Super-Small Transistor Created: Artificial Atom Powered by Single Electrons

The researchers report inNature Nanotechnologythat the transistor's central component -- an island only 1.5 nanometers in diameter -- operates with the addition of only one or two electrons. That capability would make the transistor important to a range of computational applications, from ultradense memories to quantum processors, powerful devices that promise to solve problems so complex that all of the world's computers working together for billions of years could not crack them.

In addition, the tiny central island could be used as an artificial atom for developing new classes of artificial electronic materials, such as exotic superconductors with properties not found in natural materials, explained lead researcher Jeremy Levy, a professor of physics and astronomy in Pitt's School of Arts and Sciences. Levy worked with lead author and Pitt physics and astronomy graduate student Guanglei Cheng, as well as with Pitt physics and astronomy researchers Feng Bi, Daniela Bogorin,and Cheng Cen. The Pitt researchers worked with a team from the University of Wisconsin at Madison led by materials science and engineering professor Chang-Beom Eom, including research associates Chung Wun Bark, Jae-Wan Park, and Chad Folkman. Also part of the team were Gilberto Medeiros-Ribeiro, of HP Labs, and Pablo F. Siles, a doctoral student at the State University of Campinas in Brazil.

Levy and his colleagues named their device SketchSET, or sketch-based single-electron transistor, after a technique developed in Levy's lab in 2008 that works like a microscopic Etch A Sketch^TM, the drawing toy that inspired the idea. Using the sharp conducting probe of an atomic force microscope, Levy can create such electronic devices as wires and transistors of nanometer dimensions at the interface of a crystal of strontium titanate and a 1.2 nanometer thick layer of lanthanum aluminate. The electronic devices can then be erased and the interface used anew.

The SketchSET -- which is the first single-electron transistor made entirely of oxide-based materials -- consists of an island formation that can house up to two electrons. The number of electrons on the island -- which can be only zero, one, or two -- results in distinct conductive properties. Wires extending from the transistor carry additional electrons across the island.

One virtue of a single-electron transistor is its extreme sensitivity to an electric charge, Levy explained. Another property of these oxide materials is ferroelectricity, which allows the transistor to act as a solid-state memory. The ferroelectric state can, in the absence of external power, control the number of electrons on the island, which in turn can be used to represent the 1 or 0 state of a memory element. A computer memory based on this property would be able to retain information even when the processor itself is powered down, Levy said. The ferroelectric state also is expected to be sensitive to small pressure changes at nanometer scales, making this device potentially useful as a nanoscale charge and force sensor.

The research inNature Nanotechnologyalso was supported in part by grants from the U.S. Defense Advanced Research Projects Agency (DARPA), the U.S. Army Research Office, the National Science Foundation, and the Fine Foundation.

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Hydrocarbons Deep Within Earth: New Computational Study Reveals How

The thermodynamic and kinetic properties of hydrocarbons at high pressures and temperatures are important for understanding carbon reservoirs and fluxes in Earth.

The work provides a basis for understanding experiments that demonstrated polymerization of methane to form high hydrocarbons and earlier methane forming reactions under pressure.

Hydrocarbons (molecules composed of the elements hydrogen and carbon) are the main building block of crude oil and natural gas. Hydrocarbons contribute to the global carbon cycle (one of the most important cycles of Earth that allows for carbon to be recycled and reused throughout the biosphere and all of its organisms).

The team includes colleagues at UC Davis, Lawrence Livermore National Laboratory and Shell Projects& Technology. One of the researchers, UC Davis Professor Giulia Galli, is the co-chair of the Deep Carbon Observatory's Physics and Chemistry of Deep Carbon Directorate and former LLNL researcher.

Geologists and geochemists believe that nearly all (more than 99 percent) of the hydrocarbons in commercially produced crude oil and natural gas are formed by the decomposition of the remains of living organisms, which were buried under layers of sediments in Earth's crust, a region approximately 5-10 miles below Earth's surface.

But hydrocarbons of purely chemical deep crustal or mantle origin (abiogenic) could occur in some geologic settings, such as rifts or subduction zones said Galli, a senior author on the study.

"Our simulation study shows that methane molecules fuse to form larger hydrocarbon molecules when exposed to the very high temperatures and pressures of the Earth's upper mantle," Galli said."We don't say that higher hydrocarbons actually occur under the realistic 'dirty' Earth mantle conditions, but we say that the pressures and temperatures alone are right for it to happen.

Galli and colleagues used the Mako computer cluster in Berkeley and computers at Lawrence Livermore to simulate the behavior of carbon and hydrogen atoms at the enormous pressures and temperatures found 40 to 95 miles deep inside Earth. They used sophisticated techniques based on first principles and the computer software system Qbox, developed at UC Davis.

They found that hydrocarbons with multiple carbon atoms can form from methane, (a molecule with only one carbon and four hydrogen atoms) at temperatures greater than 1,500 K (2,240 degrees Fahrenheit) and pressures 50,000 times those at Earth's surface (conditions found about 70 miles below the surface).

"In the simulation, interactions with metal or carbon surfaces allowed the process to occur faster -- they act as 'catalysts,'" said UC Davis' Leonardo Spanu, the first author of the paper.

The research does not address whether hydrocarbons formed deep in Earth could migrate closer to the surface and contribute to oil or gas deposits. However, the study points to possible microscopic mechanisms of hydrocarbon formation under very high temperatures and pressures.

Galli's co-authors on the paper are Spanu; Davide Donadio at the Max Planck Institute in Meinz, Germany; Detlef Hohl at Shell Global Solutions, Houston; and Eric Schwegler of Lawrence Livermore National Laboratory.

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New Way to Control Magnetic Properties of Graphene Discovered

The finding by a team of Maryland researchers, led by Physics Professor Michael S. Fuhrer of the UMD Center for Nanophysics and Advanced Materials is the latest of many amazing properties discovered for graphene.

A honeycomb sheet of carbon atoms just one atom thick, graphene is the basic constituent of graphite. Some 200 times stronger than steel, it conducts electricity at room temperature better than any other known material (a 2008 discovery by Fuhrer, et. al). Graphene is widely seen as having great, perhaps even revolutionary, potential for nanotechnology applications. The 2010 Nobel Prize in physics was awarded to scientists Konstantin Novoselov and Andre Geim for their 2004 discovery of how to make graphene.

In their new graphene discovery, Fuhrer and his University of Maryland colleagues have found that missing atoms in graphene, called vacancies, act as tiny magnets -- they have a"magnetic moment." Moreover, these magnetic moments interact strongly with the electrons in graphene which carry electrical currents, giving rise to a significant extra electrical resistance at low temperature, known as the Kondo effect. The results appear in the paper"Tunable Kondo effect in graphene with defects" published this month inNature Physics.

The Kondo effect is typically associated with adding tiny amounts of magnetic metal atoms, such as iron or nickel, to a non-magnetic metal, such as gold or copper. Finding the Kondo effect in graphene with vacancies was surprising for two reasons, according to Fuhrer.

"First, we were studying a system of nothing but carbon, without adding any traditionally magnetic impurities. Second, graphene has a very small electron density, which would be expected to make the Kondo effect appear only at extremely low temperatures," he said.

The team measured the characteristic temperature for the Kondo effect in graphene with vacancies to be as high as 90 Kelvin, which is comparable to that seen in metals with very high electron densities. Moreover the Kondo temperature can be tuned by the voltage on an electrical gate, an effect not seen in metals. They theorize that the same unusual properties of that result in graphene's electrons acting as if they have no mass also make them interact very strongly with certain kinds of impurities, such as vacancies, leading to a strong Kondo effect at a relatively high temperature.

Fuhrer thinks that if vacancies in graphene could be arranged in just the right way, ferromagnetism could result."Individual magnetic moments can be coupled together through the Kondo effect, forcing them all to line up in the same direction," he said.

"The result would be a ferromagnet, like iron, but instead made only of carbon. Magnetism in graphene could lead to new types of nanoscale sensors of magnetic fields. And, when coupled with graphene's tremendous electrical properties, magnetism in graphene could also have interesting applications in the area of spintronics, which uses the magnetic moment of the electron, instead of its electric charge, to represent the information in a computer.

"This opens the possibility of 'defect engineering' in graphene -- plucking out atoms in the right places to design the magnetic properties you want," said Fuhrer.

This research was supported by grants from the National Science Foundation and the Office of Naval Research.

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New Spin on Graphene Makes It Magnetic

The results, reported inScience, could be a potentially huge breakthrough in the field of spintronics.

Spintronics is a group of emerging technologies that exploit the intrinsic spin of the electron, in addition to its fundamental electric charge that is exploited in microelectronics.

Billions of spintronics devices such as sensors and memories are already being produced. Every hard disk drive has a magnetic sensor that uses a flow of spins, and magnetic random access memory (MRAM) chips are becoming increasingly popular.

The findings are part of a large international effort involving research groups from the US, Russia, Japan and the Netherlands.

The key feature for spintronics is to connect the electron spin to electric current as current can be manipulated by means routinely used in microelectronics.

It is believed that, in future spintronics devices and transistors, coupling between the current and spin will be direct, without using magnetic materials to inject spins as it is done at the moment.

So far, this route has only been demonstrated by using materials with so-called spin-orbit interaction, in which tiny magnetic fields created by nuclei affect the motion of electrons through a crystal. The effect is generally small which makes it difficult to use.

The researchers found a new way to interconnect spin and charge by applying a relatively weak magnetic field to graphene and found that this causes a flow of spins in the direction perpendicular to electric current, making a graphene sheet magnetised.

The effect resembles the one caused by spin-orbit interaction but is larger and can be tuned by varying the external magnetic field.

The Manchester researchers also show that graphene placed on boron nitride is an ideal material for spintronics because the induced magnetism extends over macroscopic distances from the current path without decay.

The team believes their discovery offers numerous opportunities for redesigning current spintronics devices and making new ones such as spin-based transistors.

Professor Geim said:"The holy grail of spintronics is the conversion of electricity into magnetism or vice versa.

"We offer a new mechanism, thanks to unique properties of graphene. I imagine that many venues of spintronics can benefit from this finding."

Antonio Castro Neto, a physics professor from Boston who wrote a news article for theSciencemagazine which accompanies the research paper commented:"Graphene is opening doors for many new technologies.

"Not surprisingly, the 2010 Nobel Physics prize was awarded to Andre Geim and Kostya Novoselov for their groundbreaking experiments in this material.

"Apparently not satisfied with what they have accomplished so far, Geim and his collaborators have now demonstrated another completely unexpected effect that involves quantum mechanics at ambient conditions. This discovery opens a new chapter to the short but rich history of graphene."

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Creative, Online Learning Tool Helps Students Tackle Real-World Problems

A new computer interface developed at Iowa State University is helping students use what they've learned in the horticulture classroom and apply it to problems they'll face when they are on the job site.

The project, called ThinkSpace, is led by a group of ISU faculty including Ann Marie VanDerZanden, professor of horticulture and associate director of ISU's Center for Excellence in Learning and Teaching.

ThinkSpace has many different features that make it an effective way to teach using ill-structured problems. This type of problem allows students to choose from multiple paths to arrive at a solution.

By contrast, well-structured problems have a straight path to the one, clear solution.

In horticulture, the ThinkSpace platform is being used for upper-level classes and requires students to access what they've learned throughout their time studying horticulture and apply it to real-world problems.

In these classes, VanDerZanden gives students computer-delivered information about residential landscape.

That information includes illustrations of the work site, descriptions of the trees on the property, explanations of the problems the homeowner is experiencing, mock audio interview files with the property owner, and about anything else a horticulture professional would discover when approaching a homeowner with a landscape problem.

Also, just like in real life, some of the information is relevant to the problem, and some information is not.

"It forces students to take this piece of information, and that piece of information, and another piece of information, and then figure out what is wrong -- in this case with a plant," said VanDerZanden.

When the students think they have determined the problem, they enter their responses into the online program.

VanDerZanden can then check the responses.

For those students on the right track, she allows them to continue toward a solution.

For those who may have misdiagnosed the situation, VanDerZanden steers the students toward the right track before allowing them to move forward.

So far, the response from students has been very positive.

"The students like the variety," said VanDerZanden."They like struggling with real-world problems, rather that something that is just made up. On the other hand, they can get frustrated because there is not a clear-cut answer."

The entire process leverages the classroom experience into something the students can use at work.

"I think this really enhances student learning," said VanDerZanden."Students apply material from previous classes to a plausible, real-world situation. For instance students see what happens when a tree was pruned really hard to allow a piece of equipment to get into the customer's yard. As a result, the tree sends out a lot of new succulent shoots, and then there is an aphid infestation in the tree. It helps students start making all of those connections."

The ThinkSpace interface was developed from existing technologies already being used in ISU's College of Veterinary Medicine, College of Engineering and department of English.

VanDerZanden and her group recently received a$446,000 grant from the United States Department of Agriculture Higher Education Challenge Grant program to further develop ThinkSpace so it could more useful to other academic areas and universities.

As part of this research, VanDerZanden is also working with faculty members at University of Pennsylvania, Philadelphia; University of Wisconsin, Madison; and Kansas State University, Manhattan.

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Privacy Mode Helps Secure Android Smartphones

"There are a lot of concerns about potential leaks of personal information from smartphones," says Dr. Xuxian Jiang, an assistant professor of computer science at NC State and co-author of a paper describing the research."We have developed software that creates a privacy mode for Android systems, giving users flexible control over what personal information is available to various applications." The privacy software is called Taming Information-Stealing Smartphone Applications (TISSA).

TISSA works by creating a privacy setting manager that allows users to customize the level of information each smartphone application can access. Those settings can be adjusted any time that the relevant applications are being run -- not just when the applications are installed.

The TISSA prototype includes four possible privacy settings for each application. These settings are Trusted, Anonymized, Bogus and Empty. If an application is listed as Trusted, TISSA does not impose additional information access restrictions. If the user selects Anonymized, TISSA provides the application with generalized information that allows the application to run, without providing access to detailed personal information. The Bogus setting provides an application with fake results when it requests personal information. The Empty setting responds to information requests by saying the relevant information does not exist or is unavailable.

Jiang says TISSA could be easily modified to incorporate additional settings that would allow more fine-grained control of access to personal information."These settings may be further specialized for different types of information, such as your contact list or your location," Jiang says."The settings can also be specialized for different applications."

For example, a user may install a weather application that requires location data in order to provide the user with the local weather forecast. Rather than telling the application exactly where the user is, TISSA could be programmed to give the application generalized location data -- such as a random location within a 10-mile radius of the user. This would allow the weather application to provide the local weather forecast information, but would ensure that the application couldn't be used to track the user's movements.

The researchers are currently exploring how to make this software available to Android users."The software modification is relatively minor," Jiang says,"and could be incorporated through an over-the-air update."

The paper,"Taming Information-Stealing Smartphone Applications (on Android)," was co-authored by Jiang; Yajin Zhou, a Ph.D. student at NC State; Dr. Vincent Freeh, an associate professor of computer science at NC State; and Dr. Xinwen Zhang of Huawei America Research Center. The paper will be presented in June at the 4th International Conference on Trust and Trustworthy Computing, in Pittsburgh, Pa. The research was supported by the National Science Foundation and NC State's Secure Open Systems Initiative, which receives funding from the U.S. Army Research Office.

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Wii Key to Helping Kids Balance

The Rice engineering students created the new device using components of the popular Nintendo game system to create a balance training system.

What the kids may see as a fun video game is really a sophisticated way to help them advance their skills. The Wii Balance Boards lined up between handrails will encourage patients age 6 to 18 to practice their balance skills in an electronic gaming environment. The active handrails, which provide feedback on how heavily patients depend on their arms, are a unique feature.

Many of the children targeted for this project have cerebral palsy, spina bifida or amputations. Using the relatively inexpensive game console components improves the potential of this system to become a cost-effective addition to physical therapy departments in the future.

Steven Irby, an engineer at Shriners' Motion Analysis Laboratory, pitched the idea to Rice's engineering mentors after the success of last year's Trek Tracker project, a computer-controlled camera system for gait analysis that was developed by engineering students at Rice's Oshman Engineering Design Kitchen (OEDK).

The engineering seniors who chose to tackle this year's new project -- Michelle Pyle, Drew Berger and Matt Jones, aka Team Equiliberators -- hope to have the system up and running at Shriners Hospital before they graduate next month.

"He (Irby) wants to get kids to practice certain tasks in their games, such as standing still, then taking a couple of steps and being able to balance, which is pretty difficult for some of them," Pyle said."The last task is being able to take a couple of steps and then turn around."

"This isn't a measurement device as much as it is a game," Irby said."But putting the two systems together is what makes it unique. The Wii system is not well suited to kids with significant balance problems; they can't play it. So we're making something that is more adaptable to them."

The game requires patients to shoot approaching monsters by hitting particular spots with their feet as they step along the Wii array, computer science student Jesus Cortez, one of the game's creators, explained. The game gets harder as the patients improve, he said, and the chance to rack up points gives them an incentive.

A further step, not yet implemented, would be to program feedback from the handrails into the game. Leaning on the rails would subtract points from the users' scores, encouraging them to improve their postures. The game would also present challenges specific to younger and older children to keep them engaged.

The programming team also includes undergraduate Irina Patrikeeva and graduate student Nick Zhu. Studio arts undergraduate Jennifer Humphreys created the artwork.

The system's components include a PC, the Wii boards (aligned in a frame) and two balance beam-like handrails that read how much force patients are putting on their hands. Communications to the PC are handled via the Wii's native Bluetooth protocol.

The students said their prototype cost far less than the$2,000 they'd budgeted. Rice supplied the computer equipment and LabVIEW software they needed to create the diagnostic software that interfaces with Shriners' existing systems, and they purchased the Wii Balance Boards on eBay.

"Small force plates that people commonly use for such measurements cost at least a couple of grand, but Wii boards -- and people have done research on this -- give you a pretty good readout of your center of balance for what they cost," Pyle said.

Jones, who is building the final unit for delivery to Shriners, said he wants patients to see the Wii boards."We're putting clear acrylic over the boards so there aren't any gaps that could trip up the younger ones," he said."We wanted to use a device that's familiar to them, but they might not be convinced it's a Wii board unless they can see it."

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