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Research Partnership with University of Warwick

Posted By Graphene Council, Wednesday, July 29, 2020
First Graphene today announced a research collaboration with world-leading experts at the University of Warwick to enhance the understanding of graphene in a range of polymer systems such as plastic and rubber.

The PhD Project will be conducted under the Warwick Collaborative Post Graduate Research Scholarship Scheme, in conjunction with the Warwick Manufacturing Group (WMG) that has established a world- recognised model for successful collaboration between academia and the private and public sectors. WMG has strong links with world-leading industrial partners such as Jaguar Land Rover, who announced in late 2019 they were relocating their advanced research group to the facility.

First Graphene will collaborate with the University’s Professor Tony McNally, who have established capability in incorporating nanomaterials, including carbon nanotubes and graphene into bulk polymer systems.

Using graphene as an additive in thermoplastic materials gives an improvement in properties such as mechanical, electrical, thermal, fire retardancy, chemical resistance and gas barrier. This provides the potential to move lower cost polymers such as polyolefins and polyamides up the “plastics performance pyramid,” creating new value for plastic manufacturers. Potential uses for these enhanced engineering plastics are light-weighting in automotive and aerospace as well as the delivery of a new generation of high-performing fire-retardant plastics in mass transport, construction, mining and oil & gas.

The project will combine WMG’s capability and First Graphene’s operational experience of graphene production and processing to investigate and optimise the impact of surface chemistry, the use of additives and optimising the mixing process technology to deliver further improvements in the properties of graphene-enhanced polymers. Existing First Graphene customers will benefit from this research, which will also enable a new range of PureGRAPH® enhanced polymer and rubber systems.

First Graphene Managing Director Craig McGuckin says this new collaboration is significant and necessary. “It reaffirms our position as the leading graphene producer and innovator. We recognise Warwick University and Warwick Manufacturing Group’s world leading expertise and our need to keep investing in collaborative projects to keep delivering improvements,” Mr McGuckin said.

“This research, which will comprise a PhD project over a three-and-a-half year period, will unlock graphene’s potential to improve strength, durability and the lifespan of a range of polymer systems.” Professor McNally, who is Professor in Nanocomposites and Director of the International Institute for Nanocomposites Manufacturing (IINM) at WMG, says he is delighted to be collaborating with First Graphene on this fundamental research.

“I look forward to working with their research team on this project which will drive real benefits in the industrial use of thermoplastic materials in a range of real-world applications,” Professor McNally said.

Mr McGuckin says using graphene as an additive in thermoplastic materials improves mechanical, electrical, and thermal properties particularly in the areas of fire retardancy, chemical resistance and gas barriers. “This provides the potential to move lower cost polymers such as polyolefins and polyamides up the so-called `plastics performance pyramid’ creating new value for plastic manufacturers.”

The Warwick Manufacturing Group (WMG) has a world-recognised model for successful collaboration between academia and the private and public sectors.

Tags:  carbon nanotubes  Craig McGuckin  First Graphene  Graphene  nanomaterials  polymers  Tony McNally  University of Warwick 

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Direct Solution Processing of Carbon Nanotubes in Solvent Cocktails

Posted By Graphene Council, Thursday, July 2, 2020
Northwestern Engineering researchers have found new ways to directly solution process carbon nanotubes using just a cocktail of common solvents.

Carbon nanotubes, cylinders made of one or more layers of graphene, are very conductive and strong and can be used as a filler to make polymer plastic materials stronger. Processing them, however, is challenging, because they often come as powders of heavily aggregated nanotubes.

In earlier work, Northwestern Engineering’s Jiaxing Huang found that cresols – an inexpensive, mass-produced simple solvent once used in household cleaners – are very effective for dispersing nanotubes. What wasn’t known was why.

Using spectroscopic studies, Huang’s team has found the answer.

“Cresol forms a charge-transfer complex with carbon nanotubes,” said Huang, professor of materials science and engineering in Northwestern’s McCormick School of Engineering. “This interaction is stabilized in low-dielectric-constant solvents to keep the nanotubes dispersed, but it is destabilized in high-dielectric-constant solvents.

“This means that we now can formulate solvent cocktails that disperse carbon nanotubes, and others that can quickly wash cresols off the nanotubes. And the beauty is that no exotic new solvents are needed – these are all common industrial solvents,” he added.

The study found that volatile compatible solvents, such as n-hexane and chloroform, can be used as the main solvent to formulate fast-evaporating nanotube inks for high-throughput techniques, such as airbrushing, to quickly create continuous and conformal carbon nanotube coatings. Next, incompatible solvents, such as acetone, can help remove residual high-boiling-point cresols without the usual need for heating.

“We now know mechanistically which cresol-‘flavored’ solvent cocktails are good to disperse nanotubes, and we know why,” Huang said. “And we also know what solvents can very easily remove residue cresols. It is a whole-circle technical solution for people thinking about solution processing of carbon nanotubes."

The study “Cresol-Carbon Nanotube Charge-Transfer Complex: Stability in Common Solvents and Implications for Solution Processing” was published July 1 in Matter. PhD student Kevin Chiou is co-author.

There have been numerous recipes to process carbon nanotubes. One previous method dispersed the carbon nanotubes through a chemical reaction to treat the surface with a layer of molecules.

The idea was to chemically graft a functional group (with a solvent-liking chemical structure) on the surface of nanotubes to make them more dispersible in solvents. That made the nanotubes more dispersible, but the process broke down the surface — important to the tube’s integrity.

Another approach required adding a molecule and dispersing agent. That method would theoretically wrap around the nanotube but not graft onto it. The problem with that, however, was that the process contaminates the nanotube material, and after processing, the agents still need removal.

This research builds on earlier work by Huang which discovered a way to disperse carbon nanotubes at unprecedentedly high concentrations without the need for additives or harsh chemical reactions to modify the nanotubes. In that work, Huang found that as the nanotubes’ concentrations increase, the material transitions from a dilute dispersion to a thick paste, then become a free-standing gel, and finally change to a kneadable dough that can be shaped and molded.

Tags:  Carbon Nanotubes  Graphene  Jiaxing Huang  Northwestern Engineering 

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New production method for carbon nanotubes gets green light

Posted By Graphene Council, Thursday, January 9, 2020
A new method of producing carbon nanotubes - tiny molecules with incredible physical properties used in touchscreen displays, 5G networks and flexible electronics - has been given the green light by researchers, meaning work in this crucial field can continue.

Single-walled carbon nanotubes are among the most attractive nanomaterials for a wide range of applications ranging from nanoelectronics to medical sensors. They can be imagined as the result of rolling a single graphene sheet into a tube.

Their properties vary widely with their diameter, what chemists call chirality - how symmetrical they are - and by how the graphene sheet is rolled.

The problem faced by researchers is that it is no longer possible to make high quality research samples of single-walled carbon nanotubes using the standard method. This was associated with the Carbon Center at Rice University, which used the high-pressure carbon monoxide (HiPco) gas-phase process developed by Nobel Laureate, the late Rick Smalley.

The demise of the Carbon Center in the mid-2010s, the divesting of the remaining HiPco samples to a third-party entity with no definite plans of further production, and the expiration of the core patents for the HiPco process, meant that this existing source of nanotubes was no longer an option.

Now however, a collaboration between scientists at Swansea University (Wales, UK), Rice University (USA), Lamar University (USA), and NoPo Nanotechnologies (India) has demonstrated that the latter's process and material design is a suitable replacement for the the Rice method.

Analysis of the Rice "standard" and new commercial-scale samples show that back-to-back comparisons are possible between prior research and future applications, with the newer HiPco nanotubes from NoPo Nanotechnologies comparing very favourably to the older ones from Rice.

These findings will go some way to reassure researchers who might have been concerned that their work could not continue as high-quality nanotubes would no longer be readily available.

Professor Andrew Barron of Swansea University's Energy Safety Research Institute, the project lead, said:
"Variability in carbon nanotube sources is known to be a significant issue when trying to compare research results from various groups. What is worse is that being able to correlate high quality literature results with scaled processes is still difficult".

Erstwhile members of the Smalley group at Rice University, which developed the original HiPco process, helped start NoPo Nanotechnologies with the aim of updating the HiPco process, and produce what they call NoPo HiPCO® SWCNTs.

Lead author Dr. Varun Shenoy Gangoli stated:
"It is in the interest of all researchers to understand how the presently available product compares to historically available Rice materials that have been the subject of a great range of academic studies, and also to those searching for a commercial replacement to continue research and development in this field."

Tags:  Andrew Barron  carbon nanotubes  Graphene  Medical  nanoelectronics  Rice University  Sensors  Swansea University  Varun Shenoy Gangoli 

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Carbon Nanotubes & Quantum Dots: Army Thinks VERY Small

Posted By Graphene Council, Thursday, January 9, 2020
While the rest of the Army works on new hypersonic missiles, robotic mini-tanks, and ultra-high-speed helicopters, the Army Research Office is diving deep into the submicroscopic world of nanotechnology and quantum mechanics.

The military is intensely interested in the potential to improve the costs and capabilities of its electronics, which in modern warfare are as vital to survival as guns and armor. But as with the Internet, radar, and other originally military technologies, there are civilian applications as well.

Carbon Nanotubes

One Army Research Office project is looking to replace traditional silicon-based semiconductors with more efficient carbon nanotubes, program manager Joe Qiu told me. The new technology is particularly useful at the very high frequencies (30-plus gigahertz) and very short wavelengths (millimeter wave) that the telecommunications industry wants to use for 5G networks – including on military bases – and for whatever replaces 5G.

“The initial deployment of 5G, they will be lower than six gigahertz, but there are plans…to improve frequencies to 28 GHz and higher,” Qiu said. “It’s not just 5G — it’s beyond 5G.”

How soon could the private sector reap the benefits of ARO-funded research?

“Commercial use of carbon nanotube-based integrated circuits? Maybe five years,” he said, then added with a laugh: “That’s an estimate. Don’t hold me to that!”

This kind of research can take a long time to bear fruit, Qiu cautioned. Army funding actually helped get the ball rolling on carbon nanotubes for electronics 10 years ago, he said, and it’s taken that long to work out the kinks.

It was mathematically proven a decade ago that nanotubes could channel electricity much more efficiently, Qiu told me. While silicon semiconductors form a lattice that lets electrons scatter in all directions – imagine downtown traffic moving through a grid of streets – carbon nanotubes essentially act like a highway that funnels all the electrons in the desired direction. (The technical term is quantum ballistic transport). But actually producing enough nanotubes of consistent size and quality and getting them to line up right took years of further work, much of it Army funded.

Last year, under a Small Business Technology Transfer (STTR) grant from ARO, the University of South California and venture-backed startup Carbonics Inc. developed working carbon nanotube transistors. The next big step is to integrate many transistors together into an actual circuit. Then, Qiu said, you can talk about integrating many circuits together to build actual equipment.

That would be a job for other parts of the Army. “The Army Research Office, our core mission actually is investing in basic science,” Qiu emphasized. ARO is just one piece of the Army Research Laboratory, which is in turn part of Combat Capabilities Development Command (formerly RDECOM), which is in turn one of the three major components of Army Futures Command, created in 2018 to coordinate all aspects of modernization from brainstorming futuristic concepts to fielding new equipment.

At ARO, said one of Qiu’s colleagues, Joseph Myers, “we’re a bunch of program managers here who support basic research likely to lead to advances in a variety of different technologies.”

Quantum Dots

While the Chinese-born, US-trained Qiu is a physicist-turned-engineer-turned-program manager, Myers is a mathematician and head of the mathematical sciences division at ARO – a field, he jokes, notoriously disconnected from mundane reality. Qiu’s carbon nanotubes are a fraction of the size of a single human hair. Their lengths vary widely, but their thickness is typically six nanometers or less. Myers is funding research on quantum dots, miniscule crystals of semiconductor whose longest dimension is no more than six nanometers, meaning they could conceivably fit inside a nanotube.

Extremely small size allows extremely fine precision. When energized, a quantum dot will always emit a very specific wavelength (which wavelength depends on the dot’s exact size). They also emit these precise frequencies more powerfully, for a longer time, than traditional semiconductors. Some companies already sell high-end “quantum LED” TV sets that use this property to produce more vivid colors: You can even get one at Best Buy.

The downside, Myers went on, is that it’s much harder to design electronics using quantum dots. Classical models of physics start to fail as you start to enter the strange domain of quantum mechanics, where seemingly solid objects turn into fuzzy fields of energy that can pulse and jump in unpredictable ways. Unlike traditional electronics that use electrical charges to represent 1s and 0s, “the physics of what’s going on isn’t as clean as zero/one anymore,” he said. “It’s got some probability of being a zero, some probability of being a one.”

To predict those probabilities precisely, using current techniques, is arduous and slow. “We largely know the equations, but the equations are just too intractable to solve exactly,” Myers said. “If you’ve got the age of the universe… you can maybe complete one of the calculations.”

“You want to do it in less than one human lifetime,” he said. “You want to do it in a day or two, or a week or so, or maybe even a few hours.”

So how much precision can you safely give up to get your results fast enough to actually use them?

Myers funded work by Southern Methodist University professor Wei Cai, who’s figured out a streamlined modeling technique, using an old Air Force supercomputer that Myers managed to get transferred to SMU before it was scrapped. (The Pentagon has a standing High Performance Computer Modernization Reutilization Program to pass on its older machines.)

Put simply (very, very simply), Cai has figured out which parts of the traditional models tend to have such a miniscule impact on the final result – about 0.000000001 percent – that you can safely ignore them. Then you can just do the calculations that actually matter.

Cai’s technique is 750 times faster than rival approaches, Myers said proudly. In its current form, he cautioned, it is still wrong about 20 percent of the time, but Cai is working on that – he’s likely to apply for further Army funding this year – and in the meantime there are ways to double-check the results.

What kind of improved technologies could you use Cai’s model to design? Besides the QLED televisions already on sale, Myers said there’s interest from multiple parts of the Army Research Laboratory that work on everything from solar panels – a useful complement to fuel-hungry diesel generators and heavy lithium-iron batteries – to military sensors and other electronics. There’s a potential medical application in improving CT scans, as well, which is potentially life-changing not just for civilians but for survivors of skull-rattling roadside bombs.

Congress and good-government watchdogs often wonder, with good reason, about oddball research projects that slip into the Pentagon budget with no clear connection to any military purpose. Then-undersecretary of the Army, Ryan McCarthy – now the secretary – was widely praised in 2017-2018 when he overhauled the service’s science & technology portfolio to cull low-payoff projects and focus 80 percent of investment on the service’s Big Six modernization priorities. But McCarthy was also very careful to leave 20 percent to continue basic research, unconstrained by near-term needs, to sow the seeds of real long-term breakthroughs.

Tags:  Carbon Nanotubes  Carbonics Inc  Graphene  Joe Qiu  quantum dots  Southern Methodist University  The Army Research Office  transistor  University of South California  Wei Cai 

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Growing carbon nanotubes with the right twist

Posted By Graphene Council, Monday, December 16, 2019
In a recently published paper in Science Advances, Feng Ding of the Center for Multidimensional Carbon Materials, within the Institute of Basic Science (IBS, South Korea) and colleagues, have achieved the creation of a specific type of carbon nanotubes (CNTs) with a selectivity of 90%, and expanded the current theory that explains the synthesis of these promising nano-cylinders.

CNTs are incredibly strong and light nanomaterials made of carbon with superior current carrying capacity and very high thermal conductivity, making them ideal for electronic applications. Although CNTs are considered as some of the most interesting materials for the future, scientists are still struggling for their controllable synthesis.

The CNTs' shape can be compared to paper tubes: in the same way as a cylinder can be created by rolling a sheet of paper, so CNTs can be imagined as a single layer of graphite rolled up on itself. Similarly, as different tubes can be produced by rolling a paper around its long side, its short side, or diagonally at different angles. Depending on the rolling direction, a graphite layer can produce different CNT structures, some are conducting and others are semiconducting, thus selectively creating a specific type of CNT will be key for their future use, such as building energy efficient computer chips. However, CNTs are not produced by rolling, but are grown nanometer after nanometer, adding carbon at the rim of nano-cylinders, one atom at a time. Despite various studies during the last three decades, the understanding on CNT growth remains very limited and rational experimental design for the growth of specific types of CNTs is challenging.

One of the most promising manufacturing methods for CNT is the chemical vapor deposition (CVD). In this process, metal nanoparticles combined with carbon-containing gases form CNTs inside a high-temperature furnace. On the tip of the tubes, the metal nanoparticles play a critical role as catalysts: they dissociate the carbon source from the gases, and assist the attachment of these carbon atoms to the CNT wall, making the tubes longer and longer. The growth of the CNT terminates once the catalyst particle is encapsulated by graphitic or amorphous carbon.

Carbon atoms are inserted onto the interface between a growing CNT and a catalyst nanoparticle, in active sites of the rim, and are available to incorporate new atoms. A previous model of CNT's growth rate showed that the latter is proportional to the density of these active sites at the interface between CNT and the catalyst, or the specific structure of the CNT.

In this study, the researchers monitored the steady growth of CNTs on a magnesium oxide (MgO) support with carbon monoxide (CO) as the carbon feedstock and cobalt nanoparticles as catalysts at 700oC. The direct experimental measurements of 16 CNTs showed how to expand the previous theory. "It was surprising that the growth rate of a carbon nanotubes only depends on the size of the catalyst particle. This implies that our previous understanding on carbon nanotubes growth was not complete," says Maoshuai He, the first author of the paper.

More specifically, carbon atoms that are deposited on the catalyst particle surface can be either incorporated on the active side of the CNT or removed by etching agents, such as H2, H2O, O2, or CO2. To explain the new experimental observations, the team included the effects of carbon insertion and removal during CNT growth and discovered that the growth rate depends on the catalyst's surface area and tube diameter ratio.

"Compared to the previous model, we added three more factors: the rate of precursor deposition, the rate of carbon removal by etching agents, and the rate of carbon insertion into a carbon nanotube wall. When feedstock dissociation cannot be balanced by carbon etching, the rate of carbon nanotube growth will no longer depend on the structure of the carbon nanotube. On the other hand, the previous theory is still valid if the etching is dominating," explains Ding, a group leader of the Center for Multidimensional Carbon Materials.

Interestingly, the new theory of CNT growth leads to a new mechanism to selectively grow a specific type of CNTs, denoted as (2n, n) CNTs, which is characterized by the maximum number of active sites at the interface between the CNT and the catalyst. This CNT structure would correspond to rolling a sheet of graphite diagonally at an angle of around 19 degrees.

"If there is no carbon etching and the carbon nanotubes growth is slow, carbon atoms on the catalyst surface will accumulate," says Jin Zhang, co-author of the study and professor of Peking University, China. "This may lead to the formation of graphitic or amorphous carbon, which are established mechanisms of carbon nanotube growth termination. In this case, only carbon nanotubes which are able to add carbon atoms on their walls, that is with the highest number of active sites, can survive."

Guided by the new theoretical understanding, the researchers were able to design experiments that produced (2n, n) CNTs with a selectivity of up to 90%: the highest selective growth of this type of CNT was achieved in the absence of any etching agent and with a high feedstock concentration.

Tags:  Carbon Nanotubes  Center for Multidimensional Carbon Materials  Feng Ding  Graphene  Institute of Basic Science  Science Advances 

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Airbus-Backed European Project Could Produce Safer Aircraft

Posted By Graphene Council, Monday, December 9, 2019
If ice accumulates on the wings, propellers or other surfaces of an aircraft, control can be dangerously inhibited. Thermoelectric ice protection systems prevent this from happening, using an ultra-thin conductive coating layer to generate heat when current is applied. Could existing technology for this application be improved? The graphene-based thermoelectric ice protection system (GICE) Spearhead Project, announced by the Graphene Flagship, is set to advance the technology readiness of graphene in thermoelectric ice protection systems.

Graphene is an ideal material to keep aircraft parts ice free, without affecting aerodynamic properties. Based on the work performed by various partners of the Graphene Flagship during earlier research phases, graphene-based ice protection systems are already in development, albeit at a low technology readiness level.

The goal of the newly launched GICE project is to advance these technologies to higher maturity by developing three technology demonstrators for specific use cases needed by key industrial partners, including Airbus and Sonaca.

Airbus is the largest European aerospace OEM and Sonaca is a strategic tier-1 supplier of components for Airbus, providing the ideal launch pad for the commercialisation of graphene-based ice protection systems.

"Thermoelectric ice protection technologies currently under investigation are based on carbon black, carbon rovings, carbon nanotubes, or metallic heating wires," explained Fabien Dezitter, Icing expert at Airbus and GICE leader. "They all have advantages and disadvantages with respect to each other, but we expect that the graphene-based solution proposed by GICE could bundle most advantages of all thermoelectric solutions.

"Advantages of graphene include flexibility of integration into complex 3D structures, low weight, reduced thermo-mechanical stress during heating cycles, higher efficiency with lower power consumption, no oxidation and chemical inertness and facile integrability into carbon fibre reinforced polymers, thermoplastics, or glass fibre reinforced polymers."

Graphene in these systems also enables precise control of heat generation to ensure the ice protection system is always at its optimum performance. These beneficial properties will help the GICE project improve the technology readiness of graphene in ice protection systems, with the final product based on the knowledge generated in the manufacturing of three demonstrators for real use cases, moving toward safer and environmentally friendlier flights.

Qualification and certification processes for new technologies in the aerospace sector are slow, which is why the GICE project endeavours to bring graphene ice protection systems up to technology readiness level six — with a system prototype demonstration tested in an icing wind tunnel by the end of the Spearhead Project in 2023.

Tags:  Airbus  carbon nanotubes  Graphene  Graphene Flagship  Sonaca  thermoelectric 

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UW Study Significantly Advances Alignment of Single-Wall Carbon Nanotubes Along Common Axis

Posted By Graphene Council, Saturday, October 19, 2019
A University of Wyoming researcher and his team have shown, for the first time, the ability to globally align single-wall carbon nanotubes along a common axis. This discovery can be valuable in many areas of technology, such as electronics, optics, composite materials, nanotechnology and other applications of materials science.

“Unlike previous efforts to align nanotubes using nanotube solution filtration, we created an automated system that could create multiple aligned films at one time,” says William Rice, an assistant professor in UW’s Department of Physics and Astronomy. “Automating the filtration system also had the effect that we could precisely control the filtration flow rate, which produced higher alignment.”

Rice was corresponding author of a paper, titled “Global Alignment of Solution-Based, Single-Wall Carbon Nanotube Films via Machine-Vision Controlled Filtration,” which was published Oct. 9 in the print version of NanoLetters, an international journal that reports on fundamental and applied research in all branches of nanoscience and nanotechnology. An online version of the paper appeared last month.

Joshua Walker, a third-year physics Ph.D. student from Cheyenne, was the paper’s lead author. Valerie Kuehl, a third-year Ph.D. chemistry student from Beulah, Colo., was a contributing author of the paper.

Single-wall carbon nanotubes are one-dimensional crystals formed by wrapping a single layer of graphite, often called graphene, into a nanoscopic cylinder. They are 0.5 to 1.5 nanometers in diameter and range from 200 to 10,000 nanometers in length. One nanometer is one-billionth of a meter.

Because of this unique geometry, carbon nanotubes can either be metals or semiconductors, depending on how the graphene is wrapped, Rice explains. Carbon nanotubes can exhibit remarkable electrical conductivity, and they possess exceptional tensile strength and thermal conductivity.

“Aligned carbon nanotubes have the potential to act as excellent optical polarizers, which are important for optically determining strain in materials. For example, if you look at your windshield with polarized glasses, you can see areas of different strain in the glass,” Rice says. “Recent work by other groups also suggests that aligned nanotubes can be used as transistors, polarized light emitters and directional heat sinks. The hope is that a new generation of all-carbon electronics can be ushered in with the use of carbon nanotubes, graphene and vacancies in diamonds.”  

Over the last decade, substantial progress has been made in the chemical control of single-wall carbon nanotubes. Rice and his team used machine-vision automation and parallelization to simultaneously produce globally aligned, single-wall carbon nanotubes using pressure-driven filtration. Feedback control enables filtration to occur with a constant flow rate that not only improves the nematic ordering of the single-wall carbon nanotubes, but also provides the ability to align a wide range of single-wall carbon nanotube types and on a variety of nanoporous membranes using the same filtration parameters.

Additionally, Rice says his research team flattened the meniscus of the nanotube solution in the glass funnel using a treatment process called silanization. This prevented the nanotubes from becoming scrambled by an uneven solution front as the nanotubes were filtered. These two advances produce nanotube films that exhibit excellent alignment across the entire structure, which was measured using a variety of polarized optical techniques. 

 “Carbon nanotubes are significant material system because of their impressive physical properties, such as extremely high thermal conductivity; a Young's modulus much greater than steel; current-carrying capacity a thousand times that of copper; and excellent light-matter coupling,” he says.

A Young's modulus is ratio of the stress (force per unit area) to the strain (percentage change in the physical dimensions) in a material, Rice says. Plastics, rubber and wood have low Young's moduli, while steel, diamond and nanotubes have high Young's moduli.

Jeffrey Fagan, a chemical engineer with the Materials Science and Engineering Division at the National Institute of Standards and Technology (NIST); Adam Biacchi, a materials chemist with the Nanoscale Device Characterization Division of NIST; Thomas Searles, an assistant professor in Howard University’s Department of Physics and Astronomy; and Angela Hight Walker, a project leader with the Nanoscale Device Characterization Division of NIST, also contributed to the paper.

Tags:  Carbon Nanotubes  composites  Graphene  Joshua Walker  optics  University of Wyoming  Valerie Kuehl  William Rice 

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MIT engineers build advanced microprocessor out of carbon nanotubes

Posted By Graphene Council, Tuesday, September 3, 2019

After years of tackling numerous design and manufacturing challenges, MIT researchers have built a modern microprocessor from carbon nanotube transistors, which are widely seen as a faster, greener alternative to their traditional silicon counterparts.

The microprocessor, described today in the journal Nature, can be built using traditional silicon-chip fabrication processes, representing a major step toward making carbon nanotube microprocessors more practical.

Silicon transistors — critical microprocessor components that switch between 1 and 0 bits to carry out computations — have carried the computer industry for decades. As predicted by Moore’s Law, industry has been able to shrink down and cram more transistors onto chips every couple of years to help carry out increasingly complex computations. But experts now foresee a time when silicon transistors will stop shrinking, and become increasingly inefficient.

Making carbon nanotube field-effect transistors (CNFET) has become a major goal for building next-generation computers. Research indicates CNFETs have properties that promise around 10 times the energy efficiency and far greater speeds compared to silicon. But when fabricated at scale, the transistors often come with many defects that affect performance, so they remain impractical.

The MIT researchers have invented new techniques to dramatically limit defects and enable full functional control in fabricating CNFETs, using processes in traditional silicon chip foundries. They demonstrated a 16-bit microprocessor with more than 14,000 CNFETs that performs the same tasks as commercial microprocessors. The Nature paper describes the microprocessor design and includes more than 70 pages detailing the manufacturing methodology.

The microprocessor is based on the RISC-V open-source chip architecture that has a set of instructions that a microprocessor can execute. The researchers’ microprocessor was able to execute the full set of instructions accurately. It also executed a modified version of the classic “Hello, World!” program, printing out, “Hello, World! I am RV16XNano, made from CNTs.”

“This is by far the most advanced chip made from any emerging nanotechnology that is promising for high-performance and energy-efficient computing,” says co-author Max M. Shulaker, the Emanuel E Landsman Career Development Assistant Professor of Electrical Engineering and Computer Science (EECS) and a member of the Microsystems Technology Laboratories. “There are limits to silicon. If we want to continue to have gains in computing, carbon nanotubes represent one of the most promising ways to overcome those limits. [The paper] completely re-invents how we build chips with carbon nanotubes.”

Joining Shulaker on the paper are: first author and postdoc Gage Hills, graduate students Christian Lau, Andrew Wright, Mindy D. Bishop, Tathagata Srimani, Pritpal Kanhaiya, Rebecca Ho, and Aya Amer, all of EECS; Arvind, the Johnson Professor of Computer Science and Engineering and a researcher in the Computer Science and Artificial Intelligence Laboratory; Anantha Chandrakasan, the dean of the School of Engineering and the Vannevar Bush Professor of Electrical Engineering and Computer Science; and Samuel Fuller, Yosi Stein, and Denis Murphy, all of Analog Devices.

Fighting the “bane” of CNFETs

The microprocessor builds on a previous iteration designed by Shulaker and other researchers six years ago that had only 178 CNFETs and ran on a single bit of data. Since then, Shulaker and his MIT colleagues have tackled three specific challenges in producing the devices: material defects, manufacturing defects, and functional issues. Hills did the bulk of the microprocessor design, while Lau handled most of the manufacturing.

For years, the defects intrinsic to carbon nanotubes have been a “bane of the field,” Shulaker says. Ideally, CNFETs need semiconducting properties to switch their conductivity on an off, corresponding to the bits 1 and 0. But unavoidably, a small portion of carbon nanotubes will be metallic, and will slow or stop the transistor from switching. To be robust to those failures, advanced circuits will need carbon nanotubes at around 99.999999 percent purity, which is virtually impossible to produce today.  

The researchers came up with a technique called DREAM (an acronym for “designing resiliency against metallic CNTs”), which positions metallic CNFETs in a way that they won’t disrupt computing. In doing so, they relaxed that stringent purity requirement by around four orders of magnitude — or 10,000 times — meaning they only need carbon nanotubes at about 99.99 percent purity, which is currently possible.

Designing circuits basically requires a library of different logic gates attached to transistors that can be combined to, say, create adders and multipliers — like combining letters in the alphabet to create words. The researchers realized that the metallic carbon nanotubes impacted different pairings of these gates differently. A single metallic carbon nanotube in gate A, for instance, may break the connection between A and B. But several metallic carbon nanotubes in gates B may not impact any of its connections.

In chip design, there are many ways to implement code onto a circuit. The researchers ran simulations to find all the different gate combinations that would be robust and wouldn’t be robust to any metallic carbon nanotubes. They then customized a chip-design program to automatically learn the combinations least likely to be affected by metallic carbon nanotubes. When designing a new chip, the program will only utilize the robust combinations and ignore the vulnerable combinations.

“The ‘DREAM’ pun is very much intended, because it’s the dream solution,” Shulaker says. “This allows us to buy carbon nanotubes off the shelf, drop them onto a wafer, and just build our circuit like normal, without doing anything else special.”

Exfoliating and tuning

CNFET fabrication starts with depositing carbon nanotubes in a solution onto a wafer with predesigned transistor architectures. However, some carbon nanotubes inevitably stick randomly together to form big bundles — like strands of spaghetti formed into little balls — that form big particle contamination on the chip.  

To cleanse that contamination, the researchers created RINSE (for “removal of incubated nanotubes through selective exfoliation”). The wafer gets pretreated with an agent that promotes carbon nanotube adhesion. Then, the wafer is coated with a certain polymer and dipped in a special solvent. That washes away the polymer, which only carries away the big bundles, while the single carbon nanotubes remain stuck to the wafer. The technique leads to about a 250-times reduction in particle density on the chip compared to similar methods.

Lastly, the researchers tackled common functional issues with CNFETs. Binary computing requires two types of transistors: “N” types, which turn on with a 1 bit and off with a 0 bit, and “P” types, which do the opposite. Traditionally, making the two types out of carbon nanotubes has been challenging, often yielding transistors that vary in performance. For this solution, the researchers developed a technique called MIXED (for “metal interface engineering crossed with electrostatic doping”), which precisely tunes transistors for function and optimization.

In this technique, they attach certain metals to each transistor — platinum or titanium — which allows them to fix that transistor as P or N. Then, they coat the CNFETs in an oxide compound through atomic-layer deposition, which allows them to tune the transistors’ characteristics for specific applications. Servers, for instance, often require transistors that act very fast but use up energy and power. Wearables and medical implants, on the other hand, may use slower, low-power transistors.  

The main goal is to get the chips out into the real world. To that end, the researchers have now started implementing their manufacturing techniques into a silicon chip foundry through a program by Defense Advanced Research Projects Agency, which supported the research. Although no one can say when chips made entirely from carbon nanotubes will hit the shelves, Shulaker says it could be fewer than five years. “We think it’s no longer a question of if, but when,” he says.

Tags:  Analog Devices  Carbon Nanotubes  Graphene  Max M. Shulaker  MIT  transistor 

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From 2D to 1D: Atomically quasi '1D' wires using a carbon nanotube template

Posted By Graphene Council, Wednesday, April 24, 2019
Updated: Tuesday, April 23, 2019
Researchers from Tokyo Metropolitan University have used carbon nanotube templates to produce nanowires of transition metal monochalcogenide (TMM), which are only 3 atoms wide in diameter. These are 50 times longer than previous attempts and can be studied in isolation, preserving the properties of atomically quasi "1D" objects. The team saw that single wires twist when perturbed, suggesting that isolated nanowires have unique mechanical properties which might be applied to switching in nanoelectronics.

Two-dimensional materials have gone from theoretical curiosity to real-life application in the span of less than two decades; the most well-known example of these, graphene, consists of well-ordered sheets of carbon atoms. Though we are far from leveraging the full potential of graphene, its remarkable electrical and thermal conductivity, optical properties and mechanical resilience have already led to a wide range of industrial applications. Examples include energy storage solutions, biosensing, and even substrates for artificial tissue.

Yet, despite the successful transition from 3D to 2D, the barrier separating 2D and 1D has been significantly more challenging to overcome. A class of materials known as transition metal monochalcogenides (TMMs, transition metal + group 16 element) have received particular interest as a potential nanowire in precision nanoelectronics. Theoretical studies have existed for over 30 years, and preliminary experimental studies have also succeeded in making small quantities of nanowire, but these were usually bundled, too short, mixed with bulk material or simply low yield, particularly when precision techniques were involved e.g. lithography. The bundling was particularly problematic; forces known as van der Waals forces would force the wires to aggregate, effectively masking all the unique properties of 1D wires that one might want to access and apply.

Now, a team led by Assistant Professor Yusuke Nakanishi from Tokyo Metropolitan University has succeeded in producing bulk quantities of well-isolated single nanowires of TMM. They used tiny, open-ended rolls of single-layered carbon, or carbon nanotubes (CNTs), to template the assembly and reaction of molybdenum and tellurium into wires from a vapor. They succeeded in producing single isolated wires of TMM, which were only 3-atoms thick and fifty times longer than those made using existing methods. These nanometer-sized CNT "test tubes" were also shown to be not chemically bound to the wires, effectively preserving the properties expected from isolated TMM wires. Importantly, they effectively "protected" the wires from each other, allowing for unprecedented access to how these 1D objects behave in isolation.

While imaging these objects using transmission electron microscopy (TEM), the team found that these wires exhibited a unique twisting effect when exposed to an electron beam. Such behavior has never been seen before and is expected to be unique to isolated wires. The transition from a straight to twisted structure may offer a novel switching mechanism when the material is incorporated into microscopic circuits. The team hope the ability to make well-isolated 1D nanowires might significantly expand our understanding of the properties and mechanisms behind the function of 1D materials.

Tags:  2D materials  Carbon Nanotubes  Graphene  nanoelectronics  Tokyo Metropolitan University  Yusuke Nakanishi 

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Carbon nanotubes can be produced in a new way by twisting ribbon-like graphene

Posted By Graphene Council, Monday, February 25, 2019
Updated: Monday, February 25, 2019
The properties of folded, bent and twisted graphene at nanoscale are difficult to study theoretically and experimentally. In his dissertation, however, Oleg Kit utilized symmetry, a time-worn concept of theoretical physics, to develop an effective method to run computer experiments on nanostructures under complex deformations.

The new method allows explorations of folding, bending and twisting in more diverse ways than previously. Information about nanostructure properties is obtained by modeling only a few atoms, instead of simulating the whole structures. As the research utilized the laws of quantum mechanics, the method provided also information about changes in the electronic structure of graphene.

The advantage of the technique is that it makes possible studies of structures with millions of atoms that lack traditional symmetries. It enabled simulations which predict that carbon nanotubes can be made by twisting graphene.

Tags:  Carbon Nanotubes  Graphene  Oleg Kit  University of Jyväskylä 

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