Researchers gauge quantum properties of nanotubes, essential for next-gen electronics

How do you get to know a material that you cannot see?

That is a question that researchers studying nanomaterials--objects with features at the sub-micrometer scales such as quantum dots, nanoparticles and nanotubes--are seeking to answer.

Though recent discoveries--including a super-resolution microscopy which won the Nobel Prize in 2014--have greatly enhanced scientists' capacity to use light to learn about these small-scale objects, the wavelength of the inspecting radiation is always much larger than the scale of the nano-objects being studied. For example, nanotubes and nanowires-the building blocks of next-generation electronic devices-have diameters that are hundreds of times smaller than the light could resolve. Researchers must find ways to circumvent this physical limitation in order to achieve sub-wavelength spatial resolution and explore the nature of these materials for future computers.

Today, a group of scientists--John A. Rogers, Eric Seabron, Scott MacLaren and Xu Xie from the University of Illinois at Urbana-Champaign; Slava V. Rotkin from Lehigh University; and,William L. Wilson from Harvard University--are reporting on the discovery of an important method for measuring the properties of nanotube materials using a microwave probe. Theirfindings have been published in ACS Nano in an article called: "Scanning Probe Microwave Reflectivity of Aligned Single-Walled Carbon Nanotubes: Imaging of Electronic Structure and Quantum Behavior at the Nanoscale."

The researchers studied single-walled carbon nanotubes. These are 1-dimensional, wire-like nanomaterials that have electronic properties that make them excellent candidates for next generation electronics technologies. In fact, the first prototype of a nanotube computer has already been built by researchers at Stanford University. The IBM T.J. Watson Research Center is currently developing nanotube transistors for commercial use.

For this study, scientists grew a series of parallel nanotube lines, similar to the way nanotubes will be used in computer chips. Each nanotube was about 1 nanometer wide--ten times smaller than expected for use in the next generation of electronics. To explore the material's properties, they then used microwave impedance microscopy (MIM) to image individual nanotubes.

"Although microwave near-field imaging offers an extremely versatile 'nondestructive' tool for characterizing materials, it is not an immediately obvious choice," explained Rotkin, a professor with a dual appointment in Lehigh's Department of Physics and Department of Materials Science and Engineering. "Indeed, the wavelength of the radiation used in the experiment was even longer than what is typically used in optical microscopy-about 12 inches, which is approximately 100,000,000 times larger than the nanotubes we measured."

He added: "The nanotube, in this case, is like a very bright needle in a very large haystack."

The imaging method they developed shows exactly where the nanotubes are on the silicon chip. More importantly, the information delivered by the microwave signal from individual nanotubes revealed which nanotubes were and were not able to conduct electric current. Unexpectedly, they were finally able to measure the nanotube quantum capacitance-a very unique property of an object from the nano-world-under these experimental conditions.

"We began our collaboration seeking to understand the images taken by the microwave microscopy and ended by unveiling the nanotube's quantum behavior, which can now be measured with atomistic resolution," said Rotkin.

As an inspection tool or metrology technique, this approach could have a tremendous impact on future technologies, allowing optimization of processing strategies including scalable enriched nanotube growth, post-growth purification, and fabrication of better device contacts. One can now distinguish, in one simple step, between semiconductor nanotubes that are useful for electronics and metallic ones that can cause a computer to failure. Moreover this set of imaging modes sheds light on the quantum properties of these 1D structures.

Lehigh University

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

Newly Discovered ‘Design Rule’ Brings Nature-Inspired Nanostructures One Step Closer

Snakes on a plane: This atomic-resolution simulation of a two-dimensional peptoid nanosheet reveals a snake-like structure never seen before. The nanosheet’s layers include a water-repelling core (yellow), peptoid backbones (white), and charged sidechains (magenta and cyan). The right corner of the top layer of the nanosheet has been “removed” to show how the backbone’s alternating rotational states give the backbones a snake-like appearance (red and blue ribbons). Surrounding water molecules are red and white. (Credit: Ranjan Mannige, Berkeley Lab)

Computer sims and microscopy research at Berkeley Lab yield first atomic-resolution structure of a peptoid nanosheet

Scientists aspire to build nanostructures that mimic the complexity and function of nature’s proteins, but are made of durable and synthetic materials. These microscopic widgets could be customized into incredibly sensitive chemical detectors or long-lasting catalysts, to name a few possible applications.

But as with any craft that requires extreme precision, researchers must first learn how to finesse the materials they’ll use to build these structures. A discovery by scientists from the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab), and reported Oct. 7 in the advance online publication of the journal Nature, is a big step in this direction.

The scientists discovered a design rule that enables a recently created material to exist. The material is a peptoid nanosheet. It’s a flat structure only two molecules thick, and it’s composed of peptoids, which are synthetic polymers closely related to protein-forming peptides.

The design rule controls the way in which polymers adjoin to form the backbones that run the length of nanosheets. Surprisingly, these molecules link together in a counter-rotating pattern not seen in nature. This pattern allows the backbones to remain linear and untwisted, a trait that makes peptoid nanosheets larger and flatter than any biological structure.

The Berkeley Lab scientists say this never-before-seen design rule could be used to piece together complex nanosheet structures and other peptoid assemblies such as nanotubes and crystalline solids.

What’s more, they discovered it by combining computer simulations with x-ray scattering and imaging methods to determine, for the first time, the atomic-resolution structure of peptoid nanosheets.

“This research suggests new ways to design biomimetic structures,” says Steve Whitelam, a co-corresponding author of the Nature paper. “We can begin thinking about using design principles other than those nature offers.”

Whitelam is a staff scientist in the Theory Facility at the Molecular Foundry, a DOE Office of Science user facility located at Berkeley Lab. He led the research with co-corresponding author Ranjan Mannige, a postdoctoral researcher at the Molecular Foundry; and Ron Zuckermann, who directs the Molecular Foundry’s Biological Nanostructures Facility. They used the high-performance computing resources of the National Energy Research Scientific Computing Center (NERSC), another DOE Office of Science user facility located at Berkeley Lab.

The Molecular Foundry scientists who helped discover a new nano design rule. From left, Ellen Robertson, Alessia Battigelli, Ron Zuckermann, Caroline Proulx, Stephen Whitelam, and Ranjan Mannige. (Credit: Roy Kaltschmidt, Berkeley Lab)

Peptoid nanosheets were discovered by Zuckermann’s group five years ago. They found that under the right conditions, peptoids self assemble into two-dimensional assemblies that can grow hundreds of microns across. This “molecular paper” has become a hot prospect as a protein-mimicking platform for molecular design.

To learn more about this potential building material, the scientists set out to learn its atom-resolution structure. This involved feedback between experiment and theory. Microscopy and scattering data gathered at the Molecular Foundry and the Advanced Light Source, also a DOE Office of Science user facility located at Berkeley Lab, were compared with molecular dynamics simulations conducted at NERSC.

The research revealed several new things about peptoid nanosheets. Their molecular makeup varies throughout their structure, they can be formed only from peptoids of a certain minimum length, they contain water pockets, and they are potentially porous when it comes to water and ions.

These insights are intriguing on their own, but when the scientists examined the structure of the nanosheets’ backbone, they were surprised to see a design rule not found in the field of protein structural biology.

Here’s the difference: In nature, proteins are composed of beta sheets and alpha helices. These fundamental building blocks are themselves composed of backbones, and the polymers that make up these backbones are all joined together using the same rule. Each adjacent polymer rotates incrementally in the same direction, so that a twist runs along the backbone.

This rule doesn’t apply to peptoid nanosheets. Along their backbones, adjacent monomer units rotate in opposite directions. These counter-rotations cancel each other out, resulting in a linear and untwisted backbone. This enables backbones to be tiled in two dimensions and extended into large sheets that are flatter than anything nature can produce.

“It was a big surprise to find the design rule that makes peptoid nanosheets possible has eluded the field of biology until now,” says Mannige. “This rule could perhaps be used to build many more unrealized structures.”

Adds Zuckermann, “We also expect there are other design principles waiting to be discovered, which could lead to even more biomimetic nanostructures.”

A simulation of a peptoid nanosheet, shown first from a top-down view with the peptoid backbones colored to highlight their snake-like structure. The view then rotates to the side, and finally transitions to an all-atom representation. (Credit: Ron Zuckermann and Ranjan Mannige, Berkeley Lab)

Other Molecular Foundry scientists who contributed to this research are Thomas Haxton, Caroline Proulx, Ellen Robertson, and Alessia Battigelli.

This research was conducted at the Molecular Foundry, a DOE Office of Science user facility located at Berkeley Lab. The work was supported by the Defense Threat Reduction Agency, with additional funding provided by the Natural Sciences and Engineering Research Council of Canada. Part of this research was carried out through a User Project at the Molecular Foundry led by New York University’s Glenn Butterfoss.

Berkeley Lab

Nanotechnology World Association

Physicists conduct most precise measurement yet of interaction between atoms and carbon surfaces

An illustration of atoms sticking to a carbon nanotube, 
affecting the electrons in its surface.David Cobden and students

Physicists at the University of Washington have conducted the most precise and controlled measurements yet of the interaction between the atoms and molecules that comprise air and the type of carbon surface used in battery electrodes and air filters — key information for improving those technologies.

A team led by David Cobden, UW professor of physics, used a carbon nanotube — a seamless, hollow graphite structure a million times thinner than a drinking straw — acting as a transistor to study what happens when gas atoms come into contact with the nanotube’s surface. Their findings were published in May in the journal Nature Physics.

Cobden said he and co-authors found that when an atom or molecule sticks to the nanotube a tiny fraction of the charge of one electron is transferred to its surface, resulting in a measurable change in electrical resistance.

“This aspect of atoms interacting with surfaces has never been detected unambiguously before,” Cobden said. “When many atoms are stuck to the minuscule tube at the same time, the measurements reveal their collective dances, including big fluctuations that occur on warming analogous to the boiling of water.”

Lithium batteries involve lithium atoms sticking and transferring charges to carbon electrodes, and in activated charcoal filters, molecules stick to the carbon surface to be removed, Cobden explained.

“Various forms of carbon, including nanotubes, are considered for hydrogen or other fuel storage because they have a huge internal surface area for the fuel molecules to stick to. However, these technological situations are extremely complex and difficult to do precise, clear-cut measurements on.”

This work, he said, resulted in the most precise and controlled measurements of these interactions ever made, “and will allow scientists to learn new things about the interplay of atoms and molecules with a carbon surface,” important for improving technologies including batteries, electrodes and air filters.

Co-authors were Oscar Vilches, professor emeritus of physics, doctoral students Hao-Chun Lee and research associate Boris Dzyubenko, all of the UW. The research was funded by the National Science Foundation.

Source: http://www.washington.edu/news/2015/05/28/physicists-conduct-most-precise-measurement-yet-of-interaction-between-atoms-and-carbon-surfaces/

Hitchhiking nanotubes show how cells stir themselves

Rice, Göttingen, VU researchers track single-molecule proteins in living cells 

Chemical engineers from Rice University and biophysicists from Georg-August Universität Göttingen in Germany and the VU University Amsterdam in the Netherlands have successfully tracked single molecules inside living cells with carbon nanotubes.

Through this new method, the researchers found that cells stir their interiors using the same motor proteins that serve in muscle contraction.

The study, which sheds new light on biological transport mechanisms in cells, appears this week in Science.

The team attached carbon nanotubes to transport molecules known as kinesin motors to visualize and track them as they moved through the cytoplasm of living cells.

“I am amazed how versatile carbon nanotubes are,” said co-author Matteo Pasquali, a Rice professor of chemical and biomolecular engineering and of chemistry. “We use them for a wide range of applications, from engineering conducting fibers to imaging in cells.”

Carbon nanotubes are hollow cylinders of pure carbon with one-atom-thick walls. They naturally fluoresce with near-infrared wavelengths when exposed to visible light, a property discovered at Rice by Professor Rick Smalley a decade ago and then leveraged by Rice Professor Bruce Weisman to image carbon nanotubes. When attached to a molecule, the hitchhiking nanotubes serve as tiny beacons that can be precisely tracked over long periods of time to investigate small, random motions inside cells.

“Any probe that can hitch the length and breadth of the cell, rough it, slum it, struggle against terrible odds, win through and still know where its protein is, is clearly a probe to be reckoned with,” said lead author Nikta Fakhri, paraphrasing “The Hitchhiker’s Guide to the Galaxy.” Fakhri, who earned her Rice doctorate in Pasquali’s lab in 2011, is currently a Human Frontier Science Program Fellow at Göttingen.

“In fact, the exceptional stability of these probes made it possible to observe intracellular motions from times as short as milliseconds to as long as hours,” she said.

For long-distance transport, such as along the long axons of nerve cells, cells usually employ motor proteins tied to lipid vesicles, the cell’s “cargo containers.” This process involves considerable logistics: Cargo needs to be packed, attached to the motors and sent off in the right direction.

“This research has helped uncover an additional, much simpler mechanism for transport within the cell interior,” said principal investigator Christoph Schmidt, a professor of physics at Göttingen. “Cells vigorously stir themselves, much in the way a chemist would accelerate a reaction by shaking a test tube. This will help them to move objects around in the highly crowded cellular environment.”

The researchers showed the same type of motor protein used for muscle contraction is responsible for stirring. They reached this conclusion after exposing the cells to drugs that suppressed these specific motor proteins. The tests showed that the stirring was suppressed as well.

The mechanical cytoskeleton of cells consists of networks of protein filaments, like actin. Within the cell, the motor protein myosin forms bundles that actively contract the actin network for short periods. The researchers found random pinching of the elastic actin network by many myosin bundles resulted in the global internal stirring of the cell. Both actin and myosin play a similar role in muscle contraction. 

The highly accurate measurements of internal fluctuations in the cells were explained in a theoretical model developed by VU co-author Fred MacKintosh, who used the elastic properties of the cytoskeleton and the force-generation characteristics of the motors.

“The new discovery not only promotes our understanding of cell dynamics, but also points to interesting possibilities in designing ‘active’ technical materials,” said Fakhri, who will soon join the Massachusetts Institute of Technology faculty as an assistant professor of physics. “Imagine a microscopic biomedical device that mixes tiny samples of blood with reagents to detect disease or smart filters that separate squishy from rigid materials.”

Co-authors of the study include graduate student Alok Wessel, technical assistant Charlotte Willms and research scientist Dieter Klopfenstein, all of the University of Göttingen.

The German Research Foundation, the Dutch Foundation for Fundamental Research on Matter, the Netherlands Organization for Scientific Research, the Welch Foundation, the National Science Foundation and the Human Frontier Science Program supported the research.

-30-

Read the abstract at   http://www.sciencemag.org/lookup/doi/10.1126/science.1250170

View a short movie of nanotube-tagged proteins moving via stirring inside cells:

http://youtu.be/cunx-xdwqqk

A thin carbon nanotube is attached to a molecular motor (yellow) that moves along microtubule filaments (green) that form the transport network of cells. This transport occurs in the highly crowded environment of the cytoplasm that includes a network of actin filaments (red). The fluorescent nanotube serves as a beacon for both the transport along the microtubule, as well as the buffeting of the microtubule by the highly agitated surrounding cytoplasm. (Credit: M. Leunissen, Dutch Data Design)

- See more at: http://news.rice.edu/2014/05/29/hitchhiking-nanotubes-show-how-cells-stir-themselves/#sthash.cQhqzdGm.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/