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Noble laureates Novoselov and Geim, left, along with Nancy Rothwell, president and vice-chancellor of the University of Manchester, meet with UK Science Minister David Willetts and Osborne to discuss plans for a new graphene-based R&D hub to be located at the school. Credit: Univ. of Manchester.

In early October, the United Kingdom’s Chancellor of the Exchequer George Osborne announced plans by the government to invest £50 million (about $80 million) in a new graphene-based R&D center. The center, to be called the Graphene Global Research and Technology Hub, will be located at the University of Manchester.

The location in many ways is a tribute to the past and ongoing work by Andre Geim and Kostya Novoselov, who discovered graphene at the University of Manchester in 2004 and were awarded the 2010 Nobel Prize in Physics. Geim and Novoselov’s pioneering work has allowed them to attract a talented team and stay at the forefront of this field, where there are a lot of ideas for commercialization being brewed.

While no timetables are being proposed in regard to real commercialization opportunities, Osborne, according to a university news release, told attendees of a Conservative Party Conference, “…We will fund a national research program that will take this Nobel-prize winning discovery from the British laboratory to the British factory floor…We’re going to get Britain making things again.”

In the same release, the university, itself, goes on to predict, “The development of the Hub will capitalize on the UK’s international leadership in the field. It will act as a catalyst to spawn new businesses, attract global companies and translate the value of scientific discovery into wealth and job creation for the UK. The center would help develop the technology to allow manufacture on a scale that would open up the promising commercial opportunities, incorporating a large doctoral training center and advanced research equipment.”

To be sure, there are many other graphene research efforts, public and private, in the UK and around the world. Responding to the news about the funding for the Manchester hub, a story at Optics.org notes, “Though it is home to the graphene discoverers, when it comes to future commercialization of the technology the UK will face stiff competition from both competing academic institutions and many of the world’s largest technology companies.”

Already several big-name companies, such as IBM, Hitachi and TDK, have received patents for novel graphene-based devices. But, as is usually the case, having a patent and having a commercial success are unrelated events. While there is a lot of promise, there is still a long way to go in fundamental research and, at the other end of the spectrum, basic processing and application methods.

Given the interest and competition, the £50 million investment could easily be dwarfed if not carefully targeted. Along these lines, the Optics.org story discusses the views of another UK graphene researcher, Karl Coleman (University of Durham), and reports, “Coleman thinks that manufacturing ought to be one of the priority areas for the future technology hub, and also points out that graphene applications go beyond the high-profile areas of electronics, displays and aerospace. ‘[We] would like to see the hub include what we sometimes call the low hanging fruits, such as capacitors, conducting inks and composites, to name just a few, that are likely to be commercialized much sooner,’ he said.”

On the other hand, Geim and Novoselov do have a high-profile electronics application in mind for graphene: the elusive replacement for silicon chip. In a paper, ”Tunable metal-insulator transition in double-layer graphene heterostructures,” recently published in Nature Physics, their group discusses the creation of double boron nitride—graphene sandwich structures. Essentially, they transferred a graphene monolayer on top of a 20-30 nanometer-thick BN crystal (prepared on a silicon wafer). The graphene was then covered with another BN crystal and another graphene monolayer. Both monolayers were given multiterminal shapes, individual electrical contacts and aligned identically over each other.

Ponomarenko with boron nitride–graphene sandwich device. Credit: Univ. of Manchester.

According to the authors of the paper (doi:10.1038/nphys2114), the four-layer structure for the first time allowed the behavior of graphene to be studied in isolation from outside effects.

A separate University of Manchester news release quotes lead author, Leonid Ponomarenko, describing the breakthrough. He says, “Creating the multilayer structure has allowed us to isolate graphene from negative influence of the environment and control graphene’s electronic properties in a way it was impossible before. …So far people have never seen graphene as an insulator unless it has been purposefully damaged, but here high-quality graphene becomes an insulator for the first time.”

Regarding the implications of this work, Geim says in the same release, “Leaving the new physics we report aside, technologically important is our demonstration that graphene encapsulated within BN  offers the best and most advanced platform for future graphene electronics. It solves several nasty issues about graphene’s stability and quality that were hanging for long time as dark clouds over the future road for graphene electronics. …We did this on a small scale but the experience shows that everything with graphene can be scaled up. …It could be only a matter of several months before we have encapsulated graphene transistors with characteristics better than previously demonstrated.”

That sounds like the kind of confidence the UK’s new graphene hub hopes to leverage.

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Investigators at Harvard’s School of Engineering and Applied Sciences have created strange optical effects, including corkscrew-like vortex beams, by reflecting light off a flat, nanostructured surface. Credit: Nanfang Yu, SEAS.

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Graphene, a two-dimensional sheet of carbon, has been the subject of much research since it was discovered in 2004. Its basic properties are fairly well documented, and papers are appearing about possible applications, for example, as supercapacitor electrodes or composite reinforcement. Some novel ideas are emerging as a recent paper on graphene-based artificial muscles illustrates.

Graphene is interesting stuff, but its range of properties is limited by its super-simple chemistry. In multilayer form, weak van der Waals bonding between layers is a limiting factor, too.

However, if two-dimensional materials with more complex chemistries could be made, the door would be opened to tune properties and engineer materials for specific applications.

Well, count among the door-openers Drexel University professors and ACerS Fellows Yury Gogotsi and Michel Barsoum, who describe a process for synthesizing such materials in a new paper, “Two-Dimensional Nanocrystals Produced by Exfoliation of Ti₃AlC₂,” in Advanced Materials (doi: 10:1002/adma.201102306).

As their paper states, “Complex, layered structures that contain more than one element may offer new properties because they provide a larger number of compositional variables that can be tuned for achieving specific properties.”

Barsoum was among the first to work on the so-called MAX phases, which are layered ternary carbides or nitrides. MAX refers to the material’s chemistry: “M” is an early transition metal (Ti, Ta, etc.), “A” is an A-group metal (Al, In, Si, etc.) and “X” is carbon or nitrogen. So far, more than 60 MAX compounds have been identified.

The layered morphology gives them some interesting physical properties that can be metal-like or ceramic-like, but their structure and chemistry also make them good precursor materials for carbide-derived carbons, which are nanostructured porous materials. CDCs are synthesized by removing the “M” and “A” with hydrofluoric acid, and we wrote about some of their anomalous supercapicitance properties in an earlier post.

Wondering whether a hybrid MAX-CDC material could be synthesized, the Drexel team began experimenting with selective removal of “A” elements. MX compounds are chemically stable, and the “A” elements tend to be weakly bonded and are more reactive.

The process was surprisingly simple: They synthesized Ti₃AlC₂ by first ball milling, and then immersing the resultant powders in a concentrated HF solution at room temperature; next, they rinsed and centrifuged the material. Finally, they used cold pressing to align flakes. They characterized the flakes with XRD, SEM and TEM, and determined the chemistries with X-ray energy dispersive spectrometry in the TEM.

By removing the aluminum (”A” element), they discovered they had formed a new two-dimensional material with the composition Ti₃C₂. Because its morphology is similar to graphene, the team refers to this class of materials as “MXene.” They report having formed nanosheets (a few layers thick) and conical scrolls.

Gogotsi says they have demonstrated the ability to synthesize MX compounds through exfoliation on a wide range of MAX compounds, including carbo-nitrides. According to the paper they already have “solid evidence for the exfoliation of Ta₄AlC₃ into Ta₄C₃ flakes,” but offered no information on the material properties of these latter two compounds.

Given that the MAX compounds comprise a well-defined family of materials, they seem to be good candidates for the Materials Genome Initiative concept. Gogotsi confirmed that they are. “These materials are a perfect case for computational materials engineering. It’s a much better and more efficient way to go after the structures of this family of materials.”

In a NanoWerk article, Gogotsi says, “We are talking about a large family of 2D metal carbides and nitrides, so exploring different structures to find the optimum chemistry for each application is the next step in our work,” plus property characterization and controlling the surface chemistries.

The potential applications of MXene materials is wide. Ab initio simulations predict that they will have large elastic moduli. By varying their surface chemistries (for example, in the paper, the surfaces are terminated by hydroxl and/or fluorine groups) interfaces and bandgaps can be tuned. The large surface areas and layered structure make these materials interesting candidates for Li-ion battery electrodes, pseudocapacitors, polymer composite fillers and other energy and electronic devices.

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A key tenet of the Materials Genome Initiative for Global Competitiveness (pdf) is using computation to reduce the time for materials development by 75%, from 20 years to 5 years. A recent press release from Fujitsu Laboratories in Japan gives an early clue about the feasibility of this approach.

Fujitsu is interested in developing materials for novel nanodevices to replace silicon large scale integration devices. The drive to shrink electronic devices is starting to run up against the physical limits of the material to be miniaturized.

Turning to computational methods, Fujitsu used a first-principles method to calculate the electrical properties of a 1,000-atom device based on carbon nanotubes and graphene electrodes. In the press release the company says the significance of this breakthrough is that “The new technology opens the door to the design of exceptionally high-speed, energy-efficient nanodevices that break totally new ground with their development.”

First-principles computation is based on the quantum mechanics of a material’s electrons and atoms, thus experimental data or empirical parameters are not needed. It is useful for simulating the properties of materials like carbon where small differences in atomic arrangement results in large property differences. Consider, for example, how different the electrical properties of charcoal, graphite and diamond are.

Electrical properties were calculated using software developed by the Japan Advanced Institute for Science and Technology and the computational power of a supercomputer at the Information Technology Center at Nagoya University. First-principles calculations are iterative and tend to need a lot of computing time and memory. Each iteration updates input values and the computation continues until the output values converge. It took about three days to calculate the electrical properties of a 1,000-atom nanodevice using about one-third of the supercomputer’s capacity.

In the press release, Fujitsu explained that they worked with JAIST to tweak the software somewhat, and that they also used a “hybrid parallel processing technique.” As a result, Fujitsu was able to include the modeling of several times more atoms than it had previously be able to do.

The nanodevice modeled is a carbon nanotube with graphene electrodes. Lithium atoms occupied the inner edges of the graphene electrodes and several hydrogen atoms bridge the atomic layer between the electrodes and the nanotube. This is a very simple system, atomically, compared to most commercial engineered materials, which often have complex compositions or atomic structures. However, the company said its success in this instance “significantly paves the way to designing novel nanodevices.”

Because the Materials Genome Initiative is aimed at elevating the United States’ national competitiveness, there is some irony of discussing the efforts of a Japanese enterprise. However, this example illustrates the type of technology—also available in the US—that the MGI intends on leveraging.

And, while Fujitsu’s work shows great promise for designing a type of nanodevice, it also demonstrates that this route to materials design requires sizeable computational investment (hardware and software). Even at the speed attained by Fujitsu, the span of potential materials compositions, crystalline structures, properties and applications make it clear that a lot of computational capacity and agility will be needed in the US.

The Fujitsu work was published in the Aug. 11 online edition of Applied Physics Express.

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Schematic showing the architecture of the sensor developed at Princeton. Credit Stephen Y. Chou; Princeton.

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Less is more: Researchers pinpoint graphene’s varying conductivity level

Researchers at North Carolina State University have found one of the first roadblocks to utilizing graphene for fast electronic devices, by showing that its conductivity decreases significantly when more than one layer is present. With the help of the high performance computers at Oak Ridge National Lab, the NC State team discovered both good and bad news about graphene: With a single layer of graphene, the mobility — and therefore conductivity — shown by the researchers’ simulations turned out to be much higher than they had originally thought; the bad news is that the mobility of electrons in bilayer graphene is roughly an order of magnitude lower than in a single graphene sheet.

Jell-O device detects organ failure

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