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Easy-to-make, ultra-low power electronics could charge out of thin air

Posted By Terrance Barkan, Wednesday, October 14, 2020
Researchers have developed a new approach to printed electronics which allows ultra-low power electronic devices that could recharge from ambient light or radiofrequency noise. The approach paves the way for low-cost printed electronics that could be seamlessly embedded in everyday objects and environments.

Electronics that consume tiny amounts of power are key for the development of the Internet of Things, in which everyday objects are connected to the internet. Many emerging technologies, from wearables to healthcare devices to smart homes and smart cities, need cost-effective transistors and electronic circuits that can function with minimal energy use.

Printed electronics are a simple and inexpensive way to manufacture electronics that could pave the way for low-cost electronic devices on unconventional substrates – such as clothes, plastic wrap or paper – and provide everyday objects with ‘intelligence’.

However, these devices need to operate with low energy and power consumption to be useful for real-world applications. Although printing techniques have advanced considerably, power consumption has remained a challenge – the different solutions available were too complex for commercial production.

Now, researchers from the University of Cambridge, working with collaborators from China and Saudi Arabia, have developed an approach for printed electronics that could be used to make low-cost devices that recharge out of thin air. Even the ambient radio signals that surround us would be enough to power them. Their results are published in the journal ACS Nano.

Since the commercial batteries which power many devices have limited lifetimes and negative environmental impacts, researchers are developing electronics that can operate autonomously with ultra-low levels of energy.

The technology developed by the researchers delivers high-performance electronic circuits based on thin-film transistors which are ‘ambipolar’ as they use only one semiconducting material to transport both negative and positive electric charges in their channels, in a region of operation called ‘deep subthreshold’ – a phrase that essentially means that the transistors are operated in a region that is conventionally regarded as their ‘off’ state. The team coined the phrase ‘deep-subthreshold ambipolar’ to refer to unprecedented ultra-low operating voltages and power consumption levels.

If electronic circuits made of these devices were to be powered by a standard AA battery, the researchers say it would be possible that they could run for millions of years uninterrupted.

The team, which included researchers from Soochow University, the Chinese Academy of Sciences, ShanghaiTech University, and King Abdullah University of Science and Technology (KAUST), used printed carbon nanotubes – ultra-thin cylinders of carbon – as an ambipolar semiconductor to achieve the result.

“Thanks to deep-subthreshold ambipolar approach, we created printed electronics that meet the power and voltage requirements of real-world applications, and opened up opportunities for remote sensing and ‘place-and-forget’ devices that can operate without batteries for their entire lifetime,” said co-lead author Luigi Occhipinti from Cambridge’s Department of Engineering. “Crucially, our ultra-low-power printed electronics are simple and cost-effective to manufacture and overcome long-standing hurdles in the field.”

“Our approach to printed electronics could be scaled up to make inexpensive battery-less devices that could harvest energy from the environment, such as sunlight or omnipresent ambient electromagnetic waves, like those created by our mobile phones and wifi stations,” said co-lead author Professor Vincenzo Pecunia from Soochow University. Pecunia is a former PhD student and postdoctoral researcher at Cambridge’s Cavendish Laboratory.

The work paves the way for a new generation of self-powered electronics for biomedical applications, smart homes, infrastructure monitoring, and the exponentially-growing Internet of Things device ecosystem.The research was funded in part by the Engineering and Physical Sciences Research Council (EPSRC).

Tags:  carbon nanotubes  Chinese Academy of Sciences  Energy  Engineering and Physical Sciences Research Council  Graphene  King Abdullah University of Science and Technology  Luigi Occhipinti  Medical  ShanghaiTech University  Soochow University  transistor  University of Cambridge  Vincenzo Pecunia 

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Metal wires of carbon complete toolbox for carbon-based computers

Posted By Graphene Council, Friday, September 25, 2020
Transistors based on carbon rather than silicon could potentially boost computers' speed and cut their power consumption more than a thousandfold -- think of a mobile phone that holds its charge for months -- but the set of tools needed to build working carbon circuits has remained incomplete until now.

A team of chemists and physicists at the University of California, Berkeley, has finally created the last tool in the toolbox, a metallic wire made entirely of carbon, setting the stage for a ramp-up in research to build carbon-based transistors and, ultimately, computers.

"Staying within the same material, within the realm of carbon-based materials, is what brings this technology together now," said Felix Fischer, UC Berkeley professor of chemistry, noting that the ability to make all circuit elements from the same material makes fabrication easier. "That has been one of the key things that has been missing in the big picture of an all-carbon-based integrated circuit architecture."

Metal wires -- like the metallic channels used to connect transistors in a computer chip -- carry electricity from device to device and interconnect the semiconducting elements within transistors, the building blocks of computers.

The UC Berkeley group has been working for several years on how to make semiconductors and insulators from graphene nanoribbons, which are narrow, one-dimensional strips of atom-thick graphene, a structure composed entirely of carbon atoms arranged in an interconnected hexagonal pattern resembling chicken wire.

The new carbon-based metal is also a graphene nanoribbon, but designed with an eye toward conducting electrons between semiconducting nanoribbons in all-carbon transistors. The metallic nanoribbons were built by assembling them from smaller identical building blocks: a bottom-up approach, said Fischer's colleague, Michael Crommie, a UC Berkeley professor of physics. Each building block contributes an electron that can flow freely along the nanoribbon.

While other carbon-based materials -- like extended 2D sheets of graphene and carbon nanotubes -- can be metallic, they have their problems. Reshaping a 2D sheet of graphene into nanometer scale strips, for example, spontaneously turns them into semiconductors, or even insulators. Carbon nanotubes, which are excellent conductors, cannot be prepared with the same precision and reproducibility in large quantities as nanoribbons.

"Nanoribbons allow us to chemically access a wide range of structures using bottom-up fabrication, something not yet possible with nanotubes," Crommie said. "This has allowed us to basically stitch electrons together to create a metallic nanoribbon, something not done before. This is one of the grand challenges in the area of graphene nanoribbon technology and why we are so excited about it."

Metallic graphene nanoribbons -- which feature a wide, partially-filled electronic band characteristic of metals -- should be comparable in conductance to 2D graphene itself.

"We think that the metallic wires are really a breakthrough; it is the first time that we can intentionally create an ultra-narrow metallic conductor -- a good, intrinsic conductor -- out of carbon-based materials, without the need for external doping," Fischer added.

Crommie, Fischer and their colleagues at UC Berkeley and Lawrence Berkeley National Laboratory (Berkeley Lab) will publish their findings in the Sept. 25 issue of the journal Science.

Tweaking the topology

Silicon-based integrated circuits have powered computers for decades with ever increasing speed and performance, per Moore's Law, but they are reaching their speed limit -- that is, how fast they can switch between zeros and ones. It's also becoming harder to reduce power consumption; computers already use a substantial fraction of the world's energy production. Carbon-based computers could potentially switch many times times faster than silicon computers and use only fractions of the power, Fischer said.

Graphene, which is pure carbon, is a leading contender for these next-generation, carbon-based computers. Narrow strips of graphene are primarily semiconductors, however, and the challenge has been to make them also work as insulators and metals -- opposite extremes, totally nonconducting and fully conducting, respectively -- so as to construct transistors and processors entirely from carbon.

Several years ago, Fischer and Crommie teamed up with theoretical materials scientist Steven Louie, a UC Berkeley professor of physics, to discover new ways of connecting small lengths of nanoribbon to reliably create the full gamut of conducting properties.

Two years ago, the team demonstrated that by connecting short segments of nanoribbon in the right way, electrons in each segment could be arranged to create a new topological state -- a special quantum wave function -- leading to tunable semiconducting properties.

In the new work, they use a similar technique to stitch together short segments of nanoribbons to create a conducting metal wire tens of nanometers long and barely a nanometer wide.

The nanoribbons were created chemically and imaged on very flat surfaces using a scanning tunneling microscope. Simple heat was used to induce the molecules to chemically react and join together in just the right way. Fischer compares the assembly of daisy-chained building blocks to a set of Legos, but Legos designed to fit at the atomic scale.

"They are all precisely engineered so that there is only one way they can fit together. It's as if you take a bag of Legos, and you shake it, and out comes a fully assembled car," he said. "That is the magic of controlling the self-assembly with chemistry."

Once assembled, the new nanoribbon's electronic state was a metal -- just as Louie predicted -- with each segment contributing a single conducting electron.

The final breakthrough can be attributed to a minute change in the nanoribbon structure.

"Using chemistry, we created a tiny change, a change in just one chemical bond per about every 100 atoms, but which increased the metallicity of the nanoribbon by a factor of 20, and that is important, from a practical point of view, to make this a good metal," Crommie said.

The two researchers are working with electrical engineers at UC Berkeley to assemble their toolbox of semiconducting, insulating and metallic graphene nanoribbons into working transistors.

"I believe this technology will revolutionize how we build integrated circuits in the future," Fischer said. "It should take us a big step up from the best performance that can be expected from silicon right now. We now have a path to access faster switching speeds at much lower power consumption. That is what is driving the push toward a carbon-based electronics semiconductor industry in the future."

Tags:  2D materials  carbon nanotubes  Felix Fischer  Graphene  graphene nanoribbons  Michael Crommie  Steven Louie  transistor  University of California Berkeley 

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A new two-dimensional carbon allotrope -- semiconducting diamane film synthesized

Posted By Graphene Council, Thursday, August 20, 2020
Atomically thin diamond, also called diamane, is a two-dimensional carbon allotrope and has attracted considerable scientific interest due to its potential physical properties. However, previous studies suggest that atomically thin diamond films are not achievable in a pristine state because diamonds possess a three-dimensional crystalline structure and would lack chemical stability when thinned down to the thickness of diamond's unit cell due to the dangling sp3 bonds. Chemical functionalization of the surface carbons with specific chemical groups was considered necessary to stabilize the two-dimensional structure, such as surface hydrogenation or fluorination, and various substrates have also been used in these synthesizing attempts. But all of these attempts change the composition of diamond films, that is to say, the successful synthesis of a pristine diamane has up until now not been achieved.

Regulating the phase transition process of carbon materials under high pressure and high temperature is always a straightforward method for achieving diamondization. Here, a team of scientists led by Drs. Feng Ke and Bin Chen from HPSTAR (the Center for High Pressure Science and Technology Advanced Research) used this direct approach, diamondization of mechanically exfoliated few-layer graphene via compression, to synthesize the long-sought-after diamane film. The study is published in Nano Letters.

The diamondization process is usually accompanied by an opening of an energy gap and a dramatic resistance increase due to the sp2-sp3 rehybridization between carbon atoms. "The in-situ electrical transport measurements of few-layer graphene are difficult to carry out under high pressure," said Feng Ke. "However, using our recently developed photolithography-based microwiring technique to prepare film electrodes on a diamond surface for resistance measurements, we are able to study the pressure-induced sp2-sp3 diamondization transition of mechanically exfoliated graphene with layer thickness ranging from 12- to bilayer at room temperature."

Their studies demonstrate that pristine h-diamane could be synthesized by compressing trilayer and thicker graphene to above 20 GPa at room temperature, which once synthesized could be preserved to about 1.0 GPa upon decompression. "The optical absorption reveals that h-diamane has an energy gap of 2.8 ± 0.3 eV, and further band structure calculations confirm an indirect band gap of 2.7-2.9 eV," explained the co-frist-author Lingkong Zhang, a PhD student at HPSTAR. "Compared to gapless graphene, semiconducting h-diamane offers exciting possibilities for carbon-based electronic devices."

The XRD measurements have shown that the few-layer graphene to h-diamane transition is a gradual structural transition, which helps to understand the continuous resistance increase and absorbance decrease in trilayer and thicker graphene with pressure above the transition pressure. Theoretical calculations indicate that a (−2110)-oriented h-diamane is energetically stable and has a lower enthalpy than its few-layer graphene precursor above the transition pressure.

"Like the discovery of graphene, carbon nanotubes, fullerenes, and other novel carbon allotropes, the realization of a pristine diamane represents another exciting achievement in materials science," added Dr. Bin Chen, "Thermal treatment at high pressure may be helpful to preserve a pristine h-diamane to ambient pressure, as suggested from the high-temperature and high-pressure method to synthesize a pressure quenchable h-diamond. The challenges still remain to achieve the preservation and industrial applications of diamane."

Tags:  2D Materials  Bin Chen  carbon nanotubes  Feng Ke  Graphene  HPSTAR 

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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, The 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, The 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, The 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, The 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, The 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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