Sunday, October 24, 2010

Graphene - An Extrordinary Carbon Form

Hi!!!!! Friends. How are you all? Hope well.
Friends actually in the last  post for a change i have posted top songs. But this time i'm back with a powerful concept that is a carbon form and has awarded the Nobel Prize in Physics for 2010 to Andre Geim and Konstantin Novoselov, both of the University of Manchester, "for groundbreaking experiments regarding the two-dimensional material graphene." It is the hardest compound now. It is Graphene

So what is Graphene and what is its importance?
For above question read the following article. Here we go..........................

What is graphene?

Graphene is a member of the class of 2-dimensional materials discovered by Professor Andre Geim's research group at the University of Manchester It consists of a hexagonal array of sp2-bonded carbon atoms, just like those found in bulk graphite. 2D materials display very interesting properties, and are fundamentally different from the 3D materials we encounter everyday. The discovery of 2D materials means that scientists now have access to materials of all dimensionalities, including 0D (quantum dots, atoms) and 1D (nanowires, carbon nanotubes).

 Why haven't we discovered these materials until now?

Largely because we haven't looked. There are theories which show that graphene should not be able to exist without being destroyed by thermal fluctuations. These fluctuations should cause the crystal to melt. Workers who tried to create atomically thin films of other materials in the past found that the films were unstable and tended to separate and 'clump up' rather than form perfect layers.

In fact, anyone who has ever written with a pencil has probably created graphene flakes. The graphite in a pencil lead separates into sheets when rubbed across paper, and the chances are that one of these sheets was only a single layer thick.

Consider the humble pencil. It may come as a surprise to learn that the now common writing instrument at one time topped the list of must-have, high-tech gadgets. In fact, the simple pencil was once even banned from export as a strategic military asset. But what is probably more unexpected is the news that every time someone scribes a line with a pencil, the resulting mark includes bits of the hottest new material in physics and nanotechnology: graphene.

Molecular Chicken Wire
Graphite, the fullerenes and graphene share the same basic structural arrangement of their constituent atoms. Each structure begins with six carbon atoms, tightly bound together chemically in the shape of a regular hexagon—what chemists call a benzene ring.At the next level of organization is graphene itself, a large assembly of benzene rings linked in a sheet of hexagons that resembles chicken wire.

Exceptional Exception
Two features of graphene make it an exceptional material. First, despite the relatively crude ways it is still being made, graphene exhibits remarkably high quality—resulting from a combination of the purity of its carbon content and the orderliness of the lattice into which its carbon atoms are arranged. Investigators have so far failed to find a single atomic defect in graphene—say, a vacancy at some atomic position in the lattice or an atom out of place. That perfect crystalline order seems to stem from the strong yet highly flexible interatomic bonds, which create a substance harder than diamond yet allow the planes to bend when mechanical force is applied. The flexibility enables the structure to accommodate a good deal of deformation before its atoms must reshuffle to adjust to the strain.

The quality of its crystal lattice is also responsible for the remarkably high electrical conductivity of graphene. Its electrons can travel without being scattered off course by lattice imperfections and foreign atoms. Even the jostling from the surrounding carbon atoms, which electrons in graphene must endure at room temperature, is relatively small because of the high strength of the interatomic bonds.

The second exceptional feature of graphene is that its conduction electrons, besides traveling largely unimpeded through the lattice, move much faster and as if they had far less mass than do the electrons that wander about through ordinary metals and semiconductors. Indeed, the electrons in graphene—perhaps “electric charge carriers” is a more appropriate term—are curious creatures that live in the weird world where rules analogous to those of relativistic quantum mechanics play an important role. That kind of interaction inside a solid, so far as anyone knows, is unique to graphene. Thanks to this novel material from a pencil, relativistic quantum mechanics is no longer confined to cosmology or high-energy physics; it has now entered the laboratory.

A carbon atom has four valence electrons; in graphene (and in graphite, a stack of graphene layers), three electrons bond in a plane with their neighbors to form a strong hexagonal pattern, like chicken-wire. The fourth electron sticks up out of the plane and is free to hop from one atom to the next. The latter pi-bond electrons act as if they have no mass at all, like photons. They can move at almost one percent of the speed of light.

Graphene under strain creates gigantic pseudo-magnetic fields 
Graphene, the extraordinary form of carbon that consists of a single layer of carbon atoms, has produced another in a long list of experimental surprises. In the current issue of the journal Science, a multi-institutional team of researchers headed by Michael Crommie,  reports the creation of pseudo-magnetic fields far stronger than the strongest magnetic fields ever sustained in a laboratory – just by putting the right kind of strain onto a patch of graphene.

"We have shown experimentally that when graphene is stretched to form nanobubbles on a platinum substrate, electrons behave as if they were subject to magnetic fields in excess of 300 tesla, even though no magnetic field has actually been applied," says Crommie. "This is a completely new physical effect that has no counterpart in any other condensed matter system."

Crommie notes that "for over 100 years people have been sticking materials into magnetic fields to see how the electrons behave, but it's impossible to sustain tremendously strong magnetic fields in a laboratory setting." The current record is 85 tesla for a field that lasts only thousandths of a second. When stronger fields are created, the magnets blow themselves apart.

What kind of uses does graphene have?

Graphene can be used for many different purposes including:
Graphene can be used to make excellent transistors. It is so thin we can easily control whether or not it conducts by applying an electric field. We would like to be able to do this with metals, but we cannot make metal films thin enough to affect their conducting state in this way. Electrons in graphene also travel ballistically over sub-micron distances. As a result, graphene-based transistors can run at higher frequencies and more efficiently that the silicon transistors we use now. At the present moment we have no way to produce entire integrated circuits from these transistors since we are limited by the size of graphenes we can produce.

Gas Sensors
Gas molecules that land on graphene affect its electronic properties in a measurable way - in fact, we have measured the effect of a single molecule associating with a graphene. This means that we can create gas sensors which are sensitive to a single atom or molecule!

Support Membranes for Transmission Electron Microscopy
Graphene is effectively the thinnest material that we can make out of atoms. Suprisingly it is also very strong, thanks to a lack of crystal boundaries to break along and very strong bonds between carbon atoms (Carbon nanotubes are made from rolled up graphene, and it has been suggested that cabling made from nanotubes would be strong enough to create an elevator into space!). As a result we can use it to hold micro- and nanoscopic objects we wish to look at in an electron microscope (e.g. DNA, nanoparticles) in a similar way we use glass slides in an optical microscope. Graphene is the perfect material for this job as it is made only of carbon, it is very thin so will not interfere with the pictures taken as much as other materials, and has a very simple crystal structure so can easily be eliminated from diffraction patterns.

Inert Coatings
Graphene is resistant to attack by many powerful acids and alkalis such as hydrofluoric acid and ammonia, so one day could be used to give objects an atomically thin protective coating which would provide protection against these agents.

Single molecule gas detection
Graphene makes an excellent sensor due to its 2D structure. The fact that its entire volume is exposed to its surrounding makes it very efficient to detect adsorbed molecules. Molecule detection is indirect: as a gas molecule adsorbs to the surface of graphene, the location of absorption experiences a local change in electrical resistance. While this effect occurs in other materials, graphene is superior due to its high electrical conductivity (even when few carriers are present) and low noise which makes this change in resistance detectable.

Integrated circuits
Graphene has the ideal properties to be an excellent component of integrated circuits. Graphene has a high carrier mobility, as well as low noise, allowing it to be used as the channel in a FET. The issue is that single sheets of graphene are hard to produce, and even harder to make on top of an appropriate substrate. Researchers are looking into methods of transferring single graphene sheets from their source of origin (mechanical exfoliation on SiO2 / Si or thermal graphitization of a SiC surface) onto a target substrate of interest. In 2008, the smallest transistor so far, one atom thick, 10 atoms wide was made of graphene.

Transparent conducting electrodes
Graphene's high electrical conductivity and high optical transparency make it a candidate for transparent conducting electrodes, required for such applications as touchscreens, liquid crystal displays, organic photovoltaic cells, and organic light-emitting diodes. In particular, graphene's mechanical strength and flexibility are advantageous compared to indium tin oxide, which is brittle, and graphene films may be deposited from solution over large areas.

Although it will likely be many years before we see any of these applications fully realised, the discovery of graphene has provided an unparalleled opportunity for scientists to investigate these possibilities.
So friends this what i want to post. I hope you will like it. This was there in mind from few days.
It is not to surprise if world bans usage of pencil. We can watch TV in a paper thin like structure. Major drawback is that its availability. There is too scarcity for Graphene. Let us all hope that there will have more technological methods in availability of graphene.
okay friends this is time to leave. So bye to all. Thanks for visiting my blog. Hope you all will like this.
Keep smiling. Take care all. Bye.......................

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