General Aspects of Carbon Nanotubes

The electrical properties of CNTs depend sensitively on the (n,m) indices and, therefore, on the diameter and chirality [4, 9, 12]. According to the m,n structural parameters values, SWCNTs can be either a metal, semiconductor or small-gap semiconductor [1,4,9,12]. When n=m, the CNTs are metallic. If n - m = 3 x integer, the CNTs present an extremely small band gap and at room temperature they have metallic behavior. For other intermediate values of n - m the behavior is that of a semiconductor with a given band gap [4,9]. This extreme sensitivity of electronic properties on structural parameters is one of the most important aspects of nanotubes that make them very unique. Calculahons have predicted that all the armehair tubes are metallie while the zigzag and chiral tubes are either metallie or semieonductor depending on their diameter and chiral angle [6,13], 

The strength of carbon bond determines the fascinating mechanical characteristics of this material that are superior to other known materials [20, 21]. CNTs are extremely flexible. In faet, they ean be twisted, flattened and bent into small circles without breaking. They ean also be eompressed without fraeture [6,7,9]. 

CNTs also possess interesting eleetroehemieal properties. Several works have demonstrated the electroactivity of CNTs due to the presenee of reactive groups on the surface [10, 22-24]. The small dimensions produee high current densities 

Gustavo A. Rivas, Maria D. Rubianes, Maria L. Pedano et al. 

---

The following chapters present the general aspects of different synthesis of nanostructured materials, such as Combustion Synthesis (Chap. 2), Spray Pyrolysis (Chap. 3), Electro spinning (Chap. 4), Catalytical Chemical Vapor Deposition applied in the Synthesis of Carbon Nanotubes and Carbon Nanotubes Forests (Chap. 5), Hydrothermal Synthesis (Chap. 6) and High-Energy Milling (Chap. 7). 

These problems have been improved in recent years by the microfabrication of sharp tips with radii less than 10 nm, the observation in an SEM or STEM of the exact radius before and after the experiment, the use of robust carbon-nanotube probes, and general improvements in control electronics. However, another method used initially was the attachment of a small colloid particle in place of the AFM tip. These particles were considered a reasonably good approximation to a single-asperity contact their radii were accurately known and remained the same for the duration of the experiment. Such probes have also been used to investigate colloids where surface roughness is an important aspect of the colloid interaction. 

---