials and processes have environmental impacts.” He proceeded to give two examples of controversial ecomaterials: (1) silicon solar cells, which are green during operation, but which require 3-5 years to reclaim the energy consumed during their manufacture, and (2) TiO₂, which is used as a photocatalyst for waste water treatment, but which produces 70 kg of wastewater during the production of 1 kg of TiO₂.

These examples show that environmental assessment is missing in materials science and engineering, according to Weng, and that a method is needed to quantitatively compare different options and tradeoffs. “Life cycle assessment [LCA] is the best framework for evaluating the environmental impact of materials,” Weng said. He noted that the European Union’s Seventh Framework Program (FP7), which bundles all research-related EU initiatives together to play a crucial role in reaching the goals of growth, competitiveness and employment in the EU, has adopted LCA requirements. The Chinese Energy Conservation and Emission Reduction (ECER) policy also requires LCA for all products and processes, he said. “All materials and processes have environmental impacts along their lifecycles that should be reduced,” Weng concluded.

United States

William Brinkman, Director of the U.S. Department of Energy’s (DOE) Office of Science, stated that the department’s research focus in materials involves efforts to (1) synthesize new materials, (2) characterize them, (3) measure and analyze them, and (4) create theories to further develop new materials. He stressed the importance of theory and simulations in these efforts. Specifically, the recently available petaflop (10¹⁵ operations/sec.) supercomputers have allowed simulations of materials to finer resolutions or at larger scales. “We used to talk about electronic band theory,” Brinkman said, “but now we discuss topological insulators with robust surface states.” One aspect of the Materials Genome Project is to find all compounds that can be made out of two metals plus oxygen for use as possible cathode materials, which could not be done in a timely fashion before petascale computers became available.

By 2021, Brinkman expects exascale (10¹⁸ operations/sec) computers to be online. But, while increasing the computing power enormously, such computers will also have drawbacks. “An exascale computer needs 100 MW of power," he said. “That’s equivalent to a small power plant.” Also, he noted that as you shrink electronic devices you lose accuracy in calculations, which leads to the challenge of how to handle an increased number of errors.

In terms of characterizing and testing new materials, Brinkman noted the abundance of x-ray, synchrotron, mass spectrometer, and microscopy technologies that have been and are still being developed. He was very excited about a new free-electron laser operating in the x-ray region, which enables femtosecond x-ray protein nanocrystallographic analysis. “A biological liquid droplet is destroyed by the laser,” he said, “but the analysis is fast enough to get its x-ray diffraction pattern before it is destroyed.” Besides this laser technology, he also mentioned the LINAC Coherent Light Source expansion project, which will provide wavelengths less than 2 angstroms; angle-resolved photoemission, which injects one photon into a material to get one electron out; and x-ray speckle imaging that allows scientists to see surface atoms in motion, making it possible to watch phase changes on a surface.

Energy Focus

Scientists Get First Detailed Look at Nitrogen Doping in Single-layer Graphene

by Glennda Chui
Deputy Editor of symmetry at the Stanford Linear Accelerator Center (SLAC)

The strength, flexibility, transparency and high electrical conductivity of single-layer graphene make it a potentially unique and valuable material for the next generation of electronic devices. Made of carbon atoms arranged in a honeycomb pattern – think of a chicken-wire fence – it is 97 percent transparent and 1,000 times stronger than steel.

Researchers are working on ways to tune the properties of graphene for specific electronic applications. One way to do that is by doping – introducing small amounts of other elements, such as nitrogen or phosphorus, that either add or subtract electrons from the system. Widely used in silicon technology, doping has been carried out experimentally in single-layer graphene sheets; but until now, the details of how the dopant atoms fit into the sheet and bond with their carbon neighbors remained elusive.

In a study reported Aug. 9 in Science, researchers from Columbia University, Sejong University in Korea, and SLAC and Brookhaven national laboratories used a combination of four techniques to make the first detailed images of nitrogen-doped graphene film [2]. They showed that individual nitrogen atoms had taken the places of carbon atoms in the two-dimensional sheet; that about half of the extra electron contributed by each nitrogen atom was distributed throughout the graphene lattice; and that this changed the electronic structure of the graphene sheet only within a short distance – about the width of two carbon atoms – from the dopant atoms. The ability to control the electronic structure at the atomic level has important implications for tuning the unique electronic properties of graphene for particular device applications.

“We’re not trying to work on existing systems and make them better. We’re looking for new directions that can potentially enable much higher efficiencies,” said paper co-author Theanne Schiros, a surface scientist at the Department of Energy’s Energy Frontier Research Center at Columbia, who is investigating graphene as a possible electrode for novel photovoltaic devices.

“Now we see that doping is a strategy that can be applied to graphene cleanly and robustly,” she said, providing a potential way to create high-quality graphene films for use in electronic applications, including solar cells.

Schiros is no stranger to SLAC, having done her Ph.D. work here under Anders Nilsson. Her current work at Columbia focuses on using X-rays from synchrotron light sources to probe novel materials for use in renewable energy technologies.

For this study, she returned to SLAC to work with Dennis Nordlund, a staff scientist at SLAC’s Stanford Synchrotron Radiation Lightsource (SSRL), where recent upgrades allowed them to automatically scan many samples of the nitrogen-doped graphene films at once.

The research team grew the films by depositing chemical vapor on a thin sheet of copper foil.

They analyzed some samples of film while it was on the copper foil, and transferred others to silicon dioxide, the standard substrate for device measurements, for testing. Each sample was examined with Raman spectroscopy and scanning tunneling microscopy (STM) at Columbia, and with X-ray beams at SLAC’s SSRL, and Brookhaven’s National Synchrotron Light Source (NSLS).

The Raman spectra showed that the nitrogen dopant had changed the electronic properties of the graphene sheet without disturbing its basic structure. X-ray measurements at SSRL beamlines 10-1 and 13-2 and NSLS beamline U7A indicated that the nitrogen atoms lay within the plane of the graphene sheet and had each bonded with three carbon neighbors; in other words, each nitrogen atom had replaced a carbon in the sheet.

Finally, the STM images showed the nitrogen atoms as bright spots on the graphene surface. By counting those spots, the researchers determined that the concentration of nitrogen dopant per carbon atom varied from .23 to .35 percent. The images also revealed that the nitrogen atoms stuck out from the graphene layer by about .6 Ångstrom, as they would if they had substituted for carbon in the lattice. These results were consistent with STM image simulations based on theory.

The lead author of the paper was Columbia physics graduate student Liuyan Zhao, working in the laboratory of Abhay N. Pasupathy, and the work was carried out in cooperation with the Energy Frontier Research Center at Columbia, which counts SLAC and Stanford among its collaborators.

While most of the research was performed at Columbia, the advanced materials characterization capabilities at SLAC and Brookhaven played an important role, Schiros said. The results demonstrate the value of the synergy between universities, DOE national labs and the DOE’s 46Energy Frontier Research Centers [4], which conduct basic and advanced research needed to establish the scientific foundation for a fundamentally new energy economy in the United States.

Image in Focus

Giraffe's Fur

An atomic force microscope false color image of lanthanum cobalt oxide perovskite film grown on a strontium titanium oxide substrate. By breaking up into grains, this material portrays the surprisingly organic beauty of inorganic thin film growth.

Credit: Virat Mehta, University of California, Berkeley
(Click image to enlarge.)

Ferroelectrics could pave way for ultra-low power computing

noreply@blogger.com (Madhawa Habarakada) — Sat, 08 Oct 2011 03:27:00 +0000

Minimum capacity

Engineers at the University of California, Berkeley, have shown that it is possible to reduce the minimum voltage necessary to store charge in a capacitor, an achievement that could reduce the power draw and heat generation of today’s electronics.

“Just like a Formula One car, the faster you run your computer, the hotter it gets. So the key to having a fast microprocessor is to make its building block, the transistor, more energy efficient,” said Asif Khan, UC Berkeley graduate student in electrical engineering and computer sciences. “Unfortunately, a transistor’s power supply voltage, analogous to a car’s fuel, has been stuck at 1 volt for about 10 years due to the fundamental physics of its operation. Transistors have not become as ‘fuel-efficient’ as they need to be to keep up with the market’s thirst for more computing speed, resulting in a cumulative and unsustainable increase in the power draw of microprocessors. We think we can change that.”

Khan, working in the lab of Sayeef Salahuddin, UC Berkeley assistant professor of electrical engineering and computer sciences, has been leading a project since 2008 to improve the efficiency of transistors.

The researchers took advantage of the exotic characteristics of ferroelectrics, a class of material that holds both positive and negative electrical charges. Ferroelectrics hold electrical charge even when you don’t apply a voltage to it. What’s more, the electrical polarization in ferroelectrics can be reversed with the application of an external electrical field.

The engineers demonstrated for the first time that in a capacitor made with a ferroelectric material paired with a dielectric – an electrical insulator – the charge accumulated for a given voltage can, in effect, be amplified, a phenomenon called negative capacitance.

The team report their results in the Sept. 12 issue of the journal Applied Physics Letters. The experiment sets the stage for a major upgrade to transistors, the on-off switch that generate the zeros and ones of a computer’s binary language.

“This work is the proof-of-principle we have needed to pursue negative capacitance as a viable strategy to overcome the power draw of today’s transistors,” said Salahuddin, who first theorized the existence of negative capacitance in ferroelectric materials as a graduate student with engineering professor Supriyo Datta at Purdue University. “If we can use this to create low-power transistors without compromising performance and the speed at which they work, it could change the whole computing industry.”

The researchers paired a ferroelectric material, lead zirconate titanate (PZT), with an insulating dielectric, strontium titanate (STO), to create a bilayer stack. They applied voltage to this PZT-STO structure, as well as to a layer of STO alone, and compared the amount of charge stored in both devices.

“There was an expected voltage drop to obtain a specific charge with the dielectric material,” said Salahuddin. “But with the ferroelectric structure, we demonstrated a two-fold voltage enhancement in the charge for the same voltage, and that increase could potentially go significantly higher.”

Since the first commercial microprocessors came onto the scene in the early 1970s, the number of transistors squeezed onto a computer chip has doubled every two years, a progression predicted by Intel co-founder Gordon Moore and popularly known as Moore’s Law. Integrated circuits that once held thousands of transistors decades ago now boast billions of the components.

But the reduced size has not led to a proportional decrease in the overall power required to operate a computer chip. At room temperature, a minimum of 60 millivolts is required to increase by tenfold the amount of electrical current flowing through a transistor. Since the difference between a transistor’s on and off states must be significant, it can take at least 1 volt to operate a transistor, the researchers said. “We’ve hit a bottleneck,” said Khan. “The clock speed of microprocessors has plateaued since 2005, and shrinking transistors further has become difficult.”

The researchers noted that it becomes increasingly difficult to dissipate heat efficiently from smaller spaces, so reducing transistor size much more would come at the risk of frying the circuit board. The solution proposed by Salahuddin and his team is to modify current transistors so that they incorporate ferroelectric materials in their design, a change that could potentially generate a larger charge from a smaller voltage. This would allow engineers to make a transistor that dissipates less heat, and the shrinking of this key computer component could continue.

Notably, the material system the UC Berkeley researchers reported shows this effect at above 200 degrees Celsius, much hotter than the 85 degrees Celsius (185 degrees Fahrenheit) at which a current day microprocessor works. The researchers are now exploring new ferroelectric materials for room temperature negative capacitance in addition to incorporating the materials into a new transistor.

This story is reprinted from material from UC Berkeley, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier.

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Electronic materials•Tools and Techniques

Better lithium-ion batteries are on the way

noreply@blogger.com (Madhawa Habarakada) — Thu, 06 Oct 2011 05:23:00 +0000

A revolutionary conducting polymer enables the use of low-cost, high-energy silicon for the next generation of lithium-ion battery anodes

Lithium-ion batteries are everywhere, in smart phones, laptops, an array of other consumer electronics, and the newest electric cars. Good as they are, they could be much better, especially when it comes to lowering the cost and extending the range of electric cars. To do that, batteries need to store a lot more energy.

The anode is a critical component for storing energy in lithium-ion batteries. A team of scientists at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) has designed a new kind of anode that can absorb eight times the lithium of current designs, and has maintained its greatly increased energy capacity after over a year of testing and many hundreds of charge-discharge cycles.

The secret is a tailored polymer that conducts electricity and binds closely to lithium-storing silicon particles, even as they expand to more than three times their volume during charging and then shrink again during discharge. The new anodes are made from low-cost materials, compatible with standard lithium-battery manufacturing technologies. The research team reports its findings inAdvanced Materials, now available online.

“High-capacity lithium-ion anode materials have always confronted the challenge of volume change – swelling – when electrodes absorb lithium,” says Gao Liu of Berkeley Lab’s Environmental Energy Technologies Division (EETD), a member of the BATT program (Batteries for Advanced Transportation Technologies) managed by the Lab and supported by DOE’s Office of Vehicle Technologies.

Says Liu, “Most of today’s lithium-ion batteries have anodes made of graphite, which is electrically conducting and expands only modestly when housing the ions between its graphene layers. Silicon can store 10 times more – it has by far the highest capacity among lithium-ion storage materials – but it swells to more than three times its volume when fully charged.”

This kind of swelling quickly breaks the electrical contacts in the anode, so researchers have concentrated on finding other ways to use silicon while maintaining anode conductivity. Many approaches have been proposed; some are prohibitively costly.

One less-expensive approach has been to mix silicon particles in a flexible polymer binder, with carbon black added to the mix to conduct electricity. Unfortunately, the repeated swelling and shrinking of the silicon particles as they acquire and release lithium ions eventually push away the added carbon particles. What’s needed is a flexible binder that can conduct electricity by itself, without the added carbon.

“Conducting polymers aren’t a new idea,” says Liu, “but previous efforts haven’t worked well, because they haven’t taken into account the severe reducing environment on the anode side of a lithium-ion battery, which renders most conducting polymers insulators.”

One such experimental polymer, called PAN (polyaniline), has positive charges; it starts out as a conductor but quickly loses conductivity. An ideal conducting polymer should readily acquire electrons, rendering it conducting in the anode’s reducing environment.

The signature of a promising polymer would be one with a low value of the state called the “lowest unoccupied molecular orbital,” where electrons can easily reside and move freely. Ideally, electrons would be acquired from the lithium atoms during the initial charging process. Liu and his postdoctoral fellow Shidi Xun in EETD designed a series of such polyfluorene-based conducting polymers – PFs for short.

Compared with the electronic structure of PAN, the absorption spectra Yang obtained for the PFs stood out immediately. The differences were greatest in PFs incorporating a carbon-oxygen functional group (carbonyl).

The icing on the anode cake is that the new PF-based anode is not only superior but economical. “Using commercial silicon particles and without any conductive additive, our composite anode exhibits the best performance so far,” says Gao Liu. “The whole manufacturing process is low cost and compatible with established manufacturing technologies. The commercial value of the polymer has already been recognized by major companies, and its possible applications extend beyond silicon anodes.”

This story is reprinted from material from Berkeley Lab, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.

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Proton-based transistor

noreply@blogger.com (Madhawa Habarakada) — Thu, 06 Oct 2011 03:37:00 +0000

Protonic parallel to electronic circuitry

Human devices, from light bulbs to iPods, send information using electrons. Human bodies and all other living things, on the other hand, send signals and perform work using ions or protons.

Materials scientists at the University of Washington have built a novel transistor that uses protons, creating a key piece for devices that can communicate directly with living things. The study is published online this week in the interdisciplinary journalNature Communications.

Devices that connect with the human body’s processes are being explored for biological sensing or for prosthetics, but they typically communicate using electrons, which are negatively charged particles, rather than protons, which are positively charged hydrogen atoms, or ions, which are atoms with positive or negative charge.

“So there’s always this issue, a challenge, at the interface – how does an electronic signal translate into an ionic signal, or vice versa?” said lead author Marco Rolandi, a UW assistant professor of materials science and engineering. “We found a biomaterial that is very good at conducting protons, and allows the potential to interface with living systems.”

In the body, protons activate “on” and “off” switches and are key players in biological energy transfer. Ions open and close channels in the cell membrane to pump things in and out of the cell. Animals including humans use ions to flex their muscles and transmit brain signals. A machine that was compatible with a living system in this way could, in the short term, monitor such processes. Someday it could generate proton currents to control certain functions directly.

A first step toward this type of control is a transistor that can send pulses of proton current. The prototype device is a field-effect transistor, a basic type of transistor that includes a gate, a drain and a source terminal for the current. The UW prototype is the first such device to use protons. It measures about 5 microns wide, roughly a twentieth the width of a human hair.

“In our device large bioinspired molecules can move protons, and a proton current can be switched on and off, in a way that’s completely analogous to an electronic current in any other field effect transistor,” Rolandi said.

The device uses a modified form of the compound chitosan originally extracted from squid pen, a structure that survives from when squids had shells. The material is compatible with living things, is easily manufactured, and can be recycled from crab shells and squid pen discarded by the food industry.

First author Chao Zhong, a UW postdoctoral researcher, and second author Yingxin Deng, a UW graduate student, discovered that this form of chitosan works remarkably well at moving protons. The chitosan absorbs water and forms many hydrogen bonds; protons are then able to hop from one hydrogen bond to the next.

Computer models of charge transport developed by co-authors M. P. Anantram, a UW professor of electrical engineering, and Anita Fadavi Roudsari at Canada’s University of Waterloo, were a good match for the experimental results.

“So we now have a protonic parallel to electronic circuitry that we actually start to understand rather well,” Rolandi said.

Applications in the next decade or so, Rolandi said, would likely be for direct sensing of cells in a laboratory. The current prototype has a silicon base and could not be used in a human body. Longer term, however, a biocompatible version could be implanted directly in living things to monitor, or even control, certain biological processes directly.

This story is reprinted from material from the University of Washington, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.

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Biomaterials•Electronic materials•Tools and Techniques

NEWS FROM THE WORLD OF MATERIALS

noreply@blogger.com (Madhawa Habarakada) — Thu, 06 Oct 2011 03:16:00 +0000

Materials in Focus

High piezoelectric properties discovered in non-polar block copolymer system

Oak Ridge National Laboratory (ORNL). See also the press release by Ron Walli of ORNL.

Image credit: ORNL. Click image to enlarge.

Image caption: Schematic of the piezoelectric effect in a non-polar block copolymer system.

The discovery of piezoelectric behavior in non-polar block copolymers that is an order of magnitude higher than that found in more traditional inorganic ceramic piezoelectric materials caught researchers from Oak Ridge National Laboratory (ORNL) in Tennessee and Aachen University in Germany off guard. “People did not expect that non-polar block copolymers would show any strong response to electric fields, so that was quite a surprise,” says Volker Urban of ORNL. “When we observed how large the effect was at first we were not sure whether we should even call this a piezoelectric effect.” However, common characteristics with conventional piezoelectric ceramics, such as linear dependence on the electric field strength, convinced them that they were observing a new form of piezoelectric material having different physics at the molecular level.

Most piezoelectric materials found to date have been perovskite ceramics, like lead zirconate titanate (PZT), whose crystalline structure is responsible for piezoelectricity. As reported recently in Advanced Materials, Urban and his colleagues experimented with the non-polar block copolymer poly(styrene-b-isoprene) in solution with toluene. The solvent makes the block copolymers more mobile, but the system retains its underlying phase morphology, such as nanoscale lamellar structures. “So you retain this phase morphology but you make the system more flexible and then you can align the lamellae much more easily in an electric field,” Urban says. “That’s really unique to our research.”

Crystalline piezoelectric materials lose their anisotropy when heated above the Curie temperature, resulting in a loss of their piezoelectric properties. The block copolymer system, however, shows an increase in piezoelectricity when crossing the order-disorder transition temperature. The researchers explain this contrasting behavior by discussing the thermodynamics of the block copolymer system, specifically the entropic gain and the enthalpic penalty as the polymer chain reaches a more Gaussian conformation.

Urban sees potential long term applications for this discovery in the areas of batteries, capacitors, and fuel cells. Polymers have already been used as membranes in fuel cells. “But what has been overlooked until now is what effect electric fields, which of course are present in these electric storage devices, may have on the structure of the polymers that are involved in the system,” Urban says. “This has been neglected completely until now.” He acknowledges that fuel cell membranes have been made from polymers that are simpler than block copolymers, so the effects will be different. But he believes that this research provides a unique perspective that may open up new avenues for the improvement of such devices in the future. [Advanced Materials]

Nano Focus

Antimagnet proposed using superconductor-metamaterial hybrid

Universitat Autònoma de Barcelona, Spain.

Image credit: Alvaro Sanchez, Universitat Autònoma de Barcelona, Spain. Click image to enlarge.

Image caption: (a) a magnet and its field; ((b) two adjacent magnets whose fields interfere; (c) antimagnetic cylinder (yellow) enclosing one of the magnets, preventing the internal magnetic field from leaking out, and preventing interference with the magnetic field of the other magnet.

Building on recent revelations about metamaterials that can cloak a region in space from electromagnetic waves, researchers at the Universitat Autònoma de Barcelona have determined through simulations that it is possible to design an antimagnet using two materials that are within the realm of possibility: metamaterials and superconductors. According to a paper published recently in the New Journal of Physics, Alvaro Sanchez and his colleagues have outlined a method of designing an antimagnet that would “switch off the magnetic interaction of a magnetic material with existing magnetic fields without modifying them.” Such a device could have applications in medical MRI or in reducing the magnetic signatures of planes or ships.

To be precise about what the researchers are proposing, they define an antimagnet as “a material forming a shell that encloses a given region in space while fulfilling the following two conditions: (i) the magnetic field created by any magnetic element inside the inner region—e.g., a permanent magnet—should not leak outside the region enclosed by the shell; and (ii) the system formed by the enclosed region plus the shell should be magnetically undetectable from outside (no interaction—e.g., no magnetic force—with any external magnetic sources).”

Sanchez and his co-authors propose a cylindrical shell for their antimagnet, although they contend that other shapes are possible. The use of a superconductor with magnetic permeability μ = 0 on the inside of the cylinder satisfies condition (i). To satisfy condition (ii), the outer shell of the cylinder would have to be made of a magnetic material with homogeneous radial and angular magnetic permeabilities. Since no known material has these properties, they propose using alternating layers of available materials. A superparamagnet made by embedding ferromagnetic nanoparticles in a non-magnetic material could be used for the first type of layer, and arrays of superconducting plates could be used for the second type, according to the researchers. A ten-layer cylinder with carefully defined permeabilities could produce the desired antimagnetic properties, they contend. The researchers recognize the difficulty of producing a practical antimagnetic device at this time, but offer the results of their simulations as a significant step in the development process. [New Journal of Physics]

Bio Focus

Proton-based transistor could provide viable bio-interface

University of Washington. See also the press release by Hannah Hickey of the University of Washington Office of News and Information.

Image credit: Uniiversity of Washington. Click image to enlarge.

Image caption: On the left is a colored photo of the University of Washington device overlaid on a graphic of the other components. On the right is a magnified image of the chitosan fibers. The white scale bar is 200 nanometers.

Researchers at the University of Washington in Seattle and collaborators at the University of Waterloo in Canada have developed a protonic field effect transistor (H⁺-FET) that controls the flow of protons instead of electrons, making it a good potential starting point for bio-interface devices. In biology, it’s generally the movement of ions (H⁺, Na⁺, K⁺, and Ca²⁺), instead of electrons, that controls processes such as ATP synthesis, neuronal signaling, and cell communication. Protons specifically play a key role in biological energy transduction mediated by ATP.

Lead author Marco Rolandi of the University of Washington coined the word “bionanoprotonics” in a recent paper in Nature Communications to describe this novel field, complementing research being done in bionanoelectronics. “We had to learn and, at times, make up all new terminology because all of a sudden there are no electrodes, there are ‘protodes’ for contacts, and there’s no electronic current, there’s protonic current,” he says.

The H⁺-FET consists of maleic chitosan nanofibers bridging the source and drain of the transistor, which are made of proton-conducting PdH_x. The prototype is built on a traditional Si/SiO₂substrate, which would have to be replaced with a biocompatible and flexible material if these devices are ever used in biological systems. Maleic chitosan is a biodegradable, non-toxic polysaccharide chitin derivative that forms many hydrogen bonds when hydrated. When an electrostatic potential is applied between source and drain, the protons dissociated from the maleic acid groups “hop” along the hydrogen bond network as described by the Grotthus mechanism. This hopping results in a protonic current from source to drain, which can be modulated by a voltage applied to the gate. The measured mobility of this current is 4.9 x 10^-3 cm²V^-1 s^-1. “We think it is actually a molecular level process rather than protons [as hydronium ions] just diffusing between the water molecules, pushing them around,” Rolandi says. Because the mechanism is specific to protons, this device will not be suitable for controlling Na⁺, K⁺, or Ca²⁺. “We wish we could work with those ions, but we’re happy with protons for now,” he says.

Future work will attempt to make a truly nanoscale device; the prototype is a microscale device with nanoscale fibers. Rolandi would like to bridge the source and drain contacts with a single nanofiber of maleic chitosan to see whether that improves the on/off ratio of the H⁺-FET, which is currently low compared to traditional semiconductors. A further goal is to interface these transistors with cell cultures. Ultimately, in the distant future, the goal is to optimize the materials and performance of H⁺-FETs in physiological conditions so that in vivo sensing and stimulation of proton-selective ion channels could become possible. [Nature Communications]

Energy Focus

MATERIALS FOR ENERGY BLOG

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Energy Quartely in MRS Bulletin, September 2011

By Dr. Russell Chianelli, The University of Texas at El Paso, M.R.T.I

Opening the grid across continents: Desert visions.

The September issue of Energy Quarterly in MRS Bulletin reports on the Desertec initiative that promises to distribute solar power from the Middle East and North Africa (MENA) for distribution to Europe. Corinna Wu describes Desertec as a centerpiece of Europe’s plans to dramatically increase renewable sources in its energy supply mix. There are many obstacles to developing the system, some political and some technical. However, one issue that arises in centralized solar with power transmission is the transmission grids that must be constructed and the materials used. In some areas, for example in the Southwestern United States, distributed energy systems involving individual people, businesses, and institutions installing solar power devices on local buildings eliminates the need for long transmission systems. However, in this case, energy storage is the issue. We look forward with interest to the competition between these two approaches.

Solid-state lighting: The future looks bright.

Also, in the September issue is an article by Prachi Patel in which she describes the progress in making LEDs (light-emitting diodes) for practical solid-state lighting devices. LEDs promise to reduce energy use by 75% and increase lifetime by a factor of ten. But technical challenges remain. LEDs are made using semiconductor materials (e.g., InGaN or GaN). However, cost and spectral properties need improvement. These issues are covered in detail in this article.

Batteries for energy: generation and storage

An interview with Yet-Ming Chiang of MIT covers a crucial issue for efficient use of energy in electrical vehicles and solar installations: batteries. Chiang is an entrepreneurial leader in next-generation nano-phosphate lithium batteries, having formed companies such as A123 Systems, which now supplies these batteries to industry, and 24M Systems, which produces flow batteries. Flow batteries are preferred for solar-produced-energy storage. The interview also discusses Chiang’s experience as an entrepreneur and the process that he followed from laboratory research to marketable products.

Image in Focus

Anode Feathers

SEM image of an anode used in lithium ion batteries. This particular sample consists of 95% pure semiconducting single-walled carbon nanotubes.

Credit: Laila Jaber Ansari, Northwestern University

(Click image to enlarge.)

NEWS FROM THE WORLD OF MATERIALS

noreply@blogger.com (Madhawa Habarakada) — Sun, 11 Sep 2011 12:59:00 +0000

Materials in Focus

Photonic edge states allow photons to bypass defects in optical circuits
Joint Quantum Institute (JQI) at the University of Maryland and the National Institute of Standards and Technology (NIST). See also the press release by Chad Boutin of NIST.

Image credit: Joint Quantum Institute. Click image to enlarge.

Image caption: Artist's rendering of the proposed JQI fault-tolerant photon delay device for a future photon-based microchip. The devices ordinarily have a single row of resonators; using multiple rows like this provides alternative pathways for the photons to travel around any physical defects.

In the quest to make robust optical chips for computers and other electronic devices, defects in the materials have proven to be a major challenge to the efficient transmission of photons. “In nanofabrication, there will always be errors in the system,” says Mohammad Hafezi of the Joint Quantum Institute (JQI) at the University of Maryland and the National Institute of Standards and Technology (NIST). “The question we asked ourselves was, ‘can we make a system that doesn’t care about defects?’”

Hafezi and his colleagues, including Jacob Taylor of JQI and Eugene Demler and Mikhail Lukin from Harvard University, answered the question affirmatively in a recent paper in Nature Physics. The answer came by considering a two dimensional array of coupled resonator optical waveguides (CROWs), which are typically used as optical delay components to slow down the transmission of digital data until it is needed. Instead of the common linear arrangement of resonator rings, they simulated a two-dimensional array of resonators. In a linear arrangement, a single defect might be enough to deflect a photon from its path. Now, simply by changing the architecture of the device and not the material, the researchers provided alternate paths, known as “photonic edge states,” that the photon could use to bypass a defect in the system.

But not just any two dimensional array would work in this case. To be effective, the device architecture must be able to make the photons experience the same two-dimensional physics as electrons experience in two dimensions in a magnetic field. “We simulated the quantum Hall effect (QHE) physics for photons,” Hafezi says. “In this way, the robustness that the electron has in the quantum Hall effect is experienced by photons, eliminating the certain effects of nanofabrication errors.” Optical delay lines were used as a first example of this potential technology; in the future, it is possible that the robust photonic architecture could be used in many photonic device components. On a more fundamental level, Hafezi is particularly interested in obtaining a better understanding of the QHE in electrons by analogy with the behavior of the photons in his simulations. [Nature Physics]

Nano Focus

Millimeter-long GaN nanowires grow horizontally on sapphire substrate
(Weizmann Institute of Science, Israel. See also the press release issued by the Weizmann Institute of Science.)
Image credit: Ernesto Joselevich. Click image to enlarge.

Image caption: Illustration of nanowires growing horizontally along nanogrooves.

Most nanowires are born standing up, rising vertically from a substrate to reach heights in the range of tens of micrometers; they typically require post-fabrication processing to form aligned arrays of nanowires suitable for use in an electronic or optical device. Attempts to grow nanowires horizontally on a surface have had some success, but the resulting nanowires were still in the micrometer length range, with limited control over their crystallographic orientation. Now, researchers at the Weizmann Institute of Science in Israel, led by Ernesto Joselevich, have reported in Science the development of a process for producing millimeter-long GaN nanowires by guided growth on various crystallographic planes of a sapphire surface. The process allows the researchers to grow “very long and perfectly aligned horizontal nanowires with exquisite control of their crystallographic orientation,” according to Joselevich.

The research team, which included Ph.D. student David Tsivion, postdoctoral fellow Mark Schvartzman, and staff scientists Ronit Popovitz-Biro and Palle von Huth, used chemical vapor deposition of GaN on eight different sapphire planes seeded with Ni catalysts to achieve these results. Analysis of the nanowires produced on these various planes revealed that those formed on surface steps and grooves were better aligned than those formed on a smooth plane. For instance, on a well-cut, smooth sapphire C-plane, nanowires grew in random triangular patterns following six isomorphic directions. By miscutting the same C-plane by 2°, the nanowires grew along only two directions, forming parallel arrays. “We found that when the substrate is cut in a slightly tilted or unstable plane,” Joselevich says, “the surface wrinkled up upon heating, and the tiny steps and grooves that formed on it made the alignment of the nanowires much better than on a smooth surface.” The authors explained this effect in the paper very simply: “graphoepitaxy overrules epitaxy.”

They report that their GaN nanowires have few defects and excellent optical and electronic properties, making them excellent potential candidates for nanoscale high-power circuits, LEDs, lasers, photovoltaic cells, photodetectors, and radio-frequency, photonic and non-linear optical devices. The relative absence of defects is atypical for semiconductors grown on a substrate, because stresses usually develop that produce defects. “We think this is because, unlike a two-dimensional film, which usually gets stressed, a nanowire can relax by shrinking or swelling sidewise, making the system much more tolerant to mismatch than one is used to seeing in continuous two-dimensional films,” Joselevich speculates. “This is a new one-dimensional nanoscale effect, which, together with the effect of graphoepitaxy, somehow changes the paradigm not only in the new field of nanowires, but also in the well-established fields of epitaxy and thin films.” [Science]

Room-temperature multiferroic materials created at interface
(Helmoltz-Zentrum Berlin (HZB). See also the press release by Eric Verbeten of Helmoltz-Zentrum Berlin.)
Image credit: HZB. Click image to enlarge.

Image caption: HZB staff scientist Florin Radu checks the BaTiO₃ sample alignment in the ALICE diffractometer.

In the search for multiferroic materials—those in which ferroelectric polarization and magnetic order exist simultaneously—researchers have traditionally pursued two paths: the study of intrinsically multiferroic materials, and the fabrication of artificial multiferroics by mixing materials having magnetic and ferroelectric properties into a single structure. While these methods have shown some success, the multiferroic properties have been observed only at very low temperatures (-270 °C), making them impractical for use in electronic devices. Now researchers in Germany, France, and the United Kingdom have produced room-temperature multiferroics by following a third path. “Our method profits from interface effects in thin films,” says Sergio Valencia of Helmoltz-Zentrum Berlin, leader of one of the groups participating in this research. “We show that, as theoretically predicted, electronic effects occurring at the interface of a ferromagnet with a ferroelectric can lead to multiferroicity in the latter.”

As reported in Nature Materials, the ferroelectric they chose was a thin film of BaTiO₃. By depositing a thin layer of ferromagnetic materials such as Fe or Co on BaTiO₃, the researchers were able to induce a remanent magnetic moment along with ferroelectricity spontaneously in the BaTiO₃ film at room temperature. Soft x-ray resonant magnetic scattering and piezoresponse force microscopy revealed remanent magnetization and hysteretic properties. “Most known multiferroic materials have virtually zero remanent magnetization (being antiferromagnets or weak ferromagnets) at room temperature,” Valencia says.

This new material offers two possibilities for practical applications in magnetic data storage devices. First, if the magnetic and ferroelectric materials are not coupled, their states could vary independently, producing a four-state memory bit in place of the two-state one now available. Alternatively, if the magnetoelectric coupling is strong, then the magnetic state of a memory bit could be changed by controlling electric fields, which consumes much less power than the current practice of altering magnetic fields. Valencia says that the next step in this investigation is to determine the strength of the electromagnetic coupling.

This research was a joint project of the Helmholtz-Zentrum-Berlin für Materialen und Energie, Berlin, Germany; the Unité Mixte de Physique CNRS/Thales, Palaiseau, France; the Université Paris-Sud, Orsay, France; the University of Cambridge, United Kingdom; the Université d’Evry-Val d’Essonne, Evry cedex, France; and the Ruhr-Universität Bochum, Bochum, Germany. [Nature Materials]

Bio Focus

Resin-based coatings have high modulus and glass transition temperature
(North Dakota State University, Fargo, ND)
Image credit: Dean Webster, North Dakota State University. Click image to enlarge.

Image caption: Molecular structure of ESEFA resin-based coating.

As part of the ongoing effort to find bio-based replacements for traditionally petrochemical-based products, researchers in the Department of Coatings and Polymeric Materials at North Dakota State University, Fargo, recently announced in Biomacromolecules (an ACS publication) the fabrication of high modulus coatings from epoxidized sucrose esters of fatty acids (ESEFA). Dean C. Webster and his colleagues Xiao Pan and Partha Sengupta crosslinked various vegetable oils through their epoxy groups to form hard, thermosetting resins that could be used as coating materials. According to Webster, earlier attempts to crosslink vegetable oils usually resulted in coatings with low moduli and glass transition temperatures (T_g). “In our paper, we have a few materials with moduli over one GPa, which I think is pretty incredible,” Webster says. “We can get fairly high glass transition temperatures out of these materials as well.” The maximum T_g reported was 103.7 °C.

Webster attributes these properties to the large number of fatty acid (CH₃-xCH₂-COOH) groups—as many as eight—that they attached to sucrose, yielding a high number of epoxy groups. “When we crosslink through those epoxy groups we can get a much higher crosslink density,” he says, “and thus a higher modulus.” The resins are also compact so the viscosity is in the moderate range, making possible a sprayable coating with very little solvent for industrial purposes. While much more testing and characterization must be done to determine viable applications and limitations of these resins before commercialization, Webster foresees possibilities for coatings that are applied and baked on metal surfaces in factory settings. In addition, he and a colleague were recently awarded an NSF grant to look at these resins as matrices for bio-based composites.[Biomacromolecules]

Energy Focus

Pipeline Alternatives to Reduce Carbon Emissions during the Operations of Liquid and Gas Fuels Transmission and Distribution in Mexico

by Lorenzo Martinez-Gomez
www.corrosionyproteccion.com

Last November at the 2010 International Materials Research Congress in Cancun, many countries confirmed strong environmental commitments and established long-range initiatives to reduce global CO₂ emissions into the atmosphere. The Cancun meeting triggered many initiatives in Mexico after the government increased the market value of Mexican carbon bonds. While Mexican carbon bonds are still priced lower than ones traded in Europe, the Mexican valuation is now priced significantly higher than U.S. carbon offsets.

The petroleum industry is a major contributor to the greenhouse gas (GHG) emissions of Mexico. Currently, production practices in the region involve large quantities of gas being burned or released to the atmosphere. Refineries and petrochemical plants are also major sources of GHGs. Transmission and distribution of liquid and gas fuels by trucking are still common practices in Mexico. Cancun and the Riviera Maya together consume over 7 million liters per day of jet fuel, diesel, and gasoline. These fuels have traditionally been transported over land from cities on the Gulf of Mexico such as Merida, Coatzacoalcos, or even Salina Cruz on the Pacific coast, averaging over 400 to 500 km in trucking transport distances per month. In central Mexico, the highly populated and industrialized valley of Cuernavaca, Cuautla, and large parts of Guerrero also rely on fuels transported by truck from Mexico City, Tlaxcala, Puebla, or Toluca.

CO₂ emissions associated with liquid or gas hydrocarbon transmission and distribution are remarkably different when the transportation method is considered. Whereas trucking is heavy in fuel consumption, pipeline delivery is by far the most reliable, cost-effective, and environmentally friendly means of fluid transportation.

Engineering projects have calculated the potential tonnage of CO₂ emissions to be saved by constructing pipeline networks to feed hydrocarbons to both the Cancun – Riviera Maya region and Cuernavaca valley, with many projects benefitting from funding based on carbon dioxide bonuses. Accurate calculations of this sort may sustain the costs of important pipeline projects based on the long-term value of the savings of carbon dioxide emissions.

Software has been developed to combine and analyze all research results involved in the calculation of the carbon signatures of pipeline and truck transportation of liquid and gas hydrocarbons. Geographical information systems were employed to perform calculations for alternative potential right-of-way trajectories, as well as the fuel consumption associated with the current trucking routes. Other considerations are related to the carbon signature of trucking as a whole, including the excess of human resources, the differential needs of metering, tanking, and logistics, and the overall critical storage facility involved.

Considering European and Mexican carbon dioxide bond values, the resulting financing opportunities for pipeline projects are significant. For the case of supplying hydrocarbons by pipeline to Cancun and the Rivera Maya, the projected carbon dioxide emission savings over 30 years could finance an important segment of the pipeline construction project. Pipeline construction to supply hydrocarbons to the Cuernavaca – Cuautla Valleys would also result in saving millions of tons of CO₂ emissions.

Image in Focus

Peppermint Towers

SEM image of VLS-grown Si microwires coated with droplets of wax (which have been false-colored using Adobe Photoshop).

Credit: Emily Warren, California Institute of Technology
(Click image to enlarge.)

NEWS FROM THE WORLD OF MATERIALS

noreply@blogger.com (Madhawa Habarakada) — Mon, 08 Aug 2011 15:14:00 +0000

Materials in Focus

Hydrogen pressure may control graphene growth
Oak Ridge National Laboratory (ORNL). See also the press release by Ron Walli of ORNL.)
Image credit: ORNL. Click image to enlarge.

Image caption: Graphene grains come in several different shapes. Hydrogen gas controls the grains' appearance.

In one currently popular way of making graphene, methane (the carbon source) is mixed with molecular hydrogen, and the two gases flow over a copper substrate at a temperature of approximately 1000 °C. The role of hydrogen in this process has been difficult to assess because its concentration has varied from essentially zero to several thousand times the amount of methane in different experiments. Now researchers from Oak Ridge National Laboratory (ORNL) and New Mexico State University, by carefully controlling the hydrogen/methane ratio, have determined that hydrogen performs two roles in the graphene formation process: (1) it acts as a co-catalyst with the copper, and (2) it acts as an etchant to control graphene grain size and shape. The results were reported recently in ACS Nano.

The group, led by Ivan Vlassiouk at ORNL, observed the growth of graphene over copper at a constant methane concentration of 30 ppm while the pressure of H₂ was varied from zero to 19 Torr. They discovered that below a hydrogen pressure of 2 Torr, no graphene formed. Between approximately 2 and 9 Torr, irregular graphene grains were formed. At hydrogen pressures of 10 Torr and above the researchers observed perfect hexagons of graphene. Kinetically, the rate of graphene formation peaked near 11 torr. The grains reached a maximum size of approximately 12 microns (edge-to-edge) at 19 Torr, at which point further grain growth ceased.

Mechanistically, below 2 Torr of hydrogen the methane has to chemisorb on the copper surface—a thermodynamically unfavorable condition. Above 2 Torr, molecular hydrogen readily dissociates on copper and promotes activation of physisorbed methane, producing surface bound CH₃ radicals. Dehydrogenation of this species eventually leads to a single layer of graphene on the copper surface. Remaining chemisorbed hydrogen etches weak carbon-carbon bonds, thereby limiting the further growth of graphene grains. [ACS Nano]

Nano Focus

Remove lens, insert algorithm
(University of California San Diego. See also the press release by Kim McDonald of the UC San Diego News Center.)
Image credit: UC San Diego. Click image to enlarge.

Image caption: Magnetic domains appear like the repeating swirls of fingerprint ridges. As the spaces between the domains get smaller, computer engineers can store more data.

By replacing the lenses of an x-ray microscope with a computer algorithm, researchers led by Oleg Shpyrko of the University of California San Diego have taken advantage of 100% efficiency in x-ray photon collection to achieve 50-nm resolution images of magnetic domains of a gadolinium/iron film. As reported recently in the Proceedings of the National Academy of Sciences, such precise imaging could prove to be invaluable to scientists and engineers who are trying to form ever smaller magnetic bits to increase the storage capacity of memory devices.

Lenses that focus x-rays are difficult to fabricate, and they generally do not have very high resolution. To avoid these problems, Shpyrko and his colleagues simply allow the incident x-ray beam to impinge on the sample and diffract, creating a Fourier transform of the sample. In the process the phase of the x-ray beam is lost. Ashish Tripathi, a graduate student in Shpyrko’s lab, did the hard work of developing an algorithm to correct for this loss. “The algorithm allows us to recover the phase that was lost in the measurement,” Shpyrko says, “and invert the image in the computer to get a real-space image. It does this in a way that does not produce any aberrations in the image, and it’s highly scalable with the new types of x-ray sources that will come on line soon.”
This technology uses every single photon that strikes the sample, according to Shpyrko, so no photons are wasted. Because the resolution is limited only by the number of photons collected, he says, “you can actually get all the way down, in principle, to the diffraction limit for x-rays, which would be atomic level resolution. We’re not there yet, but in principle it just requires more photons.”

The imaging of magnetic domains was just a first step in demonstrating the capabilities of this new x-ray microscope. The researchers are currently using it to investigate orbital ordering and charge ordering, and can envision using it to image defects in crystals and for other materials science challenges. Because it uses elemental x-ray edge photons, the microscope can also identify where specific elements are located in a sample, revealing information about the sample’s chemistry. [Proceedings of the National Academy of Sciences]

Bio Focus

Filamentary serpentine layout is key to epidermal electronic "smart skin"
(University of Illinois at Urbana-Champaign. See also the press release by Liz Ahlberg of the University of Illinois News Bureau.)
Image credit: John A. Rogers, University of Illinois. Click image to enlarge.

Image caption: University of Illinois researchers can mount electronic devices on an ultrathin, skin-like platform that mounts directly onto the skin with the ease, flexibility and comfort of a temporary tattoo.

“Narrow, wavy, and thin”—that’s how John Rogers of the University of Illinois at Urbana-Champaign describes the new “epidermal electronics” that he and his co-workers have developed for both monitoring electrical signals from the heart, brain, and muscles, and for stimulating muscles by supplying electrical signals. As reported recently in Science, they have fabricated elastomeric patches containing open, spider–web layouts of electrical circuits that have modulus and bending properties very close to that of human skin, making them easy to wear and potentially useful in sleep studies, neonatal care, and rehabilitation applications, among others.

The key to the flexibility and stretchability of the design is the “wavy” nature of the electronic circuits, known more technically as a “filamentary serpentine” layout, which consists of components with many large loops instead of shorter, linear circuit paths. “If you look at the designs that best match the properties of skin in our work, they involve the entire circuitconsisting of this filamentary serpentine shape,” Rogers says. “So not only the interconnect wires but the devices themselves—the silicon itself, including transistors and the other device components, have this serpentine geometry.” Quantitative mechanics modeling was used to determine the optimal thickness of the filaments and the loop geometry for the best skin matching.

The result is an elastomeric patch less than 7 microns thick containing an antenna LED, a wireless power coil, radio frequency coils and diodes, a temperature sensor, and electroencephalogram, electrocardiogram, and electromyogram sensors to monitor the brain, heart, and muscle signals, respectively. The circuit is attached to the skin by van der Waals forces only, so no adhesive is needed; the van der Waals forces are sufficient to maintain conformal contact with the skin, withstanding normal body movements over periods of hours without cracking or delamination. The researchers have also experimented with commercially available temporary transfer tattoos that could conceal the circuitry and provide greater adhesion if necessary.

This technology is an outgrowth of the macro-scale stretchable electronics that Rogers’ group and others have been investigating. Earlier versions were just too thick (a few mm to a cm), with elastic moduli a few orders of magnitude too high to match the skin. “We’ve extended some of those design concepts that we and others have been exploring in stretchable electronics to an extreme, in terms of design, filamentary shape, thinness, and modulus-matched substrate to enable this epidermal format,” Rogers says. “We view it as a different class of technology for that reason, but it has historical origins in flexible and, more recently, stretchable forms of electronics.” [Science]

Energy Focus

High energy density demonstrated in Li-air batteries
(Massachussetts Institute of Technology. See also the press release by David L. Chandler, MIT News Office.)
Image credit: Mitchell, Gallant, and Shao-Horn. Click image to enlarge.

Photo caption: Ions of lithium combine with oxygen from the air to form particles of lithium oxides, which attach themselves to carbon fibers on the electrode as the battery is being used. During recharging, the lithium oxides separate again into lithium and oxygen and the process can begin again.

Lithium-air (also known as Li-O₂) batteries may one day compete with lithium ion (Li-ion) batteries as the next generation energy storage device, but researchers are still in the early stages of understanding how they operate and how to improve their performance. A big step in both these directions was taken by researchers Robert Mitchell, Betar Gallant, and their colleagues at MIT recently, with their description in Energy & Environmental Science (a publication of the Royal Society of Chemistry) of a new oxygen electrode made of binder-free, all-carbon hollow nanofibers. They have achieved among the highest energy densities by weight reported to date for Li-air batteries, according to Mitchell, and in the process have observed the growth and disappearance of Li₂O₂ in the electrode during the battery’s discharging and charging stages, respectively.
The projected energy density for Li-air batteries is approximately 3 to 5 times that of Li-ion batteries. “One of the reasons is the way that Li-air batteries operate and the way that they’re designed,” Gallant says. “The heavy cathode material in a Li-ion battery is replaced with a very lightweight porous carbon support, which stores energy by reacting molecular oxygen from the air with Li ions to form a new solid phase that grows inside the carbon framework. This new phase is also significantly lighter compared to Li-ion cathodes, resulting in a gravimetric energy density that is several times higher.”
This new phase, which is typically lithium peroxide (Li₂O₂), forms when the battery is discharging, and needs a conductive scaffold in which to grow. Using chemical vapor deposition to grow nanofibers directly on a porous substrate produced a “carpet” of hollow carbon nanofibers with diameters on the order of 30 nm and a void volume greater than 90%. “Typically the electrode structure in these types of batteries is composed of nanosized carbon particles with void volumes on the order of 60%,” Mitchell says. The additional 30% of void volume “allows you to store a lot of Li₂O₂ in the electrode. We’re trying to see how much carbon is really necessary to support the reversible formation and storage of Li₂O₂.”
In the process, the researchers used ex situ SEM to observe the formation of Li₂O₂ on the sidewalls of the carbon nanofibers during discharge, starting as spheres that transformed to toroids before coalescing into monolithic Li₂O₂. During charging, they were able to see the Li₂O₂ slowly break down and disappear. “For increasing the discharge capacity, which is directly related to the amount of energy that can be stored in the battery,” Gallant says, “we’ve shown that modifying the carbon structure is one very promising approach.” [Energy & Environmental Science]

Image in Focus

Eleven Masks

Color-enhanced scanning electron micrograph of a lanthanum strontium manganite (LSM) thin layer that is deposited on a silicon substrate via spray pyrolysis process. The bizarre faces are created by rapid expansion of the film when the precursor solution droplets reach the hot surface of the substrate to decompose into the LSM oxide. Eleven strange masks can be recognized when eyes are artificially added to the original image.

Credit: Hoda Amani Hamedani, Georgia Institute of Technology
(Click image to enlarge.)

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NEWS FROM THE WORLD OF MATERIALS

noreply@blogger.com (Madhawa Habarakada) — Thu, 07 Jul 2011 15:11:00 +0000

Materials in Focus

High strength gold bridge, one atom long
(State University of New York Buffalo News Center. See also the press release by Charlotte Hsu.)
Image courtesy of University at Buffalo. Click image to enlarge.

Image caption: A bridge made of a single atom of gold has twice the strength of bulk gold, according to new UB research.

Smaller is not necessarily weaker, Harsh Deep Chopra and his colleagues at the State University of New York at Buffalo have discovered. In fact, a bridge made of just a single gold atom between a gold substrate and a gold coated cantilever tip has at least twice the modulus of the bulk, they report in a recent paper in Physical Review B. “You would think that if you make these constrictions so tiny they would become ever more fragile,” Chopra says. “Actually, they become even harder to elastically deform.” They note that when the atoms do not have the full coordination of bulk gold, the gold-gold bonds contract and strengthen, which leads to modulus enhancement. This discovery could prove to be important as nano-devices are made smaller and smaller with each generation.

To obtain these results, the researchers used a custom-built metrology instrument with unprecedented resolution and stability to make atomic-sized bridges and to measure pico-level forces and deformations. Chopra describes it as a very stable system that doesn’t require any feedback loop to be able to form samples as small as a single atom between the cantilever tip and a substrate of any metal. “We’re then able to pull and push on samples over picometer distances and measure the pico-Newton forces,” Chopra says.

Using a bottom-up approach, these scientists were able to study deformation behavior at all length scales, from the atomic level to the bulk. Starting with a single atom gold bridge and adding atoms one at a time, they discovered that pure, homogeneous shear on the close-packed plane occurs just as predicted up to about 19 atoms. Beyond this point, defects start to become visible, so an average shear distance of about 1.66 angstroms prevails for the slip distance of gold. This is still a surface-dominated effect. Somewhere between a sample diameter of 2.2 to 2.7 nm, a switch from surface- to volume-dominated deformation was expected to occur. With their picometer resolution, Chopra and his colleagues saw just that. “So with our instrumentation and method,” Chopra says, “we are able to see homogeneous shear at the atomic level, followed by the transformation to defect-dominated deformation when the sample reached about 19 atoms, and finally the transition from surface- to volume-dominated deformation as the sample reached a couple of nanometers.”

Part of Chopra’s research philosophy is being able to look at the evolution of various materials properties—be they electrical, mechanical, magnetic, or electron transport properties—as a function of size down to extreme length scales. “The Fermi wavelength of electrons in metals is the smallest relevant length scale corresponding to a single atom and the ultimate limit in device miniaturization,” Chopra explains. “We can see how these physical behaviors change as you go form one atom, two atoms, three atoms to the bulk. And when you get to the bulk, it is basically the sum total of everything that goes on at the atomic scale. So it allows you to link these atomic processes to be able to get a macroscopic description of the material.” [Physical Review B]

Zeolites with micro- and mesoporosity
Korea Advanced Institute of Science and Technology (KAIST)

Zeolites are a family of materials containing approximately 200 crystalline, microporous aluminosilicate structures with controlled pore diameters of <2 nm. This controlled pore size has made zeolites excellent filters for separating or selectively adsorbing molecules by size and shape. Zeolites are also the acid catalysts of choice for many industrial reactions. Much effort has been expended in trying to extend their pore sizes into the mesoporous range (2-50 nm) to handle larger molecules, with only modest success. Now researchers at the Korea Advanced Institute of Science and Technology (KAIST) led by Ryong Rhoo have succeeded in producing crystalline, mesoporous molecular sieves (MMS) with a hierarchy of pore sizes ranging from the micro-to the mesoporous in the same sample, as reported recently in Science.

The key to the synthesis of these unique materials lies in the use of polyquaternary ammonium surfactants. “Hexagonal mesostructures were generated by aggregation of the surfactant molecules,” the researchers wrote, “whereas the crystallization of microporous frameworks was directed by quaternary ammonium groups within the mesopore walls.” By varying the number of quaternary ammonium species in the head group of the surfactant, the researchers were able to control the thickness of the mesopore walls and the structure of the zeolitelike microporous frameworks within them. Reported mean micropore diameters ranged from 0.55 to 0.65 nm, with mean mesopore diameters ranging from 3.5 to 4.7 nm. Mesopores with diameters up to 21 nm were formed using micelle swelling agents.

Functionally, these materials showed excellent properties as acid catalysts for various reactions involving bulky organic molecules that are too large to fit into traditional zeolite catalyst pores. The researchers attribute the increased catalytic activity compared to conventional zeolites or amorphous MMSs to the ease of molecular diffusion through the mesopores, the strong acidity of the crystalline zeolitelike structures, and the high concentration of surface acid sites. [Science]

Nano Focus

Light antennas from DNA-programmed quantum dots
(University of Toronto. See also the press release from the University of Toronto "Engineering in the News" web page.)
Image courtesy of Ted Sargent, University of Toronto. Click image to enlarge.

Image caption: From top left to bottom right, DNA-functionalized quantum dots with varying valencies self-assemble into a complex "light antenna" structure.

Solar cells and other photonic devices might increase their efficiency if a “light antenna” were available to absorb incoming light and funnel it to a central junction in the circuit. As reported recently in Nature Nanotechnology, researchers at the University of Toronto have succeeded in synthesizing such antennas in a “one-pot” process that connects CdTe quantum dots together in controlled patterns using DNA strands as the linkage material.

“DNA was advantageous for a number of reasons,” says Ted Sargent, one of the lead researchers on the project. “It was straightforward to attach a portion of the DNA sequences to the surfaces of the quantum dots.” Also, they could easily control the length of this quantum dot binding domain, which features phosphorothioate linkages within the DNA backbone; these linkages have the highest affinity for the cations of the CdTe quantum dot. “The length determined how many DNA sequences could fit onto each quantum dot, thus allowing us to program the number of DNA strands, or valency, of each quantum dot,” Sargent says.

The variable valency—from one to five DNA strands per quantum dot—gave the researchers the building blocks needed to design the geometry of any structure. The well-known bonding specificity of the DNA bases allowed them to specify which quantum dots bonded to each other. Furthermore, by controlling the diameters of the quantum dots, the researchers were also able to control their optical properties, such as absorption and luminescence color.

In a demonstration of the light antenna concept, Sargent and his co-workers assembled a structure with one red quantum dot in the center bonded to four yellow quantum dots, each of which was bonded to one green one. “When we photoexcite the green particles, they rapidly transfer their energy downhill to the yellow, and then to the red, particles,” according to co-corresponding author Shana Kelley, also Professor at the University of Toronto. “In this way, these new structures function like the photosynthetic reaction centers in plants – they are light-harvesting antennas.”
[Nature Nanotechnology]

Energy Focus

Harnessing “junk” energy
(State University of New York at Buffalo and California Insititue of Technology. See also the press release by Charlotte Hsu.)

Image courtesy of State University of New York at Buffalo. Click image to enlarge.

Image caption: Mathematically designed grain structures from an enhanced version of Hertz's law.

Researchers at the State University of New York at Buffalo and the California Institute of Technology have developed a rigorous mathematical treatment that extends Hertz’s law, which describes the repulsive force between two elastic, spherical objects that are pressed together, to objects having other shapes. As reported recently inPhysical Review E, a team led by Surajit Sen modified the law first elucidated by Heinrich Hertz in 1881 to include contact between grains of irregular shapes often found in nature. “Pointy or blunt,” Sen says, “we have found a way to calculate the force” between adjacent particles. Usually nature presents us with one force law that we are stuck with, but “now we can generate almost any kind of non-linear force law,” he says.

This discovery could make it possible to harness the “junk” energy that is commonly wasted in road vibrations or rock concerts. If a material were available with a carefully designed microstructure that would propagate this energy in a controlled manner from grain to grain, it could be possible to convert the junk energy to electricity for useful purposes. “By tweaking force propagation from one grain to another, we can potentially channel energy in controllable ways, which includes slowing down how energy moves, varying the space across which it moves and potentially even holding some of it down," Sen says.

For now the discovery remains a mathematical one only. Demonstrating this effect experimentally using the mechanical forces between grains in a material could take some time, Sen concedes. But it is possible to construct a system that converts mechanical energy into electrical energy, which might make the challenge of producing a practical device less daunting. “We could have chips that take energy from road vibrations, runway noise from airports-- energy that we are not able to make use of very well,” Sen says, “and convert it into pulses, packets of electrical energy, that become useful.” [Physical Review E]

Image in Focus

Microbial Flare
Ronn S. Friedlander, Harvard-MIT Division of Health Sciences and Technology

Polarized light micrograph of an E. coli colony. Congo red staining of amyloid fibers creates the remarkable birefringence patterns seen here.

NEWS FROM THE WORLD OF MATERIALS

noreply@blogger.com (Materials Community) — Wed, 22 Jun 2011 05:57:00 +0000

Materials in Focus

Ductile or brittle at the flip of a switch
(Technical University of Hamburg and Shenyang National Laboratory for Materials Science, China)
Photo credit: Technical University of Hamburg. Click image to enlarge.

Generally, a material's basic properties are determined by its composition and microstructure during the manufacturing process. Changes in these properties may occur during extended use, but this is generally a slow process governed by creep, fatigue, or some other factor. Now, however, researchers Jörg Weissmüller at the Technical University of Hamburg and Hai-Jun Jin at the Shenyang National Laboratory for Materials Science in China have developed a hybrid nanostructure material that can change properties at the flip of a switch. As reported recently in Science, they have developed a material consisting of a nanoporous gold backbone filled with a liquid electrolyte that is capable of fast, reversible tuning of its yield strength, flow stress, and ductility through the application of an electric field. "The concept allows the user to select, for instance," the authors wrote, "a soft and ductile state for processing and a high-strength state for service as a structural material."

Starting with a gold/silver alloy, they removed the silver by corrosion, leaving a monolithic skeleton characterized by contiguous gold ligaments and an equally contiguous pore structure. The pores were then filled with a 1M HClO₄ electrolyte. Compression of this hybrid nanostructure material under different electric potential conditions revealed the change in properties. Using a sample with gold ligaments having a diameter of 20 nm, compression under a constant applied voltage of 1.03 V showed ductility up to high strain conditions. The same process performed with an applied voltage of 1.48 V showed a 36% increase in yield strength and a loss of ductility. Also, the flow stress doubled when switching from 1.03 V to 1.48 V. These changes were completely reversible when the applied voltages were reversed.

The researchers noted that at 1.48 V the gold ligaments are covered with adsorbed oxygen, while at 1.03 V they are "clean." This led them to investigate the role of surface stress and surface tension on these property variations; they concluded that neither surface stress nor surface tension was responsible. The most likely explanation according to the researchers is that the adsorbed oxygen exerts a drag on dislocations that intersect the surface, resulting in "adsorption locking," which increases the yield strength and the flow stress at the higher voltage. "For the first time we have succeeded in in producing a material which, while in service, can switch back and forth between a state of strong and brittle behavior and one of soft and malleable," Weismuller said in a press release issued by the Technical University of Hamburg. "We are still at the fundamental research stage but our discovery may bring significant progress in the development of so-called smart materials." [Science]

Nano Focus

Si nanowire-based non-volatile memory devices reduce power consumption
(NIST and George Mason University)
Photo credit: Bonevich/NIST. Click image to enlarge.

Using small, 20-nm diameter Si nanowires wrapped in HfO₂ and Al₂O₃, researchers Curt Richter at NIST and Qiliang Li at George Mason University may have found a path to creating low-power, fast-writing, non-volatile memories that could eventually replace DRAM and SRAM. The DRAM devices require frequent refreshing to retain stored data, which consumes a large part of the power. The SRAM devices used for cache memory in computers' central processing units (CPUs) are volatile and need to be powered to retain data. The standby power for data remanence is a significant part of the total power dissipation. The lower power consumption of non-volatile memory could mean longer intervals between recharging batteries in computers and other electronic devices. This is very attractive for portable and stand-alone electronics.

As reported recently in Nanotechnology, Richter, Li, and their colleagues took advantage of electrical properties of the materials and the geometry of a small diameter nanowire to improve the electrostatics of gate control. The dielectric properties of HfO₂ make it a good charge-trapping layer, and an Al₂O₃ layer acts as a blocking oxide. Richter says they can tune the stack through band engineering to produce the best possible charge trapping dielectric stacks. Then they take advantage of the small diameter of the Si nanowire to achieve 3D electrostatics, which Richter says, gives them better control than traditional 2D planar devices. "Better electrostatic control means faster, more effective turning on and off," Richter says. "And we've also tuned the gate stack so that most of the electric field is dropped just over the tunnel barrier so we have better control. That means we can hopefully operate at lower voltages and reduce power compared to more traditional dielectric stacks in planar structures."

Their goal is to achieve faster write/erase speeds for non-volatile memory with reduced power consumption. "Our plan is two-fold," Li says. "One is to reduce the channel length so we can achieve higher memory density. The second is to do more engineering on the dielectric stack so that we can get the non-volatile memory programming speed to below 1 ns, similar to SRAMs."[Nanotechnology]

Bio Focus

Attaching proteins to electrodes in ambient conditions
(University of Pennsylvania)
Image credit: Bonnell/University of Pennsylvania. Click image to enlarge.

Most research involving the attachment of proteins to electrodes to measure their electrical properties has been done in liquid solutions to understand the biological principles of the operation of proteins inside cells. But for other potential applications, such as energy harvesting or toxic chemical sensing, the protein/electrode device must function in ambient, open air conditions. Now researchers at the University of Pennsylvania led by Dawn A. Bonnell have demonstrated successful operation of a single molecular layer of artificial proteins attached to electrodes as optoelectronic devices in an ambient environment. What's more, they've developed a new AFM-based technique to quantitatively measure the resistance, capacitance, and dielectric constant of such devices, as reported in ACS Nano.

Researcher Bodhana Discher fabricated the artificial proteins used in these experiments. Device manufacture involved the self-assembly of amphiphilic protein helices in groups of four on a highly oriented pyrolitic graphite surface using microcontact printing. A single molecular layer of these helices measured 6.6 ± 0.5 nm—the height of a protein helix standing vertically on the graphite surface. The optically active molecule zinc (II) protroporphyrin (ZnPP) was inserted into the interior of the scaffold formed by these four helices; later measurements showed that approximately five ZnPP molecules occupied a single scaffold.

Using their new AFM-based technique called torsional resonance nanoimpedance microscopy, the researchers oscillated a metal AFM tip sideways rather than up and down, so as not to damage the delicate protein structures. A blue LED with a wavelength of 425 nm emitted light near the sample-tip junction to excite the ZnPP molecules. "We use a technique we call 'force stabilization' to get very near the surface," Bonnell says," without disrupting or damaging it. We call it 'soft contact.'" When combined with special circuitry that maximized the signal-to-noise ratio at a higher frequency, they were able to measure the dielectric constant quantitatively by "measuring the polarization volume change between the ground state when there is no light on the ZnPP and the excited state when the light is on it and it is absorbing photons," Bonnell says.

"You'll see lots of characterization papers on lots of different properties in these systems," Bonnell concludes, "but what was different here and I think is going to be generalized in a broader context is that we developed a technique that can measure the dielectric constant of a single-molecule-thick layer." [ACS Nano]

To hear Dawn Bonnell explain her views of the possible applications of this research (mp3, 59 sec.), click the soundwave icon:

Materials Research Society's
"Sounds of Science"

Energy Focus

Dark plasmons trap more light
(Northwestern University)
Photo credit: Northwwestern University. Click image to enlarge.

Researchers Teri Odom and Wei Zhou of Northwestern University recently reported in Nature Nanotechnology a new type of subradiant (dark) plasmon that is easily tunable by modification of the height of gold nanoparticles arranged in a large-scale, two-dimensional array. Previous attempts to make dark plasmons have involved structuring single nanoparticles or nanoparticle arrays in complex ways, in an attempt to take advantage of broken symmetries in the structure. "In our case we just change the height of the nanoparticles," Odom says. "That's easier than trying to manipulate sub-wavelength features in individual particles."

Abandoning the traditional electron beam lithographic methods, which limit the height of nanoparticles that can be made, the researchers used a template-stripping nanofabrication technique to obtain two-dimensional arrays of gold particles with heights ranging from 65 to 175 nm on transparent substrates. Experimenting with an array of 100-nm high, 160-nm diameter gold particles spaced at 400-nm intervals and covering a total area greater than 18 cm², Odom and Zhou found an out-of-plane (E0z) electric component of tranverse-magnetic polarized light that excited out-of-plane plasmon modes. These plasmon modes are narrow (FWHM~5 nm) at resonance, and strong coupling between their dipolar moments suppresses the radiative decay of the radiant (bright) plasmons, trapping light in the x-y plane of the nanoparticle array. "We're finally accessing the third dimension," Odom says. "Because we could make the gold nanoparticles so tall, we were able to discover this out-of-plane lattice mode which happens to have this dark plasmon character. We're uncovering some of the unique outcomes of being able to manipulate structure in the z-dimension."

Odom thinks these arrays, with their concentrated, in-plane local energy fields, might be valuable platforms on which to study the mechanisms of chemical reactions. Also, the scalability of the fabrication technique could lead to a coupling of plasmonic and photovoltaic applications. "Because these arrays can trap the light in a much more efficient way and because we can scale them," Odom says, speculating about the distant future, "they could provide a practical first step for plasmonics-based photovoltaics." [Nature Nanotechnology]

Graphene oxide "glue" makes stacking tandem solar cells easier
(Northwestern University)
Photo credit: Huang/Northwestern University. Click image to enlarge.

Mixing graphene oxide (GO) and the common polymer PEDOT:PSS in water produces a sticky thin film upon casting that may make it simpler to fabricate tandem solar cells, according to research published recently in the Journal of the American Chemical Society. Jiaxing Huang and his colleagues at Northwestern University describe a proof-of-concept using direct adhesive lamination of the layers of tandem devices with GO/PEDOT gel as the glue, a process which they say is much easier than creating tandem architectures via solution processes, as is now commonly done.

Tandem solar cells are multijunction devices in which two sub-cells are stacked for increased solar energy absorption. This stacking requires that the "glue" interlayers be orthogonally processable, which is not easy to achieve in solution with organic solar cells. Also, careful choice of solvents is needed at each step to avoid damaging components in other layers. No such problems arise when aqueous solutions of GO (0.1 -2 wt%) and PEDOT:PSS (1.3-1.7wt.%) are mixed to form a viscous gel that can be easily applied to many substrates. Heat treatment at 60°C turns the gel into a sticky adhesive to bond stacks together. Furthermore, despite the electrically insulating nature of GO, the conductivity of PEDOT:PSS films increases by an order of magnitude when GO is added. The authors suggest that this may be due to a conformational change in PEDOT upon contact with GO. More generally, the GO:PEDOT gel could serve as a non-metallic solder for electrical and mechanical connections in any organic electronic device. [Journal of the American Chemical Society]

NEWS FROM THE WORLD OF MATERIALS

noreply@blogger.com (Materials Community) — Tue, 01 Feb 2011 17:05:00 +0000

Materials in Focus

Thermoelectric properties of half-Heusler alloys enhanced
(Physics World)

To be of practical use, a thermoelectric material must be good at conducting electricity but poor at conducting heat. "Half-Heusler" alloys have promising thermoelectric properties but they suffer from having relatively high thermal conductivities. One way of reducing their conductivity is to squish together a fine powder of the material to form a nanocomposite containing many small grains. Heat has a hard time travelling across grain boundaries, thereby reducing the overall thermal conduction of the nanocomposite. Researchers have now used this technique on an extremely fine powder of a half-Heusler alloy, producing a nanocomposite with the best ZT (thermoelectric figure of merit) yet for a half-Heusler. [Nano Letters]

Embedded microvoids make LEDs more efficient
(North Carolina State University)
LED lighting relies on GaN thin films to create the diode structure that produces light. A new technique now reduces the number of defects in GaN films by two to three orders of magnitude by embedding microvoids. This improves the quality of the material that emits light, and for a given input of electrical power, the output of light can be increased by a factor of two – which is very big. This is particularly true for low electrical power input and for LEDs emitting in the ultraviolet range. The researchers started with a GaN film that was two microns thick and embedded half of that thickness with large voids – empty spaces that were one to two microns long and 0.25 microns in diameter. The researchers found that defects in the film were drawn to the voids and became trapped – leaving the portions of the film above the voids with far fewer defects. [Applied Physics Letters]

Growth, characterization of LiMnAs: A useful pyramid scheme
(Physics)
All electronics technologies have, at their heart, critical materials that make their function possible. These can be "old" materials such as silicon, whose major materials development was achieved by previous generations, or "new" materials such as gallium-nitride, which has been developed by our contemporaries.If the discovery and development of new materials comes to a stop, then the introduction and growth of new technologies will almost certainly come to a halt as well. Spintronics is an example of such a critical current technology, driving the creation of increased density, faster electronic memories through the electronic manipulation of magnetic moments. Researchers now report the successful growth and characterization of LiMnAs, a new candidate material for spintronic applications. They show convincing evidence of epitaxy and good film quality, and show that LiMnAs is a semiconductor, by performing optical spectroscopy. They also show that it is antiferromagnetic in thin film form by measuring its temperature-dependent magnetization. [Physical Review B]

Electrical phenomena in silicon oxide in electronics explored
(Eurekalert/ACS)
Researchers have found that silicon dioxide in computer chips, long regarded as an electrical insulator, can actually be made to act like a switch and take part in electronic processes. They have documented various electrical phenomena such as resistive switching and related nonlinear conduction, current hysteresis, and negative differential resistance, that are intrinsic to a thin layer of SiOx. This is more crucial in the area of nanoelectronics, wherein researchers thought that switching observed was due to the nano-additive but it turns out that the source of the switching might be from the underlying silicon oxide itself. The work clarifies the possible nature behind switching events in molecular and nano-scale systems investigated so far, that were not well understood. [J. American Chemical Society]

Nano Focus

Silver nanoparticles-coated paper for food packaging
(American Chemical Society)
It is known that silver nanoparticles show excellent microbicidal properties, much better than those of larger particles. Researchers have now demonstrated an effective, long-lasting method for depositing silver nanoparticles on the surface of paper that involves ultrasound waves. The coated paper showed potent antibacterial activity against E. coli and S. aureus, two causes of bacterial food poisoning, killing all of the bacteria in just three hours. This suggests its potential application as a food packaging material for promoting longer shelf life. [Langmuir]

Bio Focus

Nanoparticle divides to penetrate into tumors
(Chemistry World)

Researchers have created a nanoparticle that breaks up into smaller units once it reaches its target, allowing it to penetrate deeper into tumor tissue and deliver treatment more effectively. The new nanoparticles are 100 nm balls of gelatin that contain small particles that are only 10 nm in diameter. The gelatin nanoparticles get to the tumors, and then tumor enzymes digest the gelatin and release the smaller constituents, that then move through the tumor. In vitro studies showed that the particles penetrated tumor tissue much better traditional larger nanoparticles that remain one size. [Proceedings of the National Academy of Sciences]

New method for tethering and stretching DNA
(Nanotechweb.org)
Researchers have developed a reproducible surface chemistry technique for tethering DNA molecules onto surfaces and a new way to stretch the molecules to various lengths. DNA can be used as a molecular scaffold to make metal contacts to organic semiconductors. A key step in this process involves being able to tether the DNA to various surfaces and stretch the molecule to varying lengths. The new strategy involves synthesizing hybrid DNA-organic molecule-DNA (DOD) structures, then stretching and tethering the DOD assemblies between two microscopic metal electrodes. The researchers then make metal electrode-organic molecule-metal electrode (MOM) structures by further metallizing the DNA segments within the DOD structures. The team then exploited so-called biotin-Streptavidin linkage chemistry to tether the DNA assemblies to device surfaces. The method could eventually be used to make large-scale nanoelectronic devices based on single organic molecules. [ACS Nano]

Nanoscale transistors used to study single-molecule interactions
(Columbia University/Eurekalert)
Researchers have figured out a way to study single-molecule interactions on very short time scales using nanoscale transistors. They show how, for the first time, transistors can be used to detect the binding of the two halves of the DNA double helix with the DNA tethered to the transistor sensor. The transistors directly detect and amplify the charge of these single biomolecules. Previously, scientists have used fluorescence techniques to look at interactions at the level of single molecules. But these techniques require that the target molecules being studied be labeled with fluorescent reporter molecules, and the bandwidths for detection are limited by the time required to collect the very small number of photons emitted by these reporters. The transistors employed in this study were fashioned from carbon nanotubes which are exquisitely sensitive because the biomolecule can be directly tethered to the carbon nanotube wall creating enough sensitivity to detect a single DNA molecule. [Nature Nanotechnology]

Energy Focus

Packings of carbon nanotubes for hydrogen storage
(Chemistry World)

Researchers have designed a 3D carbon nanotube matrix that can store and release hydrogen extremely efficiently. They used a computer-based approach to design a 3D carbon nanotube structure that can store more hydrogen at room temperature than any other carbon-based material. This is a top down approach from advanced mathematics, to geometry, to computer modeling, to chemical properties. The US Department of Energy's target for hydrogen storage materials by 2015 is 6wt% while the new nanotube material has a total hydrogen uptake of 5.5wt% at room temperature. Inspired by natural sponges, the team designed a computer model that placed carbon nanotubes in the hole positions of a theoretical sponge network. [Advanced Materials]

Relativity powers lead-acid battery
(Physical Review Focus)
The lead-acid battery that starts most car engines gets about 80 percent of its voltage from relativity, according to theoretical work using computer simulations. The relativistic effect comes from fast-moving electrons in the lead atom. The computer simulations also explain why tin-acid batteries do not work, despite apparent similarities between tin and lead. The researchers are the first to derive theoretical models of the lead-acid battery from fundamental physics principles. By switching relativistic parts of their models "on" and "off", the team found that relativity accounts for 1.7 volts of a single cell, which means that about 10 of the 12 volts in a car battery come from relativistic effects. [Applied Physics Letters]

Image in Focus

ZnO Nanoflowers
Stem of nanoflowers made by coloring and combining different SEM images of a variety of ZnO nanostructures grown by thermal Chemical Vapor Deposition.
Credit: Abhishek Prasad, Michigan Technological University
(One of three Science as Art competition first place winners at the 2010 MRS Fall Meeting)

[We invite you to submit your images to the Editor for possible inclusion in this feature]

Materials - New Trends

noreply@blogger.com (Materials Community) — Sat, 25 Sep 2010 15:51:00 +0000

Materials in Focus

Artificial skin made of semiconductor nanowires
(University of California, Berkeley)
Researchers have developed a pressure-sensitive electronic material from semiconductor nanowires. The artificial skin, dubbed "e-skin", is the first such material to be made out of inorganic single crystalline semiconductors. They utilized an innovative fabrication technique that works somewhat like a lint roller in reverse. Instead of picking up fibers, nanowire "hairs" are deposited. The researchers started by growing germanium/silicon nanowires on a cylindrical drum, which was then rolled onto a sticky substrate. As the drum rolled, the nanowires were deposited, or "printed," onto the substrate in an orderly fashion, forming the basis from which thin, flexible sheets of electronic materials could be built. The researchers demonstrated the ability of the e-skin to detect pressure from 0 to 15 kilopascals, a range comparable to the force used for such daily activities as typing on a keyboard or holding an object. [Nature Materials]

Ultrasensitive, highly flexible electronic skin developed
(Stanford University)
By sandwiching a precisely molded, highly elastic rubber layer between two parallel electrodes, researchers were able to create an electronic sensor that can detect the slightest touch. It was able to detect pressures well below the pressure exerted by a 20 milligram bluebottle fly carcass that they experimented with, and with unprecedented speed. The key innovation in the new sensor is the use of a thin film of rubber molded into a grid of tiny pyramids. The thin rubber film between the two electrodes stores electrical charges, much like a battery. When pressure is exerted on the sensor, the rubber film compresses, which changes the amount of electrical charges the film can store. That change is detected by the electrodes and is what enables the sensor to transmit what it is "feeling." [Nature Materials]

Cracking the case on fracture
(Physics)
Many material engineering studies are carried out within a model of continuum plasticity, yet such models often lack sufficient microscopic detail to account for crack propagation and fracture resistance. A study now reports computer simulations showing more clearly what processes influence fracture in plastic deformation, and on what length scales. The authors modeled plastic deformation as the movement of discrete dislocations along slip planes. Specifically, a set of "obstacles" arrayed with some selected spacing restricts the movement of dislocations and modifies the plasticity. They then examined fracture by including an initial crack in the material and observing it propagate as a function of material cohesive strength, fracture energy, and obstacle spacing. They found that it is the obstacle spacing length scale that most strongly affects fracture toughness. Moreover, they propose that their model could serve as a more general simulation environment for fracture studies in various materials. [Physical Review Letters]

Energy Focus

Self-repairing photovoltaics rival conventional solar cells
(NanotechWeb)
During photosynthesis, plants harness solar radiation and convert it into energy. However, the Sun's rays damage and gradually destroy solar-cell components over time. Naturally occurring plants have developed a highly elaborate self-repair mechanism to overcome this problem that involves constantly breaking down and reassembling photodamaged light-harvesting proteins. Researchers have now succeeded in mimicking this process for the first time by creating novel self-assembling complexes that convert light into electricity. The complexes can be repeatedly broken down and reassembled by simply adding a surfactant (a solution of soap molecules). The researchers found that they can indefinitely cycle between assembled and disassembled states by adding and removing the surfactant, but the complexes are only photoactive in the assembled state. [Nature Chemistry]

Laser welding boosts efficiency of TiO₂ solar cells
(NanotechWeb)
Dye-sensitized solar cells (DSSCs) have excellent charge collection capabilities, high open-circuit voltages and good fill-factors. However, they do not completely absorb all of the photons from visible and near-infrared ranges and consequently have lower short-circuit photocurrent densities than inorganic photovoltaics. Increasing the short-circuit current density of DSSCs is a key factor in improving the efficiency of these devices. Researchers have recently demonstrated that the inter-electrode contact resistance arising from poor interfacial adhesion is responsible for a considerable portion of the total resistance in the DSSC. The group has shown that the current flow can be greatly improved by welding the interface with a laser. TiO₂ films formed on transparent conducting oxide (TCO)-coated glass substrates were irradiated with a pulsed UV laser beam at 355 nm, which transmits through TCO and glass, but is strongly absorbed by TiO₂. It was found that a thin continuous TiO₂ layer is formed at the interface as a result of the local melting of TiO₂ nanoparticles. This layer completely bridges the gap between the two electrodes and improves current flow by reducing the contact resistance. [Nanotechnology]

Carbon dioxide-free production of iron
(Highlights in Chemical Technology)
Iron metal has been conventionally produced by melting iron ore at temperatures over 2000°C in a blast furnace. This however produces large amounts of CO₂, which is released into the atmosphere and contributes to climate change. A research team has demonstrated that iron ores (Fe₂O₃ and Fe₃O₄) can be dissolved in molten lithium carbonate at temperatures of around 800°C - a process that was previously thought impossible. Adding an electrical current to the molten mix separates the iron ore into its component parts, iron and oxygen, which can be collected by two electrodes in the solution. Less energy is required to generate the lower temperatures and power the electrolysis, but the researchers also demonstrate that these can be achieved using renewable energy. The team employed their recently developed solar technique, called solar thermal electrochemical photo (STEP) - which uses the Sun's thermal energy to melt the lithium carbonate solution while the visible light energy powers the electrolysis. Using the STEP process no CO₂ is produced. [Chemical Communications]

Nano Focus

High-strength Al-alloy includes core/double-shell nanoparticles
(Northwestern University/Small)

Researchers have created a new high-strength aluminum alloy by engineering it at the nano level to give it high-strength and corrosion resistance to high temperatures. They combined aluminum with lithium, scandium, and ytterbium and they were able to create nano-particles with a core surrounded by two shells. The core is ytterbium-rich, while the first shell is rich in scandium and the second shell contains mostly lithium. This core/shell-shell structure has been achieved previously in liquid solutions but this is the first time it has been achieved by processing solely in the solid-state. They also found that some nano-particles had an unexpected structure — a single particle with two cores and two outer shells, like a double-yolked egg. This novel structure consists of two Yb-rich Al3(Li,Yb,Sc) cores with 4--5 nm diameter, two Sc-rich Al3(Li,Sc,Yb) inner shells surrounding their respective cores and one Li-rich Al3Li outer shell enfolding the previous regions and contained within an Al matrix. This is the first time this type of structure has been observed. [Small]

Nanoscale ion diffusion behavior in Li-ion battery revealed
(Oak Ridge National Laboratory)
A research team has developed the new electrochemical strain microscopy (ESM) to examine the movement of lithium ions through a battery's cathode material. The method can provide a detailed picture of ionic motion in nanometer volumes, which exceeds state-of-the-art electrochemical techniques by six to seven orders of magnitude. They achieved the results by applying voltage with an ESM probe to the surface of the battery's layered cathode. By measuring the corresponding electrochemical strain, or volume change, the team was able to visualize how lithium ions flowed through the material. Conventional electrochemical techniques, which analyze electric current instead of strain, do not work on a nanoscale level because the electrochemical currents are too small to measure. These are the first measurements of lithium ion flow at this spatial resolution, according to the authors. [Nature Nanotechnology]

Electric shock resets nanotube sensor
(Chemistry World)

Single-walled carbon nanotube (SWNTs) can be used in very small, highly sensitive chemical sensors for a variety of gases and other chemicals. The SWNTs, attached to a silicon substrate, absorb chemicals onto their surface, however many chemicals are irreversibly absorbed resulting in lengthy processes before the sensor can be reused. A study now shows that the SWNTs could be 'reset' at the simple flick of a switch. The team found that organic molecules bound to the nanotube surface are shaken off when an electric current is passed through the material, resetting the sensor ready for further use. Their technique - current-stimulated desorption (CSD) - passes a strong electric current through the SWNTs. As electrons jump across defects built into the nanotubes, they collide with molecules on the surface. When they hit an absorbed molecule, they transfer excess energy to it, and it flies off the surface. [Science]

High-speed filter uses electrified nanostructures to purify water
(Stanford University)
By dipping plain cotton cloth in a broth full of silver nanowires and carbon nanotubes, researchers have developed a new high-speed, low-cost filter that could easily be implemented to purify water. Instead of physically trapping bacteria as most existing filters do, the new filter lets them flow on through with the water. By the time the pathogens have passed through, the device kills them with an electrical field that runs through the highly conductive "nano-coated" cotton. In lab tests, over 98 percent of Escherichia coli bacteria that were exposed to 20 volts of electricity in the filter for several seconds were killed. Multiple layers of fabric were used to make the filter 2.5 inches thick. [Nano Letters]

Image in Focus

Dark Night in Desert
Colorized SEM image (5,000x) of a nano-skyline of cactus in a seemingly extraterrestrial landscape formed by Si pillars created by deep reactive ion etching decorated with Ge nanowires by vapor-liquid-solid growth.
Credit: Lucia Romano, University of Catania, Italy

[Submit your images to the Editor for possible inclusion in this feature]

Industry Focus

LED technology used in illumination system for fluorescence microscopy
Fluorescence microscopy requires an intense light source at the specific wavelength that will excite fluorescent dyes and proteins. The traditional method employs a white light, typically from a Mercury or Xenon arc lamp. Although such broad spectrum lamps can generate ample light at desired wavelengths, only a small percentage of the projected light is useful in any particular application. The other wavelengths need to be suppressed to avoid background noise that reduces image contrast and obscures the fluorescent light emissions. This process of suppressing extraneous light is complex, expensive and only partially effective: even after decades of refinements, the best filters are not 100% percent successful at blocking the bleed through of non-specific photons. Some mitigation techniques end up not only suppressing peripheral light, but also significantly diminishing the intensity of the desired wavelengths. A radically different approach is now coming to light. Recent advances in high performance Light Emitting Diode (LED) technology have enabled the practical implementation of this theoretical model. High-intensity monochromatic LEDs are now available in a variety of colors that match the excitation bandwidth of many commonly-used fluorescent dyes and proteins.

Carl Zeiss MicroImaging has incorporated this new LED technology in their Colibri illumination system, a light source system for widefield fluorescence microscopy that uses specific wavelength windows with a considerably decreased need to suppress unwanted peripheral wavelengths from a white light arc lamp. The modular Colibri system employs up to four LEDs, without any of the mechanical switching devices like filterwheels or shutters required by traditional illumination systems. With LED technology, users can now take advantage of an excellent alternative for live cell imaging, high-speed or multi-channel fluorescence microscopy, and many other applications.

NEWS FROM THE WORLD OF MATERIALS

noreply@blogger.com (Materials Community) — Wed, 16 Jun 2010 03:04:00 +0000

From Materials Today

Materials in Focus

Pulling apart molecular magnetism
(Science)

A single molecule constitutes the ultimate nanometer-scale object through which electronic transport can take place. A research team has now showed how magnetism and quantum many-body phenomena can be tuned by precise mechanical manipulation of single molecules. They investigated the magnetic states of individual spin = 1 molecules placed between two electrodes in a metal break junction. By stretching the electrodes, they explored the resulting symmetry-breaking effects of this mechanical action on the conduction properties through the molecule, focusing on magnetic anisotropy. [Science]

3-D imaging of pore structures in low-κ dielectrics
(Eurekalert/Cornell University)
Pore structures in an insulation material at a sub-nanometer scale have been imaged for the first time. Porous, low-dielectric constant materials are being used to replace silicon dioxide as the insulator between nano-scaled copper wires in current and future microelectronic devices and chips in order to speed up the electrical signals sent along these copper wires inside a computer chip, and at the same time reduce power consumption. Researchers were able to devise a method to obtain 3-D images of the pores using electron tomography, leveraging imaging advances used for CT scans and MRIs in the medical field, yielding 3-D images with near atomic resolution. [Appl. Phys. Lett.]

Reactions in a molecular single crystal
(Chemistry World)
Crystals that can alter their composition without changing the structure of their solid lattice have been developed. The crystals are made from an iridium complex bonded to dinitrogen (N₂), but other gases such as hydrogen or ammonia can diffuse through the lattice and undergo reactions. Since larger molecules such as propene cannot enter the crystalline lattice, the process is highly selective. The secret of these crystals lies in the composition: iridium ions surrounded by large pincer-like ligands. The complicated ligands give the iridium high reactivity (allowing it to complex with nitrogen gas) but also leave voids in the crystalline lattice. The voids act as tunnels, which small gases can use to traverse the structure. [Nature]

Energy Focus

NMR Observations of Li "Moss" Formation in Li Batteries
(Materials for Energy Blog)
Lithium ion batteries (LIBs) are widely used because of their large energy storage densities. There is an even larger demand for more energy from LIBs that can be met by using Li metal-containing negative electrodes instead of graphite and other anodes currently used. One of the problems with Li electrodes is that after several charge/discharge cycles in non-aqueous electrolytes, dendritic Li metal, sometimes called Li "moss," forms on the Li-metal anode. Some of these dendrites can fall off into the electrolyte. These floating Li fibers, along with those on the electrode itself, cause various problems, including short circuits and subsequent overheating. A new study now reports the use of in situ nuclear magnetic resonance (NMR) for investigating the Li dendrite formation during electrochemical cycling to better understand and control it. [Nature Materials]

Nano Focus

Performance of graphene monolayer nanocomposite
(PhysOrg.com)
A new study suggests that graphene has the potential to replace carbon fibers in high performance composites such as those used to build aircraft. Researchers placed a single graphene sheet between two layers of polymer and used Raman spectroscopy to measure the response of the carbon bonds to stretching of the graphene. The results suggested that theories developed for large materials still hold even when a material is just one atom thick. The vast body of research into traditional carbon fiber composites can consequently be tapped to design the next generation of graphene-based materials. [Advanced Materials]

Extremely high aspect ratio nanowaveguides in GaAs-AlGaAs
(NanotechWeb)

Efficient guiding and confinement of single-mode light in GaAs/AlGaAs nanowaveguides require high-aspect-ratio geometries. To prevent the structures from collapsing, almost perfectly vertical sidewalls are mandatory. In a recently published study, researchers used a top-down approach to fabricate such a nanowaveguide. High-resolution electron beam lithography patterning was carried out using an e-beam writer to define the structures. Then, a set of inductively coupled plasma (ICP) etching processes removed unwanted material from around the design. Near-ideal vertical sidewalls were obtained allowing for the production of extremely high aspect ratio (>32 for 80 nm wide) nanowaveguides. [Nanotechnology]

Fluctuations in current in a quantum dot junction
(Physics)
Traffic congestion can make life difficult for electrons in nanodevices. Now, in a new study, a team of scientists point to the subtle but significant deviations from steady-state behavior that appear if one looks at the time dependence of electrons traversing a nanoscale junction. They predict that on a femtosecond time scale, the current in a quantum dot junction is not in a steady state, as often assumed, but rather oscillates. The amplitude of this oscillation depends on how fast the bias voltage across the dot is switched on, suggesting the importance of initial conditions in determining how a single-electron device will perform. [Phys. Rev. Lett.]

Bio Focus

Molecularly imprinted polymer nanoparticles: A plastic antibody
(Eurekalert)
Scientists are reporting the first evidence that a polymer antibody — an artificial version of the proteins produced by the body's immune system to recognize and fight infections and foreign substances — works in the bloodstream of a living animal. The discovery is an advance toward medical use of simple polymer nanoparticles custom tailored to fight an array of troublesome "antigens." The researchers developed a method for making polymer nanoparticles that mimic natural antibodies in their ability to latch onto an antigen, melittin, the main toxin in bee venom. They make the antibody using molecular imprinting.They established that these polymer melittin antibodies worked like natural antibodies in mice. The animals that immediately received an injection of the melittin-targeting polymer antibody showed a significantly higher survival rate than those that did not receive the nanoparticles. [J. Am. Chem. Soc.]

Blowing bubbles to study eye disease
(Highlights in Chemical Science)
A method to probe the mechanical properties of eye tissue has been developed. One of the most common methods involves a doctor feeling the eye for regions of different stiffness to normal, but the success is highly dependent on the investigator's skill and the information gained is qualitative. Now researchers have shown that a technique used to study synthetic gels, known as cavitation rheology, can be applied to eye tissue. Cavitation rheology is performed by connecting a needle to a syringe and inserting it into soft tissue, in this case the vitreous - a gel-like tissue in the eye. The pressure inside the system is gradually increased until, at a particular pressure, a bubble forms at the end of the needle inside the tissue. The pressure at which the bubble appears is related to the mechanical properties of the material. [Soft Matter]

New technique turns proteins into glass
(Science Daily)
A method to dry and preserve proteins in a glassified form that seems to retain the molecules' properties has been developed. This glassification process is described as "molecular water surgery" because it removes virtually all the water from around a dissolved protein by pulling the water into a second solvent. The researchers were able to carefully control water removal during glassification by releasing single tiny droplets of water-dissolved protein into the organic solvent decanol with a micropipette. Preliminary evaluations showed that four test proteins undergoing such procedures retained all or most of their original activity when water was restored. The glassy microbeads measured only about 26 millionths of a meter in diameter. [Biophysical Journal]

Image in Focus

Click to enlarge

Watermelons on Pandora
Colorized scanning electron microscope image of superparamagnetic poly methyl methacrylate (PMMA) microspheres with Fe₂O₃ nanocrystals self-assembled on the surface and inside. Credit: Yongxing Hu, University of California, Riverside
(One of three Second Place winners of the Science as Art competition at the 2010 MRS Spring Meeting)

[Submit your images to the Editor for possible inclusion in this feature]

Industry Focus

Fibertect® CS Approved by EPA
Fibertect® Cotton-Soaking (CS), a three-layer flexible, inert, nonwoven, non-particulate decontamination system that has been proven to be successful in absorbing and adsorbing chemical warfare agents, may now prove useful in recovery efforts in the British Petroleum (BP) Deepwater Horizon disaster and other oil spills of similar size and severity. Fibertect® CS was developed by Texas Tech University and is manufactured by Hobbs Bonded Fibers for First Line Technology. The three layers of material consist of a top and bottom fabric with a center layer of fibrous activated carbon that is needle punched into a composite fabric. The top and bottom layers provide structural coherence, improving mechanical strength and abrasion resistance while the center layer holds volatile compounds, like oil.

Materials Today News - 25 May 2010

noreply@blogger.com (Materials Community) — Thu, 03 Jun 2010 10:47:00 +0000

Biomaterials

Self powered sensors
Just 700 rows of piezoelectric nanowires could power a nanoscopic sensor, according to new research at the Georgia Institute of Technology. ... More

Carbon

Graphene at home with defects
A team of researchers at the University of South Florida (USF) created a new defect that just might be a solution to a growing challenge in the development of future electronic devices. [Lahiri et al., Nature Nanotech., (2010), doi:10.1038/nnano.2010.53 Letter.]... More

Graphene sees the light
Researchers at IBM have made the first photodetector from graphene. ... More

Characterization

Breakthrough in fluorescent microscopy
A team of researchers has developed a new technique of fluorescence microscopy for observing objects on the nanoscale, and have also produced a new series of photostable dyes that can be used as fluorescent markers.... More

Electronic materials

Stretchable electronics that map the heart
Scientists have developed a new electronic device that allows circuits to bend, stretch and twist, and that could be used in places where normal electronics would not work, such as in the heart or brain. ... More

New shape ceramics
Researchers from North Carolina State University have developed a new way to shape ceramics using a modest electric field, making the process significantly more energy efficient.... More

Energy

A safe reaction
Nuclear reactors might one day be constructed using materials that can self-heal following radiation damage, thanks to a materials study by scientists at Los Alamos National Laboratory.... More

Magnetic materials

Quantum dots, and silicon herald new functionality
Researchers from UCLA's Henry Samueli School of Engineering and Applied Science describe the creation of a new material incorporating spintronics that could help usher in the next generation of smaller, more affordable and more power-efficient devices. [Xiu et al., Nature Mat. (2010) 9, 337.]... More

Nanotechnology

Nanoscale 'stealth' probe
Engineers at Stanford have created a nanoscale probe they can implant in a cell wall without damaging the wall. [Almquist and Melosh, PNAS (2010) 107, 5815.]... More

Surface science

Pushing droplets around
Controlling the way liquids spread across a surface is important for a wide variety of technologies, including DNA microarrays for medical research, inkjet printers and digital lab-on-a-chip systems. But until now, the designers of such devices could only control how much the liquid would spread out over a surface, not which way it would go....More

IPS gets 100mA from stamp-sized cells

noreply@blogger.com (Materials Community) — Fri, 28 May 2010 18:15:00 +0000

IPS' largest rechargeable, thin-film lithium micro-energy cell is about the size of two postage stamps (50 mm x 25 mm), and some 170 µm thin, but it claims 2.5mAh capacity and continuous current output of 100mA.

Tim Bradow, VP of business development at IPS, says that's enough for a wide range of products. This cell can provide backup power for real time clocks, memory devices, and solid-state drives, and can store the ambient energy collected by solar, piezoelectric, or thermoelectric energy harvesters to power wireless sensors, powered cards, active RFID tags, watches, consumer electronics and medical devices. Bradow also describes products in development that include remote controls that replace infrared diodes with low power RF signals and micro energy cells continuously trickle charged by solar cells, and wireless automotive switches that look to replace the cost and weight of copper wiring with RF signals and micro energy cells continually recharged with vibrational energy harvesting.

IPS uses lithium phosphorus oxynitride (LiPON) for the solid electrolyte, which provides good mobility of Li ions across the very thin electrolyte film, enabling high continuous discharge currents. The solid electrolyte also prevents electrons from leaking across the cell, so the unit does not lose charge in storage. The films are deposited on metal foil substrates in large chambers with conventional PVD tools from the flat panel industry, but with unique target materials and proprietary hardware and processes. The metal substrate also serves as the positive terminal to simplify the architecture and to eliminate the need for expensive metal deposition such as platinum. The foil also serves as a moisture-resistant encapsulant.

The small batteries can be combined for more power and capacity, but there's also still headroom for process improvement with better target materials and deposition processes, notes Bradow. The company has doubled the product's capacity in the last several years, and has demonstrated up to 4mAh on a single 25 mm x 25 mm cell in the lab.

"Solid state always wins", argues Bradow, pointing to the history of vacuum tubes, records, tapes, cameras, and, perhaps next, lighting. An additional push towards solid state may well come from environmental regulations, which now prevent the common trash disposal of a variety of wet chemical batteries in many locations around the world, and which may eventually lead to the banning of their use in certain consumer electronics.

Cymbet makes ‘batteries-in-a-chip’

noreply@blogger.com (Materials Community) — Fri, 28 May 2010 18:13:00 +0000

Cymbet Corp. uses a similar LiPON solid electrolyte, but in an even smaller form factor, for a battery-in-a-chip package that aims to make local energy storage just another electronic component on the board or in the SiP. The chip-scale batteries are finding traction for embedded backup power to replace coin cells or supercapacitors in backing up memory, microcontrollers, and real time clocks in electronic systems.

These chip-like rechargeable lithium-based batteries, with nominal capacity of 50µAh in an 8x8 mm package, are made on silicon wafers with conventional deposition and etch tools, though unconventional materials. The chips withstand up to 260°C, so they can be reflow soldered in normal board assembly. They are sold as a bare die, or packaged with a power management ASIC in a SiP. Cymbet's power management IC converts and regulates input ranging from 2.5V to 5.5V and a steady 3.3V output.

Cymbet also sees a big market developing for storing harvested energy for wireless sensor networks, to control and reduce energy usage in smart buildings, and to monitor and control industrial processes, where there is immediate ROI. Cymbet's vice-president of marketing, Steve Grady, also notes there are a lot of medical applications in the pipeline, from external devices like neurostimulators and smart patches, to internal systems that monitor processes in the body, all powered by RF induction. "There are still ecosystem issues," he notes. "But there is big potential in powered sensors, using energy storage at the point of load. The market has moved from the stage of 'that sounds interesting,' to the stage of actually shipping product in volume.'"

Consumers Hungry for Connectivity Drive Strong Semiconductor Growth

noreply@blogger.com (Materials Community) — Fri, 28 May 2010 18:12:00 +0000

Innovative new devices in an increasingly mobile and well-networked world will help to drive semiconductor growth in the coming years, although traditional drivers like PCs and cell phones still dominate.

By Aaron Hand

May 27, 2010 – As the semiconductor industry digs out of one of its worst downcycles in its history, there are several driving forces behind predictions for double-digit growth in 2010. But one key factor that's behind not only an expected two-year growth cycle but also a mitigated drop in last year's revenue is continued innovation.

Although common thinking at the beginning of last year said that semiconductor revenue could drop by 25% or more in 2009, Semico Research Corp. considered that scenario unlikely simply because of the continued underlying demand for the applications driving semiconductor usage, predicting instead a 10% decline for the year, according to Jim Feldhan, president of the Phoenix-based market analyst firm. The semiconductor market ultimately ended 2009 with a 9% drop in revenue, Feldhan said in March, noting that he expects 24% growth this year.

Traditional market drivers like PCs and cell phones continue to dominate the semiconductor markets. (Source: Semico Research)

Semiconductor content in consumer products is continuing to increase, as traditional growth drivers like PCs and cell phones keep selling, but also as consumers demand the newest entertainment and productivity options like e-readers and WiMAX devices.

"The consumer really wants entertainment, they want productivity, and they like cool stuff," Feldhan noted at SEMI's Industry Strategy Symposium (ISS) earlier this year. He has also said that Semico analysts are seeing strong consumer demand for electronics that they have not seen for several years.

According to Semico, the PC market was up overall last year, with notebooks seeing double-digit growth, netbooks gaining traction, and an increasingly mobile workforce adopting improved wireless technologies. Cell phones, and particularly smart phones, are also doing well, with new features and applications helping to drive the market. Notebook PCs are expected to bring in the most semiconductor revenue in 2010, and other top markets will include desktop PCs, and mid-range and high-end cell phones (see chart).

Notebook PCs are also one of the Top 10 growth markets, a list led by WiMAX base stations and WiMAX CPE, which are still relatively small markets. Other fast-growing markets are e-readers, digital photo frames, netbooks, portable navigation devices, DVD recorders, digital television, and handheld consoles, according to Semico. In 2010, notebooks are expected to grow 18%, netbooks 60%, smart phones 21%, and e-readers 80%.

Although Feldhan noted that it is difficult to forecast how new innovations might take off, he sees huge potential around the explosion of social media and everything it encompasses. The server market, which will already constitute the third largest semiconductor buyer this year, is likely to see even bigger growth. Millions of consumers are making videos and posting them on the Internet, and tens of millions of people are watching those videos; 80% of companies are using LinkedIn as their primary tool for finding employees; and companies are adding 1 petabyte of new storage capacity each month, according to Semico. Social media is also impacting mobile device usage; consider that 80% of Twitter usage is on mobile devices, with people updating their statuses at anytime, from anywhere. Home networking has been talked about for several years, but is really starting to take off now, with families wanting to share information in the home, Feldhan said – movies, games, books, photos and more. Drivers behind the growth of home networking include broadband and wireless communications access; electronic devices such as HDTVs, DVRs and gaming devices; and changes in life styles, including an aging population, more need for security, social networking, and increased desires for "green" living.
	A Plug Computer is designed to draw so little power that it can be left on and connected all the time. It includes a gigahertz-class CPU for performance comparable to a PC. (Source: Marvell)

Other semiconductor market drivers for the future, Feldhan predicts, include such technology innovations as 3-D movies, television and games; picoprojectors, and even cell phones integrating projectors; wireless medical devices; smart clothes; various automotive advances; and a plug computer that is "the kind of thing that's going to transform electronics," he said.

Feldhan says he expects the semiconductor industry to be looking much stronger financially by the end of this year, able to invest and continue innovating.

NEWS FROM THE WORLD OF MATERIALS

noreply@blogger.com (Materials Community) — Sat, 15 May 2010 15:47:00 +0000

Materials in Focus

Redefining electrical current law with the transistor laser
(University of Illinois)
With the transistor laser, researchers can explore the behavior of photons, electrons and semiconductors. However, harnessing these capabilities hinges on a clear understanding of the physics of the device, and data the transistor laser generated did not fit neatly within established circuit laws governing electrical currents. Kirchhoff's current law states charge input at a node is equal to the charge output. In other words, all the electrical energy going in must go out again. On a basic bipolar transistor, with ports for electrical input and output, the law applies straightforwardly. The transistor laser adds a third port for optical output, emitting light. The unique properties of the transistor laser required researchers of the present study to re-examine and modify the law to account for photon particles as well as electrons, effectively expanding it from a current law to a current-energy law. Simulations based on the modified law accurately fit data collected from the transistor laser. [J. Appl. Phys]

Cleaning AFM probe tip using a grating brush
(Ultramicroscopy)
Cleaning of atomic force microscope (AFM) tips is crucial for reliable AFM imaging and force measurements. Researchers have now demonstrated that a brush, a calibration grating with supersharp spikes, can be used to mechanically scrub away contaminants by scanning the probe against the spikes at high load at constant-force mode. This allows for removal of organic/inorganic material in a non-destructive and highly efficient manner. In addition, contamination removal and probe study can be completed in a single step. Also, colloidal/particle probes as well as standard AFM tips can be cleaned by thus method. [Ultramicroscopy]

Energy Focus

Nanoholes promise solar power
(Chemistry World)
Silicon solar cells with arrays of nano-sized holes could outperform their nanowire-based rivals, according to a new study. Nanohole arrays are less fragile and more efficient than nanowires, and can be manufactured using conventional techniques. Nanohole arrays can absorb light even better than nanowire arrays - light that enters the holes will bounce around inside until it is absorbed. In nanowire cells, light is scattered and bounces between nanowires, but the holes seem to do a better job of capturing scattered photons, which increases their energy conversion efficiency. Because the nanohole array is much less fragile than a forest of nanowires, it is also less susceptible to problems associated with broken nanowires, such as recombination of the electrons and positively charged 'holes' that carry current through the device, which boosts the cell's efficiency. [J. Am. Chem. Soc.]

Better platinum catalyst for fuel cells
(Technology Review)
A new type of catalyst could lead to fuel cells that use a fifth of the platinum they use now. The new material consists of nanoparticles with cores made of a copper-platinum alloy and an outer shell that is mostly platinum. The material is up to five times as efficient as regular platinum. Researchers have revealed the mechanism that makes this catalyst more active than regular platinum. Using x-ray scattering, they discovered that the distance between the platinum atoms that are left on the surface of the nanoparticles is less than the distance in pure platinum nanoparticles. [Nature Chemistry]

Nano Focus

Molecular robots on the rise
(National Science Foundation)
Recent molecular robotics work has produced so-called DNA walkers, or strings of reprogrammed DNA with 'legs' that enabled them to briefly walk. Now a research team has shown these molecular robotic spiders can in fact move autonomously through a specially-created, two-dimensional landscape. The spiders acted in rudimentary robotic ways, showing they are capable of starting motion, walking for awhile, turning, and stopping. In addition to be incredibly small--about 4 nanometers in diameter--the walkers are also move slowly, covering 100 nanometers in times ranging 30 minutes to a full hour by taking approximately 100 steps. [Nature]

Nanocomposites get in shape
(Highlights in Chemical Technology)
A material that rapidly heats up and changes shape when connected to a battery has been developed. Researchers blended an electrically conductive network of carbon nanofibers with a shape memory polymer (SMP) - a material that changes from a deformed shape to its original shape induced by a trigger such as a change in temperature. The network of nanofibers enabled the material to heat up very quickly, triggering a change in motion (actuation). [Soft Matter]

Bio Focus

DNA could be backbone of next generation logic chips
(PhysOrg.com)

In a recent set of experiments, researchers demonstrated that by simply mixing customized snippets of DNA and other molecules, they could create literally billions of identical, tiny, waffle-looking structures. These nanostructures will efficiently self-assemble, and when different light-sensitive molecules are added to the mixture, the waffles exhibit unique and "programmable" properties that can be readily tapped. Using light to excite these molecules, known as chromophores, simple logic gates, or switches, can be created. These nanostructures can then be used as the building blocks for a variety of applications, ranging from the biomedical to the computational. [Small]

Nanotube chip creates bioelectronic link
(Chemistry World)
A protein coupled with a carbon nanotube has provided a previously unavailable direct biological-to-electronic interface, which its developers hope could lead to brain-controlled prosthetic devices. A group of scientists produced the interface by covering a nanotube in a lipid bilayer that contains ion transporter proteins. The end goal would be to use this kind of system to make a synthetic synaptic junction to transmit signals directly into muscles and tissues. While carbon nanotubes are the right size to integrate with biological molecules, they are usually very hostile to them. Active proteins, like the sodium/potassium ATPase 'biological machine' integrated in the transistor, have therefore not previously been used to control nanoelectronic devices.The scientists came up with the trick of wrapping the nanotube in a lipid bilayer to solve this. [Nano Letters]

Cryo-electron microscope images virus structure with 3.3 Å resolution
(UCLA)
Researchers report that they have managed to image a virus structure with a resolution of 3.3 angstroms using a cryo-electron microscope. The study demonstrates the great potential of cryo-electron microscopy, or Cryo-EM, for producing extremely high-resolution images of biological samples in their native environment. The work focused on a structural study of the aquareovirus, a non-envelope virus that causes disease in fish and shellfish, in an effort to better understand how non-envelope viruses infect host cells. The group was able to determine that the aquareovirus employs a priming stage to accomplish cell infection. In its dormant state, the virus has a protective protein covering, which it sheds during priming. Once the outer shell has been shed, the virus is in a primed state and is ready to use a protein called an "insertion finger" to infect a cell. [Cell]

Image in Focus

ZnO Nanowire Arrays
SEM image of vertically aligned ZnO nanowire arrays with a standing human-like form. Color was added to the original image. Credit: Surawut Chuangchote, Kyoto University
(One of three First Place winners of the Science as Art competition at the 2010 MRS Spring Meeting)

NEWS FROM THE WORLD OF MATERIALS

noreply@blogger.com (Materials Community) — Sat, 08 May 2010 16:33:00 +0000

Materials in Focus

First images of atomic spin captured
(Ohio University)
In a new study, researchers present the first images of spin in action. They used a custom-built microscope with an iron-coated tip to manipulate cobalt atoms on a plate of manganese. Through scanning tunneling microscopy, the team repositioned individual cobalt atoms on a surface that changed the direction of the electrons' spin. Images captured showed that the atoms appeared as a single protrusion if the spin direction was upward, and as double protrusions with equal heights when the spin direction was downward. [Nature Nanotechnology]

Sign flips and spin fluctuations in iron high-Tc superconductors
(Science)
In superconductors, the key process that allows current to travel without resistance is the formation of electron pairs that move as a single quantum state. The mechanism of pairing in the high-temperature (high-Tc) cuprate superconductors is still elusive, so the recent discovery of iron-based superconductors sparked the hope that comparison with the cuprates would lead to a better understanding of pairing in both materials. Researchers now report the experimental determination of the pairing symmetry in FeSe_xTe_1–x. Combined with the recent observation of a spin fluctuation resonance in this material similar to that seen in the cuprates, a compelling hypothesis has emerged that these high-Tc superconductors share a common pairing mechanism. [Science]

Smart sensors use VO₂ grown epitaxially on Si
(North Carolina State University)
Researchers report vanadium oxide "smart sensors" integrated directly on a silicon chip. This was made possible by growing VO₂ thin films on Si using "domain matching epitaxy". They have explored the mechanisms of how such vanadium oxide sensors work in conjunction with the silicon chips to which they are attached, which yields the ability to improve the reliability of these smart sensors, and account for variable conditions the sensors may be exposed to. Specifically, they report the semiconductor to metal transition (SMT) characteristics of vanadium dioxide grown epitaxially on a Si (001) that is the basis of its sensing properties. [Appl. Phys. Lett.]

Trapped ions detect yoctonewtons force
(Nature News)
By pushing a cluster of just 60 ions with a tiny electric field, researchers have measured the most minuscule force ever. The result, measuring mere yoctonewtons (10^–24 newtons), beats previous record lows by several orders of magnitude. Previously, researchers were able to successfully measure around an attonewton (10^–18 N) of force by giving small pushes to microscopic paddles or wires and then watching them vibrate. These systems work well, but are limited by factors such as their relatively large size. The new technique eschews the paddle-type systems in favor of just 60 beryllium-9 ions. [Arxiv]

Energy Focus

Fuel cell runs on water and air
(Highlights in Chemical Technology)
A fuel cell that produces power using only water and a warm breeze has been developed by researchers.In the new cell, water is oxidized catalytically to molecular oxygen, protons and electrons at the anode, while the reverse reaction takes place at the cathode. As in normal fuel cells, the cathode and anode are separated by a polymer electrolyte membrane which allows the protons to cross to the cathode while the electrons are forced to make their way through a wire, creating a current. The water that forms at the cathode is evaporated by the air flow, keeping the water concentration gradient between the two electrodes, which acts as the driving force for the reaction. Unlike other fuel cells no change in enthalpy occurs as water reacts to form water. This means that typically minor contributions, such as changes in entropy, become key factors in the energy output. [Energy Environ. Sci.]

Nano Focus

Seeing Moiré in graphene
(PhysOrg.com)
Researchers have demonstrated that atomic scale moiré patterns can be used to measure how sheets of graphene are stacked and reveal areas of strain. They created graphene on the surface of a silicon carbide substrate by heating one side so that only carbon, in the form of multilayer sheets of graphene, was left. Using a custom-built scanning tunneling microscope, they were able to peer through the topmost layers of graphene to the layers beneath. This process, which the group dubbed atomic moir interferometry, enabled them to image the patterns created by the stacked graphene layers, which in turn allowed the group to model how the hexagonal lattices of the individual graphene layers were stacked in relation to one another. [Physical Review B]

Measuring wettability with sub-nanometer resolution
(Massachusetts Institute of Technology)
Wettability is crucial to a wide variety of processes. Until now, the only way to quantify this important characteristic of a material's surface has been to measure the shapes of the droplets that form on it, and this method has very limited resolution. But a team of researchers has found a way to obtain images using atomic force microscopy (AFM) that improves the resolution of such measurements by a factor of 10,000 or more, allowing for unprecedented precision in determining the details of the interactions between liquids and solid surfaces. In addition, the new method can be used to study curved, textured or complex solid surfaces, something that could not be done previously. [Nature Nanotechnology]

Nanosculptors could help focus light on silicon chips
(New Scientist)

Credit: IBM

Researchers have sculpted a 1:180 billion scale model of the Matterhorn, the 4478-metre-tall Alpine peak on the Swiss-Italian border. The team carved the minute mountain using a technique they have developed for making high-density computer storage. They found they could evaporate material from a surface by heating a punching needle to 330 °C and using it as a kind of chisel. They carved their microscopic Matterhorn from a glassy organic material whose molecules are held together by hydrogen bonds, forces of attraction between partially positive hydrogen ions in one molecule and electron-rich oxygen ions in another. [Science]

Atomic force microscopy of cells using a nanowire cantilever
(Lawrence Berkeley National Lab)
The core of AFM imaging is a cantilever with a sharp tip that deflects as it encounters undulations across a surface. Due to a minimum force required for imaging, conventional AFM cantilevers can deform or even tear apart living cells and other biological materials. Scientists have now developed nanowire cantilevers whose gentle touch could help discern the workings of living cells and other soft materials in their natural, liquid environment. Used in combination with a new detection mechanism, this new imaging tool is sensitive enough to investigate soft materials without the limitations present in other cantilevers. [Phys. Rev. Lett.]

Bio Focus

Nanoparticles protect bone marrow during radiation cancer therapy
(Albert Einstein College of Medicine of Yeshiva University)
Melanin-covered nanoparticles could protect bone marrow from the harmful effects of radiation therapy. Radiation therapy is used to kill cancer cells and shrink tumors. But because radiation also damages normal cells, doctors must limit the dose. Melanin, the naturally occurring pigment that gives skin and hair its color, helps shield the skin from the damaging effects of sunlight and has been shown to protect against radiation. Researchers created "melanin nanoparticles" by coating 20 nanometers diameter silica particles with several layers of melanin pigment that they synthesized in their laboratory. The researchers found that these particles successfully lodged in bone marrow after being injected into mice. Then, in a series of experiments, they investigated whether their nanoparticles would protect the bone marrow of mice treated with two types of radiation. [International Journal of Radiation Oncology*Biology*Physics]

Image in Focus

Nano PacMan made of copper oxide
Scanning electron microscope image of a copper oxide cluster, 3.5 microns in diameter, prepared by evaporation and condensation over an alumina substrate. The smiley nose and eye are present in the original SEM image, which has only been color-enhanced.
Credit: Elisabetta Comini, University of Brescia, Italy

(One of three First Place winners of the Science as Art competition at the 2010 MRS Spring Meeting)

[We invite you to submit your images to the Editor for possible inclusion in this feature]

Industry Focus

Process Advances to Accelerate 3D Manufacturing Readiness Reported at MRS Spring Meeting
With a focus on providing cost-effective and reliable solutions to speed manufacturing readiness of 3D technology options, experts from SEMATECH's 3D interconnect program based at the College of Nanoscale Science and Engineering's (CNSE) Albany NanoTech Complex outlined new developments in wafer bonding, copper removal, and wafer thinning at the 2010 Materials Research Society (MRS) Spring Meeting on April 5-9 in San Francisco, CA. 3D integration offers the promise of higher performance, higher density, higher functionality, smaller form factor, and potential cost reduction. In this emerging field, new and improved technologies and integration schemes will be necessary to realize 3D's potential as a manufacturable and affordable path to sustaining semiconductor productivity growth. At the MRS Meeting, SEMATECH researchers described several practical 3D integration achievements – applicable across various 3D processes – in areas such as high-aspect ratio TSVs, wafer bonding, and thinning of interconnect test structures.

Z-Contrast Microscope Resolves Individual Light Atoms

noreply@blogger.com (Materials Community) — Fri, 02 Apr 2010 17:11:00 +0000

Using aberration-corrected electron microscopy, Oak Ridge National Laboratory researchers obtained images that discriminate individual light atoms such as boron, carbon, nitrogen and oxygen. The images, obtained with a Z-contrast STEM built by Nion Co., offer promising applications in semiconductors, such as mapping individual dopants. more » » »

News from Semiconductor International

noreply@blogger.com (Materials Community) — Sat, 27 Feb 2010 02:04:00 +0000

Solar Industry Faces Stiff Price Drops
The solar industry faces steep price declines again in 2010, although prices will drop at a more moderate pace than last year, predicted iSuppli. While installed watts will grow by 64% this year, the market research firm said module prices will decline by an estimated 20%, following a 37.8% drop in 2009. more » » »

Q-Cells Racks Up Huge Preliminary Loss in 2009
PV cell maker Q-Cells SE reports reorganization efforts have led to a large series of write-downs and other efforts to clean up its balance sheet. For the full year, the firm generated a loss of 1.36 billion euros ($1.8B), with write-downs accounting for ~952 million euros ($1.29B) of the total. more » » »

Argonne Launches Solar Energy Research Initiative
The Department of Energy's Argonne National Laboratory announces its Alternative Energy and Efficiency Initiative, an effort to achieve "revolutionary advances" towards widespread use of solar energy through PV and other advancements. more » » »

Hitachi High-Tech, XeroCoat Sign Agreement on Anti-Reflective Coatings
Hitachi High-Technologies and XeroCoat are looking to capture a significant share of the solar market by providing anti-reflective equipment and materials. more » » »

Concentrix Solar to Deploy 1 MW CPV Plant at Chevron Facility
Solar CPV technology provider Concentrix Solar will provide CPV technology for a Chevron Plant in New Mexico. more » » »

Anwell Reports Conversion Efficiency in Its Thin-Film Solar Panels
Solar equipment manufacturing firm Anwell Technologies Ltd. reports its thin-film solar panels have achieved conversion efficiency ratings better than the industry average. more » » »

Expect Growth of Materials Used in Solar Cell, Module Production
PV industry consulting firm Linx-AEI projects the market for chemicals and materials used to make PV solar cells and modules will reach $15B by 2015. more » » »

Despatch Reports 30 UltraFlex Furnace Orders Across Europe, Asia
Despatch Industries reports it has sold 30 UltraFlex firing/drying furnaces to solar manufacturers throughout the two continents. more » » »

Natcore Inks Solar Products Deal With Chinese Consortium
Solar R&D firm Natcore Technology has formed a joint venture company in China that will develop and manufacture film-growth equipment and materials. more » » »

Call for Entries: Intersolar to Award PV Solar Innovation
The Intersolar Award program is adding recognition for PV production technology and extending eligibility to exhibitors at its North American event. more » » »

Mitsubishi Electric Develops New PV Inverter Technology
Mitsubishi Electric Corp. has developed technology to maximize output power in PV systems by incorporating a new maximum power-point tracking (MPPT) system in inverters. more » » »

T-Solar, Solarpack to Sell 173 GWh PV Solar Annually to Peru
T-Solar and Solarpack, Spanish PV solar energy solutions providers, have agreed to provide the government of Peru with four PV plants, with a total capacity of 80 MW. more » » »

CNPV Signs Strategic Partnership With Photovoltaic Experts GmbH
CNPV Solar Power SA, a Chinese solar PV product provider, will supply German PV solar developer Photovoltaic Experts GmbH with 30 MWp of PV modules. more » » »

3-D Interconnects Shape Future Solutions

noreply@blogger.com (Materials Community) — Sat, 27 Feb 2010 02:02:00 +0000

from Semiconductor International
An IEEE meeting in Santa Clara, Calif., attracted several leaders of 3-D IC technology development, who presented a list of challenges to the TSV-creation infrastructure. more » » »

3-D Interconnects Shape Future Solutions

noreply@blogger.com (Materials Community) — Thu, 18 Feb 2010 03:59:00 +0000

Scientists to Conquer Casimir Effect, Enable NEMS

noreply@blogger.com (Materials Community) — Sun, 24 Jan 2010 13:23:00 +0000

From Semiconductor International

If Argonne National Laboratory researchers are successful in their quest to nullify Casimir force effects, NEMS implementations will take off. more » » »

Veeco Revs MOCVD Tool for LED Market

noreply@blogger.com (Materials Community) — Sun, 24 Jan 2010 13:15:00 +0000

From Semiconductor International

Veeco Instruments is selling a newly designed MOCVD system to LED manufacturers, claiming higher efficiencies from a redesigned flow flange and reduced cleaning cycles. The company said it expects the booming LED backlighting market to help drive demand for ~400 MOCVD tools industry-wide next year. LEDs increasingly are being used to provide backlighting in thin LCD televisions, monitors and laptop displays. more » » »