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Carbon Nanotubes for Post silicon future, Military and Aerospace, Security and reducing Carbon Dioxide emissions

Now, for the first time, University of Wisconsin–Madison materials engineers have created carbon nanotube transistors that outperform state-of-the-art silicon transistors. The team’s CNT transistors have successfully achieved currents that are 1.9 times higher than silicon semiconductors. Carbon nanotube transistors should be able to perform five times faster or use five times less energy than silicon transistors, according to extrapolations from single nanotube measurements. “Making carbon nanotube transistors that are better than silicon transistors is a big milestone. This breakthrough in carbon nanotube transistor performance is a critical advance toward exploiting carbon nanotubes in logic, high-speed communications, and other semiconductor electronics technologies.”

Carbon nanotubes (CNTs) are hollow cylindrical tubes formed by rolling a sheet of carbon atoms arranged in a hexagonal ring, as in a sheet of graphite, either in monolayer (single walled nanotube, SWCNT) or multilayer (multi-walled nanotube, MWCNT) form. Their diameter may  range from 0.7 (SWCNT) to   50  naometers (MWCNT) and few tens of micron in length.

CNT  being a hollow tube comprised entirely of carbon, they are also extremely light weight.  They exhibit extraordinary strength and unique electrical properties, at the individual tube level: 200X the strength and 5X the elasticity of steel; 5X the electrical conductivity, 15X the thermal conductivity and 1,000X the current capacity of copper; at almost half the density of aluminum.

The novel properties of CNT make them potentially useful in a wide variety of applications: Due to their high strength and elastic modulus, CNTs are being finding application as reinforcements in composites like polymer matrix composites (PMCs). CNT fibre and thread are being envisaged for applications as reinforcements in composites or woven for bullet proof vests and high strength ropes.

They also provide large specific surface area making it a potential material for sensing applications. It can be made highly selective for a range of gases / vapours by modifying the CNT surface by functionalisation (attaching group of atoms or molecules on the graphitic structure). Their hollow structure also acts as a storage space for hydrogen, drug etc required for certain applications like energy storage and targeted drug delivery.

Depending on the diameter and the way they are rolled (chirality), electron energy band gap changes that makes them either metallic (rolled along its length – arm chair structure) or semiconducting (rolled askew –zig-zag structure) behaviour. They have large electrical conductivity and have good electron emission characteristics. These properties enable them for applications in shielding against electrostatic charges and EMI pulses; energy efficient, high resolution display devices and miniature electronics. They are replacing copper wire and cable because it’s much lighter weight.

Nanotubes to reduce CO2 emissions

Russian President Vladimir Putin said during his speech at the United Nations Climate Change Conference in Paris on November 30, 2015 that new technologies for producing carbon nanotubes will help reduce carbon dioxide emissions in Russia by roughly 160 to 180 million tons by 2030. Nanotubes shall improve the qualities of 70 percent of materials known to mankind; that is, they enhance a material’s durability. This helps increase the lifetime of metals, rubber, and other materials by two or three times. And since all sorts of items will last longer, there will be a significant reduction in energy spent for producing new materials, as well as less energy spent to recycle waste.

“Nanotubes not only provide an indirect positive effect in electronics and industry that leads to the reduction of CO2 emissions,” remarked Professor Albert Nasibulin of the Skolkovo Institute of Science and Technology, and who is also a specialist on nanomaterials. “It will also be possible to directly convert CO2 into carbon nanotubes.”

The new method of creating nanotubes from CO2 was suggested this year by scientists at George Washington University in Washington, D.C. The essence of the technology is that a high-temperature electrochemical reaction helps break down CO2 into carbon nanotubes and oxygen


 Post-Silicon Future with Carbon Nanotube Electronics

Now, for the first time, University of Wisconsin–Madison materials engineers have created carbon nanotube transistors that outperform state-of-the-art silicon transistors. Led by Michael Arnold and Padma Gopalan, UW–Madison professors of materials science and engineering, the team’s carbon nanotube transistors achieved current that’s 1.9 times higher than silicon transistors. The nanotube’s ultra-small dimension makes it possible to rapidly change a current signal traveling across it, which could lead to substantial gains in the bandwidth of wireless communications devices. The new transistors are particularly promising for wireless communications technologies that require a lot of current flowing across a relatively small area.

The most matured technology to take over silicon is the single-walled carbon nanotube after the Moore’s Law,  which stated that the number of transistors on a chip will double approximately every two years expected to come to an end in the beginning of the 2020s. 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.

Unlike its two-dimensional cousin, graphene, the carbon nanotube can be a natural semiconductor, which means it can be turned on and off to make high speed  and energy-efficient switches.  A carbon-nanotube transistor looks much the same as a silicon transistor. The main difference is that the channel is made of carbon nanotubes instead of silicon.

But researchers have struggled to isolate purely carbon nanotubes, which are crucial, because metallic nanotube impurities act like copper wires and disrupt their semiconducting properties — like a short in an electronic device. The UW–Madison team used polymers to selectively sort out the semiconducting nanotubes, achieving a solution of ultra-high-purity semiconducting carbon nanotubes.

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. These results could overcome contact resistance challenges all the way to the 1.8 nanometer node – four technology generations away.


 Flexible Electronics

Recently, Apple has been  granted the patent for a portable device that is “bendable” in half. According to Patently Apple, the technology behind the capability of the phone materials to be flexible is through carbon nanotubes. Carbon nanotubes can form conductive paths for printed circuits or other flexible substrates that are flexible and resistant to cracking such as substrates associated with touch sensors and displays and can form structural components in an electronic device.

The low-cost and large-area manufacturing of flexible and stretchable electronics using printing processes could  have potential applications ranging from personalized wearable electronics to large-area smart wallpapers and from interactive bio-inspired robots to implantable health/medical apparatus.

Carbon nanotubes (CNTs) hold great promise for high-performance flexible electronics due to their extremely high carrier mobility, superior mechanical flexibility, and stability. They could also be used to make wide-variety of applications such as flexible circuits, flexible displays, flexible solar cells, skin-like pressure sensors, and conformable RFID tags.


Solar Cells

Researchers at Northwestern University enhanced the energy efficiency of solar cells based on CNTs to over 3 percent, twice as efficient as its predecessors. Hersam and his team used a mixture of multiple chirality CNTs to maximize the amount of photocurrent produced by absorbing a broader range of solar-spectrum wavelengths. The Northwestern team will be looking to create polychiral CNT solar cells that have multiple layers with each layer being optimized for a particular solar spectrum.

Solar thermophotovoltaics

A team of MIT researchers has for the first time demonstrated a device based on a method that enables solar cells to break through a theoretically predicted ceiling on how much sunlight they can convert into electricity. They have  developed  a solar thermophotovoltaic device  which involves pairing conventional solar cells with added layers of high-tech materials, that could more than double the theoretical limit of efficiency, potentially making it possible to deliver twice as much power from a given area of panels. Those  standard solar cells  can only absorb energy from a fraction of sunlight’s color spectrum, mainly the visual light from violet to red.


But the MIT scientists added an intermediate component made up of carbon nanotubes and nanophotonic crystals that together function sort of like a funnel, collecting energy from the sun and concentrating it into a narrow band of light. One of the key  high-tech materials is  called nanophotonic crystals, which can be made to emit precisely determined wavelengths of light when heated.


The nanotubes capture energy across the entire color spectrum, including in the invisible ultraviolet and infrared wavelengths, converting it all into heat energy. As the adjacent crystals heat up to high temperatures, around 1,000 °C, they reëmit the energy as light, but only in the band that photovoltaic cells can capture and convert.


The researchers suggest that an optimized version of the technology could one day break through the theoretical cap of around 30 percent efficiency on conventional solar cells. In principle at least, solar thermophotovoltaics could achieve levels above 80 percent, though that’s a long way off, according to the scientists. But there’s another critical advantage to this approach. Because the process is ultimately driven by heat, it could continue to operate even when the sun ducks behind clouds, reducing the intermittency that remains one of the critical drawbacks of solar power. If the device were coupled with a thermal storage mechanism that could operate at these high temperatures, it could offer continuous solar power through the day and night.

Defence and Security Applications

They can replace copper wire and cable because it’s much lighter weight. They present an alternative to optical fiber, as they provide similar weight savings while utilizing the same electron based connector systems that engineers are using today. They also have good electron emission characteristics. These properties enable them for applications in shielding against electrostatic charges and EMI pulses.


Aerospace applications

Carbon based composite aircraft often get residual current from lightning strikes. They use metal to protect the aircraft, but residual current is still present. CNT enables better shielding for basically the weight of a coat of paint, and allows you to shield the internals of a carbon fiber based airplane.

Carbon nanotube sheets can act as “Faraday cage” effectively shielding sensitive electronic equipment such as radar and radios from electromagnetic interference (EMI) without adding a lot of weight to aircraft and satellites.

“Carbon nanotubes have at least the tensile strength of carbon fiber, but they are quite flexible. They don’t have the same brittleness, so the strain to failure is different. They’re able to be in a fabric like format where they can be put into the composite themselves, or be the composite themselves,” said Peter Antoinette,” CEO of Nanocomp Technologies

“One can imagine that the surface of a wing would be both structural, it would de-ice itself, it could be the antenna, it could report back to the aircraft and say ‘we are or are not integral or not’, you have enormous numbers of multifunctional applications that carbon nanotube technology can bring to aircraft and spacecraft,” said Per Antoinette.

Metis Design Corp. and the Department of Aeronautics and Astronautics at the Massachusetts Institute of Technology have developed carbon nanotube (CNT) heater based technology for aircraft electrothermal ice protection. Aircraft ice protection systems remove or prevent ice from accumulating on the leading edges of wings, stabilizers, and engine nacelles.

Products built with CNT enable the use of lightweight heaters, have lower thermal inertia and increased damage tolerance compared to traditional electrothermal systems. This technology supports the aerospace industry’s growing need for more durable, lightweight, damage-tolerant and low-power ice protection systems.


Carbon nanotube ‘stitches’ make stronger, lighter composites

The newest jets flying  today are made of advanced composite materials such as carbon fiber reinforced plastic — extremely light, durable materials that reduce the overall weight of the plane by as much as 20 percent compared to aluminum-bodied planes. However, composite materials are also surprisingly vulnerable: While aluminum can withstand relatively large impacts before cracking, the many layers in composites can break apart due to relatively small impacts.

Now MIT aerospace engineers have found that by fastening the layers of composite materials together using carbon nanotubes, the resulting material is substantially stronger and more resistant to damage than other advanced composites. In experiments to test the material’s strength, the team found that, compared with existing composite materials, the stitched composites were 30 percent stronger, withstanding greater forces before breaking apart.

They embedded tiny “forests” of carbon nanotubes within a glue-like polymer matrix, then pressed the matrix between layers of carbon fiber composites. The nanotubes, resembling tiny, vertically-aligned stitches, worked themselves within the crevices of each composite layer, serving as a scaffold to hold the layers together.

More work needs to be done, but we are really positive that this will lead to stronger, lighter planes,” says Guzman, who is now a researcher at the IMDEA Materials Institute, in Spain. “That means a lot of fuel saved, which is great for the environment and for our pockets.”


 Rice University scientists replace metal with carbon nanotubes for shielding

The Rice lab of Professor Matteo Pasquali has developed a coating that could replace the tin-coated copper braid that transmits the signal and shields the cable from electromagnetic interference. The metal braid is the heaviest component in modern coaxial data cables. Replacing the outer conductor with Rice’s flexible, high-performance coating would benefit airplanes and spacecraft, in which the weight and strength of data-carrying cables are significant factors in performance.

Rice research scientist Francesca Mirri, lead author of the paper, made three versions of the new cable by varying the carbon-nanotube thickness of the coating. She found that the thickest, about 90 microns – approximately the width of the average human hair – met military-grade standards for shielding and was also the most robust; it handled 10,000 bending cycles with no detrimental effect on the cable performance.

Replacing the braided metal conductor with the nanotube coating eliminated 97 percent of the component’s mass, Mirri said. The Air Force seems very interested in this technology, and we are currently working on a Small Business Innovation Research project with the Air Force Research Laboratory to see how far we can take it.”


Carbon nanotubes shown to protect metals against radiation damage

One of the main reasons for limiting the operating lifetimes of nuclear reactors is that metals exposed to the strong radiation environment near the reactor core become porous and brittle, which can lead to cracking and failure. Now, a team of researchers at MIT and elsewhere has found that for reactors built using aluminium, adding a tiny quantity of carbon nanotubes to the metal can dramatically slow this breakdown process.

Aluminum is currently used in not only research reactor components but also nuclear batteries and spacecraft, and it has been proposed as material for storage containers for nuclear waste. So, improving its operating lifetime could have significant benefits, says Ju Li, who is the Battelle Energy Alliance Professor of Nuclear Science and Engineering and a professor of materials science and engineering.

The researchers showed that by adding only tiny quantities of carbon nanotubes (CNTs) — about 1 percent by weight added to the meta, the 1-D structure was able to survive up to 70 DPA of radiation damage. (DPA is a unit that refers to how many times, on average, every atom in the crystal lattice is knocked out of its site by radiation.)

The metal with carbon nanotubes uniformly dispersed inside “is designed to mitigate radiation damage” for long periods without degrading, says Kang Pyo So. The nanotubes can form a percolating, one-dimensional transport network, to provide pathways for the helium to leak back out instead of being trapped within the metal, where it could continue to do damage. Helium from radiation transmutation takes up residence inside metals and causes the material to become riddled with tiny bubbles along grain boundaries and progressively more brittle, the researchers explain. The team says the method may also be usable in the higher-temperature alloys used in commercial reactors.

Explosive and Chemical Sensors

“Carbon nanotube (CNT) sensors are effective because we can leverage multiple properties (e.g., electrical, thermal, optical, chemical and structural) to determine what or how they will sense their environment. Additionally, CNTs could allow us to create flexible and even transparent sensors, as well as sensors with increasing sensitivity and specificity at a lower cost than traditional sensors, potentially simplifying actual designs and reducing manufacturing costs,” says Travis Earles from Lockheed Martin.

As an example, CNT fabrics are at the core of Lockheed Martin’s chemical sensor platform technology that can be designed to detect a wide range of gases and volatile organic compounds.

MIT Develops Wireless, Wearable Sensor for Toxic Gas

Researchers from the Massachusetts Institute of Technology (MIT) have created low-cost sensors that will give smartphones and other wireless devices the ability to detect the presence of even the smallest amounts of toxic gas. The sensors are made out of chemically altered carbon nanotubes, which break away from the insulating material wrapped around them upon the detection of toxic gas. This activates a near-field communication (NFC) alert on the device connected to the sensor.

Researchers will be using the sensors, which are able to detect toxic gas as little as 10 parts per million in the air in as fast as five seconds, to create inexpensive and lightweight radio frequency identification, or RFID, badges that can be utilized for personal security and safety from toxic gases.

These RFID badges will have military applications, as they will be able to replace all the extra equipment that soldiers have to carry around to defend themselves against toxic gas, including choking and nerve agents


Handheld sensors for explosives, deadly gases and illegal drugs

University of Utah engineers have developed a new type of carbon nanotube material for handheld sensors that will be quicker and better at sniffing out explosives, deadly gases and illegal drugs.

Zang and his team found a way to break up bundles of the carbon nanotubes with a polymer and then deposit a microscopic amount on electrodes in a prototype handheld scanner that can detect toxic gases such as sarin or chlorine, or explosives such as TNT.

When the sensor detects molecules from an explosive, deadly gas or drugs such as methamphetamine, they alter the electrical current through the nanotube materials, signaling the presence of any of those substances, Zang says.

“You can apply voltage between the electrodes and monitor the current through the nanotube,” says Zang, a professor with USTAR, the Utah Science Technology and Research economic development initiative. “If you have explosives or toxic chemicals caught by the nanotube, you will see an increase or decrease in the current.”

By modifying the surface of the nanotubes with a polymer, the material can be tuned to detect any of more than a dozen explosives, including homemade bombs, and about two-dozen different toxic gases, says Zang. The technology also can be applied to existing detectors or airport scanners used to sense explosives or chemical threats.


Future Soldiers Wearables

CNT also has excellent energy absorption capacity, therefore, have great potential applications in making antiballistic materials. A team of University of Maryland students students modified ballistic grade Kevlar 29 by embedding a network of crosslinked, functionalized carbon nanotubes (CNTs), thereby doubling the ballistic resistance of the original product.

This can lead to decreasing the number of layers required for a bulletproof vest from 30 to 15, thereby creating a lighter piece of body armor that gives the user more maneuverability without sacrificing safety.

Lawrence Livermore National Laboratory scientists and collaborators are developing a new military uniform material that repels chemical and biological agents using a novel carbon nanotube fabric. Sweat and air would be able to easily move through the nanotubes. However, the diameter of the nanotubes is smaller than the diameter of bacteria and viruses. That means they would not be able to pass through the tubes and reach the person wearing the suit.

For handling chemical warfare agents the CNTS are surface modified with a chemical warfare agent-responsive functional layer. Under direct chemical warfare agent attack, the material is designed to undergo a rapid transition from a breathable state to a protected state by closing the CNT pore entrance or by shedding the contaminated surface layer.


Fighting metal corrosion

Military equipment like Tanks, gates, doors, wickets, buildings, locks and dams, towers are made from steel and prone to corrosion. Carbon nanotubes assemble into rope-like structures that create super durable protective coatings and are electrically active to quickly and effectively fill voids created by scratches and other abrasive actions that mar metal surfaces.


IBM overcomes critical challenge scaling of contacts

In any transistor, two things scale: the channel and its two contacts. Carbon nanotubes provide high-performance channels below 10 nanometers, but as with silicon, the increase in contact resistance with decreasing size becomes a major performance roadblock. That’s a dilemma, the smaller the contacts get, the worse this problem becomes.

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. These results could overcome contact resistance challenges all the way to the 1.8 nanometer node – four technology generations away.

The researchers addressed the issue by changing the interface between a nanotube and the two metal contacts. Instead of depositing them on top of the tube, as in the conventional scheme for building nanotube transistors, they placed them at the ends of the tube and made them react with the carbon to form a different chemical compound.

The success of the new method means that the ability to deliver current to carbon nanotube transistors is now independent of the length of the metal contacts, says Wilfried Haensch, who leads IBM Research’s nanotube project. It’s now clear they can make the transistors as small as necessary, he says, and this is a big step toward the company’s goal of having carbon nanotube technology ready by 2020
Unlike its two-dimensional cousin, graphene, the carbon nanotube can be a natural semiconductor, and it’s long been eyed as a potential material for speedy and energy-efficient switches.

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.

Considerable challenges remain, Haensch acknowledges. He says the recent work overcomes only one of the three major hurdles standing in the way of commercially viable carbon nanotube transistors. Another is that nanotubes exist in two forms, metallic and semiconducting, but only the semiconducting ones are useful for transistors. The second remaining challenge is developing a reliable, nonlithographic way to place billions of nanotubes exactly where they are needed on a chip.


Chinese Researchers make Simple Black Film Made From Carbon Nanotubes Is Stronger Than Kevlar

Carbon nanotubes are super strong and stretchy at the microscopic level, But when you make a bulk material out of them, their properties are watered down because they become randomly arranged — and they need to lie in parallel to make the most of their strength. Now, a team of researchers from the East China University of Science & Technology have developed a way to create films where nanotubes are neatly aligned.

They use a technique which Chemical and Engineering News likens to glass blowing. Essentially the team uses a stream of nitrogen gas to push a layer of carbon nanotubes along the surface of tube in a furnace held at around 2,100°F. As it exits, the tubular nanotube material is wound around drum, flattening and cooling into two-layer film. The team can then compress the film by applying pressure using a system of rollers.

The film developed by them has an average tensile strength of 9.6 gigapascals. For context, kevlar fibres have a strength of about 3.7 gigapascals and carbon fibre around 7 gigapascals. It’s also relatively stretchy: it can extend by 8 per cent, which is rather more than the 2 per cent that carbon fibre can image. The properties can be exploited in multiple directions by adding layers on top of each other in different orientations.

It’s thought that the new film could be used to create strong, perhaps even structural, coatings for vehicles or aerospace parts, or new kinds of armour for military applications. Or very, very good trash bags.


Researchers from University of Wisconsin-Madison isolate ultra-high purity CNTs

Researchers have also struggled to isolate purely semiconducting carbon nanotubes, which are crucial, because metallic nanotube impurities act like copper wires and “short” the device.

Researchers from University of Wisconsin-Madison led by Associate Professor Michael Arnold and Professor Padma Gopalan, has demonstrated transistors with on-off ratios 1000 times better, and conductance 100 times better than previous cutting-edge carbon nanotube transistors. To create their transistor, the research team used polymers to selectively sort out the semiconducting nanotubes, achieving a solution of ultra-high-purity semiconducting carbon nanotubes.

Another challenge that has limited the development of high-performance carbon nanotube transistors is to control the placement and alignment of nanotubes.

UW-Madison researchers also pioneered a new technique to align the nanotubes, called floating evaporative self-assembly, or FESA, by exploiting a self-assembly phenomenon triggered by rapidly evaporating a carbon nanotube solution.

Another challenge is lack of control of the threshold voltage of CNT transistors that result in poor reliability and power-efficiency compared to rigid silicon chips. Zhenan Zhenan Bao and Yi Cui of Stanford University have developed a CNT circuit by doping it a blend of P-type and N-type semiconductors that can operate reliably despite power fluctuations and maintain low power consumption. Their technique involves depositing the dopant DMBI on the CNT circuit with an inkjet printer.

Carbon nanotubes have high thermal conductivity that could carry the excess heat away from the Computer chips being used in smartphones and supercomputers that are generating more and more heat as they are getting faster and faster.

Frank Ogletree, a physicist with the Lawrence Berkeley National Laboratory’s Materials Sciences Division have developed a technique that uses organic molecules as a bridge between the carbon nanotubes and metal—a method that greatly reduces the interface resistance that would otherwise prevent heat from flowing more efficiently between the materials. The new study’s success rests upon the organic molecules, including aminopropyl-trialkoxy-silane (APS) and cysteamine, create strong covalent bonds between the carbon nanotubes and the metal used in microchips.


Russia discovers cheaper Production technique

One of the challenges is mass-producing a product with consistent properties, each individual carbon nanotube’s having identical conductive properties. The greatest challenge is being able to drive scale to volume and decrease cost.

Today, multi-walled nanotubes are produced by CNano (U.S.), Arkema (France), Showa Denko (Japan), and Nanocyl (Belgium). But production of single-walled carbon nanotubes, which are considered of finer quality and are more expensive, until recently were carried out only in laboratories because their cost can exceed $150,000 per kilogram.

Mikhail Predtechensky, an academician from Siberia, was the first scientist to discover technology that can reduce the price of mass-produced single-walled nanotubes by 50 to 100-times, and to $3,000 per kilogram. Predtechensky co-founded OCSiAl, and in 2013 this company launched the world’s largest industrial system for synthesizing single-walled Graphetron 1.0 nanotubes.

In the near future the company plans to establish in Novosibirsk a center for prototyping technologies based on single-layered carbon nanotubes to create rubber, composites, lithium-ion batteries, and many other materials.


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