Graphene sheet Rolled

A single-walled carbon nanotube (S WNT) is a single graphene sheet rolled up in a seamless cylinder, whose diameter is of the order of few nanometers (Fig. 4.12). A double-walled carbon nanotube (DWNT) consists of rolled two graphene layers, and a multiwall carbon nanotube (MWNT) exhibits several co-axial rolls of graphene sheets, one sitting in each other and separated by about 0.35 nm. 

A nanotube can be thought of as a hexagonal sheet of carbon atoms (graphene sheet), rolled up to make a cylinder and capped at the ends by a half of a buckyball, as illustrated in Figure 17.8. Tubes typically have diameters of about 1 nm. The diameter of the smallest nanotube corresponds to the diameter of the smallest buckyball (Ceo-) The length-to-diameter ratio is typically about 104. 

Five years after the discovery of fullerenes, Iijima reported in 19911 a novel form of organized carbon which consists of hollow cylindrical structures, a few nanometers in diameter and some micrometers long. Although hollow carbon nanofibers had been prepared for several decades, their walls had never been resolved by High-Resolution Transmission Electron Microscopy (HRTEM). These HRTEM images allowed Iijima to conclude that the walls of the so-called multi-walled carbon nanotubes (MWCNTs) are made up of several concentric cylinders, each being formed by a graphene sheet rolled... 

Let us recall that nanotubes can be considered as graphene sheets rolled up in different ways. If we consider the so-called chiral vectors c = nai + na2, in which a and a2 are the basis vectors of a 2D graphite lattice, depending on the value of the integers n and m, one can define three families of tubes armchair tubes (n = m), zig-zag tubes (n or m = 0), and chiral tubes (n m 0). Band structure calculations have demonstrated that tubes are either metallic compounds, or zero-gap semiconductors, or semiconductors [6,7]. More commonly, they are divided into metallic tubes (when n-m is a multiple of 3) or semiconducting ones. 

These properties are mainly originated from the molecular structures of CNTs, which consist of graphene sheets rolled to form hollow cylinders with an extremely high aspect ratio [5]. Moreover, CNTs can be ether metallic or semiconducting tubes, depending on their diameter and/or chirality [5]. There are two types of CNTs SWNTs and MWNTs. Details, such as structure, synthesis methods, application and properties, are well documented [4], [5], [6]. 

Ideally, a SWCNT is made of a single perfect graphene sheet rolled up into a cylinder and closed by two caps (semi-fullerenes). Considering that there are different ways to roll up a section of a two-dimensional graphene sheet, the structure of SWCNTs is characterized by a roll-up vector, also called a helicity vector [11 and Chapter 14]. The diameter of these structures can vary between 0.4 and 2.5 nm and the length between a few micrometers and several millimeters. 

A molecule first discovered in 1991 by Sumio lijima, made from carbon atoms connected into a tube as small as 1 (nm) in diameter. It is equivalent to a flat graphene sheet rolled into a tube with high strength capacity and lightweight. 

CNTs are considered to be ideal candidates for a wide range of apvplications in materials science because of their exceptional mechanical, thermal, and electronic properties (Baughman Zakhidov, 2002). Carbon nanotubes exist as two types of structures singlewall carbon nanotubes (SWNTs) and multiwall carbon nanotubes (MWNTs). Fig. 1 shows the schematic pictures of different types of carbon nanotubes. SWNT can be considered as graphene sheet rolled cylinders of covalently bonded carbon atoms with very high aspect ratios of 1000 or more. MWNTs consist of a number of graphene cylinders concentrically nested like rings in a tree trunk with an interlayer distance of -0.34 nm. 

Carbon nanotubes are tubules that consist of a graphene sheet rolled up into a seamless cylinder with diameters of the order of a few nanometers. Carbon nanotubes have unique properties such as extraordinary strength and unique electrical properties and are efficient conductors of heat. Carbon nanotubes also act as extraordinary pipes in the true nanofiuidic regime. 

Ideal CNTs can be conceptualized as a graphene sheet rolled to form a cylinder with a few nanometers of diameter, micrometers and even inches [32] of length, while the ends are closed by half-fullerenes on each side (Fig. 5.2). 

The structure of CNTs consists of one, two or more, graphene sheets rolled up to make the tubes leading to variations from single (S), double (D) and multi-wall (MW) carbon nanotubes, respectively. Nanotubes naturally align themselves into ropes held together by van der Waals forces, more specifically, pi-stacking. The nature of the dispersion problem for CNTs is rather different from other... 

A CNT is a cylindrical arrangement of sp -hybridized carbon atoms, essentially a graphene sheet rolled up in the form of a tube (Figure 13.6). Nanostructures that consist of single tubular graphene sheets are called single-walled CNTs (SWCNTs), which have diameters of 0.4-3 nm. > Assemblies of multiple concentric tubular graphene sheets (with each sheet separated by 0.34 nm) are known as multiwalled CNTs (MWCNTs). MWCNTs have outer diameters of 2-100 nm and inner diameters typically of 2-10 CNTs possess specific surfaces areas of 300 m g ... 

Carbon nanotubes (CNTs) constitute one of the most important ID materials with its length-to-diameter ratio (aspect ratio) exceeding 1000 [58]. The carbon clusters in CNT are structurally built from graphene sheets rolled up around a central hoUow core into a tube [59]. Carbon nanotubes can be classified into single-walled carbon nanotubes (SWCNT) [60], double-walled carbon nanotubes (DWCNTs) [61] and... 

The fullerenes are a class of allotropes of carbon. Conceptually, these are graphene sheets rolled into tubes or spheres. These include the earbon nanotrrbes (or silicon nanotubes), which are important becairse of their meehanieal strength and electrical properties. The synthesis of C has been reported in a conventional micro-wave oven from the decomposition of camphor resin (Martinez-Reyes et al., 2012). Thermal and microwave-assisted synthesis of Diels-Alder adducts of [60] Fullerene with 2,3-pyrazinoqrrinodimethanes was carried out by Femandez-Paniagua et al. (1997). 

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