Carbon Nanotube

1. Background of CNTs
• 1991: Sumio Iijima- NEC Laboratory in Tsukuba-- used high-resolution
transmission electron microscopy to observe carbon nanotubes.
• A carbon nanotube is based on a
two-dimensional graphene sheet.
• An ideal nanotube can be thought
of as a hexagonal network of
carbon atoms that has been
rolled up to make a cylinder and
"capped" with half of a fullerene
molecule.
• Carbon nanotube diameter ~ 1nm
and its length can be a million
times greater than its width Fig.1. Roll-up of a graphene sheet to make SWNT.
Adapted from, “ M. Endo: Nanotechnology Thought
Leaders Series, 2619, 2013”.

2. Structure of CNTs
• Nanotubes can be single-walled (d
= 1-2 nm), or multi-walled (d = 5-
80 nm) or double walled.
• Multi-walled carbon nanotubes
consists of several different
single-walled carbon nanotubes
concentrically encapsulated within
one another.
• Double-walled carbon nanotubes
(DWNTs) are the manifestation of
multi-walled carbon nanotubes
(MWNTs) and its physical
properties are similar to SWNTs.

3. Structure of CNTs
A CNT is characterized by
its Chiral Vector:
Ch = n â1 + m â2,
 → Chiral Angle between
the chiral vector and one
of the basis vector.
Armchair (n,m) = (5,5) = (n, n)
where, n = m, &  = 30
Zig Zag (n,m) = (9,0) = (n, 0)
Where m = 0, n > 0 &  = 0
Chiral (n,m) = (10,5)
Where, n  m, & 0 < < 30

4. Applications of CNTs
 Structural- a. proposed as clothes
b. combat jackets
c. space elevators, etc
 Electrical - a. electronic device
b. nanotube-polymer composites.
c. electromagnetic shield
d. ultracapacitors
e. chemical gas sensor
 Paper batteries - storage devices
 Solar cells- a. developed at the New Jersey Institute of Technology use a
carbon nanotube complex.
 Medical- a. cancer treatment ( pancreatic, breast, etc)
b. Biosensor

5. Different routes for CNT production
B. Chemical Process
1. Chemical vapor deposition (CVD)
2. High pressure carbon monoxide (HiPco)
A.Physical Process
1.Arc discharge
2. Laser ablation
A. miscellaneous Process
1.Arc discharge
2. Laser ablation

6. Arc discharge
Electrical breakdown of gas between the
electrodes passing electric current through
it where one electrode act as a cathode and
other as an anode.
1991: Sumio Iijima- for the first time used
this technique to produce carbon
nanotubes.
Id = 50 – 100 A
Vd = 10 – 30 V
P (He or Ar) = 40 – 90 kPa
Fig : Schematic of the carbon arc
discharge method.
C/M electrode – SWNTs
C electrode - MWNTs

7. DC Arc Discharge
Fig: Schematic of the DC arc discharge experimental setup.

8. Unipolar Pulsed Arc Discharge
Fig: Schematic of the Unipolar pulsed arc discharge experimental setup.

9. AC Arc Discharge
Fig: Schematic of the AC arc discharge
experimental setup.

10. (a) DC arc discharge
(b) AC arc discharge
(c) Pulsed arc
discharge
Different types of arc discharge
Fig.3. Schematic of production SWNTs in different arc discharge methods.
(d) Bipolar pulsed arc
discharge

11. ● Simple operation and produce less defect SWNTs
● Continuous diffusion of electrons and ions occur in the
plasma between the electrodes in both positive and negative
part of the input current
● Both electrode take part in sublimation
● Deposition occurs in the reactor chamber walls
● No cathode deposition in the electrode and easy discharge
control
● Higher sublimation rate is obtained than other arc discharge
method
Bipolar pulsed arc discharge

12. Experimental setup and method
Fig: Schematic of the bipolar pulsed arc discharge experimental setup.

13. TEM Photograph of the Soot

15. Raman analysis of the soot

16. Chemical Vapor Deposition (CVD)
Chemical vapor deposition (CVD) is one of the facile and effective methods for preparing
carbon nanotubes, specially MWNTs. Generally, this method involves the heating of catalyst
materials to high temperature (600-1100 0C) in the presence of hydrocarbon gaseous over a
period of time. Transition metal such as Fe, Co, Ni and Y are usually used as catalyst
precursors. This is a low temperature method for the synthesis of CNTs compared to arc
discharge and laser
Fig: Chemical vapor deposition methods.
In this technique, catalyst particle is initially
deposited on a substrate. Then hydrocarbon
gaseous such as acetylene, ethylene or methane
is introduced into the reaction chamber. Due to
the decomposition of the hydrocarbon nanotubes
are formed on the substrate.

17. Laser Ablation
The laser ablation method is widely used for the production of SWNTs with the highest purity
and quality .This method of nanotube production was first introduced in 1995 by Smalley’s group
In this technique, graphite target is vaporized in a controlled environment oven containing inert
gas (helium or argon) and maintained temperature approximately 1200 0C as shown in the Fig .
The nanotubes are collected at the cooled target. The graphite target is allowed to vaporize and
sublimate by continuous bombardment of the laser beam on its surface. The carbon species are
carried away by the carrier gas to the cooler target where they condensed into nanotubes and
Fig: Schematic of laser ablation method for production of CNT.

18. Laser Ablation
other carbonaceous materials. In the absence of metal catalyst in the graphite target, the soot
collected mainly consists of MWNTs having length up to 300 nm. SWNTs were formed
when small quantities of catalyst are incorporated in the graphite target. The produced
SWNTs are self-organized, have uniformly distributed diameter and length of few hundreds
of microns. The quality of the produced nanotube depends on the oven temperature which in
turn depends on the laser power. The bottleneck of this method is that it requires an
expensive laser.
Fig: Schematic of laser ablation method for production of CNT.

19. Properties of CNT