concentric walls with the spacing between walls approximately 0.34 nm [2]. The ends of
a CNT are often capped with a hemisphere of the buck ball structure. Depending upon
chirality and diameter,  inpidual SWNT can be either semiconducting, metallic or semi
metallic Figure 1 [3].   
To study the physics of CNTs, SWNTs provide an ideal 1D model.  For practical
applications, thin films of SWNT (Figure  3), in the form  networks  (either random
networks or aligned) are used. SWNT films have many interesting properties, suitable for
various unusual multifunctional/multipurpose systems that require a combination of
electrical, mechanical, optical, and chemical properties [3].
Figure  2:  (a)  Single-wall nanotube, (b) Multi-wall nanotube with three  shells, (c)  Graphene,
which is a single sheet of graphite, the balls (spheres) represent the carbon atoms and the sticks
(lines) stand for the bonds between carbon atoms. (d) Wrapping  or folding  the dashed line
results in the armchair, zigzag or chiral, (e) The three types of single-wall CNT, an armchair
CNT, a zigzag CNT, and a chiral CNT. Simulation of CNT Antennas with SONNET®Problems and Limitations (3):http://www.youerw.com/yingyu/lunwen_5467.html