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NIST measurements show that interactions of the graphene layers with the insulating substrate material causes electrons (red, down arrow) and electron holes (blue, up arrow) to collect in “puddles”. The differing charge densities creates the random pattern of alternating dipoles and electron band gaps that vary across the layers. Credit: NIST

NIST’s latest Tech Beat has many great stories of interest to readers interested in materials science:

Understanding how glasses ‘relax’ provides some relief for manufacturers

NIST theoretician Jack Douglas and his collaborator Francis Starr of Wesleyan University have used computer simulations to gain basic insights into a fundamental problem in material science related to glass-forming materials, offering a precise mathematical and physical description of the way temperature affects the rate of flow in this broad class of materials — a long-standing goal.

Two graphene layers may be better than one

Nikolai Zhitenev, Joseph Stroscio and other researchers at the institute have shown that the electronic properties of two layers of graphene vary on the nanometer scale. The surprising new results reveal that not only does the difference in the strength of the electric charges between the two layers vary across the layers, but they also actually reverse in sign to create randomly distributed puddles of alternating positive and negative charges. The new measurements bring graphene a step closer to being used in practical electronic devices.

Good eggs: Nanomagnets offer food for thought about computer memories

NIST researchers used electron-beam lithography to make thousands of nickel-iron magnets, each about 200 nanometers in diameter. Each magnet is ordinarily shaped like an ellipse, but the researchers also made some magnets in three different egglike shapes with an increasingly pointy end. It’s all part of NIST research on nanoscale magnetic materials, devices and measurement methods to support development of future magnetic data storage systems. It turns out that even small distortions in magnet shape can lead to significant changes in magnetic properties.

New manufacturing innovations blog lifts off

The manufacturing experts at NIST’s Hollings Manufacturing Extension Partnership are now spreading the word on manufacturing innovation by blog. Launched April 4, the official MEP Blog: Manufacturing Innovations will serve as a focal point for educating U.S. manufacturers, partners and stakeholders on the latest industry trends. ”From analyzing economic data to sharing successes of our clients, we hope the Manufacturing Innovations Blog will become a site that inspires conversations about manufacturing in the U.S.,” says Roger Kilmer, director of NIST MEP.

Solar cell technology opportunities for the 21st Century

What are the major technology challenges to future growth in the solar-cell industry? Where are the big-bang-for-the-buck R&D investment opportunities? These and other questions were put to a group of 72 internationally recognized experts in the field at a 2010 special workshop. Their conclusions are summarized in a new NIST publication on Photovoltaic Technologies for the 21st Century. The workshop was led by a steering committee chaired by Roger G. Little, CEO, Spire Corporation, and Robert W. Collins, NEG Endowed Chair of Silicate and Materials Science, University of Toledo, and co-sponsored by NIST.

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This video explains one route researchers at Pacific Northwest National Lab and Princeton are taking to create better materials for batteries: materials that assemble on their own into durable nanocomposites. Details are also provided about surfactants used in conjunction with tin oxide and functionalized graphene.

The video features interviews with PNNL researcher Jun Liu and Princeton’s Ilhan Aksay who directs the school’s Ceramic Materials Lab. (Aksay is a past winner of ACerS’ Richard M. Fulrath Award.)

They hope this approach leads to an easy synthesis route at a low cost. I believe their graphene composite anode has gone into production at Targray Technology International in conjunction with Vorbeck Materials.

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Change in the wt percent of hydrogen in few-layer graphene sample created via exfoliation (EG) and arc evaporation of graphite under hydrogen (HGH). (Inset) The evolution of hydrogen as recorded by gas chromatograph. Credit: Subrahmanyam et al.

A group of researchers from the Jawaharlal Nehru Center for Advanced Scientific Research in Bangalore, India say they have come across a new approach for using graphene for hydrogen storage. They say in a paper published in the Proceedings of the National Academy of Sciences they have been able to create samples containing up to 5 wt percent hydrogen, which they say can be completely released through heating or by irradiating with a laser or UV light source. For comparison purposes, the maximum amount of hydrogen that can be contained in graphene is 7.7 wt percent.

This isn’t the first time researchers have looked at graphene. Much of this work has been done in the context of trying to find some sort of suitable solid body for hydrogen storage. Previously, some investigators began thinking about carbon nanotubes. Some storage effects were achieved, but overall the results have been disappointing.

Other research also has been done at Columbia University using single-layer graphene showing that hydrogenation can occur and be reversed through a photothermal heating process, but apparently the amount of hydrogen that is stored in the single layer was not measured (the work was focused on methods to manipulate the charge transport properties of the graphene).

The JNCASR group, led by C.N.R. Rao, looked at additional research that suggested that hydrogen loading might be better accomplished through the use of multiple layers of graphene, and decided to do some detailed studies in this area.

In brief, the group used two methods to form few-layer graphene samples: exfoliation of graphite oxide (forming 6–7 layers) and arc evaporation of graphite under hydrogen (forming 2–3 layers). The researchers hydrogenated both samples (using Birch reduction), and both samples displayed a hydrogen content of approximately 5 wt percent.

They found that the hydrogen-containing graphene is stable at room temperature “and can be stored over long periods.”

When the samples are heated, the hydrogen begins to be released around 200°C and is totally released at 500°C. As mentioned above, they also used laser and UV irradiation to break the C–H bonds and free the hydrogen.

The group feels this storage system may have potential applications, and that a better storage system may be achievable. The authors note, “Although Birch reduction enabled us to incorporate 5 wt percent of hydrogen in few-layer graphenes, it may be possible to carry out hydrogenation more effectively by other methods.” They also report they have achieved 3 wt percent storage using graphene nanoribbons, which also fully releases its hydrogen at 500°C.

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So many materials stories, so little time:

Cornell study: Graphene grains make atomic patchwork quilts

Dynamically tunable hemispherical electronic eye camera system with adjustable zoom capability

Eyeglasses that use liquid crystals to avoid the problems of bifocals

Sharp announces high-efficiency LED device for lighting purposes

Swiss and Colombian researchers develop electromagnetic wave tool to remotely detonate IEDs

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One of the editors at Nature has written a good (free) article that provides some of important perspective about the movement of nano-carbon products (fullerenes, carbon nanotubes and, more recently, graphene) from lab to sustainable markets.

Richard Van Noorden, with quotes from a number or researchers and business reps, describes what a tricky path it can be to go from super-promising materials to specific applications to efficiency-scaled production capacity.

He notes that the first of these to emerge, fullerene, has been pretty much a commercial flop. CNTs emerged in the early 1990s and their semiconducting and metallic-type properties, not to mention their ruggedness, has teased R&D groups and investors ever since. But, CNTs electrical properties can be difficult to control and manufacturing pure bulk CNTs in predictable dimensions and orientations has been illusive. The same same problems are being faced with the newer graphene.

The problem with electronics is that a decent and cheaper alternative is readily available: silicon chips. Van Noorden quotes one organic chemist who points out that, “There have been millions and person-years and trillions of dollars put into the development of silicon electronics. Asking graphene to compte with silicon now is like asking a 10-year-old to be a concert pianist because we’ve been giving him piano lessons for the last six years.”

Van Noorden provides an overview of some of the pros and cons of CNTs and graphene in various applications and how the cost-benefit model can shift over time (e.g., graphene looks more promising in touch-screen applications as the cost of indium – and thus ITO  – trends upwards .)

But even in less esoteric applications, such as using CWTs and graphene flakes in composites, these materials that can retail in the hundreds of dollars/kg are competing with substitutes that sell for less than a dollar/kg. Even with an expected stream of science and manufacturing innovations, experts like Lux Research estimate the $/kg for CNTs will only drop by half in the next ten years.

That’s not a blazing speed for price reduction, but one of the experts Van Noorden interviews points out, the arc of now-ubiquitous carbon fiber began very slowly, eventually found usage in less cost-conscious military applications and much later made its way into large-scale commercial usage.

Nevertheless, manufacturers are bringing more and more capacity on line, and as they do so, they will be scrambling for outlets. Some early niches for graphene will emerge like they have for CWTs (Van Noorden speculates that supercapacitors, such as the one I recently wrote about, electrodes and flexible electronics may pay off), but despite the excitement everyone will have to be patient — perhaps very patient — until they see the first truly transformational uses.

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