Keeping electronics cool: Findings on modified form of graphene could have impacts in managing heat dissipation

ScienceDaily (Jan. 9, 2012) — A University of California, Riverside engineering professor and a team of researchers have made a breakthrough discovery with graphene, a material that could play a major role in keeping laptops and other electronic devices from overheating.

Alexander Balandin, a professor of electrical engineering at the UC Riverside Bourns College of Engineering, and researchers from The University of Texas at Austin, The University of Texas at Dallas and Xiamen University in China, have shown that the thermal properties of isotopically engineered graphene are far superior to those of graphene in its natural state.

The research efforts were led by the Professor Rodney S. Ruoff of UT Austin and Balandin, a corresponding author for the paper, "Thermal conductivity of isotopically modified graphene." It was published online Jan. 8 by the journal Nature Materials and will later appear in the print publication.

The results bring graphene -- a single-atom thick carbon crystal with unique properties, including superior electrical and heat conductivity, mechanical strength and unique optical absorption -- one step closer to being used as a thermal conductor for managing heat dissipation in everything from electronics to photovoltaic solar cells to radars.

"The important finding is the possibility of a strong enhancement of thermal conduction properties of isotopically pure graphene without substantial alteration of electrical, optical and other physical properties," Balandin said. "Isotopically pure graphene can become an excellent choice for many practical applications provided that the cost of the material is kept under control."

He added: "The experimental data on heat conduction in isotopically engineered graphene is also crucially important for developing an accurate theory of thermal conductivity in graphene and other two-dimensional crystals."

The research used the optothermal Raman method, a thermal conductivity measuring technique developed by Balandin. In 2008, Balandin and his group members demonstrated experimentally that graphene is an excellent heat conductor. They also developed the first detailed theory of heat conduction in graphene and related two-dimensional crystals.

The work presented in the Nature Materials paper shows that the thermal conductivity of isotopically engineered graphene is strongly enhanced compared to graphene in its natural state.

Naturally occurring carbon materials, including graphene, are made up of two stable isotopes: about 99 percent of 12C (referred to as "carbon 12") and 1 percent of 13C (referred to as "carbon 13"). The difference between isotopes is in the atomic mass of the carbon atoms. The removal of just about 1 percent of carbon 13, also called isotopic purification, modifies the dynamic properties of crystal lattices and affects their thermal conductivity.

The importance of the present research is explained by practical needs for materials with high thermal conductivity. Heat removal has become a crucial issue for continuing progress in the electronics industry, owing to increased levels of dissipated power as the devices become smaller and smaller. The search for materials that conduct heat well has become essential for the design of the next generation of integrated circuits and three-dimensional electronics.

Balandin, who is also founding chair of the materials science and engineering (MS&E) program at UC Riverside, believes graphene will gradually be incorporated into different devices.

Initially, it will likely be used in some niche applications such as thermal interface materials for chip packaging or transparent electrodes in photovoltaic solar cells or flexible displays, he said.

In a few years, it could be used with silicon in computer chips, for example as interconnect wiring or heat spreaders. It also has the potential to benefit other electronic applications, including analog high-frequency transistors, which are used in wireless communications, radar, security systems and imaging.

Balandin and the following researchers contributed to the findings in the Nature Materials paper:

The team at UT Austin, which performed the isotopic purification of graphene, included Ruoff, Shanshan Chen, a post-doctoral fellow, Weiwei Cai a former post-doctoral researcher who is now a professor at the Xiamen University and Columbia Mishra, a graduate student.

The team at UT Dallas, who performed molecular dynamics simulations that compared well with the stronger thermal connectivity of the isotopically engineered graphene, included Kyeongjae Cho, a professor, and Hengji Zhang, graduate student.

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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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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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Nano research could impact flexible electronic devices

ScienceDaily (Jan. 12, 2012) — A discovery by a research team at North Dakota State University, Fargo, and the National Institute of Standards and Technology (NIST), shows that the flexibility and durability of carbon nanotube films and coatings are intimately linked to their electronic properties. The research could one day impact flexible electronic devices such as solar cells and wearable sensors. The research also provided a promising young high school student the chance to work in the lab with world-class scientists, jumpstarting her potential scientific career.

The NDSU/NIST research team, led by Erik Hobbie, Ph.D., is working to determine why thin films made from metallic single-wall carbon nanotubes are superior for potential applications that demand both electronic performance and mechanical durability. "One simple reason is that the metallic nanotubes tend to transport charge more easily when they touch each other," said Hobbie. "But another less obvious reason has to do with how much the films can flex without changing their structure at very small scales."

Results from the study are published in ACS Nano.

The team includes NDSU graduate student John M. Harris; postdoctoral researcher Ganjigunte R. Swathi Iyer; Anna K. Bernhardt, North Dakota Governor's School attendee; and NIST researchers Ji Yeon Huh, Steven D. Hudson and Jeffrey A. Fagan.

There is great interest in using carbon nanotube films and coatings as flexible transparent electrodes in electronic devices such as solar cells. "Our research demonstrates that the flexibility and durability of these films are intimately linked to their electronic properties," said Hobbie. "This is a very new idea, so hopefully, it will generate a new series of studies and questions focused on the exact origins and consequences of this effect."

Such research could potentially result in material that reduces solar cell costs, and leads to the ability to use them in clothing or foldable electronics. Electronic devices currently on the market that require transparent electrodes, like touch screens and solar cells, typically use indium tin oxide, an increasingly expensive material. "It is also very brittle," said Hobbie, "implying that it cannot be used in devices that require mechanical flexibility like wearable or foldable electronics."

Single-wall carbon nanotubes show significant promise as transparent conductive coatings with outstanding electronic, mechanical and optical properties. "A particularly attractive feature of these films is that the physical properties can be tuned through the addition or subtraction of a relatively small number of nanotubes," said Hobbie. "Thin films made from such materials hold tremendous potential for flexible electronics applications, including the replacement of indium tin oxide in liquid crystal displays and photovoltaic devices."

Thin films made from metallic single-wall carbon nanotubes show better durability as flexible transparent conductive coatings, which the researchers attribute to a combination of superior mechanical performance and higher interfacial conductivity. The research team found significant differences in the electronic manifestations of thin-film wrinkling, depending on the electronic type of the nanotubes, and examined the underlying mechanisms.

The results of this study suggest that the metallic films make better flexible transparent conductive coatings; they have higher conductivity and are more durable. "Our results are relevant to a number of ongoing efforts in transparent conducting films and flexible electronic devices," said Hobbie.

The research was supported by the National Science Foundation through CMMI-0969155 and the U.S. Department of Energy through DE-FB36-08GO88160.

The opportunity to work on such research was new to Anna Bernhardt, a high school junior from a town of 1,000 people in western North Dakota. She was among 66 of the most academically driven high school sophomores and juniors who attended a six-week intensive summer residential program on the NDSU campus for scholastically motivated students in the state.

Students receive concentrated instruction from 40 NDSU faculty through discussion groups, labs, field trips and other activities. The state of North Dakota funds the cost of participation for North Dakota students who are accepted into the program. It's available free to public school students, while private and homeschool students selected for the program can make arrangements to attend for free through their local public school district.

While it is unusual for a young student to be involved in nanotechnology research at this level, it presented an opportunity for everyone involved. Bernhardt prepared single-wall carbon nanotube samples and participated in testing of the samples. "The experience of working in a research setting has helped me to decide that I would love to do more research in the future," said the young scientist. "The biggest benefit of working in the lab was getting a taste of the true research experience. Without North Dakota's Governor's School, I would never have been able to have this experience and surely wouldn't be so certain that I would like to do more research in the future."

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Journal Reference:

John M. Harris, Ganjigunte R. Swathi Iyer, Anna K. Bernhardt, Ji Yeon Huh, Steven D. Hudson, Jeffrey A. Fagan, Erik K. Hobbie. Electronic Durability of Flexible Transparent Films from Type-Specific Single-Wall Carbon Nanotubes. ACS Nano, 2011; 111220100417004 DOI: 10.1021/nn204383t

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'Smart Connector' could save millions in lost revenue

Deterioration and damage to cellular telecommunications cables cost organizations and customers millions in lost revenue and services in the always-on digital economy. A new sensor device, smaller than a quarter, might alleviate some of the impact.

Researchers at Rochester Institute of Technology and PPC Corp. have developed the Smart Connector, a new sensor that once installed in the connecting units of coaxial cables can provide information about equipment damage and pinpoint the exact location through self-diagnosing technologies -- some of the most advanced in the field today.

The sensor is one outcome of corporate research and development initiatives established at RIT that have grown over the past few years. The university and PPC Corp. signed a licensing agreement in June. Both parties are in the process of final testing and technology transfer, says Robert Bowman, professor of electrical and microelectronic engineering in RIT's Kate Gleason College of Engineering.

The university demonstrated the feasibility of the technology and is working with PPC to further test the manufactured product, Bowman explains. "It's one thing to conduct laboratory testing and demonstrate viability, it's another thing to get it into a product. PPC worked very closely with us during this research effort, and we'll work with them as they try to integrate this technology into their product line."

Bowman and his research group worked with Noah Montena, principal engineer at PPC, a Syracuse-based telecommunications radio-frequency, or RF, connector equipment company, to design the sensor-disc system. The system monitors the primary failure modes in RF cables. Each sensor-disc contains a unique site identifier, monitors critical conditions and reports the sensor status using a technique called back scatter telemetry. Each smart connector is capable of activating or powering-down its energy capacity by extracting miniscule amounts of radio frequency energy from the coaxial cables.

"This technology is really exciting, and the impact it could have on the industry is only just becoming apparent," says Montena. "Up until now, connector and equipment failures could be detected only after tower capacity had been diminished, and only pinpointed on-site with the system shut down."

The sensors have been designed from the beginning with simplicity, robustness and cost-effectiveness in mind, and one of the advantages of collaborating on the research has been the communication of manufacturing considerations as design decisions get made, Montena adds. "Beyond cellular connectors, it is easy to imagine this technology finding a place in other high value, or 'can't fail' applications such as communications or internal networks in spacecraft or aircraft. I look forward to uncovering all the possibilities."

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Self-healing electronics could work longer and reduce waste

When one tiny circuit within an integrated chip cracks or fails, the whole chip -- or even the whole device -- is a loss. But what if it could fix itself, and fix itself so fast that the user never knew there was a problem?

A team of University of Illinois engineers has developed a self-healing system that restores electrical conductivity to a cracked circuit in less time than it takes to blink. Led by aerospace engineering professor Scott White and materials science and engineering professor Nancy Sottos, the researchers published their results in the journal Advanced Materials.

"It simplifies the system," said chemistry professor Jeffrey Moore, a co-author of the paper. "Rather than having to build in redundancies or to build in a sensory diagnostics system, this material is designed to take care of the problem itself."

As electronic devices are evolving to perform more sophisticated tasks, manufacturers are packing as much density onto a chip as possible. However, such density compounds reliability problems, such as failure stemming from fluctuating temperature cycles as the device operates or fatigue. A failure at any point in the circuit can shut down the whole device.

"In general there's not much avenue for manual repair," Sottos said. "Sometimes you just can't get to the inside. In a multilayer integrated circuit, there's no opening it up. Normally you just replace the whole chip. It's true for a battery too. You can't pull a battery apart and try to find the source of the failure."

Most consumer devices are meant to be replaced with some frequency, adding to electronic waste issues, but in many important applications -- such as instruments or vehicles for space or military functions -- electrical failures cannot be replaced or repaired.

The Illinois team previously developed a system for self-healing polymer materials and decided to adapt their technique for conductive systems. They dispersed tiny microcapsules, as small as 10 microns in diameter, on top of a gold line functioning as a circuit. As a crack propagates, the microcapsules break open and release the liquid metal contained inside. The liquid metal fills in the gap in the circuit, restoring electrical flow.

"What's really cool about this paper is it's the first example of taking the microcapsule-based healing approach and applying it to a new function," White said. "Everything prior to this has been on structural repair. This is on conductivity restoration. It shows the concept translates to other things as well."

A failure interrupts current for mere microseconds as the liquid metal immediately fills the crack. The researchers demonstrated that 90 percent of their samples healed to 99 percent of original conductivity, even with a small amount of microcapsules.

The self-healing system also has the advantages of being localized and autonomous. Only the microcapsules that a crack intercepts are opened, so repair only takes place at the point of damage. Furthermore, it requires no human intervention or diagnostics, a boon for applications where accessing a break for repair is impossible, such as a battery, or finding the source of a failure is difficult, such as an air- or spacecraft.

"In an aircraft, especially a defense-based aircraft, there are miles and miles of conductive wire," Sottos said. "You don't often know where the break occurs. The autonomous part is nice -- it knows where it broke, even if we don't."

Next, the researchers plan to further refine their system and explore other possibilities for using microcapsules to control conductivity. They are particularly interested in applying the microcapsule-based self-healing system to batteries, improving their safety and longevity.

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Journal Reference:

Benjamin J. Blaiszik, Sharlotte L. B. Kramer, Martha E. Grady, David A. McIlroy, Jeffrey S. Moore, Nancy R. Sottos, Scott R. White. Autonomic Restoration of Electrical Conductivity. Advanced Materials, 2011; DOI: 10.1002/adma.201102888

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More powerful supercomputers? New device could bring optical information processing

Researchers have created a new type of optical device small enough to fit millions on a computer chip that could lead to faster, more powerful information processing and supercomputers.

The "passive optical diode" is made from two tiny silicon rings measuring 10 microns in diameter, or about one-tenth the width of a human hair. Unlike other optical diodes, it does not require external assistance to transmit signals and can be readily integrated into computer chips.

The diode is capable of "nonreciprocal transmission," meaning it transmits signals in only one direction, making it capable of information processing, said Minghao Qi (pronounced Chee), an associate professor of electrical and computer engineering at Purdue University.

"This one-way transmission is the most fundamental part of a logic circuit, so our diodes open the door to optical information processing," said Qi, working with a team also led by Andrew Weiner, Purdue's Scifres Family Distinguished Professor of Electrical and Computer Engineering.

The diodes are described in a paper to be published online Dec. 22 in the journal Science. The paper was written by graduate students Li Fan, Jian Wang, Leo Varghese, Hao Shen and Ben Niu, research associate Yi Xuan, and Weiner and Qi.

Although fiberoptic cables are instrumental in transmitting large quantities of data across oceans and continents, information processing is slowed and the data are susceptible to cyberattack when optical signals must be translated into electronic signals for use in computers, and vice versa.

"This translation requires expensive equipment," Wang said. "What you'd rather be able to do is plug the fiber directly into computers with no translation needed, and then you get a lot of bandwidth and security."

Electronic diodes constitute critical junctions in transistors and help enable integrated circuits to switch on and off and to process information. The new optical diodes are compatible with industry manufacturing processes for complementary metal-oxide-semiconductors, or CMOS, used to produce computer chips, Fan said.

"These diodes are very compact, and they have other attributes that make them attractive as a potential component for future photonic information processing chips," she said.

The new optical diodes could make for faster and more secure information processing by eliminating the need for this translation. The devices, which are nearly ready for commercialization, also could lead to faster, more powerful supercomputers by using them to connect numerous processors together.

"The major factor limiting supercomputers today is the speed and bandwidth of communication between the individual superchips in the system," Varghese said. "Our optical diode may be a component in optical interconnect systems that could eliminate such a bottleneck."

Infrared light from a laser at telecommunication wavelength goes through an optical fiber and is guided by a microstructure called a waveguide. It then passes sequentially through two silicon rings and undergoes "nonlinear interaction" while inside the tiny rings. Depending on which ring the light enters first, it will either pass in the forward direction or be dissipated in the backward direction, making for one-way transmission. The rings can be tuned by heating them using a "microheater," which changes the wavelengths at which they transmit, making it possible to handle a broad frequency range.

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The above story is reprinted from materials provided by Purdue University. The original article was written by Emil Venere.

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Journal Reference:

Li Fan, Jian Wang, Leo T. Varghese, Hao Shen, Ben Niu, Yi Xuan, Andrew M. Weiner, and Minghao Qi. An All-Silicon Passive Optical Diode. Science, December 22, 2011 DOI: 10.1126/science.1214383

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New method for enhancing thermal conductivity could cool computer chips, lasers and other devices

ScienceDaily (Dec. 14, 2011) — The surprising discovery of a new way to tune and enhance thermal conductivity -- a basic property generally considered to be fixed for a given material -- gives engineers a new tool for managing thermal effects in smart phones and computers, lasers and a number of other powered devices.

The finding was made by a group of engineers headed by Deyu Li, associate professor of mechanical engineering at Vanderbilt University, and published online in the journal Nature Nanotechnology on Dec. 11.

Li and his collaborators discovered that the thermal conductivity of a pair of thin strips of material called boron nanoribbons can be enhanced by up to 45 percent depending on the process that they used to stick the two ribbons together. Although the research was conducted with boron nanoribbons, the results are generally applicable to other thin film materials.

An entirely new way to control thermal effects

"This points at an entirely new way to control thermal effects that is likely to have a significant impact in microelectronics on the design of smart phones and computers, in optoelectronics on the design of lasers and LEDs, and in a number of other fields," said Greg Walker, associate professor of mechanical engineering at Vanderbilt and an expert in thermal transport who was not directly involved in the research.

According to Li, the force that holds the two nanoribbons together is a weak electrostatic attraction called the van der Waals force. (This is the same force that allows the gecko to walk up walls.)

"Traditionally, it is widely believed that the phonons that carry heat are scattered at van der Waals interfaces, which makes the ribbon bundles' thermal conductivity the same as that of each ribbon. What we discovered is in sharp contrast to this classical view. We show that phonons can cross these interfaces without being scattered, which significantly enhances the thermal conductivity," said Li. In addition, the researchers found that they could control the thermal conductivity between a high and a low value by treating the interface of the nanoribbon pairs with different solutions.

The enhancement is completely reversible

One of the remarkable aspects of the effect Li discovered is that it is reversible. For example, when the researchers wetted the interface of a pair of nanoribbons with isopropyl alcohol, pressed them together and let them dry, the thermal conductivity was the same as that of a single nanoribbon. However, when they wetted them with pure alcohol and let them dry, the thermal conductivity was enhanced. Then, when they wetted them with isopropyl alcohol again, the thermal conductivity dropped back to the original low value.

"It is very difficult to tune a fundamental materials property such as thermal conductivity and the demonstrated tunable thermal conductivity makes the research especially interesting," Walker said.

One of the first areas where this new knowledge is likely to be applied is in thermal management of microelectronic devices like computer chips. Today, billions to trillions of transistors are jammed into chips the size of a fingernail. These chips generate so much heat that one of the major factors in their design is to prevent overheating. In fact, heat management is one of the major reasons behind today's multi-core processor designs.

"A better understanding of thermal transport across interfaces is the key to achieving better thermal management of microelectronic devices," Li said.

Discovery may improve design of nanocomposites

Another area where the finding will be important is in the design of "nanocomposites" -- materials made by embedding nanostructure additives such as carbon nanotubes to a host material such as various polymers -- that are being developed for use in flexible electronic devices, structural materials for aerospace vehicles and a variety of other applications.

Collaborators on the study were post-doctoral research associate Juekan Yang, graduate students Yang Yang and Scott Waltermire from Vanderbilt; graduate students Xiaoxia Wu and Youfei Jiang, post-doctoral research associate Timothy Gutu, research assistant professor Haitao Zhang, and Associate Professor Terry T. Xu from the University of North Carolina; Professor Yunfei Chen from the Southeast University in China; Alfred A. Zinn from Lockheed Martin Space Systems Company; and Ravi Prasher from the U.S. Department of Energy.

The research was performed with financial support from the National Science Foundation, Lockheed Martin's Engineering and Technology University Research Initiatives program and the Office of Naval Research.

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The above story is reprinted from materials provided by Vanderbilt University. The original article was written by David Salisbury.

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Journal Reference:

Juekuan Yang, Yang Yang, Scott W. Waltermire, Xiaoxia Wu, Haitao Zhang, Timothy Gutu, Youfei Jiang, Yunfei Chen, Alfred A. Zinn, Ravi Prasher, Terry T. Xu, Deyu Li. Enhanced and switchable nanoscale thermal conduction due to van der Waals interfaces. Nature Nanotechnology, 2011; DOI: 10.1038/nnano.2011.216

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New method for enhancing thermal conductivity could cool computer chips, lasers and other devices

ScienceDaily (Dec. 14, 2011) — The surprising discovery of a new way to tune and enhance thermal conductivity -- a basic property generally considered to be fixed for a given material -- gives engineers a new tool for managing thermal effects in smart phones and computers, lasers and a number of other powered devices.

The finding was made by a group of engineers headed by Deyu Li, associate professor of mechanical engineering at Vanderbilt University, and published online in the journal Nature Nanotechnology on Dec. 11.

Li and his collaborators discovered that the thermal conductivity of a pair of thin strips of material called boron nanoribbons can be enhanced by up to 45 percent depending on the process that they used to stick the two ribbons together. Although the research was conducted with boron nanoribbons, the results are generally applicable to other thin film materials.

An entirely new way to control thermal effects

"This points at an entirely new way to control thermal effects that is likely to have a significant impact in microelectronics on the design of smart phones and computers, in optoelectronics on the design of lasers and LEDs, and in a number of other fields," said Greg Walker, associate professor of mechanical engineering at Vanderbilt and an expert in thermal transport who was not directly involved in the research.

According to Li, the force that holds the two nanoribbons together is a weak electrostatic attraction called the van der Waals force. (This is the same force that allows the gecko to walk up walls.)

"Traditionally, it is widely believed that the phonons that carry heat are scattered at van der Waals interfaces, which makes the ribbon bundles' thermal conductivity the same as that of each ribbon. What we discovered is in sharp contrast to this classical view. We show that phonons can cross these interfaces without being scattered, which significantly enhances the thermal conductivity," said Li. In addition, the researchers found that they could control the thermal conductivity between a high and a low value by treating the interface of the nanoribbon pairs with different solutions.

The enhancement is completely reversible

One of the remarkable aspects of the effect Li discovered is that it is reversible. For example, when the researchers wetted the interface of a pair of nanoribbons with isopropyl alcohol, pressed them together and let them dry, the thermal conductivity was the same as that of a single nanoribbon. However, when they wetted them with pure alcohol and let them dry, the thermal conductivity was enhanced. Then, when they wetted them with isopropyl alcohol again, the thermal conductivity dropped back to the original low value.

"It is very difficult to tune a fundamental materials property such as thermal conductivity and the demonstrated tunable thermal conductivity makes the research especially interesting," Walker said.

One of the first areas where this new knowledge is likely to be applied is in thermal management of microelectronic devices like computer chips. Today, billions to trillions of transistors are jammed into chips the size of a fingernail. These chips generate so much heat that one of the major factors in their design is to prevent overheating. In fact, heat management is one of the major reasons behind today's multi-core processor designs.

"A better understanding of thermal transport across interfaces is the key to achieving better thermal management of microelectronic devices," Li said.

Discovery may improve design of nanocomposites

Another area where the finding will be important is in the design of "nanocomposites" -- materials made by embedding nanostructure additives such as carbon nanotubes to a host material such as various polymers -- that are being developed for use in flexible electronic devices, structural materials for aerospace vehicles and a variety of other applications.

Collaborators on the study were post-doctoral research associate Juekan Yang, graduate students Yang Yang and Scott Waltermire from Vanderbilt; graduate students Xiaoxia Wu and Youfei Jiang, post-doctoral research associate Timothy Gutu, research assistant professor Haitao Zhang, and Associate Professor Terry T. Xu from the University of North Carolina; Professor Yunfei Chen from the Southeast University in China; Alfred A. Zinn from Lockheed Martin Space Systems Company; and Ravi Prasher from the U.S. Department of Energy.

The research was performed with financial support from the National Science Foundation, Lockheed Martin's Engineering and Technology University Research Initiatives program and the Office of Naval Research.

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The above story is reprinted from materials provided by Vanderbilt University. The original article was written by David Salisbury.

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Journal Reference:

Juekuan Yang, Yang Yang, Scott W. Waltermire, Xiaoxia Wu, Haitao Zhang, Timothy Gutu, Youfei Jiang, Yunfei Chen, Alfred A. Zinn, Ravi Prasher, Terry T. Xu, Deyu Li. Enhanced and switchable nanoscale thermal conduction due to van der Waals interfaces. Nature Nanotechnology, 2011; DOI: 10.1038/nnano.2011.216

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Sharpening the lines: Advance could lead to smaller features in the quest for more compact, faster microchips

ScienceDaily (Dec. 14, 2011) — The microchip revolution has seen a steady shrinking of features on silicon chips, packing in more transistors and wires to boost chips' speed and data capacity. But in recent years, the technologies behind these chips have begun to bump up against fundamental limits, such as the wavelengths of light used for critical steps in chip manufacturing.

Now, a new technique developed by researchers at MIT and the University of Utah offers a way to break through one of these limits, possibly enabling further leaps in the computational power packed into a tiny sliver of silicon. A paper describing the process was published in the journal Physical Review Letters in November.

Postdoc Trisha Andrew PhD '10 of MIT's Research Laboratory of Electronics, a co-author of this paper as well as a 2009 paper that described a way of creating finer lines on chips, says this work builds on that earlier method. But unlike the earlier technique, called absorbance modulation, this one allows the production of complex shapes rather than just lines, and can be carried out using less expensive light sources and conventional chip-manufacturing equipment. "The whole optical setup is on a par with what's out there" in chip-making plants, she says. "We've demonstrated a way to make everything cheaper."

As in the earlier work, this new system relies on a combination of approaches: namely, interference patterns between two light sources and a photochromic material that changes color when illuminated by a beam of light. But, Andrew says, a new step is the addition of a material called a photoresist, used to produce a pattern on a chip via a chemical change following exposure to light. The pattern transferred to the chip can then be etched away with a chemical called a developer, leaving a mask that can in turn control where light passes through that layer.

While traditional photolithography is limited to producing chip features larger than the wavelength of the light used, the method devised by Andrew and her colleagues has now been shown to produce features one-eighth that size. Others have achieved similar sizes before, Andrew says, but only with equipment whose complexity is incompatible with quick, inexpensive manufacturing processes.

The new system uses "a materials approach, combined with sophisticated optics, to get large-scale patterning," she says. And the technique should make it possible to reduce the size of the lines even further, she says.

The key to beating the limits usually imposed by the wavelength of light and the size of the optical system is an effect called stimulated emission depletion imaging, or STED, which uses fluorescent materials that emit light when illuminated by a laser beam. If the power of the laser falls below a certain level, the fluorescence stops, leaving a dark patch. It turns out that by carefully controlling the laser's power, it's possible to leave a dark patch much smaller than the wavelength of the laser light itself. By using the dark areas as a mask, and sweeping the beam across the chip surface to create a pattern, these smaller sizes can be "locked in" to the surface.

That process has previously been used to improve the resolution of optical microscopes, but researchers had thought it inapplicable to photolithographic chip making. The innovation by this MIT and Utah team was to combine STED with the earlier absorbance-modulation technique, replacing the fluorescent materials with a special polymer whose molecules change shape in response to specific wavelengths of light.

In addition to enabling the manufacture of chips with finer features, the technique could also be used in other advanced technologies, such as the production of photonic devices, which use patterns to control the flow of light rather than the flow of electricity. "It can be used for any process that uses optical lithography," Andrew says.

Professor Stefan Hell, head of the Department of NanoBiophotonics at the Max Planck Institute for Biophysical Chemistry in G?ttingen, Germany, calls this work "strikingly simple and elegant" and "a most impressive demonstration of the idea of using photochromic molecules to create features that are both finer and closer together than half the wavelength of the light."

"The work shows a concrete pathway to creating tiny and dense features at the nanoscale." he adds. "Because of its future potential it needs to be actively pursued. ... These methods have the potential of shifting the paradigm of what we think that focused light can do for making nanosized features and hence mastering the nanoworld."

In addition to Andrew, the paper's authors include Rajesh Menon, formerly a research engineer at MIT and now an assistant professor of electrical engineering and computer science at Utah, and Utah postdoc Nicole Brimhall and graduate student Rajakumar Varma Manthena. The work was supported in part by grants from the U.S. Defense Advanced Research Projects Agency and the National Science Foundation.

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The above story is reprinted from materials provided by Massachusetts Institute of Technology. The original article was written by David L. Chandler, MIT News Office.

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Journal Reference:

Nicole Brimhall, Trisha Andrew, Rajakumar Manthena, Rajesh Menon. Breaking the Far-Field Diffraction Limit in Optical Nanopatterning via Repeated Photochemical and Electrochemical Transitions in Photochromic Molecules. Physical Review Letters, 2011; 107 (20) DOI: 10.1103/PhysRevLett.107.205501

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iPhone Repair: 3 Tips For Newbies (Tip 3 Could Save You A Ton Of Time)

You have about four options to get your iPhone repaired. You can take it back to its maker (which is expensive). You can find someone who's learning how to repair iPhones in their bedroom or back seat (your phone could end just being a practice session gone wrong - it happens all the time). You may find a shop that repairs iPhones and toasters. It's Like going to Vegas except, what happens to your iPhone stays with your iPhone and you, (good or bad). You could use a mail-in service. You'll be without your iPhone for some time, and it you'll pay plenty for the trouble. If you get it back and something is not right, you'll be back at the post office or FEDEX and you'll be fed up.

Here are 3 tips to make it happen fast, right, and at a reasonable price.

TIP # 1:

Find an established business with a brick and mortar location, which will be there when you need it. Check the shop out on Google Places, Yahoo, and yelp.

TIP # 2:

Ask the shop for at least one customer you can call. Call them.

Tip # 3:

Like any industry, there are high-end providers. Using a high-end provider may actually cost the same of less. At the minimum, don't use a shop that won't give you an estimate over the phone, based on what you are telling them is wrong with your phone.

The ultimate in service is a shop which will give you a firm quote over the phone, and provide valet service. Valet service means they'll come to you, transfer your data to a loaner iPhone in front of you, (so you have zero down time) and they'll return to you with your repaired iPhone no more than 24 hours later. However, don't be fooled by a repair person who is simply operating from their vehicle or home, it is likely you won't be able to find them for warranty work.

Few shops do valet-like service, but they do exist. The cost for such a service should be minimal, at most. If you can't find a shop which provides a valet-like service, the next best thing is to find one with a fast mail-in service which offers REAL time-line guarantees. Most mail-in services are only fast if you pay a substantial amount of money for the speed. You can find one which will get it back to you fast (guaranteed) without charging much for the speed.

Apple products are well made, well loved, and it is only natural that very capable and reasonable repair shops would rise up through the weeds. By following the above tips, you're bound to find an honest, experienced shop - one of the flowers, among the weeds.

What should you do next?

Please, ask questions. We'll answer any question you have about any Apple device. It is our pleasure to answer it for you, for free and without any obligation of any kind. We have done thousands of repairs. We are a family run business with two locations in Southern California. You can contact Kort, Julie or Scott Linden at: http://www.itechrepairplus.com/ Thanks for reading this - Scott R. Linden

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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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Journal Reference:

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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Copper film could lower touch screen, LED and solar cell costs

ScienceDaily (Sep. 28, 2011) — Copper nanowires may be coming to a little screen near you. These new nanostructures have the potential to drive down the costs of displaying information on cell phones, e-readers and iPads, and they could also help engineers build foldable electronics and improved solar cells, according to new research.

Duke chemist Ben Wiley and his graduate student have developed a technique to organize copper atoms in water to form long, thin, non-clumped nanowires. The nanowires are then transformed into transparent, conductive films and coated onto glass or plastic.

The new research shows that the copper nanowire films have the same properties as those currently used in electronic devices and solar cells, but are less expensive to manufacture. The results were published online Sept. 23 in Advanced Materials.

The films that currently connect pixels in electronic screens are made of indium tin oxide, or ITO. It is highly transparent, which transmits the information well. But the ITO film must be deposited from a vapor in a process that is a thousand times slower than newspaper printing, and, once the ITO is in the device, it cracks easily. Indium is also an expensive rare earth element, costing as much as $800 per kilogram.

These problems have driven worldwide efforts to find less expensive materials that can be coated or printed like ink at much faster speeds to make low-cost, transparent conducting films, Wiley said.

One alternative to an ITO film is to use inks containing silver nanowires. The first cell phone with a screen made from silver nanowires will be on the market this year. But silver, like indium, is still relatively expensive at $1400 per kilogram.

Copper, on the other hand, is a thousand times more abundant than indium or silver, and about 100 times less expensive, costing only $9 per kilogram.

In 2010, Wiley and his graduate student Aaron Rathmell showed that it was possible to form a layer of copper nanowires on glass to make a transparent conducting film.

But at that time, the performance of the film was not good enough for practical applications because the wires clumped together. The new way of growing the copper nanowires and coating them on glass surfaces eliminates the clumping problem, Wiley said.

He and Rathmell also created the new copper nanowires to maintain their conductivity and form when bent back and forth 1,000 times. In contrast, ITO films' conduction and structure break after a few bends.

Wiley said the low-cost, high-performance, and flexibility of copper nanowires make them a natural choice for use in the next generation of displays and solar cells. He co-founded a company called NanoForge Corp in 2010 to manufacture copper nanowires for commercial applications.

In early 2011, NanoForge received a $45,000 North Carolina IDEA grant for refinement and scale-up of the manufacturing process of copper nanowires, and it is now filling orders.

With continuing development, copper nanowires could be in screens and solar cells in the next few years, which could lead to lighter and more reliable displays and also to making solar energy more competitive with fossil fuels, Wiley said.

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Duke University.

Journal Reference:

Rathmell, A. R. and Wiley, B. J. he Synthesis and Coating of Long, Thin Copper Nanowires to Make Flexible, Transparent Conducting Films on Plastic Substrates. Advanced Materials, 2011 DOI: 10.1002/adma.201102284

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Graphene's shining light could lead to super-fast Internet

ScienceDaily (Aug. 31, 2011) — Writing in the journal Nature Communications, a collaboration between the Universities of Manchester and Cambridge, which includes Nobel Prize winning scientists Professor Andre Geim and Professor Kostya Novoselov, has discovered a crucial recipe for improving characteristics of graphene devices for use as photodetectors in future high-speed optical communications.

By combining graphene with metallic nanostructures, they show a twenty-fold enhancement in harvesting light by graphene, which paves the way for advances in high-speed internet and other communications.

By putting two closely-spaced metallic wires on top of graphene and shining light on this structure, researchers previously showed that this generates electric power. This simple device presents an elementary solar cell.

More importantly for applications, such graphene devices can be incredibly fast, tens and potentially hundred times faster than communication rates in the fastest internet cables, which is due to the unique nature of electrons in graphene, their high mobility and high velocity.

The major stumbling block towards practical applications for these otherwise very promising devices has so far been their low efficiency. The problem is that graphene -- the thinnest material in the world -- absorbs little light, approximately only 3%, with the rest going through without contributing to the electrical power.

The Manchester researchers have solved the problems by combining graphene with tiny metallic structures, specially arranged on top of graphene.

These so-called plasmonic nanostructures have dramatically enhanced the optical electric field felt by graphene and effectively concentrated light within the one-atom-thick carbon layer.

By using the plasmonic enhancement, the light-harvesting performance of graphene was boosted by twenty times, without sacrificing any of its speed. The future efficiency can be improved even further.

Dr Alexander Grigorenko, an expert in plasmonics and a leading member of the team, said: "Graphene seems a natural companion for plasmonics. We expected that plasmonic nanostructures could improve the efficiency of graphene-based devices but it has come as a pleasant surprise that the improvements can be so dramatic."

Professor Novoselov added: "The technology of graphene production matures day-by-day, which has an immediate impact both on the type of exciting physics which we find in this material, and on the feasibility and the range of possible applications.

"Many leading electronics companies consider graphene for the next generation of devices. This work certainly boosts graphene's chances even further."

Professor Andrea Ferrari, from the Cambridge Engineering Department, who lead the Cambridge effort in the collaboration, said "So far, the main focus of graphene research has been on fundamental physics and electronic devices.

"These results show its great potential in the fields of photonics and optoelectronics, where the combination of its unique optical and electronic properties with plasmonic nanostructures, can be fully exploited, even in the absence of a bandgap, in a variety of useful devices, such as solar cells and photodetectors."

Graphene is a novel two-dimensional material which can be seen as a monolayer of carbon atoms arranged in a hexagonal lattice.

It is a wonder material that possesses a large number of unique properties and is currently considered in many new technologies.

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

Journal Reference:

T.J. Echtermeyer, L. Britnell, P.K. Jasnos, A. Lombardo, R.V. Gorbachev, A.N. Grigorenko, A.K. Geim, A.C. Ferrari, K.S. Novoselov. Strong plasmonic enhancement of photovoltage in graphene. Nature Communications, 2011; 2: 458 DOI: 10.1038/ncomms1464

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Breakthrough could double wireless capacity with no new towers

ScienceDaily (Sep. 7, 2011) — The days of waiting for smartphones to upload video may be numbered. Rice University engineering researchers have made a breakthrough that could allow wireless phone companies to double throughput on their networks without adding a single cell tower.

Rice's new "full-duplex" technology allows wireless devices like cell phones and electronic tablets to both "talk" and "listen" to wireless cell towers on the same frequency -- something that requires two frequencies today.

"Our solution requires minimal new hardware, both for mobile devices and for networks, which is why we've attracted the attention of just about every wireless company in the world," said Ashutosh Sabharwal, professor of electrical and computer engineering at Rice. "The bigger change will be developing new wireless standards for full-duplex. I expect people may start seeing this when carriers upgrade to 4.5G or 5G networks in just a few years."

In 2010, Sabharwal and Rice colleagues Melissa Duarte and Chris Dick published the first paper showing that full-duplex was possible. That set off a worldwide race to demonstrate that the technology could actually be used in a real network. This summer, Sabharwal and Rice's Achaleshwar Sahai and Gaurav Patel set new performance records with a real-time demo of the technology that produced signal quality at least 10 times better than any previously published result.

"We showed that our approach could support higher throughput and better link reliability than anything else that's been demonstrated, which is a plus for wireless carriers," Sabharwal said. "On the device side, we've shown that we can add full duplex as an additional mode on existing hardware. Device makers love this because real estate inside mobile devices is at a premium, and it means they don't have to add new hardware that only supports full duplex."

To explain why full-duplex wireless was long thought impossible for wireless networks, Sabharwal uses the analogy of two people standing far apart inside an otherwise empty arena. If each shouts to the other at the same time, neither can hear what the other is saying. The easy solution is to have only one person speak at a time, and that's what happens on two-way radios where only one person may speak at a given time. Cell phones achieve two-way communications by using two different frequencies to send and listen.

Rice's team overcame the full-duplex hurdle by employing an extra antenna and some computing tricks. In the shouting analogy, the result is that the shouter cannot hear himself, and therefore hears the only other sound in the arena -- the person shouting from far away.

"We send two signals such that they cancel each other at the receiving antenna -- the device ears," Sabharwal said. "The canceling effect is purely local, so the other node can still hear what we're sending."

He said the cancellation idea is relatively simple in theory and had been proposed some time ago. But no one had figured a way to implement the idea at low cost and without requiring complex new radio hardware.

"We repurposed antenna technology called MIMO, which are common in today's devices," Sabharwal said. "MIMO stands for 'multiple-input multiple-output' and it uses several antennas to improve overall performance. We took advantage of the multiple antennas for our full-duplex scheme, which is the main reason why all wireless carriers are very comfortable with our technology."

Sabharwal said Rice is planning to roll its full-duplex innovations into its "wireless open-access research platform," or WARP. WARP is a collection of programmable processors, transmitters and other gadgets that make it possible for wireless researchers to test new ideas without building new hardware for each test. Sabharwal said adding full-duplex to WARP will allow other researchers to start innovating on top of Rice's breakthrough.

"There are groups that are already using WARP and our open-source software to compete with us," he said. "This is great because our vision for the WARP project is to enable never-before-possible research and to allow anyone to innovate freely with minimal startup effort."

Sabharwal's team has gone one step further and achieved asynchronous full-duplex too -- that is one wireless node can start receiving a signal while it's in the midst of transmitting. Asynchronous transmission is import for carriers wishing to maximize traffic on their networks, and Rice's team is the first to demonstrate the technology.

"We've also developed a preliminary theory that explains why our system is working the way that it is," Sabharwal said. "That's also important for carriers and device makers, because engineers aren't likely to implement something like this without a clear understanding of fundamental tradeoffs."

Rice's research has been funded by the National Science Foundation, the Roberto Rocca Education Program and Xilinx Incorporated.

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Rice University.

Journal Reference:

Achaleshwar Sahai, Gaurav Patel, Ashutosh Sabharwal. Pushing the limits of Full-duplex: Design and Real-time Implementation. arXiv, 4 Jul 2011 [link]

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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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Human gait could soon power portable electronics

ScienceDaily (Aug. 24, 2011) — If the vision of Tom Krupenkin and J. Ashley Taylor comes to fruition, one day soon your cellphone -- or just about any other portable electronic device -- could be powered by simply taking a walk.

In a paper appearing in the journal Nature Communications, Krupenkin and Taylor, both engineering researchers at the University of Wisconsin-Madison, describe a new energy-harvesting technology that promises to dramatically reduce our dependence on batteries and instead capture the energy of human motion to power portable electronics.

"Humans, generally speaking, are very powerful energy-producing machines," explains Krupenkin, a UW-Madison professor of mechanical engineering. "While sprinting, a person can produce as much as a kilowatt of power."

Grabbing even a small fraction of that energy, Krupenkin points out, is enough to power a host of mobile electronic devices -- everything from laptop computers to cell phones to flashlights. "What has been lacking is a mechanical-to-electrical energy conversion technology that would work well for this type of application," he says.

Current energy harvesting technologies are aimed at either high-power applications such as wind or solar power, or very low-power applications such as calculators, watches or sensors. "What's been missing," says Taylor, "is the power in the watts range. That's the power range needed for portable electronics."

Solar power, the researchers explain, can also be used to power portable electronics, but, unlike human motion, direct sunlight is usually not a readily available source of energy for mobile electronics users.

In their Nature Communications report, Krupenkin and Taylor describe a novel energy-harvesting technology known as "reverse electrowetting," a phenomenon discovered by the Wisconsin researchers. The mechanical energy is converted to electrical energy by using a micro-fluidic device consisting of thousands of liquid micro-droplets interacting with a novel nano-structured substrate.

This technology could enable a novel footwear-embedded energy harvester that captures energy produced by humans during walking, which is normally lost as heat, and converts it into up to 20 watts of electrical power that can be used to power mobile electronic devices. Unlike a traditional battery, the energy harvester never needs to be recharged, as the new energy is constantly generated during the normal walking process.

The initial development of this technology was funded by a National Science Foundation Small Business Innovation Research grant. Now Krupenkin and Taylor are seeking to commercialize the technology through a company they've established, InStep NanoPower.

In their work, Taylor and Krupenkin were inspired by severe limitations that current battery technology imposes on mobile electronics users. As any cellphone or laptop user knows, heavy reliance on batteries greatly restricts the utility of mobile electronic devices in many situations. What's more, many mobile electronics are used in remote areas of the world where electrical grids for recharging batteries are often not available. Cellphone users in developing countries often have to pay high fees to have cellphones charged. Similar problems face military and law enforcement personnel. Modern soldiers, for example, head into the field carrying as much as 20 pounds of batteries to power communications equipment, laptop computers and night-vision goggles.

The energy generated by the footwear-embedded harvester can be used in one of two ways. It can be used directly to power a broad range of devices, from smartphones and laptops to radios, GPS units, night-vision goggles and flashlights.

Alternatively, the energy harvester can be integrated with a Wi-Fi hot spot that acts as a "middleman" between mobile devices and a wireless network. This allows users to seamlessly utilize the energy generated by the harvester without having to physically connect their mobile devices to the footwear. Such a configuration dramatically reduces power consumption of wireless mobile devices and allows them to operate for much longer time without battery recharge, the Wisconsin researchers say.

"You cut the power requirements of your cellphone dramatically by doing this," says Krupenkin. "Your cellphone battery will last 10 times longer."

Even though energy harvesting is unlikely to completely replace batteries in the majority of mobile applications, the UW-Madison researchers believe it can play a key role in reducing cost, pollution and other problems associated with battery use. The hope, they say, is that the novel mechanical to electrical energy conversion process they pioneered can go a long way toward achieving that goal.

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by University of Wisconsin-Madison. The original article was written by Terry Devitt.

Journal Reference:

Tom Krupenkin, J. Ashley Taylor. Reverse electrowetting as a new approach to high-power energy harvesting. Nature Communications, 2011; 2: 448 DOI: 10.1038/ncomms1454

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Proton-based transistor could let machines communicate with living things

ScienceDaily (Sep. 21, 2011) — Human devices, from light bulbs to iPods, send information using electrons. Human bodies and all other living things, on the other hand, send signals and perform work using ions or protons.

Materials scientists at the University of Washington have built a novel transistor that uses protons, creating a key piece for devices that can communicate directly with living things. The study is published online in the interdisciplinary journal Nature Communications.

Devices that connect with the human body's processes are being explored for biological sensing or for prosthetics, but they typically communicate using electrons, which are negatively charged particles, rather than protons, which are positively charged hydrogen atoms, or ions, which are atoms with positive or negative charge.

"So there's always this issue, a challenge, at the interface -- how does an electronic signal translate into an ionic signal, or vice versa?" said lead author Marco Rolandi, a UW assistant professor of materials science and engineering. "We found a biomaterial that is very good at conducting protons, and allows the potential to interface with living systems."

In the body, protons activate "on" and "off" switches and are key players in biological energy transfer. Ions open and close channels in the cell membrane to pump things in and out of the cell. Animals including humans use ions to flex their muscles and transmit brain signals. A machine that was compatible with a living system in this way could, in the short term, monitor such processes. Someday it could generate proton currents to control certain functions directly.

A first step toward this type of control is a transistor that can send pulses of proton current. The prototype device is a field-effect transistor, a basic type of transistor that includes a gate, a drain and a source terminal for the current. The UW prototype is the first such device to use protons. It measures about 5 microns wide, roughly a twentieth the width of a human hair.

"In our device large bioinspired molecules can move protons, and a proton current can be switched on and off, in a way that's completely analogous to an electronic current in any other field effect transistor," Rolandi said.

The device uses a modified form of the compound chitosan originally extracted from squid pen, a structure that survives from when squids had shells. The material is compatible with living things, is easily manufactured, and can be recycled from crab shells and squid pen discarded by the food industry.

First author Chao Zhong, a UW postdoctoral researcher, and second author Yingxin Deng, a UW graduate student, discovered that this form of chitosan works remarkably well at moving protons. The chitosan absorbs water and forms many hydrogen bonds; protons are then able to hop from one hydrogen bond to the next.

Computer models of charge transport developed by co-authors M.P. Anantram, a UW professor of electrical engineering, and Anita Fadavi Roudsari at Canada's University of Waterloo, were a good match for the experimental results.

"So we now have a protonic parallel to electronic circuitry that we actually start to understand rather well," Rolandi said.

Applications in the next decade or so, Rolandi said, would likely be for direct sensing of cells in a laboratory. The current prototype has a silicon base and could not be used in a human body. Longer term, however, a biocompatible version could be implanted directly in living things to monitor, or even control, certain biological processes directly.

The other co-author is UW materials science and engineering graduate student Adnan Kapetanovic. The research was funded by the University of Washington, a 3M Untenured Faculty Grant, a National Cancer Institute fellowship and the UW's Center for Nanotechnology, which is funded by the National Science Foundation.

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by University of Washington. The original article was written by Hannah Hickey.

Journal Reference:

Chao Zhong, Yingxin Deng, Anita Fadavi Roudsari, Adnan Kapetanovic, M.P. Anantram, Marco Rolandi. A polysaccharide bioprotonic field-effect transistor. Nature Communications, 2011; 2: 476 DOI: 10.1038/ncomms1489

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Sketching with superconductors: Breakthrough in controlling defects could lead to new generation of electronic devices

ScienceDaily (Aug. 22, 2011) — Reporting in the journal Nature Materials, researchers from the London Centre for Nanotechnology and the Physics Department of Sapienza University of Rome have discovered a technique to 'draw' superconducting shapes using an X-ray beam. This ability to create and control tiny superconducting structures has implications for a completely new generation of electronic devices.

Superconductivity is a special state where a material conducts electricity with no resistance, meaning absolutely zero energy is wasted.

The research group has shown that they can manipulate regions of high temperature superconductivity, in a particular material which combines oxygen, copper and a heavier, 'rare earth' element called lanthanum. Illuminating with X-rays causes a small scale re-arrangement of the oxygen atoms in the material, resulting in high temperature superconductivity, of the type originally discovered for such materials 25 years ago by IBM scientists. The X-ray beam is then used like a pen to draw shapes in two dimensions.

A well as being able to write superconductors with dimensions much smaller than the width of a human hair, the group is able to erase those structures by applying heat treatments. They now have the tools to write and erase with high precision, using just a few simple steps and without the chemicals ordinarily used in device fabrication. This ability to re-arrange the underlying structure of a material has wider applications to similar compounds containing metal atoms and oxygen, ranging from fuel cells to catalysts.

Prof. Aeppli, Director of the London Centre for Nanotechnology and the UCL investigator on the project, said: "Our validation of a one-step, chemical-free technique to generate superconductors opens up exciting new possibilities for electronic devices, particularly in re-writing superconducting logic circuits. Of profound importance is the key to solving the notorious 'travelling salesman problem', which underlies many of the world's great computational challenges. We want to create computers on demand to solve this problem, with applications from genetics to logistics. A discovery like this means a paradigm shift in computing technology is one step closer."

Prof Bianconi, the leader of the team from Sapienza, added: "It is amazing that in a few simple steps, we can now add superconducting 'intelligence' directly to a material consisting mainly of the common elements copper and oxygen."

The X-ray experiments were performed at the Elettra (Trieste) synchrotron radiation facility. The work is published in Nature Materials , 21 August 2011 (doi:1038/nmat3088) and follows on from previous discovery of fractal-like structures in superconductors (doi:10.1038/nature09260).

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Nicola Poccia, Michela Fratini, Alessandro Ricci, Gaetano Campi, Luisa Barba, Alessandra Vittorini-Orgeas, Ginestra Bianconi, Gabriel Aeppli, Antonio Bianconi. Evolution and control of oxygen order in a cuprate superconductor. Nature Materials, 2011; DOI: 10.1038/nmat3088Michela Fratini, Nicola Poccia, Alessandro Ricci, Gaetano Campi, Manfred Burghammer, Gabriel Aeppli, Antonio Bianconi. Scale-free structural organization of oxygen interstitials in La2CuO4+y. Nature, 2010; 466 (7308): 841 DOI: 10.1038/nature09260

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Hair chemistry could help solve cold cases

Patterns of certain chemical elements get into people’s hair from the food they eat and the water they drink. CBCCanadian researchers have just finished collecting samples for a database that may help police solve cold cases based on chemical information found in people’s hair.

“Hair gives a chronological indicator of your daily habits — your dietary habits and your movements,” said Michelle Chartrand, one of the two University of Ottawa researchers involved in the project.

That’s because patterns of certain chemical elements get into people’s hair from their food and the water they drink, and the record of their past habits and locations is retained as their hair grows out.

“Carbon and nitrogen indicate what you eat,” Chartrand said. “Hydrogen is an indicator of where you are.”

Chartrand and her colleague Gilles St-Jean have spent every summer since 2008 collecting hair and water samples from across Canada, and finally finished the job this summer, with sampling in B.C. and Alberta.

Once the data is analyzed and compiled into a database linking specific patterns to locations across Canada, they hope it will help generate new leads in cold cases.

'If someone drinks a glass of wine every night from Australia, for example, does that make a difference in their hair?'— Michelle Chartrand, University of Ottawa

They’ve already begun work on several cases, including the famous case of Madame Victoria, the body of a woman in her 50s found near the Royal Victoria Hospital in 2001, which was featured on CBC’s Fifth Estate in March.

“Her hair was about 43 centimetres long, so that gives us roughly 43 months of information,” Chartrand said, noting that hair grows at a rate of about a centimetre per month.

“Based on what our analyses showed us, we believe that she lived in seven distinct locations over those past 43 months.”

The researchers were able to say with confidence that she was not from western Canada

All her time was spent east of southern Manitoba or northwestern Ontario. It appeared that she started off in northern Ontario or Quebec, then moved toward the south, never returning to any of her previous locations. The analysis also showed that she had either been ill or made a major change to her diet in the four months before her death.

That was a rich amount of information, but it wasn’t enough to uncover the identity of Madame Victoria.

Still, the researchers say they’re always willing to apply their developing technique to case work. One issue at the moment is that the cost per case can be thousands of dollars, but that is expected to go down over time.

“As it becomes more mainstream or better known,” St-Jean said, “what I suspect will probably happen is forensic labs probably will start buying this type of equipment and hiring specialists that will help them do cases.”

Hair analysis relies on the fact that hydrogen — an element found in water — comes in slightly different chemical forms called isotopes. Some isotopes are heavier than others, and their proportions vary with latitude and the distance people live from either coast. That’s because heavier isotopes have a greater tendency to fall as rain.

The body of Madame Victoria was found in Montreal in 2001 and her face was reconstructed from her skull. Analysis of her hair showed she had moved seven times in 34 months, starting from northern Quebec or Ontario and moving south. CBCOver time, as clouds drift north and away from the coasts, they gain a higher proportion of lighter isotopes, which is reflected in the water sources – and the tap water – in those regions, St-Jean said. The ratios make their way into people’s hair when they drink the local water, and can be measured using a machine called an isotope ratio mass spectrometer.

Archeologists were the first to link isotope ratios in hair to geographic locations, developing the technique about 25 years ago. One of the questions they wanted to answer was whether the people buried in mass graves at ancient Mayan temples were local or captured from other regions, St-Jean said. Analysis of their hair showed they were not locals.

Applying the technique in Canada is a little trickier, the researchers acknowledge, because of the extra sources of water and other elements that enter our bodies.

“We can get food from any part of the world, any time of the year,” Chartrand said. “That’s what makes [it] much more difficult to track modern humans.”

As part of the sample collection, the researchers gave people who offered hair samples a questionnaire about their daily habits – asking what kinds of fluids they drink, including how much bottled water, how much they travel, and so on – to try and account for that.

“If someone drinks a glass of wine every night from Australia, for example, does that make a difference in their hair?” Chartrand wonders. “These are big unknowns that we are trying to compensate for.”

So far, it appears that the local water accounts for only around 27 per cent of the hydrogen isotope signal in people’s hair, she said. But that’s enough to distinguish an Albertan from a Manitoban or a person from Toronto from a person from Thunder Bay.

The technique does have limitations. For example, everyone along the Great Lakes and St. Lawrence River from southwestern Ontario to Montreal shows a similar signal due to their common water source.

“This is not an exact science,” Chartrand said. “It’s not designed to pinpoint an exact location.”

Nor is there a standard, internationally recognized method of hair analysis that will stand up in court.

But it is on its way to becoming one more technique that can be used with other forensic evidence, the researchers said.

St-Jean added, “It is a tool that helps the investigators to point their investigation in maybe a different direction than they would have thought of.”

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