Why do nanotubes conduct electricity

Carbon can form nanoparticle structures with a variety of shapes. The fullerenes form ball shapes and tubes. Graphene consists of a sheet of carbon atoms, one atom thick. Graphene is an allotrope of carbon. Its structure resembles a single layer of graphite. Graphene has a very high melting point. It is very strong because of its large regular arrangement of carbon atoms joined by covalent bonds.

Researchers have used atomic force microscopes to physically push nanotubes around and observe their elastic properties. And, since carbon nanotubes have such a perfect structure, they avoid the degradation of strength that you get with other materials.

In addition to being strong and elastic, carbon nanotubes are also lightweight, with a density about one quarter that of steel.

While metals depend upon the movement of electrons to conduct heat, carbon nanotubes conduct heat by the vibration of the covalent bonds holding the carbon atoms together; the atoms themselves are wiggling around and transmitting the heat through the material.

The stiffness of the carbon bond helps transmit this vibration throughout the nanotube, providing very good thermal conductivity. Carbon nanotubes are a little bit sticky, as well. The electron clouds on the surface of each nanotube provide a mild attractive force between the nanotubes.

This involves forces between nonpolar molecules a molecule without a positive end and a negative end. A carbon nanotube just happens to be a nonpolar molecule. But not all nanotubes are exactly alike. Armchair nanotubes all have electrical properties like metals — but only about a third of all zigzag and chiral nanotubes have electrical properties like metal; the rest roughly two thirds have electrical properties like semiconductors.

According to Basaran, this essential difference between metals and carbon nanotubes lies in the way they conduct electricity. In conventional metals, he explained, conduction causes a scattering of electrons within the lattice of the material so that, when electrons move during conduction, they bump into atoms. This creates friction and generates heat, the same way a household iron works.

He drew an analogy, using the difference between a conventional railroad train and a magnetically levitated train. But with a magnetically levitated train, the wheels and track are not in direct contact. Without that friction, they can travel much faster. The minimal amount of friction gives carbon nanotubes a tremendous advantage over conventional metals, said Basaran.

CNTs have the intrinsic characteristics desired in material used as electrodes in batteries and capacitors, two technologies of rapidly increasing importance. Research has shown that CNTs have the highest reversible capacity of any carbon material for use in lithium-ion batteries [B. Gao, Chem.

In addition, CNTs are outstanding materials for supercapacitor electrodes [R. Ma, et al. CNTs also have applications in a variety of fuel cell components. They have a number of properties, including high surface area and thermal conductivity, which make them useful as electrode catalyst supports in PEM fuel cells. They may also be used in gas diffusion layers, as well as current collectors, because of their high electrical conductivity.

The idea of building electronic circuits out of the essential building blocks of materials — molecules — has seen a revival the past five years, and is a key component of nanotechnology. In any electronic circuit, but particularly as dimensions shrink to the nanoscale, the interconnections between switches and other active devices become increasingly important.

Their geometry, electrical conductivity, and ability to be precisely derived, make CNTs the ideal candidates for the connections in molecular electronics.

In addition, they have been demonstrated as switches themselves. CNTs have extraordinary electrical conductivity, heat conductivity, and mechanical properties. They are probably the best electron field-emitter possible. They are polymers of pure carbon and can be reacted and manipulated using the well-known and tremendously rich chemistry of carbon.

This provides opportunity to modify their structure, and to optimize their solubility and dispersion. Very significantly, CNTs are molecularly perfect, which means that they are normally free of property-degrading flaws in the nanotube structure. Their material properties can therefore approach closely the very high levels intrinsic to them. These extraordinary characteristics give CNTs potential in numerous applications.

The record-setting anisotropic thermal conductivity of CNTs is enabling many applications where heat needs to move from one place to another. Such an application is found in electronics, particularly advanced computing, where uncooled chips now routinely reach over o C. The technology for creating aligned structures and ribbons of CNTs [D. Walters, et al.

In addition, composites with CNTs have been shown to dramatically increase their bulk thermal conductivity, even at very small loadings. The superior properties of CNTs are not limited to electrical and thermal conductivities, but also include mechanical properties, such as stiffness, toughness, and strength.

These properties lead to a wealth of applications exploiting them, including advanced composites requiring high values of one or more of these properties. CNTs are the best known field emitters of any material. The sharpness of the tip also means that they emit at especially low voltage, an important fact for building low-power electrical devices that utilize this feature.

Furthermore, the current is extremely stable. An immediate application of this behavior receiving considerable interest is in field-emission flat-panel displays.

Instead of a single electron gun, as in a traditional cathode ray tube display, in CNT-based displays there is a separate electron gun or even many of them for each individual pixel in the display. Their high current density, low turn-on and operating voltages, and steady, long-lived behavior make CNTs very attractive field emitters in this application.

Other applications utilizing the field-emission characteristics of CNTs include general types of low-voltage cold-cathode lighting sources, lightning arrestors, and electron microscope sources.

Wei, et al , Appl. Fibers spun of pure CNTs have recently been demonstrated [R. Baughman, Science , ] and are undergoing rapid development, along with CNT composite fibers. Such super strong fibers will have many applications including body and vehicle armor, transmission line cables, woven fabrics and textiles. CNTs are also being used to make textiles stain resistant.

CNTs intrinsically have an enormously high surface area; in fact, for SWNTs every atom is not just on a one surface — each atom is on two surfaces, the inside and outside of the nanotube! Combined with the ability to attach essentially any chemical species to their sidewalls functionalization provides an opportunity for unique catalyst supports.