Japan nano-tech team creates palladium-like alloy: report

Japanese researchers have created an alloy with properties similar to palladium, a precious metal used in many high-tech goods, a news report said Thursday, dubbing the breakthrough"present-day alchemy".

Kyoto University professor Hiroshi Kitagawa and his team said they used nano-technology to combine rhodium and silver, elements which do not usually mix, to produce the new composite, the Yomiuri daily said.

The alloy has similar properties topalladium, which is used in cars' emission-reducing catalytic converters as well as in computers, mobile phones, flatscreen TVs and dentistry instruments.

Like other white metals, such as silver and platinum, palladium is expensive, with its deposits largely limited to South Africa and Russia.

Palladium also has applications in the production of fuel cells -- a clean andrenewable energy sourcethat produces electricity by combining hydrogen and oxygen, with water as the only byproduct.

To make the new alloy, the Kyoto team used nano-technology to"nebulise"the rhodium and silver and gradually mixed them with heated alcohol, with the two metals mixed stably at the atomic level, the report said.

Japan's industry ministry has listed 31 rare metals, including palladium and lithium, which are used in industrial products, such aselectronic devicesand batteries. Of these, 17 elements are called rare earth minerals.

Resource-poor Japan has tried to shift from its dependence on China, which controls the bulk of global rare earth production.

Kitagawa said he hopes to create morealloysusing nano-technology, without specifying which ones, the Yomiuri said.

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Researchers improve efficiency of low-cost solar cells

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(PhysOrg.com) -- As part of the recent progress in improving solar cells for widespread use, researchers from Purdue University have designed solar cells made of low-cost, abundant materials that are easily scalable and very stable. The researchers have increased the solar cells' total area efficiency to 7.2% and plan to make further improvements in the future.

The researchers, Qijie Guo, et al., have published their study on the improvedsolar cellsin a recent issue of theJournal of the American Chemical Society.They fabricated the solar cells from copper-zinc-tin-chalcogenide (CZTSSe), which is an Earth-abundant material, using a solution-based thin-film deposition method. Previous research has shown that these methods can provide high yields at lower manufacturing costs compared to other methods.

The solar cell design is based on the researchers' earlier study in which they demonstrated that solar cells fabricated using CZTS nanocrystals are potentially viable, although they had efficiencies of less than 1%. Here, the researchers made significant improvements to the design by tuning the composition of the nanocrystals as well as developing a more robust thin-film coating method.

After synthesizing the nanocrystals and applying them on asubstratefor a total film thickness of 1 micrometer, the researchers observed that the nanocrystal film featured large, densely packedgrains, which leads to improvedsolar cell efficiency. In testing, the solar cells could achieve a total area efficiency of 7.2%. As coauthor Hugh Hillhouse explained, the total area efficiency refers to the entire cell, rather than just the“active area.”

"It is the total area efficiency that matters most,"he toldPhysOrg.com.“Some people report an‘active area’ efficiency, which only includes areas that the light reaches. However, all thin film solar cells are made with metal contacts that block the light from reaching some areas. When you include this loss, we use the term‘total area’ efficiency. It is the most fair and important efficiency.”

The 7.2% efficiency was reached after“light soaking” for 15 minutes under one-sun illumination; when the light was turned off, the efficiency dropped to 6.89%.

“Light soaking simply means that we shine normal intensity simulated sunlight on the cell for a period of time before we make the measurement,” Hillhouse said.“Most likely, the light soaking allows photogenerated carriers to fill traps, shift the quasi-Fermi levels, and/or screen barriers created by band offsets. It doesn’t present a problem since real solar cells are naturally light soaked– they sit in the sun.”

Although currently there are no CZTS or CZTSSe solar cells on the market for comparison, the solar cells in this study are very competitive with other fabrication methods.

“The best cells formed by vacuum processes have only reached 6.7%,” Hillhouse said.“Typically, solar cells produced by vacuum-based processes have been more efficient, but also more expensive. For the case of CZTS, the solution phase approach (our nanocrystal route and IBM’s hydrazine route) is more efficient.”

One potential area for improvement for these solar cells lies in improving their low quantum efficiency for light of longer wavelengths (i.e., the near-infrared range). The researchers attempted to improve this efficiency by increasing the thickness of the absorber, although their initial experiments showed that thicker absorber layers also had increased resistance. In the future, they plan to optimize the fabrication for thicker films, which could further increase the overall efficiency.

“There is a lot of compositional freedom in the CZTSSe system, and it is likely that the optimum compositions, device structure, and processing conditions have not yet been found– but we are working on it,” Hillhouse said.

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New nanotube material stays rubbery over a more than 1,000 degree temperature range

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(PhysOrg.com) -- Silicone rubber is used in many applications in which a material is required to remain rubbery over a wide temperature range, since it retains its properties over the approximate range of -55°C to 300°C. Now a new material made of carbon nanotubes has been developed that retains its viscoelastic properties over a temperature range almost five times larger.

Scientists at the National Institute of Advanced Industrial Science and Technology (AIST) in Tsukuba, Japan created the nanotube material using chemical vapor deposition. The material has elastic properties of recoverable stretchiness, and viscoelastic properties that give it a thick-honey-like consistency, and allows it to stretch slowly and then spring back to its original shape. It retains these properties over the range of -196°C to 1000°C.

The research team, led by Dr. Ming Xu, has previously worked oncarbon nanotube“forests,” and development of the new material was the accidental product of an extension of this work. In the“forest” the long nanotubes grow upwards, but when the team modified the catalysts used in the process they found they could make the alignment of the nanotubes much less regular, and were able to create a random network of interconnected nanotubes, which Xu likened to a tangle of jungle vines.

They then investigated the properties of the new material and discovered it has similar viscoelastic properties to silicone rubber at roomtemperature, but unlikesiliconerubber, which becomes brittle when cold and breaks down at high temperatures, the newrubbermaterial remained flexible over a much larger temperature range and has excellent fatigue resistance properties. The researchers speculated the thermal stability could arise from energy dissipating as the carbon nanotubes zip and unzip at points of contact.

Until now, very little research has been done on the viscoelastic properties of carbon nanotubes, probably because they are difficult to make and because they oxidize readily at high temperatures. Xu said the research team is now looking for industrial applications for the new material, so they can further refine its properties to suit those applications. She also said she believed the temperature range could be extended much further, and the material could probably be made more elastic, stronger or softer, as required.

The material may find uses in space applications or rubbers for use in extremely hot environments, but the research is still at an early stage. The findings on the new material are published inScience.

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Israel's scientists think big with the very, very small

A material just one atom thick that is stronger than steel but flexes like rubber. A"mini-submarine"that can trick the immune system and deliver a payload of chemotherapy deep inside a tumour.

They sound like the fantasies of science fiction writers, but they are among the discoveries being presented at Nano Israel 2010, a nanotech conference in Tel Aviv that has attracted researchers from across the science world, united by their work with the very, very small.

The 1,500 participants at the two-day meeting which ends on Tuesday include chemists, physicists and medical researchers, all working withtiny structuresaround the thickness of a cell wall.

"We are all working to be able to manipulate molecules at anatomic level,"said Dan Peer, a professor at Tel Aviv University's Cell Research and Immunology Department.

Physicists are developing new materials by removing or adding to existing structures and nano-medical researchers are building new ways to deliver drugs.

Peer is trying to find out how to more effectively target cancer and the inflammation associated with diseases like multiple sclerosis by better directing toxic treatments like chemotherapy.

"Sometimes the drug is there, but it doesn't operate in a targeted manner,"he told AFP.

In such cases, scientists are trying to find ways to build"GPS systems"into the drugs so they travel directly tomalignant cellsor inflammation.

One way of doing that is to attach thecancer treatmentto a vitamin that tumours happily suck up, allowing the medication to penetrate the malignant cells with ease.

"You can potentially create new materials, new vehicles for drugs, like very small bubbles, like mini-submarines, which carry them into the body,"Peer told AFP.

Joseph Kost, a professor at Ben Gurion University of the Negev's chemical engineering department, is working on a technique that delivers chemotherapy drugCisplatininto tumours.

The drug is carried by a tiny vessel through gaps of between 100-1000 nanometres in size, giving scientists a"therapeutic warhead,"he said.

Once inside, researchers irradiate the drug vehicles with ultrasound, causing them to"explode"and disperse the treatment inside the tumour.

Others are looking at ways to trick the body's immune system to prevent it from identifying drug treatments as invading viruses and attacking them.

Elsewhere, physicists like Andre Geim, winner of this year's Nobel Prize for Physics, are usingnanotechnologyto develop new materials with a surprising range of applications.

Geim, a Russian scientist working in Britain, presented his work on graphene, a one-atom-thick slice of graphite that is stiffer than diamond.

"You can imagine you can make a thousand devices out of this graphene,"he told an audience of researchers from 35 countries, whose work could one day produce more efficient conductors and roll-up touchscreens for computers.

Graphene's structure could even allow it to be used for faster DNA sequencing, Geim said.

For Israel, hosting the gathering of nano-researchers is a way of showcasing a sector that the government is trying to foster.

"We see this as a major economic initiative for the future of Israel,"said Barry Breen, a spokesman for Israel's National Nanotechnology Initiative, a government advisory body."It should be a dominant economic engine."

INNI works to match Israel's nanotech researchers with private industry.

A recent project saw Jerusalem-based company 3G Solar work with scientists at Bar Ilan University to develop a solar cell that processes energy in a similar way to photosynthesis in plants.

Aharon Gedanken, a professor of chemistry at Bar Ilan University, is using nanotechnology to develop sterile hospital sheets and robes using a technique called sonochemistry.

The process uses a chemical reaction that produces"microjets,"which throw out nanoparticles of anti-bacterial metals like zinc oxide at"such a high speed that they are embedded in the surface."

The resulting fabric can be washed, even at the hospital standard of 92 degrees Celsius (197.6 degrees Fahrenheit), without losing its anti-bacterial properties.

"The vision of this project is that in the future all the fabrics in a hospital will be anti-bacterial,"he said.

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Gold and silver nano baubles

They might just be the smallest Christmas tree decorations ever. Tiny spherical particles of gold and silver that are more than 100 million times smaller than the gold and silver baubles used to decorate seasonal fir trees have been synthesized by researchers in Mexico and the US.

Writing in the December issue of theInternational Journal of Nanoparticles, materials engineer Xavier E. Guerrero-Dib, of the Universidad Autónoma de Nuevo León and colleagues there and at The University of Texas at Austin, describe the formation of gold,silverand alloyed, bimetallic nanoparticles just 25 nanometers in diameter. They used vitamin C, ascorbic acid, commonly found in tangerines, a favorite stocking filler in many parts of the world, and a soap-like, surfactant molecule known as cetyltrimethylammonium bromide, an antiseptic occasionally used in expensive cosmetics.

Reaction of silver nitrate and the gold compound chloroauric acid under these conditions led to successive reduction of the metals and the formation of different silver, gold and bimetallic nanoparticles. The precise structures of the nanoparticles were revealed using a high-resolution elemental mapping technique. The analysis shows the nanoparticles to have multiple layers, shells of gold within silver within gold, in the case of the bimetallic particles and some blending, or alloying, of the metals occurred.

Nanoparticles are of great interest to chemists and materials scientists for their potential as catalysts for speeding up chemical reactions, as novel drug-delivery agents, and as quantum dots for analytical applications. They may also be used in the fabrication of the components of future electronics devices beyond the silicon chip. Metal nanoparticles containing two or more different metals might have even more intriguing chemical, electronic and optical properties than single-metal nanoparticles because of the combination of the different chemistries of each metal as well as the size effects of the particles simply being, very, very small.

The researchers point out that the optical properties of nanoparticles depend very much on size and shape as well as the constituent metals. Gold and silver nanoparticles are particularly useful as their optical effects occur at visible wavelengths of light. The team adds that if it were possible to fine-tune the combination ofgoldand silver in the samenanoparticlesthen it might also be possible to tune theoptical propertiesof such particles.

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Researchers create new high-performance fiber

Researchers at Northwestern University have nanoengineered a new kind of fiber that could be tougher than Kevlar.

Working in a multidisciplinary team that includes groups from other universities and the MER Corporation, Horacio Espinosa, James N. and Nancy J. Farley Professor in Manufacturing&Entrepreneurship at the McCormick School of Engineering and Applied Science, and his group have created a high performance fiber from carbon nanotubes and a polymer that is remarkably tough, strong, and resistant to failure. Using state-of-the-art in-situ electron microscopy testing methods, the group was able to test and examine the fibers at many different scales— from the nano scale up to the macro scale— which helped them understand just exactly how tiny interactions affect the material's performance. Their results were recently published in the journalACS Nano.

"We want to create new-generation fibers that exhibit both superior strength and toughness,"said Espinosa said."A big issue in engineering fibers is that they are either strong or ductile— we want a fiber that is both. The fibers we fabricated show very high ductility and a very high toughness. They can absorb and dissipate large amounts of energy before failure. We also observed that the strength of the material stays very, very high, which has not been shown before. These fibers can be used for a wide variety of defense and aerospace applications."

The project is part of the Department of Defense's Multidisciplinary University Research Initiative (MURI) program, which supports research by teams of investigators that intersect more than one traditional science and engineering discipline. Espinosa and his collaborators received $7.5 million from the U.S. Army Research Office for the study of disruptive fibers, which could be used in bulletproof vests, parachutes, or compositematerialsused in vehicles, airplanes and satellites.

To create the new fiber, researchers began with carbon nanotubes—cylindrical-shaped carbon molecules, which individually have one of the highest strengths of any material in nature. When you bundle nanotubes together, however, they lose their strength— the tubes start to laterally slip between each other.

Working with the MER Corporation and using the corporation's CVD reactor, the team added a polymer to the nanotubes to bind them together, and then spun the resulting material into yarns. Then they tested the strength and failure rates of the material using in-situ SEM testing, which uses a powerful microscope to observe the deformation of materials under a scanning electron beam. This technology, which has only been available in the past few years, allows researchers to have extremely high resolution images of materials as they deform and fail and allows researchers to study materials on several different scales. They can examine individual bundles of nanotubes and the fiber as a whole.

"We learned on multiple scales how this material functions,"said Tobin Filleter, a postdoctoral researcher in Espinosa's group."We're going to need to understand how molecules function at these nanometer scales to engineer stronger and tougher fibers in the future."

The result is a material that is tougher than Kevlar— meaning it has a higher ability to absorb energy without breaking. But Kevlar is still stronger— meaning it has a higher resistance to failure. Next, researchers hope to continue to study how to engineer the interactions between carbon nanotube bundles and between the nanotubes within the bundle itself.

"Carbon nanotubes, the nanoscale building blocks of the developed yarns, are still 50 times stronger than the material we created,"said Mohammad Naraghi, a postdoctoral researcher in Espinosa's group."If we can better engineer the interactions between bundles, we can make the material stronger."

The group is currently looking at techniques— like covalently crosslinking tubes within bundles using high-energy electron radiation– to help better engineer those interactions.

Filleter and Naraghi said this work wouldn't have been possible without the interdisciplinary team that includes merging academia with industry.

"To work in an environment where we can trade information back and forth is a unique opportunity that will push the technology farther,"Naraghi said."MER has given us a unique raw material and a commercial perspective on the project. In turn, we provide the fundamental scientific understanding."

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Light touch brightens nanotubes (w/ Video)

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(PhysOrg.com) -- Rice University researchers have discovered a simple way to make carbon nanotubes shine brighter.

The Rice lab of researcher Bruce Weisman, a pioneer in nanotube spectroscopy, found that adding tiny amounts of ozone to batches of single-walled carbon nanotubes and exposing them tolightdecorates all the nanotubes withoxygen atomsand systematically changes their near-infrared fluorescence.

Chemical reactionson nanotube surfaces generally kill their limited natural fluorescence, Weisman said. But the new process actually enhances the intensity and shifts the wavelength.

He expects the breakthrough, reported online in the journalScience, to expand opportunities for biological and material uses of nanotubes, from the ability to track them in single cells to novel lasers.

Best of all, the process of making these bright nanotubes is incredibly easy --"simple enough for a physical chemist to do,"said Weisman, a physical chemist himself.

He and primary author Saunab Ghosh, a graduate student in his lab, discovered that a light touch was key."We're not the first people to study the effects of ozone reacting with nanotubes,"Weisman said."That's been done for a number of years.

"But all the prior researchers used a heavy hand, with a lot ofozone exposure. When you do that, you destroy the favorable optical characteristics of the nanotube. It basically turns off the fluorescence. In our work we only add about one oxygen atom for 2,000-3,000carbon atoms, a very tiny fraction."

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Ghosh and Weisman started with a suspension of nanotubes in water and added small amounts of gaseous or dissolved ozone. Then they exposed the sample to light. Even light from a plain desk lamp would do, they reported.

Most sections of the doped nanotubes remain pristine and absorbinfrared lightnormally, forming excitons, quasiparticles that tend to hop back and forth along the tube -- until they encounter oxygen.

"Anexcitoncan explore tens of thousands of carbon atoms during its lifetime,"Weisman said."The idea is that it can hop around enough to find one of these doping sites, and when it does, it tends to stay there, because it's energetically stable. It becomes trapped and emits light at a longer (red-shifted) wavelength.

"Essentially, most of the nanotube is turning into an antenna that absorbs light energy and funnels it to the doping site. We can make nanotubes in which 80 to 90 percent of the emission comes from doped sites,"he said.

Lab tests found the doped nanotubes' fluorescent properties to be stable for months.

Weisman said treated nanotubes could be detected without using visible light."Why does that matter? In biological detection, any time you excite at visible wavelengths, there's a little bit of background emission from the cells and from the tissues. By exciting instead in the infrared, we get rid of that problem,"he said.

The researchers tested their ability to view doped nanotubes in a biological environment by adding them to cultures of human uterine adenocarcinoma cells. Later, images of the cells excited in the near-infrared showed single nanotubes shining brightly, whereas the same sample excited with visible light displayed a background haze that made the tubes much more difficult to spot.

His lab is refining the process of doping nanotubes, and Weisman has no doubt about their research potential."There are many interesting scientific avenues to pursue,"he said."And if you want to see a single tube inside a cell, this is the best way to do it. The doped tubes can also be used for biodistribution studies.

"The nice thing is, this isn't an expensive or elaborate process,"Weisman said."Some reactions require days of work in the lab and transform only a small fraction of your starting material. But with this process, you can convert an entire nanotube sample very quickly."

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Radically simple technique developed to grow conducting polymer thin films

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(PhysOrg.com) -- Oil and water don't mix, but add in some nanofibers and all bets are off.

A team of UCLA chemists and engineers has developed a new method for coating large surfaces with nanofiber thin films that are both transparent and electrically conductive. Their method involves the vigorous agitation of water, dense oil and polymer nanofibers. After this solution is sufficiently agitated it spreads over virtually any surface, creating a film.

"The beauty of this method lies in its simplicity and versatility,"said CaliforniaNanoSystemsInstitute (CNSI) researcher Richard B. Kaner, a professor of chemistry and biochemistry and a professor of materials science and engineering at the UCLA Henry Samueli School of Engineering and Applied Science."The materials used are inexpensive and recyclable, the process works on virtually any substrate, it produces a uniform thin film which grows in seconds and the entire thing can be done at room temperature."

Conducting polymers combine the flexibility and toughness of plastics withelectrical properties. They have been proposed for applications ranging from printedelectronic circuitsto supercapacitors but have failed to gain widespread use because of difficulties processing them into films.

"Conducting polymers have enormous potential in electronics, and because this technique works with so many substrates, it can be used in a broad spectrum of applications, includingorganic solar cells, light-emitting diodes, smart glass and sensors,"said Yang Yang, a professor of materials science and engineering at the Samueli School of Engineering and Applied Science and faculty director of the Nano Renewable Energy Center at the CNSI.

One of the potential applications is smart, or switchable, glass that can change between states when an electric current is applied— for example, switching between see-through and opaque states to let light in or block it. The UCLA research group is applying the technique to other nanomaterials in addition to polymer nanofibers in the hopes of expanding the number of available applications.

The team's solution-based technique, published in the peer-reviewed journalProceedings of National Academy of Sciences, was discovered serendipitously when a transparent film of polymer spread up the walls of a container while nanofibers in water were being purified with chloroform.

"What drew me in immediately was the eerie phenomenon of what appeared to be self-propelled fluid flow,"said Julio M. D'Arcy, lead author on thePNASpaper and a senior graduate student in the Kaner's UCLA lab.

"Now I can tell people that I make films in L.A.,"he joked.

When water and oil are mixed, a blend of droplets is formed, creating a water–oil interface that serves as an entry point for trapping polymer nanofibers at liquid–liquid interfaces. As droplets unite, a change in the concentration of blended solids at the water–oil interface leads to a difference in surface tension. Spreading up a glass wall occurs as result of an attempt to reduce the surface-tension difference. Directional fluid flow leads to a continuously conductive thin film comprised of a single monolayer of polymer nanofibers. The uniformity of the film surface is due to the particles being drawn out of the water–oil interface, sandwiched between two fluids of opposing surface tensions.

Development of the technology is occurring in collaboration with Fibron Technologies Inc., with support from the National Science Foundation through a Small Business Technology Transfer grant. Fibron is a small company that has licensed the technology from UCLA. It was founded by Kaner, who serves as chief scientific adviser, and two of his former Ph.D. students— Christina Baker and Henry Tran, who have gone on to take leadership roles in the company.

Fibron's CEO, Christian Behrenbruch, said"working with UCLA to develop this technology has been a win-win. It enables us to access incredibly innovative people, but also, the NSF has helped enable the establishment of a formal and transparent IP releationship with the university. The good news is that this technology is moving rapidly into commercial development."

Other techniques exist for creating thin films of conducting polymers, but each technique tends to work only a limited number of applications, or they are not feasible for scaling up. A method has long been sought which would overcome the limitations of each of the previous methods. The water and oil technique, with a bit of nanotechnology thrown in, might provide just that— a scalable universal method for creating largethin filmsof conducting polymers.

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