Carbon nanotubes and graphene in context 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. The cylindrical carbon molecules feature high aspect ratios (length-to-diameter values) typically above 103, with diameters from about one nanometer up to tens of nanometers and lengths up to millimeters. This unique one-dimensional structure and concomitant properties endow carbon nanotubes with special natures, rendering them with unlimited potential in nanotechnology-associated applications. Carbon nanotubes are members of the fullerene family. Although the first fullerene molecules were discovered in 1985 [1], it was not until Sumio Iijima reported his findings in 1991 about needlelike carbon tubes in Nature that carbon nanotubes came to public awareness [2]. Since then, carbon nanotubes with various structures have been discovered. According to the number of graphic shells, they are mainly categorized as single-walled carbon nanotubes and multi-walled carbon nanotubes. The carbon nanotubes reported by Sumio Iijima were multi-walled carbon nanotubes synthesized by arc discharge methods. Two years later, two sets of researchers working independently, Sumio Iijima and Toshinari Ichihashi [3], along with Donald Stimson Bethune and his colleagues at International Business Machines Corporation [4], synthesized single-walled carbon nanotubes, using transition-metal catalyzed arc discharge. A single-walled carbon nanotube can be described as a long tube formed by wrapping a single graphene sheet into a cylinder with diameter of about one nanometer, the ends of which are capped by fullerene cages [5]. The fullerene structures, with alternating structures of five hexagons adjacent to one pentagon, form the surface with desired curvature to enclose the volume. The sidewalls of carbon nanotubes are made of graphene sheets consisting of neighboring hexagonal cells. Other polygon structures, such as pentagons and heptagons, constitute defects of sidewalls. The cylindrical sidewalls can be produced from different rolling directions to make single-walled carbon nanotubes with distinct structures and properties. Due to...