Saturday, January 21, 2012

Scientists pause research with lab-bred bird flu (AP)

WASHINGTON ? Scientists who created easier-to-spread versions of the deadly bird flu said Friday they're temporarily halting more research, as international specialists debate what should happen next.

Researchers from leading flu laboratories around the world signed onto the voluntary moratorium, published Friday in the journals Science and Nature.

What the scientists called a "pause" comes amid fierce controversy over how to handle research that's high-risk but potentially could bring a big payoff. Two labs ? at Erasmus University in the Netherlands and the University of Wisconsin-Madison ? created the new viruses while studying how bird flu might mutate to become a bigger threat to people.

The U.S. government funded the work but last month urged the teams not to publicly reveal the exact formula so that would-be bioterrorists couldn't copy it. Critics also worried a lab accident might allow the strains to escape. The researchers reluctantly agreed not to publish all the details as long as the government set up a system to provide them to legitimate scientists who really need to know. The National Institutes of Health is creating such a system.

"We recognize that we and the rest of the scientific community need to clearly explain the benefits of this important research and the measures taken to minimize its possible risks," lead researchers Ron Fouchier of Erasmus and Yoshihiro Kawaoka of Wisconsin wrote Friday in the letter. They were joined by nearly three dozen other flu researchers.

They called for a public international meeting to debate how to learn from the work, safely. And they agreed to hold off on additional research with the existing lab-bred strains or that leads to any new ones for 60 days.

A U.S. official praised the development.

The moratorium "is a really good idea, because a lot of very important issues are at hand," said Dr. Anthony Fauci, director of the NIH's National Institute of Allergy and Infectious Diseases, who expects most flu researchers doing such work to sign on. "There aren't a lot of people who are doing that, I can assure you."

The U.S. also wants international input; researchers are talking with the World Health Organization.

Today, the so-called H5N1 bird flu only occasionally infects people, mostly those who have close contact with sick poultry. But when it does, it's highly lethal. The lab-bred H5N1 strains were a surprise because they showed it was easier than previously thought for the virus to mutate in a way that lets it spread easily between at least some mammals ? in this case, ferrets.

Source: http://us.rd.yahoo.com/dailynews/rss/health/*http%3A//news.yahoo.com/s/ap/20120120/ap_on_he_me/us_med_bird_flu

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Planking! 'Family Matters'! 'Idol' auditions get odd

By Craig Berman

?

Rick Mckee / Fox

"American Idol" went to Pittsburgh in search of its season 11 champ on the second night of the premiere.

RECAP

?American Idol? went to Pittsburgh for Thursday?s audition episode, and as host Ryan Seacrest noted excitedly, ?They call this place ?City of Champions!? ? Of course, it doesn?t really count if it?s a nickname you give yourself, but at least we got to see the Terrible Towels waving once more this season now that the Steelers have been eliminated from the NFL playoffs.

It was a strange group of 38 that made it through from here, heavy on the quirk and light on the powerful vocals. But by the end of the hour, a couple of legitimate contenders emerged from the pity selections and the random eccentrics who have no chance of winning.

Eben Franckewitz is this season?s attempt to capture the Justin Bieber vibe. With a look as wholesome as Beaver Cleaver and a mom who says things like, ?I?m really, really proud of you, no matter what happens,? what?s not to like about this 15-year-old? Odds are somewhere around 110 percent?that you?ll be seeing a lot of him in Hollywood.

The same goes for Hallie Day, who closed the show. She?s pretty much the exact opposite of the Franckewitz backstory, having dropped out of school, gone to New York for a failed experiment with a?rock band, slinked back to Baltimore and tried to overdose on pills. Now she?s married, back in the game and is someone Jennifer Lopez thinks can win. Unlike ?Survivor,? ?Idol? doesn?t need a Redemption Island to provide second chances.

Speaking of second chances, Travis Orlando is back. The 17-year-old who told his story in last year?s auditions has fared only worse since missing his chance a year ago. He dropped out of high school, his mom walked out on the family, he got evicted and moved into a shelter with his dad and his twin brother. Other than that, it?s been an awesome 12 months. He?s all-in on music now, and he said he?s scared.

?Scared is good. Scared makes you do things you wouldn?t normally do,? J.Lo told him.

Others to watch include Reed Grimm, who broke new ground by auditioning to the theme from ?Family Matters.? If ?Idol? doesn?t work out, he should try Nick at Nite.

Mobile DJ and wedding singer Erika Van Pelt also got universal praise, though wedding singers always walk a fine line between engaging the audience and being a cornball, and she?s really close to falling on the wrong side of that divide.

Also watch Creighton Fraker, who wrote a song on the nine-hour bus ride from New York. (And from his stage persona, it looked like he might have inhaled some carbon monoxide fumes along the way.) He won the award for the most over-the-top praise of the night.
?
??A million percent yes,? Randy Jackson said.
?
?Two million percent yes,? J.Lo added.
?
Steven Tyler topped them all. ?Three gazillion percent yes. This is why I joined Idol?... to say to you you?re going to Hollywood.?
?
Uh?... OK.

Others got tickets for reasons that are impossible to fathom. Like Heejun Han, who impressed the judges by singing much better than he spoke. ?I am really impressed and shocked,? Randy said. Not as shocked as Han was when he learned he?s going to Hollywood. Or as shocked as I?ll be if he makes it past the first day there.?

Also unlikely to win is Samantha Novacek, who was memorable only because her sister Patricia came with her and planked on the audition stage. ?She sings better when I plank,? Patricia said. Uh?... if you say so. But how great would it be if Samantha made it to the group night and her fellow singers had to work their choreography around the planking? It was worth the ticket for that alone.

One of the few who were sent packing was coal miner Shane Bruce. ?What made you want to be a coal miner?? J.Lo asked him. Uh, Ms. One Percent, have you checked the unemployment numbers lately? The answer probably is that he?s in a coal-mining family and needs the work. Not everyone can hang out in New York until they hit the big time.

At any rate, it?s always a bad sign when someone introduces their song by referring to it as ?that Hallelujah song in 'Shrek.' ? Though all three judges were encouraging, he didn?t advance and was disappointed in himself. ?Just got nervous. Didn?t do as good as I know I can,? he said.

There?s always next year. As we learned again on Thursday, ?Idol?s? very sympathetic to those seeking a second chance.

Which singers do you think should not have gotten a ticket to Hollywood? Share your thoughts on our Facebook page!

Want more "Idol" during "Idol"? Follow @CraigBerman as he live tweets each show!

Related content:

Source: http://theclicker.today.msnbc.msn.com/_news/2012/01/19/10194960-pittsburgh-delivers-the-quirks-on-idol

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Friday, January 20, 2012

Wikipedia, Google protest US antipiracy proposals (AP)

NEW YORK ? January 18 is a date that will live in ignorance, as Wikipedia started a 24-hour blackout of its English-language articles, joining other sites in a protest of pending U.S. legislation aimed at shutting down sites that share pirated movies and other content.

Reddit.com shut down its social news service for 12 hours. Other sites made their views clear without cutting off surfers. Google blacked out the logo on its home page, directing surfers to a page where they could add their names to a petition against the bills.

Local listings site Craiglist took a middle route, changing its local home pages to a black screen directing users to an anti-legislation page. After 10 seconds, a link to the main site appears on the home page, but some surfers missed that and were fooled into thinking the whole site was blacked out.

The Internet companies are concerned that the Stop Online Piracy Act in the House and the Protect Intellectual Property Act under consideration in the Senate, if passed, could be used to target legitimate sites where users share content.

The 24-hour Wikipedia blackout is an unprecedented move for the online encyclopedia. The decision was reached after polling the community of contributors, but dissenters say political advocacy undermines the site's mission as a neutral source.

However, it's not complete: the block can be bypassed by changing browser settings to disable JavaScript, or by using the version of the site designed for cellphone screens.

There's also a "mirror" or copy, of Wikipedia called The Free Dictionary, but it's not up to date.

___

Online:

Wikipedia for mobiles: http://en.m.wikipedia.org/

"Mirror" site of Wikipedia: http://encyclopedia.thefreedictionary.com/

Source: http://us.rd.yahoo.com/dailynews/rss/tech/*http%3A//news.yahoo.com/s/ap/20120118/ap_on_hi_te/us_tec_internet_protest

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A Q&A on contested Internet anti-piracy bills (AP)

WASHINGTON ? Online piracy costs U.S. copyright owners and producers billions of dollars every year, but legislation in Congress to block foreign Internet thieves and swindlers has met strong resistance from high-tech companies, spotlighted by Wikipedia's protest blackout on Wednesday, warning of a threat to Internet freedom.

House and Senate bills that once seemed to be on a path toward approval now face a rockier future. House Speaker John Boehner on Wednesday said it was "pretty clear to many of us that there is a lack of consensus at this point."

Amid the high-tech campaign against the bills, several lawmakers came out in opposition. At least four Senate Republicans who had previously cosponsored the Senate bill ? Orrin Hatch of Utah, Roy Blunt of Missouri, John Boozman of Arkansas and Charles Grassley of Iowa ? issued statements Wednesday saying they were withdrawing their support. Democratic Sen. Ben Cardin of Maryland last week said that, after listening to constituent concerns, he could not vote for the Senate bill as it is currently written.

On the House side, Rep. Rick Larsen, D-Wash., issued a statement that he had heard from many of his constituents and come to the conclusion that the House and Senate bills "create unacceptable threats to free speech and free access to the Internet."

Here are some of the some of the questions being raised about the bills being considered:

Q. Why is legislation needed?

A. There's no argument that more needs to be done to protect artists, innovators and industries from copyright thieves and shield consumers from products sold on the Internet that are fake, faulty and unsafe. Creative America, a coalition of Hollywood studios, networks and unions, says content theft costs U.S. workers $5.5 billion a year. The pharmaceutical industry loses billions to Internet sellers of drugs that are falsely advertised and may be harmful.

Q. What is Congress trying to accomplish?

A. The two main bills are the Protect Intellectual Property Act, or PIPA, in the Senate, and the similar Stop Online Privacy Act, or SOPA, in the House. There are already laws on the books to combat domestic websites trafficking in counterfeit or pirated goods, but little to counter foreign violators.

The bills would allow the Justice Department, and copyright holders, to seek court orders against foreign websites accused of perpetrating or facilitating copyright infringement. While there is little the United States can do to take down those websites, the bills would bar online advertising networks and payment facilitators such as credit card companies and PayPal from doing business with an alleged violator. It also would forbid search engines from linking to such sites.

The original bills would have let copyright holders and Internet service providers block access to pirate websites. Critics and Internet engineers complained that would allow copyright holders to interfere in the behind-the-scenes system that seamlessly directs computer users to websites. They said that causing deliberate failures in the lookup system to prevent visits to pirate websites could more easily allow hackers to trick users into inadvertently visiting websites that could infect their computers. The White House also took issue with that approach, saying "We must avoid creating new cybersecurity risks or disrupting the underlying architecture of the Internet."

Responding to the critics, House Judiciary Committee Chairman Lamar Smith, R-Texas, said he is taking the blocking measure out of his bill. Senate Judiciary Committee Chairman Patrick Leahy, D-Vt., also is reworking his bill to address those cybersecurity issues.

Q. What are other concerns with the bills?

A. Critics say they would constrain free speech, curtail innovation and discourage new digital distribution methods. NetCoalition, a group of leading Internet and technology companies, says they could be forced to pre-screen all user comments, pictures and videos ? effectively killing social media. Search engines, Internet service providers and social networks could be forced shut down websites linked to any type of pirated content.

In addition, critics contend that young, developing businesses and smaller websites could be saddled with expensive litigation costs. And, they contend existing rights holders could impede new investment in the technology sector.

The White House said it would "not support any legislation that reduces freedom of expression ... or undermines the dynamic, innovative global Internet."

Leahy responded that there is nothing in the legislation that would require websites, Internet service providers, search engines, ad networks, payment processors or others to monitor their networks. He said his bill protects third parties from liability that may arise from actions to comply with a court order.

Michael O'Leary, a senior vice president at the Motion Picture Association of America, a key supporter of the legislation, said his industry is built upon a vibrant First Amendment. "We would never support any legislation that would limit this fundamental American right," he said. Neither PIPA nor SOPA "implicate free expression but focus solely on illegal conduct, which is not free speech."

Q. Who else supports the bills?

A. The most visible supporters are entertainment-related groups such as the MPAA and the National Music Publishers' Association. But the bills also enjoy support from the pharmaceutical industry, which is trying to shut down illegal online drug operations, and electronic and auto industries concerned about people going online to buy counterfeit parts that may be substandard. The U.S. Chamber of Commerce and several law enforcement groups also back the legislation.

Q. Who are the opponents?

A. In addition to Wikipedia, many major Internet and technology companies, including Google, Yahoo!, Amazon.com and eBay, are part of the NetCoalition group opposing the bills. Disparate political groups such as the liberal Democracy for America and the conservative Heritage Action have also voiced concerns about censorship.

Q. What is the status of the bills?

A. Momentum for the bills has slowed, giving the edge to Silicon Valley over Hollywood. The Senate, as its first major business when it returns to session next Tuesday, is to vote on whether to take up the bill. Sixty votes are needed to clear that legislative hurdle. It's unclear whether supporters have the votes.

Six Republicans on the Judiciary Committee last week wrote Majority Leader Harry Reid, D-Nev., saying that while the problem of intellectual property theft must be addressed, "the process at this point is moving too quickly" and a vote on moving to the bill "may be premature."

Reid replied that the vote will occur as scheduled, saying that while the bill was not perfect and he had urged Leahy to make changes, the issue was "too important to delay."

In the House, Judiciary Committee Chairman Smith said his panel would resume deliberations on SOPA in February. Meanwhile, Rep. Darrell Issa, R-Calif., chairman of the House Oversight and Government Reform Committee and an ally of the high-tech industry, said he had received assurances from GOP leaders that anti-piracy legislation would not move to the House floor this year unless there is a consensus on it.

Issa, and Sen. Ron Wyden, D-Ore., are pushing an alternative to SOPA and PIPA that would make the International Trade Commission, which already is in charge of patent infringements, responsible for taking steps to prevent money and advertising from going to rogue sites.

Issa formally introduced his bill Wednesday, saying the Internet blackout had "underscored the flawed approach taken by SOPA and PIPA" and his bill was "a smarter way to protect taxpayers' rights while protecting the Internet."

Source: http://us.rd.yahoo.com/dailynews/rss/tech/*http%3A//news.yahoo.com/s/ap/20120119/ap_on_go_co/us_internet_piracy_q_a

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Thursday, January 19, 2012

Buffett's first debt donation match - Fortune Finance - CNN.com

By Carol Loomis, senior editor-at-large

Scott Rigell

Rep. Scott Rigell

FORTUNE -- After Howard Buffett, a deeply conservative Republican whom his son Warren revered, was elected to the House of Representatives for three terms in the 1940s, Congress voted itself an annual pay raise from $10,000 to $12,500. Judging the raise unseemly, Howard Buffett refused to take it.

Today, Democrat Warren Buffett finds himself suddenly dealing with a freshman Republican Congressman whose strong principles inevitably -- and agreeably -- remind him of his father's. The legislator, 51, is Scott Rigell (pronounced RIDGE-ull) of Virginia Beach, Virginia, though he was formerly a resident of Florida, where he operated a Ford dealership in Titusville. Rigell ran for Congress in 2010 as the Republicans' establishment candidate, beating a Tea Party rival.

Rigell emerged last week on Fox News as the first (and so far, only) person to take up Buffett on his just-announced offer to a) match any contribution made by a Republican member of Congress to the Treasury to pay down debt and b) triple the match if the giver is Senator Mitch McConnell, a frequent critic of Buffett for wanting to raise tax rates on the rich. Buffett's offer was disclosed in an interview with Time, Fortune's sister publication.

A key point about Rigell is that he got to this issue before Buffett did. He had, on his own, moved in 2011 to give 15% of his Congressional salary to the Treasury for the very purpose of paying down debt. He acted, Rigell told Fox, to provide "leadership by example." This man is tough as well -- Howard Buffett would cheer! -- on governmental expenses broadly. For example, he'd like to see perks for members of Congress cut sharply and their pensions turned into 401k plans.

Rigell has strong wishes, too, about Buffett's matching offer, and he put them in a letter that reached Buffett in Omaha yesterday (read the letter here). Rigell said he would be making a 15% gift to the Treasury this year, but also hoped that Buffett would retroactively match his 2011 contribution. The amounts would be about $23,000 for 2011 (when some clerical errors resulted in the full 15% not being reached) and about $26,000 for 2012.

Buffett whipped an admiring letter back within the day (full letter below). He would indeed match both amounts, Buffett said, and was as well "heartened by both your contributions and your thoughts" -- particularly because they preceded Buffett's matching offer. To the Congressman's question about what documentation he should send to prove his payments, Buffett said don't bother: "Your word's good enough for me."

Buffett said he would send his matches to the Treasury around April 20th, waiting until then to see whether other members of Congress might join in. Buffett hopes, in fact, that an "intramural rivalry" between Republicans and Democrats might develop -- to see who can give the most.

That's the kind of Congressional rivalry, Buffett said, the American people would appreciate.

If the Congressman hasn't been in Omaha, he now has an invitation. Said Buffett, "If you are traveling near Omaha, I would enjoy getting together with you." That may not be what Rigell was expecting to hear from a Democrat yet, but conservative Congressmen who know firmly what they stand for definitely have a head start in the eyes of Buffett.

Fortune senior editor-at-large Carol Loomis, who wrote this article, is a long-time friend of Warren Buffett's and a shareholder in his company, Berkshire Hathaway.

Source: http://finance.fortune.cnn.com/2012/01/18/warren-buffett-scott-rigell-match/

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Wylie W. Vale Jr. dies at 70; researcher helped discover stress hormone

Wylie W. Vale Jr., a professor at the Salk Institute for Biological Studies in La Jolla and an internationally renowned expert on brain hormones who led a team of Salk researchers that discovered the brain hormone that triggers the body's reaction to stress, has died. He was 70.

Vale died unexpectedly in his sleep Jan. 3 while on vacation in Hana on the Hawaiian island of Maui, said his wife, Betty. The cause of death has not been determined.

The Texas-born Vale, who joined the Salk Institute in 1970, became one of the world's leading authorities on peptide hormones and growth factors that provide communication between the brain and endocrine system (the organs that produce the body's hormones).

His research team's landmark discovery came in 1981.

"He cracked one of the most challenging problems of our era: He discovered the brain hormone that serves as the on-off switch to the body's stress response, sometimes called the fight-or-flight response," said Ronald M. Evans, a professor and hormone expert at the Salk Institute.

"This has been the subject of speculation and investigation for more than a hundred years," said Evans, adding that Vale had been working on the problem for about 15.

"There was a big effort to try and find the secret for how the stress response is controlled, but the molecule was elusive, present in vanishingly small amounts," Evans said. "The technological challenge was enormous. This was like trying to climb Mt. Everest in biology."

Vale had earned a doctorate in physiology and biochemistry in 1968 at Baylor College of Medicine in Houston, where he trained in the lab under Roger Guillemin.

After Vale followed Guillemin to the Salk Institute in 1970, they continued to work together on perfecting the technology that led to isolating the first two brain peptides. That work led to Guillemin's becoming one of three American scientists who won the 1977 Nobel Prize in physiology and medicine.

In 1978, Vale struck out on his own, setting up an independent lab at the Salk Institute to continue the hunt for the elusive stress hormone.

After Vale's 1981 breakthrough, "neuropeptide discovery exploded into a whole new field of research, which continues today," Evans said.

"The molecule he isolated was called CRF ? corticotropin releasing factor," Evans said. "It's how the brain controls the production of cortisone from the adrenal gland, which is part of the stress response.

"But the discovery of CRF led to the realization that there was a small family of related neuropeptides that help to control anxiety, depression, anorexia, diabetes and drug abuse."

In 1982, Vale and his team discovered another hormone: the growth hormone releasing factor (GRF), which controls the body's growth. "It was another big advance in completing the puzzle of neuropeptides," Evans said.

Vale and his team discovered more than a dozen neuropeptides and their signaling mechanisms.

Vale co-founded two biotech companies ? Neurocrine Biosciences and Acceleron Pharma ? that have gone on to develop the medical and therapeutic potential of his discoveries.

"There are several drugs currently in the clinic and both are for controlling the stress response, as well as controlling metabolic diseases such as diabetes and heart disease," Evans said.

Another treatment that's in advanced clinical trials controls endometriosis, an inflammatory disease of the ovaries commonly linked to infertility.

Vale, who was born in Houston on July 3, 1941, and earned a bachelor's degree in biology from Rice University in 1964, also was an adjunct professor of medicine at UC San Diego. He was elected to the National Academy of Sciences in 1992.

In addition to his wife of 42 years, Vale is survived by his daughters, Elizabeth Gandhi and Susannah Howieson; his father, Wylie; his brother, Shannon; and a granddaughter.

dennis.mclellan@latimes.com

Source: http://feeds.latimes.com/~r/latimes/news/science/~3/eLWbXO36DsM/la-me-wylie-vale-20120118,0,7810239.story

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Wednesday, January 18, 2012

UCSB researchers uncover transparency limits on transparent conducting oxides

UCSB researchers uncover transparency limits on transparent conducting oxides [ Back to EurekAlert! ] Public release date: 18-Jan-2012
[ | E-mail | Share Share ]

Contact: Melissa Van De Werfhorst
melissa@engineering.ucsb.edu
805-893-4301
University of California - Santa Barbara

(Santa Barbara, Calif.) Researchers in the Computational Materials Group at the University of California, Santa Barbara (UCSB) have uncovered the fundamental limits on optical transparency in the class of materials known as transparent conducting oxides. Their discovery will support development of energy efficiency improvements for devices that depend on optoelectronic technology, such as light- emitting diodes and solar cells.

Transparent conducting oxides are used as transparent contacts in a wide range of optoelectronic devices, such as photovoltaic cells, light-emitting diodes (LEDs), and LCD touch screens. These materials are unique in that they can conduct electricity while being transparent to visible light. For optoelectronic devices to be able to emit or absorb light, it is important that the electrical contacts at the top of the device are optically transparent. Opaque metals and most transparent materials lack the balance between these two characteristics to be functional for use in such technology.

In a paper published in Applied Physics Letters [APL 100, 011914 (2012)], the UCSB researchers used cutting-edge calculation methods to investigate tin dioxide (SnO2), a widely-used conducting oxide.

Conducting oxides strike an ideal balance between transparency and conductivity because their wide band gaps prevent absorption of visible light by excitation of electrons across the gap, according to the researchers. At the same time, dopant atoms provide additional electrons in the conduction band that enable electrical conductivity. However, these free electrons can also absorb light by being excited to higher conduction-band states.

"Direct absorption of visible light cannot occur in these materials because the next available electron level is too high in energy. But we found that more complex absorption mechanisms, which also involve lattice vibrations, can be remarkably strong", says Hartwin Peelaers, a postdoctoral researcher and the lead author of the paper. The other authors are Emmanouil Kioupakis, now at the University of Michigan, and Chris Van de Walle, a professor in the UCSB Materials Department and head of the research group.

They found that tin dioxide only weakly absorbs visible light, thus letting most light pass through, so that it is still a useful transparent contact. In their study, the transparency of SnO2 declined when moving to other wavelength regions. Absorption was 5 times stronger for ultraviolet light and 20 times stronger for the infrared light used in telecommunications.

"Every bit of light that gets absorbed reduces the efficiency of a solar cell or LED", remarked Chris Van de Walle. "Understanding what causes the absorption is essential for engineering improved materials to be used in more efficient devices."

###

Van de Walle's Computational Materials Group is affiliated with the College of Engineering at UCSB. Their research explores semiconducting binary oxides, nitride semiconductors, novel channel materials and dielectrics, materials for quantum computing, photochemical hydrogen generation, and metallic nanoparticles. Learn more about Computational Materials research at http://www.mrl.ucsb.edu/~vandewalle.

Their research was supported as part of the UCSB Center for Energy Efficient Materials, an Energy Frontier Research Center funded by the United States Department of Energy, by the Belgian American Educational Foundation, and by the UCSB Materials Research Laboratory: a National Science Foundation MRSEC.



[ Back to EurekAlert! ] [ | E-mail | Share Share ]

?


AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert! system.


UCSB researchers uncover transparency limits on transparent conducting oxides [ Back to EurekAlert! ] Public release date: 18-Jan-2012
[ | E-mail | Share Share ]

Contact: Melissa Van De Werfhorst
melissa@engineering.ucsb.edu
805-893-4301
University of California - Santa Barbara

(Santa Barbara, Calif.) Researchers in the Computational Materials Group at the University of California, Santa Barbara (UCSB) have uncovered the fundamental limits on optical transparency in the class of materials known as transparent conducting oxides. Their discovery will support development of energy efficiency improvements for devices that depend on optoelectronic technology, such as light- emitting diodes and solar cells.

Transparent conducting oxides are used as transparent contacts in a wide range of optoelectronic devices, such as photovoltaic cells, light-emitting diodes (LEDs), and LCD touch screens. These materials are unique in that they can conduct electricity while being transparent to visible light. For optoelectronic devices to be able to emit or absorb light, it is important that the electrical contacts at the top of the device are optically transparent. Opaque metals and most transparent materials lack the balance between these two characteristics to be functional for use in such technology.

In a paper published in Applied Physics Letters [APL 100, 011914 (2012)], the UCSB researchers used cutting-edge calculation methods to investigate tin dioxide (SnO2), a widely-used conducting oxide.

Conducting oxides strike an ideal balance between transparency and conductivity because their wide band gaps prevent absorption of visible light by excitation of electrons across the gap, according to the researchers. At the same time, dopant atoms provide additional electrons in the conduction band that enable electrical conductivity. However, these free electrons can also absorb light by being excited to higher conduction-band states.

"Direct absorption of visible light cannot occur in these materials because the next available electron level is too high in energy. But we found that more complex absorption mechanisms, which also involve lattice vibrations, can be remarkably strong", says Hartwin Peelaers, a postdoctoral researcher and the lead author of the paper. The other authors are Emmanouil Kioupakis, now at the University of Michigan, and Chris Van de Walle, a professor in the UCSB Materials Department and head of the research group.

They found that tin dioxide only weakly absorbs visible light, thus letting most light pass through, so that it is still a useful transparent contact. In their study, the transparency of SnO2 declined when moving to other wavelength regions. Absorption was 5 times stronger for ultraviolet light and 20 times stronger for the infrared light used in telecommunications.

"Every bit of light that gets absorbed reduces the efficiency of a solar cell or LED", remarked Chris Van de Walle. "Understanding what causes the absorption is essential for engineering improved materials to be used in more efficient devices."

###

Van de Walle's Computational Materials Group is affiliated with the College of Engineering at UCSB. Their research explores semiconducting binary oxides, nitride semiconductors, novel channel materials and dielectrics, materials for quantum computing, photochemical hydrogen generation, and metallic nanoparticles. Learn more about Computational Materials research at http://www.mrl.ucsb.edu/~vandewalle.

Their research was supported as part of the UCSB Center for Energy Efficient Materials, an Energy Frontier Research Center funded by the United States Department of Energy, by the Belgian American Educational Foundation, and by the UCSB Materials Research Laboratory: a National Science Foundation MRSEC.



[ Back to EurekAlert! ] [ | E-mail | Share Share ]

?


AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert! system.


Source: http://www.eurekalert.org/pub_releases/2012-01/uoc--uru011712.php

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