Carbon nano-tube

schematic representation of the structure of a carbon nano-tube

of carbon nano-tubes, also CNT (carbon of nanotubes), are microscopically small tubular things (molecular nano-tubes) from carbon.

Their walls exist like those the Fullerene or like the levels of the graphite only out Carbon, whereby the carbon atoms take a honeycombed structure with hexagons and in each case three connection partners (given by the FR 2 - hybridizing). The diameter of the tubes lies usually within the range of 1-50 nanometers (Nm), but it became also tubeswith only 0.4 Nm diameters manufactured.Lengths of several millimeters for individual tubes and up to 20 centimeters for tube bundles were already reached [1].

One differentiates in and mehrwandigen between, between open or closed tubes (with a cover, thata cutout from a filler structure has) and between empty and filled tubes (for example with silver, liquid lead, or noble gases).

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depending upon detail of the structure is the electrical conductivity within thatTube metallically or semiconducting; there is also carbon tubes well-known, which are superconducting at low temperatures. Transistors and simple circuits with the semiconducting carbon nano-tubes were already manufactured. The research looks for now for possibilities, complex circuits out different carbon nano-tubes purposefullyto manufacture.

The mechanical characteristics of carbon nano-tubes are outstanding:
CNTs have a density of 1,3-1,4 <math> {\ rm g/cm} ^3< /math> and a tensile strength of 45 billion Pascal. Steel has a density of at least. 7,8 <math> {\ rm g/cm} ^3< /math> and a maximum tensile strength of 2 billionPascal. From it results for individual CNTs computationally at least. 135-mal better relationship from tensile strength to density than for steel.

For the electronic industry above all acceptable current load and the heat conductivity are interesting: First is appropriate roughly for 1000-mal more highly than with Kupferdrähten,the latter is almost twice as high at room temperature with 6000 W/m*K as from diamond (3320 W/m*K). Since CNTs can be also semiconductors, protruding transistors can be manufactured, the higher tensions and temperatures - and thus higher clock frequencies from them- when silicon transistors bear. First experimental, functional transistors from CNTs were already manufactured.

health effects

so far not yet sufficiently investigated are health effects, those in connection with carbon nano-tubes possibly. to arise could. An argumentation points to the oblongspatial structure, which resembles from asbestos. Studies, which are based on bioassays, show opposite results, approximately regarding inflammation reactions in the lung fabric of mice. Thus mice in the attempt CNTs with a concentration were injected, the 10.000-mal more highly thanin the environment the one which can be expected was, without recognizable inflammation reaction. Despite the continuous controversy, which begins to reach the public to limited extent also, at the beginning of 2004 the industrial magnate production of CNTs started.

applications of the nano-tubes

so farare up to few niches still no applications for nano-tubes in the industriellen production and/or in products at the market. In the universitären and industriellen research different applications are developed:

transistors from nano-tubes

thereby the semiconducting characteristic becomesused by CNTs. At each end of the tube be an electrode (SOURCE/drain), around the tube is arranged the gate electrode of the transistor. With same in principle function mode as a MOSFET - transistor expects one better performance.

nano-tube memory

By CNTs non volatile memory can be realized. The nano-tubes between two electrodes are arranged. An electrical field between the two electrodes can the nano-tube be pulled together or stretched lasting. In the stretched condition it places an electrical contactto a substrate electrode and makes possible so a current flow. Lab tests show switching times within the range of SRAM - speeds. (see also: Web left)

apart from this memory, with which the nano-tube realizes the effect principle, also the employment of nano-tube transistors and realization becomes thatCapacity with conventional DRAMs by CNTs investigates.

nano-tubes for displays

of fields of parallel set up nano-tubes can be manufactured, and those suitability in principle as construction unit for flat and luminescent screens was already demonstrated: The sharp points servethe nano-tubes as source for electrons by field mission (tiny electron gun, cold cathode already with relatively small tensions), which are accelerated as with the conventional television set against a fluorescent screen.

nano-tubes for measuring technique

CNTs become also as points for more efficient raster tunnel microscopes(RTM) uses, which are available in the trade already and which improve dissolution of the RTM around the factor 10.

nano-tubes for the improvement of plastics

of nano-tubes are mixed with conventional plastic. Thus the mechanical characteristics of the plastics become strongimproved. In addition it is possible to manufacture electrically leading plastics.

further applications

by combination of two carbon nano-tubes with different electrical characteristics can be manufactured diodes.

Whole bundles of tubes were already converted to threads or mats, those as materialto be used are. Bundles of nano-tubes, which are electrically loaded in an electrolyte, can work also as an actuator. In the semiconductor technology becomes also the employment of nano-tubes as metallic connection, e.g. in the form of vertical contacts, investigates, over thereby electrical migration problems to go around.

By the combination of two nano-tubes differently diameter and with different electrical characteristics diodes can be created. One hopes to be able to make so later whole computers of circuits of nano-tubes.

A further area of application is space travel: Space elevators are at ropesleave the earth from nano-tubes.

In addition Fujitsu works at present on radiator boxes, which consist of nano-tubes. Fujitsu would like to use the new radiator boxes firstonce for its GSM Basisstationen. In the future the nano-tubes could be used in addition, as CCU radiators.

structurethe nano-tubes

are derived designation pattern

Nanotubes of carbon nano-tubes from the carbon levels of the graphite , which are rolled up to a tube: The carbon atoms form a honeycombed structure with hexagons and in each case three connection partners. Tubes with ideally hexagonal structure have a uniform thicknessand are linear; in addition, broken or itself is possible narrowing tubes, which contain five-angular carbon rings. Depending on, like the honeycomb net of the graphite to the tube (“straight” or “diagonally”), develop helical (screw-like wound) and also not mirror-symmetric, that are rolledchirale structures are called up. In the literature for the distinction the pair of indices (n, m) is used and differentiated between 3 classes. These hot in English armchair (with (n, n), achiral, not helically), zig zag ((n, 0), achiral, helically) and chiral((n, m), chiral, helically). The first two names refer to the form of the line, which results, if one follows the CC connections along the extent.

With the pair of indices it can be also determined whether the tube is a semiconductor.If <math> \ frac {Nm} {3}< /math> a whole number is, is metallically, otherwise semiconducting the carbon nano-tube. Thus a third of all conceivable tubes is metallic, among which e.g. also all rank armchair.

Entdeckung und Herstellung

Mehrwandige Kohlenstoffnanoröhren wurden 1991 von Professor Sumio Iijima with an electron microscope coincidentally discovers. It had produced an arc discharge between carbon electrodes. 1993 was discovered the einwandigen carbon nano-tubes. They can be likewise manufactured in the arc, if one adds catalysts. The Nobelpreisträger smelling pool of broadcasting corporations E. Smalley published 1996Laser procedure for the production of einwandigen carbon nano-tubes. Graphite with a laser is cleared away (“evaporates”). In addition nano-tubes develop with the catalytic decomposition of hydrocarbons; with this procedure (English. , Briefly CVD) one knows Chemical vapor deposition whole fields ofto a large extent parallel tubes on a document to grow up leave. Everyone of the three procedures (arc, laser, gas decomposition) is in the meantime so far developed that thereby larger quantities can be manufactured evenly (in diameter, length, defects, Mehrwandigkeit) CNTs. One can today finished carbon nano-tubes ofbuy different manufacturers in gram quantities.

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