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These properties, coupled with the lightness of carbon nanotubes, gives them great potential in applications such as aerospace. The electronic properties of carbon nanotubes are also extraordinary.

MULTI-WALL NANOTUBES

Especially notable is the fact that nanotubes can be metallic or semiconducting depending on their structure. Thus, some nanotubes have conductivities higher than that of copper, while others behave more like silicon. There is great interest in the possibility of constructing nanoscale electronic devices from nanotubes, and some progress is being made in this area.

Carbon nanotube

However, in order to construct a useful device we would need to arrange many thousands of nanotubes in a defined pattern, and we do not yet have the degree of control necessary to achieve this. There are several areas of technology where carbon nanotubes are already being used. These include flat-panel displays, scanning probe microscopes and sensing devices.

The unique properties of carbon nanotubes will undoubtedly lead to many more applications. Nanohorns Single-walled carbon cones with morphologies similar to those of nanotube caps were first prepared by Peter Harris, Edman Tsang and colleagues in click here to see our paper. They were produced by high temperature heat treatments of fullerene soot - click here to see a typical image. Sumio Iijima's group subsequently showed that they could also be produced by laser ablation of graphite, and gave them the name "nanohorns".

This group has demonstrated that nanohorns have remarkable adsorptive and catalytic properties.


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Return to top Nanotube links. Wikipedia's article on carbon nanotubes. A excellent programme called Nanotube Modeler from JCrystal. A compendium of Physical properties of carbon nanotubes by Thomas A. Adams II. Shigeo Maruyama's Nanotube animation gallery. Return to top Nano sites. Return to top Commercial suppliers of carbon nanotubes and related materials. Disclaimer Listing of companies at this site does not imply endorsement of particular companies or products.

Multi-Walled Carbon Nanotubes

Chinese by Down To Five. The exact properties of the oxides, combined with different metals used to make connections, could convert the nanotubes into p- or n-type semiconductors as needed. While this process is more akin to doping an area that happens to contain nanotubes, it was effective at controlling the behavior of individual junctions.

And those metallic nanotubes still lurking in all of this? The researchers just left them in place and did a workaround in chip design. While functional units of a chip do things like add two numbers, these units are built of collections of smaller logic gates that perform simple functions: NOT flips the value of a bit, logical AND takes a value of 1 if both of its input values are 1, and so on.

There are often multiple ways of structuring these logic gates to form the same functional unit. Note: those numbers are completely made up. The key insight by the researchers behind the new chip was that certain logical functions are less sensitive to metallic nanotubes than others. So they modified an open source RISC design tool to take this information into account.

The result was a chip design that had none of the gates that were most sensitive to metallic carbon nanotubes. Memory addressing was limited to bits, and the functional units include instruction fetching, decoding, registers, execution units, and write back to memory.

The Toxic Truth About Carbon Nanotubes in Water Purification: a Perspective View

In other words, every single one of those 14, gates worked. It was also what's considered a 3D chip, in that the metal contacts below the nanotube layer were used for routing signals among the different transistors, while a separate layer of metal contacts layered above the nanotubes was used to supply power within the chip. Most critically, it works. As you can see from the image above, it successfully executed a variant of the traditional "Hello World" program that's generally used as a gentle introduction to the syntax of different programming languages.

In their paper, the researchers focus on all the ways their existing design could be improved. For example, the channel length is the distance between the metal contacts bridged by nanotubes. The metal contacts also had to be very wide in order to ensure that there were enough nanotubes bridging them.

We know in theory that improvements in both are possible, and ramping up the clockspeed is a definite option with this approach. But because this design needs to tolerate metallic nanotubes rather than getting rid of them , it's always going to need multiple nanotubes in each transistor. To establish the chiral vector, two atoms in the graphene sheet are selected, with one serving as the origin of the vector pointing toward the other atom.

What are Double-Walled Carbon Nanotubes?

The graphene sheet is then rolled in a way that allows the two atoms to coincide. Under these circumstances, the chiral vectors form a plane perpendicular to the longitude direction of nanotubes and the lengths of the chiral vectors are equal to the circumference.

The distance between adjacent shells is about 0. Various techniques have been developed to produce carbon nanotubes in sizable quantity, high yield, and purity, while maintaining a reasonable cost. Well-developed techniques include arc discharge, laser ablation, and chemical vapor deposition CVD , and most processes involve costly vacuum conditions.

Arc discharge was initially used for the synthesis of fullerenes. In a typical experimental setup, a chamber filled with low-pressure 50 to mbar inert gas helium , argon is where the reaction takes place. Two carbon rods are placed end-to-end as the electrodes, separated by a few millimeters, and a direct current of 50 to A driven by a potential difference of 20 V generates a high discharge temperature to sublime the negative electrode , leaving soot where carbon nanotubes are found.

This method is the most common way to synthesize carbon nanotubes and perhaps the easiest way. The quality of carbon nanotubes depends on the uniformity of plasma arc, catalysts , and the selection of filling gases. A mixture of carbon nanotubes is usually produced; thus, purification processes are needed to remove the fullerenes, amorphous carbon, and catalysts. Laser ablation was first employed to produce carbon nanotubes in Carbon vapors cool down rapidly during expansion, and carbon atoms quickly condense to form tubular structures with the help of catalyst particles.

The method is primarily used to synthesize SWNTs with high selectivity and in a diameter-controllable way by tailoring reaction temperatures. The resulting products are usually in the form of bundles. Laser ablation is the most costly technique due to the involvement of expensive lasers and high power input. Chemical vapor deposition CVD is the most promising way to produce carbon nanotubes on an industrial scale. The resulting reactive carbon atoms diffuse toward a catalyst-coated substrate and condense to form carbon nanotubes.

Well-aligned carbon nanotubes can be synthesized with precisely controlled morphology , provided that proper reaction conditions are maintained, including preparation of substrates, selection of catalysts, etc. Novel chemical, electrical, and mechanical properties absent in other materials have been discovered in carbon nanotubes.

Pristine carbon nanotubes are inert to most chemicals and need to be grafted with surface functional groups to increase their chemical reactivity and add new properties. For SWNTs, electrical conductivity is dependent on the chiral vector and independent of the length as determined by quantum mechanics.