 |
Complete the text about graphene with the phrases below.
|
|
|
|
APPLICATIONS. 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. (What are the applications of graphene due to its unique properties? )
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.
(http: //www. nobelprize. org/nobel_prizes/physics/laureates/2010/advanced. html)
Complete the text about graphene with the phrases below.
Graphene is a two-dimensional form of crystalline carbon either a single layer of carbon atoms, 1)……………………., or several coupled layers of this honeycomb structure. The word graphene, when used without specifying the form (e. g., bilayer graphene, multilayer graphene), 2)………………… Graphene is a parent form of all graphitic structures of carbon: graphite 3)………………..; 4)……………, which may be represented as scrolls of graphene; and buckyballs, 5)…………………
The theoretical study of graphene was started in 1947 6)…………… as a first step to understanding the electronic structure of graphite. The term graphene was introduced by chemists Hanns-Peter Boehm, Ralph Setton, and Eberhard Stumpp in 1986 7) …………………………..
In 2004 University of Manchester physicists Konstantin Novoselov and Andre Geim and colleagues isolated single-layer graphene 8)…………………….. Their “scotch-tape method” used adhesive tape to remove the top layers from a sample of graphite and then apply the layers to a substrate material. When the tape was removed, some graphene remained on the substrate in single-layer form. The achievement of the Manchester group was not only to isolate graphene flakes but also to study their physical properties. In particular, they demonstrated that electrons in graphene have a very high mobility, 9)………………. In 2010 Geim and Novoselov were awarded the Nobel Prize for Physics for their work.
|
|
|
In these first experiments, the substrate for graphene was 10)………………… It turned out that single-layer graphene created an optical contrast with the silicon dioxide that was strong enough to make the graphene visible under a standard optical microscope. This visibility has two causes. First, electrons in graphene interact very strongly with photons in the visible light frequencies, 11)…………………….. Second, the optical contrast is strongly enhanced by interference phenomena in the silicon dioxide layer; these are the same phenomena that 12)…………………….. The basic electronic structure of graphene and, as a consequence, its electric properties are very peculiar. 13)………………., one can create either electron or hole conductivity in graphene that is similar to the conductivity created in semiconductors. However, in most semiconductors there are certain energy levels where electrons and holes do not have allowed quantum states, and, because electrons and holes cannot occupy these levels, for certain gate voltages and types of chemical doping, 14)…………….. Graphene, on the other hand, does not have an insulator state, and conductivity remains finite at any doping, including zero doping. 15) …………... is a striking difference between graphene and conventional semiconductors. Electron and hole states in graphene relevant for charge-carrier transport are similar 16)……………………. The honeycomb lattice of graphene actually consists of two sublattices, designated A and B, such that each atom in sublattice A is surrounded by three atoms of sublattice B and vice versa. This simple geometrical arrangement leads to the electrons and holes in graphene having an unusual degree of internal freedom, usually called pseudospin. In fact, making the analogy more complete, pseudospin mimics the spin, 17)………………… Within this analogy, electrons and holes in graphene play the same role as particles and antiparticles (e. g., electrons and positrons) in quantum electrodynamics. At the same time, however, the velocity of the electrons and holes is only about 1/300 the speed of light. This makes graphene a test bed for high-energy physics: some quantum relativistic effects 18)…………………… have clear analogs in the physics of electrons and holes in graphene, which can be measured and studied more easily because of their lower velocity. An example is the Klein paradox, in which ultra-relativistic quantum particles, contrary to intuition, 19) …………………… Thus, graphene provides a bridge between material science and some areas of fundamental physics, such as relativistic quantum mechanics.
There is another reason why graphene is of special interest to fundamental science: it is the first and simplest example of a two-dimensional crystal—that is, 20) ………………
Modern electronics (e. g., integrated circuits in computer chips) are basically two-dimensional because they use mainly the surface of semiconducting materials. Therefore, graphene and other two-dimensional materials are considered very promising for such applications. Using graphene, for example, it should be possible to make transistors and other electronic devices 21)………………. Besides, graphene, being electrically conducting, transparent, strong, and flexible, 22)……………………. Graphene also has very high thermal conductivity and, therefore, could be used 23)……………….
|
|
|
It still, however, remains difficult to say which applications would prove to be the most popular. Progress depends not only on the basic science but also 24)……. since obtaining graphene by exfoliation is too expensive for mass production.
WRITTEN BY:
Mikhail I. Katsnelson
Britannica. com
a. using an extremely simple method of exfoliation from graphite
b. create rainbow colours in thin films such as soap film or oil on water
c. which is a three-dimensional crystal consisting of relatively weakly coupled graphene layers
d. the semiconductor acts as an insulator
e. forming a honeycomb (hexagonal) lattice
f. that are hardly reachable in experiments with subatomic particles using particle accelerators
g. absorbing about 2. 3 percent of the light’s intensity per atomic layer
h. as a combination of the word graphite, referring to carbon in its ordered crystalline form, and the suffix -ene, referring to polycyclic atomatic hydrocarbons in which the carbon atoms form hexagonal, or six-sided, ring structures.
i. to the states of ultra-relativistic quantum particles
j. penetrate easily through very high and broad energy barriers
k. silicon naturally covered with a thin transparent layer of silicon dioxide
l. spherical molecules made from graphene with some hexagonal rings replaced by pentagonal rings
m. may be a prospective material to use in touch screens
n. on the development of new ways to produce graphene on an industrial scale
o. usually refers to single-layer graphene
p. or internal angular momentum of subatomic particles
q. to remove heat from electronic circuits
r. by applying a gate voltage or using chemical doping by adsorbed atoms and molecules
s. nanotubes
t. existence of this minimal conductivity for the undoped case
u. much thinner than devices made of traditional materials
v. by physicist Philip R. Wallace
w. a solid material that contains just a single layer of atoms arranged in an ordered pattern.
x. which means that graphene could possibly be used in electronic applications
|
|
|
