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Sep 09

World’s Smallest Electric Motor Made from a Single Molecule.

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Reported by ScienceDaily, 5 Sep. 2011.

The smallest electrical motor on the planet, at least according to Guinness World Records, is 200 nanometers. Granted, that’s a pretty small motor — after all, a single strand of human hair is 60,000 nanometers wide — but that tiny mark is about to be shattered in a big way.

hemists at Tufts University have developed the world's first single molecule electric motor, which may potentially create a new class of devices that could be used in applications ranging from medicine to engineering. The molecular motor was powered by electricity from a state of the art, low-temperature scanning tunneling microscope. This microscope sent an electrical current through the molecule, directing the molecule to rotate in one direction or another. The molecule had a sulfur base (yellow); when placed on a conductive slab of copper (orange), it became anchored to the surface. The sulfur-containing molecule had carbon and hydrogen atoms radiating off to form what looks like two arms (gray); these carbon chains were free to rotate around the central sulfur-copper bond. The researchers found that reducing the temperature of the molecule to five Kelvin (K), or about minus 450 degrees Fahrenheit (ºF), enabled them to precisely impact the direction and rotational speed of the molecular motor The Tufts team plans to submit this miniature electric motor to the Guinness World Records. The research was published online Sept. 4 in Nature Nanotechnology. (Credit: Heather L. Tierney, Colin J. Murphy, April D. Jewell, Ashleigh E. Baber, Erin V. Iski, Harout Y. Khodaverdian, Allister F. McGuire, Nikolai Klebanov and E. Charles H. Sykes.)

Chemists at Tufts University’s School of Arts and Sciences have developed the world’s first single molecule electric motor, a development that may potentially create a new class of devices that could be used in applications ranging from medicine to engineering.

In research published online Sept. 4 in Nature Nanotechnology, the Tufts team reports an electric motor that measures a mere 1 nanometer across, groundbreaking work considering that the current world record is a 200 nanometer motor. A single strand of human hair is about 60,000 nanometers wide.

According to E. Charles H. Sykes, Ph.D., associate professor of chemistry at Tufts and senior author on the paper, the team plans to submit the Tufts-built electric motor to Guinness World Records.

“There has been significant progress in the construction of molecular motors powered by light and by chemical reactions, but this is the first time that electrically-driven molecular motors have been demonstrated, despite a few theoretical proposals,” says Sykes. “We have been able to show that you can provide electricity to a single molecule and get it to do something that is not just random.”

Sykes and his colleagues were able to control a molecular motor with electricity by using a state of the art, low-temperature scanning tunneling microscope (LT-STM), one of about only 100 in the United States. The LT-STM uses electrons instead of light to “see” molecules.

The team used the metal tip on the microscope to provide an electrical charge to a butyl methyl sulfide molecule that had been placed on a conductive copper surface. This sulfur-containing molecule had carbon and hydrogen atoms radiating off to form what looked like two arms, with four carbons on one side and one on the other. These carbon chains were free to rotate around the sulfur-copper bond.

The team determined that by controlling the temperature of the molecule they could directly impact the rotation of the molecule. Temperatures around 5 Kelvin (K), or about minus 450 degrees Fahrenheit (ºF), proved to be the ideal to track the motor’s motion. At this temperature, the Tufts researchers were able to track all of the rotations of the motor and analyze the data.

While there are foreseeable practical applications with this electric motor, breakthroughs would need to be made in the temperatures at which electric molecular motors operate. The motor spins much faster at higher temperatures, making it difficult to measure and control the rotation of the motor.

“Once we have a better grasp on the temperatures necessary to make these motors function, there could be real-world application in some sensing and medical devices which involve tiny pipes. Friction of the fluid against the pipe walls increases at these small scales, and covering the wall with motors could help drive fluids along,” said Sykes. “Coupling molecular motion with electrical signals could also create miniature gears in nanoscale electrical circuits; these gears could be used in miniature delay lines, which are used in devices like cell phones.”

The Changing Face of Chemistry

Students from the high school to the doctoral level played an integral role in the complex task of collecting and analyzing the movement of the tiny molecular motors.

“Involvement in this type of research can be an enlightening, and in some cases life changing, experience for students,” said Sykes. “If we can get people interested in the sciences earlier, through projects like this, there is a greater chance we can impact the career they choose later in life.”

As proof that gaining a scientific footing early can matter, one of the high school students involved in the research, Nikolai Klebanov, went on to enroll at Tufts; he is now a sophomore majoring in chemical engineering.

This work was supported by the National Science Foundation, the Beckman Foundation and the Research Corporation for Scientific Advancement.

Tufts University, located on three Massachusetts campuses in Boston, Medford/Somerville, and Grafton, and in Talloires, France, is recognized among the premier research universities in the United States. Tufts enjoys a global reputation for academic excellence and for the preparation of students as leaders in a wide range of professions. A growing number of innovative teaching and research initiatives span all campuses, and collaboration among the faculty and students in the undergraduate, graduate and professional programs across the university is widely encouraged.

Reference: Heather L. Tierney, Colin J. Murphy, April D. Jewell, Ashleigh E. Baber, Erin V. Iski, Harout Y. Khodaverdian, Allister F. McGuire, Nikolai Klebanov, E. Charles H. Sykes. Experimental demonstration of a single-molecule electric motor. Nature Nanotechnology, 2011; DOI: 10.1038/NNANO.2011.142

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Sep 08

A Whole New Light On Graphene Metamaterials: Tunable Graphene Device Is First Tool in a Kit for Putting Terahertz Light to Work.

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Reported by DOE/Lawrence Berkeley National Laboratory, 5 Sep. 2011. Also in ScienceDaily.

Long-wavelength terahertz light is invisible — it’s at the farthest end of the far infrared — but it’s useful for everything from detecting explosives at the airport to designing drugs to diagnosing skin cancer. Now, for the first time, scientists at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) and the University of California at Berkeley have demonstrated a microscale device made of graphene — the remarkable form of carbon that’s only one atom thick — whose strong response to light at terahertz frequencies can be tuned with exquisite precision.

he graphene microribbon array can be tuned in three ways. Varying the width of the ribbons changes plasmon resonant frequency and absorbs corresponding frequencies of terahertz light. Plasmon response is much stronger when there is a dense concentration of charge carriers (electrons or holes), controlled by varying the top gate voltage. Finally, light polarized perpendicularly to the ribbons is strongly absorbed at the plasmon resonant frequency, while parallel polarization shows no such response. (Credit: Lawrence Berkeley National Laboratory)

“The heart of our device is an array made of graphene ribbons only millionths of a meter wide,” says Feng Wang of Berkeley Lab’s Materials Sciences Division, who is also an assistant professor of physics at UC Berkeley, and who led the research team. “By varying the width of the ribbons and the concentration of charge carriers in them, we can control the collective oscillations of electrons in the microribbons.”

The name for such collective oscillations of electrons is “plasmons,” a word that sounds abstruse but describes effects as familiar as the glowing colors in stained-glass windows.

“Plasmons in high-frequency visible light happen in three-dimensional metal nanostructures,” Wang says. The colors of medieval stained glass, for example, result from oscillating collections of electrons on the surfaces of nanoparticles of gold, copper, and other metals, and depend on their size and shape. “But graphene is only one atom thick, and its electrons move in only two dimensions. In 2D systems, plasmons occur at much lower frequencies.”

The wavelength of terahertz radiation is measured in hundreds of micrometers (millionths of a meter), yet the width of the graphene ribbons in the experimental device is only one to four micrometers each.

“A material that consists of structures with dimensions much smaller than the relevant wavelength, and which exhibits optical properties distinctly different from the bulk material, is called a metamaterial,” says Wang. “So we have not only made the first studies of light and plasmon coupling in graphene, we’ve also created a prototype for future graphene-based metamaterials in the terahertz range.”

The team reports their research in Nature Nanotechnology, available in advanced online publication.

How to push the plasmons

In two-dimensional graphene, electrons have a tiny rest mass and respond quickly to electric fields. A plasmon describes the collective oscillation of many electrons, and its frequency depends on how rapidly waves in this electron sea slosh back and forth between the edges of a graphene microribbon. When light of the same frequency is applied, the result is “resonant excitation,” a marked increase in the strength of the oscillation — and simultaneous strong absorption of the light at that frequency. Since the frequency of the oscillations is determined by the width of the ribbons, varying their width can tune the system to absorb different frequencies of light.

The strength of the light-plasmon coupling can also be affected by the concentration of charge carriers — electrons and their positively charged counterparts, holes. One remarkable characteristic of graphene is that the concentration of its charge carriers can easily be increased or decreased simply by applying a strong electric field — so-called electrostatic doping.

The Berkeley device incorporates both these methods for tuning the response to terahertz light. Microribbon arrays were made by depositing an atom-thick layer of carbon on a sheet of copper, then transferring the graphene layer to a silicon-oxide substrate and etching ribbon patterns into it. An ion gel with contact points for varying the voltage was placed on top of the graphene.

The gated graphene microarray was illuminated with terahertz radiation at beamline 1.4 of Berkeley Lab’s Advanced Light Source, and transmission measurements were made with the beamline’s infrared spectrometer. In this way the research team demonstrated coupling between light and plasmons that were stronger by an order of magnitude than in other 2D systems.

A final method of controlling plasmon strength and terahertz absorption depends on polarization. Light shining in the same direction as the graphene ribbons shows no variations in absorption according to frequency. But light at right angles to the ribbons — the same orientation as the oscillating electron sea — yields sharp absorption peaks. What’s more, light absorption in conventional 2D semiconductor systems, such as quantum wells, can only be measured at temperatures near absolute zero. The Berkeley team measured prominent absorption peaks at room temperature.

“Terahertz radiation covers a spectral range that’s difficult to work with, because until now there have been no tools,” says Wang. “Now we have the beginnings of a toolset for working in this range, potentially leading to a variety of graphene-based terahertz metamaterials.”

The Berkeley experimental setup is only a precursor of devices to come, which will be able to control the polarization and modify the intensity of terahertz light and enable other optical and electronic components, in applications from medical imaging to astronomy — all in two dimensions.

Reference: Long Ju, Baisong Geng, Jason Horng, Caglar Girit, Michael Martin, Zhao Hao, Hans A. Bechtel, Xiaogan Liang, Alex Zettl, Y. Ron Shen, Feng Wang. Graphene plasmonics for tunable terahertz metamaterials. Nature Nanotechnology, 2011; DOI: 10.1038/nnano.2011.146

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Sep 07

Understanding Next-Generation Electronic Devices: Smallest Atomic Displacements Ever.

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Reported by ScienceDaily, 3 Sep. 2011.

An international team of scientists has developed a novel X-ray technique for imaging atomic displacements in materials with unprecedented accuracy. They have applied their technique to determine how a recently discovered class of exotic materials — multiferroics — can be simultaneously both magnetically and electrically ordered. Multiferroics are also candidate materials for new classes of electronic devices.

This photo shows the sample holder, made of copper, which was used in the experiment. The small gray crystal of TbMnO3 that was studied, is in the center, between two electrodes to apply an electric field. (Credit: Image courtesy of Luigi Paolasini)

The discovery, a major breakthrough in understanding multiferroics, is published in Science dated 2 September 2011.

The authors comprise scientists from the European Synchrotron Radiation Facility (ESRF) in Grenoble (France), the University of Oxford and the University College London (both UK). Helen Walker from the ESRF is the main author of the publication.

Everybody is familiar with the idea that magnets are polarized with a north and a south pole, which is understood to arise from the alignment of magnet moments carried by atoms in magnetic materials. Certain other materials, known as ferroelectrics, exhibit a similar effect for electrical polarisation. The exotic “multiferroic” materials combine both magnetic and ferroelectric polarizations, and can exhibit a strong coupling between the two phenomena.

This leads to the strange effect that a magnetic field can electrically polarise the material, and an electric field magnetise it. A class of strong multiferroics was discovered ten years ago and has since led to a new, rapidly growing field of research, also motivated by the promise of their exotic properties for new electronic devices. One example is a new type of electronic memory, in which an electric field writes data into the memory and a magnetic detector is used to read it. This process is faster, and uses less energy than today’s hard disk drives.

However, the origin of the electric polarisation in multiferroics remained mostly elusive to date. The team’s work unambiguously shows that the polarization in the multiferroic studied proceeds from the relative displacement of charges of different signs, rather than the transfer of charge from one atom to another.

As the displacement involves a high number of electrons, even small distances can lead to significant polarisation. The actual distance of the displacement still came as a surprise: about 20 femtometres, or about 1/100,000th of the distance between the atoms in the material. Measuring such small displacements was actually believed to be impossible.

“I think that everyone involved was surprised, if not staggered, by the result that we can now image the position of atoms with such accuracy. The work is testament to the fantastic facilities available in Grenoble to the UK science community,” says Prof. Des McMorrow, Deputy Director of the London Centre for Nanotechnology, leader of the UCL part of the project.

Walker and her colleagues developed a smart new experimental technique exploiting the interference between two competing processes: charge and magnetic scattering of a powerful, polarized X-ray beam. They studied a single crystal of TbMnO3 which shows a strong multiferroic coupling at temperatures below 30K, and were able to measure the displacements of specific atoms within it with an accuracy approaching one femtometre (10-15m). The atoms themselves are spaced apart 100,000 times this distance.

The new interference scattering technique has set a world record for accuracy in absolute measurements of atomic displacements. (It is also the first measurement of magnetostriction in antiferromagnets.) Most significantly the identification of the origin of ferroelectricty in a multiferroic material is a major step forward in the design of multiferroics for practical applications.

“By revealing the driving mechanism behind multiferroics, which offer so many potential applications, it underlines how experiments designed to understand the fundamental physics of materials can have an impact on the wider world,” concludes Dr. Helen Walker who led the work at the ESRF.

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by European Synchrotron Radiation Facility, via EurekAlert!, a service of AAAS.

Reference: H. C. Walker, F. Fabrizi, L. Paolasini, F. De Bergevin, J. Herrero-Martin, A. T. Boothroyd, D. Prabhakaran, D. F. Mcmorrow. Femtoscale Magnetically Induced Lattice Distortions in Multiferroic TbMnO3. Science, 2 September 2011: Vol. 333 no. 6047 pp. 1273-1276 DOI: 10.1126/science.1208085

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Sep 03

UCSB Physicists Demonstrate the Quantum von Neumann Architecture, a Quantum Processor, and a Quantum Memory on a Chip.

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Reported by office of Public Affairs, University of Santa Barbara, 1 Sep. 2011.

UCSB Physicists Demonstrate the Quantum von Neumann Architecture, a Quantum Processor, and a Quantum Memory on a Chip.

The quantum von Neumann machine: Two qubits are coupled to a quantum bus, realizing a quCPU. Each qubit is accompanied by a quantum memory as well as a zeroing register. The quantum memories together with the zeroing register realize the quRAM. Credit: Peter Allen, UCSB

(Santa Barbara, Calif.) –– A new paradigm in quantum information processing has been demonstrated by physicists at UC Santa Barbara. Their results are published in this week’s issue of Science Express online.

UCSB physicists have demonstrated a quantum integrated circuit that implements the quantum von Neumann architecture. In this architecture, a long-lived quantum random access memory can be programmed using a quantum central processing unit, all constructed on a single chip, providing the key components for a quantum version of a classical computer.

The UCSB hardware is based on superconducting quantum circuits, and must be cooled to very low temperatures to display quantum behavior. The architecture represents a new paradigm in quantum information processing, and shows that quantum large-scale-integration is within reach.

Matteo Mariantoni Credit: George Foulsham, Office of Public Affairs, UCSB

The quantum integrated circuit includes two quantum bits (qubits), a quantum communication bus, two bits of quantum memory, and a resetting register comprising a simple quantum computer. “Computational steps take a few billionths of a second, comparable to a classical computer, but the great power is that a quantum computer can perform a large number of calculations simultaneously,” said Matteo Mariantoni, postdoctoral fellow in the Department of Physics. “In our new UCSB architecture we have explored the possibility of writing quantum information to memory, while simultaneously performing other quantum calculations.

“On the quantum von Neumann architecture, we were able to run the quantum Fourier transform and a three-qubit Toffoli gate –– key quantum logic circuits for the further development of quantum computing,” said Mariantoni.

The UCSB experiment was pursued primarily by Mariantoni, under the direction of Andrew N. Cleland and John M. Martinis, both professors of physics. Mariantoni was supported in this work by an Elings Prize Fellowship in Experimental Science from UCSB’s California NanoSystems Institute.

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Sep 01

Barcodes Refocus Understanding of Ecosystems.

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Reported by Juli Berwald, ISNS Contributor, Inside Science News Service, 11 Aug. 2011

A DNA tool provides a high-resolution view of biodiversity and ecological processes.

(ISNS) — You’re probably familiar with barcodes, those black and white stripes on most store items that bring about the familiar “beep” when scanned at checkout. They determine whether a scanned item is a gallon of milk or a can of tomato soup.

Imperial moths from northwestern Costa Rica are caught in the act of evolution. Barcoding shows significant genetic difference between animals from different regions. However, they are still able to mate and produce fertile offspring. Credit: Coutesy of Dan Janzen (09-SRNP-1431)

Eight years ago, biologists developed their own sort of barcode that’s also used for identification, but these barcodes aren’t printed on the outside of items. Instead, they are found inside the DNA of plants and animals studied by biologists.

Research presented this week during a meeting of the Ecological Society of America reveals that genetic barcodes have become a powerful tool in ecology, not just for identification, but also for understanding ecosystem interactions.

Genetic barcodes are a sequence of a particular segment of DNA that has just the right amount of variability to identify what species it came from. When an unknown creature — or part of a creature — is found, its tissue can be barcoded. If the sequence matches another barcode in one of several international databases, the creature’s identity is revealed.

Biologist Dan Janzen of the University of Pennsylvania has been studying insects and the plants they eat in the northwestern corner of Costa Rica since 1975. Janzen and collaborators collected nearly half a million caterpillars, reared about 5,000 different species of moths and butterflies to adulthood and inventoried 2,000 species of insect parasites — or so Janzen thought.

In 2003, Janzen’s group began barcoding their insect inventory. What they had assumed was a single butterfly species eating 10 different species of plants actually turned out to be 10 separate butterfly species each consuming a single plant; what looked like a single wasp species was really 36 distinct species; and what appeared to be 16 species of flies were in fact 73 unique species.

In one instance, Janzen had collected imperial moths living just one kilometer apart. The DNA barcodes from the two populations had an 8 percent difference, evidence of a single species splitting in two.

On the French Polynesian island of Moorea near Tahiti in the South Pacific, a massive barcoding effort has been in the works for four years. From the tops of its mountains to the depths of its ocean, an international team of scientists has been identifying and barcoding all organisms larger than about a millimeter.

To date, the scientists have inventoried more than two-thirds of the island’s inhabitants — about 6,500 species. Such comprehensive coverage is the first step for studying the ecosystem in places where there aren’t many recognizable features of a critter — say, the insides of a fish’s stomach.

Deciphering a fish’s diet from its stomach contents is like determining what clothes produced the lint in your clothes dryer, explains Chris Meyer of the Smithsonian Institution and director the Moorea Biocode Project. If you find a button, it’s easy to tell what pair of shorts it came from. But what if those bits of stringy fluff came from your blue towel or your blue jeans? That’s where barcoding offers a powerful solution.

Meyer and his colleagues, Matthieu Leray and J. T. Boehm, sequenced the fluffy stomach contents of three species of fishes, teasing out barcodes from the collective mush. An astonishing 69 prey species matched barcodes from their database — an assortment of creatures including worms, other fish, mollusks, and crustaceans. Surprisingly, only two prey species — a snapping shrimp and a squat lobster — were eaten by more than one type of predator. Meyer said that the predator’s choice of prey, at least for the species in this study, “are more highly partitioned than we expected.”

Ecologists are starting to wire such detailed predator and prey linkages into ecosystem models to test how such resource partitioning might support the resilience of the reef, especially when faced with stressors such as climate change and recent increases of invasive species.

Barcoding projects are now underway throughout the globe. Near the Arctic Circle in Churchill, Canada, scientists have cataloged 6,000 species, including an unexpectedly large number of insects. In New Guinea, barcodes are used to understand the evolution of butterflies. And in Puerto Rico they’re used to decipher how forests are structured.

“Barcoding is like turning up the microscope from 10x to 100x,” Meyer said. This helps to give researchers a more detailed picture of the ecosystem than previously seen.

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