Carbon nanotubes are cylindrical structures of carbon with diameters in the nanometer range. They have extremely high tensile strength and unique electrical properties depending on their structure. Carbon nanotubes can be single-walled or multi-walled and are synthesized using arc discharge, laser ablation, or chemical vapor deposition with transition metal catalysts. They have a variety of potential applications in electronics, optics, and other fields due to their novel properties.

1. CARBON NANOTUBES

2. CARBON NANOTUBES
(CNTs) Allotropes of carbon with cylindrical sructure
having diameter in nanometer range
 Constructed with length -to – diameter ratio
(aspect ratio) upto (132 × 106 ) : 1 , significantly
larger than any other material
 Have novel properties ,making them potentially
useful in many applications in
nanotechnology,electronics ,optics and other
fields of material science

3. BONDING IN CNT
 Applied quantum chemistry , specifically, orbital hybridization
best describes chemical bonding in nanotubes
 The chemical bonding of CNTs is composed of sp2 bonds
( as in graphite) which are stronger than sp3 bonds found in
alkanes ,provide their unique strength
 NTs naturally align themselves into “ropes” held together
by van der Waals forces

4. TYPES OF CNTs
SINGLE-WALLED
NANOTUBE ( SWNT )
MULTI-WALLED
NANOTUBE ( MWNT )

5. SWNTs AND MWNTs

6. SWNTs AND MWNTs

7. SWNT
 Most SWNT have a diameter close to 1 nm, with a tube length that can be
many million times longer
 The structure of a SWNT can be conceptualized by wrapping a one –
atom-thick layer of graphite called graphene into a seamless cylinder
 The way graphene sheet is wrapped is represented by a pair of indices ( n,
m) called the chiral vector
 The intigers n,m denotes the number of unit vectors along the two directions in
the honeycomb crystal lattice of graphene
 If m=0 , the nanotubes are called zig-zag
 If n=m, the nanotubes are called armchair
 Otherwise , the nanotubes are called chiral

8. SWNT

14. MWNT
There are two models to describe the structure of MWNTs
MWNTs consist of multiple rolled layers (concentric
tubes) of graphite

15. SYNTHESIS AND PURIFICATION
OF CNTs
 CNTs were first noticed in the graphitic soot deposited on the negatively charged
electrode used in the arc discharge synthesis of fullerenes
MODIFIED ARC DISCHARGE PROCESS
 A smaller diameter anode evaporates on the face of a larger diameter cathode in a
direct current arc discharge apparatus
 The bowl that grows on the cathode contains MWNTs
 The bowl can be broken and ground and the nanotubes may be suspended in a suitable
solvent and deposited on theTEM grid for examination
 The incorporation of transition metals in catalytic amounts into the anode results in the
formation of SWNTs
 The most common metals used are Fe and Ni , but it is better to use bimetallic systems
such as Co-Ni, Co-Pt and Ni-Y
 Optimized synyhesis utilizes an Ni-Y catalyst in the atomic ratio 4:1

16. SYNTHESIS AND PURIFICATION OF
CNTs
 SWNT can be synthesized by heating a mixture of graphite
with Fe and Ni catalysts at a temperature of 12000C and
irradiating with laser
 Nanotubes thus synthesised are found to form ropes in
which individual tube organize into hexagonal assembly,
showing the homogenity of the tubes synthesized
LASER
Fe Ni 12000C
(50-70 % )

17. SYNTHESIS AND PURIFICATION OF
CNTs
 CHEMICAL VAPOUR DEPOSITION
 SWNTs and MWNTs can be synthesized
 An organometallic precursor is mixed with a carbon
containig feed gas, it is pyrolyzed in a quartz tube and the
nanotubes are collected from the cooler end of the
reaction vessel
 Nanotubes are also grown solid catalytic substrates such
as silica, quartz, alumina etc .,which contain transition
metal precursors (important for making supported
MWNT assemblies for specific applications)

18. SYNTHESIS AND PURIFICATION OF
CNTs
 Both MWNTs and SWNTs are formed with significant quantities of
carbonaceous material
 One way of separating the tubes from the carbon mass is to heat- treat
the product
 All carbon forms react with oxygen ,but they do so at different rates
 All amorphous carbon materials can be burnt off by heating the soot at
7500C for half an hour (amorphous carbon reacts at high rate than nanotubes
due to the existence of large number of deffects in it)
 At the end of the process the product (only less than 1% of the original
material is left ) obtained is essentially a mixture of nanotubes
 Acid –based cleanig procedures can also be used

19. PROPERTIES OF CNTs
 STRENGTH
 CNTs are the strongest and stiffest materials yet
discovered interms of tensile strength and elastic
modulous respectively
 This strength results from the covalent bonds
formed between individual carbon atoms
 MWNT was tested to have a tensile strength of 63
GPa (in 2000)

20. PROPERTIES OF CNTs
 HARDNESS
 Standard SWCNTs can withstand a pressure upto
24 Gpa without deformation
 They can undergo a transformation to superhard
phase nanotubes
 The bulk modulus of superhard phase nanotubes is
462-546 Gpa, even higher than that of diamond
(420 Gpa for single diamond crystal)

21. PROPERTIES OF CNTs
 KINETIC PROPERTY
 MWNTs are multiple concentric nanotubes precisely nested
within one another - These exhibit a striking telescoping
property whereby an inner nanotube core may slide , almost
without friction ,within its outer nanotube shell,thus creating an
automatically perfect rotational bearing
 This property has been utilized to create the world’s smallest
rotational motor
 Applicatios such as gigahertz mechanical oscillator are also
envisaged

22. PROPERTIES OF CNTs
 ELECTRICAL PROPERTIES
 Because of the symmetry and unique electronic structure of
graphene, the structure of nanotube strongly affect its electrical
properties
 For a given (n,m) nanotube
If n=m the nanotube is metallic
If n-m is a multiple of 3, the nanotube is semiconducting with a
very small band gap
Otherwise the nanotube is moderate semiconductor
 But this rule has exceptions because of curvature effects in small
diameter CNTs

23. PROPERTIES OF CNTs
 OPTICAL PROPERTIES
 LEDs and photodetectors based on a single
nanotube have been produced
 Their unique feature is not the efficiency , which
is relatively low, but the narrow selectivity in the
wavelength of emission and detection of light
and the possibility of its fine tuning through the
nanotube structure

24. PROPERTIES OF CNTs
 THERMAL PROPERTIES
 All nanotubes are expected to be very good
thermal conductors along the tube,exhibiting a
property known as ballistic conduction ,but good
insulators laterally to the tube axis

25. PROPERTIES
CNTs

26. APPLICATIONS OF CNTs
 A nanotube based single molecule field effect transistor has been built
 Possible to construct a heterojunction by having a junction between
nanotubes of different helicities-this approach facilitates the creation of a
device with one molecule
 In CNT based field emission displays-CNTs act as electron emitters
 For hydrogen storage both in between and inside the NTs - fuel cell
applications for automobiles
 Used in flow sensor
 Nanotube tips used as nanoprobes in AFM and STM
 In tissue engineering-CNTs act as scaffolding for bone growth