October 28, 2007, 3:52 PM CT

UD researchers with latest spintronics achievement

In a rapid follow-up to their achievement as the first to demonstrate how an electron's spin can be electrically injected, controlled and detected in silicon, electrical engineers from the University of Delaware and Cambridge NanoTech now show that this quantum property can be transported a marathon distance in the world of microelectronics-- through an entire silicon wafer.

The finding confirms that silicon--the workhorse material of present-day electronics--now can be harnessed up for new-age spintronics applications.

The results, reported in the Oct. 26 issue of the American Physical Society's prestigious journal Physical Review Letters, mark another major steppingstone in the pioneering field of spintronics, which aims to use the intrinsic "spin" property of electrons versus solely their electrical charge for the cheaper, faster, lower-power processing and storage of data than present-day electronics can offer.

The research team included Ian Appelbaum, UD assistant professor of electrical and computer engineering, and his doctoral student, Biqin Huang, and Douwe Monsma, of Cambridge NanoTech in Cambridge, Mass. Huang was the lead author of the article.

"Our new result is significant because it means that silicon can now be used to perform a number of spin manipulations both within the space of thousands of devices and within the time of thousands of logic operations, paving the way for silicon-based spintronics circuits," Appelbaum said......... Posted by: Kevin      Read more         Source

October 28, 2007, 3:16 PM CT

Industrial-grade nanowire device fabrication

In the growing catalog of nanoscale technologies, nanowirestiny rows of conductor or semiconductor atomshave attracted a great deal of interest for their potential to build unique atomic-scale electronics. But before you can buy some at your local Nano Depot, manufacturers will need efficient, reliable methods to build them in quantity. Scientists at the National Institute of Standards and Technology (NIST) believe they have one solutiona technique that allows them to selectively grow nanowires on sapphire wafers in specific positions and orientations accurately enough to attach contacts and layer other circuit elements, all with conventional lithography techniques. They detailed their results in a recent paper.*.

Despite their name, nanowires are more than just electrical connectors. Scientists have used nanowires to create transistors like those used in memory devices and prototype sensors for gases or biomolecules. However working with objects only tens of nanometers wide is challenging. A common approach in the lab is to grow nanowires like blades of grass on a suitable substrate, mow them off and mix them in a fluid to transfer them to a test surface, using some method to give them a preferred orientation. When the carrier fluid dries, the nanowires are left behind like tumbled jackstraws. Using scanning probe microscopy or similar tools, scientists hunt around for a convenient, isolated nanowire to work on, or place electrical contacts without knowing the exact positions of the nanowires. Its not a technique suitable for mass production......... Posted by: Kevin      Read more         Source

October 25, 2007, 10:04 PM CT

How lasers cut flesh

Lasers are at the cutting edge of surgery.

From cosmetic to brain surgery, intense beams of coherent light are gradually replacing the steel scalpel for a number of procedures.

Despite this increasing popularity, there is still a lot that researchers do not know about the ways in which laser light interacts with living tissue. Now, some of these basic questions have been answered in the first investigation of how ultraviolet lasers similar to those used in LASIK eye surgery cut living tissues. It was published online in Physical Review Letters on October 10.

The effect that powerful lasers have on actual flesh varies both with the wavelength, or color, of the light and the duration of the pulses that they produce. The specific wavelengths of light that are absorbed by, reflected from or pass through different types of tissue can vary substantially. Therefore, different types of lasers work best in different medical procedures.

For lasers with pulse lengths of a millionth of a second or less, there are two basic cutting regimes:

• Mid-infrared lasers with long wavelengths cut by burning. That is, they heat up the tissue to the point where the chemical bonds holding it together break down. Because they automatically cauterize the cuts that they make, infrared lasers are used frequently for surgery in areas where there is a lot of bleeding.

........ Posted by: Kevin      Read more         Source

October 23, 2007, 9:45 PM CT

Photonic Gel Films Hold Promise

By alternating layers of two different polymers - one rigid and glassy, the other soft and easily swollen with liquid or vapor - scientists funded by the National Science Foundation (NSF) report they've created photonic gel crystals that can be tuned to reflect light of a number of different colors across the visible and near-infrared spectrum.

The research results, published in the Oct. 21 online issue of Nature Materials by Principal Investigator Edwin Thomas and colleagues at the Massachusetts Institute of Technology's department of materials science and engineering, demonstrate the degree to which these photonic materials are tunable through changes in the soft layer's thickness and index of refraction. The responsiveness of the photonic crystals makes them likely candidates for active components of display, sensory or telecommunication devices.

"This is an ingenious and easy-to-implement method for making photonic materials whose optical properties can be readily tuned over a wide range [of the spectrum]," said Andrew Lovinger, director of the polymers program at NSF, which funded this research.

In one example, the scientists show very large, reversible optical changes by varying the salt content of a water solution in which these films are dipped. Multicolor patterns can be made by sequential coating of films, with the color of each region depending on the degree to which their molecules are chemically interconnected......... Posted by: Kevin      Read more         Source

October 23, 2007, 9:31 PM CT

Gel Changes Color On Demand

MIT scientists have created a new structured gel that can rapidly change color in response to a variety of stimuli, including temperature, pressure, salt concentration and humidity.

Among other applications, the structured gel could be used as a fast and inexpensive chemical sensor, said Edwin Thomas, MIT's Morris Cohen Professor of Materials Science and Engineering. One place where such an environmental sensor could be useful is a food processing plant, where the sensor could indicate whether food that must remain dry has been overly exposed to humidity.

Thomas is senior author of a paper on the work would be reported in the Oct. 21 online edition of Nature Materials.

Structured gels are those that feature an internal pattern such as layers. A critical component of the structured gel developed at MIT is a material that expands or contracts when exposed to certain stimuli. Those changes in the thickness of the gel cause it to change color, through the entire range of the visible spectrum of light.

Objects that reflect different colors depending on which way you look at them already exist, but once those objects are manufactured, their properties can't change. The MIT team set out to create a material that would change color in response to external stimuli......... Posted by: Kevin      Read more         Source

October 23, 2007, 8:46 PM CT

The Sensitive Side of Carbon Nanotubes

Blocks of carbon nanotubes can be used to create effective and powerful pressure sensors, as per a new study by scientists at Rensselaer Polytechnic Institute.

Taking advantage of the material's unique electrical and mechanical properties, scientists repeatedly squeezed a 3-millimeter nanotube block and discovered it was highly suitable for potential applications as a pressure sensor. No matter how a number of times or how hard they squeezed the block, it exhibited a constant, linear relationship between how much force was applied and electrical resistance.

"Because of the linear relationship between load and stress, it can be a very good pressure sensor," said Subbalakshmi Sreekala, a postdoctoral researcher at Rensselaer and author of the study.

A sensor incorporating the carbon nanotube block would be able to detect very slight weight changes and would be beneficial in any number of practical and industrial applications, Sreekala said. Two potential applications are a pressure gauge to check the air pressure of automobile tires, and a microelectromechanical pressure sensor that could be used in semiconductor manufacturing equipment.

Despite extensive research over the past decade into the mechanical properties of carbon nanotube structures, this study is the first to explore and document the material's strain-resistance relationship. The paper, titled "Effects of compressive strains on electrical conductivities of a macroscale carbon nanotube block," was published in a recent issue of Applied Physics Letters......... Posted by: Kevin      Read more         Source

October 22, 2007, 8:47 PM CT

Quantum cascade laser nanoantenna

Cambridge, Mass. October 22, 2007 In a major feat of nanotechnology engineering scientists from Harvard University have demonstrated a laser with a wide-range of potential applications in chemistry, biology and medicine. Called a quantum cascade (QC) laser nanoantenna, the device is capable of resolving the chemical composition of samples, such as the interior of a cell, with unprecedented detail.

Spearheaded by graduate students Nanfang Yu, Ertugrul Cubukcu, and Federico Capasso, Robert L. Wallace Professor of Applied Physics, all of Harvards School of Engineering and Applied Sciences, the findings will be published as a cover feature of the October 22 issue of Applied Physics Letters. The scientists have also filed for U.S. patents covering this new class of photonic devices.

The lasers design consists of two gold rods separated by a nanometer gap (a device known as an optical antenna) built on the facet of a quantum cascade laser, which emits invisible light in the region of the spectrum where most molecules have their tell tale absorption fingerprints. The nanoantenna creates a light spot of nanometric size about fifty to hundred times smaller than the laser wavelength; the spot can be scanned across a specimen to provide chemical images of the surface with superior spatial resolution......... Posted by: Kevin      Read more         Source

October 17, 2007, 8:13 PM CT

World's potential to produce biodiesel

What do the countries of Thailand, Uruguay and Ghana have in common" They all could become leading producers of the emerging renewable fuel known as biodiesel, says a study from the University of Wisconsin-Madison Nelson Institute for Environmental Studies.

The ease of manufacturing biodiesel from vegetable oils and animal fats has made it one of the most promising, near-term alternatives to fossil fuels. Seeking to understand which nations are best positioned today to enter the burgeoning biodiesel market, scientists Matt Johnston and Tracey Holloway of the Nelson Institute's Center for Sustainability and the Global Environment (SAGE) ranked 226 countries as per their potential to make large volumes of biodiesel at low cost.

Reported online today (Oct. 17) in Environmental Science and Technology, the analysis uncovered a number of of the usual suspects, including the United States, a top soybean grower; and Brazil, already a major biodiesel producer. The Netherlands, Gera number of, Belgium and Spain also cracked the top ten in overall volume potential.

But the scientists say the study's true motivation was to identify developing countries that already export significant amounts of vegetable oil for profit, but may not have considered refining it into biodiesel. By exporting biodiesel - a higher value commodity - these countries could improve their trade balances, says Johnston, or use the fuel to offset their own energy needs......... Posted by: Kevin      Read more         Source

October 16, 2007, 7:17 PM CT

Getting Light to Bend Backwards

While developing new lenses for next-generation sensors, scientists have crafted a layered material that causes light to refract, or bend, in a manner nature never intended.

Refraction always bends light one way, as one can see in the illusion of a "bent" drinking straw when observed through the side of a glass. A new metamaterial crafted from alternating layers of semiconductors (indium-gallium-arsenic and aluminum-indium-arsenic) acts as a single lens that refracts light in the opposite direction.

Refraction is the reason that lenses have to be curved, a trait that limits image resolution. With the new metamaterial, flat lenses are possible, theoretically allowing microscopes to capture images of objects as small as a strand of DNA. The current metamaterial lens works with infrared light, but the scientists hope the technology will expand to other wavelengths in the future.

Earlier efforts have crafted metamaterials that bend light in a similar way, but this is the first to do so using a 3-dimensional structure and a metamaterial comprised entirely of semiconductors. Those traits will prove critical for incorporating the technology into devices such as chemical threat sensors, communications equipment and medical diagnostics tools......... Posted by: Kevin      Read more         Source

October 11, 2007, 10:44 PM CT

New insights on green algae

Culminating a three-year research project, 115 researchers from around the world report in the Oct. 12 issue of the journal Science a "gold mine" of data on a tiny green alga called Chlamydomonas, with implications for human diseases.

The single-celled Chlamydomonas, a slimy organism that grows in soil and ponds, has approximately 15,000 genes, and researchers now know 95 percent of the sequence of its genome. Several years ago, they knew less than 2 percent.

"It's like having a dictionary of genes," said lead author Sabeeha Merchant, professor of biochemistry and associate director of UCLA's Molecular Biology Institute, who has studied the green alga for 20 years. "We know the words and now we want to learn to talk. Without the dictionary, you would be stuck and couldn't learn how to speak or write. We went from having a 200-word vocabulary to a 14,250-word vocabulary. Each of us is trying to learn how to put the words and sentences together in our own research programs.

"Having the genome sequence available fast-forwards our research by 10 or 20 years and allows us to make progress by leaps and bounds," she said. "The genome sequence opens the door for us to access all the genes and target our research on subsets of genes. What was just a dream 10 years ago, we have now accomplished"......... Posted by: Ashley      Read more         Source