Sunday, March 6, 2011

Nanotechnology used to prolong machine and engine life

Guojun Liu has discovered a way to use nanotechnology to reduce friction in automobile engines and machines.

"The technology should be useful in a wide range of machineries other than automobile engines," says Dr. Liu, a professor in the Department of Chemistry and an expert in polymer synthesis. "If implemented industrially, this nanotechnology should help prolong machine life and improve energy efficiency."

Dr Liu's team prepared miniscule polymer particles that were only tens of nanometers in size. These particles were then dispersed in automobile engine base oils. When tested under metal surface contact conditions that simulated conditions found in automobile engines, these tiny particles were discovered to have an unprecedented friction reduction capability.

Even at a low concentration, the nanoparticles performed much better than the friction additive that is currently used by many industries. They were able to reduce friction by 55 per cent more than the currently achievable rate.

Dr. Liu's discovery has earned the Society of Tribologists and Lubrication Engineers' Captain Alfred E. Hunt Memorial Award.

This is the first research that Dr. Liu has done in the field of friction reduction and lubrication.

Story Source:

The above story is reprinted (with editorial adaptations) from materials provided by Queen's University.

Physicists develop potent packing process

New York University physicists have developed a method for packing microscopic spheres that could lead to improvements in commercial products ranging from pharmaceutical lotions to ice cream. Their work, which relies on an innovative application of statistical mechanics, appears in the Proceedings of the National Academy of Sciences.

The study aimed to manipulate the properties of emulsions, which are a mixture of two or more immiscible liquids. The NYU researchers examined droplets of oil in water, which form the basis of a range of consumer products, including butter, ice cream, and milk.

The research was conducted in the laboratory of Jasna Brujić, an assistant professor in NYU's Department of Physics and part of its Center for Soft Matter Research.

Previously, her laboratory determined how spheres pack. These earlier findings showed how this process depends on the relative sphere sizes. In the PNAS study, Brujić and her research team sought to create a method to manipulate further how particles pack.

To do so, the researchers relied on a physical property known as "depletion attraction," a force that causes big particles to stick together by the pressure from the surrounding small ones.

Previous research has employed this process of attraction to create particulate gels, but these studies have tended to rely on thermally activated particles -- below one micron in size -- that result in complex structures known as fractals that look similar on all length scales.

In the PNAS study, the researchers used larger particles, which are not sensitive to room temperature and therefore pack under gravity alone.

To bring about depletion attraction, they added tiny polymers to the larger particles suspended in water. In essence, they used the smaller polymers to force together the larger spheres. In order to regulate the nature of this packing -- how tightly or loosely the larger particles fit together -- the researchers developed a statistical model that determines the fluctuations in the local properties of the packing.

"What we discovered is that you can control the connectivity of the particles -- how they stick together and their properties -- by manipulating the extent of the attraction," explained Brujić.

As a result of the discovery, the researchers have developed a method for potentially creating a range of materials -- from loose to dense -- based on the packing of their component parts.

The study's other authors were Ivane Jorjadze, a graduate student, and Lea-Laetitia Pontani, a postdoctoral research scientist, both from NYU's Department of Physics and the Center for Soft Matter Research, as well as Katherine Newhall, a doctoral student at Rensselaer Polytechnic Institute.

Story Source:

The above story is reprinted (with editorial adaptations) from materials provided by New York University, via EurekAlert!, a service of AAAS.

Journal Reference:

Ivane Jorjadze, Lea-Laetitia Pontani, Katherine A. Newhall, and Jasna Brujić. Attractive emulsion droplets probe the phase diagram of jammed granular matter. PNAS, February 28, 2011 DOI: 10.1073/pnas.1017716108

Engineers grow nanolasers on silicon, pave way for on-chip photonics

Engineers at the University of California, Berkeley, have found a way to grow nanolasers directly onto a silicon surface, an achievement that could lead to a new class of faster, more efficient microprocessors, as well as to powerful biochemical sensors that use optoelectronic chips.

They describe their work in a paper to be published Feb. 6 in an advanced online issue of the journal Nature Photonics.

"Our results impact a broad spectrum of scientific fields, including materials science, transistor technology, laser science, optoelectronics and optical physics," said the study's principal investigator, Connie Chang-Hasnain, UC Berkeley professor of electrical engineering and computer sciences.

The increasing performance demands of electronics have sent researchers in search of better ways to harness the inherent ability of light particles to carry far more data than electrical signals can. Optical interconnects are seen as a solution to overcoming the communications bottleneck within and between computer chips.

Because silicon, the material that forms the foundation of modern electronics, is extremely deficient at generating light, engineers have turned to another class of materials known as III-V (pronounced "three-five") semiconductors to create light-based components such as light-emitting diodes (LEDs) and lasers.

But the researchers pointed out that marrying III-V with silicon to create a single optoelectronic chip has been problematic. For one, the atomic structures of the two materials are mismatched.

"Growing III-V semiconductor films on silicon is like forcing two incongruent puzzle pieces together," said study lead author Roger Chen, a UC Berkeley graduate student in electrical engineering and computer sciences. "It can be done, but the material gets damaged in the process."

Moreover, the manufacturing industry is set up for the production of silicon-based materials, so for practical reasons, the goal has been to integrate the fabrication of III-V devices into the existing infrastructure, the researchers said.

"Today's massive silicon electronics infrastructure is extremely difficult to change for both economic and technological reasons, so compatibility with silicon fabrication is critical," said Chang-Hasnain. "One problem is that growth of III-V semiconductors has traditionally involved high temperatures -- 700 degrees Celsius or more -- that would destroy the electronics. Meanwhile, other integration approaches have not been scalable."

The UC Berkeley researchers overcame this limitation by finding a way to grow nanopillars made of indium gallium arsenide, a III-V material, onto a silicon surface at the relatively cool temperature of 400 degrees Celsius.

"Working at nanoscale levels has enabled us to grow high quality III-V materials at low temperatures such that silicon electronics can retain their functionality," said Chen.

The researchers used metal-organic chemical vapor deposition to grow the nanopillars on the silicon. "This technique is potentially mass manufacturable, since such a system is already used commercially to make thin film solar cells and light emitting diodes," said Chang-Hasnain.

Once the nanopillar was made, the researchers showed that it could generate near infrared laser light -- a wavelength of about 950 nanometers -- at room temperature. The hexagonal geometry dictated by the crystal structure of the nanopillars creates a new, efficient, light-trapping optical cavity. Light circulates up and down the structure in a helical fashion and amplifies via this optical feedback mechanism.

The unique approach of growing nanolasers directly onto silicon could lead to highly efficient silicon photonics, the researchers said. They noted that the miniscule dimensions of the nanopillars -- smaller than one wavelength on each side, in some cases -- make it possible to pack them into small spaces with the added benefit of consuming very little energy

"Ultimately, this technique may provide a powerful and new avenue for engineering on-chip nanophotonic devices such as lasers, photodetectors, modulators and solar cells," said Chen.

"This is the first bottom-up integration of III-V nanolasers onto silicon chips using a growth process compatible with the CMOS (complementary metal oxide semiconductor) technology now used to make integrated circuits," said Chang-Hasnain. "This research has the potential to catalyze an optoelectronics revolution in computing, communications, displays and optical signal processing. In the future, we expect to improve the characteristics of these lasers and ultimately control them electronically for a powerful marriage between photonic and electronic devices."

The Defense Advanced Research Projects Agency and a Department of Defense National Security Science and Engineering Faculty Fellowship helped support this research.

Story Source:

The above story is reprinted (with editorial adaptations ) from materials provided by University of California - Berkeley, via EurekAlert!, a service of AAAS.

Journal Reference:

Roger Chen, Thai-Truong D. Tran, Kar Wei Ng, Wai Son Ko, Linus C. Chuang, Forrest G. Sedgwick, Connie Chang-Hasnain. Nanolasers grown on silicon. Nature Photonics, 2011; DOI: 10.1038/nphoton.2010.315

New kinds of superconductivity? Physicists demonstrate coveted 'spin-orbit coupling' in atomic gases

Physicists at the Joint Quantum Institute (JQI), a collaboration of the National Institute of Standards and Technology (NIST) and the University of Maryland-College Park, have for the first time caused a gas of atoms to exhibit an important quantum phenomenon known as spin-orbit coupling. Their technique opens new possibilities for studying and better understanding fundamental physics and has potential applications to quantum computing, next-generation "spintronics" devices and even "atomtronic" devices built from ultracold atoms.

In the researchers' demonstration of spin-orbit coupling, two lasers allow an atom's motion to flip it between a pair of energy states. The new work, published in Nature, demonstrates this effect for the first time in bosons, which make up one of the two major classes of particles. The same technique could be applied to fermions, the other major class of particles, according to the researchers. The special properties of fermions would make them ideal for studying new kinds of interactions between two particles -- for example those leading to novel "p-wave" superconductivity, which may enable a long-sought form of quantum computing known as topological quantum computation.

In an unexpected development, the team also discovered that the lasers modified how the atoms interacted with each other and caused atoms in one energy state to separate in space from atoms in the other energy state.

One of the most important phenomena in quantum physics, spin-orbit coupling describes the interplay that can occur between a particle's internal properties and its external properties. In atoms, it usually describes interactions that only occur within an atom: how an electron's orbit around an atom's core (nucleus) affects the orientation of the electron's internal bar-magnet-like "spin." In semiconductor materials such as gallium arsenide, spin-orbit coupling is an interaction between an electron's spin and its linear motion in a material.

"Spin-orbit coupling is often a bad thing," said JQI's Ian Spielman, senior author of the paper. "Researchers make 'spintronic' devices out of gallium arsenide, and if you've prepared a spin in some desired orientation, the last thing you'd want it to do is to flip to some other spin when it's moving."

"But from the point of view of fundamental physics, spin-orbit coupling is really interesting," he said. "It's what drives these new kinds of materials called 'topological insulators.'"

One of the hottest topics in physics right now, topological insulators are special materials in which location is everything: the ability of electrons to flow depends on where they are located within the material. Most regions of such a material are insulating, and electric current does not flow freely. But in a flat, two-dimensional topological insulator, current can flow freely along the edge in one direction for one type of spin, and the opposite direction for the opposite kind of spin. In 3-D topological insulators, electrons would flow freely on the surface but be inhibited inside the material. While researchers have been making higher and higher quality versions of this special class of material in solids, spin-orbit coupling in trapped ultracold gases of atoms could help realize topological insulators in their purest, most pristine form, as gases are free of impurity atoms and the other complexities of solid materials.

Usually, atoms do not exhibit the same kind of spin-orbit coupling as electrons exhibit in gallium-arsenide crystals. While each individual atom has its own spin-orbit coupling going on between its internal components (electrons and nucleus), the atom's overall motion generally is not affected by its internal energy state.

But the researchers were able to change that. In their experiment, researchers trapped and cooled a gas of about 200,000 rubidium-87 atoms down to 100 nanokelvins, 3 billion times colder than room temperature. The researchers selected a pair of energy states, analogous to the "spin-up" and "spin-down" states in an electron, from the available atomic energy levels. An atom could occupy either of these "pseudospin" states. Then researchers shined a pair of lasers on the atoms so as to change the relationship between the atom's energy and its momentum (its mass times velocity), and therefore its motion. This created spin-orbit coupling in the atom: the moving atom flipped between its two "spin" states at a rate that depended upon its velocity.

"This demonstrates that the idea of using laser light to create spin-orbit coupling in atoms works. This is all we expected to see," Spielman said. "But something else really neat happened."

They turned up the intensity of their lasers, and atoms of one spin state began to repel the atoms in the other spin state, causing them to separate.

"We changed fundamentally how these atoms interacted with one another," Spielman said. "We hadn't anticipated that and got lucky."

The rubidium atoms in the researchers' experiment were bosons, sociable particles that can all crowd into the same space even if they possess identical values in their properties including spin. But Spielman's calculations show that they could also create this same effect in ultracold gases of fermions. Fermions, the more antisocial type of atoms, cannot occupy the same space when they are in an identical state. And compared to other methods for creating new interactions between fermions, the spin states would be easier to control and longer lived.

A spin-orbit-coupled Fermi gas could interact with itself because the lasers effectively split each atom into two distinct components, each with its own spin state, and two such atoms with different velocities could then interact and pair up with one other. This kind of pairing opens up possibilities, Spielman said, for studying novel forms of superconductivity, particularly "p-wave" superconductivity, in which two paired atoms have a quantum-mechanical phase that depends on their relative orientation. Such p-wave superconductors may enable a form of quantum computing known as topological quantum computation.

Story Source:

The above story is reprinted (with editorial adaptations) from materials provided by National Institute of Standards and Technology (NIST).

Journal Reference:

Y.-J. Lin, K. Jiménez-García, I. B. Spielman. Spin-orbit-coupled Bose-Einstein condensates. Nature, 471, 83-86 (2 March 2011) DOI: 10.1038/nature09887

Note: If no author is given, the source is cited instead.

Turning bacteria into butanol biofuel factories: Transplanted enzyme pathway makes E. coli churn out n-butanol

University of California, Berkeley, chemists have engineered bacteria to churn out a gasoline-like biofuel at about 10 times the rate of competing microbes, a breakthrough that could soon provide an affordable and "green" transportation fuel.

The development is reported online this week in advance of publication in the journal Nature Chemical Biology by Michelle C. Y. Chang, assistant professor of chemistry at UC Berkeley, graduate student Brooks B. Bond-Watts and recent UC Berkeley graduate Robert J. Bellerose.

Various species of the Clostridium bacteria naturally produce a chemical called n-butanol (normal butanol) that has been proposed as a substitute for diesel oil and gasoline. While most researchers, including a few biofuel companies, have genetically altered Clostridium to boost its ability to produce n-butanol, others have plucked enzymes from the bacteria and inserted them into other microbes, such as yeast, to turn them into n-butanol factories. Yeast and E. coli, one of the main bacteria in the human gut, are considered to be easier to grow on an industrial scale.

While these techniques have produced promising genetically altered E. coli bacteria and yeast, n-butanol production has been limited to little more than half a gram per liter, far below the amounts needed for affordable production.

Chang and her colleagues stuck the same enzyme pathway into E. coli, but replaced two of the five enzymes with look-alikes from other organisms that avoided one of the problems other researchers have had: n-butanol being converted back into its chemical precursors by the same enzymes that produce it.

The new genetically altered E. coli produced nearly five grams of n-buranol per liter, about the same as the native Clostridium and one-third the production of the best genetically altered Clostridium, but about 10 times better than current industrial microbe systems.

"We are in a host that is easier to work with, and we have a chance to make it even better," Chang said. "We are reaching yields where, if we could make two to three times more, we could probably start to think about designing an industrial process around it."

"We were excited to break through the multi-gram barrier, which was challenging," she added.

Among the reasons for engineering microbes to make fuels is to avoid the toxic byproducts of conventional fossil fuel refining, and, ultimately, to replace fossil fuels with more environmentally friendly biofuels produced from plants. If microbes can be engineered to turn nearly every carbon atom they eat into recoverable fuel, they could help the world achieve a more carbon-neutral transportation fuel that would reduce the pollution now contributing to global climate change. Chang is a member of UC Berkeley's year-old Center for Green Chemistry.

The basic steps evolved by Clostridium to make butanol involve five enzymes that convert a common molecule, acetyl-CoA, into n-butanol. Other researchers who have engineered yeast or E. coli to produce n-butanol have taken the entire enzyme pathway and transplanted it into these microbes. However, n-butanol is not produced rapidly in these systems because the native enzymes can work in reverse to convert butanol back into its starting precursors.

Chang avoided this problem by searching for organisms that have similar enzymes, but that work so slowly in reverse that little n-butanol is lost through a backward reaction.

"Depending on the specific way an enzyme catalyzes a reaction, you can force it in the forward direction by reducing the speed at which the back reaction occurs," she said. "If the back reaction is slow enough, then the transformation becomes effectively irreversible, allowing us to accumulate more of the final product."

Chang found two new enzyme versions in published sequences of microbial genomes, and based on her understanding of the enzyme pathway, substituted the new versions at critical points that would not interfere with the hundreds of other chemical reactions going on in a living E. coli cell. In all, she installed genes from three separate organisms - Clostridium acetobutylicum, Treponema denticola and Ralstonia eutrophus -- into the E. coli.

Chang is optimistic that by improving enzyme activity at a few other bottlenecks in the n-butanol synthesis pathway, and by optimizing the host microbe for production of n-butanol, she can boost production two to three times, enough to justify considering scaling up to an industrial process. She also is at work adapting the new synthetic pathway to work in yeast, a workhorse for industrial production of many chemicals and pharmaceuticals.

The work was supported by UC Berkeley, the Camille and Henry Dreyfus Foundation, the Arnold and Mabel Beckman Foundation and the Dow Sustainable Products and Solutions Program.

Story Source:

The above story is reprinted from materials provided by University of California - Berkeley, via EurekAlert!, a service of AAAS.

Journal Reference:

Brooks B Bond-Watts, Robert J Bellerose, Michelle C Y Chang. Enzyme mechanism as a kinetic control element for designing synthetic biofuel pathways. Nature Chemical Biology, 2011; DOI: 10.1038/nchembio.537

Scalable method for making graphene

New research from the University of Pennsylvania demonstrates a more consistent and cost-effective method for making graphene, the atomic-scale material that has promising applications in a variety of fields, and was the subject of the 2010 Nobel Prize in Physics.

As explained in a recently published study, a Penn research team was able to create high-quality graphene that is just a single atom thick over 95% of its area, using readily available materials and manufacturing processes that can be scaled up to industrial levels.

"I'm aware of reports of about 90%, so this research is pushing it closer to the ultimate goal, which is 100%," said the study's principal investigator, A.T. Charlie Johnson, professor of physics. "We have a vision of a fully industrial process."

Other team members on the project included postdoctoral fellows Zhengtang Luo and Brett Goldsmith, graduate students Ye Lu and Luke Somers and undergraduate students Daniel Singer and Matthew Berck, all of Penn's Department of Physics and Astronomy in the School of Arts and Sciences.

The group's findings were published on Feb. 10 in the journal Chemistry of Materials.

Graphene is a chicken-wire-like lattice of carbon atoms arranged in thin sheets a single atomic layer thick. Its unique physical properties, including unbeatable electrical conductivity, could lead to major advances in solar power, energy storage, computer memory and a host of other technologies. But complicated manufacturing processes and often-unpredictable results currently hamper graphene's widespread adoption.

Producing graphene at industrial scales isn't inhibited by the high cost or rarity of natural resources -- a small amount of graphene is likely made every time a pencil is used -- but rather the ability to make meaningful quantities with consistent thinness.

One of the more promising manufacturing techniques is CVD, or chemical vapor deposition, which involves blowing methane over thin sheets of metal. The carbon atoms in methane form a thin film of graphene on the metal sheets, but the process must be done in a near vacuum to prevent multiple layers of carbon from accumulating into unusable clumps.

The Penn team's research shows that single-layer-thick graphene can be reliably produced at normal pressures if the metal sheets are smooth enough.

"The fact that this is done at atmospheric pressure makes it possible to produce graphene at a lower cost and in a more flexible way," Luo, the study's lead author, said.

Whereas other methods involved meticulously preparing custom copper sheets in a costly process, Johnson's group used commercially available copper foil in their experiment.

"You could practically buy it at the hardware store," Johnson said.

Other methods make expensive custom copper sheets in an effort to get them as smooth as possible; defects in the surface cause the graphene to accumulate in unpredictable ways. Instead, Johnson's group "electropolished" their copper foil, a common industrial technique used in finishing silverware and surgical tools. The polished foil was smooth enough to produce single-layer graphene over 95% of its surface area.

Working with commercially available materials and chemical processes that are already widely used in manufacturing could lower the bar for commercial applications.

"The overall production system is simpler, less expensive, and more flexible" Luo said.

The most important simplification may be the ability to create graphene at ambient pressures, as it would take some potentially costly steps out of future graphene assembly lines.

"If you need to work in high vacuum, you need to worry about getting it into and out of a vacuum chamber without having a leak," Johnson said. "If you're working at atmospheric pressure, you can imagine electropolishing the copper, depositing the graphene onto it and then moving it along a conveyor belt to another process in the factory."

This research was supported by Penn's Nano/Bio Interface Center through the National Science Foundation.

Story Source:

The above story is reprinted (with editorial adaptations) from materials provided by University of Pennsylvania.

Journal Reference:

Zhengtang Luo, Ye Lu, Daniel W. Singer, Matthew E. Berck, Luke A. Somers, Brett R. Goldsmith, A. T. Charlie Johnson. Effect of Substrate Roughness and Feedstock Concentration on Growth of Wafer-Scale Graphene at Atmospheric Pressure. Chemistry of Materials, 2011; : 110210120716054 DOI: 10.1021/cm1028854