History and IntroductionThe experiments on the synthesis of new carbon clusters during the mid-1980s by Harry Kroto and Richard Smalley are the prelude to the story of nanotubes. From the vaporization of graphite and its expected condensation in carbon clusters of different sizes, particular structures containing precisely 60 and 70 carbons appear to be much stable. The unexpected results brought into the spotlight the now famous C60 and its closed shell similar to a soccer ball.The family of fullerene is discovered and published in Nature in 1985. Five years later, the success in the synthesis of C60 in bulk quantity by Wolfgang Kratschmer and Donald Huffmann gave to the community, the opportunity to study the properties of this new form of carbon. During the 15 years, an impressive number of publications and extraordinary results appeared on bucky ball and its derivatives.During this time in the early-1990s, Sumio Iijima was investigating by electron microscopy technique the carbon soot and deposit produced by a Kratschmer-Huffman’s machine. From his findings, he concluded to the existence of novel graphitic structures, another new form of carbon similar to tiny tubules of graphite presumably closed at each ends. If the anterior existence of nanotubes is well established, Iijima’s work pointed out to the exceptional properties and potential applications of these nanostructures. An important step was accomplished in 1992, by improving the method of synthesis and the capacity of production with gram quantities. In 1993, another key point is the successful synthesis of single walled carbon nanotubes which are considered to be the ideal nanotubes with a very single layer. The diameter appeared to be amazingly small compared to multi-walled carbon nanotubes. In 1997, high yields of single walled nanotubes were achieved by electric arc techniques with the help of optimized conditions. This definitely extends the possibilities of investigations of single and multi-walled carbon nanotubes. Fig1: (A) Single walled nanotube(SWNT) (B) Multi walled nanotube(MWNT)Downsized the 10000 times a human hair, we get the size and shape of a typical nanotube. These molecules are few nanometers in diameter and several microns in length. Single carbon nanotubes come often as tightly bundles of single walled nanotubes entangled as curly locks. The packing of the nanotubes inside a bundle is more or less triangular with an intertube distance about 3.14 A. Here, the bundle is about 20 nanotubes but can be made of hundreds of individuals. This assembly of nanotubes is stabilized by van der Waals interactions. If the distribution of nanotube diameters is quite narrow within a bundle, it has been shown that the arrangement of the carbon is diverse. In the case of multi-walled nanotubes, at least two concentric nanotubes of different diameters are encapsulated. Their lengths are from hundreds of nanometers to tens of micrometers, with diameter of few to hundreds of nanometers.Synthesis of NanotubesA wide variety of processes is now available to produce carbon nanotubes. They can be classified, first into high temperature methods like the electric arc, laser ablation and solar beam based on the sublimation of a graphitic rod in inert atmosphere and second into process working at moderate temperature like the catalytic chemical vapor deposition which produces nanotubes from the pyrolysis of hydrocarbons. Originally, the electric arc discharge setup developed by Kratschmer-Huffman was invented for fullerene production. In a helium or argon atmosphere a DC current is applied through two high purity graphite electrodes. In these conditions, the temperature can reach 6000K which is high enough to sublimate continuously the graphite from the rod of the anode. At the cathode where the temperature is lower, a deposit and soot are produced. Fullerene like C60 and C70 are generally found in large quantities in the soot whereas nanotubes are present in the deposit and its vicinity. Later, this apparatus was successfully used by different groups to grow in a very simple and cheap way single walled nanotubes with the help of suitable catalyst like Ni,Co,Pt,Rh,Fe… incorporated inside the anode. In addition, it was rapidly shown that the characteristics of the nanotubes could be easily change by playing with the current, the pressure, the nature of the catalyst. This finding was a breakthrough and allowed the community to investigate the properties of carbon nanotubes to a very large extend.The reactor contains a lot of black soot, carbon filaments and the deposit. The material to be collected which contains a high density of carbon nanotubes is in the central part of the collaret and looks like webs. High temperature routes are known to produce high quality materials which mean higher graphitization of the nanotubes. They can be used also to produce large quantities of single walled carbon nanotubes. The as-produced nanotubes are produced are presented at different magnifications using scanning electron microscopy images.It shows a high resolution transmission electron microscopy image of one bundle containing about 20 single walled nanotubes. We turn now to the chemical catalytic vapor deposition method. This process was originally developed in order to decompose hydrocarbons e.g. methane, acetylene etc. over catalysts e.g. Ni, Co, Fe, Pt. This technique allows to grow nanotube at predefined locations on substrates where nanosized metal particles are deposited. To finish, one has to mention that if some methods of production are now well established, nanotubes are still not prepared in pure form. For example, single walled carbon nanotubes samples are contaminated by graphite structures, amorphous carbon and magnetic particles used as catalyst. In order to study the intrinsic properties of the nanotube, more or less sophisticated strategies of purification have been developed. Only with the help of magnetic fields used to trap magnetic impurities, highly purified bulk samples have been obtained which offer the opportunity to use magnetic resonance spectroscopy.Electronic Properties of Carbon NanotubesFrom the beginning, theoretical calculations have proposed that the electronic properties of the carbon nanotubes depend strongly on their geometrical structures. Thus, nanotubes can be metals or semiconductors depending on their diameter or chirality. Practically, from the pair of integer (n,m), it is possible to determine the electronic properties of the nanotubes. It was established, that if n-m is multiple of 3 the nanotube is metallic with a constant density of state over a large plateau above and below the Fermi level. In all others case, nanotubes are semiconductors with an energy gap inversely proportional to the radius R. Therefore, one third of the single walled nanotubes are metallic with some exceptions for small diameters below 8A, because of their higher curvatures. This result is easy to remain and directly related to the periodic boundary conditions along the circumference of the nanotube which discretize the electronic states in one direction perpendicular to the nanotube axis. Another interesting feature concerns the van Hove singularities related to the strong one dimensional character of the electronic states in the nanotubes. Actually, in the case of armchair nanotubes m=n and small radius nanotubes detailed calculations and low temperature experiments have show that the curvature opens at tiny gap. However, such pseudo gap can be ignored for properties and applications around room temperature.