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What is a Carbon Nanotube?
Discovery:This new class of materials was first observed by Endo (1975) and later by Iijima
CNT is a tubular form of carbon with diameter as small as 1nm.
Length: few nm to microns.
CNT is configurationally equivalent to a two dimensional graphene
sheet rolled into a tube.
2 Types of Bonding related to
• Covalent Bonding – Strong bond between individual neighbouring carbon atoms
in a single tube
•Bonding found along the 2-D plane in a hexagonally close packed sheet of graphite
• Van der Waal Forces – Weak bond between the individual nanotubes themselves
• Bonding between separate layers of graphite
• (Reason why graphite is an excellent lubricant, and why talcum powder feel so
• Nanotubes are composed entirely of sp2 bonds, similar to graphite. Stronger
than the sp3 bonds found in diamond. This bonding structure provides them
with their unique strength.
• Nanotubes naturally align themselves into "ropes" held together by Van Der
• Under high pressure, nanotubes can merge together, trading some sp2 bonds
for sp3 bonds, giving great possibility for producing strong, unlimited-length
wires through high-pressure nanotube linking.
Typical Values of a Single Walled Carbon
• Equilibrium Structure
• Average Diameter of SWNT's 1.2-1.4 nm
• Distance from opposite Carbon Atoms 2.83 Å
• Analogous Carbon Atom Separation 2.456 Å
• Parallel Carbon Bond Separation 2.45 Å
• Carbon Bond Length 1.42 Å
• C - C Tight Bonding Overlap Energy ~ 2.5 eV
• Lattice Constant 17 Å
• Covalent bonding is a very strong bond (can often be stronger than Ionic
• Weak VdW forces allow rolling up of indivitual graphite sheets into tubes.
• Electrons are shared between Carbon atoms so as to fill outer electron
• Covalent bonds are highly directional (unlike Ionic) therefore only a few
characteristic shapes are found.
• Carbon Nanotubes exhibit quite different properties related to size and
width of tube but the bonding type remains the same.
Electronic Structure Of Single Wall CNT
• Zigzag: A single wall CNT with one of the indices as zero (0,m or m,0)
and zero chiral angle is called as zigzag CNT. It has zigzag type ending
at the CNT edge.
• Armchair: A single wall CNT with equal indices (n=m) and 300 chiral
angle is called as single armchair CNT. It has arms of chair type ending
of CNT edges.
• Chiral: A single wall CNT with unequal indices (n,m) and chiral angle
between 00-300 is called as chiral CNT.
Nanotube’s chirality can be mathematically
defined in terms of a chiral vector Ch , which
can determine the tube diameter d.
Where (m,n) are indices and a is lattice
How CNTs are made
• Arc discharge
• CNTs Can be found in the carbon soot of graphite electrodes during an arc discharge
involving high current. This process yields CNTs with lengths up to 50 microns.
• Laser Ablation
• In the laser ablation process, a pulsed laser vaporizes a graphite target in a high-temperature
reactor while an inert gas is inserted into the reactor. Nanotubes develop on the cooler
surfaces of the reactor as the vaporized carbon condenses.
• Other methods where CNTs are created:
- Chemical Vapor Decomposition
- Natural, incidental, and controlled flame environments
• Carbon nanotubes have the strongest tensile strength of any material known.
• It also has the highest modulus of elasticity.
SWNT ~1 (from 1 to 5) 13-53E 16
0.94T 126.2T 23.1
Zigzag SWNT 0.94T 94.5T 15.6-17.5
Chiral SWNT 0.92
MWNT 0.8-0.9E 150
Stainless Steel ~0.2 ~0.65-1 15-50
Kevlar ~0.15 ~3.5 ~2
KevlarT 0.25 29.6
• If the nanotube structure is armchair then the
electrical properties are metallic
• If the nanotube structure is chiral then the
electrical properties can be either
semiconducting with a very small band gap,
otherwise the nanotube is a moderate
• In theory, metallic nanotubes can carry an
electrical current density of 4×109 A/cm2 which is
more than 1,000 times greater than metals such
• All nanotubes are expected to be very good thermal conductors along
the tube, but good insulators laterally to the tube axis.
• It is predicted that carbon nanotubes will be able to transmit up to
6000 watts per meter per Kelvin at room temperature; compare this
to copper, a metal well-known for its good thermal conductivity,
which transmits 385 watts per meter per K.
• The temperature stability of carbon nanotubes is estimated to be up
to 2800oC in vacuum and about 750oC in air.
Applications Of CNTs
• Nanotubes hold the promise of creating novel devices, such as
carbon-based single-electron transistors, that significantly smaller
than conventional transistors.
World’s Smallest Transistor
In 2016 Berkeley Lab-led research breaked major barrier
in transistor size by creating gate only 1 nanometer long!
Various properties of CNTs that allow it to be used in FETs and
switching components of electronic circuits:
• CNTs act as a channel for flow of electrons from source to drain.
• Switching time of CNT based FET is very fast
• It can be joined with metal-semiconductor to form metal-
semiconductor junction that allows the current to flow in only one
direction, thus acting as a rectifier.
Nanotubes’ excellent strength to weight ratio
creates the potential
to build an elevator to
Field Emission and Shielding
• The emission of electrons by a substance under the influence of high applied
electric field is called as field emission.
• CNTs have a low value of threshold electric field for emission of high current
• The high aspect ratios of CNTs makes them ideal field-emission materials.
• CNTs have several advantages over traditionally used field emission materials like
Si or W.
1. They are physically inert to sputtering
2. Chemically inert
3. Can carry a huge current density of 109 A/cm2
4. Longer life
5. More efficient
Emission property of CNT can be used in flat panel display, television,
computer monitors, microwave amplifiers, and in electron guns in
• Since CNTs are good electrical conductors it means they are very poor
transmitter of electromagnetic energy. Thus CNT reinforced plastic
plastic composite could be a light weight shielding material for
Thus this shielding property of CNT can be used in military ,
computer controlled weapons and in communications.
• Graphite and carbon fiber electrodes are commonly used in fuel cells,
batteries and other electrochemical applications.
Advantages of considering CNTs for energy storage are their:-
I. Small dimensions
II. Smooth surface topology
III. Perfect surface specificity
Because of their cylindrical and hollow geometry and nanometer scale
diameters, it has been predicted that CNTs can store a liquid or a gas
in the inner cores through capillary effect. Therefore CNTs can be used
to a gas like hydrogen for making hydrogen fuel cell. This could
revolutionize battery technology.
Catalyst: Any agent, material or chemical compound which is used to
enhance the rate of reaction is called a catalyst.
CNTs have properties such as:
Large specific surface areas
Excellent electron conductivity
Good chemical inertness
Relatively high oxidation stability
which makes it a promising support material for
Physical and Chemical Sensors
Physical Sensors-are used o examine environmental conditions whereas the Chemical
sensors are used to detect the kind and concentration of the substances in the
CNTs suit this task very well especially because all their atoms are found on the
surface of the structure.
There is strong dependence of the properties of CNTs:
These properties make CNT a very useful material for chemical, biological and
physical sensors. Small changes in the environment of the CNTs can cause drastic
change in current voltage relationship. The change in the magnitude and direction of
current depends upon the kind of molecule attached to the surface of nanotubes.
Physical sensors are sensitive to external parameters such as temperature, pressure,
mechanical strain etc. In the sensing process, the sensor generates a signal that can
be measured and assigned to a certain value.
• The carbon nanotubes(CNT) reinforced functionally graded
composite materials(FGCM) is expected to be the new generation
material having a wide range of unexplored potential applications in
various technological areas such as aerospace, defence, energy,
automobile, medicine, structural and chemical industry.
• Nanotubes and other Fullerenes can be filled with molecules that
have either an electronic or structural property which can be used to
represent the quantum bit (Qubit) of information, and which can be
associated with other adjacent Qubits.
• According to scientists at the National Institute of Standards and
Technology, carbon nanotubes shorter than about 200 nanometers
readily enter into human lung cells similar to the way asbestos does,
and may pose an increased risk to health.
• Carbon nanotubes along with the majority of nanotechnology, are
an unexplored matter, and many of the possible health hazards are