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Friday, December 30, 2011

People don't just think with their guts; logic plays a role too




For decades, science has suggested that when people make decisions, they tend to ignore logic and go with the gut. But Wim De Neys, a psychological scientist at the University of Toulouse in France, has a new suggestion: Maybe thinking about logic is also intuitive. He writes about this idea in the January issue of Perspectives on Psychological Science, a journal of the Association for Psychological Science.
Psychologists have partly based their conclusions about reasoning and decision-making on questions like this one:
"Bill is 34. He is intelligent, punctual but unimaginative and somewhat lifeless. In school, he was strong in mathematics but weak in social studies and humanities.
Which one of the following statements is most likely?
(a) Bill plays in a rock band for a hobby.
(b) Bill is an accountant and plays in a rock band for a hobby."
Most people will let their stereotypes about accountants rule and pick (b). But, in fact, we have no idea what Bill does for a living—he could be a politician, a concert pianist, or a drug dealer—so it's more likely that only one random possibility, the rock band, is true, than that both (a) and (b) would happen to be true.
This line of research has suggested that people don't use logic when making decisions about the world. But the truth is more complicated, De Neys says. When most people read a question like the one above, there's a sense that something isn't quite right. "That feeling you have, that there's something fishy about the problem—we have a wide range of ways to measure that conflict," De Neys says. For example, he has shown with brain imaging that when people are thinking about this kind of problem, a part of their brain that deals with conflict is active. "They stick to their gut feeling and don't do the logical thing, but they do sense that what they are doing is wrong," De Neys says.
De Neys thinks this sense, that something isn't quite right with the decision you're making, comes from an intuitive sense of logic. Other scientists have found that children start thinking logically very early. In one study, 8-month-old babies were surprised if someone pulled mostly red balls out of a box that contained mostly white balls, proof that babies have an innate sense of probability before they can even talk. It makes sense, De Neys says, that this intuitive sense of logic would stick around in adults.
This research deals with the basics of how we think, but De Neys says it may help explain more complex decision-making. If you want to teach people to make better decisions, he says, "It's important to know which component of the process is faulty." For example, if you want to understand why people are smoking, and you think it's because they don't understand the logic—that smoking kills—you might put a lot of energy into explaining how smoking is bad for them, when the actual problem is addiction. It's a long way from a question about Bill's career to understanding something like why someone decides to get married, for example; but research like this should help," De Neys says.
Provided by Association for Psychological Science
"People don't just think with their guts; logic plays a role too." December 29th, 2011. http://medicalxpress.com/news/2011-12-people-dont-guts-logic-role.html
 

Posted by
Robert Karl Stonjek

Evidence found for brain injury in diet-induced obesity




(Medical Xpress) -- The first evidence, reported today, of structural changes in the brains of rodents and humans with diet-induced obesity may help explain one of the most vexing problems of body weight control.
Dr. Michael W. Schwartz, professor of medicine at the University of Washington, is the senior author of the study.
The well-established tendency to regain weight lost through dieting and exercise, as re-confirmed by a prominent Australian study earlier this year, is the single largest obstacle to successful obesity treatment. Body weight is controlled by complex interactions between hormones and neurons in a brain area known as the hypothalamus. These interactions influence appetite and food intake and , in most obese people, conspire to prevent permanent weight loss.
“Obese individuals,” said Schwartz, “are biologically defending their elevated body weight.” The mechanism for this phenomenon is the object of intense investigation by neuroendocrinologists.
Schwartz said, “To explain a biologically elevated body weight ‘set-point,’ investigators in the field have speculated about the existence of fundamental changes to brain neurocircuits that control energy balance. Our findings are the first to offer direct evidence of such a structural change, and they include evidence in humans as well as in mice and rats.”
His group studied the results of a high-fat diet in the brains of mice and rats that were bred to become obese on this diet. They found evidence of very early and lasting injury to a specific part of the hypothalamus in these animals. Using brain imaging, they also found signs of similar damage in the same area of the brain in obese humans.  
“We did not prove cause and effect between the hypothalamic neuron injury and defense of elevated body weight - that comes next - but this amounts to solid evidence of a change affecting the key hypothalamic area for body weight control with the potential to explain the problem,” said Schwartz.
Dr. Josh Thaler, assistant professor of medicine, is the first author of the paper, which will be published in the January 3 issue of Journal of Clinical Investigation and is entitled “Obesity Is Associated with Hypothalamic Injury in Rodents and Humans.” Co-authors include Ellen A. Schur, Stephan J. Guyenet, Bang H. Hwang, Xiaolin Zhao, David A. Sarruf, T. Nguyen, Jonathan Fischer, Miles. E. Matsen, Brente E. Wisse, Gregory Morton , Denis G. Baskin,  and their colleagues in the UW Department of Radiology and at Yale and the University of Cincinnati.
More information: Read the Journal of Clinical Investigation paper: http://www.jci.org … s/view/59660
 


Provided by University of Washington
"Evidence found for brain injury in diet-induced obesity." December 29th, 2011. http://medicalxpress.com/news/2011-12-evidence-brain-injury-diet-induced-obesity.html
 

Posted by
Robert Karl Stonjek

Brain's connective cells are much more than glue; they also regulate learning and memory




Brain's connective cells are much more than glue; they also regulate learning and memoryThis is a network of neurons (in red) and glia cells (in green) grown in a petri dish. Blue dots are the cells' nuclei. Credit: Pablo Blinder/American Friends of Tel Aviv University (AFTAU)
Glia cells, named for the Greek word for "glue," hold the brain's neurons together and protect the cells that determine our thoughts and behaviors, but scientists have long puzzled over their prominence in the activities of the brain dedicated to learning and memory. Now Tel Aviv University researchers say that glia cells are central to the brain's plasticity — how the brain adapts, learns, and stores information.
According to Ph.D. student Maurizio De Pittà of TAU's Schools of Physics and Astronomy and Electrical Engineering, glia cells do much more than hold the brain together. A mechanism within the glia cells also sorts information for learning purposes, De Pittà says. "Glia cells are like the brain's supervisors. By regulating the synapses, they control the transfer of information between neurons, affecting how the brain processes information and learns."
De Pittà's research, led by his TAU supervisor Prof. Eshel Ben-Jacob, along with Vladislav Volman of The Salk Institute and the University of California at San Diego and Hugues Berry of the Université de Lyon in France, has developed the first computer model that incorporates the influence of glia cells on synaptic information transfer. Detailed in the journal PLoS Computational Biology, the model can also be implemented in technologies based on brain networks such as microchips and computer software, Prof. Ben-Jacob says, and aid in research on brain disorders such as Alzheimer's disease and epilepsy.
Regulating the brain's "social network"
The brain is constituted of two main types of cells: neurons and glia. Neurons fire off signals that dictate how we think and behave, using synapses to pass along the message from one neuron to another, explains De Pittà. Scientists theorize that memory and learning are dictated by synaptic activity because they are "plastic," with the ability to adapt to different stimuli.
But Ben-Jacob and colleagues suspected that glia cells were even more central to how the brain works. Glia cells are abundant in the brain's hippocampus and the cortex, the two parts of the brain that have the most control over the brain's ability to process information, learn and memorize. In fact, for every neuron cell, there are two to five glia cells. Taking into account previous experimental data, the researchers were able to build a model that could resolve the puzzle.
The brain is like a social network, says Prof. Ben-Jacob. Messages may originate with the neurons, which use the synapses as their delivery system, but the glia serve as an overall moderator, regulating which messages are sent on and when. These cells can either prompt the transfer of information, or slow activity if the synapses are becoming overactive. This makes the glia cells the guardians of our learning and memory processes, he notes, orchestrating the transmission of information for optimal brain function.
New brain-inspired technologies and therapies
The team's findings could have important implications for a number of brain disorders. Almost all neurodegenerative diseases are glia-related pathologies, Prof. Ben-Jacob notes. In epileptic seizures, for example, the neurons' activity at one brain location propagates and overtakes the normal activity at other locations. This can happen when the glia cells fail to properly regulate synaptic transmission. Alternatively, when brain activity is low, glia cells boost transmissions of information, keeping the connections between neurons "alive."
The model provides a "new view" of how the brain functions. While the study was in press, two experimental works appeared that supported the model's predictions. "A growing number of scientists are starting to recognize the fact that you need the glia to perform tasks that neurons alone can't accomplish in an efficient way," says De Pittà. The model will provide a new tool to begin revising the theories of computational neuroscience and lead to more realistic brain-inspired algorithms and microchips, which are designed to mimic neuronal networks.
Provided by Tel Aviv University
"Brain's connective cells are much more than glue; they also regulate learning and memory." December 29th, 2011.http://medicalxpress.com/news/2011-12-brain-cells-memory.html
 
Posted by
Robert Karl Stonjek

7 Superb Sentences By 7 Superb Persons


7 Superb Sentences
 
 
Shakespeare....
 
 "Never Play With The Feelings Of Others
 
 Because You May Win The Game
 
 But The Risk Is That You Will Surely Lose
 
 The Person For A Life Time".
 
 
 
Napoleon....
 
 "The world suffers a lot. Not because of the violence of bad people,
 
 But because of the silence of good people!"
 
 
 
 
 "I am thankful to all those who said NO to me
 
 It's because of them I did it myself.."
 
 
 
Abraham Lincoln....
 
 
 "If friendship is your weakest point then you are the strongest person in the world"
 
 
 
Shakespeare....
 
 
 "Laughing Faces Do Not Mean That There Is Absence Of Sorrow!
 
 
 
William Arthur....
 
 
 "Opportunities Are Like Sunrises,
 
 
 
Hitler....
 
 
 "When You Are In The Light, Everything
 
 But When You Enter Into The Dark, Even Your Own Shadow Doesn't Follow You."
 
 
 
Shakespeare....
 
 
 "Coin Always Makes Sound But The Currency
 
 Notes Are Always Silent. So
 
 When Your Value Increases
 Keep Yourself Calm and Silent"
 
 
Dr Abdul Kalaam....
 
 "It Is Very Easy To Defeat Someone, But It Is Very Hard To Win Someone" 
 
 

GOLDEN PICTURE...!!!


என்றும் இளமையுடன் வாழ ஆரஞ்ச் பழச்சாறு




என்றும் இளமையுடன் வாழ எவருக்குத்தான் ஆசை இருக்காது. தற்போது 20 வயது இளைஞன் கூட நாற்பது வயது அடைந்தவன் போல் காட்சி அளிக்கிறார்கள்.
நல்ல திடகாத்திரமான இளைஞர்களை இன்று காணமுடியவில்லை. இதற்குக் காரணம் இராசயனம் கலந்த உணவுகள், அரைவேக்காட்டு உணவுகள், பதப்படுத்தப்பட்ட உணவுகள், குளிரூட்டப்பட்ட உணவுகள், சத்தற்ற உணவுகள், உடலுக்குத் தேவையான உடற்பயிற்சி இல்லாமை போன்றவையே.
உடற்பயிற்சி செய்வதுடன் உடலுக்குத் தேவையான சத்துக்களை நேரடியாகக் கொடுக்கும் பழங்களையும், பழச்சாறுகளையும் சாப்பிட்டு வந்தால் உடலை என்றும் இளமையாக வைத்திருக்கலாம்.
எங்கும் எப்போதும் கிடைக்கும் ஆரஞ்சு பழச் சாறின் மருத்துவக் குணங்களையும், அதன் சத்துக்களையும் அறிந்துகொள்வோம்.
சில உணவுகள் சாப்பிட்டதும் அவை உடலில் சில மாற்றங்களை உண்டுபண்ணி பித்த நீரை அதிகம் சுரக்கச் செய்கின்றன. இதனால் உடலில் உள்ள செல்களின் செயல்பாடுகள் முடக்கப்படுகின்றன.
இந்த பித்த நீர் இரத்தத்தில் கலந்து இரத்தத்தில் உள்ள இரும்புச் சத்துக்களை அழித்து விடுகிறது. இதனால் இரத்தம் அசுத்தமடைகிறது. பித்த நீர் தலைக்கேறி கண் பார்வை நரம்புகளை பாதிப்படையச் செய்கிறது. மேலும் ஞாபக மறதி ஏற்படுகிறது. சருமம் பாதித்து சுருங்கச் செய்கிறது.
தலைமுடி நரைக்கச் செய்கிறது. இதுபோல் இனிப்பு மற்றும் கொழுப்பு உணவுகளை 300 கலோரி அளவு சாப்பிட்ட பிறகு ஒரு மணி நேரம் கழித்து இரத்தத்தை பரிசோதித்துப் பார்த்தால் பித்த நீர் அதிகம் சுரந்து இரத்தத்தில் கலந்திருப்பதை அண்மையில் கண்டறிந்துள்ளனர்.
இந்த பித்த நீர் அதிகம் சுரப்பதைத் தடுக்கவும், உடலுக்குத் தேவையான அனைத்து சத்துக்களையும் தரும் பழச்சாறுகளில் ஆரஞ்சும் ஒன்று. ஆரஞ்சு பழச்சாறு சாப்பிட்டவர்களின் இரத்தத்தில் பித்த நீரில் அளவு குறைவாக இருக்கிறது.
ஆரஞ்சு சாறில் உள்ள வைட்டமின் சி, நோய் எதிர்ப்பு சக்தியை அதிகரித்து உடலை புத்துணர்வுடன் இருக்கச் செய்கிறது. இதனால் உடலில் அணுக்கள் நன்கு செயல்பட ஆரம்பிக்கும். உடலும் முதுமை அடையாமல் இளமைத் தோற்றத்துடன் காட்சியளிக்கும்.
ஒரு சிலருக்கு திடீரென்று குடல் புண் தொண்டைப் புண் ஏற்படுகிறது. இதற்குக் காரணம் பிராய்லர் கோழி வறுவல், ஐஸ்கிரீம் மற்றும் கேக் வகைகளை அதிகமாக சாப்பிடுவதே.
இதனால் உடல் சூடாகி வாயுக்கள் சீற்றமாகி புண்களை ஏற்படுத்துகிறது. சில சமயங்களில் இது புற்றுநோயாகக் கூட மாறலாம். இருதய நோய்களுக்கும் இந்த உணவு வகைகளே காரணமாகின்றன.
இத்தகைய பாதிப்புகளிலிருந்து விடபட இந்த உணவுகளை தவிர்த்து தினமும் 150 மி.லி ஆரஞ்சு சாறை அருந்தி வரவேண்டும். இருமுறை கூட அருந்தலாம். ஆரஞ்சு பழத்தை தினமும் உணவில் சேர்த்துக்கொள்வது நல்லது. ஆரஞ்சில் உள்ள கால்சியமும், வைட்டமின் சியும் உடல் திசுக்களை புதுப்பிக்கின்றன.
ஆரஞ்சு பழச்சாறு நன்கு பசியைத் தூண்டும். மலச்சிக்கலைப் போக்கும். செரிமானமாகாத உணவுகளை ஜீரணமாக்கும். கழிவுகள் உடனே வெளியேற்றி குடலை சுத்தமாக்கும். ஆரஞ்சுப் பழச்சாறை இரத்தம் உறிஞ்சிக் கொள்வதால் உடனடியாக உடலுக்கு வெப்பமும் சக்தியும் கிடைத்து விடுகிறது.
ஆரஞ்சு பழச்சாறு நோய்க் கிருமிகளை அழிக்கும் திறன் கொண்டது. ஜலதோஷம் உடனே குணமாகும். ஆரஞ்சுப் பழச்சாற்றில் சிறிது வெந்நீர் கலந்து அருந்தி வந்தால் ஜலதோஷம் குணமாகும்.
ஆரஞ்சு பழச்சாறை இரவு படுக்கைக்கு செல்லும் முன் அருந்தி வந்தால் நல்ல தூக்கம் கிடைக்கும். ஆரஞ்சு பழத்தில் ஏ, பி, சி போன்ற வைட்டமின்களும், ஏழுவகையான தாதுக்களும் உள்ளடங்கியுள்ளது.

கைபேசி பாவனையாளர்களுக்கு புதிய அச்சுறுத்தல்




உலகில் அதிகமானோர் உபயோகப்படுத்தும் கைபேசிகள் ஜி.எஸ்.எம்(Global System for Mobile Communications) தொழிநுட்பத்தின் மூலமே இயங்குகின்றது.
புள்ளிவிபரங்களின் படி உலகத் தொலைபேசிகளில் 80 சதவீதம் இத்தொழில்நுட்பத்தின் மூலமே இயங்குகின்றது.
இந்நிலையில் ஜேர்மனியா நாட்டு ஆராய்ச்சி அமைப்பான Security Research Labs இன் தலைவரான கார்ஸ்டன் நோஹல் ஜி.எஸ்.எம் கைபேசிகளில் காணப்படும் பாதுகாப்புப் குறைபாடு தொடர்பில் ஆய்வறிக்கையொன்றினை வெளியிட்டுள்ளார்.
அதன் படி ஜி.எஸ்.எம் தொழில்நுட்பத்தில் இயங்கும் அனைத்து கைபேசிகளில் பாதுகாப்புக் குறைபாடு காணப்படுவதாகவும், இதன் மூலம் எமது கைபேசிகளிலிருந்து நாம் அறியாதவகையில் அழைப்புகளை மேற்கொள்ளமுடிவதுடன், குறுந்தகவல்களையும் அனுப்பமுடியுமென நோஹல் எச்சரிகை விடுத்துள்ளார்.
அதாவது நமது கைபேசிகள் நாம் அறியாத வகையில் ஹெக்கர்களின் கைகளுக்குள் சிக்குவதாகும்.
இப்பாதுகாப்புக் குறைபாட்டின் மூலம் குறைந்த மணித்தியாலத்தில் அதிக கைபேசிகளை தமது கட்டுப்பாட்டுக்குள் கொண்டுவர ஹெக்கர்களால் முடியுமென நோஹல் குறிப்பிட்டுள்ளார்.
பொதுவாக சி.டி.எம்.ஏ உட்பட மற்றைய வலையமைப்புகளை விட ஜி.எஸ்.எம் ஆனது பாதுகாப்பாகக் கருதப்படுகின்றது.
எனினும் தற்போது வெளியாகியுள்ள செய்தியானது பாவனையாளர்களுக்கும், சேவை வழங்குநர்களுக்கும் சற்று அதிர்ச்சியளிப்பதாகவே உள்ளது.
ஸ்மார்ட் போன்களின் விற்பனையானது தற்காலத்தில் வெகுவாக அதிகரித்துள்ளமையானது ஹெக்கர்களின் கவனத்தினை கைபேசி உலகத்தினை நோக்கித் திருப்பியுள்ளது.

Diet, nutrient levels linked to cognitive ability, brain shrinkage



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New research has found that elderly people with higher levels of several vitamins and omega 3 fatty acids in their blood had better performance on mental acuity tests and less of the brain shrinkage typical of Alzheimer’s disease – while “junk food” diets produced just the opposite result.
The study was among the first of its type to specifically measure a wide range of blood nutrient levels instead of basing findings on less precise data such as food questionnaires, and found positive effects of high levels of vitamins B, C, D, E and the healthy oils most commonly found in fish.
The research was done by scientists from the Oregon Health and Science University in Portland, Ore., and the Linus Pauling Institute at Oregon State University. It was published today in Neurology, the medical journal of the American Academy of Neurology.



“This approach clearly shows the biological and neurological activity that’s associated with actual nutrient levels, both good and bad,” said Maret Traber, a principal investigator with the Linus Pauling Institute and co-author on the study.
“The vitamins and nutrients you get from eating a wide range of fruits, vegetables and fish can be measured in blood biomarkers,” Traber said. “I’m a firm believer these nutrients have strong potential to protect your brain and make it work better.”
The study was done with 104 people, at an average age of 87, with no special risk factors for memory or mental acuity. It tested 30 different nutrient biomarkers in their blood, and 42 participants also had MRI scans to measure their brain volume.
“These findings are based on average people eating average American diets,” Traber said. “If anyone right now is considering a New Year’s resolution to improve their diet, this would certainly give them another reason to eat more fruits and vegetables.”
Among the findings and observations:

  • The most favorable cognitive outcomes and brain size measurements were associated with two dietary patterns – high levels of marine fatty acids, and high levels of vitamins B, C, D and E. 

  • Consistently worse cognitive performance was associated with a higher intake of the type of trans-fats found in baked and fried foods, margarine, fast food and other less-healthy dietary choices. 

  • The range of demographic and lifestyle habits examined included age, gender, education, smoking, drinking, blood pressure, body mass index and many others. 

  • The use of blood analysis helped to eliminate issues such as people’s flawed recollection of what they ate, and personal variability in nutrients absorbed. 

  • Much of the variation in mental performance depended on factors such as age or education, but nutrient status accounted for 17 percent of thinking and memory scores and 37 percent of the variation in brain size. 

  • Cognitive changes related to different diets may be due both to impacts on brain size and cardiovascular function. 
The epidemiology of Alzheimer’s disease has suggested a role for nutrition, the researchers said in their study, but previous research using conventional analysis, and looking in isolation at single nutrients or small groups, have been disappointing. The study of 30 different blood nutrient levels done in this research reflects a wider range of nutrients and adds specificity to the findings.
The study needs to be confirmed with further research and other variables tested, the scientists said.
-Health Research News (Food & Nutrition)
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This work was supported by the National Institutes of Health. 

New Theory Emerges for Where Some Fish Became Four-Limbed Creatures


Romer's desert hypothesis, left, and Retallack's flooded woodland, right. (Credit: Image courtesy of University of Oregon)                                                                                      Science Daily — A small fish crawling on stumpy limbs from a shrinking desert pond is an icon of can-do spirit, emblematic of a leading theory for the evolutionary transition between fish and amphibians. This theorized image of such a drastic adaptation to changing environmental conditions, however, may, itself, be evolving into a new picture.

This scenario comes from the late Devonian, about 390 million years ago to roughly 360 million years ago. Paleontologist Alfred Romer, who died in 1973 after serving on the faculties at the University of Chicago and Harvard University, saw this time as a period of struggle and escape -- and important in fish-tetrapod transition -- to ensure survival.
University of Oregon scientist Gregory J. Retallack, professor of geological sciences, says that his discoveries at numerous sites in Maryland, New York and Pennsylvania suggests that "such a plucky hypothetical ancestor of ours probably could not have survived the overwhelming odds of perishing in a trek to another shrinking pond."
Reporting in the May 2011 issue of the Journal of Geology, Retallack, who also is co-director of paleontological collections at the UO's Museum of Natural and Cultural History, argues for a very different explanation. He examined numerous buried soils in rocks yielding footprints and bones of early transitional fossils between fish and amphibians of Devonian and Carboniferous geological age. What he found raises a major challenge to Romer's theory.
"These transitional fossils were not associated with drying ponds or deserts, but consistently were found with humid woodland soils," he said. "Remains of drying ponds and desert soils also are known and are littered with fossil fish, but none of our distant ancestors. Judging from where their fossils were found, transitional forms between fish and amphibians lived in wooded floodplains. Our distant ancestors were not so much foolhardy, as opportunistic, taking advantage of floodplains and lakes choked with roots and logs for the first time in geological history."
Limbs proved handy for negotiating woody obstacles, and flexible necks allowed for feeding in shallow water, Retallack said. By this new woodland hypothesis, the limbs and necks, which distinguish salamanders from fish, did not arise from reckless adventure in deserts, but rather were nurtured by a newly evolved habitat of humid, wooded floodplains.
The findings, he said, dampen both the desert hypothesis of Romer and a newer inter-tidal theory put forth by Grzegorz Niedbwiedzki and colleagues at the University of Warsaw. In 2010, they published their discovery of eight-foot-long, 395-million-year-old tetrapods in ancient lagoonal mud in southeastern Poland, where Retallack also has been studying fossil soils with Polish colleague Marek Narkeiwicz.
"Ancient soils and sediments at sites for transitional fossils around the world are critical for understanding when and under what conditions fish first walked," Retallack said. "The Darwin fish of chrome adorning many car trunks represents a particular time and place in the long evolutionary history of life on earth."  UO Academic Support Funds supported Retallack's research.

New Technique Makes It Easier to Etch Semiconductors



Metal-assisted chemical etching uses two steps. First, a thin layer of gold is patterned on top of a semiconductor wafer with soft lithography (left). The gold catalyzes a chemical reaction that etches the semiconductor form the top down, creating three-dimensional structures for optoelectronic applications (right). (Credit: Graphic by Xiuling Li)                                       Science Daily — Creating semiconductor structures for high-end optoelectronic devices just got easier, thanks to University of Illinois researchers.

A semiconductor's physical properties can vary depending on its structure, so semiconductor wafers are etched into structures that tune their electrical and optical properties and connectivity before they are assembled into chips.
The team developed a method to chemically etch patterned arrays in the semiconductor gallium arsenide, used in solar cells, lasers, light emitting diodes (LEDs), field effect transistors (FETs), capacitors and sensors. Led by electrical and computer engineering professor Xiuling Li, the researchers describe their technique in the journal Nano Letters.
Semiconductors are commonly etched with two techniques: "Wet" etching uses a chemical solution to erode the semiconductor in all directions, while "dry" etching uses a directed beam of ions to bombard the surface, carving out a directed pattern. Such patterns are required for high-aspect-ratio nanostructures, or tiny shapes that have a large ratio of height to width. High-aspect-ratio structures are essential to many high-end optoelectronic device applications.
While silicon is the most ubiquitous material in semiconductor devices, materials in the III-V (pronounced three-five) group are more efficient in optoelectronic applications, such as solar cells or lasers.
Unfortunately, these materials can be difficult to dry etch, as the high-energy ion blasts damage the semiconductor's surface. III-V semiconductors are especially susceptible to damage.
To address this problem, Li and her group turned to metal-assisted chemical etching (MacEtch), a wet-etching approach they had previously developed for silicon. Unlike other wet methods, MacEtch works in one direction, from the top down. It is faster and less expensive than many dry etch techniques, according to Li. Her group revisited the MacEtch technique, optimizing the chemical solution and reaction conditions for the III-V semiconductor gallium arsenide (GaAs).
The process has two steps. First, a thin film of metal is patterned on the GaAs surface. Then, the semiconductor with the metal pattern is immersed in the MacEtch chemical solution. The metal catalyzes the reaction so that only the areas touching metal are etched away, and high-aspect-ratio structures are formed as the metal sinks into the wafer. When the etching is done, the metal can be cleaned from the surface without damaging it.
"It is a big deal to be able to etch GaAs this way," Li said. "The realization of high-aspect-ratio III-V nanostructure arrays by wet etching can potentially transform the fabrication of semiconductor lasers where surface grating is currently fabricated by dry etching, which is expensive and causes surface damage."
To create metal film patterns on the GaAs surface, Li's team used a patterning technique pioneered by John Rogers, the Lee J. Flory-Founder Chair and a professor of materials science and engineering at the U. of I. Their research teams joined forces to optimize the method, called soft lithography, for chemical compatibility while protecting the GaAs surface. Soft lithography is applied to the whole semiconductor wafer, as opposed to small segments, creating patterns over large areas -- without expensive optical equipment.
"The combination of soft lithography and MacEtch make the perfect combination to produce large-area, high-aspect-ratio III-V nanostructures in a low-cost fashion," said Li, who is affiliated with the Micro and Nanotechnology Laboratory, the Frederick Seitz Materials Research Laboratory and the Beckman Institute for Advanced Science and Technology at the U. of I.
Next, the researchers hope to further optimize conditions for GaAs etching and establish parameters for MacEtch of other III-V semiconductors. Then, they hope to demonstrate device fabrication, including distributed Bragg reflector lasers and photonic crystals.
"MacEtch is a universal method as long as the right condition for deferential etching with and without metal can be found," Li said.
The Department of Energy and the National Science Foundation supported this work.

Sai Baba