CNT

Carbon nanotubes (CNTs) are quasi one-dimensional nanostructures with extreme mechanical characteristics and tuneable electrical properties (Loiseau A., 2006). It is a tubular form of carbon with diameter as small as 1 nm and few nm to microns of length. It can be described as a two dimensional graphene sheet rolled into a tube.

It is characterized by its Chiral Vector R (n, m) : R = n â₁ + m â₂,  with Ø as an angle.

With its Chiral Vector, we can classify CNTs : -  Armchair nanotube (n,m) = (5,5), Ø = 30°

                                                                       -     Zig zag nanotube (n,m) = (9,0), Ø = 0°

                                                                       -     Chiral nanotube (n,m) = (10,5), 0° < Ø < 30°

There are three tyes of CNTs :

-  Single wall CNT (SWCNT)

Consist of just one layer of carbon, greater tendency to align into ordered bundles, and used to test the theory of nanotube properties

  -  Multiple wall CNT (MWCNT)

        Consist of 2 or more layers of carbon and tend to form unordered clumps

                    -  Can be metallic or semiconducting depending on their geometry

SWCNT

MWCNT

CNT properties : 

1.       Because of C-C covalent bonding and seamless hexagonal network architecture , it becomes  the strongest and most flexible molecular material

2.      Young’s modulus of over 1 TPa vs 70 GPa for aluminium, 700 GPa for C-fiber. Strength to weight ratio 500 time ˃ for Al; similar improvements over steel and titanium; one order of magnitude improvement over graphine / epoxy

3.       Maximum strain ~ 10% much higher than any material

4.   Thermal conductivity ~ 3000 W/mK in the axial direction with small values in the radial direction

5.       Electrical conductivity six orders of magnitude higher than copper

6.       Can be metallic or semiconducting depending on chirality

-      ‘tunable “ bandgap

-  Electronic properties can be tailored through application of external magnetic field, application of mechanical deformation

7.       Very high current carrying capacity

8.    Excellent field emitter : high aspect ratio and small tip radius of curvature are ideal for field emission (Dresselhaus)

9.    Because of its special band structure, it can escape such a fate and remain conducting over lengths greater than one micron down to very low temperature (C. Dekker, 2000).

Many researches have been done for their synthesis and several methods of them are :

a.       Electric arc discharge

b.       Laser ablation

c.       Chemical vapor deposition (CVD)

CNTs Applications :

1.       Electronic devices (nanotube TV’s, nano-wiring)

2.       High strenght composites (100 times as strong as steel and 1/6 the weight)

3.       Conductive composites

4.       Medical applications (encase drug into nanotube capsule for more predictable time release)

                     5.   Catalytic application

References :  Loiseau A, Launois P, Petit P, Roche S, Salvetat JP, Understanding Carbon nanotubes from basics
                                            to applications. Springer, Lecture Notes in Physics; 2006. Vol. 677

                  M.S. Dresselhaus, G. Dresselhaus, Ph. Avouris, Topics in Applied Physics ; Carbon Nanotubes:
                                            Synthesis, Structure, Properties and Applications

                  C. Dekker, Phys. Today 52 (5) (1999) 22. See also reviews on nanotubes in Phys. World 6, 1 (2000)