IBM claims breakthrough on carbon nanotubes

IBM Research (NYSE: IBM) today announced a major engineering breakthrough that could accelerate carbon nanotubes replacing silicon transistors to power future computing technologies.

IBM scientists demonstrated a new way to shrink transistor contacts without reducing performance of carbon nanotube devices, opening a pathway to dramatically faster, smaller and more powerful computer chips beyond the capabilities of traditional semiconductors. The results will be reported in the October 2 issue of Science (DOI: 10.1126/science.aac8006).

IBM's breakthrough overcomes a major hurdle that silicon and any semiconductor transistor technologies face when scaling down. In any transistor, two things scale: the channel and its two contacts. As devices become smaller, increased contact resistance for carbon nanotubes has hindered performance gains until now. These results could overcome contact resistance challenges all the way to the 1.8 nanometer node – four technology generations away.

Carbon nanotube chips could greatly improve the capabilities of high performance computers, enabling Big Data to be analyzed faster, increasing the power and battery life of mobile devices and the Internet of Things, and allowing cloud data centers to deliver services more efficiently and economically.

Silicon transistors, tiny switches that carry information on a chip, have been made smaller year after year, but they are approaching a point of physical limitation. With Moore's Law running out of steam, shrinking the size of the transistor – including the channels and contacts – without compromising performance has been a vexing challenge troubling researchers for decades.

IBM has previously shown that carbon nanotube transistors can operate as excellent switches at channel dimensions of less than ten nanometers – the equivalent to 10,000 times thinner than a strand of human hair and less than half the size of today’s leading silicon technology. IBM's new contact approach overcomes the other major hurdle in incorporating carbon nanotubes into semiconductor devices, which could result in smaller chips with greater performance and lower power consumption.

Earlier this summer, IBM unveiled the first 7 nanometer node silicon test chip, pushing the limits of silicon technologies and ensuring further innovations for IBM Systems and the IT industry. By advancing research of carbon nanotubes to replace traditional silicon devices, IBM is paving the way for a post-silicon future and delivering on its $3 billion chip R&D investment announced in July 2014.

“These chip innovations are necessary to meet the emerging demands of cloud computing, Internet of Things and Big Data systems,” said Dario Gil, vice president of Science & Technology at IBM Research. “As silicon technology nears its physical limits, new materials, devices and circuit architectures must be ready to deliver the advanced technologies that will be required by the Cognitive Computing era. This breakthrough shows that computer chips made of carbon nanotubes will be able to power systems of the future sooner than the industry expected.”

A New Contact for Carbon Nanotubes

Carbon nanotubes represent a new class of semiconductor materials that consist of single atomic sheets of carbon rolled up into a tube. The carbon nanotubes form the core of a transistor device whose superior electrical properties promise several generations of technology scaling beyond the physical limits of silicon.

Electrons in carbon transistors can move more easily than in silicon-based devices, and the ultra-thin body of carbon nanotubes provide additional advantages at the atomic scale. Inside a chip, contacts are the valves that control the flow of electrons from metal into the channels of a semiconductor. As transistors shrink in size, electrical resistance increases within the contacts, which impedes performance. Until now, decreasing the size of the contacts on a device caused a commensurate drop in performance – a challenge facing both silicon and carbon nanotube transistor technologies.

IBM researchers had to forego traditional contact schemes and invented a metallurgical process akin to microscopic welding that chemically binds the metal atoms to the carbon atoms at the ends of nanotubes. This ‘end-bonded contact scheme’ allows the contacts to be shrunken down to below 10 nanometers without deteriorating performance of the carbon nanotube devices.

“For any advanced transistor technology, the increase in contact resistance due to the decrease in the size of transistors becomes a major performance bottleneck,” Gil added. “Our novel approach is to make the contact from the end of the carbon nanotube, which we show does not degrade device performance. This brings us a step closer to the goal of a carbon nanotube technology within the decade.”

IBM

Nanotechnology World Association

Nanotubes self-organize and wiggle: evolution of a non-equilibrium system demonstrates maximum entropy production

The second law of thermodynamics tells us that all systems evolve toward a state of maximum entropy, wherein all energy is dissipated as heat, and no available energy remains to do work. Since the mid-20^th century, research has pointed to an extension of the second law for nonequilibrium systems: the Maximum Entropy Production Principle (MEPP) states that a system away from equilibrium evolves in such a way as to maximize entropy production, given present constraints.Consecutive snapshots of the sample illustrating the formation of nanotube chains. The distance between electrodes is 1 cm, applied voltage is 400 V, and the series resistor is 100 MOhm. Panel (a) demonstrates the photograph of the ER fluid before the voltage is applied and the schematic of the experimental setup. The following photographs are taken after 45, 90, and 1500 seconds of interaction with the electric field. Originally printed in Scientific Reports, 5, article number 8323, doi 10.1038/srep08323. Reprinted with the permission of the authors.
Now physicists Alexey Bezryadin, Alfred Hubler, and Andrey Belkin from the University of Illinois at Urbana-Champaign, have demonstrated the emergence of self-organized structures that drive the evolution of a non-equilibrium system to a state of maximum entropy production. The authors suggest MEPP underlies the evolution of the artificial system’s self-organization, in the same way that it underlies the evolution of ordered systems (biological life) on Earth.
The team’s results are published in Nature Publishing Group’s online journal Scientific Reports.

(l to r) Professor Alexey Bezryadin, Assoc. Professor Alfred Hubler, and Postdoc Andrey Belkin
“Toward the final stages of this regime, the appendages were not destroyed during the avalanches, but rather retracted until the avalanche ended, then reformed their connection. So it was obvious that the avalanches correspond to the ‘feeding cycle’ of the ‘nanotube inset’,” comments Bezryadin.

MEPP may have profound implications for our understanding of the evolution of biological life on Earth and of the underlying rules that govern the behavior and evolution of all nonequilibrium systems. Life emerged on Earth from the strongly nonequilibrium energy distribution created by the Sun’s hot photons striking a cooler planet. Plants evolved to capture high energy photons and produce heat, generating entropy. Then animals evolved to eat plants increasing the dissipation of heat energy and maximizing entropy production.

In their experiment, the researchers suspended a large number of carbon nanotubes in a non-conducting non-polar fluid and drove the system out of equilibrium by applying a strong electric field. Once electrically charged, the system evolved toward maximum entropy through two distinct intermediate states, with the spontaneous emergence of self-assembled conducting nanotube chains.

In the first state, the “avalanche” regime, the conductive chains aligned themselves according to the polarity of the applied voltage, allowing the system to carry current and thus to dissipate heat and produce entropy. The chains appeared to sprout appendages as nanotubes aligned themselves so as to adjoin adjacent parallel chains, effectively increasing entropy production. But frequently, this self-organization was destroyed through avalanches triggered by the heating and charging that emanates from the emerging electric current streams. (Watch the video.)

“The avalanches were apparent in the changes of the electric current over time,” said Bezryadin.

Following avalanches, the chains with their appendages “wiggled,” resembling a living thing, similar to an insect.

In the second relatively stable stage of evolution, the entropy production rate reached maximum or near maximum. This state is quasi-stable in that there were no destructive avalanches.  

The study points to a possible classification scheme for evolutionary stages and a criterium for the point at which evolution of the system is irreversible—wherein entropy production in the self-organizing subsystem reaches its maximum possible value. Further experimentation on a larger scale is necessary to affirm these underlying principals, but if they hold true, they will prove a great advantage in predicting behavioral and evolutionary trends in nonequilibrium systems.

The authors draw an analogy between the evolution of intelligent life forms on Earth and the emergence of the wiggling bugs in their experiment. The researchers note that further quantitative studies are needed to round out this comparison. In particular, they would need to demonstrate that their “wiggling bugs” can multiply, which would require the experiment be reproduced on a significantly larger scale.

Such a study, if successful, would have implications for the eventual development of technologies that feature self-organized artificial intelligence, an idea explored elsewhere by co-author Alfred Hubler, funded by the Defense Advanced Research Projects Agency.

“The general trend of the evolution of biological systems seems to be this: more advanced life forms tend to dissipate more energy by broadening their access to various forms of stored energy,” Bezryadin proposes. “Thus a common underlying principle can be suggested between our self-organized clouds of nanotubes, which generate more and more heat by reducing their electrical resistance and thus allow more current to flow, and the biological systems which look for new means to find food, either through biological adaptation or by inventing more technologies.

“Extended sources of food allow biological forms to further grow, multiply, consume more food and thus produce more heat and generate entropy. It seems reasonable to say that real life organisms are still far from the absolute maximum of the entropy production rate. In both cases, there are ‘avalanches’ or ‘extinction events’, which set back this evolution. Only if all free energy given by the Sun is consumed, by building a Dyson sphere for example, and converted into heat then a definitely stable phase of the evolution can be expected.”

“Intelligence, as far as we know, is inseparable from life,” he adds. “Thus, to achieve artificial life or artificial intelligence, our recommendation would be to study systems which are far from equilibrium, with many degrees of freedom—many building blocks—so that they can self-organize and participate in some evolution. The entropy production criterium appears to be the guiding principle of the evolution efficiency.”

http://engineering.illinois.edu/news/article/10591 

Carbon nanotube fibers outperform copper

Scanning electron microscope images show typical carbon nanotube
fibers created at Rice University and broken into two by high-current-induced
Joule heating. Rice researchers broke the fibers in different conditions –
air, argon, nitrogen and a vacuum – to see how well they handled high current.
The fibers proved overall to be better at carrying electrical current than
copper cables of the same mass. (Credit: Kono Lab/Rice University)

Tests show bundles beat traditional cables for transmitting electricity

On a pound-per-pound basis, carbon nanotube-based fibers invented at Rice University have greater capacity to carry electrical current than copper cables of the same mass, according to new research.

While individual nanotubes are capable of transmitting nearly 1,000 times more current than copper, the same tubes coalesced into a fiber using other technologies fail long before reaching that capacity.

But a series of tests at Rice showed the wet-spun carbon nanotube fiber still handily beat copper, carrying up to four times as much current as a copper wire of the same mass.

That, said the researchers, makes nanotube-based cables an ideal platform for lightweight power transmission in systems where weight is a significant factor, like aerospace applications.

The analysis led by Rice professors Junichiro Kono and Matteo Pasquali appeared online this week in the journal Advanced Functional Materials. Just a year ago the journal Science reported that Pasquali’s lab, in collaboration with scientists at the Dutch firm Teijin Aramid, created a very strong conductive fiber out of carbon nanotubes.

Present-day transmission cables made of copper or aluminum are heavy because their low tensile strength requires steel-core reinforcement.

Scientists working with nanoscale materials have long thought there’s a better way to move electricity from here to there. Certain types of carbon nanotubes can carry far more electricity than copper. The ideal cable would be made of long metallic “armchair” nanotubes that would transmit current over great distances with negligible loss, but such a cable is not feasible because it’s not yet possible to manufacture pure armchairs in bulk, Pasquali said.

In the meantime, the Pasquali lab has created a method to spin fiber from a mix of nanotube types that still outperforms copper. The cable developed by Pasquali and Teijin Aramid is strong and flexible even though at 20 microns wide, it’s thinner than a human hair.

Illustration by Tanyia Johnson

Pasquali turned to Kono and his colleagues, including lead author Xuan Wang, a postdoctoral researcher at Rice, to quantify the fiber’s capabilities.

Pasquali said there has been a disconnect between electrical engineers who study the current carrying capacity of conductors and materials scientists working on carbon nanotubes. “That has generated some confusion in the literature over the right comparisons to make,” he said. “Jun and Xuan really got to the bottom of how to do these measurements well and compare apples to apples.”

The researchers analyzed the fiber’s “current carrying capacity” (CCC), or ampacity, with a custom rig that allowed them to test it alongside metal cables of the same diameter. The cables were tested while they were suspended in the open air, in a vacuum and in nitrogen or argon environments.

Electric cables heat up because of resistance. When the current load exceeds the cable’s safe capacity, they get too hot and break. The researchers found nanotube fibers exposed to nitrogen performed best, followed by argon and open air, all of which were able to cool through convection. The same nanotube fibers in a vacuum could only cool by radiation and had the lowest CCC.

“The outcome is that these fibers have the highest CCC ever reported for any carbon-based fibers,” Kono said. “Copper still has better resistivity by an order of magnitude, but we have the advantage that carbon fiber is light. So if you divide the CCC by the mass, we win.”

Kono plans to further investigate and explore the fiber’s multifunctional aspects, including flexible optoelectronic device applications.

A test rig designed by the Kono Lab at Rice allowed nanofiber and copper cables of equivalent mass to be compared. Image courtesy of the Kono Lab

Pasquali suggested the thread-like fibers are light enough to deliver power to aerial vehicles. “Suppose you want to power an unmanned aerial vehicle from the ground,” he mused. “You could make it like a kite, with power supplied by our fibers. I wish Ben Franklin were here to see that!”

The paper’s co-authors are Rice alumnus Natnael Behabtu and graduate students Colin Young and Dmitri Tsentalovich. Kono is a professor of electrical and computer engineering, of physics and astronomy, and of materials science and nanoengineering. Pasquali is a professor of chemical and biomolecular engineering, chemistry, and materials science and nanoengineering. Tsentalovich, Kono and Pasquali are members of the Richard E. Smalley Institute for Nanoscale Science and Technology.

The research was supported by the Department of Energy, the National Science Foundation, the Robert A. Welch Foundation, Teijin Aramid BV, the Air Force Office of Scientific Research and the Department of Defense National Defense Science and Engineering Graduate Fellowship.

Source: http://news.rice.edu/2014/02/13/rices-carbon-nanotube-fibers-outperform-copper-2/#sthash.XsDxaPt9.dpuf

Cooling Microprocessors with Carbon Nanotubes

“Cool it!” That’s a prime directive for microprocessor chips and a promising new solution to meeting this imperative is in the offing. Researchers with the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab) have developed a “process friendly” technique that would enable the cooling of microprocessor chips through carbon nanotubes.

Frank Ogletree, a physicist with Berkeley Lab’s Materials Sciences Division, led a study in which organic molecules were used to form strong covalent bonds between carbon nanotubes and metal surfaces. This improved by six-fold the flow of heat from the metal to the carbon nanotubes, paving the way for faster, more efficient cooling of computer chips. The technique is done through gas vapor or liquid chemistry at low temperatures, making it suitable for the manufacturing of computer chips.

“We’ve developed covalent bond pathways that work for oxide-forming metals, such as aluminum and silicon, and for more noble metals, such as gold and copper,” says Ogletree, who serves as a staff engineer for the Imaging Facility at the Molecular Foundry, a DOE nanoscience center hosted by Berkeley Lab. “In both cases the mechanical adhesion improved so that surface bonds were strong enough to pull a carbon nanotube array off of its growth substrate and significantly improve the transport of heat across the interface.”

Ogletree is the corresponding author of a paper describing this research in Nature Communications. The paper is titled “Enhanced Thermal Transport at Covalently Functionalized Carbon Nanotube Array Interfaces.” Co-authors are Sumanjeet Kaur, Nachiket Raravikar, Brett Helms and Ravi Prasher.

Overheating is the bane of microprocessors. As transistors heat up, their performance can deteriorate to the point where they no longer function as transistors. With microprocessor chips becoming more densely packed and processing speeds continuing to increase, the overheating problem looms ever larger. The first challenge is to conduct heat out of the chip and onto the circuit board where fans and other techniques can be used for cooling. Carbon nanotubes have demonstrated exceptionally high thermal conductivity but their use for cooling microprocessor chips and other devices has been hampered by high thermal interface resistances in nanostructured systems.

From left, Brett Helms, Frank Ogletree and Sumanjeet Kaur at the Molecular Foundry used organic molecules to form strong covalent bonds between carbon nanotubes and metal surfaces, improving by six-fold the flow of heat from the metal to the carbon nanotubes. (Photo by Roy Kaltschmidt)

“The thermal conductivity of carbon nanotubes exceeds that of diamond or any other natural material but because carbon nanotubes are so chemically stable, their chemical interactions with most other materials are relatively weak, which makes for  high thermal interface resistance,” Ogletree says. “Intel came to the Molecular Foundry wanting to improve the performance of carbon nanotubes in devices. Working with Nachiket Raravikar and Ravi Prasher, who were both Intel engineers when the project was initiated, we were able to increase and strengthen the contact between carbon nanotubes and the surfaces of other materials. This reduces thermal resistance and substantially improves heat transport efficiency.”

Sumanjeet Kaur, lead author of the Nature Communications paper and an expert on carbon nanotubes, with assistance from co-author and Molecular Foundry chemist Brett Helms, used reactive molecules to bridge the carbon nanotube/metal interface – aminopropyl-trialkoxy-silane (APS) for oxide-forming metals, and cysteamine for noble metals. First vertically aligned carbon nanotube arrays were grown on silicon wafers, and thin films of aluminum or gold were evaporated on glass microscope cover slips. The metal films were then “functionalized” and allowed to bond with the carbon nanotube arrays. Enhanced heat flow was confirmed using a characterization technique developed by Ogletree that allows for interface-specific measurements of heat transport.

“You can think of interface resistance in steady-state heat flow as being an extra amount of distance the heat has to flow through the material,” Kaur says. “With carbon nanotubes, thermal interface resistance adds something like 40 microns of distance on each side of the actual carbon nanotube layer. With our technique, we’re able to decrease the interface resistance so that the extra distance is around seven microns at each interface.”

Although the approach used by Ogletree, Kaur and their colleagues substantially strengthened the contact between a metal and individual carbon nanotubes within an array, a majority of the nanotubes within the array may still fail to connect with the metal. The Berkeley team is now developing a way to improve the density of carbon nanotube/metal contacts. Their technique should also be applicable to single and multi-layer graphene devices, which face the same cooling issues.

“Part of our mission at the Molecular Foundry is to help develop solutions for technology problems posed to us by industrial users that also raise fundamental science questions,” Ogletree says. “In developing this technique to address a real-world technology problem, we also created tools that yield new information on fundamental chemistry.”

This work was supported by the DOE Office of Science and the Intel Corporation.

#  #  #

The Molecular Foundry is one of five DOE Nanoscale Science Research Centers (NSRCs), national user facilities for interdisciplinary research at the nanoscale, supported by the DOE Office of Science. Together the NSRCs comprise a suite of complementary facilities that provide researchers with state-of-the-art capabilities to fabricate, process, characterize, and model nanoscale materials, and constitute the largest infrastructure investment of the National Nanotechnology Initiative. The NSRCs are located at DOE’s Argonne, Brookhaven, Lawrence Berkeley, Oak Ridge and Sandia and Los Alamos national laboratories. 

Lawrence Berkeley National Laboratory addresses the world’s most urgent scientific challenges by advancing sustainable energy, protecting human health, creating new materials, and revealing the origin and fate of the universe. Founded in 1931, Berkeley Lab’s scientific expertise has been recognized with 13 Nobel prizes. The University of California manages Berkeley Lab for the U.S. Department of Energy’s Office of Science. For more, visit www.lbl.gov.

The DOE Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.

Source: http://newscenter.lbl.gov/news-releases/2014/01/22/cooling-microprocessors-with-carbon-nanotubes/

Carbon Nanotubes Promise Improved Flame-Resistant Coating

An easy-to-apply, NIST-developed coating significantly 

reduces the flammability of foam used in furniture. 

The thin coating is deposited onto the surface of all 

the nooks and crannies of the porous foam (top), with 

heat-dissipating multiwalled carbon nanotubes 

(MWCNT) uniformly distributed throughout (bottom). 

(Color added for clarity.)
Credit: Kim/NIST

Using an approach akin to assembling a club sandwich at the nanoscale, National Institute of Standards and Technology (NIST) researchers have succeeded in crafting a uniform, multi-walled carbon-nanotube-based coating that greatly reduces the flammability of foam commonly used in upholstered furniture and other soft furnishings.

The flammability of the nanotube-coated polyurethane foam was reduced 35 percent compared with untreated foam. As important, the coating prevented melting and pooling of the foam, which generates additional flames that are a major contributor to the spread of fires.

Nationwide, fires in which upholstered furniture is the first item ignited account for about 6,700 home fires annually and result in 480 civilian deaths, or almost 20 percent of home fire deaths between 2006 and 2010, according to the National Fire Protection Association.

The innovative NIST technique squeezes nanotubes between two everyday polymers and stacks four of these trilayers on top of each other. The result is a plastic-like coating that is thinner than one-hundredth the diameter of human hair and has flame-inhibiting nanotubes distributed evenly throughout.

The brainchild of NIST materials scientists Yeon Seok Kim and Rick Davis, the fabrication method is described in the January 2014 issue of Thin Solid Films.* Kim and Davis write that the technique can be used with a variety of types of nanoparticles to improve the quality of surface coatings for diverse applications.

The pair experimented with a variety of layer-by-layer coating methods before arriving at their triple-decker approach. All had failed to meet their three key objectives: entire coverage of the foam's porous surface, uniform distribution of the nanotubes, and the practicality of the method. Inmost of these trials, the nanotubes—cylinders of carbon atoms resembling rolls of chicken wire—did not adhere strongly to the foam surface.

So, Kim and Davis opted to doctor the nanotubes themselves, borrowing a technique often used in cell culture to make DNA molecules stickier. The method attached nitrogen-containing molecules—called amine groups—to the nanotube exteriors.

This step proved critical: The doctored nanotubes were uniformly distributed and clung tenaciously to the polymer layers above and below. As a result, the coating fully exploits the nanotubes' rapid heat-dissipating capability.

Gram for gram, the resulting coating confers much greater resistance to ignition and burning than achieved with the brominated flame retardants commonly used to treat soft furnishings today. As important, says Davis, a "protective char layer" forms when the nanotube-coated foam is exposed to extreme heat, creating a barrier that prevents the formation of melt pools.

"This kind of technology has the potential to reduce the fire threat associated with burning soft furniture in homes by about a third," Davis says.

Source: http://www.nist.gov/el/fire_research/flame-011414.cfm

Engineers create light-activated ‘curtains’

Forget remote-controlled curtains. A new development by researchers at the University of California, Berkeley, could lead to curtains and other materials that move in response to light, no batteries needed.

Engineers have created a new light-reactive material made up of carbon nanotubes and plastic polycarbonate. This video demonstrates experimental “curtains” that are engineered to either open or close in response to light. (Video courtesy of Javey Research Group)

“The advantages of this new class of photo-reactive actuator is that it is very easy to make, and it is very sensitive to low-intensity light,” said Javey, who is also a faculty scientist at the Lawrence Berkeley National Lab. “The light from a flashlight is enough to generate a response.”

The researchers described their experiments in a paper published this week in the journal Nature Communications. They were able to tweak the size and chirality – referring to the left or right direction of twist – of the nanotubes to make the material react to different wavelengths of light. The swaths of material they created, dubbed “smart curtains,” could bend or straighten in response to the flick of a light switch.

“We envision these in future smart, energy-efficient buildings,” said Javey. “Curtains made of this material could automatically open or close during the day.”  

Other potential applications include light-driven motors and robotics that move toward or away from light, the researchers said.

Other co-authors include Xiaobo Zhang, study lead author and former Ph.D. student in the Javey Lab, and researchers from the Berkeley Sensor and Actuator Center.

The National Science Foundation and the Department of Energy helped support this work.

Source: http://newscenter.berkeley.edu/2014/01/09/smart-curtains/

Countdown to Zero: New “zero-dimensional” carbon nanotube may lead to superthin electronics and synthetic cells

Synthetic, man-made cells and ultrathin electronics built from a new form of “zero-dimensional” carbon nanotube may be possible through research at the University of Pittsburgh Swanson School of Engineering. The research, ““Zero-Dimensional” Single-Walled Carbon Nanotubes,” was published in the journal Angewandte Chemie.

Principal investigators are Steven R. Little, PhD, associate professor, CNG Faculty Fellow and Chair of the Department of Chemical and Petroleum Engineering; and Anna C. Balazs, PhD, the Distinguished Robert v. d. Luft Professor of Chemical and Petroleum Engineering. Co-investigators include Riccardo Gottardi, PhD, Ri.MED Foundation Fellow, whose research focuses on nanotechnology and biomedical engineering; Alexander Star, PhD, associate professor of chemistry; Bhaskar Godugu, PhD, research assistant professor and director of Pitt’s mass spectrometry facility; Susheng Tan, PhD, research assistant professor; postdoctoral researchers Yanan Chen, PhD and Kaladhar Kamalasanan, PhD; and Sam Rothstein, PhD, CSO and co-founder of Qrono Inc.

“Since its discovery, carbon nanotubes have held the promise to revolutionize the field of electronics, material science and even medicine,” says Dr. Little. “Zero-dimensional carbon nanotubes present the possibility to build ultrathin, superfast electronic devices, far superior to the best existing ones and it could be possible to build strong and ultralight cars, bridges, and airplanes.”

One of the most difficult hurdles is processing the carbon nanotubes into smaller forms. However, previous research at Pitt has managed to cut the carbon nanotubes into the smallest dimensions ever to overcome this problem.

“We have confirmed that these shorter nanotubes are more dispersible and potentially easier to process for industrial as well as biomedical application, and could even constitute the building blocks for the creation of synthetic cells,” says Dr. Gottardi.

The organization of the atoms within nanotubes makes them particularly interesting materials to work with. However, they are barely soluble, making industrial processing difficult. One aspect of the team’s research will focus on creating more soluble and therefore more usable carbon nanotubes. These shorter nanotubes have the same dimensions as many proteins that compose the basic machinery of living cells, presenting the potential for cell or protein-level biomedical imaging, protein or nucleic acid vaccination carriers, drug delivery vehicles, or even components of synthetic cells.

Overall, the project is aimed at developing and working with these more dispersible carbon nanotubes with the aim of making them easier to process. The creation of the smaller nanotubes is the first step toward reaching this goal.

Source: http://www.engineering.pitt.edu/News.aspx?id=2147509468

Scientists scale terahertz peaks in nanotubes

Rice U. researchers find plasmonic root of terahertz signals in some carbon nanotubes 

Carbon nanotubes carry plasmonic signals in the terahertz range of the electromagnetic spectrum, but only if they’re metallic by nature or doped.

In new research, the Rice University laboratory of physicist Junichiro Kono disproved previous theories that dominant terahertz response comes from narrow-gap semiconducting nanotubes.

Knowing that metallic or doped nanotubes respond with plasmonic waves at terahertz frequencies opens up the possibility that the tubes can be used in a wide array of optoelectronic amplifiers, detectors, polarizers and antennas.

The work by Kono and his Rice colleagues appeared online recently in the American Chemical Society journal Nano Letters.

Scientists have long been aware of a terahertz peak in nanotubes, the tiny cylinders of rolled-up carbon that show so much promise for advanced materials. But experiments on batches of nanotubes, which generally grow in a willy-nilly array of types, failed to reveal why it was there.

The origin of the peak was not explainable because researchers were only able to experiment on mixed batches of nanotube types, said Qi Zhang, a graduate student in Kono’s group and lead author of the paper. “All the previous work was done with a mixture of semiconducting and metallic tubes. We are the first to clearly identify the plasmonic nature of this terahertz response,” he said.

Rice’s growing expertise in separating nanotubes by type allowed Kono and his group to test for terahertz peaks in batches of pure metallic nanotubes known as “armchairs” as well as nonmetallic, semiconducting tubes.

“Metallic carbon nanotubes are expected to show plasmon resonance in the terahertz and infrared range, but no group has clearly demonstrated the existence of plasmons in carbon nanotubes,” Zhang said. “Previously, people proposed one possible explanation — that the terahertz peak is due to interband absorption in the small band gaps in semiconducting nanotubes. We rejected that in this paper.”

Plasmons are free electrons on the surface of metals like gold, silver or even aluminum nanoparticles that, when triggered by a laser or other outside energy, ripple like waves in a pond. Strong waves can trigger plasmon responses in adjacent nanoparticles. They are being investigated at Rice and elsewhere for use in sophisticated electronic and medical applications.

The Kono group’s research showed plasmons rippling at terahertz frequencies only along the length of a nanotube, but not across its width. “The only way charge carriers can move around is in the long direction,” Kono said. The researchers previously used this fact to demonstrate that aligned carbon nanotubes act as an excellent terahertz polarizer with performance better than commercial polarizers based on metallic grids.

Nanotubes can be thousands of times longer than they are wide, and the ability to grow them (or cut them) to specific lengths or to dope semiconducting nanotubes to add free carriers would make the tubes highly tunable for terahertz frequencies, Kono said.

“This paper only clarifies the origin of this effect,” he said. “Now that we understand it, there’s so much to do. We will be making various terahertz devices, architectures and systems based on carbon nanotube plasmons.”

Rice alumni Erik Hároz, now a postdoctoral researcher at Los Alamos National Laboratory, and Lei Ren, a researcher at TGS, co-authored the paper with undergraduate student Zehua Jin, postdoctoral researcher Xuan Wang, senior research scientist Rolf Arvidson and Andreas Lüttge, a research professor of Earth science and chemistry, all of Rice. Kono is a professor of electrical and computer engineering and of physics and astronomy and of materials science and nanoengineering.

The Department of Energy, the National Science Foundation and the Robert A. Welch Foundation supported the research.

Source: http://news.rice.edu/2013/12/09/scientists-scale-terahertz-peaks-in-nanotubes/

Carbon nanostructures grow under extreme particle bombardment

Even at a plasma bombardment that is 10,000 times more intense than the standard production method, carbon nanostructures such as these can develop. 
Credit: K.Bystrov/DIFFER.

Nanostructures, such as graphene and carbon nanotubes, can develop under far extremer plasma conditions than was previously thought. Plasmas (hot, charged gases) are already widely used to produce interesting nanostructures. In the scientific journal Carbon, FOM PhD researcher Kirill Bystrov shows that carbon nanostructures can also develop under far extremer conditions than those normally used for this purpose.

DIFFER's Pilot-PSI device has been built to expose wall materials to plasmas that will rage in future fusion reactors. Such plasmas are 10,000 times more intense than those normally used for the construction of nanomaterials. Using Pilot-PSI, Bystrov's international team demonstrated that this extreme environment provides unexpected possibilities for producing nanostructures.

Out of equilibrium 

Plasmas offer major advantages for the controlled production of advanced materials. In the plasma ions and electrons can be brought far out of their thermal equilibria. Under these conditions, the deposition processes can proceed very differently from those at thermal equilibrium. In the widely used technique of plasma-enhanced chemical vapour deposition (PECVD) the plasma density and the quantity of material supplied (carbon) determine which nanostructures develop. The further plasma is from its thermal equilibrium, the more exotic the structures that develop.

Even at a plasma bombardment that is 10,000 times more intense than the standard production method, carbon nanostructures such as these can develop. 
Credit: K.Bystrov / DIFFER

Variation 

After they had exposed various materials such as tungsten, molybdenum and graphite to a plasma with a carbon supply, Bystrov's team discovered a layer full of exotic carbon nanostructures: multi-walled or extra long nanotubes, cauliflower structures and layers of graphene. Varying parameters such as the plasma density, temperature and composition yielded different structures each time. Bystrov: "It was most surprising that an enormous particle bombardment like that which occurs on the edge of a fusion reactor can yield such delicate structures". The influence of the material on which the deposited structures formed was found to be surprisingly small: on all three of the surfaces tested the same types of structures developed.

Versatile machines
 
With the research, Bystrov and his colleagues do not yet have a competitor for the PECVD technique. "Our interest is in demonstrating that you can allow interesting processes to occur in environments 10,000 times more intense than you would expect," Bystrov writes in his publication. Research leader dr. Greg De Temmerman from the Plasma Surface Interactions team at DIFFER: "We set up these experiments to investigate what happens with the wall materials in future fusion reactors. This research demonstrates that the conditions in Pilot-PSI and its big brother Magnum-PSI are also interesting far outside the fusion community. These are highly versatile machines".

Contact 

Kirill Bystrov, MSc, PhD researcher plasma-wall interaction, +31 (0)30 609 69 30.
Dr. Greg De Temmerman, research leader plasma wall interaction, +31 (0)30 609 69 44.
Gieljan de Vries, MSc, Head of Communication FOM Institute DIFFER, +31 (0)30 609 69 02.

Reference 

Spontaneous synthesis of carbon nanowalls, nanotubes and nanotips using high flux density plasmas, Carbon, 28 November 2013. DOI: 10.1016/j.carbon.2013.11.051 

Source: http://www.fom.nl/live/english/news/archives/pressreleases2013/artikel.pag?objectnumber=241874

Nanotubes can solder themselves, markedly improving device performance

University of Illinois researchers have developed a way to heal gaps in wires too small for even the world’s tiniest soldering iron.

Led by electrical and computer engineering professor Joseph Lyding and graduate student Jae Won Do, the Illinois team published its results in the journal Nano Letters. 

Carbon nanotubes are like tiny hollow wires of carbon just 1 atom thick – similar to graphene but cylindrical. Researchers have been exploring using them as transistors instead of traditional silicon, because carbon nanotubes are easier to transport onto alternate substrates, such as thin sheets of plastic, for low-cost flexible electronics or flat-panel displays. 

Carbon nanotubes themselves are high-quality conductors, but creating single tubes suitable to serve as transistors is very difficult. Arrays of nanotubes are much easier to make, but the current has to hop through junctions from one nanotube to the next, slowing it down. In standard electrical wires, such junctions would be soldered, but how could the gaps be bridged on such a small scale?

VIEW VIDEO | Illinois professor Joseph Lyding narrates an animation demonstrating the process of nano-soldering, which improves nanotube transistors. Metal self-deposits onto hotspot junctions, healing gaps between nanotubes.  | Video courtesy of Joe Lyding

“It occurred to me that these nanotube junctions will get hot when you pass current through them,” said Lyding, “kind of like faulty wiring in a home can create hot spots. In our case, we use these hot spots to trigger a local chemical reaction that deposits metal that nano-solders the junctions.”

Lyding’s group teamed with Eric Pop, an adjunct professor of electrical and computer engineering, and John Rogers, Swanlund professor in materials science and engineering, experts on carbon nanotube synthesis and transfer, as well as chemistry professor Greg Girolami. Girolami is an expert in a process that uses gases to deposit metals on a surface, called chemical vapor deposition (CVD).

The nano-soldering process is simple and self-regulating. A carbon nanotube array is placed in a chamber pumped full of the metal-containing gas molecules. When a current passes through the transistor, the junctions heat because of resistance as electrons flow from one nanotube to the next. The molecules react to the heat, depositing the metal at the hot spots and effectively “soldering” the junctions. Then the resistance drops, as well as the temperature, so the reaction stops. (See video for demonstration of the process.)

The nano-soldering takes only seconds and improves the device performance by an order of magnitude – almost to the level of devices made from single nanotubes, but much easier to manufacture on a large scale.

“It would be easy to insert the CVD process in existing process flows,” Lyding said. “CVD technology is commercially available off-the-shelf. People can fabricate these transistors with the ability to turn them on so that this process can be done. Then when it’s finished they can finish the wiring and connect them into the circuits. Ultimately it would be a low-cost procedure.”

Now, the group is working to refine the process.

“We think we can make it even better,” Lyding said. “This is the prelude, we hope, but it’s actually quite significant.”

The National Science Foundation and the Office of Naval Research supported this work.  Lyding and Rogers also are affiliated with the Beckman Institute for Advanced Science and Technology at the U. of I.

Source: http://news.illinois.edu/news/13/1125nanosoldering_JosephLyding.html