Graphite Mimics Iron's Magnetism: New Nanotech Applications.

SOURCE

ScienceDaily (Oct. 5, 2009) — Researchers of Eindhoven University of Technology and the Radboud University Nijmegen in The Netherlands show for the first time why ordinary graphite is a permanent magnet at room temperature. The results are promising for new applications in nanotechnology, such as sensors and detectors. In particular graphite could be a promising candidate for a biosensor material. The results will appear online on 4 October in Nature Physics.

Graphite is a well-known lubricant and forms the basis for pencils. It is a layered compound with a weak interlayer interaction between the individual carbon (graphene) sheets. Hence, this makes graphite a good lubricant.

Unexpected:
It is unexpected that graphite is ferromagnetic. The researchers Jiri Cervenka and Kees Flipse (Eindhoven University of Technology) and Mikhail Katsnelson (Radboud University Nijmegen) demonstrated direct evidence for ferromagnetic order and explain the underlying mechanism. In graphite well ordered areas of carbon atoms are separated by 2 nanometer wide boundaries of defects. The electrons in the defect regions (the red/yellow area in picture 1) behave differently compared to the ordered areas (blue in picture 1), showing similarities with the electron behaviour of ferromagnetic materials like iron and cobalt.

Debate settled:
The researchers found that the grain boundary regions in the individual carbon sheets are magnetically coupled, forming 2-dimensional networks (picture 2). This interlayer coupling was found to explain the permanent magnetic behaviour of graphite. The researchers also show experimental evidence for excluding magnetic impurities to be the origin of ferromagnetism, ending ten years of debate.

Carbon in spintronics:
Surprisingly, a material containing only carbon atoms can be a weak ferro magnet. This opens new routes for spintronics in carbon-based materials. Spins can travel over relative long distances without spin-flip scattering and they can be flipped by small magnetic fields. Both are important for applications in spintronics. Carbon is biocompatible and the explored magnetic behaviour is therefore particularly promising for the development of biosensors.
The research was funded by Nanoned and FOM.
Journal reference:
Jiri Cervenka, Mikhail Katsnelson and Kees Flipse. Room-temperature ferromagnetism in graphite driven by 2D networks of point defects. Nature Physics, October 4, 2009 DOI: 10.1038/NPHYS1399
Adapted from materials provided by Eindhoven University of Technology, via EurekAlert!, a service of AAAS.

Step Forward For Nanotechnology: Controlled Movement Of Molecules.

SOURCE

ScienceDaily (Oct. 1, 2009) — Scientists in the United Kingdom are reporting an advance toward overcoming one of the key challenges in nanotechnology: Getting molecules to move quickly in a desired direction without help from outside forces.

Their achievement has broad implications, the scientists say, raising the possibility of coaxing cells to move and grow in specific directions to treat diseases. It also could speed development of some long-awaited nanotech innovations. They include self-healing structures that naturally repair tears in their surface and devices that deliver medication to diseased while sparing healthy tissue.
The study is scheduled for the October issue of ACS Nano, a monthly journal.
Mark Geoghegan and colleagues note long-standing efforts to produce directed, controlled movement of individual molecules in the nano world, where objects are about 1/50,000ththe width of a human hair. The main solutions so far have involved use of expensive, complex machines to move the molecules and they have been only partially successful, the scientists say.
The scientists used a special surface with hydrophobic (water repelling) and hydrophilic (water-attracting) sections. The region between the two sections produced a so-called "energy gradient" which can move tiny objects much like a conveyor belt. In lab studies, the scientists showed that plastic nanoparticles (polymer molecules) moved quickly and in a specific direction on this surface. "This could have implications in many technologies such as coaxing cells to move and grow in given directions, which could have major implications for the treatment of paralysis," the scientists said.
Journal reference:
Burgos et al. Directed Single Molecule Diffusion Triggered by Surface Energy Gradients. ACS Nano, 2009; 090923111502009 DOI: 10.1021/nn900991r
Adapted from materials provided by American Chemical Society, via EurekAlert!, a service of AAAS.

Spallation Neutron Source First Of Its Kind To Reach Megawatt Power.

SOURCE

ScienceDaily (Oct. 1, 2009) — The Department of Energy's Spallation Neutron Source (SNS), already the world's most powerful facility for pulsed neutron scattering science, is now the first pulsed spallation neutron source to break the one-megawatt barrier.

"Advances in the materials sciences are fundamental to the development of clean and sustainable energy technologies. In reaching this milestone of operating power, the Spallation Neutron Source is providing scientists with an unmatched resource for unlocking the secrets of materials at the molecular level," said Dr. William F. Brinkman, Director of DOE's Office of Science.
SNS operators at DOE's Oak Ridge National Laboratory pushed the controls past the megawatt mark on September 18 as the SNS ramped up for its latest operational run.
"The attainment of one megawatt in beam power symbolizes the advancement in analytical resources that are now available to the neutron scattering community through the SNS," said ORNL Director Thom Mason, who led the SNS project during its construction. "This is a great achievement not only for DOE and Oak Ridge National Laboratory, but for the entire community of science."
Before the SNS, the world's spallation neutron sources operated in the hundred-kilowatt range. The SNS actually became a world-record holder in August 2007 when it reached 160 kilowatts, earning it an entry in the Guinness Book of World Records as the world's most powerful pulsed spallation neutron source.
Beam power isn't merely a numbers game. A more powerful beam means more neutrons are spalled from SNS's mercury target. For the researcher, the difference in beam intensity is comparable to the ability to see with a car's headlights versus a flashlight. More neutrons also enhance scientific opportunities, including flexibility for smaller samples and for real-time studies at shorter time scales. For example, experiments will be possible that use just one pulse of neutrons to illuminate the dynamics of scientific processes.
Eventually, the SNS will reach its design power of 1.4 megawatts. The gradual increase of beam power has been an ongoing process since the SNS was completed and activated in late April 2006.
In the meantime, scientists have been performing cutting-edge experiments and materials analysis as its eventual suite of 25 instruments comes on line. As DOE Office of Science user facilities, the SNS and its companion facility, the High Flux Isotope Reactor, host researchers from around the world for neutron scattering experiments.
ORNL is managed by UT-Battelle for the Department of Energy.
Adapted from materials provided by DOE/Oak Ridge National Laboratory.

Physicists Create First Atomic-scale Map Of Quantum Dots.

SOURCE

ScienceDaily (Sep. 30, 2009) — University of Michigan physicists have created the first atomic-scale maps of quantum dots, a major step toward the goal of producing "designer dots" that can be tailored for specific applications.

Quantum dots—often called artificial atoms or nanoparticles—are tiny semiconductor crystals with wide-ranging potential applications in computing, photovoltaic cells, light-emitting devices and other technologies. Each dot is a well-ordered cluster of atoms, 10 to 50 atoms in diameter.
Engineers are gaining the ability to manipulate the atoms in quantum dots to control their properties and behavior, through a process called directed assembly. But progress has been slowed, until now, by the lack of atomic-scale information about the structure and chemical makeup of quantum dots.
The new atomic-scale maps will help fill that knowledge gap, clearing the path to more rapid progress in the field of quantum-dot directed assembly, said Roy Clarke, U-M professor of physics and corresponding author of a paper on the topic published online Sept. 27 in the journal Nature Nanotechnology.
Lead author of the paper is Divine Kumah of the U-M's Applied Physics Program, who conducted the research for his doctoral dissertation.
"I liken it to exploration in the olden days," Clarke said of dot mapping. "You find a new continent and initially all you see is the vague outline of something through the mist. Then you land on it and go into the interior and really map it out, square inch by square inch.
"Researchers have been able to chart the outline of these quantum dots for quite a while. But this is the first time that anybody has been able to map them at the atomic level, to go in and see where the atoms are positioned, as well as their chemical composition. It's a very significant breakthrough."
To create the maps, Clarke's team illuminated the dots with a brilliant X-ray photon beam at Argonne National Laboratory's Advanced Photon Source. The beam acts like an X-ray microscope to reveal details about the quantum dot's structure. Because X-rays have very short wavelengths, they can be used to create super-high-resolution maps.
"We're measuring the position and the chemical makeup of individual pieces of a quantum dot at a resolution of one-hundredth of a nanometer," Clarke said. "So it's incredibly high resolution."
A nanometer is one-billionth of a meter.
The availability of atomic-scale maps will quicken progress in the field of directed assembly. That, in turn, will lead to new technologies based on quantum dots. The dots have already been used to make highly efficient lasers and sensors, and they might help make quantum computers a reality, Clarke said.
"Atomic-scale mapping provides information that is essential if you're going to have controlled fabrication of quantum dots," Clarke said. "To make dots with a specific set of characteristics or a certain behavior, you have to know where everything is, so that you can place the atoms optimally. Knowing what you've got is the most important thing of all."
In addition to Clarke, co-authors of the Nature Nanotechnology paper are Sergey Shusterman, Yossi Paltiel and Yizhak Yacoby.
The research was sponsored by a grant from the National Science Foundation. The U.S. Department of Energy supported work at Argonne National Laboratory's Advanced Photon Source.
Adapted from materials provided by University of Michigan.

Carbon Nanostructure Research May Lead To Revolutionary New Devices.

SOURCE

ScienceDaily (Sep. 28, 2009) — Dr. Jiwoong Park of Cornell University, who receives funding for basic research from the Air Force Office of Scientific Research (AFOSR), is investigating carbon nanostructures that may some day be used in electronic, thermal, mechanical and sensing devices for the Air Force.

"Devices that are required in many of the Air Force missions are somewhat different from commercial ones in the sense that they are often exposed to harsh environments while maintaining their maximum performance," Park said. "Carbon-based nanostructures, including carbon nanotubes and graphenes (thin layers of graphite) present many exciting properties that may lead to new device structures."
Park's team of researchers is examining single molecules, nanocrystals, nanowires, carbon nanotubes and their arrays in an effort to find a "bridging" material that has a stable structure for making molecular-level bonds. In addition, they are seeking an effective tool for resolving functional and structural challenges. If successful, they will be able to apply the research to future technological advances.
Park's research may contribute to the discovery of new electronic and optical devices that will revolutionize electrical engineering and bioengineering as well as physical and materials science.
As a result of Park's highly innovative work, the U.S. government has selected him to be a 2008 PECASE (Presidential Early Career Award in Science and Engineering) Award winner. The prestigious and much sought after award is the highest honor the government presents to promising scientists and engineers at the beginning of their careers. Each award winner receives a citation, a plaque, and up to $1 million in funding from the nominating agency (AFOSR).
"I fully expect that over the five-year period of the PECASE award, Professor Park will have established himself as a world leader in carbon nanotube and graphene research," said Dr. Harold Weinstock, the AFOSR program manager responsible for nominating Park.
Adapted from materials provided by Air Force Office of Scientific Research.

New Nanochemistry Technique Encases Single Molecules In Microdroplets.

SOURCE

ScienceDaily (Sep. 28, 2009) — Inventing a useful new tool for creating chemical reactions between single molecules, scientists at the National Institute of Standards and Technology (NIST) have employed microfluidics—the manipulation of fluids at the microscopic scale—to make microdroplets that contain single molecules of interest.

By combining this new microfluidic "droplet-on-demand" method with "optical tweezers" that could merge multiple droplets and cause their molecular contents to react, the research may ultimately lead to a compact, integrated setup for obtaining single-molecule information on the structure and function of important organic materials, such as proteins, enzymes, and DNA.
With the aid of NIST's Center for Nanoscale Science and Technology, physicists Carlos López-Mariscal and Kristian Helmerson created a tiny microfluidic device with a channel through which water can flow. Squeezed into a narrow stream by a mixture of oils whose viscosity, or resistance to flow, exerts pressure on it, the water then enters a narrow constriction. The water's abrupt pressure drop—accompanied by a dash of detergent—breaks its surface tension, splitting it into small droplets. (This same effect occurs when a thin stream of water falling from a faucet breaks up into small drops.)
The droplet sizes are highly uniform and can be tuned by adjusting the width of the constriction. With this technique, the researchers made droplets about a micrometer in diameter—or half an attoliter (half a billionth of a billionth of a liter) in volume.
In the microfluidic channel, the water is laced with desired molecules of just the right concentration, so that resulting droplets each pick up on average just one molecule of interest. Inside each droplet, the individual molecules of interest slosh around freely in the relatively roomy sphere, along with the water molecules that make up the bulk of every droplet.
By using laser beams, the researchers can move two or more single-molecule-containing droplets, cause them to coalesce, and observe the reactions through optical methods. For their initial reactions, the researchers are mixing fluorescent molecules that emit different colors, but in the future, they envision more interesting chemical reactions, such as those between an infectious agent and an antibody, or a chromosome and a drug. The researchers can shape a laser beam into any desired pattern and thereby trap not only single drops, but arrays of them, opening up new possibilities for single-molecule spectroscopy.
Journal reference:
C. López-Mariscal and K. Helmerson. Optical trapping of hydrosomes. Proc. SPIE, 2009; 7400, 740026
Adapted from materials provided by National Institute of Standards and Technology (NIST).

Discovery Brings New Type Of Fast Computers Closer To Reality.

SOURCE

ScienceDaily (Sep. 28, 2009) — Physicists at UC San Diego have successfully created speedy integrated circuits with particles called “excitons” that operate at commercially cold temperatures, bringing the possibility of a new type of extremely fast computer based on excitons closer to reality.

Their discovery, detailed this week in the advance online issue of the journal Nature Photonics, follows the team’s demonstration last summer of an integrated circuit—an assembly of transistors that is the building block for all electronic devices—capable of working at 1.5 degrees Kelvin above absolute zero. That temperature, equivalent to minus 457 degrees Fahrenheit, is not only less than the average temperature of deep space, but achievable only in special research laboratories.
Now the scientists report that they have succeeded in building an integrated circuit that operates at 125 degrees Kelvin, a temperature that while still a chilly minus 234 degrees Fahrenheit, can be easily attained commercially with liquid nitrogen, a substance that costs about as much per liter as gasoline.
“Our goal is to create efficient devices based on excitons that are operational at room temperature and can replace electronic devices where a high interconnection speed is important,” said Leonid Butov, a professor of physics at UCSD, who headed the research team. “We’re still in an early stage of development. Our team has only recently demonstrated the proof of principle for a transistor based on excitons and research is in progress.”
Excitons are pairs of negatively charged electrons and positively charged “holes” that can be created by light in a semiconductor such as gallium arsenide. When the electron and hole recombine, the exciton decays and releases its energy as a flash of light.
The fact that excitons can be converted into light makes excitonic devices faster and more efficient than conventional electronic devices with optical interfaces, which use electrons for computation and must then convert them to light for use in communications devices.
"Our transistors process signals using excitons, which like electrons can be controlled with electrical voltages, but unlike electrons transform into photons at the output of the circuit,” Butov said. “This direct coupling of excitons to photons allows us to link computation and communication."
Other members of the team involved in the discovery were physicists Gabriele Grosso, Joe Graves, Aaron Hammack and Alex High at UC San Diego, and materials scientists Micah Hanson and Arthur Gossard at UC Santa Barbara.
Their research was supported by the Army Research Office, the Department of Energy and the National Science Foundation.
Adapted from materials provided by University of California - San Diego.