In nature, there is a special structural modification of carbon, in which the graphene plane (a layer of carbon one atom thick) is rolled into a tube. Such carbon tubes, up to several nanometers in diameter, can reach several centimeters in length; and in principle it is possible to connect individual tubes to each other and obtain even more extended structures from them.
To date, there are hundreds of methods for the synthesis of carbon nanotubes, which make it possible to obtain structures of various lengths, diameters, wall thicknesses, imperfections, etc.
Timeline of carbon nanotubes (Wikipedia)
Carbon nanotubes are single-walled and multi-walled; they find application in various fields. Single-walled, for example, when added to a lead-acid battery, allow you to increase the number of charge-discharge cycles of such a battery.
Multi-walled, which is a coaxial structure in which a smaller diameter tube is nested in a larger diameter tube, are also applicable; for example, being represented by a misoriented array, multi-walled carbon nanotubes exhibit a memristor effect: resistive switching is possible due to the formation of conductive channels from carbon nanotubes oriented by an electric field. Next, we consider the electrical properties of carbon nanotube structures that were discovered as a result of fundamental research.
Individual carbon nanotubes are of little use for obtaining thermoelectricity. However, being arranged into compacted structures such as mats with a size of 2x1x0.1 mm, they can do something.
Thus, multilayer carbon nanotubes obtained using catalyst materials in an experiment (Voronezh, VGTU) demonstrated thermo-EMF in the range from 40 to 60 V / K in the temperature range from 50 to 300 K. The result is at least 7 times higher than this parameter single-crystal graphite.
Fundamentally, thin one-dimensional materials at temperatures near absolute zero prevent the passage of Cooper pairs responsible for superconductivity. But scientists (Yekaterinburg, Ural Federal University, Chi Ho Wong) decided to slightly change the structure of the conductor: they added a zigzag chain of carbon atoms inside the nanotube, which has no bonds with the atoms of the tube, nevertheless affects the shape of the tube, its bends. The angles between links in a chain can be mathematically calculated and modified. As a result, scientists managed to achieve the transition of a carbon nanotube to a superconducting state at a temperature above absolute zero by 45 degrees!
Single-walled Carbon Nanotubes: Structure, Properties, Applications
Hybrid materials from carbon nanotubes with nanoparticles have been adopted by scientists to obtain more efficient light sources (Novosibirsk, INC SB RAS). The bottom line is that at the end of a carbon nanotube, with an electric field strength of only 1 V/m, electron emission already occurs.
This is how you can create efficient low-voltage field cathodes for light panels: take a conductive silicon substrate and place on it an array of carbon nanotubes with quantum dots (for example, based on cadmium chalcogenides) grown at their ends. By varying the temperature during cultivation, the scientists managed to obtain nanoparticles of various sizes at the ends of the carbon tubes, with larger or smaller defects, which ultimately led to different colors of the glow (green, red, orange, blue).
Photoconductivity is the phenomenon of a change in the electrical conductivity of a substance when it absorbs electromagnetic radiation. Scientists (Minsk, Research Institute of Yap BSU) managed to demonstrate that the photoconductivity in the terahertz range of a film of single-walled carbon nanotubes is due to the action of two factors:
1) a change in the relaxation time of electrons due to the electron-phonon interaction and
2) the presence of a localized plasma resonance in the tube.
The sign of photoconductivity in this case depends on the length of the tube, and not on its chirality: the plus sign is for tubes less than 1 µm long and the minus sign is for long tubes more than 10 µm.
Carbon Nanotube Review, Definition, Structure, Properties, Applications: