Structure of carbon nanotubes

Structure of carbon nanotubes Junjie Chen Department of Energy and Power Engineering, School of Mechanical and Power Engineering, Henan Polytechnic University, 2000 Century Avenue, Jiaozuo, Henan, 454000, P.R. China Contributor: Junjie Chen, ORCID: 0000-0002-5022-6863, E-mail address: koncjj@gmail.com Carbon nanotubes, also called buckytubes, are nanoscale hollow tubes composed of carbon atoms. Single-walled carbon nanotubes are one of the allotropes of carbon, intermediate between fullerene cages and flat graphene, with diameters in the range of one nanometer. Although not made this way, single-walled carbon nanotubes can be idealized as cutouts from a two-dimensional hexagonal lattice of carbon atoms rolled up along one of the Bravais lattice vectors of the hexagonal lattice to form a hollow cylinder. In this construction, periodic boundary conditions are imposed over the length of this roll-up vector to yield a helical lattice of seamlessly bonded carbon atoms on the cylinder surface. Multi-walled carbon nanotubes consisting of nested single-walled carbon nanotubes weakly bound together by van der Waals interactions in a tree ring-like structure. If not identical, these carbon nanotubes are very similar to Oberlin, Endo, and Koyama's long straight and parallel carbon layers cylindrically arranged around a hollow tube. Multi-walled carbon nanotubes are also sometimes used to refer to double-walled and triple-walled carbon nanotubes. Carbon nanotubes can exhibit remarkable electrical conductivity, while others are semiconductors. They also have exceptional tensile strength and thermal conductivity because of their nanostructure and strength of the bonds between carbon atoms. In addition, they can be chemically modified. These properties are expected to be valuable in many areas of technology, such as electronics, optics, composite materials, nanotechnology, and other applications of materials science. Rolling up a hexagonal lattice along different directions to form different infinitely long single-walled carbon nanotubes indicates that all of these carbon nanotubes not only have helical but also translational symmetry along the carbon nanotube axis and many also have nontrivial rotational symmetry about this axis. In addition, most are chiral, meaning the carbon nanotube and its mirror image cannot be superimposed. This construction also allows single-walled carbon nanotubes to be labeled by a pair of integers. The structure of an ideal single-walled carbon nanotube is that of a regular hexagonal lattice drawn on an infinite cylindrical surface, whose vertices are the positions of the carbon atoms. Since the length of the carbon-carbon bonds is fairly fixed, there are constraints on the diameter of the cylinder and the arrangement of the atoms on it. In the study of carbon nanotubes, one defines a zigzag path on a graphene-like lattice as a path that turns 60 degrees, alternating left and right, after stepping through each bond. It is also conventional to define an armchair path as one that makes two left turns of 60 degrees followed by two right turns every four steps. On some carbon nanotubes, there is a closed zigzag path that goes around the carbon nanotube. One says that the carbon nanotube is of the zigzag type or configuration, or simply is a zigzag carbon nanotube. If the carbon nanotube is instead encircled by a closed armchair path, it is said to be of the armchair type, or an armchair carbon nanotube. An infinite carbon nanotube that is of the zigzag or armchair type consists entirely of closed zigzag or armchair paths, connected to each other. 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 single-walled carbon nanotubes, electrical conductivity is dependent on the chiral vector and independent of the length as determined by quantum mechanics. Along the longitude directions, carbon nanotubes show superior mechanical strength, with the highest known tensile strength and elastic modulus among known materials.Contributor: Junjie Chen, ORCID: 0000-0002-5022-6863, E-mail address: koncjj@gmail.com, Department of Energy and Power Engineering, School of Mechanical and Power Engineering, Henan Polytechnic University, 2000 Century Avenue, Jiaozuo, Henan, 454000, P.R. Chin