Single Wall Carbon Nanotubes in the Presence of Vacancies and Related Energy Gaps

Abstract

Carbon nanotube family is one of the most important elements in nanotechnology. High ratio of surface to volume of nano materials cause to appear nanotechnology. This matter is one of the most important properties of produced materials at nano scales. At this scale, materials begin replace their bulky behavior with surface one. Some of physical relations that are used for ordinary materials, also abandoned. In fact, at this scale, laws of quantum physics play a key role and it will be possible to control special properties of material such as melting point, magnetic behavier, charge capacitance and even colour of material with no change in their chemical properties. This text is concentrated on some most important carbon nanotubes. Carbon atoms can form chemical bonds by hybridizing the atomic orbitals of their valence bonds and assume many structural forms such as graphite, diamond, carbon fibers, fullerenes, and carbon nanotubes. Carbon nanotubes (CNTs) discovered by Sumio Iijima in 1991 [Iijima,1991], are one of the most exciting quasi-1-D solids that exhibit fascinating electrical, optical, and mechanical properties such as high current density, large mechanical stiffness, and field emission characteristics [Choi et al., 1999; Saito & Dresselhaus ,1998]. These properties of CNTs enable a wide range of applications in the various fields such as electron emission [Bonard et al., 1999; Dresselhaus et al., 2001; poole et al. 2003], energy storage [Meyyappan , 2005, Chambers et al., 1998], composites [Dresselhaus et al., 2001; Meyyappan et al., 2005], solar cells [Lee, 2005; Pradhan et al., 2006; Wei et al., 2007], nanoprobes and sensors [Dai et al., 1996], and biomedicine [Sinha et al., 2005]. A single-wall carbon nanotube (SWCNT) is a graphene sheet rolled into a cylindrical shape with a diameter of about 0.7 2.0 nm [Saito et al.,1998], but A multiwall carbon nanotube (MWCNT) comprises a number of graphene sheets rolled concentrically with an inner diameter of about 5 nm [Harris, 2005 ]. Since the aspect ratio of the carbon nanotube cylinders (length/diameter) is as large as 104-105 [Saito et al., 1998], these nanotubes can be considered as one-dimensional nanostructures. CNTs according to their structures are classified to three types of armchair, zig zag, and chiral [Saito et al., 1998]. The terms ‘zigzag’ and ‘armchair’ refer to the arrangement of hexagons around the circumference. Armchair and zigzag nanotubes are defined by a carbon nanotube whose mirror image has an identical structure to the original one. On the contrary, Chiral nanotubes in which the hexagons are arranged helically around the tube axis, exhibit a spiral symmetry whose mirror image cannot be superposed on to the original one [Saito et al., 1998 & Harris, 2009].