Chips are down

Graphene is a modified form of the all-carbon pencil lead material graphite and is being touted as the material of choice for a future generation of computer chips to augment, or even usurp, silicon. Now, three research teams have devised new approaches to handling graphene that could accelerate development of this material.

Carbon has several allotropes – same element, different forms. Graphite is the stuff of pencil lead and exists as layer upon layer of hexagonally patterned chicken wire type sheets with a carbon at each vertex. Diamond is the hardest known materials and exists as a robust tetrahedrally bonded network of carbon atoms. Fullerenes and nanotubes are tiny spheres, spheroids, and tubes. Amorphous carbon, which has a mixture of the trivalent and tetravalent bonded carbon atoms. Graphene is akin to single layers of graphite.

Nitin P. Padture

Nitin P. Padture

Andre Geim and colleagues at The University of Manchester and colleagues focused on experimental measurements of the intriguing electronic properties of graphene after theoreticians had predicted them. Now, research teams around the globe are further investigating this intriguing substance. However, processing graphene is not without limitations. As such, various efforts have focused on ways to simplify the handling of the material.

Rod Ruoff and his colleagues at the University of Texas at Austin have found a way to disperse chemically modified graphene in a wide variety of organic solvents. This could open the door to developing graphene in conductive films, polymer composites, ultracapacitors, batteries, paints, inks and plastic electronics, the team says.

Rod Ruoff

Rod Ruoff

By using ‘solubility parameters’ ubiquitously applied by industry to determine the solvents most likely to dissolve certain materials or to create good colloids, we have developed a set of solubility parameters for chemically modified graphenes, explains Ruoff. We believe that this approach will have exceptional utility for technology transition in use of colloidal suspensions of graphene sheets.

Tomás Palacios

Tomás Palacios

In parallel, but unconnected work, a team at Ohio State University, led by Nitin Padture are developing a technique for mass producing computer chips made from graphene. Graphene has huge potential, it’s been dubbed the new silicon, says Padture, but there hasn’t been a good process for high-throughput manufacturing it into chips.

Graphene’s chickenwire structure

Graphene’s chickenwire structure

He and his colleagues have found a way to mesh the graphene fabrication process with standard microelectronics manufacturing methods. In their first series of experiments, the team stamped high-definition features just ten graphene layers thick on to a silicon oxide substrate, making this a potential mass-production method.

A graphene frequency multiplier (Photo by Donna Coveney)

A graphene frequency multiplier (Photo by Donna Coveney)

In other work to be published in the May issue of Electron Device Letters, MIT researchers, led by Tomás Palacios, have built an experimental graphene chip known as a frequency multiplier. Frequency multipliers are widely used in telecommunications and computing applications. However, current technology suffers from noise interference that requires energy-intensive filtering. The graphene frequency multiplier system has but a single transistor and so, these researchers say, efficiently produces a very clean output that needs no filtering.

Further reading

Nano. Lett., 2009, in press
http://dx.doi.org/10.1021/nl803798y

Adv Mater, 2009, 21, 1243-1246
http://dx.doi.org/10.1002/adma.200802417

Nanoscience and Technology Lab
http://bucky-central.me.utexas.edu/

Nitin P. Padture homepage
http://www.matsceng.ohio-state.edu/faculty/padture/padturewebpage/

Tomás Palacios homepage
http://web.mit.edu/tpalacios/

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carbon

Flush with nanoparticles

What happens to carbon-based nanoparticles when they enter groundwater? Can municipal water supplies filter them out? And, if they cannot will they cause health problems? These are crucial questions that need answers now, as nanotechnology grows. Now, a new study by Kurt Pennell, of the Georgia Institute of Technology, and colleagues, suggests that subtle differences in the solution properties of the water carrying such particles can determine their ultimate fate.

Pennell and colleagues have studied the transportation of the archetypal nanoparticle, the soccerball-shaped carbon-60 molecule known as buckminsterfullerene, or the buckyball for short. While C60 is a well-studied molecule little is known about its environmental impact, moreover, little is known about what happens to this material and related materials, such as carbon nanotubes when they enter groundwater.

Kurt Pennell (standing) and Younggang Wang flush with success in water transport experiments on nanoparticles (Georgia Tech Photo: Gary Meek)

Kurt Pennell (standing) and Younggang Wang flush with success in water transport experiments on nanoparticles (Georgia Tech Photo: Gary Meek)

The researchers explain that in slightly salty water, clusters of C60 might aggregate and adhere tightly to soil particles or filtration system particles. However, in water contaminated with natural organic compounds or synthetic surfactants, such as detergents and soaps, isolated C60 particles would be stabilized and so be transported further in water.

In some cases, the nanoparticles move very little and you would get complete retention in the soil,” explains Pennell, But in different solution conditions or in the presence of a stabilizing agent, such as a surfactant, they can travel just like water. The movement of these nanoparticles is very sensitive to the solution conditions.

The buckyball, an archetypal nanoparticle

The buckyball, an archetypal nanoparticle

Pennell and his team have published detailed research funded by the US Environmental Protection Agency into the transport and retention of C60 nanoparticles in the journal Environmental Science and Technology.

We want to figure out now what will happen to these nanoparticles and how toxic they will be in the environment, says Pennell. The team hopes to build up a mechanistic model of what makes nanoparticles flow well in certain conditions and aggregate in others. When we look at real soils with finer particles, we will expect to see more retention, he says.

For municipal drinking water filtration, the sensitivity to solution characteristics means local conditions may play a key role. Under most conditions, you should be able to remove nanoparticles from the water, he adds, But you will have to be careful if the nanoparticles are stabilized by a natural surfactant or humic acid. If those are present in the water, the nanoparticles could go right through.

Further reading

Environ. Sci. Tech., 2008, in press
http://dx.doi.org/10.1021/es800128m

Dr. Kurt D. Pennell
http://people.ce.gatech.edu/~kp48/

Nanotech threat to your safety
https://www.sciencebase.com/science-blog/nanotech-threat-to-your-safety.html

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nanotechnology
fullerenes

Buckyball Necklace

A new type of polymer material made by stringing together the tiny football-shaped fullerene molecules has been synthesised by chemists in Spain. Under the microscope, the material resembles a string of pearls.

It’s almost fifteen years since, as deputy editor on the RSC journal Chemical Communications, I assisted in the publication of Sir Harry Kroto’s seminal paper on the discovery of buckminsterfullerene. In that time, these all-carbon molecules with their spherical, or more precisely truncated icosahedral structure have hit the science headlines many times and have even raised questions in the House of Lords.

Building blocks of a buckypearl necklace (Credit: Angewandte/Martin)

Building blocks of a buckypearl necklace (Credit: Angewandte/Martin)

Unlike their cylindrical counterparts the carbon nanotubes, fullerenes are yet to reveal their killer application. Recently, Nazario Martín and his colleagues at the University of Madrid, have developed a novel electroactive fullerene receptor molecule, a molecule that specifically recognizes and binds to the surfaces of fullerenes.

Now, the team has taken that research one step further to make hybrid molecules chimeras that bring together the fullerene receptors with fullerene themselves to form linear aggregates of molecules lined up like a string of pearls. Atomic force microscopy reveals that some strings have up to 35 buckypearls

Nazario Martin

Nazario Martin

The researchers describe the recognition of fullerenes by the receptor as involving a pincer-like grasp in which aromatic carbon rings on the pincer latch on to sections of the fullerene surface. More technically, the new buckyball receptor is a pi-extended analogue of tetrathiafulvalene (TTF),2-[9-(1, 3-dithiol-2-ylidene)anthracen-10(9H)-ylidene]-1,3-dithiole (exTTF). The complete receptor is composed of two exTTF units connected through an isophthalic diester spacer. It is the resulting large and concave aromatic surface of the exTTF units that act as the recognition motifs for the convex surface of the fullerene (C60) molecule.

This recognition process leads to a strong bond between the pincer and the pinched. Numerous analytical techniques were used to demonstrate the chemical structure of the resulting materials, including nuclear magnetic resonance spectroscopy, mass spectrometry, UV-Visible spectroscopy, and atomic force microscopy.

The researchers also point out that under certain conditions, it is possible for electrons to transfer from one complementary system to the other, which could endow the new materials with interesting electromagnetic properties for optoelectronic applications.

Further reading

Angew. Chem. Int. Edn
http://dx.doi.org/10.1002/anie.200703049

Nazario Martín Group homepage
http://www.ucm.es/info/fullerene/

Suggested searches

fullerenes