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2) Describe your university years using word combinations and phrases from the text
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1) Find additional information about Andre Geim’s scientific career after he defended his PhD thesis (you can find this information in Geim’s Nobel lecture: http: //www. nobelprize. org/nobel_prizes/physics/laureates/2010/geim-lecture. html)
2) Describe your university years using word combinations and phrases from the text
to bring everyone to a particular level, to feel confident enough, to get all the highest marks, despite the pressure, to graduate from the university, to be proud of one’s alma mater, to do one’s utmost, to become an independent researcher, to extract information about smth, prominent scientists, to be quite an exceptional university, challenging problems, to really understand science rather than merely memorize it, to thoroughly enjoy smth, to require understanding of more than one area of physics
Advanced Information
Read the text about graphene and answer the questions
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?
STRUCTURE. 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.
PROPERTIES. 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.
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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.
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.
HISTORY. 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. (what is the background of the research into graphene? )
OBTAINING AND DESCRIBING PROPERTIES. 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. /…/( How unusual was the fiest method of obtaining graphene? )
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