A forest of nanorods: Amazing nanostructures created by glancing-angle deposition

Just as landscape photographs shot in low-angle light dramatically accentuate subtle swales and mounds, depositing metal vapors at glancing angles turns a rough surface into amazing nanostructures with a vast range of potential properties.

For decades,vapor depositionhas been a standard technique for creating modern microelectronic circuits. But nearly all of industry's efforts have been devoted to making structures as flat and smooth as possible. Rather than placing metal sources in the high-noon position used to make featureless structures, Daniel Gall of Rensselaer Polytechnic Institute is one of several dozen research leaders who place them at very narrow angles akin to sunrise or sunset illumination. Metal atoms then hit primarily any high spots on the target surface. Continued deposition creates a forest of nanorods, rather than flat films, since each growing rod shadows a volume behind it. Starting with a patterned substrate yields a regular array of nanoscale columns, like skyscrapers in downtown Manhattan.

Gall describes his research today at the AVS 57th International Symposium&Exhibition, which takes place this week at the Albuquerque Convention Center in New Mexico.

In his talk, Gall reveals a new theory that predicts how the deposition temperature and diffusion affects the diameters of the nanorods.

"Atomsmoving by surface diffusion typically smooth the surface,"Gall says."Atomic shadowing causes the opposite effects, making thesurfacerough. Glancing-angle deposition extends shadowing effects to higher temperatures, which lead to larger-diameternanorods."

He also illustrates his presentation with images of a variety ofnanostructurescreated in his lab, including curiously shaped half-moons made when he started with a pattern of self-assembled spheres.

Future applications for nanorod structures such as Gall's include nanosensors, optical elements, fuel-cell cathodes and electrical contacts for buffering thermal expansion.

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Scientists create highly ordered artificial spin ice using nanotechnology

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(PhysOrg.com) -- An international team of researchers has succeeded in creating artificial spin ice in a state of thermal equilibrium for the first time, allowing them to examine the precise configuration of this important nanomaterial.

Scientists from the University of Leeds, the US Department of Energy's Brookhaven National Laboratory and the UK Science and Technology Facilities Council's Rutherford Appleton Laboratory say the breakthrough will allow them to study in much greater detail a scientific phenomenon known as 'magnetic monopoles', which are thought to exist in such structures. Their findings are published today in the journalNature Physics.

Artificial spin ice is built using nanotechnology and is made up of millions of tiny magnets, each thousands of times smaller than a grain of sand. The magnets exist in a lattice in what is known as a 'frustrated' structure. Like water ice, the geometry of the structure means that all of the interactions between the atoms cannot be satisfied at the same time.

"It's like trying to seat alternating male and female diners around a table with an odd number of seats– however much you re-arrange them you will never succeed,"said Dr Christopher Marrows from the University of Leeds, co-author of the paper.

In spin ice, magnetic dipoles with a north and south pole are arranged in tetrahedron structures. Each dipole has magnetic moments, similar to the protons on H2O molecules inwater ice, which attract and repel each other. Consequently, the dipoles arrange themselves into the lowest possible energy state, which is two poles pointing in and two pointing out.

Dr Marrows said:"Spin ices have created a lot of excitement in recent years as it has been realised that they are a playground for physicists studying magnetic monopole excitations and Dirac string physics in the solid state. However, until now all of the samples of these artificial structures created in the lab have been what we call 'jammed'.

"What we have done is find a way to un-jam spin ice and get it into a well-ordered ground state known as thermal equilibrium. We can then freeze a sample into this state, and use a microscope to see which way all the little magnets are pointing. It's the equivalent of being able take a picture of every atom in a room as it allows us to inspect exactly how the structure is configured."

Jason Morgan, PhD student at the University of Leeds and lead author of the paper, was the first member of the team to observe the sample in equilibrium. He said:"Getting the sample to self-order in such a way has never been achieved experimentally before and for a while had been considered impossible. But when we looked at the sample using magnetic force microscopy and saw this beautiful periodic structure we knew instantly that we had achieved an ordered ground state."

The researchers have also been able to observe individual excitations out of this ground state within their sample, which they say is evidence for monopole dynamics within thelattice.

Magnetic monopoles– magnets with only a single north or south pole¬¬– are former hypothetical particles that are now thought to exist in spin ice. There is hope among scientists that understanding these monopoles in more detail could lead to advances in a novel technology field known as 'magnetricity'– a magnetic equivalent to electricity.

Co-author Sean Langridge, a Science and Technology Facilities Council (STFC) Fellow and visiting Professor at the University of Leeds, added:"In the naturally occurring spin-ice systems this ground state is predicted but has not been experimentally observed.

"Now that is has been observed in an artificial system the next step is to observe dynamically the excitations from this ground state. We can only do this by controlling the interactions with state of the art lithographic techniques. This level of control will provide an even greater level of understanding in this fascinating system."

The team created"artificial"spin ice samples at Brookhaven using a state-of-the-artnanotechnologytool called an electron beam writer. A similar£4 million facility is shortly to be opened at the University of Leeds which will be unique to the UK and will allow continued collaboration with the researchers at Brookhaven.

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Technique allows researchers to examine how materials bond at the atomic level

(PhysOrg.com) -- An approach pioneered by researchers at North Carolina State University gives scientists new insight into the way silicon bonds with other materials at the atomic level. This technique could lead to improved understanding of and control over bond formation at the atomic level, and opportunities for the creation of new devices and more efficient microchips.

Manufacturers build silicon-based devices from layers of different materials. Bonds– the chemical interaction between adjacent atoms– are what give materials their distinctive characteristics.“Essentially, a bond is the glue that holds two atoms together, and it is this glue that determines material properties, like hardness and transparency,” says Dr. Kenan Gundogdu, assistant professor of physics at NC State and co-author of the research.“Bonds are formed as materials come together. We have influenced the assembly process ofsiliconcrystals by applying strain duringbondformation. Manufacturers know that strain makes a difference in how bonds form, but up to now there hasn’t been much understanding of how this works on theatomic level.”

Gundogdu, along with Dr. David Aspnes, Distinguished University Professor of Physics, and doctoral candidate Bilal Gokce, used optical spectroscopy along with a method of analysis pioneered by Aspnes and former graduate student Dr. Eric Adles that allowed them to examine what was happening on the atomic scale when strain was applied to a silicon crystal.

“Strain has been used to affect overall chemistry for a long time,” Aspnes says.“However, no one has previously observed differences in chemical behavior of individual bonds as a result of applying strain in one direction. Now that we can see what is actually happening, we’ll gain a much better understanding of its impact on the atomic scale, and ideally be able to put it to use.”

According to Gundogdu,“Application of even small amount of strain in one direction increases the chemical reactivity of bonds in certain direction, which in turn causes structural changes. Up to now, strain has been applied when devices are made. But by looking at the effect on the individual atomic bonds we now know that we can influence chemical reactions in a particular direction, which in principle allows us to be more selective in the manufacturing process.”

The research appears online in the Sept. 27Proceedings of the National Academy of Sciences.

“While we are able to exert some directional control over reaction rates, there remains much that we still don’t understand,” Aspnes adds.“Continuing research will allow us to identify the relevant hidden variables, and silicon-based devices may become more efficient as a result.”

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The effects of hydrogen on growing carbon nanotubes

Carbon nanotubes -- long, hollow cylinders of carbon billionths of a meter in diameter -- have many potential uses in nanotechnology, optics, electronics, and many other fields. The exact properties of nanotubes depend on their structure, and scientists as yet have little control over that structure, which is determined during the initial formation -- or growth -- of the nanotubes. In fact, says chemical engineer and materials scientist Eray Aydil of the University of Minnesota,"we do not know precisely how the nanotubes grow."

In a paper in the American Institute of Physics'Journal of Applied Physics, Aydil, professor of chemical engineering and materials science and the Ronald L. and Janet A. Christenson Chair in Renewable Energy, and his colleagues shed new light on the process. In particular, the researchers examined the influence of hydrogen gas.

"Carbon nanotubes grow from a metal catalyst particle that is immersed in a gas like methane,"Aydil explains."Sometimeshydrogen gasis also added and it was found that a little bit of hydrogen helps to grow carbon nanotubes with nice straight walls and with few defects. However, too much hydrogen addition gives fibers with thick walls, instead of nanotubes, or no growth at all."

To understand why, Aydil and colleagues usedtransmission electron microscopyand other methods to systematically image and characterize the effects of increasing concentrations of hydrogen."It turns out that the iron metal catalysts turn to iron carbide by reacting with the carbon in methane. Iron carbide is a hard material that is not easily deformed, and carbon nanotubes grown from such catalysts tend to have nice straight walls,"he says.

Adding more hydrogen to the mix causes iron carbide to turn into iron -- which is more malleable and ductile, and"deforms into shapes that give rise to more fiber-like structures rather than hollow carbon nanotubes,"he says. At higher concentrations, hydrogen etches the forming carbon nanotubes,"and growth stops all together. It is the interaction of the hydrogen with the catalysts and its effect on the catalyst's structure that controls thecarbon nanotubestructure."

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Nanogenerators grow strong enough to power small conventional electronics (w/ Video)

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Blinking numbers on a liquid-crystal display (LCD) often indicate that a device's clock needs resetting. But in the laboratory of Zhong Lin Wang at Georgia Tech, the blinking number on a small LCD signals the success of a five-year effort to power conventional electronic devices with nanoscale generators that harvest mechanical energy from the environment using an array of tiny nanowires.

In this case, themechanical energycomes from compressing a nanogenerator between two fingers, but it could also come from a heartbeat, the pounding of a hiker's shoe on a trail, the rustling of a shirt, or thevibrationof a heavy machine. While these nanogenerators will never produce large amounts ofelectricityfor conventional purposes, they could be used to power nanoscale and microscale devices– and even to recharge pacemakers or iPods.

Wang's nanogenerators rely on the piezoelectric effect seen in crystalline materials such aszinc oxide, in which an electric charge potential is created when structures made from the material are flexed or compressed. By capturing and combining the charges from millions of these nanoscale zinc oxide wires, Wang and his research team can produce as much as three volts– and up to 300 nanoamps.

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In the laboratory of Zhong Lin Wang at Georgia Tech, a blinking LCD signals the success of a five-year effort to power conventional electronic devices using nanoscale generators that harvest mechanical energy from the environment. Credit: Georgia Tech

"By simplifying our design, making it more robust and integrating the contributions from many morenanowires, we have successfully boosted the output of our nanogenerator enough to drive devices such as commercial liquid-crystal displays, light-emitting diodes and laser diodes,"said Wang, a Regents' professor in Georgia Tech's School of Materials Science and Engineering."If we can sustain this rate of improvement, we will reach some true applications in healthcare devices, personal electronics, or environmental monitoring."

Recent improvements in the nanogenerators, including a simpler fabrication technique, were reported online last week in the journalNano Letters. Earlier papers in the same journal and in Nature Communications reported other advances for the work, which has been supported by the Defense Advanced Research Projects Agency (DARPA), the U.S. Department of Energy, the U.S. Air Force, and the National Science Foundation.

"We are interested in very small devices that can be used in applications such as health care, environmental monitoring and personal electronics,"said Wang."How to power these devices is a critical issue."

The earliest zinc oxide nanogenerators used arrays of nanowires grown on a rigid substrate and topped with a metal electrode. Later versions embedded both ends of the nanowires in polymer and produced power by simple flexing. Regardless of the configuration, the devices required careful growth of the nanowire arrays and painstaking assembly.

In the latest paper, Wang and his group members Youfan Hu, Yan Zhang, Chen Xu, Guang Zhu and Zetang Li reported on much simpler fabrication techniques. First, they grew arrays of a new type of nanowire that has a conical shape. These wires were cut from their growth substrate and placed into an alcohol solution.

The solution containing the nanowires was then dripped onto a thin metal electrode and a sheet of flexible polymer film. After the alcohol was allowed to dry, another layer was created. Multiple nanowire/polymer layers were built up into a kind of composite, using a process that Wang believes could be scaled up to industrial production.

When flexed, these nanowire sandwiches– which are about two centimeters by 1.5 centimeters– generated enough power to drive a commercial display borrowed from a pocket calculator.

Wang says the nanogenerators are now close to producing enough current for a self-powered system that might monitor the environment for a toxic gas, for instance, then broadcast a warning. The system would include capacitors able to store up the small charges until enough power was available to send out a burst of data.

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Compressing a nanogenerator between two fingers is enough to drive a liquid-crystal display. Credit: Courtesy Zhong Lin Wang

While even the current nanogenerator output remains below the level required for such devices as iPods or cardiac pacemakers, Wang believes those levels will be reached within three to five years. The current nanogenerator, he notes, is nearly 100 times more powerful than what his group had developed just a year ago.

Writing in a separate paper published in October in the journal Nature Communications, group members Sheng Xu, Benjamin J. Hansen and Wang reported on a new technique for fabricating piezoelectric nanowires from lead zirconate titanate– also known as PZT. The material is already used industrially, but is difficult to grow because it requires temperatures of 650 degrees Celsius.

In the paper, Wang's team reported the first chemical epitaxial growth of vertically-aligned single-crystal nanowire arrays of PZT on a variety of conductive and non-conductive substrates. They used a process known as hydrothermal decomposition, which took place at just 230 degrees Celsius.

With a rectifying circuit to convert alternating current to direct current, the researchers used the PZT nanogenerators to power a commercial laser diode, demonstrating an alternative materials system for Wang's nanogenerator family."This allows us the flexibility of choosing the best material and process for the given need, although the performance of PZT is not as good as zinc oxide for power generation,"he explained.

And in another paper published inNano Letters, Wang and group members Guang Zhu, Rusen Yang and Sihong Wang reported on yet another advance boosting nanogenerator output. Their approach, called"scalable sweeping printing,"includes a two-step process of (1) transferring vertically-aligned zinc oxide nanowires to a polymer receiving substrate to form horizontal arrays and (2) applying parallel strip electrodes to connect all of the nanowires together.

Using a single layer of this structure, the researchers produced an open-circuit voltage of 2.03 volts and a peak output power density of approximately 11 milliwatts per cubic centimeter.

"From when we got started in 2005 until today, we have dramatically improved the output of our nanogenerators,"Wang noted."We are within the range of what's needed. If we can drive these small components, I believe we will be able to power small systems in the near future. In the next five years, I hope to see this move into application."

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Ultrathin alternative to silicon for future electronics

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There's good news in the search for the next generation of semiconductors. Researchers with the U.S. Department of Energy's Lawrence Berkeley National Laboratory and the University of California Berkeley, have successfully integrated ultra-thin layers of the semiconductor indium arsenide onto a silicon substrate to create a nanoscale transistor with excellent electronic properties. A member of the III–V family of semiconductors, indium arsenide offers several advantages as an alternative to silicon including superior electron mobility and velocity, which makes it an oustanding candidate for future low-power, high-speed electronic devices.

"We've shown a simple route for the heterogeneous integration of indium arsenide layers down to a thickness of 10 nanometers onsiliconsubstrates,"says Ali Javey, a faculty scientist in Berkeley Lab's Materials Sciences Division and a professor of electrical engineering and computer science at UC Berkeley, who led this research.

"The devices we subsequently fabricated were shown to operate near the projected performance limits of III-V devices with minimal leakage current. Our devices also exhibited superior performance in terms of current density and transconductance as compared to silicon transistors of similar dimensions."

For all its wondrouselectronic properties, silicon has limitations that have prompted an intense search for alternative semiconductors to be used in future devices. Javey and his research group have focused on compound III–V semiconductors, which feature superb electron transport properties. The challenge has been to find a way of plugging these compound semiconductors into the well- established, low-cost processing technology used to produce today's silicon-based devices. Given the large lattice mismatch between silicon and III-V compound semiconductors, direct hetero-epitaxial growth of III-V on silicon substrates is challenging and complex, and often results in a high volume of defects.

"We've demonstrated what we are calling an 'XOI,' or compound semiconductor-on-insulator technology platform, that is parallel to today's 'SOI,' or silicon-on-insulator platform,"says Javey."Using an epitaxial transfer method, we transferred ultrathin layers of single-crystal indium- arsenide on silicon/silica substrates, then fabricated devices using conventional processing techniques in order to characterize the XOI material and device properties."

The results of this research have been published in the journalNature,in a paper titled,"Ultrathin compound semiconductor on insulator layers for high-performance nanoscale transistors."Co-authoring the report with Javey were Hyunhyub Ko, Kuniharu Takei, Rehan Kapadia, Steven Chuang, Hui Fang, Paul Leu, Kartik Ganapathi, Elena Plis, Ha Sul Kim, Szu-Ying Chen, Morten Madsen, Alexandra Ford, Yu-Lun Chueh, Sanjay Krishna and Sayeef Salahuddin.

To make their XOI platforms, Javey and his collaborators grew single-crystal indium arsenide thin films (10 to 100 nanometers thick) on a preliminary source substrate then lithographically patterned the films into ordered arrays of nanoribbons. After being removed from the source substrate through a selective wet-etching of an underlying sacrificial layer, the nanoribbon arrays were transferred to the silicon/silicasubstratevia a stamping process.

Javey attributed the excellent electronic performance of the XOI transistors to the small dimensions of the active"X"layer and the critical role played by quantum confinement, which served to tune the material's band structure and transport properties. Although he and his group only used indium arsenide as their compound semiconductor, the technology should readily accommodate other compound III/V semiconductors as well.

"Future research on the scalability of our process for 8-inch and 12-inch wafer processing is needed,"Javey said.

"Moving forward we believe that the XOI substrates can be obtained through a wafer bonding process, but our technique should make it possible to fabricate both p- and n- type transistors on the same chip for complementary electronics based on optimal III–V semiconductors.

"Furthermore, this concept can be used to directly integrate high performance photodiodes, lasers, and light emitting diodes on conventional silicon substrates. Uniquely, this technique could enable us to study the basic material properties of inorganicsemiconductorswhen the thickness is scaled down to only a few atomic layers."

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Scientists crack materials mystery in vanadium dioxide

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(PhysOrg.com) -- A systematic study of phase changes in vanadium dioxide has solved a mystery that has puzzled scientists for decades, according to researchers at the Department of Energy's Oak Ridge National Laboratory.

Scientists have known that vanadium dioxide exhibits several competing phases when it acts as an insulator at lower temperatures. However, the exact nature of the phase behavior has not been understood since research began on vanadium dioxide in the early 1960s.

Alexander Tselev, a research associate from the University of Tennessee-Knoxville working with ORNL's Center for Nanophase Materials Sciences, in collaboration with Igor Luk'yanchuk from the University of Picardy in France used acondensed matter physicstheory to explain the observed phase behaviors of vanadium dioxide, a material of significant technological interest for optics and electronics.

"We discovered that the competition between several phases is purely driven by the lattice symmetry,"Tselev said."We figured out that the metallic phase lattice of vanadium oxide can 'fold' in different ways while cooling, so what people observed was different types of its folding."

Vanadium dioxide is best known in the materials world for its speedy and abrupt phase transition that essentially transforms the material from a metal to an insulator. The phase change takes place at about 68 degrees Celsius.

"These features ofelectrical conductivitymake vanadium dioxide an excellent candidate for numerous applications in optical, electronic and optoelectronic devices,"Tselev said.

Devices that might take advantage of the unusual properties of VO2 include lasers, motion detectors and pressure detectors, which could benefit from the increased sensitivity provided by the property changes of vanadium dioxide. The material is already used in technologies such asinfrared sensors.

Researchers said their theoretical work could help guide future experimental research in vanadium dioxide and ultimately aid the development of new technologies based on VO₂.

"In physics, you always want to understand how the material ticks,"said Sergei Kalinin, a senior scientist at the CNMS."The thermodynamic theory will allow you to predict how the material will behave in different external conditions."

The results were published in the American Chemical Society'sNano Letters. The research team also included Ilia Ivanov, John Budai and Jonathan Tischler at ORNL and Evgheni Strelcov and Andrei Kolmakov at Southern Illinois University.

The team's theoretical research expands upon previous experimental ORNL studies with microwave imaging that demonstrated how strain and changes of crystal lattice symmetry can produce thin conductive wires in nanoscale vanadium dioxide samples.

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Mechanical engineering at the molecular level: Self-assembly of nano-rotors (w/ Video)

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German scientists from the Technische Universitaet Muenchen have managed to direct the self-assembly of rod-shaped molecules into rotors only few nanometers in size. The tiny systems serve the study of forces that act on molecules on surfaces and in cage-like structures. Their findings are published in the current online issue of the<i>Proceedings of the National Academy of Sciences</i>.

In the nanoworld many things are different. Scientists only recently started unveiling and harnessing the underlying laws and principles. A team associated with Professor Johannes Barth from the Physics Department of the TU Muenchen have now succeeded in capturing rod-shaped molecules in a two-dimensional network in such a way that they autonomously form small rotors that turn in their honeycomb-like cages.

Nature itself provides the role model for such self-organizing systems. This is how proteins bring reactants so close together that reactions can take place– reactions that are possible only in very close proximity. These effects are put to use in catalysts: surface reactants find their way to each other on the surface of these facilitators. However, the coveted dream of using self-organization effects in such a way that nano machines assemble themselves is still a thing of the future.

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Driven by thermal energy, the nano-rotors start rotating. Credit: Video: Florian Klappenberger, TUM

The rotors developed in Garching are an important step in this direction. First, the physicists built up an extensive nano lattice by allowing cobalt atoms and rod-shaped molecules of sexiphenyl-dicarbonitrile to react with each other on a silver surface. This results in a honeycomb-like lattice of extreme regularity with astonishing stability. Just like graphene, for which its discoverers were awarded the Nobel Prize only a few weeks ago, this lattice is exactly one atom thick.

When the researchers added further molecular building blocks, the rods spontaneously gathered, typically in groups of three, in a honeycomb cell while neighboring cells remained empty. The chummy molecules must have had a reason for organizing themselves in threesomes. Under a scanning tunneling microscope the scientists were able to recognize why. The three molecules oriented themselves in such a way that the nitrogen ends each faced a phenyl-ring hydrogen atom. This triple-bladed rotor arrangement is so energetically advantageous that the molecules maintain this structure even when thermal energy drives it to rotation.

Because the honeycomb-cell is not round, but hexagonal, there are two different positions for the rotors that can be distinguished as a result of the interactions between the outer nitrogen atoms and the hydrogen atoms of the cell wall. Furthermore, the three molecules arrange in a clockwise and a counter-clockwise manner. In experiments at various carefully controlled temperatures the physicists were able to"freeze"all four states and examine them closely. They could thus determine the energy of these thresholds from the temperature at which the rotation resumed.

"We hope that in future we will be able to extend these simple mechanical models to optical or electronic switching,"says Professor Johannes Barth."We can set a specific cell size, we can specifically bring in furthermoleculesand study their interaction with the surface and the cell wall. These self-organizing structures hold enormous potential."

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World-first to provide building blocks for new nano devices

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(PhysOrg.com) -- Scientists at The University of Nottingham have made a major breakthrough that could help shape the future of nanotechnology, by demonstrating for the first time that 3-D molecular structures can be built on a surface.

The discovery could prove a significant step forward towards the development of new nano devices such as cutting-edge optical and electronic technologies and even molecular computers.

In a paper published in the prestigious journalNature Chemistry, the team of chemists and physicists at Nottingham have shown that by introducing a 'guest' molecule they can buildmoleculesupwards from a surface rather than just 2-D formations previously achieved.

A naturalbiological processknown as 'self-assembly' meant that once the scientists introduced other molecules on to a surface their host then spontaneously arranged them into a rational 3-D structure.

Professor Neil Champness said:"It is the molecular equivalent of throwing a pile of bricks up into the air and then as they come down again they spontaneously build a house.

"Until now this has only been achievable in 2-D, so to continue the analogy the molecular 'bricks' would only form a path or a patio but our breakthrough now means that we can start to build in the third dimension. It's a significant step forward tonanotechnology."

Previously, scientists have employed a technique found in nature of usinghydrogen bondsto hold DNA together to build two-dimensional molecular structure.

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The new process involved introducing a guest molecule— in this case a 'buckyball' or C₆₀— on to a surface patterned by an array of tetracarboxylic acid molecules. The spherical shape of the buckyballs means they sit above the surface of the molecule and encourage other molecules to form around them. It offers scientists a completely new and controlled way of building up additional layers on the surface of the molecule.

The work is the culmination of four years' of research led by Professors Champness and Beton from the School of Chemistry and the School of Physics and Astronomy.

The research paper is the second significant breakthrough to be reported by the team in recent weeks. In September, a paper inNature Communicationsrevealed they had demonstrated for the first time the way in which an irregularly shaped molecule is adsorbed on asurface. It represents a step towards being able to harness the potential of these molecules, which have extremely useful properties, by organising them to form structures. They could offer a way of building new data storage devices that are orders of magnitude smaller than their existing silicon-based counterparts.

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Damaging graphene to create a band gap

(PhysOrg.com) --"Graphene offers a lot of interesting potential applications for nanoelectronics,"Florian Banhart tells<i>PhysOrg.com</i>,"but there is no band gap. This is a well-known problem. Without the band gap, switching as needed in electronic devices is difficult."

Banhart, a scientist at the University of Strasbourg in Strasbourg, France, believes that there is a solution to this problem.“Everyone tries to solve this problem, trying to create different properties in order to create aband gap. Our solution is doping with metal atoms attached to reconstructeddefectsin thegraphene.”

Working with Ovidiu Cretu and Julio Rodríguez-Manzo at the University of Stasbourg, and with Arkady Krasheninnikov at the University of Helsinki, Risto Nieminen at Aalto University in Finland and Litao Sun at Southeast University in Nanjing, China, Banhart developed a method to modify the properties of graphene. The group’s work is published inPhysical Review Letters:“Migration and Localization of Metal Atoms on Strained Graphene.”

“The idea is to be able to attach something to the surface of the graphene, changing some of the properties to get a band gap,” Banhart explains. By creating reconstructed defects, we can enhance the activity of the graphene and attach metal atoms firmly, possibly producing a band gap.”

Banhart and his colleagues created graphene layers that were then damaged.“We used an electron beam to damage the graphene,” Banhart says.“For this paper, we used tungsten atoms to bond to the graphene. The defects we created made it possible for the tungsten atoms to be trapped by the defects, creating stable bonds.”

Reconstructed defects increase the activity seen in graphene, making bonding to other atoms possible.“The graphene surface is normally rather inert,” Banhart explains,“but defects such as pentagonal or heptagonal rings enhance its activity. We saw enhanced chemical activity with the graphene.”

Even though Banhart and his colleagues hope that this work will lead to the eventual creation of nanoelectronic devices made with graphene, he points out that they were unable to show definitive evidence of band gap creation.“There is no evidence that we did create a band gap,” he admits.“But perhaps tungsten is not ideal. We used it because it is large, and easy to see with the electron microscope when trapped by the graphene.”

Banhart says that the tungsten has served its purpose, showing that it is possible to attachmetal atomsto graphene with the help of defects on the graphene’s surface. He also points out that their recent work shows that it is possible to use this technique to modify graphene’s properties locally.“We have shown that our method might be used in the future to control graphene’s electronic properties better.”

The next step is to try to trap other atoms using defects in graphene. Banhart would also like to do more tests on the electronic properties of graphene doped in this manner.“It would be good to do more tests of graphene,” he says.“With more experiments, we should be able to begin to model the electronic structure of graphene more accurately. Once we better understand the properties of graphene, we should be able to better manipulate them so that we can get a band gap, and so that we can use them in nanoelectronic devices.”

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AFM tips from the microwave

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Scientists from the Friedrich-Schiller-University Jena (Germany) have succeeded in improving a fabrication process for Atomic Force Microscopy (AFM) probe tips.

Atomic Force Microscopy is able to scan surfaces so that even tiniestnano structuresbecome visible. Knowledge about these structures is for instance important for the development of new materials and carrier systems for active substances. The size of the probe is highly important for the image quality as it limits the dimensions that can be visualized– the smaller the probe, the smaller the structures that are revealed.

Carbon nanotubes are supposed to be a superior material for the improvement of such scanning probes. However, it is difficult to attach them on scanning probes, which limits their practical use.

Chemists of the Friedrich-Schiller-University Jena found a way to overcome these problems. The research team of Prof. Dr. Ulrich S. Schubert succeeded in developing a new type of process that allows the growth of carbon nanotubes on the actual scanning probe. These innovative discoveries are published in theNano Lettersand areavailable online.

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Dr. Stephanie Hoeppener from Jena University holds a glass cylinder with carbon nanotubes for atomic force microscopy. Credit: Jan-Peter Kasper/University Jena

For this process the Jena scientists are usingmicrowaveradiation for a gentle but very fast growth of the nanotubes. The growth starts at small cobalt particles, that are being taken up with the help of the AFM tip."The metal particles strongly heat up in the microwave and reach a temperature that is sufficient to convert alcohol vapor into carbon. The heating process works similar like a forgotten spoon in the kitchen microwave which also absorbs the microwave radiation very effectively,"explains Tamara Druzhinina from Schubert's research team."Carbon nanotubes can be grown very quickly due to the special conditions inside of the microwave which can generate a pressure up to 20 bar"adds her colleague Dr. Stephanie Hoeppener.

The Jena chemist Prof. Schubert points out the practical benefits of the process:"The method we developed can potentially result in a very cost-efficient production technology of for instance high resolution probes for Scanning Force Microscopy. These are already available on the market but they are very expensive at 350 Euro each. With the process we can reach a price level, that would justify the use of such tips also just for routine measurements."

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Scientists build world's smallest 'water bottle'

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Scientists have designed and built a container that holds just a single water molecule. The container consists of a fullerene cage and a phosphate moiety that acts as the“cap” to keep the water inside.

The researchers, Qianyan Zhang, et al., from institutes in Beijing and Germany, have published their study on the tinyfullerenecage in a recent issue ofAngewandte Chemie. While previous research has shown that fullerene cages can be used to surround molecules, here the chemists also designed a way to close (and re-open) the cage to let a water molecule in and out.

One of the keys was making the cap the exact size to allow a single water molecule to pass through, and modifying the classic carbon-60 form of fullerene accordingly. Due to its chemical properties, thephosphatemoiety used for the cap can be easily removed and re-attached to the edge of an orifice in the fullerene cage, and can sufficiently lock a single water molecule inside.

The tiny container could have applications in transporting small molecules or radioactive atoms for medical purposes and other uses.

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New microscope reveals ultrastructure of cells

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German researchers at Helmholtz-Zentrum Berlin have developed a new X-ray nanotomography microscope. Using their new system, they can reveal the structures on the smallest components of mammalian cells in three dimensions.

For the first time, there is no need to chemically fix, stain or cut cells in order to study them. Instead, whole living cells are fast-frozen and studied in their natural environment. The new method delivers an immediate 3-D image, thereby closing a gap between conventional microscopic techniques.

The new microscope delivers a high-resolution 3-D image of the entire cell in one step. This is an advantage overelectron microscopy, in which a 3-D image is assembled out of many thin sections. This can take up to weeks for just one cell. Also, the cell need not be labelled with dyes, unlike influorescence microscopy, where only the labelled structures become visible. The new X-ray microscope instead exploits the natural contrast between organic material and water to form an image of all cell structures. Dr. Gerd Schneider and his microscopy team at the Institute forSoft MatterandFunctional Materialshave published their development inNature Methods.

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This is a conventional TEM image of a stained thin section. Credit: HZB

With the high resolution achieved by their microscope, the researchers, in cooperation with colleagues of the National Cancer Institute in the USA, have reconstructed mouse adenocarcinoma cells in three dimensions. The smallest of details were visible: the double membrane of thecell nucleus, nuclear pores in the nuclear envelope, membrane channels in the nucleus, numerous inva­ginations of the inner mitochondrial membrane and inclusions in cell organelles such as lysosomes. Such insights will be crucial for shedding light on inner-cellular processes: such as how viruses or nanoparticles penetrate into cells or into the nucleus, for example.

This is the first time the so-called ultrastructure of cells has been imaged with X-rays to such precision, down to 30 nanometres. Ten nanometres are about one ten-thousandth of the width of a human hair. Ultrastructure is the detailed structure of a biological specimen that is too small to be seen with an optical microscope.

Researchers achieved this high 3-D resolution by illuminating the minute structures of the frozen-hydrated object with partially coherent light. This light is generated by BESSY II, the synchrotron source at HZB. Partial coherence is the property of two waves whose relative phase undergoes random fluctuations which are not, however, sufficient to make the wave completely incoherent. Illumination with partial coherent light generates significantly higher contrast for small object details compared to incoherent illumination. Combining this approach with a high-resolution lens, the researchers were able to visualize the ultrastructures ofcellsat hitherto unattained contrast.

The new X-ray microscope also allows for more space around the sample, which leads to a better spatial view. This space has always been greatly limited by the setup for the sample illumination. The required monochromatic X-ray light was created using a radial grid and then, from this light, a diaphragm would select the desired range of wavelengths. The diaphragm had to be placed so close to the sample that there was almost no space to turn the sample around. The researchers modified this setup: Monochromatic light is collected by a new type of condenser which directly illuminates the object, and the diaphragm is no longer needed. This allows the sample to be turned by up to 158 degrees and observed in three dimensions. These developments provide a new tool in structural biology for the better understanding of the cell structure.

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Nanoscale probe reveals interactions between surfaces and single molecules

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(PhysOrg.com) -- As electronics become smaller and smaller the need to understand nanoscale phenomena becomes greater and greater. Because materials exhibit different properties at the nanoscale than they do at larger scales, new techniques are required to understand and to exploit these new phenomena. A team of researchers led by Paul Weiss, UCLA's Fred Kavli Chair in NanoSystems Sciences, has developed a tool to study nanoscale interactions. Their device is a dual scanning tunneling and microwave-frequency probe that is capable of measuring the interactions between single molecules and the surfaces to which the molecules are attached.

"Our probe can generate data on the physical, chemical, and electronic interactions between singlemoleculesand substrates, the contacts to which they are attached. Just as insemiconductor devices, contacts are critical here,"remarked Weiss, who directs UCLA's CaliforniaNanoSystemsInstitute and is also a distinguished professor of chemistry and biochemistry&materials science and engineering.

The team, which also includes theoretical chemist Mark Ratner from Northwestern University and synthetic chemist James Tour from Rice University, published their findings in the peer-reviewed journalACS Nano.

For the past 50 years, the electronics industry has endeavored to keep up with Moore's Law, the prediction made by Gordon E. Moore in 1965 that the size of transistors in integrated circuits would halve approximately every two years. The pattern of consistent decrease in the size of electronics is approaching the point where transistors will have to be constructed at the nanoscale to keep pace. However, researchers have encountered obstacles in creating devices at the nanoscale because of the difficulty of observing phenomena at such minute sizes.

The connections between components are a vital element of nanoscale electronics. In the case of molecular devices, polarizability measures the extent to which electrons of the contact interact with those of the single molecule. Two key aspects of polarizability measurements are the ability to do the measurement on a surface with subnanometer resolution, and the ability to understand and to control molecular switches in both the on and off states.

To measure the polarizability of single molecules the research team developed a probe capable of simultaneous scanning tunneling microscopy (STM) measurements and microwave difference frequency (MDF) measurements. With the MDF capabilities of the probe, the team was able to locate single molecule switches on substrates, even when the switches were in the off state, a key capability lacking in previous techniques. Once the team located the switches, they could use the STM to change the state to on or off and to measure the interactions in each state between the single molecule switches and the substrate.

The new information provided by the team's probe focuses on what the limits of electronics will be, rather than targeting devices for production. Also, because the probe is capable of a wide variety of measurements— including physical, chemical and electronic— it could enable researchers to identify submolecular structures in complex biomolecules and assemblies.

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Securing the nation with fingerprinting materials

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Lawrence Livermore National Laboratory researchers may have found a way to improve Raman spectroscopy as a tool for identifying substances in extremely low concentrations. Potential applications for Raman spectroscopy include medical diagnosis, drug/chemical development, forensics and highly portable detection systems for national security.

The ability to identify molecules at low concentrations with great specificity and provide non-invasive, nondestructive measurements has led to the increasing use of Raman spectroscopy as an accepted analytical technique. But a shortcoming of this technique has been its lack of sensitivity and reliability at extremely low concentrations.

Raman spectroscopy consists of observing the scattering of light, usually from a laser, by molecules of a transparent substance. The difference in the wavelength ofscattered lightand incident light can provide detailed information about the nature of the substance.

"Raman scattering provides a nice fingerprint of materials of interest for national security,"said Tiziana Bond of LLNL's Center for Micro and Nano Technology.

Bond and her group develop surface-enhanced Raman spectroscopy (SERS), a method that increases sensitivity orders of magnitude by improving signals. While showing great potential, the substrates used for SERS, typically roughened metal surfaces, have yielded variable signals considered, as yet, unreliable. The roughened surface enhances the interaction of the molecule with the metal. The challenge has been to find a way to create a substrate with uniform topographic features that yield consistent signal enhancements.

Some of this work is described in a paper published in the September 2010 edition ofNanotechnologyentitled"Rigorous Surface Enhanced Raman Spectral Characterization of Large-Area, High-Uniformity, Silver-Coated Tapered Silica Nanopillar Arrays,"which was published by Bond and her group in collaboration with researchers from the University of Illinois at Urbana-Champaign.

Improved nano-engineering techniques and semiconductor manufacture methods have enabled the production of SERS substrates -- the base layer or texture on 4- to 6-inch wafers -- that are more reliable. The key is substrates with"reproducibility"sufficient for reliable analysis. LLNL researchers have worked on several techniques to achieve a more robust and uniform substrate that maintains high sensitivity and reproducibility.

Electromagnetic and chemical enhancements are two factors that affect SERS total enhancement (with respect to Raman). The first is stronger and accounts for 106-108 magnitude improvements, while the second is typically responsible for 10-100 factors. To exploit the electromagnetic effects, the metallic nanostructures need to be properly designed.

In an article entitled"Plasmon Resonant Cavities in Vertical Nanowire Arrays"published inNano Lettersearlier this year, Bond's group, investigate an innovative design using a vertical a gold-coated nanowire array substrate that would provide strong and controllable enhancement. The LLNL team's innovation is the fabrication of"tunable"plasmon resonant cavities in the vertical wire arrays -- cavities are the space between the vertical wires. Mihail Bora, a postdoc that joined Bond's group a year ago, is heavily involved in this part of the project and explains that surface plasmons are electromagnetic waves similar to light, except they are confined on metallic surfaces. Tuning of plasmon resonance is achieved by controlling the geometrical dimensions of the cavity.

They introduce the smallest optical resonant cavity that is thousands of times smaller than wavelength of light and showed that it is possible to go beyond this diffraction limit by using surface plasmons. Resonant cavities are currently used for surface enhancedRaman spectroscopyto detect chemical analytes (concentration)."By confining the light in such tight spaces we are able to create intense fields that are useful in increasing the spectroscopy signal,"Bond said.

These design features offer a number of advantages. For example, it allows the sensitivity of the substrates to be tuned, or adapted, to different wavelengths offering researchers greater versatility.

Among possible application extensions of the plasmonic substrate beyond the enhancement of SERS are enabling the demonstration of sub-wavelength plasmonic lasers, and broadband nanoantenna arrays for photovoltaics by playing with geometry factors.

The group's work has been funded by Defense Advanced Research Projects Agency (DARPA) and LLNL's Laboratory Directed Research and Development (LDRD) program.

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Imaging tool may aid nanoelectronics by screening tiny tubes

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Researchers have demonstrated a new imaging tool for rapidly screening structures called single-wall carbon nanotubes, possibly hastening their use in creating a new class of computers and electronics that are faster and consume less power than today's.

The semiconductingnanostructuresmight be used to revolutionize electronics by replacing conventional silicon components and circuits. However, one obstacle in their application is that metallic versions form unavoidably during the manufacturing process, contaminating the semiconducting nanotubes.

Now researchers have discovered that an advanced imaging technology could solve this problem, said Ji-Xin Cheng, an associate professor of biomedical engineering and chemistry at Purdue University.

"The imaging system uses a pulsing laser to deposit energy into the nanotubes, pumping the nanotubes from a ground state to an excited state,"he said."Then, another laser called a probe senses the excited nanotubes and reveals the contrast between metallic and semiconductor tubes."

The technique, called transient absorption, measures the"metallicity"of the tubes. The detection method might be combined with another laser to zap the unwanted metallic nanotubes as they roll off of the manufacturing line, leaving only the semiconducting tubes.

Findings are detailed in a research paper appearing online this week in the journalPhysical Review Letters.

Single-wall nanotubes are formed by rolling up a one-atom-thick layer of graphite calledgraphene, which could eventually rival silicon as a basis forcomputer chips. Researchers in Cheng's group, working withnanomaterialsfor biomedical studies, were puzzled when they noticed the metallicnanoparticlesand semiconducting nanowires transmitted and absorbed light differently after being exposed to the pulsing laser.

Then researcher Chen Yang, a Purdue assistant professor of physical chemistry, suggested the method might be used to screen the nanotubes for nanoelectronics.

"When you make nanocircuits, you only want the semiconducting ones, so it's very important to have a method to identify the metallic nanotubes,"Yang said.

The paper was written by Purdue physics doctoral student Yookyung Jung; biomedical engineering research scientist Mikhail N. Slipchenko; Chang-Hua Liu, an electrical engineering graduate student at the University of Michigan; Alexander E. Ribbe, manager of the Nanotechnology Group in Purdue's Department of Chemistry; Zhaohui Zhong, an assistant professor of electrical engineering and computer science at Michigan; and Yang and Cheng. The Michigan researchers produced the nanotubes.

Semiconductors such as silicon conduct electricity under some conditions but not others, making them ideal for controlling electrical current in devices such as transistors and diodes.

The nanotubes have a diameter of about 1 nanometer, or roughly the length of 10 hydrogen atoms strung together, making them far too small to be seen with a conventional light microscope.

"They can be seen with an atomic force microscope, but this only tells you the morphology and surface features, not the metallic state of the nanotube,"Cheng said.

The transient absorption imaging technique represents the only rapid method for telling the difference between the two types of nanotubes. The technique is"label free,"meaning it does not require that the nanotubes be marked with dyes, making it potentially practical for manufacturing, he said.

The researchers performed the technique with nanotubes placed on a glass surface. Future work will focus on performing the imaging when nanotubes are on a silicon surface to determine how well it would work in industrial applications.

"We have begun this work on a silicon substrate, and preliminary results are very good,"Cheng said.

Future research also may study how electrons travel inside individual nanotubes.

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Team develops nanoscale light sensor compatible with 'Etch-a-Sketch' nanoelectronic platform

University of Pittsburgh researchers have created a nanoscale light sensor that can be combined with near-atomic-size electronic circuitry to produce hybrid optic and electronic devices with new functionality. The team, which also involved researchers from the University of Wisconsin at Madison, reports in<i>Nature Photonics</i>that the development overcomes one of nanotechnology's most daunting challenges.

The group, led by Jeremy Levy, a professor of physics and astronomy in Pitt's School of Arts and Sciences, fashioned a photonic device less than 4 nanometers wide, enabling on-demand photonic interaction with objects as small as single molecules orquantum dots. In another first, the tiny device can be electrically tuned to change its sensitivity to different colors in thevisible spectrum, which may forgo the need for the separate light filters other sensors typically require. Levy worked with Pitt postdoctoral researcher and lead author Patrick Irvin, postdoctoral researchers Daniela Bogorin and Cheng Cen, and Pitt graduate student Yanjun Ma. Also part of the team were University of Wisconsin-Madison researchers Chang-Beom Eom, a professor of materials science and engineering, and research associates Chung Wung Bark and Chad Folkman.

The researchers produced thephotonic devicesvia a rewritablenanoelectronicsplatform developed in Levy's lab that works like a microscopic Etch A Sketch, the drawing toy that initially inspired him. His technique, first reported inNature Materialsin March 2008, is a method to switch an oxide crystal between insulating and conducting states. Applying a positive voltage to the sharp conducting probe of anatomic force microscopecreates conducting wires only a few nanometers wide at the interface of two insulators—a 1.2 nanometer-thick layer of lanthanum aluminate grown on a strontium titanate substrate. The conducting nanowires can then be erased with reverse voltage, rendering the interface an insulator once more.

In February 2009, Levy reported in Science that his platform could be used to sculpt a high-density memory device and a transistor called a"SketchFET"with features a mere two nanometers in size.

In this recent work, Levy and his colleagues demonstrated a robust method for incorporating light sensitivity into these electronic circuits, using the same techniques and materials. Photonic devices generate, guide, or detect light waves for a variety of applications, Levy said. Light is remarkably sensitive to the properties of such nanoscale objects as single molecules or quantum dots, but the integration of semiconductor nanowire and nanotube photonic devices with other electronic circuit elements has always been a challenge.

"These results may enable new possibilities for devices that can sense optical properties at the nanoscale and deliver this information in electronic form,"Levy said.

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Scientists demonstrate more efficient way to connect nanoparticles for single-electron devices

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(PhysOrg.com) -- By connecting single nano-objects together, scientists can fabricate tiny solid-state devices through which a precisely controlled single-electron current can flow. In the past several years, scientists have been developing different methods for connecting single nano-objects, such as metallic nanoparticles, semiconducting nanocrystals, and molecules. However, as the size of the nano-objects decreases, the efficiency of these methods also decreases, so that most methods result in a low yield at the scale of a few nanometers. In a new study, scientists have developed a new way to connect single nano-objects that could overcome these challenges and enable the creation of new nanodevices.

The researchers, Anne Bernard-Mantel from CNRS and the Universite Paris-Sud in Palaiseau, France, and coauthors have published their study on the new high-yield method of connecting single nano-objects in a recent issue ofNanotechnology. In addition to the increased efficiency at small scales, the new method is also compatible with a more diverse range of materials, such as highly oxygen-sensitive ferromagnetic materials. In contrast, previous methods could not use these metals due to their susceptibility to oxidation problems.

In their study, the scientists demonstrated two similar fabrication processes. Both processes start with a bottom electrode and thin layer of alumina. In the first process, an assembly ofnanoparticlesis deposited, followed by another thin layer of alumina, and then a resist layer. Using a nanoindentation technique, the scientists drilled a nanohole into the resist layer and then filled it with metal to form the topelectrode. The bottom of the nanohole comes to an extremely sharp point that connects with only one nanoparticle. In the second process, the only difference is that the alumina assembly is deposited after the resist layer.

The final result is a solid-state device consisting of an assembly of nanoparticles, while only one nanoparticle is connected to both the top and bottom electrodes. The scientists demonstrated the processes with nanoparticles as small as 2 nm in diameter. They also used different materials, including metallic and semiconducting nanoparticles, as well as non-magnetic and ferromagnetic electrodes.

In contrast with complex and expensive techniques such as electron beam lithography, the new method offers a simpler, cheaper alternative that also provides a higher yield at very small scales. Because the new method is also compatible with ferromagnetic materials, it could be used for investigating nanospintronics. Other possibilities include fabricating chemically grown nanoparticles and molecular nanomagnets.

“The next step is now to adapt this technology to connect isolated molecular magnets,” coauthor Karim Bouzehouane of CNRS and the Universite Paris-Sud toldPhysOrg.com.

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Nanostructured materials repel water droplets before they have a chance to freeze (w/ Video)

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(PhysOrg.com) -- Engineers from Harvard University have designed and demonstrated ice-free nanostructured materials that literally repel water droplets before they even have the chance to freeze.

The finding, reported online inACS Nanoon November 9th, could lead to a new way to keep airplane wings, buildings, powerlines, and even entire highways free of ice during the worst winter weather. Moreover, integrating anti-ice technology right into a material is more efficient and sustainable than conventional solutions like chemical sprays, salt, and heating.

A team led by Joanna Aizenberg, Amy Smith Berylson Professor of Materials Science at the Harvard School of Engineering and Applied Sciences (SEAS) and a Core Member of the Wyss Institute for Biologically Inspired Engineering at Harvard, focused on preventing rather than fighting ice buildup.

"We wanted to take a completely different tact and design materials that inherently prevent ice formation by repelling thewater droplets,"says Aizenberg."From past studies, we also realized that the formation of ice is not a static event. The crucial approach was to investigate the entire dynamic process of how droplets impact and freeze on a supercooled surface."

For initial inspiration, the researchers turned to some elegant solutions seen in nature. For example, mosquitos can defog their eyes, and water striders can keep their legs dry thanks to an array of tiny bristles that repel droplets by reducing the surface area each one encounters.

"Freezing starts with droplets colliding with a surface,"explains Aizenberg."But very little is known about what happens when droplets hit surfaces at low temperatures."

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Dynamic behavior of single droplets impinging upon tilted surfaces.

To gain a detailed understanding of the process, the researchers watched high-speed videos of supercooled droplets hitting surfaces that were modeled after those found in nature. They saw that when a cold droplet hits the nanostructured surface, it first spreads out, but then the process runs in reverse: the droplet retracts to a spherical shape and bounces back off the surface before ever having a chance to freeze.

By contrast, on a smooth surface without the structured properties, a droplet remains spread out and eventually freezes.

"We fabricated surfaces with various geometries and feature sizes—bristles, blades, and interconnected patterns such as honeycombs and bricks—to test and understand parameters critical for optimization,"says Lidiya Mishchenko, a graduate student in Aizenberg's lab and first author of the paper.

The use of such precisely engineered materials enabled the researchers to model the dynamic behavior of impacting droplets at an amazing level of detail, leading them to create a better design for ice-preventing materials.

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Sequential images of ice layer removal from hydrophilic Al, fluorinated hydrophobic Si, and microstructured fluorinated Si (SHS).

Another important benefit of testing a wide variety of structures, Mishchenko adds, was that it allowed the team to optimize for pressure-stability. They discovered that the structures composed of interconnected patterns were ideally suited for stable, liquid-repelling surfaces that can withstand high-impact droplet collisions, such as those encountered in driving rain or by planes in flight.

The nanostructured materials prevent the formation of ice even down to temperatures as low as -25 to -30 degrees Celsius. Below that, due to the reduced contact area that prevents the droplets from fully wetting the surface, any ice that forms does not adhere well and is much easier to remove than the stubborn sheets that can form on flat surfaces.

"We see this approach as a radical and much needed shift in anti-ice technologies,"says Aizenberg."The concept of friction-free surfaces that deflectsupercooled waterdroplets before ice nucleation can even occur is more than just a theory or a proof-of-principle experiments. We have begun to test this promising technology in real-world settings to provide a comprehensive framework for optimizing these robust ice-free surfaces for a wide range of applications, each of which may have a specific set of performance requirements."

In comparison with traditional ice prevention or removal methods like salting or heating, thenanostructured materialsapproach is efficient, non-toxic, and environmentally friendly. Further, when chemicals are used to de-ice a plane, for example, they can be washed away into the environment and their disposal must be carefully monitored. Similarly, salt on roads can lead to corrosion and run-off problems in local water sources.

The researchers anticipate that with their improved understanding of the ice forming process, a new type of coating integrated directly into a variety of materials could soon be developed and commercialized.

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New probe memory could achieve user densities over 10 terabits per square inch

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(PhysOrg.com) -- Researchers have proposed a new strategy for writing data for scanned-probe memories with user densities that are potentially more than twice as high as those achieved with conventional approaches. While previous research has shown that scanned-probe memories have the potential to achieve storage densities of up to 4 Tbit/in², the new study shows how the density could be increased to 10 Tbit/in²or more.

The researchers, David Wright, et al., from the University of Exeter in Devon, England, and theIBMZurich Research Laboratory in Rueschlikon, Switzerland, have published their study on the new write strategy in a recent issue ofApplied Physics Letters.

“We have shown that we can get ultra-high densities without the need for ultra-sharp tips,” Wright toldPhysOrg.com.“Note that 'conventional' storage technologies like magnetic hard disk drives are currently 'stuck' at just under 1 Tbit/in²densities and their road map does not predict reaching 10 Tbit/in²until 2015 in the lab and 2020 for production.”

As the researchers explain, the conventional method of writing for scanned-probe memories involves writing tiny marks with a probe, and recording the data in these marks. In this method, the tip size of the probe determines the size of the recorded mark, which limits the density. An alternative write strategy is mark-length recording, in which information is stored in the transitions between the marks rather than in the marks themselves. One of the advantages of mark-length recording is that it doesn't rely as heavily on the sharpness of the probe tip as the conventional mark-position recording approach.

“The key was realizing and demonstrating that continuous scanning (which is very bad for tip wear) is not needed to implement a mark-length scheme,” Wright explained.

This is because mark-length recording can use one of the disadvantages of mark-position recording to its advantage: intersymbol interference. In the mark-position approach, bits written too close to each other can interfere with each other, so a minimum distance between bits is needed, which limits the achievable density. However, in mark-length recording, this interference can be exploited to merge marks together to make longer marks without the need for continuous tip scanning.

Although mark-length recording has already been known to increase thestorage densityin traditional memory systems, such as magnetic and optical disk storage, scanned-probe memories have typically used only mark-position writing. Here, the researchers demonstrate how mark-length recording can be used in scanned-probe memories, as well. In the experiment, a voltage is applied between the probe tip and a phase-change medium, which heats and activates the phase-change layer. The medium can be read by sensing the change in electrical resistivity of the written medium.

As the researchers explain, a direct comparison of the densities using these two approaches is not straightforward, but the new approach should increase the user density by at least 50%. By making further improvements, such as using sharper probe tips and ultrasmooth writing surfaces, the researchers predict that much higher densities can be achieved.

The work is part of a large EU-funded project called Probe-basedTerabyteMemories (ProTeM) (http://www.protem-fp6.org), which involves the development of scanned probe storage materials and techniques for ultra-high density, ultra-low power, small form-factor archival, and back-up memories.

“Organizations and individuals are storing ever-increasing amounts of data and want to store it reliably, with low power consumption, and ideally in a small physical format,” Wright said.“The goal of our work is doing this with probe storage systems.”

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Advance could change modern electronics: High-performance 'metal-insulator-metal' diode created

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Researchers at Oregon State University have solved a quest in fundamental material science that has eluded scientists since the 1960s, and could form the basis of a new approach to electronics.

The discovery, just reported online in the professional journalAdvanced Materials, outlines the creation for the first time of a high-performance"metal-insulator-metal"diode.

"Researchers have been trying to do this for decades, until now without success,"said Douglas Keszler, a distinguished professor of chemistry at OSU and one of the nation's leadingmaterial scienceresearchers."Diodes made previously with other approaches always had poor yield and performance.

"This is a fundamental change in the way you could produce electronic products, at high speed on a huge scale at very low cost, even less than with conventional methods,"Keszler said."It's a basic way to eliminate the current speed limitations of electrons that have to move through materials."

A patent has been applied for on the new technology, university officials say. New companies, industries and high-tech jobs may ultimately emerge from this advance, they say.

The research was done in the Center for Green Materials Chemistry, and has been supported by the National Science Foundation, the Army Research Laboratory and the Oregon Nanoscience andMicrotechnologiesInstitute.

Conventional electronics made with silicon-based materials work with transistors that help control the flow of electrons. Although fast and comparatively inexpensive, this approach is still limited by the speed with which electrons can move through these materials. And with the advent of ever-faster computers and more sophisticated products such as liquid crystal displays, current technologies are nearing the limit of what they can do, experts say.

By contrast, a metal-insulator-metal, or MIM diode can be used to perform some of the same functions, but in a fundamentally different way. In this system, the device is like a sandwich, with the insulator in the middle and two layers of metal above and below it. In order to function, the electron doesn't so much move through the materials as it"tunnels"through theinsulator– almost instantaneously appearing on the other side.

"When they first started to develop more sophisticated materials for the display industry, they knew this type of MIM diode was what they needed, but they couldn't make it work,"Keszler said."Now we can, and it could probably be used with a range of metals that are inexpensive and easily available, like copper, nickel or aluminum. It's also much simpler, less costly and easier to fabricate."

The findings were made by researchers in the OSU Department of Chemistry; School of Electrical Engineering and Computer Science; and School of Mechanical, Industrial and Manufacturing Engineering.

In the new study, the OSU scientists and engineers describe use of an"amorphous metal contact"as a technology that solves problems that previously plagued MIM diodes. The OSU diodes were made at relatively low temperatures with techniques that would lend themselves to manufacture of devices on a variety of substrates over large areas.

OSU researchers have been leaders in a number of important material science advances in recent years, including the field of transparent electronics. University scientists will do some initial work with the new technology in electronic displays, but many applications are possible, they say.

High speed computers and electronics that don't depend on transistors are possibilities. Also on the horizon are"energy harvesting"technologies such as the nighttime capture of re-radiated solar energy, a way to produce energy from the Earth as it cools during the night.

"For a long time, everyone has wanted something that takes us beyond silicon,"Keszler said."This could be a way to simply print electronics on a huge size scale even less expensively than we can now. And when the products begin to emerge the increase in speed of operation could be enormous."

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Electron billiards in nanoscale circuits: Characterizing photoelectrons with quantum point contacts

In solar cells, solar radiation boosts electrons to higher energy states, thereby releasing them from their atomic bonds as electricity begins to flow. Scientists led by Professor Alexander Holleitner, physicist at the Technische Universitaet Muenchen (TUM, Germany), have developed a novel method to analyze the way photogenerated electrons move in the smallest photodetectors. They present the fruits of their research in the current issue of the magazine<i>Nano Letters</i>.

At the heart of the method is a so-called quantum point contact (QPC). This is a narrow conductive channel in a semiconductor circuit. The scientists created a 70-nanometer narrow channel, about as wide as the wavelength ofelectronsin the semiconductor. The key is that only one electron at a time will fit through the channel, making possible extremely high-precision measurements of the electric current. As described in the current publication, this method was applied to photogenerated electrons for the first time ever.

In the experimental set-up it is not the sun, but rather a laser beam that kicks the electrons into their excited state. These electrons are then analyzed using a quantum point contact. In the process, the scientists were able to demonstrate for the first time that photogenerated electrons can flow several micrometers before colliding with crystalline atoms. They also established that the geometric form of a circuit has a strong influence on electron paths. Electrons can even"run around corners"when they rebound from circuit boundaries, not unlike billiard balls.

The insights and analytic opportunities made possible by this novel technique are relevant to a whole range of applications. These include, most notably, the further development of electronic components such as photodetectors, high electron mobility transistors (HEMT), and components that utilize the magnetic spin of electrons to process information.

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