Stupendous Materials

Feel-good glass

2012-07-05T19:46:00.003+05:30

New window coating lets the right light through

Daylight acts on our body clock and stimulates the brain. Fraunhofer researchers have made use of this knowledge and worked with industry partners to develop a coating for panes of glass that lets through more light. Above all, it promotes the passage through the glass of those wavelengths of light that govern our hormonal balance.

Most people prefer to live in homes that are airy and flooded with light. Nobody likes to spend much time in a dark and dingy room. That’s no surprise, since daylight gives us energy and has a major impact on our sense of wellbeing. It is a real mood lifter. But not everyone is lucky enough to live in a generously glazed home, and office spaces – where we spend many hours of each day – are often not exactly bright and breezy. Modern heat-insulating, sun-protection glazing for offices and housing doesn’t make things any better, since it isn’t optimized to allow the light that governs our hormonal balance to pass through: instead, a distinctly noticeable percentage of incident sunlight in this effective part of the spectrum is reflected away.

Anti-reflective glass that is more transmissive overall to daylight is reserved for certain special applications, such as in glass covers for photovoltaic modules or in glazing for shop windows. The aim with this kind of glass is to avoid nuisance reflections and to achieve maximum light transmission at the peak emission wavelength of sunlight. This is the wavelength at which the human retina is also most sensitive to light. “However, our biorhythms are not affected by the wavelengths that brighten a room the most, but rather by blue light,” explains graduate engineer Walther Glaubitt, a researcher at the Fraunhofer Institute for Silicate Research ISC in Würzburg. That is why he and his team have developed glass that is designed to be particularly transmissive to light in the blue part of the spectrum. The secret is a special, long-lasting and barely perceptible inorganic coating that is only 0.1 micrometers thick. “Nobody’s ever made glass like this before. It makes you feel as if the window is permanently open,” says Glaubitt. One reason the glass gives this impression is that it exhibits maximum transmission at wavelengths between 450 and 500 nanometers – which is exactly where the effects of blue light are at their strongest.

Why is it that the blue part of the light spectrum has such an impact on our sense of wellbeing? “There is a nerve connecting the human retina to the hypothalamus, which is the control center for the autonomic nervous system,” explains Glaubitt’s team colleague Dr. Jörn Probst. Special receptors sit at the end of the nerve connection which are sensitive to blue light, converting it into light-and-dark signals and sending these to the area of the brain that functions as our biological clock. There, one of the things these nerve impulses do is regulate melatonin levels. A lack of light leads to high levels of melatonin, which can result in problems sleeping and concentrating, as well as depression and other psychological impairments. Seasonal affective disorder, also known as winter depression, is one possible outcome of unusually high melatonin levels. “The coating we’ve developed helps people to feel they can perform better and makes it less likely they will fall ill,” says Probst.

Industrial partner Centrosolar Glas GmbH & Co. KG is responsible for applying the coating to the glass while UNIGLAS GmbH & Co. KG, the company that brought the product to market maturity, handles the remaining finishing work as well as sales. It is about to launch a triple-glazing product featuring this innovative glass, for which a patent is pending, under the name UNIGLAS | VITAL® feel-good glass. Fitting triple glazing to a room does not make it seem appreciably darker, but it does affect the light that enters the room in a way that is detrimental to our biorhythms. This is especially true for people who have little opportunity to spend time outdoors and are obliged to spend most of their time in rooms with only small windows. “Thanks to the special ISC coating, this is not the case with our UNIGLAS | VITAL® feel-good glass. Instead, the light quality achieved is very close to that of single glazing,” says Thomas Fiedler, the Technical Director of UNIGLAS. Its transmissivity to light is increased across the entire range from 380 to 580 nanometers, which is to say in the portion of the spectrum that is responsible for promoting wellbeing. At 460 nanometers, the light transmissivity of UNIGLAS | VITAL® is 79 percent. Comparable triple glazing only lets through 66 percent of light at this wavelength. Meanwhile, the coating has no impact on the window’s heat-insulating properties.

But the ISC researchers haven’t quite reached their ultimate goal: “Up to now we’ve only applied our special coating to the side of the glass facing into the cavity between panes,” says Glaubitt. “In future we will also be coating the glazing’s exposed surfaces – in other words, the outside and the inside of the window. That will allow us to achieve around 95 percent light transmissivity at 460 nanometers.”

Etching the next generation of microchips

2012-07-03T22:20:00.001+05:30

By Hannah Hickey

A University of Washington lab has been working for more than a decade on fusion energy, harnessing the energy-generating mechanism of the sun. But in one of the twists of scientific discovery, on the way the researchers found a potential solution to a looming problem in the electronics industry.

To bring their solution to market two UW engineers have launched a startup, Zplasma, that aims to produce the high-energy light needed to etch the next generation of microchips.

"In order to get smaller feature sizes on silicon, the industry has to go to shorter wavelength light," said Uri Shumlak, a UW professor of aeronautics and astronautics. “We’re able to produce that light with enough power that it can be used to manufacture microchips.”

The UW beam lasts up to 1,000 times longer than competing technologies and provides more control over the million-degree plasma that produces the light.

University of Washington

The lab equipment includes a small system that measures plasma for electronics applications, attached to a larger tank containing plasma for energy research.

For more than four decades the technology industry has kept up with Moore's Law, a prediction that the number of transistors on a computer chip will double every two years. This trend has allowed ever-smaller, faster, lighter and less energy-intensive electronics. But it's hit a roadblock: the 193-nanometer ultraviolet light now being used cannot etch circuits any smaller.

The industry has determined that the future standard for making microchips will be 13.5-nanometer light, a wavelength less than 1/14 the current size that should carry the industry for years to come. Such extreme ultraviolet light can be created only from plasmas, which are high-temperature, electrically charged gases in which electrons are stripped from their nuclei.

The electronics industry is trying to produce this extreme ultraviolet light in various ways. One takes a droplet of tin and shoots it with a laser to make plasma that releases a brief spark of light. But so far this spark is too brief. Chip manufacturers use a $100 million machine to bounce light off a series of mirrors and eventually project the light onto a silicon wafer; each step absorbs some of the light's energy.

"Over the past decade, the primary issue with these extreme ultraviolet light sources is they just can't produce enough power," Shumlak said. "It's a stumbling block for the whole semiconductor industry."

Fusion scientists, it turns out, are plasma experts. The hydrogen plasma in the sun is so hot that hydrogen nuclei fuse together and release energy. Scientists around the world, including at the UW, are working to replicate this on Earth. A fusion reactor would use hydrogen as its fuel and emit helium as a waste product, a technically challenging but clean source of energy.

The UW group's specialty is a lower-cost version of a fusion reactor that uses currents flowing through the material, rather than giant magnets, to contain the million-degree plasma. Their method also produces plasma that is stable and long-lived.

"It's a completely different way to make the plasma that gives you much more control," said Brian Nelson, a UW research associate professor of electrical engineering.

University of Washington

Four capacitors supply up to 10,000 volts of energy to separate the xenon electrons from their nuclei, creating an electrically charged plasma.

The first time they triggered the experiment in 1999, an engineer looking through the glass said, "That was really bright!" That was when the proverbial light bulb went off, Nelson said, and the team began to explore applications for bright high-energy light.

They may have found that application in the microchip industry. Light produced through techniques now being considered by the chip industry generate a spark that lasts just 20 to 50 nanoseconds. Zplasma's light beam lasts 20 to 50 millionths of a second, about 1,000 times longer.

"That translates directly into more light output, more power depositing on the wafer, such that you can move it through in some reasonable amount of time," Shumlak said.

An initial grant from the UW's Center for Commercialization allowed the team to verify that it could produce 13.5-nanometer light. A gift last fall from theWashington Research Foundation helped the team shrink the equipment from the size of a broomstick to a new version the size of a pin, which can produce a sharp beam.

The company was established last year with help from the UW's Center for Commercialization and Henry Berg, a technology entrepreneur who met the researchers through the center's Entrepreneurs in Residence program. Berg is now CEO of Zplasma.

The company is seeking "smart money" from corporate investors who can integrate the new technology with existing industrial processes.

"I hope this gets implemented into the industry and has an impact," Shumlak said.

The group will continue its fusion research project funded by the U.S. Department of Energy. Raymond Golingo, a UW research scientist in aeronautics and astronautics, is co-author of the patent for the technology issued in 2008.

Making Materials Untouchable

2012-07-01T23:09:00.000+05:30

New designs for materials that repel all liquids.

KATHERINE BOURZAC

Materials under development at MIT could lead to coatings that repel both water and oil. A group of MIT researchers have created an improved set of design rules for making any surface impervious to any liquid, be it water or gasoline. Such materials could eventually have promise as fingerprint-repelling coatings, fuel filters, self-washing car paints, and stain-resistant clothing.

Air drying: Water (dyed blue) and hexadecane (dyed red), an oil, bead up on an omniphobic surface, which repels all liquids. The droplets in this photo, which are separated from the surface by air pockets, are about three millimeters in diameter.

Last year, the MIT group, led by chemical engineer Robert Cohen and mechanical engineerGareth McKinley, created the first superoleophobic, or oil-repellant, surfaces. They started with a polymer developed by the Air Force that contains large numbers of oil-repelling fluorine groups. The MIT researchers made the material even more oil resistant by using lithography to pattern it with overhanging microstructures. These tiny structures create air pockets that help suspend liquids and prevent them from penetrating to the surface. The MIT researchers found that the surfaces are both superoleophobic and also superhydrophobic, or water repelling. Because they repel everything, they're called omniphobic.

Although these were the least wettable materials ever developed, it wasn't clear last year how much pressure the materials could withstand before the liquid would sag into the air pocket, causing the surface to fail. In their new work, the MIT researchers used mathematical models of surface properties to predict how changes in the surface geometry would improve resistance to pressure, allowing them to make surfaces that withstand greater pressure. Based on the properties of a given surface and a given liquid, the models can predict the contact angle between them. A high contact angle means that the liquid will bead up and easily roll off. The MIT researchers use their equations to predict how best to modify a surface in order to increase the contact angle.

These design rules don't just apply to one particular material. The MIT researchers have shown that a combination of structure and chemistry can turn any surface omniphobic, says Weihua Ming, a professor in the nanostructured-polymers research group at the University of New Hampshire. The MIT surfaces, says Di Gao, a professor of chemical and petroleum engineering at the University of Pittsburgh, are truly superomniphobic: they repel all liquids, causing them to bead up and roll off.

However, you won't find these coatings on your next iPod. Major practical issues remain. "The issue with a lot of these surfaces is that they may not be mechanically robust," says Chuck Extrand, principal scientist at Entegris, which makes fluid-handling equipment for the semiconductor industry. But Extrand says that in principle, it's possible to make these surfaces more durable. "I'm still hopeful we'll find something that's mechanically robust," he says.

Right now, to make flat omniphobic surfaces, the researchers need to make them on a silicon wafer using lithography. However, the team is working on designs for spraying or dip-coating flat surfaces.

Synthetic platelets

2012-07-01T20:53:00.000+05:30

Biomimetic research aids healing

Synthetic platelets have been developed by UC Santa Barbara researchers, in collaboration with researchers at Scripps Research Institute and Sanford-Burnham Institute in La Jolla, Calif. Their findings are published in the journal Advanced Materials in a paper titled "Platelet Mimetic Particles for Targeting Thrombi in Flowing Blood."

Platelets are the components of blood that allow it to prevent excessive bleeding and to heal wounds. The unique physical and biochemical properties of platelets play an important role in performing these complex biological tasks. Smaller than red blood cells, platelets are flexible, disk-shaped cells that are 2-4 micrometers in size.
"Upon further optimization and exhaustive testing, the synthetic platelets could be used for various biomedical applications," said the paper's first author Nishit Doshi, a researcher from the Department of Chemical Engineering.

The challenge Doshi and colleagues faced was to develop a comparably sized particle –– roughly 1/50th of the diameter of a strand of hair –– that had key structural properties of real platelets.

"In order to mimic the size, shape, and surface functionality of natural platelets synthetically, polymeric particles are particularly attractive," said Doshi. "However, polymeric particles are orders of magnitude more rigid than platelets."

To solve the problem of flexibility, researchers at UC Santa Barbara used a polymeric "template" –– a core upon which layers of proteins and polyelectrolytes were deposited, layered, and crosslinked to create a stable synthetic platelet-shaped particle. The rigid polymeric core was then dissolved to give the particle the desired flexibility. The particle was then coated with proteins found on the surface of activated natural platelets or damaged blood vessels, a procedure performed by the researchers at Scripps Research Institute.
These synthetic platelets may be used to not only perform the typical functions of human platelets; but may also be used to carry imaging agents to identify damaged blood vessels or to deliver drugs that dissolve blood clots.

The synthetic platelets represent the latest and one of the most advanced in a line of efforts over the last century to mimic platelet function. While clotting factors and platelets from outside donors are used widely to halt bleeding, immune system responses and thrombosis have been issues. Non-platelet-derived substitutes have also received attention; however, said Doshi, these do not resemble the physical features of natural platelets.

"This development is a significant milestone in the field of biomimetic materials," said Samir Mitragotri, professor of chemical engineering, director of UC Santa Barbara's Center for Bioengineering, and an author of the paper. "By capitalizing on our capabilities in engineering materials, with the expertise in platelet biology that exists in Professor Ruggeri's laboratory, our synthetic platelets combine unique physical and biological attributes that mimic natural platelets." Biomaterials research is one of the principal focus areas in UCSB's Center for BioEngineering. In 2009, Doshi and colleagues in the Mitragotri laboratory developed synthetic red blood cells.

"This work is a marvelous demonstration of the power of material synthesis applied to medical problems. The synthetic platelets can have profound implications in wound-healing problems for trauma and wounds arising in both battlefield situations and during surgery," said Frank Doyle, director of UCSB's Institute of Collaborative Biotechnologies and the Associate Dean of Research of UCSB's College of Engineering.

Nanodiamonds cut through dirt to bring back ‘bling’ to low temperature laundry

2012-07-01T13:28:00.001+05:30

Nanodiamonds, pieces of carbon less than ten-thousandths the diameter of a human hair, have been found to help loosen crystallized fat from surfaces in a project led by research chemists at the University of Warwick that transforms the ability of washing powders to shift dirt in eco friendly low temperature laundry cycles.

These new findings tackle a problem that forces consumers to wash some of their laundry at between 60 and 90 degrees centigrade more than 80 times a year.

Even with modern biological washing powders, some fats and dirt cannot be removed at the lower temperatures many prefer to use for their weekly wash.

A desire to reduce the significant energy burden of regular high temperature washes, and understand the behaviour of these new materials, brought University of Warwick scientists and colleagues at Aston University together in a project funded by the UK Engineering and Physical Sciences Research Council (EPSRC) and P&G plc.

This “Cold Water Cleaning Initiative” funded a group of chemists, physicists and engineers led by Dr Andrew Marsh in the University of Warwick’s Department of Chemistry to explore how new forms of carbon might work together with detergents in everyday household products.

Dr Andrew Marsh said: “We found that the 5 nanometre diamonds changed the way detergents behaved at 25 degrees centigrade, doubling the amount of fat removed when using one particular commercial detergent molecule.

"Even at temperatures as low as 15 degrees centigrade, otherwise hard-to-remove fat could be solubilised from a test surface.

"The physical and chemical insight already gained paves the way for future research to explore how this unique behaviour might be exploited in other ways.”

Metallic hydrogen: Hard pressed

2012-07-01T13:09:00.004+05:30

Two physicists say they have forced hydrogen to become an exotic metal thought to exist only in the hearts of giant planets. Now they must face their critics.
Ivan Amato

Samples crushed between two diamonds can be probed with lasers.

BEN SMITH

Mikhail Eremets and Ivan Troyan work only with the very best, gem-quality diamonds. Nothing else can handle the stresses involved — not when the two physicists make a habit of forcing the diamonds' tips together until the pressure between them reaches levels normally found at the centre of the Earth.

Eremets and Troyan, both at the Max Planck Institute for Chemistry in Mainz, Germany, are not alone in this strange pursuit. Their apparatus, known as a diamond anvil cell, is a standard fixture in high-pressure research labs. But they have provoked widespread agitation in their research community by claiming to have crushed hydrogen in their cells until it gave up being a diatomic gas, and instead became a shiny, presumably monatomic, solid that conducted electricity like a metal.

The arguments over this alleged discovery — one of the most sought-after results in high-pressure research — have been raging ever since Eremets and Troyan published their results last November. “We could just read their paper and say it was wrong,” declares condensed-matter physicist William Nellis, an associate of Harvard University's physics department in Cambridge, Massachusetts, and one of the team's most vocal challengers.

But others, such as Raymond Jeanloz, a planetary scientist and high-pressure-materials researcher at the University of California, Berkeley, are keeping an open mind. Whether Eremets and Troyan are eventually proved right or wrong about metallic hydrogen, Jeanloz says, “what I feel is beautiful about their work is that they did a bazillion different experiments at these extreme conditions. They lit a fire under a couple of research groups.”

On 26 June, the main figures in this controvery will gather in Biddeford, Maine, during a Gordon Research Conference on high-pressure science. The result could be a meeting of minds — or a display of fireworks. “This is a very intense field,” says Jeanloz. High-pressure scientists have been trying — and failing — to make metallic hydrogen ever since theorists first predicted its existence in 1935. Anyone claiming success can expect an all-out critique from rival groups — especially considering what is at stake.

Not only would making metallic hydrogen in the laboratory allow researchers to do planetary science at the bench — gas-giant planets such as Jupiter, or the even larger ones being discovered around distant stars, are thought to have huge amounts of the stuff in their interiors — but it could point the way towards an entirely new world of high-pressure phenomena.

“Hydrogen is the simplest atom, the simplest molecule and perhaps the most complicated elemental solid,” says Arthur Ruoff, a high-pressure physicist at Cornell University in Ithaca, New York. In 1968, Cornell physicist Neil Ashcroft predicted that solid metallic hydrogen might be a superconductor. In 2004, calculations by Ashcroft and others suggested that, under certain combinations of pressure and temperature, hydrogen atoms would rearrange themselves into a new kind of quantum liquid with attributes of both superconductors, which conduct electricity without resistance, and superfluids, which flow without resistance.

Bright future

Such exotic behaviours become particularly interesting if some of these phases of hydrogen turn out to be metastable. This would mean that the phases could retain their high-pressure forms for an indefinite period once external forces are removed, much as diamonds formed by high temperatures and pressures deep inside Earth remain diamonds even after they reach the surface, instead of immediately reverting to carbon's more stable form, graphite. Nellis and others have imagined a host of applications for metastable metallic hydrogen, ranging from super-lightweight structural materials that would allow entire cities floating on the sea to be built, to rocket fuel that packs nearly four times as much propellant power per kilogram as the liquid hydrogen used in the most powerful rockets today.

First, however, comes the reality check. Diamond anvil cells can use only vanishingly small sample sizes. (The volume of Eremets and Troyan's hydrogen samples was about 160 cubic micrometres — somewhat smaller than an average human cell.) High-pressure experiments are fraught with the potential for error. And even the most experienced researchers run the risk of fooling themselves. The question is whether Eremets and Troyan are among them.

In their experiments, the Mainz physicists started with pairs of brilliant-cut diamonds. They trimmed each of the diamonds' points into a flat surface, or culet, 20–30 micrometres across, then aligned the diamonds with those truncated tips almost touching, on either side of a piece of metal foil pierced with a culet-sized hole that would enclose a minuscule experimental chamber.

Through a gem darkly

For each experiment, Eremets and Troyan loaded hydrogen gas into the hole, and started tightening a set of screws that forced the diamonds closer together. As the culets bit into the foil at the rim of the hole, the metal deformed around them to form a seal trapping the hydrogen. And as the force exerted by the screws was focused down onto the culets, the pressure in the chamber began to skyrocket.

Mikhail Eremets (left) and Ivan Troyan stand by the apparatus they used to create what they believe to be metallic hydrogen.

CARSTEN COSTARD

This is where high-pressure experiments often go awry. Although the anvil's diamond jaws are made of one of the hardest materials known, superpressured hydrogen routinely infiltrates them, making them brittle and causing the gems to crack like cheap plastic cups. This also spoils the gemstones' transparency, stopping the physicists from seeing what is happening in the chamber. Eremets and Troyan addressed that problem by applying semi-transparent coatings to protect their diamonds from the infiltration of hydrogen. But even so, they went through about 100 pairs of diamonds as they worked out the bugs of their apparatus and ran trials and controls.

When the pressure inside their anvils reached 200 billion pascals (200 GPa), or about 2 million times Earth's atmospheric pressure at sea level, the two Mainz physicists saw spectroscopic signs that the diatomic hydrogen molecules had begun to interact in a way that signalled that they were becoming a solid.

At 220 GPa, the sample chamber became dark, another sign that hydrogen had apparently assumed a condensed phase. Eremets and Troyan found that laser pulses fired through the transparent diamond triggered small flows of electrons that they could detect by means of copper and gold electrodes deposited on the culet surfaces — behaviour characteristic of semiconducting materials, in which electrons need a small energy kick to flick them out of orbit around atoms and into a conductive flow.

At 240 GPa, Eremets and Troyan recorded small currents even without the laser shots, an indication that room-temperature thermal vibrations alone could nudge the electrons into a conductive mood.

And at about 270 GPa, the researchers saw their samples' electrical resistance suddenly drop by several orders of magnitude, just as their spectroscopy was showing that the hydrogen's molecular vibrations were slowing down and morphing in ways suggestive of a phase transition — and the samples were becoming shiny like a metal.

“It is hard to sit on data like these,” says Eremets. He and Troyan are convinced that their findings are at least consistent with having made metallic hydrogen.

But others are not so sure. Sceptics note that pitfalls are everywhere in experiments such as these. If an experimenter peers through the diamonds and sees the sample begin to darken, for example, that may mean that it is becoming a solid — or that the hydrogen is reacting with the foil or other impurities to form metal hydrides. If odd electrical signals start coming in from the culet electrodes, they may indicate the formation of a new phase of hydrogen — or that the diamond jaws are deforming, causing the electrodes to short out or emit spurious signals. Eremets says that he and Troyan are well aware of such pitfalls, and did their best to avoid them. Nonetheless, says Ruoff, “I don't know anybody who thinks their claim is valid”.

One fact that troubles Ruoff and other critics is that the resistance rises as the sample's temperature drops. This is contrary to normal metallic behaviour, in which the resistance goes down as the temperature does. But when reviewers of the paper raised that issue, says Eremets, he successfully argued that the upward trend is consistent with that seen in a disordered metal, in which the atomic structure is more like that of a glass than a crystal.

Russell Hemley, a high-pressure-materials researcher at the Carnegie Institution of Washington in Washington DC, is sceptical of Eremets and Troyan's claims for another reason: if the hydrogen really becomes metallic, then the shininess that the Mainz team reports at optical wavelengths ought to be accompanied by equally strong reflectivity at infrared wavelengths. Eremets and Troyan were not able to get good infrared data on their samples. But Hemley says that in his own experiments with hydrogen at similar pressures, “we see it transmitting” in the infrared. Moreover, in a paper published in April, Hemley and his colleagues report signs that hydrogen squeezed up to 360 GPa holds on to its diatomic character and fails to morph into a monatomic metal. Adding to the complexity of the situation, some theorists suggested that, if squeezed enough, even intact hydrogen molecules might develop a new and crowded bonding pattern that could have metallic properties.

Eremets and Troyan are standing their ground. “Our measurements are not perfect,” Eremets concedes, but he insists that “metallic hydrogen remains a viable interpretation”. He points to a paper published in March by Eugene Gregoryanz, a physicist at the University of Edinburgh, UK, and his colleagues. “They observe a new phase, the same Raman spectra and a darkening of the sample” at around 220 GPa, says Eremets. Clearly, he argues, something is happening at that point — although Gregoryanz and his colleagues attributed the changes to formation, not of metallic hydrogen, but of a previously unseen, graphene-like phase of molecular hydrogen.

In an effort to clarify the situation, Eremets and Troyan travelled to Villigen in Switzerland in late April, to gather infrared spectra using the synchrotron light source at the Paul Scherrer Institute there. The data could reveal vibrations in the lattice structures of high-pressure hydrogen samples that would help theoreticians to identify specific structures of any solid phases that might be present, Eremets says. Such structural information would not, by itself, prove that the hydrogen had become metallic. But Eremets and Troyan also plan to attempt more thorough and extensive electrical measurements, which could prove conclusive.

Looking back, Eremets admits that he and Troyan probably should have been more circumspect in their paper — conveying the message that they might have made metallic hydrogen, rather than claiming more strongly that they had done so, as they did in their abstract and their concluding paragraphs.

Meanwhile, the race for metallic hydrogen continues, as other high-pressure research groups pursue their own experiments. Jeanloz points out that many members of this community, himself included, have mingled over the years as collaborators, postdocs, supervisors and mentors, only to go on to become each other's staunchest critics and rivals, unlikely to let the slightest chink in an argument go unchallenged. What emerges from this dynamic, say Jeanloz and others, is a creative tension that could eventually force those who claim to have produced metallic hydrogen to do enough experiments, with enough controls, to compile enough lines of evidence to convince even the pickiest of critics. Until then, the trophy seems to be up for grabs.

Rice researchers develop paintable battery

2012-07-01T12:32:00.000+05:30

Researchers at Rice University have developed a lithium-ion battery that can be painted on virtually any surface.

The rechargeable battery created in the lab of Rice materials scientist Pulickel Ajayan consists of spray-painted layers, each representing the components in a traditional battery. The research appears in Nature’s online, open-access journal Scientific Reports.

“This means traditional packaging for batteries has given way to a much more flexible approach that allows all kinds of new design and integration possibilities for storage devices,” said Ajayan, Rice’s Benjamin M. and Mary Greenwood Anderson Professor in Mechanical Engineering and Materials Science and of chemistry. “There has been lot of interest in recent times in creating power sources with an improved form factor, and this is a big step forward in that direction.”

Rice University graduate student Charudatta Galande, Professor Pulickel Ajayan and graduate student Neelam Singh show off the first test device for their paintable batteries, an array of standard ceramic tiles combined with a solar cell and an array of LEDs, which the batteries powered for six hours. Photo by Jeff Fitlow

Lead author Neelam Singh, a Rice graduate student, and her team spent painstaking hours formulating, mixing and testing paints for each of the five layered components – two current collectors, a cathode, an anode and a polymer separator in the middle.

The materials were airbrushed onto ceramic bathroom tiles, flexible polymers, glass, stainless steel and even a beer stein to see how well they would bond with each substrate.

In the first experiment, nine bathroom tile-based batteries were connected in parallel. One was topped with a solar cell that converted power from a white laboratory light. When fully charged by both the solar panel and house current, the batteries alone powered a set of light-emitting diodes that spelled out “RICE” for six hours; the batteries provided a steady 2.4 volts.

The researchers reported that the hand-painted batteries were remarkably consistent in their capacities, within plus or minus 10 percent of the target. They were also put through 60 charge-discharge cycles with only a very small drop in capacity, Singh said.

Ceramic tiles coated with battery paints and then heat-sealed powered LEDs spelling out "RICE" for six hours in an experiment at Rice University. The lithium-ion batteries can be painted on virtually any surface. Photo by Jeff Fitlow

Each layer is an optimized stew. The first, the positive current collector, is a mixture of purified single-wall carbon nanotubes with carbon black particles dispersed in N-methylpyrrolidone. The second is the cathode, which contains lithium cobalt oxide, carbon and ultrafine graphite (UFG) powder in a binder solution. The third is the polymer separator paint of Kynar Flex resin, PMMA and silicon dioxide dispersed in a solvent mixture. The fourth, the anode, is a mixture of lithium titanium oxide and UFG in a binder, and the final layer is the negative current collector, a commercially available conductive copper paint, diluted with ethanol.

“The hardest part was achieving mechanical stability, and the separator played a critical role,” Singh said. “We found that the nanotube and the cathode layers were sticking very well, but if the separator was not mechanically stable, they would peel off the substrate. Adding PMMA gave the right adhesion to the separator.” Once painted, the tiles and other items were infused with the electrolyte and then heat-sealed and charged.

A beer stein served as an able substrate for a paintable battery developed at Rice University. Photo by Jeff Fitlow

Singh said the batteries were easily charged with a small solar cell. She foresees the possibility of integrating paintable batteries with recently reported paintable solar cells to create an energy-harvesting combination that would be hard to beat. As good as the hand-painted batteries are, she said, scaling up with modern methods will improve them by leaps and bounds. “Spray painting is already an industrial process, so it would be very easy to incorporate this into industry,” Singh said.

The Rice researchers have filed for a patent on the technique, which they will continue to refine. Singh said they are actively looking for electrolytes that would make it easier to create painted batteries in the open air, and they also envision their batteries as snap-together tiles that can be configured in any number of ways.

“We really do consider this a paradigm changer,” she said.

Co-authors of the paper are graduate students Charudatta Galande and Akshay Mathkar, alumna Wei Gao, now a postdoctoral researcher at Los Alamos National Laboratory, and research scientist Arava Leela Mohana Reddy, all of Rice; Rice Quantum Institute intern Andrea Miranda; and Alexandru Vlad, a former research associate at Rice, now a postdoctoral researcher at the Université Catholique de Louvain, Belgium.

The Advanced Energy Consortium, the National Science Foundation Partnerships for International Research and Education, Army Research Laboratories and Nanoholdings Inc. supported the research.

Nerve regrowth protein identified

2012-06-29T10:35:00.001+05:30

A protein needed to re-grow injured nerves in limbs has been identified, raising the prospect of new treatments.

The findings, in mice, have implications for helping patients recover from peripheral nerve injuries.

They also open up new pathways for investigating how to regenerate neurons in the spinal cord and brain.

Peripheral nerves provide the sense of touch and drive the muscles that move the arms, legs and feet.

Unlike central nervous system nerves of the spinal cord, they can regrow after being cut or crushed. But how this happens is still not well understood.

Scientists conducting the new research, reported in the journal Neuron, identified a signalling protein that helps switch on the regeneration process.

The molecule, called leucine zipper kinase (DLK), regulates signals that tell a nerve cell it has been injured, often communicating over distances of several feet.

Mice lacking DLK were unable to regrow severed nerves.

Lead researcher Professor Aaron DiAntonio, from Washington University in St Louis, US, said: "DLK is a key molecule linking an injury to the nerve's response to that injury, allowing the nerve to regenerate.

"How does an injured nerve know that it is injured? How does it take that information and turn on a regenerative programme and regrow connections? And why does only the peripheral nervous system respond this way, while the central nervous system does not? We think DLK is part of the answer."

Understanding the role of DLK may also be relevant to the central nervous system, say the researchers.

"Since this sort of signalling doesn't appear to happen in the central nervous system, it's possible these nerves don't 'know' when they are injured," said Prof DiAntonio.

"It's an exciting idea - but not at all proven - that activating DLK in the central nervous system could promote its regeneration."

A Better Way to Get Hydrogen from Water

2012-06-25T20:10:00.004+05:30

Caltech researchers demonstrate a clean technique for using heat and catalysts to split water into hydrogen and oxygen.

KEVIN BULLIS

An experimental approach to splitting water might lead to a relatively cheap and clean method for large-scale hydrogen production that doesn't require fossil fuels. The process splits water into hydrogen and oxygen using heat and catalysts made from inexpensive materials.

Heat-driven water splitting is an alternative to electrolysis, which is expensive and requires large amounts of electricity. The new approach, developed by Caltech chemical-engineering professor Mark Davis, avoids the key problems with previous heat-driven methods of water splitting. It works at relatively low temperatures and doesn't produce any toxic or corrosive intermediate products.

Almost all the hydrogen used now in industrial processes, such as making gasoline, comes from reforming natural gas. If automakers start selling large numbers of hydrogen-fuel-cell vehicles, as they've said they plan to do eventually, the hydrogen for those is also likely to come from natural gas unless processes like the one at Caltech are commercialized.

The basic approach in high-temperature water splitting is to heat up an oxidized metal to drive off oxygen, then add water. In Davis's case, the starting material is magnesium oxide, and the reactions are facilitated by shuttling sodium ions in and out of it. "Without the sodium, the temperatures would go up well over 1,000 °C," Davis says. With it, the reactions work at temperatures of 850 °C or lower.

The technology is probably far from being commercialized. It still requires pretty high temperatures—a couple of hundred degrees higher, for example, than those used to drive steam turbines at coal and nuclear power plants. Producing those temperatures without fossil fuels would probably involve one of two technologies, neither of which is being used commercially right now: high-temperature nuclear reactors or high-concentration solar thermal facilities that use rings of mirrors to concentrate sunlight more intensely than occurs today in solar thermal power plants.

The Caltech approach would also need to be tested to make sure the water-splitting cycle can run repeatedly. So far, the researchers have shown that the same materials can be reused five times, but "if you were going to have one of these things work for real, you'd need to run it for thousands of cycles," Davis says. He says such testing is beyond the scope of his lab. "We feel good about the potential for many cycles on this one, but until you do it, you don't know," he says. "All we did here is prove the chemistry could work."

The rate of hydrogen production would also need to be increased—for example, by switching to materials with a higher surface area. And Davis hopes to lower the temperatures needed still further. The goal is to use this process or a similar one to make use of waste heat at steel mills and power plants. "This is a good start, but the lower we go, the better," he says.

Speeding Up Materials Design

2012-06-25T19:06:00.006+05:30

A new computer program accurately predicts the behavior of proposed materials, which means faster development of new electronics and solar cells.

Model material: This organic semiconductor,
one of the best ever made, was predicted by computer
models, then made in the lab.

A chemical compound designed with the aid of a Harvard-created computer program has turned out to be one of the best organic electronic materials to date. This new material, an organic semiconductor, could be used to make new electronics such as colorful displays that roll up. It's an important proof of principle for using computers to aid materials design.
Organic semiconductors could enable less expensive, lightweight electronics that can take new forms, such as flexible displays and printed solar cells. It's hoped that the materials will also make solar power more widespread, because it should be less expensive to make solar cells from them than from silicon and other inorganic materials. But in the decades since chemists began working with organic semiconductors, progress has been slow, and these materials have found limited applications, such as in short-lived portable solar cells. The main challenge is that these materials just don't conduct electrons and their positive counterparts, holes, nearly as fast as conventional semiconductors like silicon, making them much less efficient.
The new organic semiconductor, predicted using a computer modeling program developed by Harvard chemistry professor Alán Aspuru-Guzik, and then synthesized by researchers at Stanford University, conducts charge much faster than the silicon material used in most of today's display electronics. That means it could be used to make brighter displays that provide crisper video. And the new material is sufficiently speedy to make electronics for organic light-emitting diode (OLED) displays used in cell phones and televisions or to control radio-frequency identification (RFID) tags used to track stuff.
For many years, scientists have talked about the potential of computational modeling to shorten the materials development process. When chemists develop new materials, "most work is based on intuition," says Zhenan Bao, the Stanford professor of chemical engineering whose group made and tested the new material. Unfortunately, intuition is hit or miss—a new molecule that seems promising may not do what researchers expect it to. By prescreening potential materials using Aspuru-Guzik's computer program, chemists can focus the months or years needed to synthesize and test new compounds on those that seem most promising.
Computational screening has been a great success in some areas, including energy storage. Gerbrand Ceder, a professor at MIT, has computationally predicted faster-charging battery materials that are currently being commercialized by the company A123 Systems. Until recently, computational methods hadn't been applied to making better organic semiconductors, which pose a different set of challenges, says Aspuru-Guzik. But now theoretical chemists have generated enough foundational knowledge, and experimentalists enough data, to make successful predictive models.

New Process Makes Heat-Harvesting Materials Cheaply

2012-06-24T23:10:00.000+05:30

Such materials could be used to cool computers and buildings, and harvest waste heat in cars.

BY PRACHI PATEL

High-efficiency thermoelectric materials could lead to new types of cooling systems, and new ways to scavenge waste heat for electricity. Researchers at Rensselaer Polytechnic Institute in Troy, New York, have now developed an easy, inexpensive process to make such materials.

The materials made by the RPI team already perform as well as those on the market, and the new process, which involves zapping chemicals in a microwave oven, offers room for improvement. "We haven't even optimized the process yet," says Ganpati Ramanath, a materials science and engineering professor at RPI. "We're confident that we can increase the efficiency further."

Thermoelectric materials convert heat into electricity, and vice versa. They are used in niche applications such as power generation on spacecraft and temperature-controlled car seats. If they were cheaper and more efficient, they could perhaps be used to make lightweight refrigerators, cooling systems for computer chips and buildings, and for using car exhaust heatto power electronics such as headlights and the radio.

Cooked to order: Zapping raw materials in a microwave oven and drying the resulting solution produces a black powder (top) made of hexagonal bismuth telluride nanoplates (bottom).
RPI

Good thermoelectrics need to conduct electricity well but heat poorly. One way to boost the heat-transfer efficiency of such materials is to give them nanoscale features that block the flow of heat without restricting electric current.

Researchers have made nanostructured materials by breaking up crystals into fine powder. But this process is energy intensive and only results in high-efficiency p-type thermoelectric materials—the kind rich in positively charged particles called holes. But both p-type and n-type materials (which have an abundance of electrons) are needed for practical devices.

"We've shown that we can make both p- and n-type materials, and we can do this very scalably and more cost-effectively," Ramanath says. "We can make gram quantities in minutes."

Ramanath and his colleagues make a solution from raw materials such as tellurium and bismuth chloride in an organic solvent, and put it in a domestic microwave oven for two to three minutes. They get a solution containing hexagonal nanoplates, which they press together and heat to make nanopellets. By using a solvent containing sulfur, the researchers get sulfur-doped nanoplates that are n-type.

The technique, presented in a Nature Materials paper posted online last week, makes p-type materials that are as efficient as the best ones on the market, while the n-type materials are at least 25 percent more efficient. One of the biggest commercial thermoelectric device manufacturers is now interested in adopting the new materials and process.

"This is the first nanostructured n-type mat with a high [efficiency] value," says John Badding, a professor of chemistry at Penn State University.

The key breakthrough of the RPI work, according to Badding, is that the researchers are building the nanostructured materials from the bottom up using chemistry. This means they can fine-tune the properties of the building blocks and their assembly to improve the material's properties. "The way they're making the material is a big deal," he says. "The hope is that in the future, this type of approach could lead to better [efficiency]."

New Process Makes Heat-Harvesting Materials Cheaply

2012-06-24T23:00:00.000+05:30

Such materials could be used to cool computers and buildings, and harvest waste heat in cars.

PRACHI PATEL

Cooked to order: Zapping raw materials in a microwave oven and drying the resulting solution produces a black powder (top) made of hexagonal bismuth telluride nanoplates (bottom).
RPI

Thermoelectric materials convert heat into electricity, and vice versa. They are used in niche applications such as power generation on spacecraft and temperature-controlled car seats. If they were cheaper and more efficient, they could perhaps be used to make lightweight refrigerators, cooling systems for computer chips and buildings, and for using car exhaust heat to power electronics such as headlights and the radio.

"We've shown that we can make both p- and n-type materials, and we can do this very scalably and more cost-effectively," Ramanath says. "We can make gram quantities in minutes."

"This is the first nanostructured n-type mat with a high [efficiency] value," says John Badding, a professor of chemistry at Penn State University.

High-Speed Materials Discovery

2012-06-24T22:57:00.005+05:30

A new way to identify battery materials suitable for mass production could revolutionize energy storage.

DAVID H. FREEDMAN

1/ Wildcat starts with a wide range of precursor materials that may have potential for energy storage and other applications. Credit: Frank Rogozienski

Choosing the optimal materials for batteries is a particularly tricky problem. The devices have three principal components: an anode, a cathode, and an electrolyte. Not only can each be formed from almost any blend of a huge number of compounds, but the three components have to work well together. That leaves many millions of promising combinations to explore.

3/ Cathodes, anodes, and electrolytes are assembled into small working batteries, which are tested by the thousand in this tower. Testing materials together allows dud combinations to be eliminated quickly. Credit: Frank Rogozienski

To hunt down winning combinations, Wildcat has adopted a strategy originally developed by drug discovery labs: high-throughput combinatorial chemistry. Instead of testing one material at a time, Wildcat methodically runs through thousands of tests in parallel, synthesizing and testing some 3,000 new material combinations a week. "We've got materials in the pipeline that could triple energy density," says CEO Mark Gresser.

Others have tried the combinatorial technique to find new battery materials, but they've run into a stumbling block. The easy way to test thousands of materials is to deposit a sample of each one in a thin film atop a substrate. This approach did allow previous researchers to turn up promising materials for battery components—but then candidates would typically prove unsuited to cost-effective large-scale production processes.

To process so many samples, Wildcat relies heavily on automation. This assay machine weighs and records vials of materials. Credit: Frank Rogozienski

To avoid that time-wasting detour, Wildcat found ways to produce samples using miniaturized versions of large-scale production techniques. In effect, the candidate materials are being tested for ease of manufacturing at the same time as they're being tested for performance. Wildcat also tests the materials wired together as actual batteries, and in a variety of potential operating conditions. "There are a lot of variables that affect battery performance, including temperature and voltage, and we examine all of them," says Gresser. The result is that a material that performs well in a Wildcat test bed will probably perform well in field tests.

If Wildcat is successful, its efforts could lead to batteries that are smaller or more powerful than their present-day counterparts—improvements that will appeal to the makers of smart phones and electric vehicles alike.

Nanoparticles engineered at Notre Dame promise to improve blood cancer treatment

2012-06-24T14:56:00.005+05:30

Researchers from the University of Notre Dame have engineered nanoparticles that show great promise for the treatment of multiple myeloma (MM), an incurable cancer of the plasma cells in bone marrow.

One of the difficulties doctors face in treating MM comes from the fact that cancer cells of this type start to develop resistance to the leading chemotherapeutic treatment, doxorubicin, when they adhere to tissue in bone marrow.

“The nanoparticles we have designed accomplish many things at once,” says Başar Bilgiçer, assistant professor of chemical and biomolecular engineeringand chemistry and biochemistry, and an investigator in Notre Dame’s Advanced Diagnostics and Therapeutics(AD&T) initiative.

“First, they reduce the development of resistance to doxorubicin. Second, they actually get the cancer cells to actively consume the drug-loaded nanoparticles. Third, they reduce the toxic effect the drug has on healthy organs.”

The nanoparticles are coated with a special peptide that targets a specific receptor on the outside of multiple myeloma cells. These receptors cause the cells to adhere to bone marrow tissue and turn on the drug resistance mechanisms. But through the use of the newly developed peptide, the nanoparticles are able to bind to the receptors instead and prevent the cancer cells from adhering to the bone marrow in the first place.

The particles also carry the chemotherapeutic drug with them. When a particle attaches itself to an MM cell, the cell rapidly takes up the nanoparticle, and only then is the drug released, causing the DNA of cancer cell to break apart and the cell to die.

“Our research on mice shows that the nanoparticle formulation reduces the toxic effect doxorubicin has on other tissues, such as the kidneys and liver,” adds Tanyel Kiziltepe, a research assistant professor with the Department of Chemical and Biomolecular Engineering and AD&T.

“We believe further research will show that the heart is less affected as well. This could greatly reduce the harmful side-effects of this chemotherapy.”

The group had to tackle three important problems associated with all nanoparticle-based therapies, explainsJonathan Ashley, one of the leading researchers of the project.

“There was some complex bioengineering involved in developing the particles. We were able to precisely control the number of drug and targeting elements on each nanoparticle, achieve homogeneous nanoparticle size distribution and eliminate the batch-to-batch variability in particle production.”

Before advancing to human clinical trials, the team plans further research and testing to improve the design of the nanoparticles and to find the optimum amount and combination of chemotherapy drugs for this new treatment.

The research is described in greater detail in a recent edition of Nature’s Blood Cancer Journal. It was supported by funding from the Indiana Clinical and Translational Sciences Institute.

Mind the gap

2012-06-22T18:53:00.005+05:30

Extending Roadway Life: GTRI Researchers Develop Prototype Automated Pavement Crack Detection and Sealing System

Sealing cracks in roadways ensures a road’s structural integrity and extends the time between major repaving projects, but conventional manual crack sealing operations expose workers to dangerous traffic and cover a limited amount of roadway each day.

Example of a pavement crack filled with GTRI’s prototype automated pavement crack detection and sealing system. In road tests, the system was able to detect cracks smaller than one-eighth-inch wide and efficiently fill cracks from a vehicle moving at a speed of three miles per hour. (Click image for high-resolution version. Credit: Jonathan Holmes)

To address these challenges, the Georgia Tech Research Institute (GTRI) developed a prototype automated pavement crack detection and sealing system with funding from the Georgia Department of Transportation. In road tests, the system was able to detect cracks smaller than one-eighth-inch wide and efficiently fill cracks from a vehicle moving at a speed of three miles per hour.

“Our prototype system has proved in many ways that a commercial-scale automated crack sealing system is viable,” said Jonathan Holmes, the GTRI research engineer currently leading the project, which began in 2003. “We demonstrated solutions to technical challenges — including the high-speed firing of nozzles, automated crack detection and navigation — in a real-time, limited-scale system.”

An automated crack sealing system would increase the level of safety for the workers involved, require fewer personnel and increase the amount of roadway covered per day. In addition, the system could save transportation departments money because sealing cracks extends the time before a roadway needs to be completely repaved.

GTRI researchers developed the prototype automated pavement crack detection and sealing system shown here. An automated crack sealing system would increase the level of safety for the workers involved, require fewer personnel and increase the amount of roadway covered per day. (Click image for high-resolution version. Credit: Jonathan Holmes)

The prototype system, which was mounted on a trailer, consists of a stereo camera, light-emitting diodes (LEDs) of two different colors, and an assembly to provide a continuous supply of sealant to longitudinal and transverse sealant distribution systems. The operation required only one worker to drive the vehicle pulling the trailer.

As the system traveled along a road lane, the LEDs illuminated the road in two directions — parallel and perpendicular to the road — and the stereo camera took two pictures of the road simultaneously, which were analyzed using thresholding and filtering algorithms. Within 100 milliseconds of taking the images, the computer onboard the trailer generated a “crack map” specifying the location and shape of any cracks shown in the images.

Based on the cracks found in the image, the master controller instructed the sealant applicator valves when to fire. To fill longitudinal cracks, a single dispensing nozzle capable of continuous operation was attached to a linear servo axis. The transverse sealant distribution system consisted of 12 nozzles spaced evenly across one foot. The transverse and diagonal distribution prototype was intended to represent one module that could be replicated and joined together to service a full-width roadway lane.

In multiple road tests, the prototype system proved to be a successful proof-of-concept for the automation of crack sealing operations.

Before a full-scale system can be successfully implemented by transportation departments, several issues must be addressed, according to Holmes. First, the crack detection algorithm will need to be improved. The researchers tested their crack detection algorithm on more than 100,000 images they collected of cracks on state roads and found the program correctly identified more than 83 percent of the cracks.

“Our crack detection algorithm was limited because we used a vision-based system, which was confounded by regions of high contrast caused by features other than pavement cracks, including dark stains in the pavement, lane stripes, raised-pavement markers, crack sealant and debris,” said Holmes. “A full-scale system may require a fusion of multiple imaging sensors, such as a 3-D laser scanning system.”

Holmes also suggested changes will be necessary in the way the sealant was supplied to the longitudinal and transverse distribution systems before a full-scale system can be realized.

David Jared, acting chief of research & development at the Georgia Department of Transportation Office of Materials and Research, and GTRI principal research engineers Wayne Daley and Wiley Holcombe, research scientist Colin Usher, and research engineers Sergio Grullon and Steven Robertson also worked on this project.

Romeo and Juliet generating solar power???

2012-06-21T21:54:00.002+05:30

BY JARED SAGOFF

Drawn together by the force of nature, but pulled apart by the force of man – it sounds like the setting for a love story, but it is also a basic description of how scientists have begun to make more efficient organic solar cells.

At the atomic level, organic solar cells function like the feuding families inRomeo and Juliet. There’s a strong natural attraction between the positive and negative charges that a photon generates after it strikes the cell, but in order to capture the energy, these charges need to be kept separate.

When these charges are still bound together, they are known to scientists as an exciton. “The real question that this work tries to answer is how to design a material that will make splitting the exciton require less energy,” said senior chemist Lin Chen of the U.S. Department of Energy’s (DOE) Argonne National Laboratory.

Improvements in the efficiencies of organic solar cells will eventually
make them competitive with traditional silicon-based solar cells and,
hopefully, ultimately with fossil fuels.

Excitons can be thought of as a sort of “quasiparticle,” Chen said, because they exhibit certain unique behaviors. When the two charged regions of the exciton – the electron and a region known as a “hole” – are close together, they are difficult to pry apart.

When energy is added to the system, however, the charges begin to separate, rendering the electrons and holes completely free and eventually allowing for the possibility of generating current and extracting electricity

“The closer the hole and the electron regions are inside an exciton, the more likely they are to recombine without generating electricity,” Chen said. “But if they are already ‘pre-separated,’ or polarized, the more likely they are to escape from this potential trap and become effective charge carriers.”

In the new experiment, Chen and her colleagues examined how four different molecules in the polymer layer in the middle of a solar cell generated different exciton dynamics. They discovered that more heavily polarized excitons yielded more efficient polymer-based solar cells.

“If the conventional exciton, right after it is generated, contains the hole and electron in almost the same location, these new materials are generating an exciton that is much more polarized at the beginning,” Chen said. Currently, the collaborative team is exploring new materials for high-efficiency organic solar cells based on these findings.

Organic solar cells still have a ways to go to get close to the efficiency of their inorganic, silicon-based competitors, but they remain much more attractive from a cost perspective. Further research into the electronic dynamics of organic photovoltaics is essential to improving their efficiency and thus making solar power cost-competitive with conventional energy sources, Chen said.

The work has been recently published in the Journal of the American Chemical Society.

Quantum bar magnets in a transparent salt

2012-06-21T21:32:00.000+05:30

Scientists have managed to switch on and off the magnetism of a new material using quantum mechanics, making the material a test bed for future quantum devices.

The international team of researchers led from the Laboratory for Quantum Magnetism (LQM) in Switzerland and the London Centre for Nanotechnology (LCN), found that the material, a transparent salt, did not suffer from the usual complications of other real magnets, and exploited the fact that its quantum spins – which are like tiny atomic magnets - interact according to the rules of large bar magnets.

The study is published in Science.

Anybody who has played with toy bar magnets at school will remember that opposite poles attract, lining up parallel to each other when they are placed end to end, and anti-parallel when placed adjacent to each other.

As conventional bar magnets are simply too large to reveal any quantum mechanical nature, and most materials are too complex for the spins to interact like true bar magnets, the transparent salt is the perfect material to see what’s going on at the quantum level for a dense collection of tiny bar magnets.

The team were able to image all the spins in the special salt, finding that the spins are parallel within pairs of layers, while for adjacent layer pairs, they are antiparallel, as large bar magnets placed adjacent to each other would be. The spin arrangement is called “antiferromagnetic”. In contrast, for ferromagnets such as iron, all spins are parallel.

By warming the material to only 0.4 degrees Celsius above the absolute “zero” of temperature where all classical (non-quantum) motion ceases, the team found that the spins lose their order and point in random directions, as iron does when it loses its ferromagnetism when heated to 870 Celsius, much higher than room temperature because of the strong and complex interactions between electron spins in this very common solid.

The team also found that they could achieve the same loss of order by turning on quantum mechanics with an electromagnet containing the salt. Thus, physicists now have a new toy, a collection of tiny bar magnets, which naturally assume an antiferromagnetic configuration and for which they can dial in quantum mechanics at will.

“Understanding and manipulating magnetic properties of more traditional materials such as iron have of course long been key to many familiar technologies, from electric motors to hard drives in digital computers,” said Professor Gabriel Aeppli, UCL Director of the LCN.

“While this may seem esoteric, there are deep connections between what has been achieved here and new types of computers, which also rely on the ability to tune quantum mechanics to solve hard problems, like pattern recognition in images.”

Images. Top: Bar magnets line up parallel when they are end-to-end, and antiparallel when they are adjacent to each other. Bottom: Antiferromagnetic arrangement of the spins (coloured arrows) in the magnetic salt used by the Swiss-German-US-London team.

Read More:http://www.ucl.ac.uk/news/news-articles/1206/120612-quantum-bar-magnets

Is that really just a fly? Swarms of cyborg insect drones are the future of military surveillance

2012-06-20T20:45:00.001+05:30

The kinds of drones making the headlines daily are the heavily armed CIA and U.S. Army vehicles which routinely strike targets in Pakistan - killing terrorists and innocents alike.

But the real high-tech story of surveillance drones is going on at a much smaller level, as tiny remote controlled vehicles based on insects are already likely being deployed.

Over recent years a range of miniature drones, or micro air vehicles (MAVs), based on the same physics used by flying insects, have been presented to the public.

The fear kicked off in 2007 when reports of bizarre flying objects hovering above anti-war protests sparked accusations that the U.S. government was accused of secretly developing robotic insect spies.

Fingertip: The US Air Force unveiled insect-sized spies 'as tiny as bumblebees' that could not be detected and would be able to fly into buildings

Official denials and suggestions from entomologists that they were actually dragonflies failed to quell speculation, and Tom Ehrhard, a retired Air Force colonel and expert on unmanned aerial craft, told the Daily Telegraph at the time that 'America can be pretty sneaky.'

The following year, the US Air Force unveiled insect-sized spies 'as tiny as bumblebees' that could not be detected and would be able to fly into buildings to 'photograph, record, and even attack insurgents and terrorists.'

Around the same time the Air Force also unveiled what it called 'lethal mini-drones' based on Leonardo da Vinci's blueprints for his Ornithopter flying machine, and claimed they would be ready for roll out by 2015.

That announcement was five years ago and, since the U.S. military is usually pretty cagey about its technological capabilities, it raises the question as to what it is keeping under wraps.

The University of Pennsylvania GRASP Lab recently showed off drones that swarm, a network of 20 nano quadrotors flying in synchronized formations.

The SWARMS goal is to combine swarm technology with bio-inspired drones to operate 'with little or no direct human supervision' in 'dynamic, resource-constrained, adversarial environments.'

Researchers have now developed bio-inspired drones with bug eyes, bat ears, bird wings, and even honeybee-like hairs to sense biological, chemical and nuclear weapons

However, it is most likely the future of hard-to-detect drone surveillance will mimic nature.

Research suggests that the mechanics of insects can be reverse-engineered to design midget machines to scout battlefields and search for victims trapped in rubble.

Scientists have taken their inspiration from animals which have evolved over millennia to the perfect conditions for flight.

Nano-biomimicry MAV design has long been studied by DARPA, and in 2008 the U.S. government's military research agency conducted a symposium discussing 'bugs, bots, borgs and bio-weapons.'

Researchers have now developed bio-inspired drones with bug eyes, bat ears, bird wings, and even honeybee-like hairs to sense biological, chemical and nuclear weapons.

And the U.S. isn't the only country to have poured money into spy drone miniaturisation. France has developed flapping wing bio-inspired microdrones.

The Netherlands BioMAV (Biologically Inspired A.I. for Micro Aerial Vehicles) developed a Parrot AR Drone last year - which is now available in the U.S. as a 'flying video game'.

Not so tiny but a good spy: A ShadowHawk drone with SWAT team members

Zoologist Richard Bomphrey, of Oxford University, has conducted research to generate new insight into how insect wings have evolved over the last 350 million years.

He said last year: 'Nature has solved the problem of how to design miniature flying machines.

'By learning those lessons, our findings will make it possible to aerodynamically engineer a new breed of surveillance vehicles that, because they are as small as insects and also fly like them, completely blend into their surroundings.'

The insect manoeuvrability which allows flies the ability to land precisely and fly off again at speed may one day prove a crucial tactical advantage in wars and could even save lives in disasters.

The military would like to develop tiny robots that can fly inside caves and barricaded rooms to send back real-time intelligence about the people and weapons inside.

Dr Bomphrey said: 'Scary spider robots were featured in Michael Crichton's 1980s film Runaway - but our robots will be much more scaled down and look more like the quidditch ball in the Harry Potter films, because of its ability to hover and flutter.

'The problem for scientists at the moment is that aircrafts can't hover and helicopters can't go fast. And it is impossible to make them very small.

'With insects you get a combination of both these assets in miniature. And when you consider we have been flying for just over a hundred years as opposed to 350 million years, I would say it is they who have got it right, and not us!'

Read more: http://www.dailymail.co.uk/sciencetech/article-2161647/Is-really-just-fly-Swarms-cyborg-insect-drones-future-military-surveillance.html#ixzz1yLZJX3bY

"FOLLOW THE BLOG"

2012-06-17T19:40:00.001+05:30

Making the most of it

2012-06-12T20:32:00.001+05:30

Solar cells for multiple wavelengths

Conventional solar cells generate electricity when an incoming photon excites an electron across the band gap; the energy gap between the valence and conduction bands. If the incoming photon does not have enough energy, the electron cannot bridge the gap. If the photon possesses too much energy then the electron is excited high into the conduction band, and the extra energy is lost as heat. One approach to building more efficient photovoltaics is therefore to convert more of the spectrum into useful energy in both the low and high energy regions.

One way to achieve this goal is to lay different semiconductors on top of each other, within the same device. Each semiconductor layer would be optimized for a different wavelength (energy), and so a device with enough layers could make use of the whole spectrum. Dr Nair López explained, “Current high efficiency multijunction solar cells are based on a complex technology requiring growth of a multiplicity of thin films to produce three separate p/n junctions”. This results in an expensive device.

One alternative would be to fabricate a material that had an “intermediate band” between a valence and conduction band that were widely separated in energy. It would then be possible for high energy photons to directly excite electrons into the conduction band, without losing energy as heat, while low energy photons could be utilized through a two-step process. By having just a single p/n junction, but using similar production methods to multijunction solar cells, the cost of constructing the device should be reduced.

Perhaps surprisingly such a solar cell has never been experimentally demonstrated. Until now. Researchers at Lawrence Berkeley National Laboratory have used highly mismatched alloys (HMAs) to construct of such a device [López et al., Phys Rev Lett (2011) 106, 028701]. These alloys, in this case GaNAs based materials, can provide exotic band structures thanks to the combination of the individual semiconductors.

The resulting solar cell was sensitive to a broad spectrum of energies, ranging from ~1.1 – 3.2 eV; covering the entire optical spectrum. However, there is still work to be done, as López told us, “The effort in this area is still in the R&D stage. There is a need to improve the quality of the light absorbing material and to increase the charge collection efficiency”.

Stewart Bland

Underwater solar power?

2012-06-12T20:16:00.003+05:30

Photovoltaics get submerged

Scientists at the U.S. Naval Research Laboratory, Electronics Science and Technology Division, dive into underwater photovoltaic research to develop high bandgap solar cells capable of producing sufficient power to operate electronic sensor systems at depths of 9 meters.

Underwater autonomous systems and sensor platforms are severely limited by the lack of long endurance power sources. To date, these systems must rely on on-shore power, batteries or solar power supplied by an above water platform. Attempts to use photovoltaics have had limited success, primarily due to the lack of penetrating sunlight and the use of solar cells optimized more towards the unimpeded terrestrial solar spectrum.

"The use of autonomous systems to provide situational awareness and long-term environment monitoring underwater is increasing," said Phillip Jenkins, head, NRL Imagers and Detectors Section. "Although water absorbs sunlight, the technical challenge is to develop a solar cell that can efficiently convert these underwater photons to electricity."

Even though the absolute intensity of solar radiation is lower underwater, the spectral content is narrow and thus lends itself to high conversion efficiency if the solar cell is well matched to the wavelength range. Previous attempts to operate solar cells underwater have focused on crystalline silicon solar cells and more recently, amorphous silicon cells.

High-quality gallium indium phosphide (GaInP) cells are well suited for underwater operation. GaInP cells have high quantum efficiency in wavelengths between 400 and 700 nanometers (visible light) and intrinsically low dark current, which is critical for high efficiency in lowlight conditions.

The filtered spectrum of the sun underwater is biased toward the blue/green portion of the spectrum and thus higher bandgap cells such as GaInP perform much better than conventional silicon cells, states Jenkins.

Preliminary results at a maximum depth of 9.1 meters reveal output to be 7 watts per square meter of solar cells, sufficient to demonstrate there is useful solar power to be harvested at depths commonly found in nearshore littoral zones.

The finest gold dust in the world

2012-06-11T21:59:00.000+05:30

Locating single Au atoms

Most people value large chunks of gold – but scientists at the Vienna University of Technology are interested in gold at the smallest possible scale, because single gold atoms are potentially the most reactive catalysts for chemical reactions. However, when gold atoms are placed on a surface they tend to ball up into tiny nuggets consisting of several atoms. A team of surface scientists now managed to fix single gold atoms on special sites of an iron-oxide surface. This could open the door to more efficient catalysts, requiring less of the precious material.

Gold is a noble metal and does not usually bond with other elements, but as a catalyst it facilitates chemical reactions. It can, for example, facilitate the conversion of poisonous carbon monoxide to carbon dioxide. The effectiveness of gold as a catalyst depends on the size of the gold particles. Some evidence suggests that it works best if the gold is present in the form of single atoms. So far, however, this could not be studied in detail. “If individual gold atoms are put on a surface, they usually cluster up, forming nanoparticles”, says Gareth Parkinson, who oversaw the experiments in the research group of Professor Ulrike Diebold at the Institute for Applied Physics at the TU Vienna.

Higher temperatures lead to a higher mobility of the gold atoms, so in order to stop the atoms from clustering, most surfaces must be cooled to a temperature so low that the desired chemical reactions would stop entirely. The researchers at the TU Vienna found a special kind of iron-oxide surface, which locks the single gold atoms in place.

The key to success is a slight deformation of the iron-oxide crystal structure. The oxygen atoms of the topmost layer are not aligned in perfectly straight lines, they are bent into wiggles by the atoms below. At the points where the lines of oxygen atoms are close to each other, the gold atoms attach permanently without losing grip. Even if the surface is heated, the gold atoms stay put – only at 500 degrees celsius they start forming clusters.

“When a gold atom hits the iron oxide surface, it diffuses to one of the sites where it can be attached to the surface”, says Gareth Parkinson. That way, many single gold atoms can be placed close to each other. When a gold atom hits a position already occupied by another gold atom, however, the two bond and start moving across the surface, picking up additional gold atoms along the way. When they have reached a critical size of at least five atoms, they become immobile again and the miniature gold nugget comes to rest.

Ulrike Diebold expects that the new method will answer important open questions about catalysis. “We have created an ideal model system for probing the chemical reactivity of single atomic species”, says Diebold. The recent experiments will also help to advance theoretical research: the quantum mechanically complex bonding between single atoms and this particular surfaces provide an excellent test case for theoretical calculations of highly correlated electron systems.

Plastics as strong as steel

2012-06-11T20:20:00.001+05:30

Environmentally friendly plastic that could replace metals

As landfills overflow with discarded plastics, scientists have been working to produce a biodegradable alternative that will reduce pollution. Now a Tel Aviv University researcher is giving the quest for environmentally friendly plastics an entirely new dimension — by making them tougher than ever before.

Prof. Moshe Kol of TAU's School of Chemistry is developing a super-strength polypropylene — one of the world's most commonly used plastics — that has the potential to replace steel and other materials used in everyday products. This could have a long-term impact on many industries, including car manufacturing, in which plastic parts could replace metallic car parts.

Durable plastics consume less energy during the production process, explains Prof. Kol. And there are additional benefits as well. If polypropylene car parts replaced traditional steel, cars would be lighter overall and consume less fuel, for example. And because the material is cheap, plastic could provide a much more affordable manufacturing alternative.

Although a promising field of research, biodegradable plastics have not yet been able to mimic the durability and resilience of common, non-biodegradable plastics like polypropylene. Prof. Kol believes that the answer could lie in the catalysts, the chemicals that enable their production.

Plastics consist of very long chains called polymers, made of simple building blocks assembled in a repeating pattern. Polymerization catalysts are responsible for connecting these building blocks and create a polymer chain. The better the catalyst, the more orderly and well-defined the chain — leading to a plastic with a higher melting point and greater strength and durability. This is why the catalyst is a crucial part of the plastic production process.

Prof. Kol and his team of researchers have succeeded in developing a new catalyst for the polypropylene production process, ultimately producing the strongest version of the plastic that has been created to date. "Everyone is using the same building blocks, so the key is to use different machinery," he explains. With their catalyst, the researchers have produced the most accurate or "regular" polypropylene ever made, reaching the highest melting point to date.

By 2020, the consumption of plastics is estimated to reach 200 million tons a year. Prof. Kol says that because traditional plastics aren't considered green, it's important to think creatively to develop this material, which has become a staple of daily life, with the least amount of harm to the environment. Cheaper and more efficient to produce in terms of energy consumption, as well as non-toxic, Prof. Kol's polypropylene is good news for green manufacturing and could revolutionize the industry. The durability of the plastic results in products that require less maintenance — and a much longer life for parts made from the plastic.

Beyond car parts, Prof. Kol envisions a number of uses for this and related plastics, including water pipes, which he says could ultimately conserve water use. Drinking water for the home has been traditionally carried by steel and cement pipes. These pipes are susceptible to leakage, leading to waste and therefore higher water bills. But they are also very heavy, so replacing them can be a major, expensive operation.

"Plastic pipes require far fewer raw materials, weighing ten times less than steel and a hundred times less than cement. Reduced leaking means more efficient water use and better water quality," Prof. Kol explains. The replacement of steel water pipes by those made of plastic is becoming more common, and the production of plastics with even greater strength and durability will make this transition even more environmentally-friendly.

Erbium nanowire material enhances energy technologies

2012-06-10T21:18:00.001+05:30

Superior optical properties

Arizona State University researchers have created a new compound crystal material that promises to help produce advances in a range of scientific and technological pursuits.

ASU electrical engineering professor Cun-Zheng Ning says the material, called erbium chloride silicate, can be used to develop the next generations of computers, improve the capabilities of the Internet, increase the efficiency of silicon-based photovoltaic cells to convert sunlight into electrical energy, and enhance the quality of solid-state lighting and sensor technology.

The breakthrough involves the first-ever synthesis of a new erbium compound in the form of a single-crystal nanowire, which has superior properties compared to erbium compounds in other forms.

Erbium is one of the most important members of the rare earth family in the periodic table of chemical elements. It emits photons in the wavelength range of 1.5 micrometers, which are used in the optical fibers essential to high-quality performance of the Internet and telephones.

Erbium is used in doping optical fibers to amplify the signal of the Internet and telephones in telecommunications systems. Doping is the term used to describe the process of inserting low concentrations of various elements into other substances as a way to alter the electrical or optical properties of the substances to produce desired results. The elements used in such processes are referred to as dopants.

“Since we could not dope as many erbium atoms in a fiber as we wish, fibers had to be very long to be useful for amplifying an Internet signal. This makes integrating Internet communications and computing on a chip very difficult,” Ning explains.

“With the new erbium compound, 1000 times more erbium atoms are contained in the compound. This means many devices can be integrated into a chip-scale system,” he says. “Thus the new compound materials containing erbium can be integrated with silicon to combine computing and communication functionalities on the same inexpensive silicon platform to increase the speed of computing and Internet operation at the same time.”

Erbium materials can also be used to increase the energy-conversion efficiency of silicon solar cells.

Silicon does not absorb solar radiation with wavelengths longer than 1.1 microns, which results in waste of energy – making solar cells less efficient.

Erbium materials can remedy the situation by converting two or more photons carrying small amounts of energy into one photon that is carrying a larger amount of energy. The single, more powerful photon can then be absorbed by silicon, thus increasing the efficiency of solar cells.

Erbium materials also help absorb ultraviolet light from the sun and convert it into photons carrying small amounts of energy, which can then be more efficiently converted into electricity by silicon cells. This color-conversion function of turning ultraviolet light into other visible colors of light is also important in generating white light for solid-state lighting devices.

While erbium’s importance is well-recognized, producing erbium materials of high quality has been challenging, Ning says.

The standard approach is to introduce erbium as a dopant into various host materials, such as silicon oxide, silicon, and many other crystals and glasses.

What is unique about the new erbium material synthesized by Ning’s group is that erbium is no longer randomly introduced as a dopant. Instead, erbium is part of a uniform compound and the number of erbium atoms is a factor of 1000 more than the maximum amount that can be introduced in other erbium-doped materials.

Increasing the number of erbium atoms provides more optical activity to produce stronger lighting. It also enhances the conversion of different colors of light into white light to produce higher-quality solid-state lighting and enables solar cells to more efficiently convert sunlight in electrical energy.

Like many scientific discoveries, the synthesis of this new erbium material was made somewhat by accident.

“Similar to what other researchers are doing, we were originally trying to dope erbium into silicon nanowires. But the characteristics demonstrated by the material surprised us,” he says. “We got a new material. We did not know what it was, and there was no published document that described it. It took us more than a year to finally realize we got a new single-crystal material no one else had produced.”

Ning and his team are now trying to use the new erbium compound for various applications, such as increasing silicon solar cell efficiency and making miniaturized optical amplifiers for chip-scale photonic systems for computers and high-speed Internet.

“Most importantly,” he says, “there are many things we have yet to learn about what can be achieved with use of the material. Our preliminary studies of its characteristics show it has many amazing properties and superior optical quality. More exciting discoveries are waiting to be made.”

Graphene’s shining light could lead to super-fast internet

2012-06-10T20:28:00.001+05:30

Internet connection speeds could be tens of times faster than they currently are, thanks to research by University of Manchester scientists using wonder material graphene.

Writing in the journal Nature Communications, a collaboration between the Universities of Manchester and Cambridge, which includes Nobel Prize winning scientists Professor Andre Geim and Professor Kostya Novoselov, has discovered a crucial recipe for improving characteristics of graphene devices for use as photodetectors in future high-speed optical communications.

By combining graphene with metallic nanostructures, they show a twentyfold enhancement in harvesting light by graphene, which paves the way for advances in high-speed internet and other communications.

By putting two closely-spaced metallic wires on top of graphene and shining light on this structure, researchers previously showed that this generates electric power. This simple device presents an elementary solar cell.

More importantly for applications, such graphene devices can be incredibly fast, tens and potentially hundred times faster than communication rates in the fastest internet cables, which is due to the unique nature of electrons in graphene, their high mobility and high velocity.

The major stumbling block towards practical applications for these otherwise very promising devices has so far been their low efficiency. The problem is that graphene – the thinnest material in the world – absorbs little light, approximately only 3%, with the rest going through without contributing to the electrical power.

The Manchester researchers have solved the problems by combining graphene with tiny metallic structures, specially arranged on top of graphene.

These so-called plasmonic nanostructures have dramatically enhanced the optical electric field felt by graphene and effectively concentrated light within the one-atom-thick carbon layer.

By using the plasmonic enhancement, the light-harvesting performance of graphene was boosted by twenty times, without sacrificing any of its speed. The future efficiency can be improved even further.

Dr Alexander Grigorenko, an expert in plasmonics and a leading member of the team, said: “Graphene seems a natural companion for plasmonics. We expected that plasmonic nanostructures could improve the efficiency of graphene-based devices but it has come as a pleasant surprise that the improvements can be so dramatic.”

Professor Novoselov added: “The technology of graphene production matures day-by-day, which has an immediate impact both on the type of exciting physics which we find in this material, and on the feasibility and the range of possible applications.

“Many leading electronics companies consider graphene for the next generation of devices. This work certainly boosts graphene’s chances even further.”

Professor Andrea Ferrari, from the Cambridge Engineering Department, who lead the Cambridge effort in the collaboration, said “So far, the main focus of graphene research has been on fundamental physics and electronic devices.

“These results show its great potential in the fields of photonics and optoelectronics, where the combination of its unique optical and electronic properties with plasmonic nanostructures, can be fully exploited, even in the absence of a bandgap, in a variety of useful devices, such as solar cells and photodetectors"