Sunday, November 29, 2009

How size matters for catalysts

Study links size, activity, electronic properties

SALT LAKE CITY, – University of Utah chemists demonstrated the first conclusive link between the size of catalyst particles on a solid surface, their electronic properties and their ability to speed chemical reactions. The study is a step toward the goal of designing cheaper, more efficient catalysts to increase energy production, reduce Earth-warming gases and manufacture a wide variety of goods from medicines to gasoline.

Catalysts are substances that speed chemical reactions without being consumed by the reaction. They are used to manufacture most chemicals and many industrial products. The world's economy depends on them.

Scott Anderson and Bill Kaden, University of Utah

Caption: University of Utah chemistry Professor Scott Anderson and doctoral student Bill Kaden work on the elaborate apparatus they use to produce and study catalysts, which are substances that speed chemical reactions without being consumed. The world economy depends on catalysts, and the Utah research is aimed at making cheaper, more efficient catalysts, which could improve energy production and reduce emissions of Earth-warming gases.

Credit: William Kunkel, University of Utah. Usage Restrictions: None.
"One of the big uncertainties in catalysis is that no one really understands what size particles of the catalyst actually make a chemical reaction happen," says Scott Anderson, a University of Utah chemistry professor and senior author of the study in the Friday, Nov. 6 issue of the journal Science. "If we could understand what factors control activity in catalysts, then we could make better and less expensive catalysts."

"Most catalysts are expensive noble metals like gold or palladium or platinum," he adds. "Say in a gold catalyst, most of the metal is in the form of large particles, but those large particles are inactive and only nanoparticles with about 10 atoms are active. That means more than 90 percent of gold in the catalyst isn't doing anything. If you could make a catalyst with only the right size particles, you could save 90 percent of the cost or more."
In addition, "there's a huge amount of interest in learning how to make catalysts out of much less expensive base metals like copper, nickel and zinc," Anderson says. "And the way you are going to do that is by 'tuning' their chemical properties, which means tuning the electronic properties because the electrons control the chemistry."

The idea is to "take a metal that is not catalytically active and, when you reduce it to the appropriate size [particles], it can become catalytic," Anderson says. "That's the focus of our work – to try to identify and understand what sizes of metal particles are active as catalysts and why they are active as catalysts."

In the new study, Anderson and his students took a step toward "tuning" catalysts to have desired properties by demonstrating, for the first time, that the size of metal catalyst "nanoparticles" deposited on a surface affects not only the catalyst's level of activity, but the particles' electronic properties.

Anderson conducted the study with chemistry doctoral students Bill Kaden and William Kunkel, and with former doctoral student Tianpin Wu. Kaden was first author.

The Economy Depends on Catalysts

"Catalysts are a huge part of the economy," Anderson says. "Catalysts are used for practically every industrial process, from making gasoline and polymers to pollution remediation and rocket thrusters."

Catalysts are used in 90 percent of U.S. chemical manufacturing processes and to make more than 20 percent of all industrial products, and those processes consume large amounts of energy, according to the U.S. Department of Energy (DOE).

In addition, industry produces 21 percent of U.S. Earth-warming carbon dioxide emissions – including 3 percent by the chemical industry, DOE says.

Thus, improving the efficiency of catalysts is "the key to both energy savings and carbon dioxide emissions reductions," the agency says.

Catalysts also are used in drug manufacturing; food processing; fuel cells; fertilizer production; conversion of natural gas, coal or biomass into liquid fuels; and systems to reduce pollutants and improve the efficiency of combustion in energy production.

The North American Catalysis Society says catalysts contribute 35 percent or more of global Gross Domestic Product. "The biggest part of this contribution comes from generation of high energy fuels (gasoline, diesel, hydrogen), which depend critically on the use of small amounts of catalysts in … petroleum refineries," the group says.

"The development of inexpensive catalysts … is pivotal to energy capture, conversion and storage," says Henry White, professor and chair of chemistry at the University of Utah. "This research is vital to the energy security of the nation."

Catalyst Research: What Previous Studies and the New Study Showed

Many important catalysts – such as those in catalytic converters that reduce motor vehicle emissions – are made of metal particles that range in size from microns (millionths of a meter) down to nanometers (billionths of a meter).

As the size of a catalyst metal particle is reduced into the nanoscale, its properties initially remain the same as a larger particle, Anderson says. But when the size is smaller than about 10 nanometers – containing about 10,000 atoms of catalyst – the movements of electrons in the metal are confined, so their inherent energies are increased.

When there are fewer than about 100 atoms in catalyst particles, the size variations also result in fluctuations in the electronic structure of the catalyst atoms. Those fluctuations strongly affect the particles' ability to act as a catalyst, Anderson says.

Previous experiments documented that electronic and chemical properties of a catalyst are affected by the size of catalyst particles floating in a gas. But those isolated catalyst particles are quite different than catalysts that are mounted on a metal oxide surface – the way the catalyst metal is supported in real industrial catalysts.

Past experiments with catalysts mounted on a surface often included a wide variety of particle sizes. So those experiments failed to detect how the catalyst's chemical activity and electronic properties vary depending with the size of individual particles.

Anderson was the first American chemist to sort metal catalyst particles by size and demonstrate how their reactivity changes with size. In previous work, he studied gold catalyst particles deposited on titanium dioxide.

The new study used palladium particles of specific sizes that were deposited on titanium dioxide and used to convert carbon monoxide into carbon dioxide.

The study not only showed how catalytic activity varies with catalyst particle size, "but we have been able to correlate that size dependence with observed electronic differences in the catalyst particles," Kaden says. "People had speculated this should be happening, but no one has ever seen it."

Anderson says it is the first demonstration of a strong correlation between the size and activity of a catalyst on a metal surface and electronic properties of the catalyst.

How the Study was Conducted

Using an elaborate apparatus in Anderson's laboratory, the chemists aimed a laser beam to vaporize palladium, creating electrically charged, palladium nanoparticles in a vapor carried by a stream of helium gas.

Electromagnetic fields are used to capture the particles and send them through a mass spectrometer, which selects only the sizes of palladium particles Anderson and colleagues want to study. The desired particles then are deposited on a single crystal of titanium oxide that measures less than a half-inch on a side.

Next, the chemists use various methods to characterize the sample of palladium catalyst particles: specifically the palladium catalyst's electronic properties, physical shape and chemical activity. ###

University of Utah Public Relations 201 Presidents Circle, Room 308 Salt Lake City, Utah 84112-9017 (801) 581-6773 fax: (801) 585-3350 www.unews.utah.edu

Saturday, November 28, 2009

Tiny injector to speed development of new, safer, cheaper drugs

It's no bigger than a stamp packet but it has the potential to allow rapid development of a new generation of drugs and genetic engineering organisms, and to better control in-vitro fertilization.

Engineering researchers at McMaster University have fabricated a palm-sized, automated, micro-injector that can insert proteins, DNA and other biomolecules into individual cells at volumes exponentially higher than current procedures, and at a fraction of the cost. This will allow scientists to vastly increase preclinical trials for drug development and genetic engineering, and provide greater control of the process.

Micro-injection of Zebrafish Embryos

Caption: (a) Zebrafish embryo immobilized by suction capillary. (b) Needle inserted into yolk sack. (c) Electroosmotic pumping of methylene blue solution into the embryo by the application of 25 V for 10 s. (d) Needle retracted from the embryo.

Credit: McMaster Engineering. Usage Restrictions: Email genen@mcmaster.ca for permission to publish.

Microinjection Device

Caption: This photo shows a microinjection device loaded into a fixture which immobilizes the left substrate and ensures planar and linear motion of the movable substrate.

Credit: McMaster Engineering. Usage Restrictions: Please email genen@mcmaster.ca for permission to publish photos.
In a paper published in the current issue of Lab on a Chip journal, researchers describe the construction and operation of a microfluidic micro-injector, which achieved an almost 80 per cent success rate in injecting Zebrafish embryos.

"This device is to drug discovery what the assembly line was to the automobile or the silicon chip to information technology," explains Ravi Selvaganapathy, assistant professor of mechanical engineering at McMaster and lead author of the research. "It turns what was a complex, resource-intensive process available to a few into an automated, predictable, reliable, and low-cost system accessible to almost anyone."

The micro-injector has a cell-wide channel cast on a silicon chip that guides cells and embryos to the injection site. A similar channel guides the injection reagent to a needle as thin as 10 micrometers (one-tenth the diameter of a human hair). The researchers have developed a buckling method to drive the needle through a cell's pliable outer membrane accurately and to the proper depth. The injection dosage is controlled electrically, as is monitoring of the needle's position. The researchers have also developed methods to sharpen the needle, ensuring minimal injection damage or interference to the cell.

Notably absent is the need for a microscope or optical magnification to conduct the process, which is required for manual injection and to monitor transfection methods. The microfluidic device also allows easy integration of post-processing operations including cell sorting and the testing of cell viability on the same chip.
"Almost every researcher would be able to have this device at their disposal in their own labs," said Selvaganapathy. "The micro-injectors can easily be run in parallel and allow for scientists to test far greater combinations of materials in a much shorter time than current processes. It also makes it more feasible to pursue drug discovery for many so-called neglected diseases."

The micro-injector also holds great promise for in-vitro fertilization as it provides far greater accuracy and control than current manual injections procedures, which have high rates of failure, require trained expertise and can be time intensive.

The micro-injector has achieved numerous firsts for cell transfection procedures:

* Buckling based actuation of injection needle providing low cost but precise actuation with uniform injection depth and consistent alignment;
* Injection format that could allow needles as small as 100 nanometres, half the size of current injectors, virtually eliminating cell damage and interference with cell functions;
* Electro-osmotic injection which provides electrical control of reagent injected into cell for accurate and uniform dosage;
* Elimination of expensive optical magnification needed for manual injection or to monitor quality control.

###

Contact: Gene Nakonechny genen@mcmaster.ca 905-525-9140 x26781 McMaster University

Thursday, November 26, 2009

UD wins $4.4 million to develop next-generation magnets

The University of Delaware has won a $4.4 million grant from the U.S. Department of Energy's Advanced Research Projects Agency (ARPA-E) to lead a multidisciplinary, multi-institutional research project to develop the next generation of high-performance permanent magnets.

Stronger magnets are essential for increasing the energy efficiency of electronics, automobiles, information technology, and communications systems in the 21st-century, and for supporting the development of hybrid/electric vehicles, wind turbines, environmentally friendly transportation systems, and new energy storage systems, among other applications.

Nanocomposite Magnets Schematic

Caption: This is a schematic representation of the bottom-up assembly concept to develop high-energy nanocomposite materials for next-generation magnets.

Credit: Courtesy, George Hadjipanayis, University of Delaware. Usage Restrictions: Must include credit to University of Delaware.

George Hadjipanayis, University of Delaware

Caption: George Hadjipanayis, the Richard B. Murray Professor of Physics and chairperson of the Department of Physics and Astronomy at the University of Delaware, is the principal investigator on a $4.4 million grant from the US Department of Energy's Advanced Research Projects Agency to develop the next generation of high-performance permanent magnets.

Credit: University of Delaware. Usage Restrictions: Credit to University of Delaware must be included.
The UD project is one of 37 selected nationwide by the agency, collectively totaling $151 million, which "have great potential to revolutionize the U.S. energy sector," according to Shane Kosinski, ARPA-E's acting deputy director. They represent the first round of projects funded under ARPA-E, which is receiving $400 million to deploy under the American Recovery and Reinvestment Act.

George Hadjipanayis, the Richard B. Murray Professor of Physics and chairperson of the Department of Physics and Astronomy at the University of Delaware, is the principal investigator on the project. He will coordinate a team of chemists, material scientists, physicists, and engineers from the University of Delaware, University of Nebraska, Northeastern University, and Virginia Commonwealth University; the U.S. Department of Energy's Ames Laboratory at Iowa State University, in Ames, Iowa; and the Electron Energy Corporation in Landisville, Pa.

According to Hadjipanayis, the strongest permanent magnets today are made from an alloy of three elements: neodymium (Nd), iron (Fe), and boron (B). Hadjipanayis was one of the three researchers who discovered the Nd-Fe-B magnets in the early 1980s.

In the new project, he and his team will be working to identify new materials that will result in magnets twice as strong as those currently in existence.

"This is the first time that such a large concerted effort will be undertaken in the U.S. on the development of high-energy magnets that involves the best expertise available in our country on this type of materials," Hadjipanayis said.

An article in the Sept. 11, 2009, edition of the journal Science reported that the demand for Nd-Fe-B magnets is growing at about 15 percent per year, for use in products ranging from magnetic resonance imaging machines, to cell phones, headphones, and even prototype magnetic refrigerators. Yet neodymium (Nd), which is a member of the rare earth metals on the periodic table of the elements, is growing increasingly scarce.
The UD-led team will explore three different routes over the three-year project, Hadjipanayis said. The first route will be to discover new materials in tertiary rare earth-transition metal-element X systems that have not yet been explored due to synthesis difficulties such as vapor pressure, high reactivity, toxicity, or their refractory nature. The second route will be to develop materials that are free of rare earth metals and stabilized by the addition of small non-magnetic atoms (Fe-Co-X); and the third route will be to use the bottom-up approach to develop high-energy nanocomposite materials consisting of a uniform and nanoscale mixture of high anisotropy hard (Nd-Fe-B) and high magnetization soft (Fe) magnetic phases.

"We hope our efforts will provide the fundamental innovations and breakthroughs which could have a major impact in re-establishing the United States as a leader in the science, technology, and commercialization of this very important class of materials," Hadjipanayis said.

More than 3,600 concept papers were received in response to the first ARPA-E solicitation, from which the U.S. Department of Energy requested 300 full applications and ultimately selected 37 based on rigorous review and evaluation. ###

Funding for the projects is provided through the American Recovery and Reinvestment Act (ARRA), also known as the federal stimulus package, which was enacted by Congress earlier this year.

The listing of UD's federal stimulus-funded projects is available online on UD's Stimulus Working Group Web site (http://www.udel.edu/recovery/), which is updated every two weeks.

Contact: Tracey Bryant tbryant@udel.edu 302-831-8185 University of Delaware

Tuesday, November 24, 2009

Breakthrough in industrial-scale nanotube processing

Rice pioneers method for processing carbon nanotubes in bulk fluids.

HOUSTON -- (Nov. 2009) -- Rice University scientists today unveiled a method for the industrial-scale processing of pure carbon-nanotube fibers that could lead to revolutionary advances in materials science, power distribution and nanoelectronics. The result of a nine-year program, the method builds upon tried-and-true processes that chemical firms have used for decades to produce plastics. The research is available online in the journal Nature Nanotechnology.

"Plastics is a $300 billion U.S. industry because of the massive throughput that's possible with fluid processing," said Rice's Matteo Pasquali, a paper co-author and professor in chemical and biomolecular engineering and in chemistry. "The reason grocery stores use plastic bags instead of paper and the reason polyester shirts are cheaper than cotton is that polymers can be melted or dissolved and processed as fluids by the train-car load. Processing nanotubes as fluids opens up all of the fluid-processing technology that has been developed for polymers."

SWNT Liquid Crystal

Caption: The liquid-crystaline phase of carbon nanotubes dissolved in chlorosulfonic acid.

Credit: Matteo Pasquali/Rice University. Usage Restrictions: Must credit:
The report was co-authored by an 18-member team of scientists from Rice's Richard E. Smalley Institute for Nanoscale Science and Technology, the University of Pennsylvania and the Technion-Israel Institute of Technology. Co-authors include Smalley Institute namesake Rick Smalley, the late Nobel laureate chemist who developed the first high-throughput method for producing high-quality carbon nanotubes, as well as Virginia Davis, a former doctoral student of Pasquali's and Smalley's who is now a professor at Auburn University, and Micah Green, a former postdoctoral researcher of Pasquali's who is now a professor at Texas Tech University.
The new process builds upon the 2003 Rice discovery of a way to dissolve large amounts of pure nanotubes in strong acidic solvents like sulfuric acid. The research team subsequently found that nanotubes in these solutions aligned themselves, like spaghetti in a package, to form liquid crystals that could be spun into monofilament fibers about the size of a human hair.

"That research established an industrially relevant process for nanotubes that was analogous to the methods used to create Kevlar from rodlike polymers, except for the acid not being a true solvent," said Wade Adams, director of the Smalley Institute and co-author of the new paper. "The current research shows that we have a true solvent for nanotubes -- chlorosulfonic acid -- which is what we set out to find when we started this project nine years ago."

Following the 2003 breakthrough with acid solvents, the team methodically studied how nanotubes behaved in different types and concentrations of acids. By comparing and contrasting the behavior of nanotubes in acids with the literature on polymers and rodlike colloids, the team developed both the theoretical and practical tools that chemical firms will need to process nanotubes in bulk.

"Ishi Talmon and his colleagues at Technion did the critical work required to help get direct proof that nanotubes were dissolving spontaneously in chlorosulfonic acid," Pasquali said. "To do this, they had to develop new experimental techniques for direct imaging of vitrified fast-frozen acid solutions."

Talmon said, "This was a very difficult study. Matteo's team not only had to pioneer new experimental techniques to achieve this, they also had to make significant extensions to the classical theories that were used to describe solutions of rods. The Technion team had to develop a new methodology to enable us to produce high-resolution images of the nanotubes dispersed in chlorosulfonic acid, a very corrosive fluid, by state-of-the-art electron microscopy at cryogenic temperatures."

Co-author Nicholas Parra-Vasquez, a Rice graduate student advised by Pasquali who is now working in France, said, "In looking at the project when I started, I had no idea where it was going to end up and how much work needed to be done. The project encompassed many students and professors, as well as collaborations with other schools. Because of this, it was a slow process but one that left no avenue unchecked. Looking on it now, I can't believe how big it became -- how much effort was put into every point found."

Few technological breakthroughs have been hyped as much as carbon nanotubes. Since their discovery in 1991, nanotubes have been touted as everything from a cure for cancer to a solution for the world's energy crisis. The hype is all the more remarkable given that nanotubes are notoriously difficult to work with and that chemists worldwide struggled for years even to make them.

So why the hype? Put simply, carbon nanotubes are remarkable. While they are roughly the same size and shape as some rodlike polymer molecules, nanotubes can conduct electricity as well as copper, and they can be either metals or semiconductors. They can be tagged with antibodies to diagnose diseases or heated with radio waves to destroy cancer. They've been used to make transistors far smaller than those in today's finest microchips. Nanotubes also weigh about one-sixth as much as steel but can be up to 100 times stronger.

"Kevlar, the polymer fiber used in bulletproof vests, is about five to 10 times stronger than our strongest nanotube fibers today, but in principle we should be able to make our fibers about 100 times stronger," Pasquali said. "If we can realize even 20 percent of our potential, we will have a great material, perhaps the strongest ever known.

"The electrical conductivity is already pretty good," he said. "It's about the same of the best-conducting carbon-carbon fibers, and that could be improved 200 times if better production methods for metallic nanotubes can be found."

The new research appears just as the Smalley Institute prepares for a 10th anniversary celebration Nov. 5 of the creation of Smalley's "HiPco" reactor, the first system capable of producing high-quality nanotubes in bulk. HiPco, short for high-pressure carbon monoxide process, broke the logjam on nanotube production and cleared the way for more scientific study and for industry to begin using them in some materials. Industrial nanotube reactors today generate several tons of low-quality carbon nanotubes per year, and the worldwide market for nanotubes is expected to top $2 billion annually within the next decade.

But a final breakthrough remains before the true potential of high-quality carbon nanotubes can be realized. That's because HiPco and all other methods of making high-end, "single-walled" nanotubes generate a hodgepodge of nanotubes with different diameters, lengths and molecular structures. Scientists worldwide are scrambling to find a process that will generate just one kind of nanotube in bulk, like the best-conducting metallic varieties, for instance.

"One good thing about the process that we have right now is that if anybody could give us one gram of pure metallic nanotubes, we could give them one gram of fiber within a few days," Pasquali said. ###

The research was funded by the Office of Naval Research, the Air Force Office of Scientific Research, the Air Force Research Laboratory, the National Science Foundation, the USA-Israel Binational Science Foundation and the Welch Foundation. The other co-authors are the Smalley Institute's Pradeep Rai, Natnael Behabtu, Valentin Prieto, Richard Booker, Hua Fan and Robert Hauge; the University of Pennsylvania's Wei Zhou and John Fischer; and the Technion-Israel Institute of Technology's Judith Schmidt, Ellina Kesselman and Yachin Cohen.

Contact: Jade Boyd jadeboyd@rice.edu 713-348-6778 Rice University

Monday, November 23, 2009

3-D system based on optical fiber could provide new options for photovoltaics

Hidden solar cells. Converting sunlight to electricity might no longer mean large panels of photovoltaic cells atop flat surfaces like roofs.

Using zinc oxide nanostructures grown on optical fibers and coated with dye-sensitized solar cell materials, researchers at the Georgia Institute of Technology have developed a new type of three-dimensional photovoltaic system. The approach could allow PV systems to be hidden from view and located away from traditional locations such as rooftops.

"Using this technology, we can make photovoltaic generators that are foldable, concealed and mobile," said Zhong Lin Wang, a Regents professor in the Georgia Tech School of Materials Science and Engineering. "Optical fiber could conduct sunlight into a building's walls where the nanostructures would convert it to electricity. This is truly a three dimensional solar cell."

Zhong Lin Wang with 3-D Solar Cell

Caption: Georgia Tech Regents professor Zhong Lin Wang holds a prototype three-dimensional solar cell that could allow PV systems to be located away from rooftops.

Credit: Georgia Tech Photo: Gary Meek. Usage Restrictions: None.

Closeup of Solar Cell Based on Optical Fiber

Caption: This close-up shows the brown light-absorbing material for the three-dimensional solar cell grown on optical fiber by researchers at the Georgia Institute of Technology.

Credit: Georgia Tech Photo: Gary Meek. Usage Restrictions: None.

3-D Solar Cells Based on Optical Fiber

Caption: Georgia Tech researchers Yaguang Wei, Zhong Lin Wang and Benjamin Weintraub (left-right) examine a prototype of their three-dimensional solar cell based on optical fiber.

Credit: Georgia Tech Photo: Gary Meek. Usage Restrictions: None.
Details of the research were published in the early view of the journal Angewandte Chemie International on October 22. The work was sponsored by the Defense Advanced Research Projects Agency (DARPA), the KAUST Global Research Partnership and the National Science Foundation (NSF).

Dye-sensitized solar cells use a photochemical system to generate electricity. They are inexpensive to manufacture, flexible and mechanically robust, but their tradeoff for lower cost is conversion efficiency lower than that of silicon-based cells. But using nanostructure arrays to increase the surface area available to convert light could help reduce the efficiency disadvantage, while giving architects and designers new options for incorporating PV into buildings, vehicles and even military equipment.

Fabrication of the new Georgia Tech PV system begins with optical fiber of the type used by the telecommunications industry to transport data. First, the researchers remove the cladding layer, then apply a conductive coating to the surface of the fiber before seeding the surface with zinc oxide. Next, they use established solution-based techniques to grow aligned zinc oxide nanowires around the fiber much like the bristles of a bottle brush. The nanowires are then coated with the dye-sensitized materials that convert light to electricity.

Sunlight entering the optical fiber passes into the nanowires, where it interacts with the dye molecules to produce electrical current. A liquid electrolyte between the nanowires collects the electrical charges. The result is a hybrid nanowire/optical fiber system that can be up to six times as efficient as planar zinc oxide cells with the same surface area.

"In each reflection within the fiber, the light has the opportunity to interact with the nanostructures that are coated with the dye molecules," Wang explained. "You have multiple light reflections within the fiber, and multiple reflections within the nanostructures. These interactions increase the likelihood that the light will interact with the dye molecules, and that increases the efficiency."

Wang and his research team have reached an efficiency of 3.3 percent and hope to reach 7 to 8 percent after surface modification. While lower than silicon solar cells, this efficiency would be useful for practical energy harvesting. If they can do that, the potentially lower cost of their approach could make it attractive for many applications.

By providing a larger area for gathering light, the technique would maximize the amount of energy produced from strong sunlight, as well as generate respectable power levels even in weak light. The amount of light entering the optical fiber could be increased by using lenses to focus the incoming light, and the fiber-based solar cell has a very high saturation intensity, Wang said.

Wang believes this new structure will offer architects and product designers an alternative PV format for incorporating into other applications.
"This will really provide some new options for photovoltaic systems," Wang said. "We could eliminate the aesthetic issues of PV arrays on building. We can also envision PV systems for providing energy to parked vehicles, and for charging mobile military equipment where traditional arrays aren't practical or you wouldn't want to use them."

Wang and his research team, which includes Benjamin Weintraub and Yaguang Wei, have produced generators on optical fiber up to 20 centimeters in length. "The longer the better," said Wang, "because longer the light can travel along the fiber, the more bounces it will make and more it will be absorbed."

Traditional quartz optical fiber has been used so far, but Wang would like to use less expensive polymer fiber to reduce the cost. He is also considering other improvements, such as a better method for collecting the charges and a titanium oxide surface coating that could further boost efficiency.

Though it could be used for large PV systems, Wang doesn't expect his solar cells to replace silicon devices any time soon. But he does believe they will broaden the potential applications for photovoltaic energy.

"This is a different way to gather power from the sun," Wang said. "To meet our energy needs, we need all the approaches we can get." ###

Contact: John Toon jtoon@gatech.edu 404-894-6986 Georgia Institute of Technology Research News

Sunday, November 22, 2009

An exquisite container VIDEO

A gold nanocage covered with a polymer is a smart drug delivery system

In campy old movies, Lucretia Borgia swans around emptying powder from her ring into wine glasses carelessly left unattended. The poison ring is usually a confection of gold filigree holding a cabochon or faceted gemstone that can be broken to empty the ring's contents. It is invariably enormous — so large it is rather odd nobody seems to notice it.

Lucretia would have given her eyeteeth for the "smart capsule" devised in Younan Xia's laboratory at Washington University in St. Louis. A tiny cage of gold covered with a smart polymer, it responds to light, opening to empty its contents, and resealing when the light is turned off.



Caption: Lycurgus, King of the Edoni in Thrace, is ensnared by the nymph Ambrosia in the form of a vine. The famous Roman cup looks green when lit from outside but glows pink when lit from inside. Gold nanocages made at Washington University exploit the same physical effect that underlies the cup's color change. For high-resolution images of the cup please go to the British Museum site: http://www.britishmuseum.org/explore/highlights/highlight_objects/pe_mla/t/the_lycurgus_cup.aspx

Credit: The British Museum. Usage Restrictions: Please see British Museum site for usage restrictions

How to Make a Nanocage

Caption: Start with a silver (grey) nanocube with clipped corners. Dunk the cube in chloroauric acid (HAuCl4). Because gold (yellow) has greater affinity for electrons than does silver, the gold ions will pull electrons from the silver and precipitate on the silver cube. As this process continues, the silver cube is eroded from within, the silver ions leaving through pores that open in the clipped corners of the cube. As the gold skin approaches the desired thickness, the triangular corners become squared-off holes, a slightly more favorable configuration energetically.

Credit: Younan Xia, Washington University in St. Louis. Usage Restrictions: None.

How to Make a Smart Capsule

Caption: Attach a smart polymer to your gold nanocage, seen here in cross section with the pores at the corners. To load the cages, shake them in a solution of the drug at a temperature above the polymer's critical temperature. Let the cages cool, so that the polymer chains stand up like brushes, sealing the cage's pores. To release the drug, expose the cages to laser light (the lightning bolt) at their resonant frequency, heating them just enough to drive the polymer over its critical temperature. The polymer chains will collapse, opening the pores, and releasing the drug. The cage can be resealed simply by turning off the light.

Credit: Younan Xia, Washington University in St. Louis. Usage Restrictions: None.
Infinitely more cunning and discreet than Lucretia's ring, the nanocage is too small to be seen — except indirectly: billions change the color of liquid in a test tube.

No Lucretia, Xia is a healer rather than a poisoner. The smart nanocage is designed to be filled with a medicinal substance, such as a chemotherapy drug or bactericide. Releasing carefully titrated amounts of a drug only near the tissue that is the drug's intended target, this delivery system will maximize the drug's beneficial effects while minimizing its side effects.

The method for making the capsules and tests of their performance appeared online on Nov. 1, 2009, as part of the advance online publications program of the journal Nature Materials.

The first step in making a smart capsule is to mix up a batch of silver nanocubes. Tiny single-crystal cubes of silver can be made by adding silver nitrate (AgNO3) to a solution that donates electrons to the silver ions, allowing them to precipitate as solid silver. The addition of another chemical encourages the silver atoms to deposit on some parts of a seed crystal rather than others, coaxing the seeds to form sharp-edged cubes rather than misshapen lumps.

A second step clips all eight corners off the cubes.

The clipped silver cubes then serve as "sacrificial templates," on which the gold cages take shape. When the silver nanocubes are heated in cloroauric acid (HAuCl4), the gold ions in the acid steal electrons from the silver atoms in the cubes. The silver dissolves and the gold precipitates.

A gold skin forms on the silver cubes as the cubes are hollowed out from within. The silver atoms enter solution through pores that form in the clipped corners of the cubes.

"But the really cool part," says Xia, "and the cool part of nanotechnology generally, is that the tiny gold cages have very different properties than bulk gold." In particular, they respond differently to light.

The physicist Michael Faraday was the first to realize that a suspension of gold particles glowed ruby-red because the particles were extremely small. "His original sample of a gold colloid is still in the Faraday Museum in London," says Xia, Ph.D., the James M. McKelvey Professor in the Department of Biomedical Engineering. "Isn't that amazing? It's over 150 years later and it's still there."

The color is caused by a physical effect called surface plasmon resonance. Some of the electrons in the gold particles are not anchored to individual atoms but instead form a free-floating electron gas. Light falling on these electrons can drive them to oscillate as one. This collective oscillation, the surface plasmon, picks a particular wavelength, or color, out of the incident light, and this is the color we see.

The strong response at a particular wavelength, called resonance, is what makes a violin string vibrate at a particular pitch or lets a kid pump a swing high in the sky by kicking at just the right moment.

What's more, the surface plasmon resonance is tunable in much the same sense that a violin is tunable.

"Faraday used solid particles to make his colloid," comments Xia. "You can tune the resonant wavelength by changing the particles' size, but only within narrow limits. You can't get to the wavelengths we want."

The wavelengths he wants are the ones at which human tissue is relatively transparent, so that cages in the bloodstream can be opened by laser light shone on the skin.

The color of nanocages can be tuned over a wider range than solid particles by altering the thickness of the cages' walls, says Xia.
As more gold is deposited and the shells thicken, a suspension of nanocages shifts from red, to purple, to bright blue, to dark blue, to the wavelengths in the near-infrared.

Xia's team wants to hit a narrow window of tissue transparency that lies between 750 and 900 nanometers, in the near-infrared. This window is bordered on one side by wavelengths strongly absorbed by blood and on the other by those strongly absorbed by water.

Light in this sweet spot can penetrate as deep as several inches in the body.

"People used to do a demonstration at talks," Xia says, laughing. "They'd put a red diode laser in their mouths, and the audience could see it from outside, because the diode's wavelength is 780 nanometers, a wavelength at which flesh is pretty transparent."

Here things get even trickier and yet more amazing. The resonance actually has two parts. At the resonant frequency, light can be scattered off the cages, absorbed by them, or a combination of these two processes.

Just as they can tune the surface plasmon resonance, the scientists can adjust how much energy is absorbed rather than scattered by manipulating the size and porosity of the nanocages.

Xia illustrates the difference between scattering and absorption with a marvelous Roman artifact, the 4th-century Lycurgus Cup. The cup looks jade-green from the outside but turns pink when lit from the inside.

Modern analysis shows the ancient glass contains nanoparticles of a silver-gold alloy that scatters light strongly at a wavelength in the green part of the spectrum. When the cup is lit from inside, however, the green light is absorbed, and we see the remaining light, which is predominantly red, the complementary color to green.

It's actually the absorption component that the scientists exploit to open and close the nanocages. When the light is absorbed it is converted to heat, and the nanocages are covered with a special polymer that responds to heat in an interesting way.

The polymer, poly(N-isopropylacrylamide), and its derivatives has what's called a critical temperature. When it reaches this temperature it undergoes a transformation called a phase change.

If the temperature is lower than the critical temperature, the polymer chains are water-loving and stand out from the cage like brushes. The brushes seal the cage's pores and prevent its cargo from leaking out. If the temperature is above the critical temperature, on the other hand, the polymer chains shun water, shrink together and collapse. As they shrink, the pores of the cage open, and its contents flood out.

"It's a bit counter-intuitive," says Xia. "Typically when you go to higher temperature, a molecule will expand, but this one does the opposite."

Like everything else about this system, the polymer is tunable. The scientists can control its critical temperature by altering its composition. For medical applications, they tune the critical temperature to one right above body temperature (37 degrees Celsius) but well below 42 degrees Celsius (107 degree Fahrenheit), the temperature at which heat would begin to kill cells.

Next comes the fun part. Once they had made their smart capsules, the scientists tested them by loading them with a bright red dye called alazarin crimson, or rose madder. The dye made it easy to detect and measure any release with a spectrometer.

The cages were loaded by shaking them in a solution of the dye at a temperature above the critical temperature of the smart polymer. Next, they were dunked in an ice bath to trigger the polymer to close the pores and trap the dye inside the cages. The cages were then opened again by bathing them in the light of a near-infrared laser. Absorbed light warmed the gold cages above the critical temperature and provoked the polymer's phase change. The polymer collapsed, the cages' pores were exposed, and dye spilled out.

Next the team loaded capsules with doxorubicin, a common chemotherapy drug and, triggering the drug's release with a laser, killed breast cancer cells growing in wells on a plastic plate.

And finally, they loaded the capsules with an enzyme that snips open the cell walls of bacteria and used them to kill a bacterium that is a normal part of the flora of our mouths and throats.

Lucretia, eat your heart out. ###

Contact: Diana Lutz dlutz@wustl.edu 314-935-5272 Washington University in St. Louis

Friday, November 20, 2009

Pittsburgh Pitt-led researchers create nanoparticle coating to prevent freezing rain buildup VIDEO

Inspired by water-resistant lotus leaves, the Pitt-developed solution repels freezing rain and provides the first evidence of anti-icing ability in superhydrophobic coatings, team reports in Langmuir

PITTSBURGH—Preventing the havoc wrought when freezing rain collects on roads, power lines, and aircrafts could be only a few nanometers away. A University of Pittsburgh-led team demonstrates in the Nov. 3 edition of Langmuir a nanoparticle-based coating developed in the lab of Di Gao, a chemical and petroleum engineering professor in Pitt's Swanson School of Engineering, that thwarts the buildup of ice on solid surfaces and can be easily applied.


The paper, by lead author and Pitt doctoral student Liangliang Cao, presents the first evidence of anti-icing properties for a burgeoning class of water repellants—including the Pitt coating—known as superhydrophobic coatings. These thin films mimic the rutted surface of lotus leaves by creating microscopic ridges that reduce the surface area to which water can adhere. But the authors note that because ice behaves differently than water, the ability to repulse water cannot be readily applied to ice inhibition. Cao's coauthors include Gao, Jianzhong Wu, a chemical engineering professor at the University of California at Riverside, and Andrew Jones and Vinod Sikka of Ross Technology Corporation of Leola, Pa.

The team found that superhydrophobic coatings must be specifically formulated to ward off ice buildup. Gao and his team created different batches made of a silicone resin-solution combined with nanoparticles of silica ranging in size from 20 nanometers to 20 micrometers, at the largest. They applied each variant to aluminum plates then exposed the plates to supercooled water (-20 degrees Celsius) to simulate freezing rain.

Cao writes in Langmuir that while each compound containing silica bits of 10-or-fewer micrometers deflected water, only those with silica pieces less than 50 nanometers in size completely prevented icing. The minute surface area of the smaller fragments means they make minimal contact with the water. Instead, the water mostly touches the air pockets between the particles and falls away without freezing. Though not all superhydrophobic coatings follow the Pitt recipe, the researchers conclude that every type will have a different particle-scale for repelling ice than for repelling water.

Gao tested the coating with 50-nanometer particles outdoors in freezing rain to determine its real-world potential. He painted one side of an aluminum plate and left the other side untreated. The treated side had very little ice, while the untreated side was completely covered. He produced similar results on a commercial satellite dish where the glossed half of the dish had no ice, but the other half was encrusted. ###

The Langmuir paper is available on Pitt's Web site at www.pitt.edu/news2009/DiGao in PDF format

Contact: Morgan Kelly mekelly@pitt.edu 412-624-4356 University of Pittsburgh

Thursday, November 19, 2009

A little nano, a lot of oil

Rice cuts deal to research graphene-infused drilling fluids. Nano additive would improve productivity of wells.

HOUSTON – A wall of graphene a single nanometer wide could be the difference between an oil well that merely pays for itself and one that returns great profit.

Rice University and Houston-based M-I SWACO, the world's largest producer of drilling fluids for the petrochemical industry, have signed an agreement for research funds to develop a graphene additive that will improve the productivity of wells.

James Tour, Rice's Chao Professor of Chemistry

James Tour’s lab will work with M-I SWACO’s researchers to optimize the effectiveness of graphene additives to drilling fluids, also known as muds.

graphene additive for drilling fluids

Rice's Tour Lab is developing a graphene additive for drilling fluids that would keep well shafts from clogging.
The company will spend $450,000 over two years for research by the lab of James Tour, Rice's Chao Professor of Chemistry and professor of mechanical engineering and materials science and of computer science.

Tour's lab will work with M-I SWACO's researchers to optimize the effectiveness of graphene additives to drilling fluids, also known as muds.

Water- or oil-based muds are typically forced downhole through a drill to keep the drillhead clean and to remove cuttings as the fluid streams back up toward the surface. But the fluids themselves can clog pores in the shaft through which oil should flow.

The nanoscaled graphene additive, just a little per barrel, would be forced by the fluid's own pressure to form a thin filter cake on the shaft wall; this will prevent muds from clogging the pores.
When the fluids are removed along with the drill head, the formation pressure – that is, the pressure of the oil or gas inside the ground – would force the filter cake out through the pores and into the shaft. "When you release the hydrostatic pressure and pull the drill bit out, there's much more pressure inside the rock than in the hole," Tour said. "The filter blows out and the oil flows."

James Bruton, M-I SWACO's vice president for research and engineering, said the time is right for his company to investigate the use of nanoparticles. "It's something we've wanted to get into, but it was obvious we would have to partner with those who are in the know about nanotechnology. So when a friend of our CEO's who knows Professor Tour asked if we were interested in visiting with him, we were happy to say yes."

Bruton said the cost of drilling fluids can reach $200 to $300 per barrel, and a well in the Gulf of Mexico might require more than 20,000 barrels to drill. "It's not a cheap undertaking for our customers, so the performance of the fluids is paramount," he said.

Tour emphasized the nanomaterials being studied are "clean tech" components in an environmentally sensitive field. "We've shown them to be nontoxic in many forms," he said. "It's all graphite-based, and that often comes from the ground anyway."

While the company's current focus is on drilling muds, Bruton said future research would focus on using graphene in completion fluids and other drilling products. "The ideas for using nanotechnologies are endless," he said.

"People often ask me what are we developing, and most of the time they want to know what's coming out tomorrow, next week, next month or next quarter," Bruton said. "In reality, I have to worry about things we're going to implement two to five years from now. That's where the step changes are. That's where we hope and believe nanotechnology, with Rice and Jim's group, will help us get to where we need to go." ###

Contact: David Ruth druth@rice.edu 713-348-6327 Rice University

Tuesday, November 17, 2009

Magnetic mixing creates quite a stir VIDEO

Sandia researcher solves problem of mixing liquids in tiny volumes, ALBUQUERQUE, N.M. – Sandia researchers have developed a process that can mix tiny volumes of liquid, even in complicated spaces.

Researchers currently use all types of processes to try and create mixing, with only "mixed" success. "In small devices," says Sandia materials scientist Jim Martin "people have tried all kinds of pillars and mixing cells to initiate mixing, but these approaches don't work well." Researchers need simpler and more reliable ways to mix in tiny places such as micrometer-sized channels, Martin said.

"Mixing liquids in tiny volumes," Martin said, "is surprisingly difficult." When fluid is pushed down a big pipe, eddies are generated that create mixing.



Caption: Microfluids often must be mixed, but scientists have lacked a simple and reliable way to do it. Now, Sandia researcher Jim Martin and his colleagues have developed a new way to mix tiny volumes. Jim calls the approach vortex field mixing.

Credit: Sandia Labs Usage Restrictions: News or educational use.
But if fluid is pushed down a small pipe no eddies are generated and mixing does not occur unless you subject the fluid to tremendous pressure, which isn't usually easy or feasible, he said.

Martin's discovery of how to mix tiny liquid volumes arose from LDRD-funded research directed at improving the sensitivity of the chemical sensors developed in his lab. That project, "Field-Structured Composite Studies," was a joint effort with Rod Williamson (now retired).
While their LDRD project did not lead to the expected results, Martin and Williamson were surprised by the wide variety of physical effects they discovered along the way, including magnetic mixing. These effects, Martin said, ended up being much more interesting and important than the original goal.

Since the project began, Department of Energy's Division of Material Science and Engineering, Office of Basic Energy Sciences, has started a new project whose goal is to better understand the fundamental science of field-structured composites. So the program succeeded even as it failed, and eventually Martin and graduate student intern Doug Read developed better ways to increase sensor sensitivity.

In the new method of mixing, when one turns on a particular kind of magnetic field, the magnetic particles suspended in the fluid form chains like strings of pearls. The chains start swirling around and that's what does the mixing. The particles are then removed magnetically, leaving a nice mixed-up liquid.
More technically, the new mixing method, which Jim calls vortex field mixing, subjects a suspension of microscopic, magnetizable particles to a magnetic field whose direction is constantly spinning in a motion similar to a spinning top as it is about to collapse on its side, but much faster. In this "vortex field" the particles assemble into countless microscopic chains that follow the field motion, stirring every nook and cranny of the fluid. The vortex field stirs the liquid vigorously, and surprising fluid effects are possible, such as a kind of washing machine agitation where the spinning direction alternates periodically.

Currently, Martin, Lauren Rohwer, and graduate intern Kyle Solis work with the vortex field mixing, among other projects. Their experimental report, recently appearing in the July issue of Physical Review, has generated interest, including a Physical Review Focus article and a Research Highlight in the September MRS Bulletin.

This type of magnetic mixing with particles that assemble into micro-stir bars isn't like the magnetic mixing done in high school chemistry class.
Kyle Solis, a graduate student intern in Nanomaterials Sciences

Caption: Kyle Solis, a graduate student intern in Nanomaterials Sciences, prepares a sample for mixing using a new approach called vortex field mixing.

Credit: Photo by Randy Montoya. Usage Restrictions: Photo to be used for news or educational purposes.

"In your high school chemistry class," Martin says "when you mixed a beaker of water on a stir plate, underneath the plate was a permanent magnet spinning around to make the stir bar spin. If that hidden magnet suddenly became twice as strong, the magnetic field would double but you wouldn't see any increase in the stirring at all.

"With our process," Martin said "if we make the magnetic field twice as strong, the stirring becomes four times as strong because the stronger field makes the particle chains longer."

With conventional stir-bar mixing you can increase the mixing torque by increasing the speed of the stir bar instead. It's easy to feel this effect by simply holding the beaker slightly above the stir plate. In vortex field mixing increasing the speed of the wobbling doesn't help, because the chains simply break into smaller pieces and the mixing torque doesn't change at all.

Vortex field mixing stirs just as effectively with magnetic nanoparticles as with traditional micrometer-size powders. In fact, excellent mixing torques have been obtained using 100 nanometer particles. This means even the tiniest fluid volumes can be mixed, as well as the largest.

As strange as these effects are, they were initially predicted by Martin in a theory paper published in the January 2009 issue of Physical Review. This paper also explains why a simple rotating magnetic field doesn't induce mixing, and predicts the optimal wobbling angle of the magnetic field.

Vortex field mixing requires only the modest magnetic fields provided by simple wire coils that can be scaled to the size of the fluid cavity. After mixing, a researcher can trap the particles with a permanent magnet, decant the mixed liquid and recycle the particles endlessly. ###

This work was supported by the Division of Materials Science and Engineering, Office of Basic Energy Sciences, U.S. Department of Energy (DOE).

Sandia National Laboratories is a multiprogram laboratory operated by Sandia Corporation, an autonomous Lockheed Martin company, for the U.S. Department of Energy's National Nuclear Security Administration. With main facilities in Albuquerque, N.M., and Livermore, Calif., Sandia has major R&D responsibilities in national security, energy and environmental technologies, and economic competitiveness.

Sandia news media contact: Stephanie Holinka, slholin@sandia.gov (505) 284-9227

Contact: Stephanie Holinka slholin@sandia.gov 505-284-9227 DOE/Sandia National Laboratories

Sunday, November 15, 2009

Caltech scientists first to trap light and sound vibrations together in nanocrystal

Optomechanical crystals could be used in information processing, as supersensitive biosensors, and more.

PASADENA, Calif.—Researchers at the California Institute of Technology (Caltech) have created a nanoscale crystal device that, for the first time, allows scientists to confine both light and sound vibrations in the same tiny space.

"This is a whole new concept," notes Oskar Painter, associate professor of applied physics at Caltech. Painter is the principal investigator on the paper describing the work, which was published this week in the online edition of the journal Nature. "People have known how to manipulate light, and they've known how to manipulate sound. But they hadn't realized that we can manipulate both at the same time, and that the waves will interact very strongly within this single structure."

Optomechanical Crystal

Caption: (At top) This is a scanning electron micrograph of the optomechanical crystal. (At bottom) This is a closer view of the device's nanobeam.

Credit: M. Eichenfield, et. al., Nature, Advanced Online Publication (Oct. 18, 2009) Usage Restrictions: With credit as given above.
Indeed, Painter points out, the interactions between sound and light in this device—dubbed an optomechanical crystal—can result in mechanical vibrations with frequencies as high as tens of gigahertz, or 10 billion cycles per second. Being able to achieve such frequencies, he explains, gives these devices the ability to send large amounts of information, and opens up a wide array of potential applications—everything from lightwave communication systems to biosensors capable of detecting (or weighing) a single macromolecule. It could also, Painter says, be used as a research tool by scientists studying nanomechanics. "These structures would give a mass sensitivity that would rival conventional nanoelectromechanical systems because light in these structures is more sensitive to motion than a conventional electrical system is."

"And all of this," he adds, "can be done on a silicon microchip."
Optomechanical crystals focus on the most basic units—or quanta—of light and sound. (These are called photons and phonons, respectively.) As Painter notes, there has been a rich history of research into both photonic and phononic crystals, which use tiny energy traps called bandgaps to capture quanta of light or sound within their structures.

What hadn't been done before was to put those two types of crystals together and see what they are capable of doing. That is what the Caltech team has done.

"We now have the ability to manipulate sound and light in the same nanoplatform, and are able to interconvert energy between the two systems," says Painter. "And we can engineer these in nearly limitless ways."

The volume in which the light and sound are simultaneously confined is more than 100,000 times smaller than that of a human cell, notes Caltech graduate student Matt Eichenfield, the paper's first author. "This does two things," he says. "First, the interactions of the light and sound get stronger as the volume to which they are confined decreases. Second, the amount of mass that has to move to create the sound wave gets smaller as the volume decreases. We made the volume in which the light and sound live so small that the mass that vibrates to make the sound is about ten times less than a trillionth of a gram."

Eichenfield points out that, in addition to measuring high-frequency sound waves, the team demonstrated that it's actually possible to produce these waves using only light. "We can now convert light waves into microwave-frequency sound waves on the surface of a silicon microchip," he says.

These sound waves, he adds, are analogous to the light waves of a laser. "The way we have designed the system makes it possible to use these sound waves by routing them around on the chip, and making them interact with other on-chip systems. And, of course, we can then detect all these interactions again by using the light. Essentially, optomechanical crystals provide a whole new on-chip architecture in which light can generate, interact with, and detect high-frequency sound waves."

These optomechanical crystals were created as an offshoot of previous work done by Painter and colleagues on a nanoscale "zipper cavity," in which the mechanical properties of light and its interactions with motion were strengthened and enhanced. (That release can be found at http://media.caltech.edu/press_releases/13263.)

Like the zipper cavity, optomechanical crystals trap light; the difference is that the crystals trap—and intensify—sound waves, as well. Similarly, while the zipper cavities worked by funneling the light into the gap between two nanobeams—allowing the researchers to detect the beams' motion relative to one another—optomechanical crystals work on an even tinier scale, trapping both light and sound within a single nanobeam.

"Here we can actually see very small vibrations of sound trapped well inside a single 'string,' using the light trapped inside that string," says Eichenfield. "Importantly, although the method of sensing the motion is very different, we didn't lose the exquisite sensitivity to motion that the zipper had. We were able to keep the sensitivity to motion high while making another huge leap down in mass."

"As a technology, optomechanical crystals provide a platform on which to create planar circuits of sound and light," says Kerry Vahala, the Ted and Ginger Jenkins Professor of Information Science and Technology and professor of applied physics, and coauthor on the Nature paper. "These circuits can include an array of functions for generation, detection, and control. Moreover," he says, "optomechanical crystal structures are fabricated using materials and tools that are similar to those found in the semiconductor and photonics industries. Collectively, this means that phonons have joined photons and electrons as possible ways to manipulate and process information on a chip."

And these information-processing possibilities are well within reach, notes Painter. "It's not one plus one equals two, but one plus one equals ten in terms of what you can do with these things. All of these applications are much closer than they were before."

"This novel approach to bringing both light and sound together and letting them play off of each other exemplifies the forward-thinking work being done by the Engineering and Applied Science (EAS) division," says Ares Rosakis, chair of EAS and Theodore von Kármán Professor of Aeronautics and Mechanical Engineering at Caltech. ###

Other authors on the Nature paper, "Optomechanical crystals," include Caltech graduate student Jasper Chan and postdoctoral scholar Ryan Camacho. Funding for their work was provided by a Defense Advanced Research Projects Agency seed grant and by grants from the National Science Foundation.

For more information, visit the Caltech Media Relations website at media.caltech.edu.

Contact: Lori Oliwenstein lorio@caltech.edu 626-395-3631 California Institute of Technology

Saturday, November 14, 2009

Is your microrobot up for the (NIST) challenge?

The scientists and engineers who introduced the world to tiny robots demonstrating soccer skills are creating the next level of friendly competition designed to advance microrobotics—the field devoted to the construction and operations of useful robots whose dimensions are measured in micrometers (millionths of a meter).

The National Institute of Standards and Technology (NIST), in collaboration with IEEE, is inviting university and collegiate student teams currently engaged in microrobotic, microelectronic or MicroElectroMechanical Systems (MEMS) research to participate in the 2010 NIST Mobile Microrobotics Challenge. The competition will be held as part of the IEEE International Conference on Robotics and Automation in May 2010 in Anchorage, Alaska.

Microrobot Sized Next to Fly Head

Caption: A microrobot used at the RoboCup 2009 nanosoccer competition by the team from Switzerland's ETH Zurich is compared in size to the head of a fruit fly. The robot, which is operated under a microscope, is 300 micrometers in length or slightly larger than a dust mite.

Credit: ETH Zurich. Usage Restrictions: None.
Viewed under a microscope, the microbots are operated by remote control and move in response to changing magnetic fields or electrical signals transmitted across a microchip playing field. The bots are a few tens of micrometers to a few hundred micrometers long, but their masses can be just a few nanograms (billionths of a gram). They are manufactured from materials such as aluminum, nickel, gold, silicon and chromium.

Like the NIST-coordinated "nanosoccer" events at the 2007 and 2009 RoboCup competitions (see www.nist.gov/public_affairs/calmed/nanosoccer), the Mobile Microrobotics Challenge will pit tiny robotic contestants against each other in three tests: (1) a two-millimeter dash in which microrobots sprint across a distance equal to the diameter of a pin head;
(2) a microassembly task where the competitors must insert pegs into designated holes; and (3) a freestyle competition where each team chooses a task for its robot that emphasizes one or more abilities from among system reliability, level of autonomy, power management and task complexity.

These events are designed to "road test" agility, maneuverability, response to computer control and the ability to move objects—all skills that future industrial microbots will need for tasks such as microsurgery within the human body or the manufacture of tiny components for microscopic electronic devices.

NIST is organizing the 2010 Mobile Microrobotics Challenge with the IEEE Robotics and Automation Society. NIST's goal in coordinating competitions between the world's smallest robots is to show the feasibility and accessibility of technologies for fabricating MEMS, which are tiny mechanical devices built onto semiconductor chips. The contests also drive innovation in this new field of robotics by inspiring young scientists and engineers to become involved. ###

To apply for the NIST Mobile Microrobotics Challenge, teams must submit a proposal by Dec. 31, 2009, by electronic mail to microrobotics2010@nist.gov, or by standard mail to: NIST Microrobotics Challenge 2010, c/o Craig McGray, NIST, 100 Bureau Dr., MS 8120, Gaithersburg, MD 20899-8120. Proposals must include: a roster of individuals contributing to the team; contact information for the team leader; a list of the facilities available for fabrication, operation and characterization of microrobots; an overview of the microrobot design; an overview of the intended capabilities of the microrobot; and an overview of the fabrication process to be used.

For more information, go to www.nist.gov/eeel/semiconductor.

Contact: Michael E. Newman michael.newman@nist.gov 301-975-3025 National Institute of Standards and Technology (NIST)

Wednesday, November 11, 2009

University of Cincinnati researchers create all-electric spintronics

Multidisciplinary team of UC researchers first to find an innovative and novel way to control an electron’s spin orientation using purely electrical means.

A multidisciplinary team of UC researchers is the first to find an innovative and novel way to control an electron's spin orientation using purely electrical means.

Their findings were recently published in the prestigious, high-profile journal "Nature Nanotechnology," in an article titled "All-Electric Quantum Point Contact Spin-Polarizer."

For decades, the transistors inside radios, televisions and other everyday electronic items have transmitted data by controlling the movement of the charge of an electron.

Philippe Debray, Marc Cahay, Partha Pratim Das and Krishna Chetry, University of Cincinnati

Caption: Professors Philippe Debray (left) and Marc Cahay discuss their spintronics reseach with graduate students Partha Pratim Das (on stepladder) and Krishna Chetry (far right).

Credit: Lisa Ventre, UC Photo Services. Usage Restrictions: None.

Quantum Point Contact Spin Polarizer Device

Caption: (Left) Scanning electron micrograph of the quantum point contact schematically illustrates unpolarized (spin up and spin down) electrons incident on the left coming out of the device spin-polarized with spin up. (Right) Spatial distribution of spin polarization in the quantum point contact constriction.

Credit: Illustration by Professor Philippe Debray, University of Cincinnati, Usage Restrictions: None.
Scientists have since discovered that transistors that function by controlling an electron's spin instead of its charge would use less energy, generate less heat and operate at higher speeds. This has resulted in a new field of research — spin electronics or spintronics — that offers one of the most promising paradigms for the development of novel devices for use in the post-CMOS (complementary metal–oxide–semiconductor) era.

Until now, scientists have attempted to develop spin transistors by incorporating local ferromagnets into device architectures. This results in significant design complexities, especially in view of the rising demand for smaller and smaller transistors," says Philippe Debray, research professor in the Department of Physics in the McMicken College of Arts & Sciences. "A far better and practical way to manipulate the orientation of an electron's spin would be by using purely electrical means, like the switching on and off of an electrical voltage. This will be spintronics without ferromagnetism or all-electric spintronics, the holy grail of semiconductor spintronics."

The team of researchers led by Debray and Professor Marc Cahay (Department of Electrical and Computer Engineering) is the first to find an innovative and novel way to control an electron's spin orientation using purely electrical means.

"We used a quantum point contact — a short quantum wire — made from the semiconductor indium arsenide to generate strongly spin-polarized current by tuning the potential confinement of the wire by bias voltages of the gates that create it," Debray says.
In the diagram at left, (Left) Scanning electron micrograph of the quantum point contact schematically illustrates unpolarized (spin up and spin down) electrons incident on the left coming out of the device spin-polarized with spin up. (Right) Spatial distribution of spin polarization in the quantum point contact constriction.

Debray continues, "The key condition for the success of the experiment is that the potential confinement of the wire must be asymmetric — the transverse opposite edges of the quantum point contact must be asymmetrical. This was achieved by tuning the gate voltages. This asymmetry allows the electrons — thanks to relativistic effects — to interact with their surroundings via spin-orbit coupling and be polarized. The coupling triggers the spin polarization and the Coulomb electron–electron interaction enhances it."

Controlling spin electronically has major implications for the future development of spin devices. The work by Debray's team is the first step. The next experimental step would be to achieve the same results at a higher temperature using a different material such as gallium arsenide. ###

This work was supported by National Science Foundation awards ECCS 0725404 and DMR 0710581.

Contact: Wendy Beckman wendy.beckman@uc.edu 513-556-1826 University of Cincinnati

Monday, November 09, 2009

Study shows how carbon nanotubes can affect lining of the lungs

Carbon nanotubes are being considered for use in everything from sports equipment to medical applications, but a great deal remains unknown about whether these materials cause respiratory or other health problems. Now a collaborative study from North Carolina State University, The Hamner Institutes for Health Sciences, and the National Institute of Environmental Health Sciences shows that inhaling these nanotubes can affect the outer lining of the lung, though the effects of long-term exposure remain unclear.

Using mice in an animal model study, the researchers set out to determine what happens when multi-walled carbon nanotubes are inhaled.

Inhaled carbon nanotubes

Inhaled carbon nanotubes accumulate within cells at the pleural lining of the lung as visualized by light microscopy.
Specifically, researchers wanted to determine whether the nanotubes would be able to reach the pleura, which is the tissue that lines the outside of the lungs and is affected by exposure to certain types of asbestos fibers which cause the cancer mesothelioma. The researchers used inhalation exposure and found that inhaled nanotubes do reach the pleura and cause health effects.

Short-term studies described in the paper do not allow conclusions about long-term responses such as cancer.
However, the inhaled nanotubes "clearly reach the target tissue for mesothelioma and cause a unique pathologic reaction on the surface of the pleura, and caused fibrosis," says Dr. James Bonner, associate professor of environmental and molecular toxicology at NC State and senior author of the study. The "unique reaction" began within one day of inhalation of the nanotubes, when clusters of immune cells (lymphocytes and monocytes) began collecting on the surface of the pleura. Localized fibrosis, or scarring on parts of the pleural surface that is also found with asbestos exposure, began two weeks after inhalation.

The study showed the immune response and fibrosis disappeared within three months of exposure. However, this study used only a single exposure to the nanotubes. "It remains unclear whether the pleura could recover from chronic, or repeated, exposures," Bonner says. "More work needs to be done in that area and it is completely unknown at this point whether inhaled carbon nanotubes will prove to be carcinogenic in the lungs or in the pleural lining."

The mice received a single inhalation exposure of six hours as part of the study, and the effects on the pleura were only evident at the highest dose used by the researchers – 30 milligrams per cubic meter (mg/m3). The researchers found no health effects in the mice exposed to the lower dose of one mg/m3. ###

The study, "Inhaled Carbon Nanotubes Reach the Sub-Pleural Tissue in Mice," was co-authored by Bonner, Dr. Jessica Ryman-Rasmussen, Dr. Arnold Brody, and Dr. Jeanette Shipley-Phillips of NC State, Dr. Jeffrey Everitt who is an adjunct faculty at NC State, Dr. Mark Cesta of the National Institute of Environmental Health Sciences (NIEHS), Earl Tewksbury, Dr. Owen Moss, Dr. Brian Wong, Dr. Darol Dodd and Dr. Melvin Andersen of The Hamner Institutes for Health Sciences. The study is published in the Oct. 25 issue of Nature Nanotechnology and was funded by The Hamner Institutes for Health Sciences, NIEHS and NC State's College of Agriculture and Life Sciences.

Note to Editors: The presentation abstract follows.

“Inhaled Carbon Nanotubes Reach the Sub-Pleural Tissue in Mice”

Authors: Jessica Ryman-Rasmussen, Arnold Brody, Jeanette Shipley-Phillips, James Bonner, Jeffrey Everitt, North Carolina State University; Mark Cesta, National Institute of Environmental Health Sciences; Earl Tewksbury, Owen Moss, Brian Wong, Darol Dodd, Melvin Andersen, The Hamner Institutes for Health Sciences.

Published: Oct. 25, 2009, Nature Nanotechnology.

Abstract: Carbon nanotubes are shaped like fibres and can stimulate inflammation at the surface of the peritoneum when injected into the abdominal cavity of mice, raising concerns that inhaled nanotubes may cause pleural fibrosis and/or mesothelioma. Here, we show that multiwalled carbon nanotubes reach the subpleura in mice after a single inhalation exposure of 30 mg m-3 for 6 h. Nanotubes were embedded in the subpleural wall and within subpleural macrophages. Mononuclear cell aggregates on the pleural surface increased in number and size after 1 day and nanotube-containing macrophages were observed within these foci. Subpleural fibrosis unique to this form of nanotubes increased after 2 and 6 weeks following inhalation. None of these effects was seen in mice that inhaled carbon black nanoparticles or a lower dose of nanotubes (1 mg m-3). This work suggests that minimizing inhalation of nanotubes during handling is prudent until further long-term assessments are conducted.

Contact: Matt Shipman matt_shipman@ncsu.edu 919-515-6386 North Carolina State University

Saturday, November 07, 2009

Penn study: Transforming nanowires into nano-tools using cation exchange reactions

PHILADELPHIA –- A team of engineers from the University of Pennsylvania has transformed simple nanowires into reconfigurable materials and circuits, demonstrating a novel, self-assembling method for chemically creating nanoscale structures that are not possible to grow or obtain otherwise.

The research team, using only chemical reactants, transformed semiconducting nanowires into a variety of useful, nanoscale materials including nanoscale metal strips with periodic stripes and semiconducting patterns, purely metallic nanowires, radial heterostructures and hollow semiconducting nanotubes in addition to other morphologies and compositions.

Extent of Cation-Exchange Reactions

Caption: Using only chemical reactants, engineers transformed semiconducting nanowires into a variety of useful, nanoscale materials.

Credit: Ritesh Agarwal, the University of Pennsylvania. Usage Restrictions: None.
Researchers used ion exchange, one of the two most common techniques for solid phase transformation of nanostructures. Ion (cation/anion) exchange reactions exchange positive or negative ions and have been used to modify the chemical composition of inorganic nanocrystals, as well as create semiconductor superlattice structures. It is the chemical process, for example, that turns hard water soft in many American households.
Future applications of nanomaterials in electronics, catalysis, photonics and bionanotechnology are driving the exploration of synthetic approaches to control and manipulate the chemical composition, structure and morphology of these materials. To realize their full potential, it is desirable to develop techniques that can transform nanowires into tunable but precisely controlled morphologies, especially in the gas-phase, to be compatible with nanowire growth schemes. The assembly, however, is an expensive and labor-intensive process that prohibits cost-effective production of these materials.

Recent research in the field has enabled the transformation of nanomaterials via solid-phase chemical reactions into nonequilibrium, or functional structures that cannot be obtained otherwise.

In this study, researchers transformed single-crystalline cadmium sulfide nanowires into composition-controlled nanowires, core−shell heterostructures, metal-semiconductor superlattices, single-crystalline nanotubes and metallic nanowires by utilizing size-dependent cation-exchange reactions along with temperature and gas-phase reactant delivery control. This versatile, synthetic ability to transform nanowires offers new opportunities to study size-dependent phenomena at the nanoscale and tune their chemical/physical properties to design reconfigurable circuits.

Researchers also found that the speed of the cation exchange process was determined by the size of the starting nanowire and that the process temperature affected the final product, adding new information to the conditions that affect reaction rates and assembly.

"This is almost like magic that a single-component semiconductor nanostructure gets converted into metal-semiconductor binary superlattice, a completely hollow but single crystalline nanotube and even a purely metallic material," said Ritesh Agarwal, assistant professor in the Department of Materials Science and Engineering at Penn. "The important thing here is that these transformations cannot take place in bulk materials where the reaction rates are incredibly slow or in very small nanocrystals where the rates are too fast to be precisely controlled. These unique transformations take place at 5-200 nanometer-length scales where the rates can be controlled very accurately to enable such intriguing products. Now we are working with theoreticians and designing new experiments to unravel this 'magic' at the nanoscale."

The fundamental revelation in this study is a further clarification of nanoscale chemical phenomena. The study also provides new data on how manufacturers can assemble these tiny circuits, electrically connecting nanoscale structures through chemical self-assembly.

It also opens up new possibilities for the transformation of nanoscale materials into the tools and circuits of the future, for example, self-assembling nanoscale electrical contacts to individual nanoscale components, smaller electronic and photonic devices such as a series of electrically connected quantum dots for LEDs or transistors, as well as improved storage capacities for batteries. ###

The study, published in the current issue of the journal Nano Letters, was conducted by Bin Zhang, Yeonwoong Jung, Lambert Van Vug and Agarwal of the Department of Materials Science and Engineering in Penn's School of Engineering and Applied Science.

The work was supported by a National Science Foundation Career Award and a Penn Materials Research Science and Engineering Center grant.

Contact: Jordan Reese jreese@upenn.edu 215-573-6604 University of Pennsylvania

Thursday, November 05, 2009

Tissue engineering could improve hand use for wounded soldiers

Animal studies at University of Michigan Health System also show potential to restore sense of touch.

Modern tissue engineering developed at the University of Michigan could improve the function of prosthetic hands and possibly restore the sense of touch for injured patients.

Researchers will present their updated findings Wednesday at the 95th annual Clinical Congress of the American College of Surgeons.

The research project, funded by the Department of Defense, arose from a need for better prosthetic devices for troops wounded in Afghanistan and Iraq. “Most of these individuals are typically using a prosthesis design that was developed decades ago,” says Paul S. Cederna, M.D., a plastic and reconstructive surgeon at U-M Health System and associate professor of surgery at the U-M Medical School. “This effort is to make a prosthesis that moves like a normal hand.”

Tissue engineering could improve hand use for wounded soldiersU-M researchers may help overcome some of the shortcomings of existing robotic prosthetics, which have limited motor control, provide no sensory feedback and can be uncomfortable and cumbersome to wear.

“There is a huge need for a better nerve interface to control the upper extremity prostheses,” says Cederna.
When a hand is amputated, the nerve endings in the arm continue to sprout branches, growing a mass of nerve fibers that send flawed signals back to the brain.

The researchers created what they called an “artificial neuromuscular junction” composed of muscle cells and a nano-sized polymer placed on a biological scaffold. Neuromuscular junctions are the body's own nerve-muscle connections that enable the brain to control muscle movement.

That bioengineered scaffold was placed over the severed nerve endings like a sleeve. The muscle cells on the scaffold and in the body bonded and the body’s native nerve sprouts fed electrical impulses into the tissue, creating a stable nerve-muscle connection.

In laboratory rats, the bioengineered interface relayed both motor and sensory electrical impulses and created a target for the nerve endings to grow properly.

“The polymer has the ability to pick up signals coming out of the nerve, and the nerve does not grow an abnormal mass of nerve fibers,” explains Cederna.

The animal studies indicate the interface may not only improve fine motor control of prostheses, but can also relay sensory perceptions such as touch and temperature back to the brain.

Laboratory rats with the interface responded to tickling of feet with appropriate motor signals to move the limb, says Cederna.

The Department of Defense and the Army have already provided $4.5 million in grants to support the research. Meanwhile, the research team has submitted a proposal to the Defense Advance Research Project Agency to begin testing the bioengineered interface in humans in three years.

Additional U-M authors of the study include William M. Kuzon, Jr., M.D., Ph.D., professor of surgery and head of the Division of Plastic Surgery; David C. Martin, Ph.D., chair of materials science and engineering at the University of Delaware and former professor of materials science and engineering and macromolecular science at U-M; Daryl R. Kipke, Ph.D. professor of biomedical engineering; Melanie Urbancheck, Ph.D., assistant research professor; and Brent M. Egeland, M.D., surgical resident.

Resources: U-M Department of Surgery Division of Plastic Surgery //surgery.med.umich.edu/plastic/

American College of Surgeons 95th Annual Clinical Congress //www.facs.org/clincon2009/

Contact: Jennifer Burke Labriola burkepr@gmail.com 203-405-1479 American College of Gastroenterology