lunedì 28 settembre 2009

Carbon Nanostructure Research May Lead To Revolutionary New Devices.

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.

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.


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.

Nanotechnology: Artificial Pore Created.

ScienceDaily (Sep. 28, 2009) — Using an RNA-powered nanomotor, University of Cincinnati (UC) biomedical engineering researchers have successfully developed an artificial pore able to transmit nanoscale material through a membrane.
In a study led by UC biomedical engineering professor Peixuan Guo, PhD, members of the UC team inserted the modified core of a nanomotor, a microscopic biological machine, into a lipid membrane. The resulting channel enabled them to move both single- and double-stranded DNA through the membrane.
Their paper, “Translocation of double-stranded DNA through membrane-adapted phi29 motor protein nanopores,” will appear in the journal Nature Nanotechnology, Sept. 27, 2009. The engineered channel could have applications in nano-sensing, gene delivery, drug loading and DNA sequencing," says Guo.
Guo derived the nanomotor used in the study from the biological motor of bacteriophage phi29, a virus that infects bacteria. Previously, Guo discovered that the bacteriophage phi29 DNA-packaging motor uses six molecules of the genetic material RNA to power its DNA genome through its protein core, much like a screw through a bolt.
"The re-engineered motor core itself has shown to associate with lipid membranes, but we needed to show that it could punch a hole in the lipid membrane," says David Wendell, PhD, co-first author of the paper and a research assistant professor in UC’s biomedical engineering department. "That was one of the first challenges, moving it from its native enclosure into this engineered environment."
In this study, UC researchers embedded the re-engineered nanomotor core into a lipid sheet, creating a channel large enough to allow the passage of double-stranded DNA through the channel.
Guo says past work with biological channels has been focused on channels large enough to move only single-stranded genetic material.
"Since the genomic DNA of human, animals, plants, fungus and bacteria are double stranded, the development of single pore system that can sequence double-stranded DNA is very important," he says.
By being placed into a lipid sheet, the artificial membrane channel can be used to load double-stranded DNA, drugs or other therapeutic material into the liposome, other compartments, or potentially into a cell through the membrane.
Guo also says the process by which the DNA travels through the membrane can have larger applications.
"The idea that a DNA molecule travels through the nanopore, advancing nucleotide by nucleotide, could lead to the development of a single pore DNA sequencing apparatus, an area of strong national interest," he says.
Using stochastic sensing, a new analytical technique used in nanopore work, Wendell says researchers can characterize and identify material, like DNA, moving through the membrane.
Co-first author and UC postdoctoral fellow Peng Jing, PhD, says that, compared with traditional research methods, the successful embedding of the nanomotor into the membrane may also provide researchers with a new way to study the DNA packaging mechanisms of the viral nanomotor.
"Specifically, we are able to investigate the details concerning how double-stranded DNA translocates through the protein channel," he says.
The study is the next step in research on using nanomotors to package and deliver therapeutic agents directly to infected cells. Eventually, the team's work could enable use of nanoscale medical devices to diagnose and treat diseases.
"This motor is one of the strongest bio motors discovered to date," says Wendell, "If you can use that force to move a nanoscale rotor or a nanoscale machine … you're converting the force of the motor into a machine that might do something useful."
Funding for this study comes from the National Institutes of Health's Nanomedicine Development Center. Guo is the director of one of eight NIH Nanomedicine Development Centers and an endowed chair in biomedical engineering at UC.
Coauthors of the study include UC research assistant professor David Wendell, PhD, postdoctoral fellow Peng Jing, PhD, graduate students Jia Geng and Tae Jin Lee and former postdoctoral fellow Varuni Subramaniam from Guo’s previous lab at Purdue University. Carlo Montemagno, dean of the College of Engineering and College of Applied Science, also contributed to the study.
Journal reference:
. Translocation of double-stranded DNA through membrane-adapted phi29 motor protein nanopores. Nature Nanotechnology, Sept. 27, 2009
Adapted from materials provided by
University of Cincinnati Academic Health Center.

sabato 26 settembre 2009

Prototype Device Developed To Detect Dark Matter


ScienceDaily (Sep. 25, 2009) — A team of researchers from the University of Zaragoza (UNIZAR) and the Institut d'Astrophysique Spatiale (IAS, in France) has developed a "scintillating bolometer" -- a device that the scientists will use in efforts to detect the dark matter of the universe, and which has been tested at the Canfranc Underground Laboratory in Huesca, Spain.
"One of the biggest challenges in physics today is to discover the true nature of dark matter, which cannot be directly observed – even though it seems to make up one-quarter of the matter of the Universe. So we have to attempt to detect it using prototypes such as the one we have developed", Eduardo García Abancéns, a researcher from the UNIZAR's Laboratory of Nuclear Physics and Astroparticles, tells SINC.
García Abancéns is one of the scientists working on the ROSEBUD project (an acronym for Rare Objects SEarch with Bolometers UndergrounD), an international collaborative initiative between the Institut d'Astrophysique Spatiale (CNRS-University of Paris-South, in France) and the University of Zaragoza, which is focusing on hunting for dark matter in the Milky Way.
The scientists have been working for the past decade on this mission at the Canfranc Underground Laboratory, in Huesca, where they have developed various cryogenic detectors (which operate at temperatures close to absolute zero: −273.15 °C). The latest is a "scintillating bolometer", a 46-gram device that, in this case, contains a crystal "scintillator", made up of bismuth, germinate and oxygen (BGO: Bi4Ge3O12), which acts as a dark matter detector.
"This detection technique is based on the simultaneous measurement of the light and heat produced by the interaction between the detector and the hypothetical WIMPs (Weakly Interacting Massive Particles) which, according to various theoretical models, explain the existence of dark matter", explains García Abancéns.
The researcher explains that the difference in the scintillation of the various particles enables this method to differentiate between the signals that the WIMPs would produce and others produced by various elements of background radiation (such as alpha, beta or gamma particles).
In order to measure the miniscule amount of heat produced, the detector must be cooled to temperatures close to absolute zero, and a cryogenic facility, reinforced with lead and polyethylene bricks and protected from cosmic radiation as it housed under the Tobazo mountain, has been installed at the Canfranc underground laboratory.
"The new scintillating bolometer has performed excellently, proving its viability as a detector in experiments to look for dark matter, and also as a gamma spectrometer (a device that measures this type of radiation) to monitor background radiation in these experiments", says García Abancéns.
The scintillating bolometer is currently at the Orsay University Centre in France, where the team is working to optimise the device's light gathering, and carrying out trials with other BGO crystals.
This study, published recently in the journal Optical Materials, is part of the European EURECA project (European Underground Rare Event Calorimeter Array). This initiative, in which 16 European institutions are taking part (including the University of Zaragoza and the IAS), aims to construct a one-tonne cryogenic detector and use it over the next decade to hunt for the dark matter of the Universe.
Methods of detecting dark matter
Direct and indirect detection methods are used to detect dark matter, which cannot be directly observed since it does not emit radiation. The former include simultaneous light and heat detection (such as the technique used by the scintillating bolometers), simultaneous heat and ionisation detection, and simultaneous light and ionisation detection, such as research into distinctive signals (the most famous being the search for an annual modulation in the dark matter signal caused by the orbiting of the Earth).
There are also indirect detection methods, where, instead of directly seeking the dark matter particles, researchers try to identify other particles, (neutrinos, photons, etc.), produced when the Universe's dark matter particles are destroyed.
Journal reference:
N. Coron, E. García, J. Gironnet, J. Leblanc, P. de Marcillac, M. Martínez, Y. Ortigoza, A. Ortiz de Solórzano, C. Pobes, J. Puimedón, T. Redon, M.L. Sarsa, L. Torres y J.A. Villar. A BGO scintillating bolometer as dark matter detector prototype. Optical Materials, 2009; 31 (10): 1393 DOI:
Adapted from materials provided by FECYT - Spanish Foundation for Science and Technology, via EurekAlert!, a service of AAAS.

mercoledì 23 settembre 2009

ATLAS e-News: Catching the elusive black hole

Professor Stephen Hawking, a central figure in black hole theory, during his recent visit to CERN with colloquium organiser, Luis Alvarez-Gaume on his left.

This time last year, talk of black holes overwhelmed the global news media. Closer to home, black holes are also making mischief – this time overwhelming the Trigger system.It turns out that if blacks hole event occurs in the first few months of data taking, we may actually be none the wiser. Not, as some tabloid newspapers were purporting, because we’ll be swallowed into oblivion, but rather because they’ll be masked as flawed events by the Trigger system.The problem, according to Ignacio Aracena, who works on jets and missing ET, is not that there is nothing to trigger on. Quite the contrary, plenty of final state particles will be produced, but to such an extent that the system will be inundated.“We expect that black holes will decay in essentially all the Standard Model particles,” says Ignacio. “But for black holes the number of jets is way higher [than for other events]. I’m not a black hole expert, but it’s something like 10 jets with high transverse momentum.”Compare this to, for example, a supersymmetry event where perhaps four or so jets, some missing transverse energy and a handful of leptons are expected, and you begin to get a sense of the challenge that black holes pose. They pretty much light up the whole detector.“For the trigger, the main idea of having a sequential selection was to focus on interesting physics objects and then only do the reconstruction in the trigger in that region,” Ignacio explains. Since there is only limited time available to process events at Levels 1 and 2, reading out the whole detector simply isn’t possible.The situation right now is that the Trigger system is virtually thrown whenever Monte Carlo black hole events are run. Processing the jets and retrieving all the data for them just takes too long; the time-out feature built into the algorithms kicks in before processing is complete, and data is instead dumped into the debug stream. This is a safety store where potentially interesting, but problematic, data is filed – corrupted or noisy data, or events that crash during execution – for later reprocessing offline.“This debug stream handling will be done in quasi-real time,” says Anna Sfyrla, who works on it, and adds: “Events with time-outs will usually be recovered during this reprocessing.” Recovered events are saved in datasets and made available for analysis, but so far there are no plans for these to be re-integrated into the physics online datasets.“In the long term, we’ll have to find a strategy to select these events,” says Ignacio. Allowing the system to be snowed under trying to process black hole data, at the expense of picking out and processing other physics events, is not an option. “From an analysis point of view, of course it would be helpful to know that you have black hole events in a specific data set. But we have a broad physics program and you have to keep the whole system running.”Eventually, a specific trigger chain, or even a specific data stream will likely be set up to select events that have large jet multiplicity with a high transverse energy. However, Ignacio concedes that with the current focus on really understanding the detector, its noise-levels and its responses, “It’s probably not something that we’re going to claim to see in the first two years.” Which means that if black hole events occur at all, the debug stream will be where they’re discovered.In the meanwhile, cosmic running is continually helping to improve the performance of algorithms – an optimisation process that will continue with the arrival of beam and collisions. “In this context, any improvements we make, even while taking cosmic data, are going to benefit [the eventual online identification of black holes],” says Ignacio. “Having this finally sent to a specific data stream will be the sum of all the efforts that we’re making right now and will do in the future.”

Ceri Perkins
ATLAS e-News

Is the Large Hadron Collider worth its massive price tag?


Scientists at Cern near Geneva are close to turning on their particle accelerator a year after it blew up. In their latest video, physicists hunting the Higgs boson ask what price society is willing to pay to understand the universe.

A month or so ago I was sat at a table outside the canteen at Cern, the European nuclear research organisation in Switzerland, nursing an espresso and watching an impromptu volleyball match play out across a giant blue magnet daubed with white paint. The graffiti read: "LH...C'est pas sorcier". It's not rocket science.
Maybe it's not, but what the scientists are trying to do at Cern is no easier. The underground accelerator, the Large Hadron Collider, is vast and vastly complex. It's almost no surprise it didn't spring to life and start churning out data as soon as they flicked the on switch this time last year.
I was at Cern to talk to scientists about the long march that is the hunt for the Higgs boson. The particle was predicted 45 years ago. You can think of it as a tell-tale fingerprint that confirms the existence of an extraordinary field that permeates the entirety of space, from the infinitesimal pinch between the constituents of atomic nuclei and the incomprehensible stretches of nothingness that separate galaxies.
The field is a big deal. According to physicists' best theories, it contains energy that it shares with the smallest building blocks of matter, such as electrons and quarks, the latter being the constituents of protons and neutrons in the atomic nucleus. The field gives the particles mass, and in doing so, brings stability and structure to the universe.
There are only two places in the world that have the capability to hunt for the Higgs boson: Fermilab near Chicago and Cern. Today, Fermilab is home to the world's most powerful particle collider, the Tevatron. Cern will take over that title in November, at least they will if they get the LHC up and running this time.
Cern has seen glimpses of what might be the Higgs boson before in 2000, with an older machine that was ripped out of the ground to make room for the Large Hadron Collider. If those glimpses were real, the Higgs is fairly light and could take a long time to find with LHC.
I've written about the Colliding Particles project here before. A team of Higgs hunters at University College London have teamed up with a film maker to produce a series of video shorts that follow their exploits. I can't praise them enough. They blast many full length TV science documentaries out of the water. They have a coherent narrative, they have engaging characters, they let you in on what happens to our £80m-a-year Cern subscription.
In the first video, the team talk about a new way to hunt for the Higgs. In this, their fifth video, it's time to pitch the idea to other Cern physicists. If the idea is accepted,
their "Eurostar" idea becomes part of the formal search for the missing particle. As luck would have it, they've roped in that bloke from The Mummy and Four Weddings to do their presentation. Or maybe it's his younger brother.
There's more to it though. The Large Hadron Collider is an expensive beast and in times of global financial meltdown and looming environmental problems, it's not unfair to wonder whether this kind of basic research is a luxury we can't afford. It's a question the physicists ponder and perhaps never fully answer.
The Large Hadron Collider might well be the last machine of its kind that ever gets built. But the fact that it was built is extremely heartening. This is a machine so large it takes hours to jog around. It cost billions of Euros and took many years to build. That governments were willing to pay for it, with no idea what it might or might not find, speaks volumes about the price society is willing to pay to understand more about our place in the universe.

domenica 20 settembre 2009

New X-ray Technique Illuminates Reactivity Of Environmental Contaminants.


ScienceDaily (Sep. 20, 2009) — A chemical reaction can occur in the blink of an eye.
Thanks to a new analytical method employed by researchers at the University of Delaware, scientists can now pinpoint, at the millisecond level, what happens as harmful environmental contaminants such as arsenic begin to react with soil and water under various conditions.
Quantifying the initial rates of such reactions is essential for modeling how contaminants are transported in the environment and predicting risks.
The research method, which uses an analytical technique known as quick-scanning X-ray absorption spectroscopy (Q-XAS), was developed by a research team led by Donald Sparks, S. Hallock du Pont Chair of Plant and Soil Sciences and director of the Delaware Environmental Institute at UD. The work is reported in the Sept. 10 Early Edition of the Proceedings of the National Academy of Sciences and will be in the Sept. 22 print issue.
Postdoctoral researcher Matthew Ginder-Vogel is the first author of the study, which also involved Ph.D. student Gautier Landrot and Jason Fischel, an undergraduate student at Juniata College who has interned in Sparks's lab during the past three summers.
The research method was developed using beamline X18B at the National Synchrotron Light Source at Brookhaven National Laboratory in Upton, N.Y. The facility is operated by the U.S. Department of Energy.
“This method is a significant advance in elucidating mechanisms of important geochemical processes, and is the first application, at millisecond time scales, to determine in real-time, the molecular scale reactions at the mineral/water interface. It has tremendous applications to many important environmental processes including sorption, redox, and precipitation,” Sparks said.
“My group and I have been conducting kinetics studies on soils and soil minerals for 30 years,” Sparks added. “Since the beginning I have been hopeful that someday we could follow extremely rapid reaction processes and simultaneously collect mechanistic information.”
X-ray spectroscopy was invented years ago to illuminate structures and materials at the atomic level. The technique has been commonly used by physicists, chemists, materials scientists, and engineers, but only recently by environmental scientists.
“In studying soil kinetics, we want to know how fast a contaminant begins to stick to a mineral,” Ginder-Vogel says. “In general, these reactions are very rapid -- 90 percent of the reaction is over in the first 10 seconds. Now we can measure the first few seconds of these reactions that couldn't be measured before. We can now look at things as they happen versus attempting to freeze time after the fact,” he notes.
For their study, the UD researchers made millisecond measurements of the oxidation rate of arsenic by hydrous manganese oxide, which is a mineral that absorbs heavy metals and nutrients.
Contamination of drinking water supplies by arsenic is a serious health concern in the United States and abroad. The poisonous element occurs naturally in rocks and minerals and is also used in a wide range of products, from wood preservatives and insecticides, to poultry feed.
The toxicity and availability of arsenic to living organisms depends on its oxidation state -- in other words, the number of electrons lost or gained by an atom when it reacts with minerals and microbes. For example, arsenite [As(III)] is more mobile and toxic than its oxidized counterpart, arsenate [As(V)].
“Our technique is important for looking at groundwater flowing through minerals,” Ginder-Vogel notes. “We look at it as a very early tool that can be incorporated into predictive modeling for the environment.”
A native of Minnesota, Ginder-Vogel started out as a chemist in college, but says he wanted to do something more applied. As he was completing his doctorate at Stanford University under Prof. Scott Fendorf, a UD alumnus who studied under Sparks, Ginder-Vogel saw the advertisement for a postdoctoral position in Sparks's lab and jumped at the opportunity.
“The University of Delaware has the reputation as one of the best research institutions in the country for soil science, and Don Sparks is a leader in the field,” Ginder-Vogel notes.
Ginder-Vogel says one of the coolest things about the current research is its interdisciplinary nature.
“What's novel about soil chemistry is that we can take bits of pieces from different fields -- civil and environmental engineering, materials science, chemistry, and biochemistry -- and apply it in unique ways,” he says. “It's fun to contribute to a new research method in our field.”
The research was funded by the U.S. Department of Agriculture (USDA) and by two grants from the National Science Foundation, including one from the NSF-Delaware Experimental Program to Stimulate Competitive Research (EPSCoR). The U.S. Department of Energy supported the research team's use of the National Synchrotron Light Source.
Journal reference:
Matthew Ginder-Vogel, Gautier Landrot, Jason S. Fischel, and Donald L. Sparks. Quantification of rapid environmental redox processes with quick-scanning x-ray absorption spectroscopy (Q-XAS). Proceedings of the National Academy of Sciences, 2009; DOI:
Adapted from materials provided by University of Delaware.

Strain On Nanocrystals Could Yield Colossal Results

ScienceDaily (Sep. 18, 2009) — In finally answering an elusive scientific question, researchers with the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) have shown that the selective placement of strain can alter the electronic phase and its spatial arrangement in correlated electron materials. This unique class of materials is commanding much attention now because they can display properties such as colossal magnetoresistance and high-temperature superconductivity, which are highly coveted by the high-tech industry.
Junqiao Wu, a physicist who holds joint appointments with Berkeley Lab’s Materials Sciences Division and the University of California-Berkeley’s Department of Materials Science and Engineering, led the study in which it was demonstrated that irregularities in the micro-domain structure of correlated electron materials - a phenomenon known as “phase inhomogeneity” - can be generated by external stimuli and could be engineered at the sub-micron scale to achieve desired properties.
“By continuously tuning strain over a wide range in single-crystal vanadium oxide micro- and nano-scale wires, we were able to engineer phase inhomogeneity along the wires,” says Wu. “Our results shed light on the origin of phase inhomogeneity in correlated electron materials in general, and open opportunities for designing and controlling phase inhomogeneity of correlated electron materials for future devices.”
Wu is the corresponding author of a paper describing this work which was published in the journal Nature Nanotechnology and is entitled: “Strain engineering and one-dimensional organization of metal-insulator domains in single crystal VO2 beams.” Co-authoring the paper with Wu were Jinbo Cao, Elif Ertekin, Varadharajan Srinivasan, Wen Fan, Simon Huang, Haimei Zheng, Joanne Yim, Devesh Khanal, Frank Ogletree and Jeffrey Grossman.
Whereas in conventional materials, the motion of one electron is relatively independent of any other, in “correlated electron materials” quantum effects enable electrons to act collectively, like dancers in a chorus line. Emerging from this collective electronic behavior are properties such as colossal magnetoresistance, where the presence of a magnetic field increases electrical resistance by orders of magnitude, or high-temperature superconductivity, in which the materials lose all electrical resistance at temperatures much higher than conventional superconductors.
Frequently observed spatial phase inhomogeneities are believed to be critical to the collective electronic behavior of correlated electron materials. However, despite decades of investigation, the question of whether such phase inhomogeneities are intrinsic to correlated electron materials or caused by external stimuli has remained largely unanswered.
“This question is not only important for our understanding of the physics behind correlated electron materials,” says Wu, “it also directly determines the spatial scale of correlated electron material device applications.”
To determine if phase inhomogeneity can be caused by external effects, Wu and his colleagues worked with vanadium oxide, a representative correlated electron material that features a metal-nonmetal transition, where in the nonmetal state its electrons can no longer carry an electrical current. After synthesizing the vanadium oxide into flexible single-crystal micro- and nanowires, the research team subjected the wires to strain by bending them to different curvatures. Different curvatures yielded different strains, and the phase transitions were measured in each of the strained areas.
“The metal-nonmetal domain structure was determined by competition between elastic deformation, thermodynamic and domain wall energies in this coherently strained system,” says Wu. “A uniaxial compressive strain of approximately 1.9-percent was able to drive the metal-nonmetal transition at room temperature.”
The ability to fabricate single-crystal micro- and nanowires of vanadium oxide that were free of structural defects made it possible to apply such high strain without plastic deformation or fracturing of the material, Wu says. Bulk and even thin film samples of vanadium oxide cannot tolerate a strain of even one-percent without suffering dislocations.
Wu says that in the future strain engineering might be achieved by interfacing a correlated electron material such as vanadium oxide with a piezoelectric - a non-conducting material that creates a stress or strain in response to an electric field.
“By applying an electric field, the piezoelectric material would strain the correlated electron material to achieve a phase transition that would give us the desired functionality,” says Wu. ”To reach this capability, however, we will first need to design and synthesize such integrated structures with good material quality.”
This work was supported in part by Berkeley Lab through its Laboratory Directed Research and Development Program, and in part by a grant from the National Science Foundation.
Adapted from materials provided by
DOE/Lawrence Berkeley National Laboratory.

venerdì 11 settembre 2009


This 3'30'' video represents the first graphical result of the two major aspects of our research: protein motion and visual representation. The main program used is Blender, an open source 3D animation and special effects package, which we have equipped with other scripts. We also make large use of other scientific (VMD, Swiss-PDBviewer with Gromos43B1, Chimera, Reduce – MolProbity, PDB2PQR,, APBS, and several home made scripts and programs) and graphical programs (Blender, Maya Autodesk, The Gimp, Djv_view, ImageMagick).
It shows a short trip to the interior of a cell, starting inside a small capillary vase. After navigating the vein, we meet some white cells, and we take a close look at one of them. We see the surface from a distance, so that we can observe the membrane dynamics, with no specific object clearly distinguished. We than 'land' on the surface and first see some glycolipids up close; when we look around we get a view of a membrane raft, with a crowd of many proteins, all in constant motion. One very erratic protein is a channel (protein that allow potassium ions to get out of the cell), into which we fall to get inside the cell.
Once inside we see Calmodulin, a very flexible small protein that we observe for a while before travelling along a microtubule, towards a place where Calcium waves are pulsing. Here our favourite protein is hit by Calcium and undergoes a major conformational change. This is shown from different perspectives, until we quickly move towards the periplasmic region of the cell, where the contractile ring is operating to split the cell in two at the time of cell division.
For a more detailed explanation of the scientific and the graphical aspects of the video, scene by scene, download this file.
See the video (Flash Player required)