Theory explains how new material could improve electronic shelf life

ScienceDaily (Jan. 9, 2012) — Research by UT Dallas engineers could lead to more-efficient cooling of electronics, producing quieter and longer-lasting computers, and cellphones and other devices.

Much of modern technology is based on silicon's use as a semiconductor material, but research recently published in the journal Nature Materials shows that graphene conducts heat about 20 times faster than silicon.

"Heat is generated every time a device computes," said "Dr. Kyeongjae "KJ" Cho, associate professor of materials science and engineering and physics at UT Dallas and one of the paper's authors. "For example a laptop fan pumps heat out of the system, but heat removal starts with a chip on the inside. Engineered graphene could be used to remove heat -- fast."

It was demonstrated in 2004 that graphite could be changed into a sheet of bonded carbon atoms called graphene, which is believed to be the strongest material ever measured. Although much research has focused on the strength and electronics of the material, Cho has been studying its thermal conductivity.

As electronics become more complex and decrease in size, the challenge to remove heat from the core becomes more difficult, he said. Desktop and laptop computers have fans.

Smaller electronic devices such as cellphones have other thermoelectric cooling devices.

"The performance of an electronic device degrades as it heats up, and if it continues the device fails," said Cho, also a visiting professor at Seoul National University in South Korea.

"The faster heat is removed, the more efficient the device runs and the longer it lasts."

Research assistant Hengji Zhang of UT Dallas is also an author of the paper. Cho and Zhang have published prior papers in the Journal of Nanomaterials and Physical Review B about graphene's thermal conductivity. For the Nature Materials paper, researchers at UT Austin conducted an experiment about graphene's heat transfer. They used a laser beam to heat the center of a portion of graphene, then measured the temperature difference from the middle of the graphene to the edge. Cho's theory helped explain their findings.

"We refined our modeling work taking into account their experimental conditions and found we have quantitative agreement," Cho said. "By understanding how heat transfers through a two-dimensional graphene system, we can further manipulate its use in semiconductor devices used in everyday life." For this purpose, Cho and Zhang are preparing a follow-up article on how to control the thermal conductivity in graphene.

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Theory explains how new material could improve electronic shelf life

ScienceDaily (Jan. 9, 2012) — Research by UT Dallas engineers could lead to more-efficient cooling of electronics, producing quieter and longer-lasting computers, and cellphones and other devices.

Much of modern technology is based on silicon's use as a semiconductor material, but research recently published in the journal Nature Materials shows that graphene conducts heat about 20 times faster than silicon.

"Heat is generated every time a device computes," said "Dr. Kyeongjae "KJ" Cho, associate professor of materials science and engineering and physics at UT Dallas and one of the paper's authors. "For example a laptop fan pumps heat out of the system, but heat removal starts with a chip on the inside. Engineered graphene could be used to remove heat -- fast."

It was demonstrated in 2004 that graphite could be changed into a sheet of bonded carbon atoms called graphene, which is believed to be the strongest material ever measured. Although much research has focused on the strength and electronics of the material, Cho has been studying its thermal conductivity.

As electronics become more complex and decrease in size, the challenge to remove heat from the core becomes more difficult, he said. Desktop and laptop computers have fans.

Smaller electronic devices such as cellphones have other thermoelectric cooling devices.

"The performance of an electronic device degrades as it heats up, and if it continues the device fails," said Cho, also a visiting professor at Seoul National University in South Korea.

"The faster heat is removed, the more efficient the device runs and the longer it lasts."

Research assistant Hengji Zhang of UT Dallas is also an author of the paper. Cho and Zhang have published prior papers in the Journal of Nanomaterials and Physical Review B about graphene's thermal conductivity. For the Nature Materials paper, researchers at UT Austin conducted an experiment about graphene's heat transfer. They used a laser beam to heat the center of a portion of graphene, then measured the temperature difference from the middle of the graphene to the edge. Cho's theory helped explain their findings.

"We refined our modeling work taking into account their experimental conditions and found we have quantitative agreement," Cho said. "By understanding how heat transfers through a two-dimensional graphene system, we can further manipulate its use in semiconductor devices used in everyday life." For this purpose, Cho and Zhang are preparing a follow-up article on how to control the thermal conductivity in graphene.

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Imperfections may improve graphene sensors

Although they found that graphene makes very good chemical sensors, researchers at Illinois have discovered an unexpected "twist" -- that the sensors are better when the graphene is "worse" -- more imperfections improved performance.

"This is quite the opposite of what you would want for transistors, for example," explained Eric Pop, an assistant professor of electrical and computer engineering and a member of the interdisciplinary research team. "Finding that the less perfect they were, the better they worked, was counter intuitive at first."

The research group, which includes researchers from both chemical engineering and electrical engineering, and from a startup company, Dioxide Materials, reported their results in the November 23, 2011 issue of Advanced Materials.

"The objective of this work was to understand what limits the sensitivity of simple, two-terminal graphene chemiresistors, and to study this in the context of inexpensive devices easily manufactured by chemical vapor deposition (CVD)," stated lead authors Amin Salehi-Khojin and David Estrada.

The researchers found that the response of graphene chemiresistors depends on the types and geometry of their defects.

"Nearly-pristine graphene chemiresistors are less sensitive to analyte molecules because adsorbates bind to point defects, which have low resistance pathways around them," noted Salehi-Khojin, a research scientist at Dioxide Materials and post-doctoral research associate in the Department of Chemical and Biomolecular Engineering (ChemE) at Illinois. "As a result, adsorption at point defects only has a small effect on the overall resistance of the device. On the other hand, micrometer-sized line defects or continuous lines of point defects are different because no easy conduction paths exist around such defects, so the resistance change after adsorption is significant."

"This can lead to better and cheaper gas sensors for a variety of applications such as energy, homeland security and medical diagnostics" said Estrada who is a doctoral candidate in the Department of Electrical and Computer Engineering.

According to the authors, the two-dimensional nature of defective, CVD-grown graphene chemiresistors causes them to behave differently than carbon nanotube chemiresistors. This sensitivity is further improved by cutting the graphene into ribbons of width comparable to the line defect dimensions, or micrometers in this study.

"What we determined is that the gases we were sensing tend to bind to the defects," Pop said. "Surface defects in graphene are either point-, wrinkle-, or line-like. We found that the points do not matter very much and the lines are most likely where the sensing happens."

"The graphene ribbons with line defects appear to offer superior performance as graphene sensors," said ChemE professor emeritus and Dioxide Materials CEO Richard Masel. "Going forward, we think we may be able engineer the line defects to maximize the material's sensitivity. This novel approach should allow us to produce inexpensive and sensitive chemical sensors with the performance better than that of carbon nanotube sensors."

Pop is also affiliated with the Beckman Institute for Advanced Science and the Micro and Nanotechnology Laboratory at Illinois. Additional authors of the paper, Polycrystalline Graphene Ribbons as Chemiresistors," include Kevin Y. Lin, Myung-Ho Bae, and Feng Xiong. This work was supported by Dioxide Materials, by ONR grants N00014-09-1-0180 and N00014-10-1-0061, and the NDSEG Graduate Fellowship (D.E.).

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Amin Salehi-Khojin, David Estrada, Kevin Y. Lin, Myung-Ho Bae, Feng Xiong, Eric Pop, Richard I. Masel. Polycrystalline Graphene Ribbons as Chemiresistors. Advanced Materials, 2011; DOI: 10.1002/adma.201102663

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New switch could improve electronics

Researchers at the University of Pittsburgh have invented a new type of electronic switch that performs electronic logic functions within a single molecule. The incorporation of such single-molecule elements could enable smaller, faster, and more energy-efficient electronics.

The research findings, supported by a $1 million grant from the W.M. Keck Foundation, were published online in the Nov. 14 issue of Nano Letters.

"This new switch is superior to existing single-molecule concepts," said Hrvoje Petek, principal investigator and professor of physics and chemistry in the Kenneth P. Dietrich School of Arts and Sciences and codirector of the Petersen Institute for NanoScience and Engineering (PINSE) at Pitt. "We are learning how to reduce electronic circuit elements to single molecules for a new generation of enhanced and more sustainable technologies."

The switch was discovered by experimenting with the rotation of a triangular cluster of three metal atoms held together by a nitrogen atom, which is enclosed entirely within a cage made up entirely of carbon atoms. Petek and his team found that the metal clusters encapsulated within a hollow carbon cage could rotate between several structures under the stimulation of electrons. This rotation changes the molecule's ability to conduct an electric current, thereby switching among multiple logic states without changing the spherical shape of the carbon cage. Petek says this concept also protects the molecule so it can function without influence from outside chemicals.

Because of their constant spherical shape, the prototype molecular switches can be integrated as atom-like building blocks the size of one nanometer (100,000 times smaller than the diameter of a human hair) into massively parallel computing architectures.

The prototype was demonstrated using an Sc3N@C80 molecule sandwiched between two electrodes consisting of an atomically flat copper oxide substrate and an atomically sharp tungsten tip. By applying a voltage pulse, the equilateral triangle-shaped Sc3N could be rotated predictably among six logic states.

The research was led by Petek in collaboration with chemists at the Leibnitz Institute for Solid State Research in Dresden, Germany, and theoreticians at the University of Science and Technology of China in Hefei, People's Republic of China. The experiments were performed by postdoctoral researcher Tian Huang and research assistant professor Min Feng, both in Pitt's Department of Physics and Astronomy.

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Tian Huang, Jin Zhao, Min Feng, Alexey A. Popov, Shangfeng Yang, Lothar Dunsch, Hrvoje Petek. A Molecular Switch Based on Current-Driven Rotation of an Encapsulated Cluster within a Fullerene Cage. Nano Letters, 2011; 111123145903006 DOI: 10.1021/nl2028409

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Algorithm developed to improve remote electrocardiography

ScienceDaily (Aug. 23, 2011) — Today someone in a remote village in India is able to run an electrocardiogram (ECG) via their smart phone on a loved one having a potential heart attack and send to a doctor in New Delhi for analysis.

Mobile technology is already bringing health care to places it has never been able to reach. However, there is still room for error that can lead to misdiagnosis.

Xiaopeng Zhao, assistant professor in the Department of Mechanical, Aerospace and Biomedical Engineering at the University of Tennessee, Knoxville, is working to eliminate these errors. Zhao and his team of graduate and undergraduate students and physicians have developed an award-winning algorithm that improves the effectiveness of ECGs.

The ECG is the most commonly performed screening tool for a variety of cardiac abnormalities. However, it is estimated that about 4 percent of all ECGs are taken with misplaced electrodes, leading to faulty diagnoses and mistreatments.

Zhao's algorithm examines interferences that result from electrode misplacement and disturbances, including patient motion and electromagnetic noise. Unlike conventional algorithms used to evaluate ECGs, Zhao's algorithm is more reliable because it is based on a matrix which simultaneously tests for irregular patterns caused by such interferences. Therefore, instead of a typical "yes-no" type of classification result, Zhao's produces a more accurate A-F letter grade of the ECG -- indicating specific weaknesses in the test. The algorithm also makes recommendations as to where to accurately place the electrodes.

Zhao's team has implemented the algorithm in a java program, which can be installed and operated on a smart phone. The program takes only a split second to execute on a smart phone and assess a 10-second ECG. The speed is key in situations where a second can mean the difference between life and death.

The goal is for users in remote areas to be able to know which ECGs are accurate to decrease misdiagnoses and ultimately save lives. The algorithm is also helpful in intensive care units where medical staff may be overworked, as well as for novice health professionals.

"There is a large population that does not receive good health care because they live in rural communities," said Zhao. "This algorithm helps to bring the doctor to their home through the help of mobile phone technology. We hope our invention brings their health care quality more in line with that of the developed world by reducing errors and improving the quality of ECGs."

The algorithm recently won the top spots in Physionet Challenge 2011 -- first, first and third places. Sponsored by the National Institutes for Health, Physionet and the annual Computing in Cardiology conference jointly host a series of challenge problems that are either unsolved or not well-solved. Starting in 2000, a new challenge topic is announced each year, aiming to stimulate work on important clinical problems and to foster rapid progress towards their solution.

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Smartphone battery life could dramatically improve with new invention

ScienceDaily (Sep. 16, 2011) — A new "subconscious mode" for smartphones and other WiFi-enabled mobile devices could extend battery life by as much as 54 percent for users on the busiest networks.

University of Michigan computer science and engineering professor Kang Shin and doctoral student Xinyu Zhang will present their new power management approach Sept. 21 at the ACM International Conference on Mobile Computing and Networking in Las Vegas. The approach is still in the proof-of-concept stage and is not yet commercially available.

Even when smartphones are in power-saving modes and not actively sending or receiving messages, they are still on alert for incoming information and they're searching for a clear communication channel. The researchers have found that this kind of energy-taxing "idle listening" is occurring during a large portion of the time phones spend in power-saving mode -- as much as 80 percent on busy networks. Their new approach could make smartphones perform this idle listening more efficiently. It's called E-MiLi, which stands for Energy-Minimizing Idle Listening.

To find out how much time phones spend keeping one ear open, Shin and Zhang conducted an extensive trace-based analysis of real WiFi networks. They discovered that, depending on the amount of traffic in the network, devices in power-saving modes spend 60 to 80 percent of their time in idle listening. In previous work, they demonstrated that phones in idle listening mode expend roughly the same amount of power as they do when they're fully awake.

"My phone isn't sending or receiving anything right now," Shin said, lifting his power-skinned iPhone, "but it's listening to see if data is coming in so I can receive it right away. This idle listening often consumes as much power as actively sending and receiving messages all day."

Here's how E-MiLi works: It slows down the WiFi card's clock by up to 1/16 its normal frequency, but jolts it back to full speed when the phone notices information coming in. It's well known that you can slow a device's clock to save energy. The hard part, Shin said, was getting the phone to recognize an incoming message while it was in this slower mode.

"We came up with a clever idea," Shin said. "Usually, messages come with a header, and we thought the phone could be enabled to detect this, as you can recognize that someone is calling your name even if you're 90 percent asleep."

When used with power-saving mode, the researchers found that E-MiLi is capable of reducing energy consumption by around 44 percent for 92 percent of mobile devices in real-world wireless networks.

In addition to new processor-slowing software on smartphones, E-MiLi requires new firmware for phones and computers that would be sending messages. They need the ability to encode the message header -- the recipient's address -- in a new and detectable way. The researchers have created such firmware, but in order for E-MiLi use to become widespread, WiFi chipset manufacturers would have to adopt these firmware modifications and then companies that make smartphones and computers would have to incorporate the new chips into their products.

Shin points out that E-MiLi is compatible with today's models, so messages sent with future devices that use E-MiLi's encoding would still be received as usual on smartphones without E-MiLi. E-MiLi can also be used with other wireless communication protocols that require idle listening, such as ZigBee.

Shin is the Kevin and Nancy O'Connor Professor of Computer Science. This research was funded by the National Science Foundation. The paper is titled "E-MiLi: Energy-Minimizing Idle Listening in Wireless Networks." The university is pursuing patent protection for the intellectual property, and is seeking commercialization partners to help bring the technology to market.

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New aromatic take-away coffee lid formulated to improve the taste of coffee

 Mint Urban Technologies has introduced an aromatic coffee lid for take-away cups, which it claims improves the taste of coffee by enhancing its bouquet

Hong Kong-based Mint Urban Technologies has introduced an aromatic coffee lid for take-away cups which it claims improves the taste of coffee when drinking through the lid. The aroma is not "mint," as the company's ill-chosen name suggests, but an aromatic material formulated to enhance the bouquet of the coffee. The secret of the new Aroma Lid is in the plastic, according to Mint's Marc Miller. "Coffee lids block the aroma coming from the coffee," says Miller. "Because taste is 95 percent smell, the lids are stopping us from experiencing the full taste of our favorite morning brew." If the Aroma Lid can indeed enhance the taste of coffee, it could be a significant product - the take-away coffee industry uses 100 billion lids every year.

The idea behind the Aroma Lid is that original coffee taste and smell can be preserved by adding a second lid element to the common coffee lid design; the second element consisting of aromatic material that can enhance, rather than detract, from the original smell.

"Premium Coffee is judged by its aroma", says Miller. "Coffee consists of 800 distinct flavors and not unlike fine wine, has a "nose" or "bouquet". Certain notes are more prized than others and the Aroma Lid only uses these finer notes to enhance the taste."

Mint Urban firmly believes that coffee doesn't taste as good when consumed through the typical coffee lid. "Heat from the coffee heats the plastic in a standard lid, and a plastic fragrance is emitted," according to Mint's Mike Newcomb. "This odor, however subtle, gives coffee a 'plastic aftertaste' that can compromise the taste of an otherwise excellent cup of coffee."

Furthermore, the heat of the coffee, traveling through the drinking spout, heats up the plastic again, causing a distinct fragrance of plastic.

"The aroma we use is very light" says Miller. "We only need it to be very subtle in order for the brain receptors to recognize the enhanced aroma. The bottom line is that the Aroma Lid will make coffee taste better than any other coffee lid on the market."

Mint is offering the new aromatic double-lids in two ways - as generic, non-branded lids, and in brand-customizable form for companies wishing to enhance and promote their existing product names without changing anything else.

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