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Read the text about graphene and answer the questions
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1) What is graphene and what is its electronic structure like?
2) Which of graphene’s properties make it indispensable in a great number of applications?
3) Were Andre Geim and Konstantin Novoselov the first to study graphene? In what way did their research turn out to be a breakthrough?
Two-dimensional (2D) crystalline materials have recently been identified and analyzed. The first material in this new class is graphene, a single atomic layer of carbon. This new material has a number of unique properties, which makes it interesting for both fundamental studies and future applications.
The electronic properties of this 2D-material lead to, for instance, an unusual quantum Hall effect. It is a transparent conductor which is one atom thin. It also gives rise to analogies with particle physics, including an exotic type of tunneling which was predicted by the Swedish physicist Oscar Klein.
In addition, graphene has a number of remarkable mechanical and electrical properties. It is substantially stronger than steel, and it is very stretchable. The thermal and electrical conductivity is very high and it can be used as a flexible conductor. /…/
Graphene is a single layer of carbon packed in a hexagonal (honeycomb) lattice, with a carbon-carbon distance of 0.142 nm. It is the first truly two-dimensional crystalline material and it is representative of a whole class of 2D materials including for example single layers of Boron-Nitride (BN) and Molybdenum-disulphide (MoS2), which have both been produced after 2004.
The electronic structure of graphene is rather different from usual three-dimensional materials. Its Fermi surface is characterized by six double cones. In intrinsic (undoped) graphene the Fermi level is situated at the connection points of the cones. Since the density of states of the material is zero at that point, the electrical conductivity of intrinsic graphene is quite low and is of the order of the conductance quantum σ ~ e2 /h; the exact prefactor is still debated. The Fermi level can however be changed by an electric field so that the material becomes either n-doped (with electrons) or p-doped (with holes) depending on the polarity of the applied field. Graphene can also be doped by adsorbing, for example, water or ammonia on its surface. The electrical conductivity for doped graphene is potentially quite high, at room temperature it may even be higher than that of copper.
Close to the Fermi level the dispersion relation for electrons and holes is linear. Since the effective masses are given by the curvature of the energy bands, this corresponds to zero effective mass. The equation describing the excitations in graphene is formally identical to the Dirac equation for massless fermions which travel at a constant speed. The connection points of the cones are therefore called Dirac points. This gives rise to interesting analogies between graphene and particle physics, which are valid for energies up to approximately 1eV, where the dispersion relation starts to be nonlinear. One result of this special dispersion relation, is that the quantum Hall effect becomes unusual in graphene.
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Graphene is practically transparent. In the optical region it absorbs only 2.3% of the light. This number is in fact given by π α, where α is the fine structure constant that sets the strength of the electromagnetic force. In contrast to low temperature 2D systems based on semiconductors, graphene maintains its 2D properties at room temperature. Graphene also has several other interesting properties, which it shares with carbon nanotubes. It is substantially stronger than steel, very stretchable and can be used as a flexible conductor. Its thermal conductivity is much higher than that of silver.
Graphene had already been studied theoretically in 1947 by
P.R. Wallace as a text book example for calculations in solid state physics. He predicted the electronic structure and noted the linear dispersion relation. The wave equation for excitations was written down by J.W. McClure already in 1956, and the similarity to the Dirac equation was discussed by G.W. Semenoff in 1984.
It came as a surprise to the physics community when Andre Geim, Konstantin Novoselov and their collaborators from the University of Manchester (UK), and the Institute for Microelectronics Technology in Chernogolovka (Russia), presented their results on graphene structures. They published their results in October of 2004 in Science. In this paper they described the fabrication, identification and Atomic Force Microscopy (AFM) characterization of graphene. They used a simple but effective mechanical exfoliation method for extracting thin layers of graphite from a graphite crystal with Scotch tape and then transferred these layers to a silicon substrate. This method was first suggested and tried by
R. Ruoff’s group who were, however, not able to identify any monolayers. The Manchester group succeeded by using an optical method with which they were able to identify fragments made up of only a few layers./…/
Graphene has a number of properties which makes it interesting for several different applications. It is an ultimately thin, mechanically very strong, transparent and flexible conductor. Its conductivity can be modified over a large range either by chemical doping or by an electric field. The mobility of graphene is very high which makes the material very interesting for electronic high frequency applications. Recently it has become possible to fabricate large sheets of graphene. Using near-industrial methods, sheets with a width of 70cm have been produced. Since graphene is a transparent conductor it can be used in applications such as touch screens, light panels and solar cells, where it can replace the rather fragile and expensive Indium-Tin-Oxide (ITO). Flexible electronics and gas sensors are other potential applications. The quantum Hall effect in graphene could also possibly contribute to an even more accurate resistance standard in metrology. New types of composite materials based on graphene with great strength and low weight could also become interesting for use in satellites and aircraft.
The development of this new material, opens new exiting possibilities. It is the first crystalline 2D-material and it has unique properties, which makes it interesting both for fundamental science and for future applications. The breakthrough was done by Geim, Novoselov and their co-workers; it was their paper from 2004 which ignited the development. For this they are awarded the Nobel Prize in Physics 2010.
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(http://www.nobelprize.org/nobel_prizes/physics/laureates/2010/advanced.html)
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A Chip Off the Old Block [2]
Sometimes the old gives rise to the new in wonderfully unexpected ways. Such was the case with graphene: an entirely new form of carbon, the world's first 2-dimensional material and the subject of the 2010 Nobel Prize in Physics. This novel wonder material, which offers possibilities ranging from faster computers to new insights into quantum physics, was produced from plain, familiar old graphite, the stuff that fills your pencils. Pencils work because graphite is made from layer upon layer of carbon atoms arranged in sheets a single atom thick; every time you move the pencil across the paper, clumps of these sheets shear off (срезать, скалывать) and are left on the paper. Graphene, which consists of just one of these sheets, can, it turned out, also be sheared off a lump of graphite.
Andre Geim and Konstantin Novoselov, this year's Nobel Laureates, actually isolated Graphene in 2004 in one of their 'Friday evening experiments' where they habitually play with new ideas. They ended up using another familiar material, ordinary sticky tape, to 'exfoliate' a graphite crystal and found that, after several rounds, they were able to peel off the elusive graphene monolayers. Virtually transparent and of atomic thickness, graphene can only be seen under very specific conditions, and coincidentally Geim and Novoselov chose exactly the right substrate to place their flakes on, allowing them to view them in an ordinary microscope. A new research field was born.
Graphene's remarkable strength and extreme conductivity, it is a hundred times stronger than steel and more conductive than copper, result from its hexagonal lattice of carbon atoms permeated by a sea of delocalized electrons. Aside from the insights into fundamental quantum physics they offer, graphene's properties have set the world's material scientists dreaming of, and exploring, a wealth of possible applications. Among the most realistic is its potential use in touch screens where the transparency, strength and conductivity it offers appear to provide a highly desirable combination. Perhaps most immediately enticing (заманчивый) is the vision of further miniaturizing computer chips by using graphene's atomic scale to overcome the size constraints now being encountered with silicon-based components.
Previous results of the Geim lab's playful approach to physics have included levitating live frogs, in a demonstration of the importance of diamagnetism, and the biomimetic nanomaterial known as gecko tape. As Geim himself says, "getting some play during working hours for which you are paid is the best job I can recommend for anyone around!"
(by Adam Smith, Editor-in-Chief, Nobelprize.org)
Unit 11
The Accelerating Expansion of the Universe 
The Nobel Prize in Physics 2011 —
Press Release
October 4, 2011
The Royal Swedish academy of Sciences decided to award the Nobel Prize in Physics for 2011 "for the discovery of the accelerating expansion of the Universe through observations of distant supernovae". The prize is awarded with one half jointly to Saul Perlmutter The Supernova Cosmology Project Lawrence Berkeley National Laboratory and University of California, Berkeley, CA, USA, and the other half jointly to Brian P. Schmidt the High-z Supernova Search Team Australian National University, Weston Creek, Australia, and Adam G. Riess the High-z Supernova Search Team Johns Hopkins University and Space Telescope Science Institute, Baltimore, MD, USA.
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Written in the stars
"Some say the world will end in fire, some say in ice..."
What will be the final destiny of the Universe? Probably it will end in ice, if we are to believe this year's Nobel Laureates in Physics. They have studied several dozen exploding stars, called supernovae, and discovered that the Universe is expanding at an ever-accelerating rate. The discovery came as a complete surprise even to the Laureates themselves.
In 1998, cosmology was shaken at its foundations as two research teams presented their findings. Headed by Saul Perlmutter, one of the teams had set to work in 1988. Brian Schmidt headed another team, launched at the end of 1994, where Adam Riess was to play a crucial role.
The research teams raced to map the Universe by locating the most distant supernovae. More sophisticated telescopes on the ground and in space, as well as more powerful computers and new digital imaging sensors (CCD, Nobel Prize in Physics in 2009), opened the possibility in the 1990s to add more pieces to the cosmological puzzle.
The teams used a particular kind of supernova, called type Ia supernova. It is an explosion of an old compact star that is as heavy as the Sun but as small as the Earth. A single such supernova can emit as much light as a whole galaxy. All in all, the two research teams found over 50 distant supernovae whose light was weaker than expected — this was a sign that the expansion of the Universe was accelerating. The potential pitfalls had been numerous, and the scientists found reassurance in the fact that both groups had reached the same astonishing conclusion.
For almost a century, the Universe has been known to be expanding as a consequence of the Big Bang about 14 billion years ago. However, the discovery that this expansion is accelerating is astounding. If the expansion will continue to speed up the Universe will end in ice.
The acceleration is thought to be driven by dark energy, but what that dark energy is remains an enigma — perhaps the greatest in physics today. What is known is that dark energy constitutes about three quarters of the Universe. Therefore the findings of the 2011 Nobel Laureates in Physics have helped to unveil a Universe that to a large extent is unknown to science. And everything is possible again.
(http://www.nobelprize.org/nobel_prizes/physics/laureates/2011/press.html)
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