Tailored optical material from DNA: Nano spiral staircases modify light

There was a lot of excitement a few years ago following the discovery of the DNA origami technique. The approach could be used to build nanoparticles of a given shape and size. However, real applications, such as nano-tweezers, remained out of reach. An international team of researchers led by Professor Tim Liedl of the Ludwig-Maximillians-Universitaet Muenchen and Professor Friedrich Simmel of the Technische Universitaet Muenchen have now succeeded in building nanoparticles using optically active DNA building blocks that can be used to modify light in very specific ways.

Coupling light and nanostructures may help significantly reduce the size of optical sensors for medical and environmental applications, while at the same time making them more sensitive. However, the size of a light wave stretching out over 400 to 800 nanometers is gigantic in comparison to nanostructures of only a few nanometers. Yet in theory, when tiniest structures work together in very specific ways, even small objects can interact very well with light. Unfortunately it is not possible to produce the requisite three-dimensional structures with nano-scale precision in sufficient quantities and purity using conventional methods.

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A team of scientists from Technische Universitaet Muenchen and Ludwig-Maximilians-Universitaet Muenchen succeeded in building up nano spiral staircases from artificial DNA using the DNA-origami method. The DNA strand carries nine gold particles which lead to strong interactions with circular polarized visible light. Credit: Animation: Tim Liedl /LMU

"With DNA origami, we have now found a methodology that fulfills all of these requirements. It makes it possible to define in advance and with nanometer precision the three-dimensional shape of the object being created," says Professor Friedrich Simmel, who holds the Chair for Biomolecular Systems and Bionanotechnology at the TU Muenchen. Programmed solely using the sequence of basic building blocks, the nano-elements fold themselves into the desired structures." Friedrich Simmel's team successfully built nano spiral staircases 57 nanometers high and 34 nanometers in diameter with 10 nanometer gold particles attached at regular intervals.

On the surface of the gold particles the electrons react with the electromagnetic field of the light. The small clearance between the particles ensures that the gold particles of a DNA strand work in unison, thereby amplifying the interactions many fold. Professor Alexander O. Govorov, theoretical physicist at the Ohio State University in Athens, USA, had predicted that the effect should depend on the spacing, size and composition of the metal particles. Using the DNA origami method, the Munich physicists built up nanostructures in which they varied these parameters.

The results of these experiments confirm the predictions of their colleagues in every regard: Aqueous solutions of right-handed and left-handed nano spiral staircases differ visibly in their interactions with circular polarized light. Spiral staircases with large particles show a significantly stronger optical response than those with small particles. The chemical composition of the particles also had a large effect: When the gold particles were coated with a layer of silver, the optical resonance shifted from the red to the shorter wave blue domain.

By combining theoretical calculations and the possibilities of DNA origami, the researchers are now able to produce nano-optical materials with precisely specified characteristics. Professor Tim Liedl describes the path the research might follow: "We will now investigate whether we can use this method to influence the refraction index of the materials we manufacture. Materials with a negative refractive index could be used to develop novel optical lens systems – so-called super lenses."

More information: DNA-based Self-Assembly of Chiral Plasmonic Nanostructures with Tailored Optical Response. Anton Kuzyk, Robert Schreiber, Zhiyuan Fan, Günther Pardatscher, Eva-Maria Roller, Alexander Högele, Friedrich C. Simmel, Alexander O. Govorov und Tim Liedl.
Nature Volume 482, 7389, pp 311-314. DOI: 10.1038/nature10889

Provided by Technische Universitaet Muenchen

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Stay super-dry with Nokia's nanotechnology

The drop of water falls, bounces, and rolls away without trace – leaving the leaf clean and water repellant.

Now scientists at the Nokia Research Center in Cambridge believe they may be able to replicate the same effect on your phone, using nanotechnology.

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Chris Bower, the Principal Scientist at the NRC in Cambridge, sums it up:

“Like many scientists we are trying to copy what nature has been doing perfectly for thousands of years.”

To achieve the water-resistant, and stain-resistant, qualities of a lotus leaf the team at NRC is in the final stages of designing a Superhydrophobic coating which would be applied to the outside of a mobile phone.

If you’ve ever used a Teflon non-stick frying pan you’ll be familiar with ordinary hydrophobic coatings already available– but Superhydrophobic coatings add  a nanostructure to trap a layer of air over the surface which ensures that a drop of water never reaches it.

Chris Bower produces two hand-held Nokia maze tiles to demonstrate the difference. First he drops water on a surface that has no coating at all: “The water spreads, like this, and coats the surface,” he says.

Then Bower makes a drop of water fall on the maze with the ordinary hydrophobic coating. As predicted, the water holds its form, and you can guide it – a bit uncertainly – around the maze.

Trying the maze with the Superhydrophobic coating makes a dramatic difference:  the water drops and almost bounces up again, beading tightly together – and then almost skids over the surface.     

Bower explains: “A hydrophobic coating – like Teflon – has a low surface energy and a high contact angle of 120 deg, which makes water form discrete droplets on the surface.”

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He goes on to explain that Superhydrophobic coatings have a contact angle that can approach 180 degrees – and the liquid forms discrete drops that literally bounce off the surface:

“The difference is the nano-structured coating, trapping air at the interface, that makes sure the liquid never actually touches the surface.”

Making the nano-coating can be done in a variety of ways: “There are very thin nano-coatings which essentially just deposit a layer of molecules, or more conventional coatings of fluoropolymers or silicones which can be several micrometers thick. It could be deposited from a solution, spray coated, or dip coated.”

The Team at the NRC in Cambridge have set up a demonstration of a Nokia Lumia 710 which has been treated with a Superhydrophobic coating made in their labs. 

The water drops onto the Superhydrophobic coated Lumia710, bounces, and rolls off – falling onto a thin layer of Graphene beneath that has also been treated with a Superhydrophobic coating. 

In this case the Graphene layer is acting as a sensor which detects the water drop and triggers a high speed camera to capture slow-motion movies so you can see the droplet bouncing off a Superhydrophobic surface.

Bower estimates that Graphene is likely to have a significant impact on mobile devices:

“Graphene is the ultimate surface, it has no bulk so it is very sensitive. Its the strongest known material, its the hardest known material, it has electric performance 100 times better than silicon.”

Graphene is already being used in anti-static coatings, and Bower says it will probably be used as a direct replacement for the transparent conductor Indium Tin Oxide in display screens.  

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So what can a Superhydrophobic coating on your phone actually do?

Bower can’t guarantee that you can take your mobile diving in deeps seas and it will emerge unscathed – the holes and lines in a mobile phone make it hard to guarantee it could ever be completely waterproof.

But a Superhydrophobic coating makes it likely that you can drop your phone in a bowl of water, or in a cup of coffee, and it will survive.

“It will improve the water resistance, fingerprint resistance and antireflection properties of the device.”

Although the technology is in place to coat the inside of a phone already, Bower says that it is much more difficult to create a coating that is strong enough to use as an external coating:  

“The biggest challenge is making nanostructures robust enough to withstand every day wear and tear. You could put a superhydrophobic coating inside a device now because people can’t degrade it, it can’t get knocked around in your pocket. To put it on the outside is much, much tougher. But you want it on the outside because that’s where you see the effects of keeping your phone really clean.”

The team at the Nokia NRC in Cambridge are “pretty close”, he says, to perfecting a robust exterior Superhydrophobic coating.

Superhydrophobia is only one part of building a new form of phones. At the Cambridge NRC the team are working on using nano-technology to make phones that not only survive being immersed in liquids, but that can also stretch, bend and flex: 

“We’re creating a new kind of interactivity, Bower says, “A whole new haptic language for how you use your phone.”

Even so, Bower adds, nature still triumphs. No one has yet created a Superhydrophobic coating that can repair itself, like a lotus leaf. That’s the challenge that still lies ahead.

Source: Nokia Conversations

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Diamond brightens the performance of electronic devices

Two new studies performed at the U.S. Department of Energy’s Argonne National Laboratory have revealed a new pathway for materials scientists to use previously unexplored properties of nanocrystalline-diamond thin films. While the properties of diamond thin films are relatively well-understood, the new discovery could dramatically improve the performance of certain types of integrated circuits by reducing their "thermal budget."

For decades, engineers have sought to build more efficient electronic devices by reducing the size of their components. In the process of doing so, however, researchers have reached a "thermal bottleneck," said Argonne nanoscientist Anirudha Sumant.

In a thermal bottleneck, the excess heat generated in the device causes undesirable effects that affect its performance. "Unless we come-up with innovative ways to suck the heat off of our electronics, we are pretty much stuck with this bottleneck," Sumant explained.

The unusually attractive thermal properties of diamond thin films have led scientists to suggest using this material as a heat sink that could be integrated with a number of different semiconducting materials. However, the deposition temperatures for the diamond films typically exceed 800 degrees Celsius—roughly 1500 degrees Fahrenheit, which limits the feasibility of this approach.

"The name of the game is to produce diamond films at the lowest possible temperature. If I can grow the films at 400 degrees, it makes it possible for me to integrate this material with a whole range of other semiconductor materials," Sumant said.

By using a new technique that altered the deposition process of the diamond films, Sumant and his colleagues at Argonne’s Center for Nanoscale Materials were able to both reduce the temperature to close to 400 degrees Celsius and to tune the thermal properties of the diamond films by controlling their grain size. This permitted the eventual combination of the diamond with two other important materials: graphene and gallium nitride.

According to Sumant, diamond has much better heat conduction properties than silicon or silicon oxide, which were traditionally used for fabrication of graphene devices. As a result of better heat removal, graphene devices fabricated on diamond can sustain much higher current densities.

In the other study, Sumant used the same technology to combine diamond thin films with gallium nitride, which is used extensively in high-power light emitting devices (LED). After depositing a 300 nm-thick diamond film on a gallium nitride substrate, Sumant and his colleagues noticed a considerable improvement in the thermal performance. Because a difference within an integrated circuit of just a few degrees can cause a noticeable change in performance, he called this result "remarkable."

"The common link between these experiments is that we’re finding new ways of dissipating heat more effectively while using less energy, which is the key," Sumant said. "These processes are crucial for industry as they look for ways to overcome conventional limits on semiconducting circuits and pursue the next generation of electronics."

The results of the two studies were reported in Nano Letters and Advanced Functional Materials. Both of these studies were carried out in collaboration with Prof. Alexander Balandin at the University of California-Riverside and his graduate students Jie Yu, Guanxiong Liu and Dr. Vivek Goyal, a recent Ph.D. graduate.

Funding for the research conducted at the Center for Nanoscale Materials was provided by the Basic Energy Sciences program of the U.S. Department of Energy’s Office of Science.

More information: The papers can be found online at:
http://onlinelibra … 786/abstract
http://pubs.acs.or … 21/nl204545q

Provided by Argonne National Laboratory (news : web)

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Two scientific articles on graphene-based sensors prove popular in the research community

The first article is on creating a glucose detector by combining graphene with a glucose-sensing enzyme and chitosan. Because graphene has a high surface-to-volume ratio and excellent electron conductivity, the researchers immobilized enzymes in graphene/chitosan nanocomposite film and demonstrated the excellent sensitivity and stability for measuring glucose. This article, in Biosensors and Bioelectronics in 2009, has been cited 128 times, and is in the list of most-cite articles of the journal.

In another popular article, the authors reviewed graphene-based sensors. They covered the fundamental science, including how electrons move between the graphene electrode and the enzyme without mediators. They also discuss graphene-based electrodes for detecting dopamine and other biomolecules for industrial and clinical uses. Scientists have cited the paper 123 times, and it was the second most accessed article in Wiley's Electroanalysis in February 2012.

More information: Shao Y, J et al.  2010.  "Graphene Based Electrochemical Sensors and Biosensors: A Review."  Electroanalysis 22(10):1027-1036.  doi:10.1002/elan.200900571

Kang X, et al.  2009.  "Glucose Oxidase-Graphene-Chitosan Modified Electrode for Direct Electrochemistry and Glucose Sensing."  Biosensors and Bioelectronics 25(4):901-905.  doi:10.1016/j.bios.2009.09.004

Provided by Pacific Northwest National Laboratory (news : web)

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Barrier to faster graphene devices identified and suppressed

This single-atom-thick honeycomb of carbon atoms is lighter than aluminum, stronger than steel and conducts heat and electricity better than copper. As a result, scientists around the world are trying to turn it into better computer displays, solar panels, touch screens, integrated circuits and biomedical sensors, among other possible applications. However, it has proven extremely difficult to reliably create graphene-based devices that live up to its electrical potential when operating at room temperature and pressure.

Now, writing in the Mar. 13 issue of the journal Nature Communications, a team of Vanderbilt physicists reports that they have nailed down the source of the interference inhibiting the rapid flow of electrons through graphene-based devices and found a way to suppress it. This allowed them to achieve record-levels of room-temperature electron mobility – the measure of the speed that electrons travel through a material – three times greater than those reported in previous graphene-based devices.

According to the experts, graphene may have the highest electron mobility of any known material. In practice, however, the measured levels of mobility, while significantly higher than in other materials like silicon, have been considerably below its potential.

"The problem is that, when you make graphene, you don't get just graphene. You also get a lot of other stuff," said Kirill Bolotin, assistant professor of physics, who conducted the study with Research Associate A.K.M. Newaz. "Graphene is extraordinarily susceptible to external influences so the electrical fields created by charged impurities on its surface scatter the electrons traveling through the graphene sheets, making graphene-based transistors operate slower and heat up more."

A number of researchers had proposed that the charged impurities that are omnipresent on the surface of graphene were the main culprits, but it wasn't completely certain. Also, several other theories had been advanced to explain the phenomenon.

"Our study shows without question that the charged crap is the problem and, if you want to make better graphene devices, it is the enemy that you need to fight," Bolotin said.

At the same time, the experiment didn't find evidence supporting one of the alternative theories, that ripples in the graphene sheets were a significant source of electron scattering

In order to get a handle on the mobility problem, Bolotin's team suspended sheets of graphene in a series of different liquids and measured the material's electric transport properties. They found that graphene's electron mobility is dramatically increased when graphene is submerged in electrically neutral liquids that can absorb large amounts of electrical energy (have large dielectric constants). They achieved the record-level mobility of 60,000 using anisole, a colorless liquid with a pleasant, aromatic odor used chiefly in perfumery.

"These liquids suppress the electrical fields from the impurities, allowing the electrons to flow with fewer obstructions," Bolotin said.

Now that the source of the degradation in electrical performance of graphene has been clearly identified, it should be possible to come up with reliable device designs, Bolotin said.

According to the physicist, there is also a potential advantage to graphene's extraordinary sensitivity to its environment that can be exploited. It should make extremely sensitive sensors of various types and, because it is made entirely of carbon, it is biocompatible and so should be ideal for biological sensors.

Provided by Vanderbilt University (news : web)

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Touch of gold improves nanoparticle fuel-cell reactions

Now chemists at Brown University have created a triple-headed metallic nanoparticle that they say outperforms and outlasts all others at the anode end in formic-acid fuel-cell reactions. In a paper published in the Journal of the American Chemical Society, the researchers report a 4-nanometer iron-platinum-gold nanoparticle (FePtAu), with a tetragonal crystal structure, generates higher current per unit of mass than any other nanoparticle catalyst tested. Moreover, the trimetallic nanoparticle at Brown performs nearly as well after 13 hours as it did at the start. By contrast, another nanoparticle assembly tested under identical conditions lost nearly 90 percent of its performance in just one-quarter of the time.

"We've developed a formic acid fuel-cell catalyst that is the best to have been created and tested so far," said Shouheng Sun, chemistry professor at Brown and corresponding author on the paper. "It has good durability as well as good activity."

Gold plays key roles in the reaction. First, it acts as a community organizer of sorts, leading the iron and platinum atoms into neat, uniform layers within the nanoparticle. The gold atoms then exit the stage, binding to the outer surface of the nanoparticle assembly. Gold is effective at ordering the iron and platinum atoms because the gold atoms create extra space within the nanoparticle sphere at the outset. When the gold atoms diffuse from the space upon heating, they create more room for the iron and platinum atoms to assemble themselves. Gold creates the crystallization chemists want in the nanoparticle assembly at lower temperature.

Gold also removes carbon monoxide (CO) from the reaction by catalyzing its oxidation. Carbon monoxide, other than being dangerous to breathe, binds well to iron and platinum atoms, gumming up the reaction. By essentially scrubbing it from the reaction, gold improves the performance of the iron-platinum catalyst. The team decided to try gold after reading in the literature that gold nanoparticles were effective at oxidizing carbon monoxide — so effective, in fact, that gold nanoparticles had been incorporated into the helmets of Japanese firefighters. Indeed, the Brown team's triple-headed metallic nanoparticles worked just as well at removing CO in the oxidation of formic acid, although it is unclear specifically why.

The authors also highlight the importance of creating an ordered crystal structure for the nanoparticle catalyst. Gold helps researchers get a crystal structure called "face-centered-tetragonal," a four-sided shape in which iron and platinum atoms essentially are forced to occupy specific positions in the structure, creating more order. By imposing atomic order, the iron and platinum layers bind more tightly in the structure, thus making the assembly more stable and durable, essential to better-performing and longer-lasting catalysts.

In experiments, the FePtAu catalyst reached 2809.9 mA/mg Pt (mass-activity, or current generated per milligram of platinum), "which is the highest among all NP (nanoparticle) catalysts ever reported," the Brown researchers write. After 13 hours, the FePtAu nanoparticle has a mass activity of 2600mA/mg Pt, or 93 percent of its original performance value. In comparison, the scientists write, the well-received platinum-bismuth nanoparticle has a mass activity of about 1720mA/mg Pt under identical experiments, and is four times less active when measured for durability.

The researchers note that other metals may be substituted for gold in the nanoparticle catalyst to improve the catalyst's performance and durability.

"This communication presents a new structure-control strategy to tune and optimize nanoparticle catalysis for fuel oxidations," the researchers write.

Sen Zhang, a third-year graduate student in Sun's lab, helped with the nanoparticle design and synthesis. Shaojun Guo, a postdoctoral fellow in Sun's lab performed electrochemical oxidation experiments. Huiyuan Zhu, a second-year graduate student in Sun's lab, synthesized the FePt nanoparticles and ran control experiments. The other contributing author is Dong Su from the Center for Functional Nanomaterials at Brookhaven National Laboratory, who analyzed the structure of the nanoparticle catalyst using the advanced electron microscopy facilities there.

Provided by Brown University (news : web)

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Using graphene foam to detect subtle traces of hazardous gases, explosives

A student in the Department of Mechanical, Aerospace, and Nuclear Engineering at Rensselaer, Yavari’s sensor opens the door to a new generation of gas detectors for use by bomb squads, defense and law enforcement officials, as well as in industrial settings. For this innovation, Yavari has been named the winner of the 2012 $30,000 Lemelson-MIT Rensselaer Student Prize. He is among the three 2012 $30,000 Lemelson-MIT Collegiate Student Prize winners announced today.

“Innovating solutions to the challenges of tomorrow requires a certain kind of individual—one who is ready and willing to take calculated risks and seize promising opportunities. These architects of change push forward the state of the art, and can affect progress on a global scale,” said Rensselaer President Shirley Ann Jackson. “Fazel Yavari, with his creative exploitation of graphene to create a promising new gas sensor, is a stellar example of such an architect of change. We congratulate him, and applaud all of the winners and finalists of the Lemelson-MIT Collegiate Student Prize for innovating a bolder, brighter future.”

Yavari is the sixth recipient of the Lemelson-MIT Rensselaer Student Prize. First given in 2007, the prize is awarded annually to a Rensselaer senior or graduate student who has created or improved a product or process, applied a technology in a new way, redesigned a system, or demonstrated remarkable inventiveness in other ways.

“This year’s Lemelson-MIT Collegiate Student Prize winners and finalists from MIT, RPI, and UIUC are helping to fulfill the country’s need for innovation. These students’ passion for invention and their ideas will improve people’s lives around the world,” states Joshua Schuler, executive director of the Lemelson-MIT Program. “We applaud their accomplishments that will also undoubtedly inspire future generations of inventors.”

Graphene-Powered Gas Detection

With his project, titled “High Sensitivity Detection of Hazardous Gases Using a Graphene Foam Network,” Yavari overcomes the shortcomings that have prevented nanostructure-based gas detectors from reaching the marketplace.

Detecting trace amounts of hazardous gases present within air is a critical safety and health consideration in many different situations, from industrial manufacturing and chemical processing to bomb detection and environmental monitoring. Conventional gas sensors are either too bulky and expensive, which limits their use in many applications, or they are not sensitive enough to detect trace amounts of gases. Also, many commercial sensors require very high temperatures in order to adequately detect gases, and in turn require large amounts of power.

Researchers have long sought to leverage the power of nanomaterials for gas detection. Individual nanostructures like graphene, an atom-thick sheet of carbon atoms arranged like a nanoscale chicken-wire fence, are extremely sensitive to chemical changes. However, creating a device based on a single nanostructure is costly, highly complex, and the resulting devices are extremely fragile, prone to failure, and offer inconsistent readings.

Yavari has overcome these hurdles and created a device that combines the high sensitivity of a nanostructured material with the durability, low price, and ease of use of a macroscopic device. His new graphene foam sensor, about the size of a postage stamp and as thick as felt, works at room temperature, is considerably less expensive to make, and still very sensitive to tiny amounts of gases. The sensor works by reading the changes in the graphene foam’s electrical conductivity as it encounters gas particles and they stick to the foam’s surface. Another benefit of Yavari’s device is its ability to quickly and easily remove these stuck chemicals by applying a small electric current.

The new graphene foam sensor has been engineered to detect the gases ammonia and nitrogen dioxide, but can be configured to work with other gases as well. Ammonia detection is important as the gas is commonly used in industrial processes, and ammonia is a byproduct of several explosives. Nitrogen dioxide is also a byproduct of several explosives, as well as a closely monitored pollutant found in combustion exhaust and auto emissions. Yavari’s sensor can detect both gases in quantities as small as 0.5 parts-per-million at room temperature.  

Provided by Rensselaer Polytechnic Institute (news : web)

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Nanotube technology leading to fast, lower-cost medical diagnostics

The new findings have almost tripled the speed of prototype nano-biosensors, and should find applications not only in medicine but in toxicology, environmental monitoring, new drug development and other fields.

The research was just reported in Lab on a Chip, a professional journal. More refinements are necessary before the systems are ready for commercial production, scientists say, but they hold great potential.

“With these types of sensors, it should be possible to do many medical lab tests in minutes, allowing the doctor to make a diagnosis during a single office visit,” said Ethan Minot, an OSU assistant professor of physics. “Many existing tests take days, cost quite a bit and require trained laboratory technicians.

“This approach should accomplish the same thing with a hand-held sensor, and might cut the cost of an existing $50 lab test to about $1,” he said.

The key to the new technology, the researchers say, is the unusual capability of carbon nanotubes. An outgrowth of nanotechnology, which deals with extraordinarily small particles near the molecular level, these nanotubes are long, hollow structures that have unique mechanical, optical and electronic properties, and are finding many applications.

In this case, carbon nanotubes can be used to detect a protein on the surface of a sensor. The nanotubes change their electrical resistance when a protein lands on them, and the extent of this change can be measured to determine the presence of a particular protein – such as serum and ductal protein biomarkers that may be indicators of breast cancer.

The newest advance was the creation of a way to keep proteins from sticking to other surfaces, like fluid sticking to the wall of a pipe. By finding a way to essentially “grease the pipe,” OSU researchers were able to speed the sensing process by 2.5 times.

Further work is needed to improve the selective binding of proteins, the scientists said, before it is ready to develop into commercial biosensors.

“Electronic detection of blood-borne biomarker proteins offers the exciting possibility of point-of-care medical diagnostics,” the researchers wrote in their study. “Ideally such electronic biosensor devices would be low-cost and would quantify multiple biomarkers within a few minutes.”

This work was a collaboration of researchers in the OSU Department of Physics, Department of Chemistry, and the University of California at Santa Barbara. A co-author was Vincent Remcho, professor and interim dean of the OSU College of Science, and a national expert in new biosensing technology.

The research was supported by the U.S. Army Research Laboratory through the Oregon Nanoscience and Microtechnologies Institute.

Provided by Oregon State University (news : web)

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All-inorganic nanocrystals boost infrared emission

Conventional methods for synthesizing nanocrystals include capping them with long-chain organic molecules to control particle size, morphology, and stability. But molecular vibrations associated with those ligands sap the particles' excitation energies, reducing IR emission efficiency and stability.

In a wholly unique approach, the research team devised a solution-phase method for making core/shell nanocrystals in which conventional organic groups are replaced with inorganic As2S3 ligands. These all-inorganic particles are then mildly heated to convert the ionic ligands to an IR-transparent As2S3 matrix. Low-temperature integration of nanocrystals into transparent inorganic matrices is an important step for their optical and optoelectronic integration The new data suggest that dielectric screening is the major cause of slow radiative rates in conventional lead chalcogenide nanocrystals. Effective integration reduces the dielectric contrast and enables fast radiative rates. This is especially useful for nanocrystals emitting in the IR region where few host materials can provide good optical transparency.

More information: M.V. Kovalenko et al., " Inorganically Functionalized PbS-CdS Colloidal Nanocrystals: Integration into Amorphous Chalcogenide Glass and Luminescent Properties," J. Am. Chem. Soc, 134, 2457-2460 (2012) (online)

Provided by Argonne National Laboratory (news : web)

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Molecular graphene heralds new era of 'designer electrons'

"The behavior of electrons in materials is at the heart of essentially all of today's technologies," said Hari Manoharan, associate professor of physics at Stanford and a member of SLAC's Stanford Institute for Materials and Energy Sciences, who led the research. "We're now able to tune the fundamental properties of electrons so they behave in ways rarely seen in ordinary materials."

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Pictured is a version of molecular graphene in which the electrons are tuned to respond as if they're experiencing a very high magnetic field (red areas) when none is present. Scientists from Stanford and SLAC National Accelerator Laboratory calculated the positions where carbon atoms in graphene should be to make its electrons believe they were being exposed to a magnetic field of 60 Tesla, more than 30 percent higher than the strongest continuous magnetic field ever achieved on Earth (a 1 Tesla magnetic field is about 20,000 times stronger than the Earth?s). The researchers then used a scanning tunneling microscope to place carbon monoxide molecules (black circles) at precisely those positions. The electrons responded by behaving exactly as expected -- as if they were exposed to a real field. Credit: Manoharan Lab, Stanford/SLAC

Their first examples, reported today in Nature, were hand-crafted, honeycomb-shaped structures inspired by graphene, a pure form of carbon that has been widely heralded for its potential in future electronics. Initially, the electrons in this structure had graphene-like properties; for example, unlike ordinary electrons, they had no mass and traveled as if they were moving at the speed of light in a vacuum. But researchers were then able to tune these electrons in ways that are difficult to do in real graphene. This video is not supported by your browser at this time.

This video shows carbon monoxide molecules (black circles) being moved one at a time by a scanning tunneling microscope into the hexagonal "molecular graphene" arrangement. The molecules repel the free-flowing electrons (yellow-orange) on the copper surface, forcing them into a honeycomb pattern. Credit: Manoharan Lab, Stanford/SLAC

To make the structure, which Manoharan calls molecular graphene, the scientists use a scanning tunneling microscope to place individual carbon monoxide molecules on a perfectly smooth copper surface. The carbon monoxide repels the free-flowing electrons on the copper surface and forces them into a honeycomb pattern, where they behave like graphene electrons.

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This graphic shows the effect that a specific pattern of carbon monoxide molecules (black/red) has on free-flowing electrons (orange/yellow) atop a copper surface. Ordinarily the electrons behave as simple plane waves (background). But the electrons are repelled by the carbon monoxide molecules, placed here in a hexagonal pattern. This forces the electrons into a honeycomb shape (foreground) mimicking the electronic structure of graphene, a pure form of carbon that has been widely heralded for its potential in future electronics. The molecules are precisely positioned with the tip of a scanning tunneling microscope (dark blue). Image credit: Hari Manoharan / Stanford University.

To tune the electrons' properties, the researchers repositioned the carbon monoxide molecules on the surface; this changed the symmetry of the electron flow. In some configurations, electrons acted as if they had been exposed to a magnetic or electric field. In others, researchers were able to finely tune the density of electrons on the surface by introducing defects or impurities. By writing complex patterns that mimicked changes in carbon-carbon bond lengths and strengths in graphene, the researchers were able to restore the electrons' mass in small, selected areas. This video is not supported by your browser at this time.

Molecular Manipulation. An individual carbon monoxide molecule (black/red) on the copper surface (yellow atoms) is positioned by the scanning tunneling microscope tip (comprised of iridium atoms, magenta). To manipulate the molecule, the quantum mechanical tunneling conditions are changed until the tip exerts an attractive force upon the molecule. The tip drags the molecule from its initial position to a desired final position. Once the molecule reaches its final position, the tunneling conditions are changed back to normal conditions suitable for imaging rather than manipulation. This process is repeated hundreds of times to create a molecular graphene lattice.

"One of the wildest things we did was to make the electrons think they are in a huge magnetic field when, in fact, no real field had been applied," Manoharan said. Guided by the theory developed by co-author Francisco Guinea of Spain, the Stanford team calculated the positions where carbon atoms in graphene should be to make its electrons believe they were being exposed to magnetic fields ranging from zero to 60 Tesla, more than 30 percent higher than the strongest continuous magnetic field ever achieved on Earth. The researchers then moved carbon monoxide molecules to steer the electrons into precisely those positions, and the electrons responded by behaving exactly as predicted – as if they had been exposed to a real field. This video is not supported by your browser at this time.

Tunable Pseudomagnetic Field. This video shows the progression of different molecular graphene structures that produce "phantom" magnetic fields of 0, 15, 30, 45 and 60 Tesla. The strongest continuous magnetic field actually achieved on Earth is 45 Tesla. (A 1 Tesla magnetic field is about 20,000 times stronger than the Earth's.) Each particular arrangement of carbon monoxide molecules (black circles) on a copper surface causes the copper's surface electrons (yellow-orange) to behave as if they're experiencing a very high magnetic field, although none is actually present.

"Our new approach is a powerful new test bed for physics," Manoharan said. "Molecular graphene is just the first in a series of possible designer structures. We expect that our research will ultimately identify new nanoscale materials with useful electronic properties."

Provided by SLAC National Accelerator Laboratory (news : web)

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Graphene and DNA: 'Wonder material' may hold key to fast, inexpensive genetic sequencing

But when scientists found a way—using, essentially, a piece of ordinary sticky tape—to peel off a layer of graphite that was just a single atom thick, they called the two-dimensional material graphene and, in 2010, won the Nobel Prize in physics for the discovery.

Now, researchers at the University of Delaware have conducted high-performance computer modeling to investigate a new approach for ultrafast DNA sequencing based on tiny holes, called nanopores, drilled into a sheet of graphene.

"Graphene is a two-dimensional sheet of carbon atoms arranged in a honeycomb pattern" Branislav Nikolic, associate professor of physics and astronomy, said. "The mechanical stability of graphene makes it possible to use an electron beam to sculpt a nanopore in a suspended sheet of graphene, as demonstrated in 2008 by Marija Drndic at the University of Pennsylvania.”

Graphene has been among the fastest-growing areas of study in nanoscience and technology over the past five years, Nikolic said. He calls it a wonder material that has remarkable mechanical, electronic and optical properties and is being investigated for a variety of applications as diverse as plastic packaging and next-generation gigahertz transistors.

In the sequencing that he and other physicists have proposed, a tiny hole a few nanometers in diameter is drilled into a sheet of graphene and DNA is threaded through that nanopore. Then, a current of ions flowing vertically through the pore or an electronic current flowing transversely through the graphene is used to detect the presence of different DNA bases within the nanopore.

“Since graphene is only one atom thick, the nanopore through which DNA is threaded has contact with only a single DNA base,” Nikolic said.

In 2010, three experimental teams—led by Jene Golovchenko of Harvard, Cees Dekker of Delft and Drndic—demonstrated DNA detection using nanopores in large-area graphene. However, Nikolic said, the process moved too quickly for the existing electronics to detect single DNA bases.

The new device concept proposed by the UD researchers uses graphene nanoribbons—thin strips of graphene that are less than 10 nanometers wide—with a nanopore drilled in their interior. Chemists, engineers, materials scientists and physicists have devised various methods over the past three years to fabricate nanoribbons with a specific zigzag pattern of carbon atoms along their edges, Nikolic said. Nanoribbons could enable fast and low-cost (less than $1,000) DNA sequencing, he said, because of the quantum-mechanically generated electronic currents that flow along those edges.

Such quick and inexpensive DNA sequencing could usher in an era of personalized medicine, Nikolic said.

"We used the knowledge acquired from several years of theoretical and computational research on the electronic transport in graphene to increase the magnitude of the detection current in our biosensor by a thousand to million times when compared to other recently considered devices," Nikolic said. "Two years ago, scientists would have told me our device was impossible, but there are so many people working on graphene that nothing is impossible anymore.

"Every time physicists think something is impossible, materials scientists or chemists come to the rescue—and vice versa."

Nikolic said he and postdoctoral researcher Kamal Saha have employed their home-grown massively parallel computational codes to simulate the operation of the proposed nanoelectronic biosensor from first principles, using the supercomputer Chimera that UD acquired with support from a National Science Foundation grant.

"This project has to run on 500-1,000 processors for several months continuously," he said. "We couldn't have done it without UD Chimera becoming fully operational in early 2011."

Nikolic, Saha and Drndic have recently published the results of this research in an article in the prestigious Nano Letters, a journal with an impact factor of 12.219 published by the American Chemical Society.  Colleagues, led by Drndic at the University of Pennsylvania, will now seek to fabricate the biosensors in their lab, guided by the simulations presented in the article. Nikolic said that this research synergy will, in turn, allow for simulations of improved device designs. 

Provided by University of Delaware (news : web)

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Chemistry in one dimension offers surprising result

"Chemistry on the nanometer scale often appears to be different compared to chemistry in the normal scale and carbon nanotubes provide ideal conditions for studies of reactions in nanospace," says Alexandr Talyzin, docent at the Department of Physics, Umeå University.

The standard approch to make chemical recations inside of single walled carbon nanotubes, SWNTs, is to fill the inner space with molecules (e.g. fullerenes, thus forming so called peapods) and make them react with each other.

The nanotube walls will then protect the encapsulated molecules from outer space and make reactions with molecules and atoms outside the tube impossible. Once the SWNTs are filled with C60 molecules there is not enough space for hydrogen molecules to go in. That was the common opinion when the research groups started their experiments a few years ago.

But their experiments leave no doubt, hydrogen does actually penetrate into peapods and react with fullerenes. The evidence is rather direct, when the temperature and pressure of hydrogenation is taken to extreme values the fullerene cage collapses completely and large hydrogen molecules are formed. This was confirmed both by Raman spectroscopy and high resolution TEM.

The study provides one more example that chemical reactions in nanoreactors are not always the same as in “normal” conditions. In three-dimensional structure molecules can react with their neighbours in all possible directions, up, down, right, left etc.

"Inside of carbon nanotubes fullerene molecule have only two neighbours, lets say to the right and to the left. Similarly, the reaction with hydrogen is also limited to one-dimension," says Alexandr Talyzin.

A great advantage is that even single molecules inside of SWNTs can be observed using high resolution electron microscopy, something extremely difficult for bulk powders, he adds. High quality images collected at Aalto University allowed the scientists to observe not only hydrogen induced collapse of C60, but also hydrogen-driven coalescence of molecules into chain polymers and tubules.

"What we learned is a rather general result for nano-chemistry. Now we have direct evidence that molecules inside of SWNts can be reacted with gases. It opens enormous possibilities for synthesis of novel hybrid materials and chemical modification of encapsulated molecules and materials," says Alexandr Talyzin.

More information: “Hydrogen driven collapse of C60 inside of SWNTs” is published on line in Angewandte Chemie, http://onlinelibra … 946/abstract

Provided by Umea University

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Straintronics: Engineers create piezoelectric graphene

Graphene is a wonder material. It is one-hundred-times better at conducting electricity than silicon. It is stronger than diamond. And, at just one atom thick, it is so thin as to be essentially a two-dimensional material. Such promising physics have made graphene the most studied substance of the last decade, particularly in nanotechnology. In 2010, the researchers who first isolated it shared the Nobel Prize.

Yet, while graphene is many things, it is not piezoelectric. Piezoelectricity is the property of some materials to produce electric charge when bent, squeezed or twisted. Perhaps more importantly, piezoelectricity is reversible. When an electric field is applied, piezoelectric materials change shape, yielding a remarkable level of engineering control.

Piezoelectrics have found application in countless devices from watches, radios and ultrasound to the push-button starters on propane grills, but these uses all require relatively large, three-dimensional quantities of piezoelectric materials.

Now, in a paper published in the journal ACS Nano, two materials engineers at Stanford have described how they have engineered piezoelectrics into graphene, extending for the first time such fine physical control to the nanoscale.

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Listen to Stanford engineers Evan Reed and Mitchell Ong discuss their piezoelectric graphene. Credit: ACS Nano

Straintronics

"The physical deformations we can create are directly proportional to the electrical field applied and this represents a fundamentally new way to control electronics at the nanoscale," said Evan Reed, head of the Materials Computation and Theory Group at Stanford and senior author of the study. "This phenomenon brings new dimension to the concept of 'straintronics' for the way the electrical field strains — or deforms — the lattice of carbon, causing it to change shape in predictable ways."

"Piezoelectric graphene could provide an unparalleled degree of electrical, optical or mechanical control for applications ranging from touchscreens to nanoscale transistors," said Mitchell Ong, a post-doctoral scholar in Reed's lab and first author of the paper.

Using a sophisticated modeling application running on high-performance supercomputers, the engineers simulated the deposition of atoms on one side of a graphene lattice — a process known as doping — and measured the piezoelectric effect.

They modeled graphene doped with lithium, hydrogen, potassium and fluorine, as well as combinations of hydrogen and fluorine and lithium and fluorine on either side of the lattice. Doping just one side of the graphene, or doping both sides with different atoms, is key to the process as it breaks graphene's perfect physical symmetry, which otherwise cancels the piezoelectric effect.

The results surprised both engineers.

"We thought the piezoelectric effect would be present, but relatively small. Yet, we were able to achieve piezoelectric levels comparable to traditional three-dimensional materials," said Reed. "It was pretty significant."

Designer piezoelectricity

"We were further able to fine tune the effect by pattern doping the graphene—selectively placing atoms in specific sections and not others," said Ong. "We call it designer piezoelectricity because it allows us to strategically control where, when and how much the graphene is deformed by an applied electrical field with promising implications for engineering."

While the results in creating piezoelectric graphene are encouraging, the researchers believe that their technique might further be used to engineer piezoelectricity in nanotubes and other nanomaterials with applications ranging from electronics, photonics, and energy harvesting to chemical sensing and high-frequency acoustics.

"We're already looking now at new piezoelectric devices based on other 2D and low-dimensional materials hoping they might open new and dramatic possibilities in nanotechnology," said Reed.

Provided by Stanford School of Engineering

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Researchers show the way forward for improving organic and molecular electronic devices

"We have shown that when the molecules in organic thin films are aligned in particular directions, there is much better conductance," says Miquel Salmeron, a leading authority on nanoscale surface imaging who directs Berkeley Lab's Materials Sciences Division and who led this study. "Chemists already know how to fabricate organic thin films in a way that can achieve such an alignment, which means they should be able to use the information provided by our methodology to determine the molecular alignment and its role on charge transport across and along the molecules. This will help improve the performances of future organic electronic devices."

Salmeron and Shaul Aloni, also of the Materials Sciences Division, are the corresponding authors of a paper in the journal Nano Letters that describes this work. The paper is titled "Electron Microscopy Reveals Structure and Morphology of One Molecule Thin Organic Films." Other co-authors were Virginia Altoe, Florent Martin and Allard Katan.

Organic electronics, also known as plastic or polymer electronics, are devices that utilize carbon-based molecules as conductors rather than metals or semiconductors. They are prized for their low costs, light weight and rubbery flexibility. Organic electronics are also expected to play a big role in molecular computing, but to date their use has been hampered by low electrical conductance in comparison to metals and semiconductors.

"Chemists and engineers have been using their intuition and trial-and-error testing to make progress in the field but at some point you hit a wall unless you understand what is going on at the molecular level, for example, how electrons or holes flow through or across molecules, how the charge transport depends on the structure of the organic layers and the orientation of the molecules, and how the charge transport responds to mechanical forces and chemical inputs," Salmeron says. "With our experimental results, we have shown that we can now provide answers for these questions."

In this study, Salmeron and his colleagues used electron diffraction patterns to map the crystal structures of molecular films made from monolayers of short versions of commonly used polymers containing long chains of thiophene units. They focused specifically on pentathiophene butyric acid (5TBA) and two of its derivatives (D5TBA and DH5TBA) that were induced to self-assemble on various electron-transparent substrates.

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Electron diffraction patterns provide a wealth of information about the morphology, structure, and quality of monolayer organic thin films. Credit: Image from Berkeley Lab's Molecular Foundry

Pentathiophenes - molecules containing a ring of four carbon and one sulfur atoms - are members of a well-studied and promising family of organic semiconductors.

Obtaining structural crystallographic maps of monolayer organic films using electron beams posed a major challenge, as Aloni explains.

"These organic molecules are extremely sensitive to high energy electrons," he says. "When you shoot a beam of high energy electrons through the film it immediately affects the molecules. Within few seconds we no longer see the signature intermolecular alignment of the diffraction pattern. Despite this, when applied correctly, electron microscopy becomes essential tool that can provide unique information on organic samples."

Salmeron, Aloni and their colleagues overcame the challenge through the combination of a unique strategy they developed and a transmission electron microscope (TEM) at the Molecular Foundry's Imaging and Manipulation of Nanostructures Facility. Electron diffraction patterns were collected as a parallel electron beam was scanned over the film, then analyzed by computer to generate structural crystallographic maps.

"These maps contain uncompromised information of the size, symmetry and orientation of the unit cell, the orientation and structure of the domains, the degree of crystallinity, and any variations on the micrometer scale," says first author Altoe. "Such data are crucial to understanding the structure and electrical transport properties of the organic films, and allow us to track small changes driven by chemical modifications of the support films."

In their paper, the authors acknowledge that to gain structural information they had to sacrifice some resolution.

"The achievable resolution of the structural map is a compromise between sample radiation hardness, detector sensitivity and noise, and data acquisition rate," Salmeron says. "To keep the dose of high energy electrons at a level the monolayer film could support and still be able to collect valuable information about its structure, we had to spread the beam to a 90 nanometer diameter. However a fast and direct control of the beam position combined with the use of fast and ultrasensitive detectors should allow for the use of smaller beams with a higher electron flux, resulting in a better than 10 nanometer resolution."

While the combination of organic molecular films and substrates in this study conduct electrical current via electron holes (positively-charged energy spaces), Salmeron and his colleagues say their structural mapping can also be applied to materials whose conductance is electron-based.

"We expect our methodology to have widespread applications in materials research," Salmeron says.

Provided by Lawrence Berkeley National Laboratory (news : web)

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Scientists produce graphene using microorganisms

Chemical reduction of graphene oxide (GO) flakes is widely used for the synthesis of graphene. In this process, the critical stage of reducing GO flakes into graphene requires the exposure of the GO to hydrazine. This reduction process has fundamental limitations for large scale production; in particular because of the hydrazine vapor is highly toxic.

The method developed by the Toyohashi Tech team was inspired by a recent report showing that graphene oxide behaves as a terminal electron acceptor for bacteria, where the GO is reduced by microbial action in the process of breathing or electron transport. Notably, the Toyohashi Graphene Research Group method is a hybrid approach, where chemically derived graphene oxide flakes are reduced by readily available microorganisms extracted from a river bank near the Tempaku Campus of Toyohashi University of Technology, Aichi, Japan. Raman scattering measurements showed that the GO flakes had indeed been reduced.

The approach offers a low-cost, highly efficient, and environmentally friendly method for the mass production of high quality graphene for the electronics industry.

More information: Y. Tanizawa et al. Microorganism mediated synthesis of reduced graphene oxide films, IOP Journal of Physics: Conference Series (in press), http://iopscience. … rg/1742-6596

Provided by Toyohashi University of Technology

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Researchers help assess economic impact of nanotech on green & sustainable growth

Georgia Institute of Technology researchers Philip Shapira and Jan Youtie helped answer that question through research presented March 27th at the International Symposium on Assessing the Economic Impact of Nanotechnology held in Washington, D.C.  The researchers highlighted the importance of full lifecycle assessments to understand the impacts of nanotechnologies on green economic development in such areas as energy, the environment and safe drinking water.

“Nanotechnology promises to foster green and sustainable growth in many product and process areas,” said Shapira, a professor with Georgia Tech’s School of Public Policy and the Manchester Institute of Innovation Research at the Manchester Business School in the United Kingdom. “Although nanotechnology commercialization is still in its early phases, we need now to get a better sense of what markets will grow and how new nanotechnology products will impact sustainability. This includes balancing gains in efficiency and performance against the net energy, environmental, carbon and other costs associated with the production, use and end-of-life disposal or recycling of nanotechnology products.”

But because nanotechnology underlies many different industries, assessing and forecasting its impact won’t be easy. “Compared to information technology and biotechnology, for example, nanotechnology has more of the characteristics of a general technology such as the development of electric power,” said Youtie, director of policy research services at Georgia Tech’s Enterprise Innovation Institute. “That makes it difficult to analyze the value of products and processes that are enabled by the technology. We hope that our paper will provide background information and help frame the discussion about making those assessments.”

The symposium is sponsored by the Organization for Economic Cooperation and Development and by the U.S. National Nanotechnology Initiative. Support for Georgia Tech research into the societal impacts of nanotechnology has come from the National Science Foundation through the Center for Nanotechnology in Society based at Arizona State University.

For their paper, co-authors Shapira and Youtie examined a subset of green nanotechnologies that aim to enable sustainable energy, improve environmental quality, and provide healthy drinking water for areas of the world that now lack it. They argue that the lifecycle of nanotechnology products must be included in the assessment.

“In examining the economic impact of these green nanotechnologies, we have to consider the lifecycle, which includes such issues as environmental health and safety, as well as the amount of energy required to produce materials such as carbon nanotubes,” said Shapira.

Environmental concerns have been raised about what happens to nanomaterials when they get into water supplies, he noted. In addition, some nanostructures use toxic elements such as cadmium. Energy required for producing nano-enabled products is also an important consideration, though it may be balanced against the energy saved – and pollution reduced – through the use of such products, Shapira said.

Research into these societal issues, which is being conducted in parallel with the research and development of nanotechnology – may allow the resulting nano-enabled products to avoid the kinds of the controversies that have hindered earlier technologies.

“Scientists, policy-makers and other observers have found that some of the promise of prior rounds of technology was limited by not anticipating and considering societal concerns prior to the introduction of new products,” Youtie said. “For nanotechnology, it is vital that these issues are being considered even during the research and development stage, before products hit the market in significant quantities.”

The nanotechnology industry began with large companies that had the resources to invest in research and development. But that is now changing, Youtie said.

“A lot of small companies are involved in novel nanomaterials development,” she said. “Large companies often focus on integrating those nanomaterials into existing products or processes.”

Among the goals of the OECD symposium are development of methodologies and approaches for estimating the impacts of green nanotechnology on jobs and new product sales. Existing forecasts have come largely from proprietary models used by private-sector firms.

“While these private forecasts have high visibility, their information and methods are often proprietary,” Shapira noted. “We also need to develop open and peer-reviewed models in which approaches are transparent and everyone can see the methods and assumptions used.”

In their paper, Youtie and Shapira cite several examples of green nanotechnology, discuss the potential impacts of the technology, and review forecasts that have been made. Examples of green nanotechnology they cite include:

• Nano-enabled solar cells that use lower-cost organic materials, as opposed to current photovoltaic technologies that require rare materials such as platinum;
• Nanogenerators that use piezoelectric materials such as zinc oxide nanowires to convert human movement into energy;
• Energy storage applications in which nanotechnology materials improve existing batteries and nano-enabled fuel cells;
• Thermal energy applications, such as nano-enabled insulation;
• Fuel catalysis in which nanoparticles improve the production and refining of fuels and reduce emissions from automobiles;
• Technologies used to provide safe drinking water through improved water treatment, desalination and reuse.

Provided by Georgia Institute of Technology (news : web)

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Dye-sensitized solar cells with carbon nanotube transparent electrodes offer significant cost savings

A typical dye-sensitized solar cell comprises a porous layer of TiO2 nanoparticles immersed in an organic dye. The dye absorbs the sunlight and converts the energy into electricity, which flows into the TiO2 nanoparticles. The sun-facing side of the solar cell is usually covered with a transparent electrode that carries the charge carriers away from the TiO2 and out of the solar cell. “Unfortunately, ITO electrodes are brittle and crack easily,” says Huang. “They are also expensive and could incur up to 60% of the total cost of the dye-sensitized solar cell.”

Huang and his team therefore replaced the ITO electrode with a thin film of carbon nanotubes. Carbon nanotubes conduct electricity and are almost transparent, flexible and strong, which make them the ideal material for transparent electrodes. The only drawback is that photo-generated charge carriers in the nanotube may recombine with ions in the dye, which reduces the power conversion efficiency of the solar cell.

To overcome this problem, Huang and his team placed a TiO2 thin film in between the carbon nanotube thin film and the porous layer. They found that the performance of dye-sensitized solar cells with TiO2 thin film was significantly better than those without. However, they also found that the solar conversion efficiency of their new dye-sensitized solar cells was only 1.8%, which is lower than that of conventional solar cells using ITO electrodes. This is due to the higher electrical resistances and reduced optical transparency of the carbon nanotube films, which limits the amount of sunlight entering the cell.

“We are now studying different ways to enhance the conductivity and transparency of the films,” says Huang. “Furthermore, we are planning to replace the bottom platinum electrode with carbon nanotube thin film to reduce the cost of dye-sensitized solar cells further.”

If successful, the results could have a great impact on the cost and stability of dye-sensitized solar cells.

More information: Research article in Applied Physics Letters.

Provided by Agency for Science, Technology and Research (A*STAR)

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Solar cell turns windows into generators

For the past four years a team of researchers from Flinders University has been working to make this dream a reality – and now the notion of solar-powered windows could be coming to a not too distant future near you.

As part of his just-completed PhD, Dr. Mark Bissett from the School of Chemical and Physical Sciences has developed a revolutionary solar cell using carbon nanotubes.

A promising alternative to traditional silicon-based solar cells, carbon nanotubes are cheaper to make and more efficient to use than their energy-sapping, silicon counterparts.

“Solar power is actually the most expensive type of renewable energy – in fact the silicon solar cells we see on peoples’ roofs are very expensive to produce and they also use a lot of electricity to purify,” Dr. Bissett said.

“The overall efficiency of silicon solar cells are about 10 per cent and even when they’re operating at optimal efficiency it could take eight to 15 years to make back the energy that it took to produce them in the first place because they’re produced using fossil fuels,” he said.

Dr. Bissett said the new, low-cost carbon nanotubes are transparent, meaning they can be “sprayed” onto windows without blocking light, and they are also flexible so they can be weaved into a range of materials including fabric – a concept that is already being explored by advertising companies.

While the amount of power generated by solar windows would not be enough to completely offset the energy consumption of a standard office building, Dr. Bissett said they still had many financial and environmental advantages.

“In a new building, or one where the windows are being replaced anyway, adding transparent solar cells to the glass would be a relatively small cost since the cost of the glass, frames and installation would be the same with or without the solar component,” Dr. Bissett said.

“It’s basically like tinting the windows except they’re able to produce electricity, and considering office buildings don’t have a lot of roof space for solar panels it makes sense to utilise the many windows they do have instead.”

Dr. Bissett said the technology mimics photosynthesis, the process whereby plants obtain energy from the sun.

“A solar cell is created by taking two sheets of electrically conductive glass and sandwiching a layer of functionalized single-walled carbon nanotubes between the glass sheets,” he said.

“When light shines on the cell, electrons are generated within the carbon nanotubes and these can be used to power electrical devices.”

Although small prototypes have been developed in the lab, he said the next step would be to test the carbon cells on an “industrial stage”.

If all goes to plan, the material could be on the market within 10 years.

“When we first started the research we had no idea if it would work because we were the first in the world to try it so it’s pretty exciting that we’ve proved the concept, and hopefully it will be commercially available in a few year’s time,” Dr. Bissett said.

Dr. Bissett is a winner of Flinders inaugural Best Student Paper Award, a now annual program which aims to recognise excellence in student research across the University.

Provided by Flinders University

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New method offers control of strain on graphene membranes

A group of physicists from the University of Arkansas and other institutions have developed a technique that allows them to control the mechanical property, or strain, on freestanding graphene, sheets of carbon one-atom thick suspended over the tops of tiny squares of copper. By controlling the strain on freestanding graphene, they also can control other properties of this important material.

“If you subject graphene to strain, you change its electronic properties,” said physics professor Salvador Barraza-Lopez. Strain on freestanding graphene causes the material to behave as if it is in a magnetic field, even though no magnets are present, a property that scientists will want to exploit -- if they can control the mechanical strain.

To control the mechanical strain, University of Arkansas researchers developed a new experimental approach. Physicists Peng Xu, Paul Thibado and students in Thibado’s group examined freestanding graphene membranes stretched over thin square “crucibles,” or meshes, of copper. They performed scanning tunneling microscopy with a constant current to study the surface of the graphene membranes. This type of microscopy uses a small electron beam to create a contour map of the surface. To keep the current constant, researchers change the voltage as the scanning tunneling microscope tip moves up and down, and the researchers found that this causes the freestanding graphene membrane to change shape.

“The membrane is trying to touch the tip,” Barraza-Lopez said. They discovered that the electric charge between the tip and the membrane influences the position and shape of the membrane. So by changing the tip voltage, the scientists controlled the strain on the membrane. This control becomes important for controlling the pseudo-magnetic properties of graphene.

In conjunction with the experiments, Barraza-Lopez, Yurong Yang of the University of Arkansas and Nanjing University, and Laurent Bellaiche of the University of Arkansas examined theoretical systems involving graphene membranes to better understand this new-found ability to control the strain created by the new technique. They verified the amount of strain on these theoretical systems and simulated the location of the scanning tunneling microscopy tip in relation to the membrane. While doing so, they discovered that the interaction of the membrane and tip depends upon the tip’s location on the freestanding graphene. This allows scientists to calculate the pseudo-magnetic field for a given voltage and strain.

“If you know the strain, you can use theory and compute how big the pseudo-magnetic field may be,” said Barraza-Lopez. They found that because of the boundaries created by the square copper crucible, the pseudo-magnetic field swings back and forth between positive and negative values, so scientists are reporting the maximum value for the field instead of a constant value.

“If you were able to make the crucibles triangular, you would be closer to having non-oscillating fields,” Barraza-Lopez said. “This would bring us closer to using this pseudo-magnetic property of graphene membranes in a controlled way.”

The researchers report their findings in Physical Review B Rapid Communications.

More information: PRB 85, 121406(R) (2012)

Provided by University of Arkansas (news : web)

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Nanostarfruits are pure gold for research

Starfruit-shaped gold nanorods synthesized by chemist Eugene Zubarev and Leonid Vigderman, a graduate student in his lab at Rice’s BioScience Research Collaborative, could nourish applications that rely on surface-enhanced Raman spectroscopy (SERS).

The research appeared online this month in the American Chemical Society journal Langmuir.

The researchers found their particles returned signals 25 times stronger than similar nanorods with smooth surfaces. That may ultimately make it possible to detect very small amounts of such organic molecules as DNA and biomarkers, found in bodily fluids, for particular diseases.

“There’s a great deal of interest in sensing applications,” said Zubarev, an associate professor of chemistry. “SERS takes advantage of the ability of gold to enhance electromagnetic fields locally. Fields will concentrate at specific defects, like the sharp edges of our nanostarfruits, and that could help detect the presence of organic molecules at very low concentration.”

SERS can detect organic molecules by themselves, but the presence of a gold surface greatly enhances the effect, Zubarev said. “If we take the spectrum of organic molecules in solution and compare it to when they are adsorbed on a gold particle, the difference can be millions of times,” he said. The potential to further boost that stronger signal by a factor of 25 is significant, he said.

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Nanostarfruits begin as gold nanowires with pentagonal cross-sections. Rice chemist Eugene Zubarev believes silver ions and bromide combine to form an insoluble salt that retards particle growth along the pentagons' flat surfaces. Credit: Zubarev Lab/Rice University

Zubarev and Vigderman grew batches of the star-shaped rods in a chemical bath. They started with seed particles of highly purified gold nanorods with pentagonal cross-sections developed by Zubarev’s lab in 2008 and added them to a mixture of silver nitrate, ascorbic acid and gold chloride.

Over 24 hours, the particles plumped up to 550 nanometers long and 55 nanometers wide, many with pointy ends. The particles take on ridges along their lengths; photographed tip-down with an electron microscope, they look like stacks of star-shaped pillows.

Why the pentagons turn into stars is still a bit of a mystery, Zubarev said, but he was willing to speculate. “For a long time, our group has been interested in size amplification of particles,” he said. “Just add gold chloride and a reducing agent to gold nanoparticles, and they become large enough to be seen with an optical microscope. But in the presence of silver nitrate and bromide ions, things happen differently.”

When Zubarev and Vigderman added a common surfactant, cetyltrimethylammonium bromide (aka CTAB), to the mix, the bromide combined with the silver ions to produce an insoluble salt. “We believe a thin film of silver bromide forms on the side faces of rods and partially blocks them,” Zubarev said.

This in turn slowed down the deposition of gold on those flat surfaces and allowed the nanorods to gather more gold at the pentagon’s points, where they grew into the ridges that gave the rods their star-like cross-section. “Silver bromide is likely to block flat surfaces more efficiently than sharp edges between them,” he said.

The researchers tried replacing silver with other metal ions such as copper, mercury, iron and nickel. All produced relatively smooth nanorods. “Unlike silver, none of these four metals form insoluble bromides, and that may explain why the amplification is highly uniform and leads to particles with smooth surfaces,” he said.

The researchers also grew longer nanowires that, along with their optical advantages, may have unique electronic properties. Ongoing experiments with Stephan Link, an assistant professor of chemistry and chemical and biomolecular engineering, will help characterize the starfruit nanowires’ ability to transmit a plasmonic signal. That could be useful for waveguides and other optoelectronic devices.

But the primary area of interest in Zubarev’s lab is biological. “If we can modify the surface roughness such that biological molecules of interest will adsorb selectively on the surface of our rugged nanorods, then we can start looking at very low concentrations of DNA or cancer biomarkers. There are many cancers where the diagnostics depend on the lowest concentration of the biomarker that can be detected.”

Provided by Rice University (news : web)

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Nanowires have superior electrical, mechanical properties and can be put to good use in pressure sensors

Most miniaturized pressure sensors harness the intrinsic properties of piezoresistive materials. A structural change in such a material, induced for example by an external force, results in a complementary change in its electrical resistance. However, piezoresistive materials have two major limitations. Firstly, these materials are not particularly sensitive, which means that low pressures produce weak electronic signals. Secondly, these materials can generate a lot of electrical noise, which can mask the true measurement signal. An ideal transducer should have a high signal-to-noise ratio (SNR). Park and his co-workers have now used nanowires to create a pressure sensor with enhanced SNR properties.

Previous research has shown that nanowires can exhibit high piezoresistive effects because of their small size. To take advantage of this, Park and his co-workers used state-of-the-art material processing techniques to suspend two silicon nanowires between two electrodes on a silicon-on-insulator substrate. Each wire was a few hundred nanometers long and approximately 10 nanometers wide. They were covered in amorphous silicon which both protected them and acted as an electrical connection, referred to as the gate. The researchers attached to this a circular diaphragm: a two-layer membrane of silicon nitride and silicon dioxide. Any stress in the diaphragm was therefore transferred to the nanowire structure.

The team characterized their sensor by passing a controlled stream of air across it. Ammeters measured the current flowing through the device as a known electrical potential was applied across the two electrodes. An additional voltage, the gate bias, was also applied between one of the electrodes and the gate. Park and his co-workers demonstrated that they could achieve a four-fold increase in pressure sensitivity by reversing the direction of this gate bias. This, they believe, is a result of the bias voltage controlling the confinement of the electrons within the nanowire channels — a concept commonly employed in so-called field-effect transistors. An assessment of the device noise characteristics also showed significant improvements with the right choice of operating parameters.

Park and his co-workers believe that the device provides a promising route for applications requiring miniaturized pressure sensors that use little power.

More information: Research article in Journal of Micromechanics and Microengineering

Provided by Agency for Science, Technology and Research (A*STAR)

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Multiple groups claim to create first atom-thick silicon sheets

Smaller means faster in electronics. Conventional electronic devices based on silicon are being miniaturized, but they start to malfunction as they approach the limits of the single atom scale. Consequently, manufacturers need to find new solutions for faster electronics in the coming years. Because silicene and graphene are essentially two-dimensional they can work at the single atom level.

"This is why silicene is so important. It might take you to that ultimate [size] limit," said Lok C. Lew Yan Voon, a nanomaterial expert from Wright State University in Ohio who coined the term "silicene" in 2007.

According to Lew Yan Voon, electronic devices based on silicene could reliably exhibit the critical on-off function required for transistors, the building blocks of computers. Graphene, however, has struggled to achieve this function, stymieing its practical use as a transistor.

"The electronics industry is fighting against carbon," said Guy Le Lay, a silicene researcher from Aix-Marseille University in France. "To change to graphene, in principle, would be very nice, but it's very complicated."

Because electronics manufacturers have built an infrastructure around silicon, they remain hesitant to fully embrace graphene as the basis for future super-fast processors. Silicene, however, presents an attractive prospect, according to its proponents.

In a forthcoming research paper, Le Lay and his colleagues claim to be the first group to have clear proof of synthesized silicene sheets. The work will appear in Physical Review Letters.

Le Lay hopes that this research will segue into transistors soon.

"The aim is to have a demonstration of a device in two and a half years," said Le Lay.

The advantage silicene transistors would have over their graphene counterparts stems from silicene's unique structure. In silicene, a few silicon atoms exist above and below the main two-dimensional surface and electrons in these two regions have distinct energies. Applying electrical voltages enables electrons to jump across this energy gap and allows silicene to transition between an "on" and "off" state.

Le Lay's team claims to have created the first sheets that pave the way for such applications. But Le Lay and his colleagues have several competitors.

Research groups from China and Japan recently unveiled similar results, and another team announced the synthesis of silicene in an Applied Physics Letters paper published in late 2010. The latter group, however, didn't have enough proof to make that claim, said Le Lay. Le Lay added that the Japanese group does not have as much evidence as his group.

"[Le Lay] wants to own the fatherhood of silicene like it's his thing, but actually it's not," said Abdelkader Kara, a theoretical physicist specializing in silicene at the University of Central Florida in Orlando and coauthor of the 2010 research paper.

Although Kara's group claimed to have synthesized silicene in 2010, they only used one detection method to prove their claim: scanning tunneling microscope images. The device relies on quantum-mechanical effects to produce images on the atomic scale, with greater detail than images from traditional microscopes.

Such images, however, can be deceiving. According to the French team behind the newer research, the 2010 results didn't conclusively indicate that silicene was formed. Instead, something subtle was cropping up in the images, Le Lay's group claims.

Most silicene researchers have been attempting to grow silicene on top of silver because silver atoms and silicon atoms don't interact strongly. While this allows the silicene to form independently from the silver substrate, it can be difficult to differentiate between genuine silicene sheets and silver structures, said Le Lay.

"There's something tricky with the silver surface. The silver surface can mimic the honeycomb surface that looks like silicene," said Patrick Vogt, a silicene researcher at Technical University of Berlin and lead author of the forthcoming research done with Guy Le Lay. "The real silicene structure looks different."

Kara counters that they had sufficient proof for silicene synthesis back in 2010 based on how the silicon atoms aligned themselves at an angle with the silver substrate. The microscope images revealed a honeycomb structure that the silver surface could not have formed alone, said Kara.

"[Scanning tunneling microscope] images of course can be deceiving," said Kara. "We did a very careful job of looking at the silicon, and that's why the paper was accepted [for scientific publication]."

Nonetheless, Le Lay and Vogt weren't satisfied. To ensure that they had truly created silicene, Vogt's research group analyzed their sample in a number of ways. They measured electrical and chemical properties in addition to comparing actual images with simulated theoretical predictions. Proving the synthesis of silicene requires converging evidence from these different sources, said Le Lay.

Also, the team found that the observed distance between the silicon atoms matched theoretical predictions better than the results from 2010.

Kara agrees that Le Lay's team took an important step forward in silicene research, but he believes that they don't deserve too much credit for silicene's discovery.

Kara added that the credit for pioneering experimental silicene research should go to his colleagues, Bernard Aufray and Hamid Oughaddou, who worked on the 2010 paper.

Wright State's Lew Yan Voon, who wasn't affiliated with either Kara's or Le Lay's research, acknowledges that there were some discrepancies between the 2010 paper and theoretical predictions. Consequently, it remains unclear who synthesized silicene first, said Lew Yan Voon.

"The positive note is that more and more groups are reporting [synthesis of silicene]," said Lew Yan Voon. "There was a time when people said you couldn't even create it."

Despite the uncertainty over who created silicene first, researchers agree what needs to be done next. To take full advantage of silicene's properties, physicists need to grow it on an insulating material that won't conduct electricity like silver. Once silicene can be grown on an insulator, it will be much easier to develop silicene transistors and other devices.

Scientists may develop silicene devices that dramatically increase processing speed relatively soon, but large challenges remain, according to Le Lay.

"From this to applications is another big step. It's not trivial," said Le Lay.

Source: Inside Science News Service (news : web)

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Researchers theorize cold compression of graphite results in new superhard carbon allotropes

An allotrope is a substance that is essentially the same as another, with just minor differences in structure. Thus, both graphite and diamonds are allotropes of carbon. In their paper, the research team shows, via mathematical calculations, that subjecting a graphite allotrope to varying degrees of both cold and high pressure, would result in small changes to the structure, resulting in two new carbon allotropes.

Prior to this work, other researchers have theorized that applying pressure at room temperature (more than 10 GigaPascals) to graphite would also result in structural changes, creating new allotropes (M10-carbon, monoclinic M-carbon, orthorhombic W-carbon or cubic body center C4 carbon) though thus far it isn’t clear if those changes would remain in effect after the pressure is removed.

The new allotropes that theoretically would be produced by exerting pressure under cold conditions, which the team have called H-carbon and S-carbon, would also apparently be more stable than the allotropes produced without the cold, and even more stable, they say, than graphite under pressure, which means they would be more likely to survive in their compressed state after being returned to normal conditions.

By using mathematical models to predict the creation of new carbon allotropes, researchers pave the way for real world experiments to find out if the new materials would truly exist, and if so, to what purpose they might be used. New carbon allotropes would have different optical properties, such as their degree of transparency, for example or how well they reflect light, than already well understood allotropes that are already being used in real world applications,. Such properties in new allotropes, if they can be caused to persist under reasonable conditions, might lead to new and better products.

But before researchers begin trying to produce these new allotropes, more theoretical work will need to be done to see if there are others out there still waiting to be discovered.

More information: New Superhard Carbon Phases Between Graphite and Diamond, arXiv:1203.5509v1 [cond-mat.mtrl-sci] http://arxiv.org/abs/1203.5509

Abstract
Two new carbon allotropes (H-carbon and S-carbon) are proposed, as possible candidates for the intermediate superhard phases between graphite and diamond obtained in the process of cold compressing graphite, based on the results of first-principles calculations.Both H-carbon and S-carbon are more stable than previously proposed M-carbon and W-carbon and their bulk modulus are comparable to that of diamond. H-carbon is an indirect-band-gap semiconductor with a gap of 4.459 eV and S-carbon is a direct-band-gap semiconductor with a gap of 4.343 eV. S-carbon is even more stable than the Z-carbon which is the most table carbon phase proposed recently. The transition pressure from cold compressing graphite is 10.08 GPa and 5.93 Gpa for H-carbon and S-carbon,respectively, which is in consistent with the recent experimental report.

via Arxiv Blog

? 2012 PhysOrg.com

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Researchers find simple and cheap way to mass-produce graphene nanosheets

Graphene, which is made from graphite, the same stuff as "lead" in pencils, has been hailed as the most important synthetic material in a century. Sheets conduct electricity better than copper, heat better than any material known, are harder than diamonds yet stretch.

Scientists worldwide speculate graphene will revolutionize computing, electronics and medicine but the inability to mass-produce sheets has blocked widespread use.

A description of the new research will be published the week of March 26 in the online Early Edition of the Proceedings of the National Academy of Sciences.

Jong-Beom Baek, professor and director of the Interdisciplinary School of Green Energy/Advanced Materials & Devices, Ulsan National Institute of Science and Technology, Ulsan, South Korea, led the effort.

"We have developed a low-cost, easier way to mass produce better graphene sheets than the current, widely-used method of acid oxidation, which requires the tedious application of toxic chemicals," said Liming Dai, professor of macromolecular science and engineering at Case Western Reserve and a co-author of the paper.

Here's how:

Researchers placed graphite and frozen carbon dioxide in a ball miller, which is a canister filled with stainless steel balls. The canister was turned for two days and the mechanical force produced flakes of graphite with edges essentially opened up to chemical interaction by carboxylic acid formed during the milling.

The carboxylated edges make the graphite soluble in a class of solvents called protic solvents, which include water and methanol, and another class called polar aprotic solvents, which includes dimethyl sulfoxide.

Once dispersed in a solvent, the flakes separate into graphene naonsheets of five or fewer layers.

To test whether the material would work in direct formation of molded objects for electronic applications, samples were compressed into pellets. In a comparison, these pellets were 688 times better at conducting electricity than pellets yielded from the acid oxidation of graphite.

After heating the pellets at 900 degrees Celsius for two hours, the edges of the ball-mill–derived sheets were decarboxylated, that is, the edges of the nanosheets became linked with strong hydrogen bonding to neighboring sheets, remaining cohesive. The compressed acid-oxidation pellet shattered during heating.

To form large-area graphene nanosheet films, a solution of solvent and the edge-carboxylated graphene nanosheets was cast on silicon wafers 3.5 centimeters by 5 centimeters, and heated to 900 degrees Celsius. Again, the heat decarboxylated the edges, which then bonded with edges of neighboring pieces. The researchers say this process is limited only by the size of the wafer. The electrical conductivity of the resultant large-area films, even at a high optical transmittance, was still much higher than that of their counterparts from the acid oxidation.

By using ammonia or sulfur trioxide as substitutes for dry ice and by using different solvents, "you can customize the edges for different applications," Baek said. "You can customize for electronics, supercapacitors, metal-free catalysts to replace platinum in fuel cells. You can customize the edges to assemble in two-dimensional and three-dimensional structures."

Provided by Case Western Reserve University (news : web)

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Discovery of new catalyst promises cheaper, greener drugs

"It is always important to strive to make industrial syntheses more green, and using iron catalysts is not only much less toxic, but it is also much more cost effective," said Jessica Sonnenberg, a PhD student and lead author of a paper published this week in the Journal of the American Chemical Society.

The research, which was directed by Robert Morris, chair of the Department of Chemistry, involved several steps. Suspecting the existence of nanoparticles, the team first set out to identify the iron catalysts. They then conducted investigations using an electron microscope to confirm that the iron nanoparticles were actually being formed during catalysis. The next step was to ensure that the iron nanoparticles were the active catalytic agents. This was done with polymer and poisoning experiments which showed that only the iron atoms on the surface of a nanoparticle were active.

But a further challenge remained. "Catalysts, even cheap iron ones developed for these types of reaction, still suffer one major downfall," explained Sonnenberg. "They require a one-to-one ratio of very expensive organic ligands – the molecule that binds to the central metal atom of a chemical compound – to yield catalytic activity. Our discovery of functional surface nanoparticles opens the door to using much smaller ratios of these expensive compounds relative to the metal centres. This drastically reduces the overall cost of the transformations."

Provided by University of Toronto (news : web)

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Development of a new method for the boron-doping of two dimensional carbon materials

A crucial issue in the field of organic electronics is the development of efficient electron transporting materials. The recent development of hole-transporting materials in the field of in organic photovoltaics has resulted in an improvement of the light-to-electricity conversion efficiency to 10%, even though the electron-transporting materials have been limited almost to fullerene derivatives. The development of new electron-transporting materials is therefore a key step for the development of organic photovoltaic materials with significantly increased light-to-electricity conversion efficiencies. A promising molecular design approach for novel electron-transporting materials is the incorporation of boron atoms (boron-doping) into two dimensional carbon networks (Fig.1). However, in order to successfully implement the concept of "boron-doping" into the development of these materials, the crucial problem of stabilizing the resulting boron-containing organic compounds has to be overcome.

The research group proposed a new concept for the kinetic stabilization of boron-containing materials based on "structural constraint" (Fig.2). They have developed an effective synthetic method for the synthesis of model compounds and showed that a series of corresponding boron-containing carbon materials revealed high electron accepting abilities as well as high stability towards air and heat. These results demonstrate a new paradigm for the kinetic stabilization of boron-containing two dimensional carbon polycyclic skeletons in the absence of bulky aryl groups. These results should furthermore allow the development of a new class of fascinating 2D carbon materials with boron as the key element. The application of this method to boron-embedded graphene, low molecular weight polycyclic carbon materials, as well as fullerenes and carbon nanotubes would lead to the development of excellent electron-transporting materials that can realize higher light-to-electricity conversion efficiencies in organic photovoltaics.

More information: "Planarized Triarylboranes: Stabilization by Structural Constraint and Their Plane-to-Bowl Conversion"
Zhiguo Zhou, et al. Planarized Triarylboranes: Stabilization by Structural Constraint and Their Plane-to-Bowl Conversion. J. Am. Chem. Soc., Article ASAP Publication Date (Web): February 28, 2012 DOI:10.1021/ja211944q

Provided by Kyoto University

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Graphene: Potential for modelling cell membrane systems

Graphene could also play an important role in the modelling of cell membranes. For example, the lipid bilayer is the fundamental structure of cell membranes, and the structure and dynamic of bilayer membranes govern the transport of materials and information in and out of cells.

Ryugo Tero and his colleagues in the Graphene Research Group at Toyohashi University of Technology have established a new procedure to fabricate artificial planar lipid membranes on graphene oxide (GO) and reduced graphene oxide (r-GO) as a means of detecting biomolecules such as lipids and proteins on and inside lipid bilayers.

An aqueous solution of GO was prepared by chemical exfoliation and dropped onto a thermally oxidized and cleaned SiO2/Si substrate (Fig.1A). The resulting GO/SiO2/Si was incubated in a vesicle suspension of phospholipid (dioleoylphosphatidylcholine: DOPC). Subsequent observation with an atomic force fluorescence microscopy (Fig.1B) and revealed the presence of two planar DOPC bilayer membranes stacked on GO with the assistance of calcium ion (5 mM), and that the DOPC bilayers on GO were fluid and continuous with the surrounding DOPC bilayers on the bare SiO2 surfaces (Fig. 1C).

Lipid bilayer/monolayer stacking structures were obtained on hydrophobic r-GO, which was produced by reducing GO with hydrazine vapour. Artificial lipid bilayers on graphene and its derivatives could be a new cell membrane model system for the researche on fundamental processes in cell membrane reactions.

These results will be a part of the presentation in MRS (Material Research Society) Spring Meeting 2012 at San Francisco on April 12 (Symposium EE: New Functional Nanocarbon Devices).

More information: Y. Okamoto, et al. 'Fabrication of Supported Lipid Bilayer on Graphene Oxide," IOP Journal of Physics: Conference Series (in press).

K. Tsuzuki, et al. 'Reduced Graphene Oxide as the Support for Lipid Bilayer Membrane,' IOP Journal of Physics: Conference Series (in press).

Provided by Toyohashi University of Technology

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