These are allotropes of carbon with
a cylindrical nanostructure.
Nanotubes have been constructed with length-to-
diameter ratio of up to 132,000,000:1
Nanotubes are members of the fullerene structural family.
Naturally align themselves into "ropes" held together
by van der Waals forces.
The chemical bonding of nanotubes is composed entirely
of sp2 bonds.
In 1991 Sumio Iijima (Japanese Scientist) observed
Multiwalled carbon Nanotube and in 1993 he discovered
Single wall carbon Nanotube.
Arc evaporation technique involves evaporation of
graphite anode rod and condensation of the deposit
on the cathode rod under inert atmosphere.
A plasma is achieved by making a gas to conduct
electricity by providing a potential difference across
Electrodes are made of conducting materials
In arc discharge method, two high purity graphite
electrodes as anode and cathode are held a short
distance apart under a helium atmosphere.
Inert gas is meant for cooling / condensation
of the sample.
The chamber must be connected both to a
vacuum line with a diffusion pump and to
Important parameters of gas
1000 torr Soot/ Carbon onions
500 torr Carbon nanotubes
100 torr Fullerenes
20 torr Amorphous carbon/soot
Therefore pressure & type of inert gas
used determines the structure of carbons to
In arc evaporation method, graphite rods are
used as electrodes.
Graphite rods with 99.99% purity are used.
Major impurities in graphite are sulphur
atoms as Sulphur changes the morphology of
The anode is a long rod of 6mm diameter &
the cathode is a short rod of 9mm diameter
Cooling of Electrode
Efficient cooling of the electrodes & the
chamber are essential to produce good quality
nanotubes and also to avoid excessive sintering.
Without proper cooling-sintering occurs-with a
hard deposit of mass
With proper cooling-sintering does not occurs-
forms a uniform deposit i.e., Homogeneous
deposit with aligned bundles of nanotubes.
Current & Voltage
DC power supply is given in the range of 50-100mA
and the discharge voltage is between 20 – 50 V.
DISTANCE BETWEEN ELECTRODES
The position of the anode can be adjustable from outside
Distance between the electrodes must be constant to obtain
a stable current.
The two electrodes are maintained at constant distance for
When two electrodes are in contact / not at a particular
distance - fullerenes can be formed.
Arc Discharge Method Parameters of SWNTs:
In the arc discharge production method sulfur
functions as a SWNTs growth promoter and
surfactant when added together with Ni/Fe/Co,
Ni/Co, Ni/Y/Fe or Ni/Ce/Fe catalysts into the anode.
The metal-sulfur interactions change surface
tension and melting point of small droplets of
metals. This can support the creation of SWNTs for
metals which in pure form catalyze badly.
The highest yield of web product containing the
smallest concentration of metals was obtained for
the sample C where the composition of the anode
is Fe:Y:S:C at6.6%:1.1%:1.6%:90.7%.
SEM images of the samples which were synthesized
(a) in an air atmosphere at 300 Torr and
(b) in the helium atmosphere at 500 Torr
SEM images of MWNT’s produced by arc
discharge (Kunsan National Univ)