Materials Today in collaboration with Thermo Scientific are offering a short 45 minute webinar to introduce how Raman spectroscopy can help explore properties of graphene materials.

The presentation will include an overview of several significant applications of Raman spectroscopy:

• measuring thickness
• monitoring chemical properties
• monitoring physical properties

This webinar will be helpful for anyone who is either just starting working with graphene materials or wanting to learn more about Raman spectroscopy.

When: July 28 2011, 16h00 (BST) / 11h00 (EST)
Register here

• Synthesis and selection methods
• Electronic, optical and mechanical properties of carbon nanotubes, graphene and related devices
• Functionnalization, dispersion, processing
• Metrology and standardization
• Composites and materials science
• Other applications and industrial issues

Andre Geim and his colleague (and former postdoctoral assistant) Konstantin Novoselov first produced graphene in 2004 by repeatedly peeling away graphite strips with adhesive tape to isolate a single atomic plane. They analyzed its strength, transparency, and conductive properties in a paper for Science the same year.

It’s a worthy Nobel, for the simple reason that graphene may be one of the most promising and versatile materials ever discovered. It could hold the key to everything from super small computers to high-capacity batteries. Graphene properties are attractive to materials scientists and electrical engineers for a whole host of reasons, not least of which is the fact that it might be possible to build circuits that are smaller and faster than what you can build in silicon.

Imagine “crystals one atom or molecule thick, essentially two-dimensional planes of atoms shaved from conventional crystals,” said Nobel winner Andre Geim. “Graphene is stronger and stiffer than diamond, yet can be stretched by a quarter of its length, like rubber. Its surface area is the largest known for its weight.” Here are some applications of graphene.

Super-Small Transistors

The Manchester team in 2008 created a 1-nanometer graphene transistor, only one atom thick and 10 atoms across. This is not only smaller than the smallest possible silicon transistor; Novoselov claimed that it could very well represent the absolute physical limit of Moore’s Law governing the shrinking size and growing speed of computer processors.

“It’s about the smallest you can get,” Novoselov said. “From the point of view of physics, graphene is a goldmine. You can study it for ages.”

Super-Dense Data Storage

Researchers around the world have already put graphene to work. A Rice University team In 2008 created a new type of graphene-based, flash-like storage memory, more dense and less lossy than any existing storage technology. Two University of South Florida researchers earlier this year reported techniques to enhance and direct its conductivity by creating wire-like defects to send current flowing through graphene strips.

Energy Storage

The energy applications of graphene are also extraordinarily rich. Texas’s Graphene Energy is using the film to create new ultracapacitators to store and transmit electrical power. Companies currently using carbon nanotubes to create wearable electronics are beginning to switch to graphene, which is thinner and potentially less expensive to produce. Much of the emerging research is devoted to devising more ways to produce graphene quickly, cheaply and in high quantities.

Photonics: Solar Cells and Flexible Touchscreens

A Cambridge University team argues in a paper of Nature Photonics that the true potential of graphene lies in its ability to conduct light as well as electricity. Strong, flexible, light-sensitive graphene could improve the efficiency of solar cells and LEDs, as well as aiding in the production of next-generation devices like flexible touch screens, photodetectors and ultrafast lasers. In particular, graphene could replace rare and expensive metals like platinum and indium, performing the same tasks with greater efficiency at a fraction of the cost.

High-Energy Particle Physics

In pure science, according to Geim, graphene “makes possible experiments with high-speed quantum particles that researchers at CERN near Geneva, Switzerland, can only dream of.” Because graphene is effectively only two-dimensional, electrons can move through its lattice structure with virtually no resistance. In fact, they behave like Heisenberg’s relative particles, with an effective resting mass of zero.

It’s slightly more complicated than this, but here’s a quick and dirty explanation. To have mass in the traditional sense, objects need to have volume; electrons squeezed through two-dimensional graphene have neither. In other words, the same properties that makes graphene such an efficient medium for storing and transmitting energy also demonstrate something fundamental about the nature of the subatomic universe.

Source: original article

Invited speakers

• Pulickel Ajayan (Rice University, USA)
• Eva Andrei (Rutgers, USA)
• Sarah Burke (British Columbia, Canada)
• Millie Dresselhaus (MIT, USA)
• Toshiaki Enoki (Tokyo Inst. of Tech., Japan)
• Klaus Ensslin (ETH, Switzerland)
• Andrea C. Ferrari (Cambridge, UK)
• Andre Geim (Manchester, UK) ***
• Paco Guinea (Madrid, Spain)
• Tony Heinz (Columbia, USA)
• Pablo Jarillo-Herrero (MIT, USA) ***
• Francesco Mauri (Paris, France)
• Kostya Novoselov (Manchester, UK)
• Francois M. Peeters (Antwerpen, Belgium)
• Alain Penicaud (Bordeaux, France)
• Vitor Manuel Pereira (Boston University, USA)
• Nuno Peres (Minho, Portugal)
• Rod Ruoff (Austin, USA)
• Lieven Vandersypen (Delft, Netherlands) ***
• Amir Yacoby (Harvard, USA) ***

*** To be confirmed

Please visit the Conference Web site for more information. Registration and abstract submission are already open.

Organizers

Marcos A. Pimenta
Antonio H. Castro Neto
Luiz Gustavo Cancado

The technique works with multiple forms of graphene and is poised to become an important finding for the development of graphene electronics. The research is published in the Science journal. Scientists who work with nanocircuits are enthusiastic about graphene because electrons meet with less resistance when they travel along graphene compared to silicon and because today’s silicon transistors are nearly as small as allowed by the laws of physics. Graphene also has the edge due to its thickness – it’s a carbon sheet that is a single atom thick. While graphene nanoelectronics could be faster and consume less power than silicon, no one knew how to produce graphene nanostructures on such a reproducible or scalable method. That is until now.

“We’ve shown that by locally heating insulating graphene oxide, both the flakes and epitaxial varieties, with an atomic force microscope tip, we can write nanowires with dimensions down to 12 nanometers. And we can tune their electronic properties to be up to four orders of magnitude more conductive. We’ve seen no sign of tip wear or sample tearing,” said Elisa Riedo, associate professor in the School of Physics at the Georgia Institute of Technology.

On the macroscopic scale, the conductivity of graphene oxide can be changed from an insulating material to a more conductive graphene-like material using large furnaces. Now, the research team used TCNL to increase the temperature of reduced graphene oxide at the nanoscale, so they can draw graphene-like nanocircuits. They found that when it reached 130 degrees Celsius, the reduced graphene oxide began to become more conductive.

“So the beauty of this is that we’ve devised a simple, robust and reproducible technique that enables us to change an insulating sample into a conducting nanowire. These properties are the hallmark of a productive technology,” said Paul Sheehan, head of the Surface Nanoscience and Sensor Technology Section at the Naval Research Laboratory in Washington, D.C.

The research team tested two types of graphene oxide – one made from silicon carbide, the other with graphite powder. “I think there are three things about this study that make it stand out,” said William P. King, associate professor in the Mechanical Science and Engineering department at the University of Illinois at Urbana-Champaign. “First, is that the entire process happens in one step. You go from insulating graphene oxide to a functional electronic material by simply applying a nano-heater.  Second, we think that any type of graphene will behave this way. Third, the writing is an extremely fast technique. These nanostructures can be synthesized at such a high rate that the approach could be very useful for engineers who want to make nanocircuits.”

Source: original article

This growing interest, triggered by the numerous potential applications of graphene in future nanotechnology, motivates the creation of an interdisciplinary school on graphene. The school is aimed at PhD students, post-doctoral and young researchers in the first instance. The School is taking place in Cargèse, France from October 12 to October 22, 2010 at the Institut d’Etudes Scientifiques de Cargèse.

The school, initiated by the GdR-I «Graphene and Nanotubes», will deal with properties and characterization of monolayers and multilayers of graphene and graphene-based nano-objects, from the points of views of physicists, chemists and material scientists. Both fundamental and applied aspects will be considered. It will offer participants both background lectures, essential for the interdisciplinary approach that is proposed, and specialized courses, which will include the most recent developments in the field. Practical training on numerical simulations and experimentation such scanning tunnelling microscopy will be organized. The lecturers of the school are researchers known for their pedagogic skills and internationally recognized for their expertise in the field of graphene. The participants will be encouraged to present their own work (also in adjacent fields) during poster sessions.

Detailed information about the GDR-I and the School is available on their website.

The research team that conducted the new investigation features physicists from the US National Institutes of Standards and Technology (NIST) and the Georgia Institute of Technology (Georgia Tech). The experts say that the moire patterns can also be used on multiple grids or atom arrays, not only on two. They add that using “atomic moire interferometry” can also help scientists determine the rotational orientation of the graphene sheets used in a variety of technological applications. Their work is published in the Physical Review B journal.

Given that one of the most complex areas of graphene research today is figuring out how the material changes its properties when stacked in multiple layers, being able to obtain a map of the strains that develop within it is extremely important. The electronic and transport properties of the single-atom-thick carbon compound can now be analyzed and determined with a much higher degree of accuracy than ever before, the NIST/Georgia Tech team says. Due to its revolutionary semiconducting properties, graphene is now hailed as the material of the future, at least in the electronics industry.

For the new experiments, Georgia Tech experts developed sheets of graphene on a silicon carbide substrate. After the samples were transferred at NIST, scientists here used a custom-built scanning tunnelling microscope (STM) to look at the graphene samples. The high resolve power on this instrument allows the experts to peer deep within the sample, past the topmost layer. It was through this method that the moire patterns became visible. Distinguishing them is fairly easy because of the hexagonal arrangement of carbon atoms in graphene. Any layers that are misplaced on top of others are immediately clear.

Source: original article

Layers of h-BN a single atom thick have the same lattice structure as graphene, but electrically the materials are at opposite ends of the spectrum: h-BN is an insulator, whereas graphene, the single-atom-layer form of carbon, is highly conductive. The ability to assemble them into a single lattice could lead to a rich variety of 2-D structures with electric properties ranging from metallic conductor to semiconductor to insulator.

Because graphene is a conductor and h-BN is an insulator, the proportion of one to the other determines how well this new material conducts electrons. Lijie Ci and Li Song, both postdoctoral research scientists, found that by putting down domains of h-BN and carbon via chemical vapor deposition (CVD), they were able to control the ratio of materials in the film that resulted. The ratio of non-conductive boron nitride to highly conductive graphene determines the electrical properties of the new material.

Ci and Song are primary authors of a paper about the work that appeared in the online edition of Nature Materials. “From a graphene perspective, it now gives us an opportunity to explore band-gap engineering in two-dimensional layered systems,” Ajayan, their research director, said. The whole phase diagram of boron, carbon and nitrogen is fascinating, unexplored and offers a great playground for materials scientists.

“This is only the first instance showing that these structures can indeed be grown in 2-D like graphene,” Ajayan said. “I think the whole new field will be exciting for basic physics and electro-optical applications.” Graphene has been the subject of intense study in recent years for its high conductivity and the possibility of manipulating it on scales that go well below the theoretical limits for silicon circuitry. A layer of graphene is a hexagonal lattice of carbon atoms. In bulk, it’s called graphite, the stuff of pencil lead. Graphene was first isolated in 2004 by British scientists who used Scotch tape to pull single-atom layers from graphite.

“Graphene is a very hot material right now,” said Song, who had teamed with Ci to investigate doping graphene with various materials to determine its semiconducting properties. Knowing that both boron and nitrogen had already been used in doping bulk graphite, they decided to try cooking it via CVD onto a copper base. Structurally, h-BN is the same as graphene, a hexagon-shaped lattice of carbon atoms that looks like chicken wire. Ci and Song found that through CVD, graphene and h-BN merged into a single atomic sheet, with pools of h-BN breaking up the carbon matrix.

The critical factor for electronic materials is the band gap, which must be tuned in a controlled manner for applications. Graphene is a zero-gap material, but ways have been proposed to tailor this gap by patterning it into nanoscale strips and doping it with other elements. A one-atom-thick layer of a graphene and boron nitride hybrid is visible to the naked eye when deposited on a glass slide. Researchers are able to achieve fine control of the new material’s conductivity.

Ci and Song took a different approach through CVD, controlling the ratio of carbon to h-BN over a large, useful range. It remains challenging to produce single layers of the hybrid material, as most lab-grown films contain two or three layers. The researchers also cannot yet control the placement of h-BN pools in a single sheet or the rotational angles between layers – but they’re working on it.

In fact, having multiple layers of the hybrid at various angles creates even more possibilities, they said. “For pure graphene, this rotation will affect the electronic properties,” said Ci. The researchers are considering producing these materials on industrial-scale wafers. Graphene sheets several inches wide have already been synthesized in other labs, Ci said. And because graphene can be lithographically patterned and cut into shapes, the new material has great potential to be fabricated into useful devices with controllable electrical properties.

Source: original article