A team of researchers led by chemist Paul Alivisatos, director of Berkeley Lab, and Prashant Jain, a chemist now with the University of Illinois, has discovered why nanocrystals made from multiple components in solution via the exchange of cations (positive ions) have been poor light emitters. The problem, they found, stems from impurities in the final product. The team also demonstrated that these impurities can be removed through heat.

"By heating these nanocrystals to 100 degrees Celsius, we were able to remove the impurities and increase their luminescence by 400-fold within 30 hours," says Jain, a member of Alivisatos' research group when this work was done.

"When the impurities were removed the optoelectronic properties of nanocrystals made through cation-exchange were comparable in quality to dots and nanorods conventionally synthesized."

Says Alivisatos, "With our new findings, the cation-exchange technique really becomes a method that can be widely used to make novel high optoelectronic grade nanocrystals."

Jain is the lead author and Alivisatos the corresponding author of a paper describing this work in the journal Angewandte Chemie titled "Highly Luminescent Nanocrystals From Removal of Impurity Atoms Residual From Ion Exchange Synthesis." Other authors were Brandon Beberwyck, Lam-Kiu Fong and Mark Polking.

Quantum dots and nanorods are light-emitting semiconductor nanocrystals that have a broad range of applications, including bio-imaging, solar energy and display screen technologies. Typically, these nanocrystals are synthesized from colloids - particles suspended in solution.

As an alternative, Alivisatos and his research group developed a new solution-based synthesis technique in which nanocrystals are chemically transformed by exchanging or replacing all of the cations in the crystal lattice with another type of cation.

This cation-exchange technique makes it possible to produce new types of core/shell nanocrystals that are inaccessible through conventional synthesis. Core/shell nanocrystals are heterostructures in which one type of semiconductor is enclosed within another, for example, a cadmium selenide (CdSe) core and a cadmium sulfide (CdS) shell.

"While holding promise for the simple and inexpensive fabrication of multicomponent nanocrystals, the cation-exchange technique has yielded quantum dots and nanorods that perform poorly in optical and electronic devices," says Alivisatos, a world authority on nanocrystal synthesis who holds a joint appointment with the University of California (UC) Berkeley, where he is the Larry and Diane Bock professor of Nanotechnology.

As Jain tells the story, he was in the process of disposing of CdSe/CdS nanocrystals in solution that were six months old when out of habit he tested the nanocrystals under ultraviolet light.

To his surprise he observed significant luminescence. Subsequent spectral measurements and comparing the new data to the old showed that the luminescence of the nanocrystals had increased by at least sevenfold.

"It was an accidental finding and very exciting," Jain says, "but since no one wants to wait six months for their samples to become high quality I decided to heat the nanocrystals to speed up whatever process was causing their luminescence to increase."

Jain and the team suspected and subsequent study confirmed that impurities - original cations that end up being left behind in the crystal lattice during the exchange process - were the culprit.

"Even a few cation impurities in a nanocrystal are enough to be effective at trapping useful, energetic charge-carriers," Jain says.

"In most quantum dots or nanorods, charge-carriers are delocalized over the entire nanocrystal, making it easy for them to find impurities, no matter how few there might be, within the nanocrystal.

By heating the solution to remove these impurities and shut off this impurity-mediated trapping, we give the charge-carriers enough time to radiatively combine and thereby boost luminescence."

Since charge-carriers are also instrumental in electronic transport, photovoltaic performance, and photocatalytic processes, Jain says that shutting off impurity-mediated trapping should also boost these optoelectronic properties in nanocrystals synthesized via the cation-exchange technique.

]]> Wed, 08 FEB 2012 08:55:15 AEST Houston TX (SPX) Feb 06, 2012 - A painstaking study by Rice University has brought a wealth of new information about single-walled carbon nanotubes through analysis of their fluorescence.

The current issue of the American Chemical Society journal ACS Nano features an article about work by the Rice lab of chemist Bruce Weisman to understand how the lengths and imperfections of individual nanotubes affect their fluorescence - in this case, the light they emit at near-infrared wavelengths.

The researchers found that the brightest nanotubes of the same length show consistent fluorescence intensity, and the longer the tube, the brighter. "There's a rather well-defined limit to how bright they appear," Weisman said. "And that maximum brightness is proportional to length, which suggests those tubes are not affected by imperfections."

But they found that brightness among nanotubes of the same length varied widely, likely due to damaged or defective structures or chemical reactions that allowed atoms to latch onto the surface.

The study first reported late last year by Weisman, lead author/former graduate student Tonya Leeuw Cherukuri and postdoctoral fellow Dmitri Tsyboulski detailed the method by which Cherukuri analyzed the characteristics of 400 individual nanotubes of a specific physical structure known as (10,2).

"It's a tribute to Tonya's dedication and talent that she was able to make this large number of accurate measurements," Weisman said of his former student.

The researchers applied spectral filtering to selectively view the specific type of nanotube. "We used spectroscopy to take this very polydisperse sample containing many different structures and study just one of them, the (10,2) nanotubes," Weisman said. "But even within that one type, there's a wide range of lengths."

Weisman said the study involved singling out one or two isolated nanotubes at a time in a dilute sample and finding their lengths by analyzing videos of the moving tubes captured with a special fluorescence microscope. The movies also allowed Cherukuri to catalog their maximum brightness.

"I think of these tubes as fluorescence underachievers," he said. "There are a few bright ones that fluoresce to their full potential, but most of them are just slackers, and they're half as bright, or 20 percent as bright, as they should be.

"What we want to do is change that distribution and leave no tube behind, try to get them all to the top. We want to know how their fluorescence is affected by growth methods and processing, to see if we're inflicting damage that's causing the dimming.

"These are insights you really can't get from measurements on bulk samples," he said.

Graduate student Jason Streit is extending Cherukuri's research. "He's worked up a way to automate the experiments so we can image and analyze dozens of nanotubes at once, rather than one or two. That will let us do in a couple of weeks what had taken months with the original method," Weisman said.

]]> Wed, 08 FEB 2012 08:55:15 AEST Berkeley CA (SPX) Feb 06, 2012 - A relatively fast, easy and inexpensive technique for inducing nanorods - rod-shaped semiconductor nanocrystals - to self-assemble into one-, two- and even three-dimensional macroscopic structures has been developed by a team of researchers with the U.S. Department of Energy (DOE)'s Lawrence Berkeley National Laboratory (Berkeley Lab). This technique should enable more effective use of nanorods in solar cells, magnetic storage devices and sensors.

It should also help boost the electrical and mechanical properties of nanorod-polymer composites.

Leading this project was Ting Xu, a polymer scientist who holds joint appointments with Berkeley Lab's Materials Sciences Division and the University of California (UC) Berkeley's Departments of Materials Sciences and Engineering, and Chemistry.

Xu and her research group used block copolymers - long sequences or "blocks" of one type of monomer bound to blocks of another type of monomer - as a platform to guide the self-assembly of nanorods into complex structures and hierarchical patterns. Block copolymers have an innate ability to self-assemble into well-defined arrays of nano-sized structures over macroscopic distances.

"Ours is a simple and versatile technique for controlling the orientation of nanorods within block copolymers," Xu says.

"By varying the morphology of the block copolymers and the chemical nature of the nanorods, we can provide the controlled self-assembly in nanorods and nanorod-based nanocomposites that is critical for their use in the fabrication of optical and electronic devices."

Xu is the corresponding author of a paper describing this research that has been published in the journal Nano Letters under the title "Direct Nanorod Assembly Using Block Copolymer-Based Supramolecules." Co-authoring the paper were Kari Thorkelsson, Alexander Mastroianni and Peter Ercius.

Nanorods - particles of matter a thousand times smaller than the stuff of today's microtechnologies - display highly coveted optical, electronic and other properties not found in macroscopic materials.

To fully realize their vast technological promise, however, nanorods must be able to assemble themselves into complex structures and hierarchical patterns, similar to what nature routinely accomplishes with proteins.

Xu and her research group first enlisted block copolymers as allies in this self-assembly effort in 2009, working with the spherical nanoparticles commonly known as quantum dots. In that study, they lashed quantum dots to block copolymers via a "mediator" of small adhesive molecules.

In this latest development, Xu and her group again made use of adhesive molecules, but this time to mediate between the nanorods and supramolecules of block copolymers. A supramolecule is a group of molecules that act as a single molecule able to perform a specific set of functions.

"Block copolymer supramolecules self-assemble and form a wide range of morphologies that feature microdomains typically a few to tens of nanometers in size," Xu says. "As their size is comparable to that of nanoparticles, the microdomains of block copolymer supramolecules provide an ideal structural framework for the co-assembly of nanorods."

Xu and her group incorporate nanorods into solutions of block copolymer supramolecules that form spherical, cylindrical and lamellar microdomains. During the drying process energy is contributed to the system from the interactions between nanorod ligands and polymers, the entropy associated with polymer chain deformation upon nanorod incorporation, and the interactions between individual nanorods.

Xu and her group observed that these energetic contributions determine the placement and distribution of the nanorods, as well as the overall morphology of the nanorod-block copolymer composites.

These energetic contributions can be easily tuned by varying the supramolecular morphology, which is accomplished simply by attaching different types of small molecules to the side chains of the block copolymers.

"We can readily access a wide library of nanorod assemblies including arrays of nanorods aligned parallel to block copolymer cylindrical microdomains, continuous nanorod networks, and nanorod clusters," Xu says.

"Since the macroscopic alignment of block copolymer microdomains can be obtained in bulk and in thin films by the application of external fields, our technique should open up a viable route to manipulate the macroscopic alignments of nanorods."

This new technique can produce ordered arrays of nanorods that are macroscopically aligned with tunable distances between individual rods - a morphology that lends itself to the production of plasmonics, which are materials that hold great promise for superfast computers, ultra-powerful optical microscopes, and even the creation of invisibility carpets.

It is also a straightforward nanoparticle self-assembly technique that can produce a continuous network of nanorods with nanoscopic separation distances. Such networks can enhance the macroscopic properties of nanocomposites, including electrical conductivity and material strength.

Xu credits much of the success of this research to the exceptional capabilities and staff at the National Center for Electron Microscopy (NCEM), a DOE national user facility at Berkeley Lab, which is home to the world's most powerful electron microscopes.

"For the study of three-dimensional nanorod assemblies, we needed to implement high-resolution tomography and this posed a challenge not only for collecting the imaging data but also for processing it," Xu says. "The expertise and skill of NCEM's Peter Ercius was invaluable."

Xu and her group are now investigating the self-assembly of semiconductor nanocrystals that take the shapes of cubes or tetrapods, both of which have important potential applications for photovoltaic and other technologies.

"We'd also like to investigate the self-assembly of nanoparticles into combinations of different shapes," Xu says.

]]> Wed, 08 FEB 2012 08:55:15 AEST Houston TX (SPX) Feb 03, 2012 - Rice University scientists have created a nano-infused oil that could greatly enhance the ability of devices as large as electrical transformers and as small as microelectronic components to shed excess heat.

Research in the lab of Rice materials scientist Pulickel Ajayan, which appears in the American Chemical Society journal ACS Nano, could raise the efficiency of such transformer oils by as much as 80 percent in a way that is both cost-effective and environmentally friendly.

The Rice team headed by lead authors Jaime Taha-Tijerina, a graduate student, and postdoctoral researcher Tharangattu Narayanan focused their efforts on transformers for energy systems. Transformers are filled with mineral oils that cool and insulate the windings inside, which must remain separated from each other to keep voltage from leaking or shorting.

The researchers discovered that a very tiny amount of hexagonal boron nitride (h-BN) particles, two-dimensional cousins to carbon-based graphene, suspended in standard transformer oils are highly efficient at removing heat from a system.

"We don't need a large amount of h-BN," Narayanan said. "We found that 0.1 weight percentage of h-BN in transformer oil enhances it by nearly 80 percent."

"And at 0.01 weight percentage, the enhancement was around 9 percent," Taha-Tijerina said. "Even with a very low amount of material, we can enhance the fluids without compromising the electrically insulating properties."

Taha-Tijerina, who was employed by a transformer manufacturer in Mexico before coming to Rice, said others working on similar compounds are experimenting with particles of alumina, copper oxide and titanium oxide, but none of the compounds has the combination of qualities exhibited by h-BN.

Narayanan said the h-BN particles, about 600 nanometers wide and up to five atomic layers thick, disperse well in oil and, unlike highly conductive graphene, are highly resistant to electricity.

With help from co-author Matteo Pasquali, a Rice professor of chemical and biomolecular engineering and of chemistry, the team determined that the oil's viscosity - another important quality - is minimally affected by the presence of the nanoparticle fillers.

"Our research shows that with new materials and innovative approaches, we can add enormous value to applications that exist today in industry," said Ajayan, Rice's Benjamin M. and Mary Greenwood Anderson Professor in Mechanical Engineering and Materials Science and of chemistry.

"Thermal management is a big issue in industry, but the right choice of materials is important; for transformer cooling, one needs dispersants in oils that take heat away, yet remain electrically insulating. Moreover, the two-dimensional nature of the fillers keeps them stable in oils without settling down for long periods of time."

]]> Wed, 08 FEB 2012 08:55:15 AEST Houston TX (SPX) Feb 03, 2012 - The Air Force Research Laboratory in Dayton, Ohio, has experimentally confirmed a theory by Rice University Professor Boris Yakobson that foretold a pair of interesting properties about nanotube growth: That the chirality of a nanotube controls the speed of its growth, and that armchair nanotubes should grow the fastest.

The work is a sure step toward defining all the mysteries inherent in what Yakobson calls the "DNA code of nanotubes," the parameters that determine their chirality - or angle of growth - and thus their electrical, optical and mechanical properties. Developing the ability to grow batches of nanotubes with specific characteristics is a critical goal of nanoscale research.

The new paper by Air Force senior researcher Benji Maruyama; former Air Force colleague Rahul Rao, now at the Honda Research Institute in Ohio; Yakobson and their co-authors appeared this week in the online version of the journal Nature Materials.

It's an interesting denouement in a saga that began with a 2009 paper by Yakobson and his collaborators. That paper, which presented the theoretical physicist's dislocation theory of chirality-controlled growth, described how nanotubes emerge as if single threads of atoms weave themselves into the now-familiar chicken-wire-like tubes. It also garnered a bit of controversy over what precisely the results meant.

"Boris caught some heat over it," Maruyama said. "The experimental work out there indicated his theory might be true, but they couldn't confirm it. The good part about our work is that it's fairly unambiguous."

Yakobson, Rice's Karl F. Hasselmann Professor of Mechanical Engineering and Materials Science and professor of chemistry, took it all in stride.

"The criticism didn't affect anything; it was actually the best advertisement and motivation for further work," he said. "In fact, (nanotube pioneer Sumio) Iijima noted early that 'helicity may aid the growth.' We have transformed it into a verifiable equation."

Experimental confirmation of a theory is never final but always satisfying, he admitted, and the Air Force lab was uniquely equipped to prove the linkage between the speed of a nanotube's growth and its chiral angle.

The chirality of a single-walled nanotube is determined by the way its carbon atoms are "rolled." Yakobson has described it as similar to rolling up a newspaper; sometimes the type lines up, and sometimes it doesn't.

That alignment determines the nanotubes' electrical properties. Metallic armchair nanotubes, so named for the shape of their uncapped edges, are particularly desirable because electrons pass through from tip to tip with no resistance, while semiconducting nanotubes are useful for electronics, among other applications.

Rao developed a technique in Maruyama's lab to measure the growth rates of individual nanotubes. "It's an impressive setup," Yakobson said. "They can grow individual tubes in very low density and identify their signatures - their chirality - and at the same time measure how rapidly they grow."

The technique involved mounting catalyst nanoparticles on microscopic silicon pillars and firing tightly controlled lasers at them. Heat from the laser triggered the nanotubes to grow through a standard technique called chemical vapor deposition, and at the same time, the researchers analyzed nanotube growths via Raman spectroscopy.

From the spectra, they could tell how fast a nanotube grew and at what point growth terminated. Subsequent electron microscope images confirmed the spectra were from individual single-walled nanotubes, while chiral angles were determined by comparing post-growth Raman spectra and nanotube diameters to the Kataura plot, which maps chirality based on band gap and diameter.

They noted in the paper that the results provide a basis for further research into growing specific types of nanotubes. "Now that we know what the growth rate is for a particular chirality nanotube, one could think about trying to achieve growth of that specific chirality by influencing growth conditions accordingly," Rao said. "So, basically, we now have another 'knob' to turn."

"This work is at a very early development stage, and it's all about post-nucleation," Yakobson said. "Nucleation sets what I think of as the genetic code - very primitive compared to biology - that determines the chirality and the speed of growth of a nanotube."

He said it may be possible someday to dictate the form of a nanotube as it begins to bubble up from a catalyst, "but it will take a lot of ingenuity."

Yakobson revealed a formula last year that defined the nucleation probability through the edge energies for graphene, which is basically a cut-and-flattened nanotube. But the earlier and related dislocation theory applies to the following growth, and if confirmed further may turn out to be his masterwork.

"The dislocation theory of growth is elegant and simple," Rao said. "It's still too early to say that it is the only growth mechanism, but Boris should be given plenty of credit for proposing this bold idea in the first place."

Co-authors are former Rice graduate student Tonya Leeuw Cherukuri and David Liptak, both researchers at the Air Force lab. The Air Force Office of Scientific Research and the National Research Council funded the work. Read the abstract here.

]]> Wed, 08 FEB 2012 08:55:15 AEST Washington DC (SPX) Feb 01, 2012 - The physical property of magnetism has historically been associated with metals such as iron, nickel and cobalt; however, graphite - an organic mineral made up of stacks of individual carbon sheets - has baffled researchers in recent years by showing weak signs of magnetism.

The hunt for an explanation has not been without controversy, with several research groups proposing different theories.

The most recent suggestion, published, 27 January, in the journal EPL (Europhysics Letters), has been put forward by a research group from the University of Manchester that includes Nobel prize-winning scientist Professor Sir Andre Geim.

The research group, led by Dr Irina Grigorieva, found that magnetism in many commercially available graphite crystals is down to micron-sized clusters of predominantly iron that would usually be difficult to find unless the right instruments were used in a particular way.

Finding the way to make graphite magnetic could be the first step to utilising it as a bio-compatible magnet for use in medicine and biology as effective biosensors.

To arrive at their conclusions, the researchers firstly cut up a piece of commercially-available graphite into four sections and measured the magnetisation of each piece.

Surprisingly, they found significant variations in the magnetism of each sample. It was reasonable for them to conclude that the magnetic response had to be caused by external factors, such as small impurities of another material.

To check this hypothesis, the researchers peered deep into the structure of the samples using a scanning electron microscope (SEM) - a very powerful microscope that images samples by scanning it with a beam of electrons - and found that there were unusually heavy particles positioned deep under the surface.

The majority of these particles were confirmed to be iron and titanium, using a technique known as X-ray microanalysis. As oxygen was also present, the particles were likely to be either magnetite or titanomagnetite, both of which are magnetic.

The researchers were also able to deduce how many magnetic particles would be needed, and how far apart they would need to be spaced in order to create the originally observed magnetism. The observations from their experiments agreed with their estimations, meaning the visualised magnetic particles could account for the whole magnetic signal in the sample.

Dr Grigorieva, said: "The excitement around the findings of ferromagnetism in graphite, i.e. pure carbon, is due to the fact that magnetism is not normally found in organic matter. If we can learn to create and control magnetism in carbon-based materials, especially graphene, this will be an important development for sensors and spintronics."

The paper can be downloaded here.

]]> Wed, 08 FEB 2012 08:55:15 AEST Washington DC (SPX) Jan 30, 2012 - The Air Force Office of Scientific Research (AFOSR), along with other funding agencies, helped a Rice University research team make graphene suitable for a variety of organic chemistry applications-especially the promise of advanced chemical sensors, nanoscale electronic circuits and metamaterials.

Ever since the University of Manchester's Andre Geim and Konstantin Novoselov received the 2010 Nobel Prize in Physics for their groundbreaking graphene experiments, there has been an explosion of graphene related discoveries; but graphene experimentation had been ongoing for decades and many ultimate graphene associated breakthroughs were already well under way in various labs when the Nobel committee acknowledged the significance of this new wonder material.

And one such laboratory was Dr. James Tour's at Rice, whose team found a way to attach various organic molecules to sheets of graphene, making it suitable for a range of new applications.

Starting with graphene's two-dimensional atomic scale honeycomb lattice of carbon atoms, the Rice team built upon previous graphene community discoveries to transform graphene's one sheet structure into a superlattice.

While carbon is a key part in most organic chemical reactions, graphene poses a problem in that it plays an inert role-not responding to organic chemical reactions.

The Rice team solved this dilemma by treating graphene with hydrogen. This classic hydrogenation process restructured the graphene honeycomb lattice into a two-dimensional, semiconducting superlattice called graphane.

The hydrogenation process can then be tailored to make particular patterns in the superlattice to be followed by the attachment of mission specific molecules to where those hydrogen molecules are located. These mission specific molecular catalysts allow for the possibility of a wide variety of functionality.

They can not only be used as the basis for creating graphene-based organic chemistry, but tailored for electronics and optics applications, as well as novel types of metamaterials for nanoengineering highly efficient thermoelectric devices and sensors for various chemicals or pathogens.

The beauty of this process is the promise it holds for future devices with the ability to efficiently accomplish a wide variety of highly sophisticated functions in one small affordable device.

Dr. Charles Lee, the AFOSR program manager who funded this research, notes that graphene chemistry in general can enable smart materials for many special applications and that this latest effort in particular can contribute to future electronics applications and may be a way to arrive at faster and less energy consuming electronics.

]]> Wed, 08 FEB 2012 08:55:15 AEST Riverside, CA (SPX) Jan 27, 2012 - A research team led by physicists at the University of California, Riverside has identified a property of "bilayer graphene" (BLG) that the researchers say is analogous to finding the Higgs boson in particle physics.

Graphene, nature's thinnest elastic material, is a one-atom thick sheet of carbon atoms arranged in a hexagonal lattice. Because of graphene's planar and chicken wire-like structure, sheets of it lend themselves well to stacking.

BLG is formed when two graphene sheets are stacked in a special manner. Like graphene, BLG has high current-carrying capacity, also known as high electron conductivity. The high current-carrying capacity results from the extremely high velocities that electrons can acquire in a graphene sheet.

The physicists report online Jan. 22 in Nature Nanotechnology that in investigating BLG's properties they found that when the number of electrons on the BLG sheet is close to 0, the material becomes insulating (that is, it resists flow of electrical current) - a finding that has implications for the use of graphene as an electronic material in the semiconductor and electronics industries.

"BLG becomes insulating because its electrons spontaneously organize themselves when their number is small," said Chun Ning (Jeanie) Lau, an associate professor of physics and astronomy and the lead author of the research paper. "Instead of moving around randomly, the electrons move in an orderly fashion. This is called 'spontaneous symmetry breaking' in physics, and is a very important concept since it is the same principle that 'endows' mass for particles in high energy physics."

Lau explained that a typical conductor has a huge number of electrons, which move around randomly, rather like a party with ten thousand guests with no assigned seats at dining tables. If the party only has four guests, however, then the guests will have to interact with each other and sit down at a table. Similarly, when BLG has only a few electrons the interactions cause the electrons to behave in an orderly manner.

New quantum particle
Allan MacDonald, the Sid W. Richardson Foundation Regents Chair in the Department of Physics at The University of Texas at Austin and a coauthor on the research paper, noted that team has measured the mass of a new type of massive quantum particle that can be found only inside BLG crystals.

"The physics which gives these particles their mass is closely analogous to the physics which makes the mass of a proton inside an atomic nucleus very much larger than the mass of the quarks from which it is formed," he said. "Our team's particle is made of electrons, however, not quarks."

MacDonald explained that the experiment the research team conducted was motivated by theoretical work which anticipated that new particles would emerge from the electron sea of a BLG crystal.

"Now that the eagerly anticipated particles have been found, future experiments will help settle an ongoing theoretical debate on their properties," he said.

Practical applications
An important finding of the research team is that the intrinsic "energy gap" in BLG grows with increasing magnetic field.

In solid state physics, an energy gap (or band gap) refers to an energy range in a solid where no electron states can exist. Generally, the size of the energy gap of a material determines whether it is a metal (no gap), semiconductor (small gap) or insulator (large gap). The presence of an energy gap in silicon is critical to the semiconductor industry since, for digital applications, engineers need to turn the device 'on' or conductive, and 'off' or insulating.

Single layer graphene (SLG) is gapless, however, and cannot be completely turned off because regardless of the number of electrons on SLG, it always remains metallic and a conductor.

"This is terribly disadvantageous from an electronics point of view," said Lau, a member of UC Riverside's Center for Nanoscale Science and Engineering. "BLG, on the other hand, can in fact be turned off. Our research is in the initial phase, and, presently, the band gap is still too small for practical applications. What is tremendously exciting though is that this work suggests a promising route - trilayer graphene and tetralayer graphene, which are likely to have much larger energy gaps that can be used for digital and infrared technologies. We already have begun working with these materials."

Lau and MacDonald were joined in the research by J. Velasco Jr. (the first author of the research paper), L. Jing, W. Bao, Y. Lee, P. Kratz, V. Aji, M. Bockrath, and C. Varma at UCR; R. Stillwell and D. Smirnov at the National High Magnetic Field Laboratory, Tallahassee, Fla.; and Fan Zhang and J. Jung at The University of Texas at Austin. ]]> Wed, 08 FEB 2012 08:55:15 AEST Washington DC (SPX) Jan 27, 2012 - Despite extensive investment in nanotechnology and increasing commercialization over the last decade, insufficient understanding remains about the environmental, health, and safety aspects of nanomaterials.

Without a coordinated research plan to help guide efforts to manage and avoid potential risks, the future of safe and sustainable nanotechnology is uncertain, says a new report from the National Research Council.

The report presents a strategic approach for developing research and a scientific infrastructure needed to address potential health and environmental risks of nanomaterials. Its effective implementation would require sufficient management and budgetary authority to direct research across federal agencies.

Nanoscale engineering manipulates materials at the molecular level to create structures with unique and useful properties - materials that are both very strong and very light, for example.

Many of the products containing nanomaterials on the market now are for skin care and cosmetics, but nanomaterials are also increasingly being used in products ranging from medical therapies to food additives to electronics. In 2009, developers generated $1 billion from the sale of nanomaterials, and the market for products that rely on these materials is expected to grow to $3 trillion by 2015.

The committee that wrote the report found that over the last seven years there has been considerable effort internationally to identify research needs for the development and safe use of nanotechnology, including those of the National Nanotechnology Initiative (NNI), which coordinates U.S. federal investments in nanoscale research and development.

However, there has not been sufficient linkage between research and research findings and the creation of strategies to prevent and manage any risks. For instance, little progress has been made on the effects of ingested nanomaterials on human health and other potential health and environmental effects of complex nanomaterials that are expected to enter the market over the next decade.

Therefore, there is the need for a research strategy that is independent of any one stakeholder group, has human and environmental health as its primary focus, builds on past efforts, and is flexible in anticipating and adjusting to emerging challenges, the committee said.

Because the number of products containing nanoscale materials is expected to explode, and future exposure scenarios may not resemble those of today, selecting target materials to study on the basis of existing market size - as is the practice now - is problematic. To help guide research, the committee noted the following four research categories, which should be addressed within five years:

+ identify and quantify the nanomaterials being released and the populations and environments being exposed;

+ understand processes that affect both potential hazards and exposure;

+ examine nanomaterial interactions in complex systems ranging from subcellular to ecosystems; and

+ support an adaptive research and knowledge infrastructure for accelerating progress and providing rapid feedback to advance research.

While surveying the existing resources for research, the committee acknowledged a gap between funding and the level of activity required to support the committee's strategy.

The committee concluded that any reduction in the current funding level of approximately $120 million per year over the next five years for health and environmental risk research by federal agencies would be a setback to nanomaterials risk research.

Moreover, additional modest resources from public, private, and international initiatives are needed in critical areas - informatics, nanomaterial characterization, benchmarking nanomaterials, characterization of sources, and development of networks for supporting collaborative research - to derive maximum strategic value from the research investments.

Implementation of the strategy should also include the integration of domestic and international participants involved in nanotechnology-related research, including the NNI, federal agencies, the private sector, non-governmental organizations, and the academic community.

The committee said that the current structure of the NNI - which has only coordinating functions across federal agencies and no top-down budgetary or management authority to direct nanotechnology-related environmental, health, and safety research - hinders its accountability for effective implementation.

In addition, there is concern that dual and potentially conflicting roles of the NNI, such as developing and promoting nanotechnology while identifying and mitigating risks that arise from its use, impede application and evaluation of health and environmental risk research.

To carry out the research strategy effectively, a clear separation of management and budgetary authority and accountability between promoting nanotechnology and assessing potential environmental and safety risks is essential.

Pre-publication copies of A Research Strategy for Environmental, Health, and Safety Aspects of Engineered Nanomaterials are available from the National Academies Press

]]> Wed, 08 FEB 2012 08:55:15 AEST Houston TX (SPX) Jan 24, 2012 - Graphene is largely transparent to the eye and, as it turns out, largely transparent to water. A new study by scientists at Rice University and Rensselaer Polytechnic Institute (RPI) has determined that gold, copper and silicon get just as wet when clad by a single continuous layer of graphene as they would without.

The research, reported this week in the online edition of Nature Materials, is significant for scientists learning to fine-tune surface coatings for a variety of applications.

"The extreme thinness of graphene makes it a totally non-invasive coating," said Pulickel Ajayan, Rice's Benjamin M. and Mary Greenwood Anderson Professor in Mechanical Engineering and Materials Science and of chemistry.

"A drop of water sitting on a surface 'sees through' the graphene layers and conforms to the wetting forces dictated by the surface beneath. It's quite an interesting phenomenon unseen in any other coatings and once again proves that graphene is really unique in many different ways." Ajayan is co-principal investigator of the study with Nikhil Koratkar, a professor of mechanical, aerospace and nuclear engineering at RPI.

A typical surface of graphite, the form of carbon most commonly known as pencil lead, should be hydrophobic, Ajayan said.

But in the present study, the researchers found to their surprise that a single-atom-thick layer of the carbon lattice presents a negligible barrier between water and a hydrophilic - water-loving - surface. Piling on more layers reduces wetting; at about six layers, graphene essentially becomes graphite.

An interesting aspect of the study, Ajayan said, may be the ability to change such surface properties as conductivity while retaining wetting characteristics.

Because pure graphene is highly conductive, the discovery could lead to a new class of conductive, yet impermeable, surface coatings, he said.

The caveat is that wetting transparency was observed only on surfaces (most metals and silicon) where interaction with water is dominated by weak van der Waals forces, and not for materials like glass, where wettability is dominated by strong chemical bonding, the team reported.

But such applications as condensation heat transfer - integral to heating, cooling, dehumidifying, water harvesting and many industrial processes - may benefit greatly from the discovery, according to the paper. Copper is commonly used for its high thermal conductivity, but it corrodes easily.

The team coated a copper sample with a single layer of graphene and found the subnanometer barrier protected the copper from oxidation with no impact on its interaction with water; in fact, it enhanced the copper's thermal effectiveness by 30 to 40 percent.

"The finding is interesting from a fundamental point of view as well as for practical uses," Ajayan said.

"Graphene could be one of a kind as a coating, allowing the intrinsic physical nature of surfaces, such as wetting and optical properties, to be retained while altering other specific functionalities like conductivity."

The paper's co-authors are Rice graduate student Hemtej Gullapalli, RPI graduate students Javad Rafiee, Xi Mi, Abhay Thomas and Fazel Yavari, and Yunfeng Shi, an assistant professor of materials science and engineering at RPI.

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