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Posted: Oct 04, 2010

Upcoming AVS symposium will highlight latest alternative energy and nanotechnology breakthroughs

(Nanowerk News) This month in Albuquerque, New Mexico, scientists and engineers from around the world will convene to discuss some of the latest breakthroughs in nanotechnology, alternative energy, materials research, and medicine at the AVS 57th International Symposium & Exhibition, from October 17-22, 2010 in the Albuquerque Convention Center.
Meeting Highlights
1) "ARPES" TECHNIQUE EXPANDS KNOWLEDGE OF PLUTONIUM PROPERTIES
Scientists have long pursued a deeper understanding of the elusive properties of plutonium (Pu), because of its potential application to defense, threat reduction, and energy policy. Plutonium materials exhibit enhanced mass, magnetism, multiple solid-state allotropes, superconductivity, and other properties, according to physicist John Joyce at Los Alamos National Laboratory in NM.
"This wide range of complex properties is both scientifically interesting and also very challenging to understand," says Joyce, "largely because of the complexity of the Plutonium electronic structure."
Central to the understanding of these electronic properties is an accurate picture of the plutonium 5f electrons. Photoemission provides a direct window into the electronic structure, including the 5f electrons, because photoemission measurements can be directly compared to electronic structure calculations. A technique called angle-resolved photoemission (ARPES) adds a component called "crystal momentum" to the measurements, providing a two-dimensional landscape for comparison to theory. The ARPES technique has enabled Joyce and colleagues to investigate how 4f and 5f electronic structure drives the chemistry, physics, and materials science of lanthanide and actinide materials.
"LANL currently has the world's only ARPES capability for transuranic materials including plutonium," says Joyce. "This unique capability provides an opportunity for a deeper understanding of plutonium electronic structure and places our plutonium research on a level comparable to other types of materials research."
The presentation, "Angle-Resolved Photoemission and the 5f Electronic Structure of Pu Materials" is at 9:40 a.m. on Monday, October 18, 2010.
2) PINNING MOLECULES TO A SURFACE
Using techniques common in semiconductor production, a group of researchers at Columbia University has developed ways to control the position of biological molecules, such as DNA, on surfaces with resolution on the order of the size a single molecule. The research could have applications in the study of DNA-protein interactions, for diagnostic investigations, and as a tool for driving self-organization of functional nanostructures on surfaces.
"We are developing a platform for nanoscale biological applications as the material science necessary to place and organize structures as small as one molecule," says Matteo Palma.
The researchers used high-resolution lithographic techniques to fabricate arrays of metal dots with diameters less than 10 nanometers on glass or silicon. By using the dots as anchors for molecules with specific chemical properties, they were able to bind DNA molecules and DNA nanostructures to the surface in a way that retains their shape and function. This provides a platform to study biomolecular interactions. The high resolution of the placement allows precise control of the position and interaction of individual molecules, such as DNA and proteins, and opens the possibility of building electronic devices on the scale of a single molecule.
The presentation, "Bio-functionalization of Nanopatterned Surfaces and their Integration with DNA Nanostructures" is at 2:40 p.m. on Monday, October 18, 2010.
3) WATER AND ITS AMBIGUOUS ROLE IN NUCLEAR WASTE STORAGE
Scientists at the Institute for Transuranium Elements in Germany are studying the effects of oxidation and reduction that water may have on spent nuclear fuel. The solution is challenging because waste fuel is mainly comprised of the so-called group of actinide elements, which includes uranium (U) and plutonium (Pu), and which have peculiar and unpredictable properties.
While most studies indicate water causes actinides to oxidize (lose electrons), recent findings have shown that under certain circumstances exactly the opposite may happen -- water can indeed cause "reduction" of the actinides (gaining of electrons).
Thomas Gouder and colleagues are using X-ray photoemission spectroscopy and other techniques to investigate the adsorption of water ice on the surface of plutonium-dioxide (PuO2) thin-films. Looking at thin-films is akin to understanding the surface of a material, where oxidation and reduction take place first. To isolate the effect, the actinide films are confined to a few atomic layers, where the transformation is best observed.
Previous studies found that water may oxidize PuO2, which may have serious safety implications. In a surprising twist, the group found that under appropriate conditions, the reverse may be true -- that the actinides are actually adding electrons upon their exposure to water ice -- in other words, PuO2 is reducing to Pu2O3, not oxidizing. The process is attributed to a photochemical surface-reaction involving the 5f states of the electrons.
"Understanding the extent of this effect may be of great importance for the prediction of the long-term storage properties of nuclear waste and thus is an intimate part of handling the nuclear legacy," says Gouder.
The paper, "Electronic Structure and Surface Reactivity of Actinide Systems" is at 2:40 p.m. on Monday, October 18, 2010.
4) SMART DUST
Motors at the molecular level are hard to build, so Henry Hess and his colleagues at Columbia University borrowed motor protein molecules (kinesin) from fruit flies, and stuck them onto a substrate in the lab. Then these motors were used to pass along microtubules -- much as people are passed around a crowd at a rock-concert process by "crowd surfing."
Macromolecular motors, says Hess, "enable a number of advances in nanoscience, and the study of molecular shuttle technology leads to novel approaches to classic problems in biomedical engineering (such as protein adsorption), as well as perspective on the biological cell as a nanoscale factory."
The tiny motors could be useful, for example, in measuring forces in molecular reactions, in building artificial muscles, in exploring the topology of a surface (like a miniature creeping Mars rover), in actuating little valves for steering chemicals and bio-molecules through microfluidic chips, and in capturing and carrying molecules to special detection sites.
Indeed, the Columbia researchers would like to devise an array of such sub-millimeter, dust-sized sensors. This "smart dust" arrangement was actually furnished with molecules (analytes) to measure by molecular shuttles.
The presentation, "Molecular Shuttles for 'Smart Dust' Biosensors, Active Self-Assembly, and Protein-Resistant Coatings" is at 2:40 p.m. on Monday, October 18, 2010.
5) GRAPHENE RESONATORS
Stretched across an opening, a small portion of graphene -- a single-atom-layer-thin piece of material made of carbon atoms -- can be made to vibrate like a drumhead. The vibrations can be measured by reflecting light from the surface. This reveals the resonant modes (again like a drum) of the graphene sheet.
Harold Craighead, an expert on the vibrating nature of various membranes, has now made a study of the characteristic vibrations of various graphene shapes. "I believe we have made significant progress in this area and we are now making and testing large arrays of nearly identical resonant devices made with lithography-based techniques," says Craighead. "I think this makes graphene more likely to be employed in practical systems."
Craighead will also be reporting on other types of membranes at the meeting. For example, he coats silicon nitride membranes with a hydroscopic polymer chosen to bind to specific airborne compounds. When those particles stick to the polymer, the resonant frequency of the membrane is altered. Thus the process can be used in building sensitive medical and environmental sensors. Lab website: www.hgc.cornell.edu.
The presentation, "Mechanical Devices Incorporating Ultra-Thin Membranes" is at 8:00 a.m. on Thursday, October 21, 2010.
6) GRAPHENE AND ITS PROGENY
Avik Ghosh of the University of Virginia will discuss device and circuit level properties of graphitic materials. In his own work he models the electronic properties of many different materials at the atomic level, and finds graphene -- one-atom-thick sheets of carbon -- to be very promising. Electrons move very quickly through graphene, which is beneficial for fast electronics. Furthermore, graphene, being a planar material, will most likely be more easy to process into electronic components than carbon nanotubes.
One drawback with graphene, and related to the very fact of its excellence as a conductor, is the fact that its conductivity cannot easily be modulated. For gating, for acting as a switch, a material needs to be able to turn from a good to a bad conductor very quickly. By using bilayers of graphene or through chemical doping and by narrowing them into thin ribbons, we can now expect to achieve conductivities that vary over an order of magnitude. Even this might not be enough for fast-switching applications required by electronic devices. Moreover, research from the Ghosh group shows that such a conductivity variation comes at a price by reducing the mobility of the electrons even for very pure samples.
"It is hard to predict what will happen," Ghosh says about progress in the upcoming year. "I would personally like to see purer graphene samples, the development of ways to transfer graphene to other useful substrates for transistor applications, systematic studies to relate the chemistry, mobility and conductance modulation in graphene ribbons, and ways to create nanoribbons arrays for circuit applications."
The presentation, "Graphene and Its Progeny: from Fundamental Material Properties to Device Applications" is at 2:00 p.m. on Tuesday, October 19, 2010.
7) WORLD'S FIRST ELECTRICALLY-DRIVEN, SINGLE-MOLECULE MOTOR
Heather Tierney, a member of the Charles Sykes group at Tufts University, works with tiny motors made from single molecules. What makes them motors is the fact that the molecules can be set into rotary motion by injecting energy. The input energy in this case happens to be electrical energy, and not the chemical or light energy used by previous work with molecular motors. Rather, the electricity comes from the sharp tip of a scanning tunneling microscope (STM). According to Tierney, "This is the first ever directed molecular rotation induced using electrical energy; in essence we have created the world's first electrically-driven single-molecule motor."
Tierney believes that her motors will fit into the larger effort to reproduce the machine environment of the macroscopic world at the nanometer level. It might even be possible to store data, Tierney says. "We could use the halted position of these molecules in their six possible states; whereas binary memory has two possible values, our would have six, all in a molecule about 1 nm in size." Lab website: ase.tufts.edu/chemistry/sykes
The presentation, "Understanding and Controlling Rotation at the Single-Molecule Level: Turning Rotors into Motors" is at 10:40 a.m. on Tuesday, October 19, 2010.
8) THE HOLY GRAIL OF SPINTRONICS
Scientists at the University of Cincinnati in Ohio have realized a breakthrough by orienting an electron's spin to an "up" or "down" position using only electrical control. Such all-electric spintronics or spin electronics, once achieved, will offer a new paradigm for the development of novel devices for use in the post-CMOS era. It may transform the whole semiconductor industry.
Since an electron's spin is associated with a magnetic moment, until now spin devices have used ferromagnetic materials to orient electron's spin "up" or "down" and filter or sense the orientation with an external magnetic field.
"This makes the devices bulky and adds to design complexities," says Philippe Debray. "Ferromagnetic electrodes have stray magnetic fields that can affect device performance."
"Finally, magnetic fields are forbiddingly difficult to control both on length scale and at high speeds," adds Debray.
Today's electronic devices such as cell phones and computers that use high-speed digital information processing are based on moving around the electron's charge and manipulate it using electric fields. This costs energy. As the device size shrinks and miniaturizes to the nanoscale, the cost in energy becomes exceedingly high. Rather than moving charges around a circuit, spin-based devices would operate by flipping the electron's spin orientation. Since it takes less time and energy to flip a spin than to move charge, spin devices will be ultra fast and highly energy efficient. In spin-based digital information processing, the two orientations of the electron spin -- "up" and "down" -- can be used to represent or encode the bits 1s and 0s. Spin-based computing promises to be much faster and will require much less energy.
"If you want to go high speed at low energy cost, you need all-electric spin devices," says Debray. "It is the holy grail of spintronics."
Debray and co-workers fabricated in indium arsenide semiconductor a short quantum wire -- called a quantum point contact -- that confined the electrons in a narrow channel. By tuning the voltage of gates adjacent to the wire, the team succeeded in constricting one edge of the wire more than the other. This triggered spin "polarization" or flipping the electron's orientation via relativistic interaction of the electron spin with its motion. The "up" or "down" orientation could be chosen at will. These all-electric quantum point contacts can act as small switches that can generate or filter electrons by their spin state, "on demand".
Currently, these spin valves require very low temperatures to function. But Debray is exploring new materials that, theoretically, will allow them to function at room temperature.
The presentation, "All-Electric Spintronics with Quantum Point Contacts: From Spin Physics to Spin Electronics" is at 2:00 p.m. on Tuesday, October 19, 2010.
9) WEAR ON THE ATOMIC-SCALE: THE MOVIE
Anyone who has ever had to have their car's brake pads replaced is familiar with the concept of wear. But what is it like at the atomic scale, where the rubbing of two surfaces past each other really goes on? A group at the University of Pennsylvania runs an extremely sharp probe -- part of an atomic force microscope (AFM) -- over a surface and images the whole thing in real time with a transmission electron microscope (TEM). Not only can you make a movie this way, but you can measure how many atoms are being worn off the probe as it moves across the surface.
"These are the finest-scale wear measurements that we know of," says PhD candidate Tevis Jacobs, one of the Penn researchers. The current measurements can detect volume changes as small as 20 cubic nanometers. Furthermore, the measurements reveal not just how much material was removed in the sliding process but how the material was removed. That is, the measurements can tell the difference between the removal of large chunks (fracturing) or small removals indicating gradual wearing, potentially occurring one atom at a time.
Aspects of this work will be presented both by Professor Rob Carpick in the Nanometer-scale Science & Technology symposium and by Tevis Jacobs in the Surface Science Post-Deadline Discovery Session. Lab website: www.me.upenn.edu/faculty/carpick.html
The presentation, "Atomic-scale Processes in Friction and Wear: From Diamond to Graphene" is at 2:40 p.m. on Wednesday, October 20, 2010.
10) NEW WAY OF LOOKING AT BIOLOGICAL MATERIALS
A team of researchers in Japan has developed an instrument capable of making secondary ion mass spectrometry (SIMS) measurements of biological materials under low vacuum.
Jiro Matsuo, an associate professor at Kyoto University's Quantum Science and Engineering Center, and colleagues will discuss recent progress in this area and new techniques that enable taking the most powerful analysis techniques out of a vacuum system to see surfaces in "real" environments.
"For many years, materials science has centered around performing analysis in extremely controlled environments, primarily in a vacuum system to provide a 'non-perturbing' environment," explains Matsuo. "This situation is changing and it is now recognized that the vacuum system itself can be quite an aggressive environment, which can result in substantial changes to the surface of modern materials of interest, including biological, medical and organic materials used in cosmetics."
This new technique opens the door to new possibilities for SIMS analysis, also known as "wet" SIMS, of biological materials.
The presentation, "Wet SIMS: A Novel Molecular Imaging Technique for Biological Material Analysis " is at 5:00 p.m. on Wednesday, October 20, 2010.
11) PROBING FOR ANSWERS WITH INFRARED IMAGING
Carol Hirschmugl, a physics professor at the University of Wisconsin–Milwaukee, and colleagues will give a presentation describing how a new, chemically sensitive infrared microscope with multiple, parallel detection channels greatly expands the ability to examine biological structures and to track their changes.
Hirschmugl will discuss how the InfraRed Environmental Imaging (IRENI) facility at the Synchrotron Radiation Center, located on the University of Wisconsin's sister campus in Madison, combines light emitted from electrons traveling close to the speed of light with a mid-infrared microscope and camera to provide high-resolution images (1 micron) of biological samples. IRENI is capable of tracking any changes in the sample that occur in response to changes in their environment—a very desirable feature to a wide range of research disciplines.
"From the earliest experiments with optical microscopes, researchers have examined the appearance of microbes and other microscopic plants and animals, striving to identify the various organelles and sub-cellular structures evident to help them infer their biological function," explains Hirschmugl. "Beyond the visual appearance of these structures, knowledge of their chemical makeup can provide great insight into how these sub-cellular structures function in a living cell. Moreover, tracking the changes in their chemical makeup allows scientists to understand the organism's response to changing environmental conditions."
This microscope provides researchers across a broad array of disciplines ranging from soft matter condensed physics, nanoscience, biology, chemistry, veterinary science, engineering, environmental science to geology with a new interdisciplinary tool to the broader science community.
The presentation, "Synchrotron Based Infrared Imaging at the Diffraction Limit " is at 2:20 p.m. on Wednesday, October 20, 2010.
12) NEW PARADIGM FOR PLASMA PROCESSING
There's a new paradigm for plasma processing: Using microscale plasmas to realize nanoscale materials. Future electronics devices will incorporate nanoscale materials such as carbon nanotubes and silicon nanowires that cannot be fabricated using current plasma technology, in part due to limitations associated with photolithography.
Mohan Sankaran, associate professor in Case Western Reserve University's Department of Chemical Engineering, will give a presentation highlighting the advantages of using "microplasmas" for the synthesis of well-defined nanomaterials.
Low-pressure, large-volume plasmas are indispensible to materials processing in applications ranging from microelectronics to medicine, Sankaran explains. "For example, in the electronics industry, plasmas are used to precisely deposit or etch thin films from vapor precursors. There are limitations, however, to this technology, including the cost associated with vacuum equipment and the inability to manipulate materials at the nanoscale."
Sankaran's research is focused on developing a very different kind of plasma: A microplasma that operates at atmospheric pressure and very small volumes (less than a nanoliter) for nanomaterials synthesis. Microplasmas are a special class of electrical discharges formed in geometries in which at least one dimension is less than 1 millimeter.
"Under the very different processing conditions present in a microplasma, vapor precursors are dissociated in the gas phase to form nanoparticles rather than deposit as a film. Other nanomaterials can be grown by this approach as well, including carbon nanotubes and silicon nanowires," he notes.
Microplasmas show the potential to make large-scale amounts of a wide range of nanomaterials much more cost effective for emerging applications in nanoelectronics, catalysis, sensors and photovoltaics.
The presentation, "Microscale, Atmospheric-Pressure Plasmas for Nanomaterials Synthesis" is at 2:40 p.m. on Monday, October 18, 2010.
13) PAVING THE WAY TO HIGH-DENSITY MRAM DEVICES
Magnetic random access memory (MRAM) is known to combine many desirable characteristics for data storage systems, such as non-volatility, low-voltage operation, unlimited read and write endurance, as well as fast read and write operations. MRAM is also considered attractive because it can advantageously replace the commercial and conventional RAM chip technologies for computer data storage, because in MRAM information isn't stored as electric charge or current flow, but rather by as magnetically oriented domains.
Jérémy Pereira, researcher at the France's Centre National de la Recherche Scientifique's Laboratoire des Technologies de la Microélectronique, and colleagues will be discussing their MRAM research at the meeing.
"Today MRAM integration is limited by magnetic tunneling junction (MTJ) etching, which is done by dual-beam ion beam etching (IBE). IBE isn't scalable because of shadowing effects, which limits storage density," says Pereira. "Moreover, the IBE process can lead to magnetic materials re-deposition on the pattern sidewalls that can short-circuit the dielectric tunnel junction."
Pereira and colleagues are proposing to develop a full reactive ion etching (RIE) process for the patterning of thermally assisted MRAM dots as an alternative to an IBE one. The magnetic materials composing the MTJ junction are etched using carbon monoxide/ammonia (CO/NH3)-based plasmas, assisted by temperature. This process avoids corrosion issues from oxygen (O2) and chlorine (Cl2) gases, according to Pereira, while yielding vertical profiles without deposits.
This may prove to be a good alternative to IBE processes—paving the way to production of high-density MRAM devices.
The presentation, "Etching of Magnetic Stack for Development of Thermally-assisted Magnetic Access Random Memory" is at 10:40 a.m. on Tuesday, October 19, 2010.
14) A NEW 'HELICON SOURCE' FOR PLASMAS
Helicons are low-frequency electromagnetic waves that require a direct-current (DC) magnetic field. Previous helicon sources developed for industry required electromagnets weighing 200 lbs and a large power supply to energize them.
Francis F. Chen, professor emeritus, and colleagues in the University of California–Los Angeles' Electrical Engineering Department have found a clever way to use permanent magnets weighing only 3 lbs to do the same thing. In fact, an entire high-density source can now be smaller than a coffee maker.
"Most transistor chips, flat panel displays and plastic packaging are made using exposure to a plasma at one stage or another. Plasmas are generated efficiently with 'helicon' sources, but these usually require a large, heavy magnet. Our helicon source uses small permanent magnets, and an array of these small sources can cover a large area uniformly for either batch or roll-to-roll plasma processing," explains Chen.
The presentation, "PM Helicons: A Better Mousetrap" is at 2:40 p.m. on Tuesday, October 19, 2010.
Source: AVS
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