Carbon nanotubes are cylindrical nanostructures made of rolled up graphene sheets with extraordinary mechanical and electrical properties. They can be single-walled or multi-walled depending on the number of concentric cylinders. Carbon nanotubes have a wide range of potential applications due to their strength, conductivity, and other properties including use in electronics, sensors, energy storage, and more. However, their toxicity must still be addressed before many applications.

1. CARBON NANOTUBES
DIVYA C.S
2ND
M.Sc BPS
CBPST, KOCHI

2. • Carbon nanotubes-nanostructures with large application
potential
• Carbon nanotube is a sheet of graphite rolled into tube with
bonds at the end of sheet forming the bonds that close the tube
• Allotropes of carbon (graphite ， diamond ， Amorphous carbon
and Fullerene ) (cylindrical members of the fullerene structural
family)
• With a nanostructure. length-to-diameter ratio of up to
132,000,000:1,which is significantly larger than any other material.
• Extraordinary strength and unique electrical properties, efficient
thermal conductors. (limited by their potential toxicity)
• They are less than 100 nanometers in diameter and can be as thin as 1
INTRODUCTION

3. • Carbon nanotubes are fullerene-related structures
which consist of graphene cylinders closed at either
end with caps containing pentagonal rings.
• Discovered in 1991 by the Japanese electron
microscopist Sumio Iijima.
• These are large macromolecules that are unique for
their size, shape, and remarkable physical properties.

4. • Carbon nanotubes have been synthesized for a long time as products
from the action of a catalyst over the gaseous species originating from
the thermal decomposition of Hydrocarbons.
• The worldwide enthusiasm came unexpectedly in 1991, after the
catalyst-free formation of nearly perfect concentric multiwall carbon
nanotubes (c-MWNTs ） was reported as by-products of the
formation of fullerenes by the electric-arc technique
• Economical aspects are leading the game to a greater and greater
extent. According to experts, the world market is predicted to be more
than 430M$ in 2004 and estimated to grow to several b $ before 2009.

5. Nanotubes could be produced in bulk
quantities by varying the arc-evaporation
conditions.
Nanotube hemispheric
• Nanotubes have a very broad range of
electronic, thermal, and structural
properties that change depending on the
different kinds of nanotube (defined by
its diameter, length, and chirality, or
twist).
• Besides having a single cylindrical wall
(SWNTs), Nanotubes can have multiple
walls (MWNTs)--cylinders inside the
other cylinders.

6. NANOTUBE GEOMETRY
There are three unique geometries of carbon nanotubes. The
three different geometries are also referred to as flavors. The
three flavors are armchair, zig-zag, and chiral [e.g. zig-zag (n, 0);
armchair (n, n); and chiral (n, m)]. These flavors can be classified
by how the carbon sheet is wrapped into a tube

7. • The (n,m) nanotube naming
scheme can be thought of as a
vector (Ch) in an infinite
graphene sheet that describes
how to "roll up" the graphene
sheet to make the nanotube.
T denotes the tube axis, and a1
and a2 are the unit vectors of
graphene in real space
Structure of Carbon Nanotubes
Single-Wall Nanotubes SWNTs

8. Most single-walled nanotubes (SWNT) have a diameter of
close to 1 nanometer, with a tube length that can be many
millions of 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
the graphene sheet is wrapped is represented by a pair of
indices (n,m) called the chiral vector. The integers n and m
denote the number of unit vectors along two directions in
the honeycomb crystal lattice of graphene. If m = 0, the
nanotubes are called "zigzag". If n = m, the nanotubes are
called "armchair". Otherwise, they are called "chiral".

9. Single-Wall Nanotubes SWNTs
Armchair (n,n)
The chiral vector is
bent, while the
translation vector
stays straight
Graphene
nanoribbon
The chiral vector is
bent, while the
translation vector
stays straight
Zigzag (n,0) Chiral (n,m) n and m can be
counted at the end
of the tube
Graphene
nanoribbon

10. Single-Wall Nanotubes SWNTs
Fig. 3.3 Image of two neighboring chiral SWNTs within a
SWNT bundle as seen by high resolution scanning
tunneling microscopy (by courtesy of Prof. Yazdani,
University of Illinois at Urbana, USA)

11. SWNT Rope

12. Multiwall Nanotubes MWNT
longitudinal view of a concentric multiwall carbon nanotube
(c-MWNT) prepared by electric arc.
•Multi-walled nanotubes (MWNT)
consist of multiple rolled layers
(concentric tubes) of graphite;
•In the Russian Doll , sheets of
graphite are arranged in
concentric cylinders;
•In the Parchment model, a single
sheet of graphite is rolled in
around itself, resembling a scroll
of parchment or a rolled
newspaper. (3.3 Å);

13. Nanobud
•carbon nanotubes + fullerenes.
•useful properties of both fullerenes and
carbon nanotubes.
•In particular, they have been found to be
exceptionally good field emitters.
• In composite materials, the attached
fullerene molecules may function as
molecular anchors preventing slipping of
the nanotubes, thus improving the
composite’s mechanical properties

14. Extreme carbon nanotubes
•The longest carbon nanotubes (18.5 cm long) was reported in 2009. These
nanotubes were grown on Si substrates using an improved chemical vapor
deposition (CVD) method and represent electrically uniform arrays of
single-walled carbon nanotubes
•The thinnest carbon nanotube is armchair (2,2) CNT with a diameter of 3 Å
•The thinnest free standing single-walled carbon nanotube is about 4.3 Å
in diameter. Researchers suggested that it can be either (5,1) or (4,2)
SWCNT, but exact type of carbon nanotube remains questionable.

15. Synthesis of Carbon Nanotube
1 Laser Ablation – Experimental Devices
- graphite pellet
containing the catalyst put
in an inert gas filled quartz
tube;
-oven maintained at a
temperature of 1,200 ◦
C;
-energy of the laser beam
focused on the pellet;
-vaporize and sublime the
graphiteSketch of an early laser vaporization apparatus
The carbon species are there after deposited as soot in different regions:
water-cooled copper collector, quartz tube walls.

16. 2 Synthesis with CO2 laser
Fig. 3.10 Sketch of a synthesis reactor with a
continuous CO2 laser device
Vaporization of a target at a
fixed temperature by a
continuous CO2 laser beam (λ =
10.6μm). The power can be varied
from 100Wto 1,600 W.
The synthesis yield is controlled
by three parameters: the
cooling rate of the medium
where the active, secondary
catalyst particles are formed,
the residence time, and the
temperature (in the 1,000–
2,100K range) at which SWNTs
nucleate and grow.

17. 3 Electric-Arc Method – Experimental Devices
Sketch of an electric arc reactor. It consists
of a cylinder of about 30 cm in diameter
and about 1m in height.
After the triggering of the arc
between two electrodes, a
plasma is formed consisting
of the mixture of carbon
vapor, the rare inert gas
(helium or argon), and the
vapors of catalysts.
The vaporization is the
consequence of the energy
transfer from the arc to the
anode made of graphite
doped with catalysts.

18. Properties of Carbon Nanotube
•The strongest and stiffest materials .
•1/50,000th the thickness of a human hair.
•In 2000, a MWCN was tested to have a tensile strength of 63 gigapascals (the
ability to endure tension of 6300 kg on a cable with cross-section of 1 mm2
.)
•low density for a solid of 1.3 to 1.4 g·cm−3
•Standard single walled carbon nanotubes can withstand a pressure up to 24GPa
without deformation (hardness)
•Extraordinary electrical conductivity, heat conductivity, and mechanical properties.
• They are probably the best electron field-emitter known, largely due to their high
length-to-diameter ratios

19. Kinetic properties
Multi-walled nanotubes, multiple concentric nanotubes precisely nested within one
another, exhibit a striking telescoping property whereby an inner nanotube core may
slide, almost without friction, within its outer nanotube shell thus creating an
atomically perfect linear or rotational bearing.
Electrical properties
Semiconductor
Thermal properties
The strength of the atomic bonds in carbon nanotubes allows them to withstand
high temperatures. Because of this, carbon nanotubes have been shown to be very
good thermal conductors.

20. Application: Efficient Field
Emitters
The electrons are taking out from
the tips and sent onto an electron
sensitive screen layer.
Replacing the glass support and
protection of the screen by some
polymer-based material will even
allow the develop of flexible screens.
Fig. 3.28 (a) Principle of a field-emitter-
based screen. (b) SEM image of a
nanotube-based emitter system (top
view). Round dots are MWNT tips
seen through the holes
corresponding to the extraction grid.
The first commercial
flat TV sets and computers using
nanotube-based screens are
about to be seen in stores.
(Motorola, NEC, NKK, Samsung,
Thales, Toshiba, etc.)

21. Fig. 3.29a,b Demonstration of the ability of SWNTs in detecting
molecule traces in inert gases.
(a) Increase in a single
SWNT conductance when 20 ppm
of NO2 are added to an
argon gas flow.
(b) Same with 1% NH3 added to the
argon
gas flow
Application: Chemical
Sensors

22. • AFM probe tips. Single-walled carbon nanotubes have been attached to
the tip of
an AFM probe to make the tip "sharper". . Also, the flexibility of the nanotube
prevents damage to the sample surface and the probe tip if the probe tip
happens to "crash" into the surface. They attached carbon nanotubes to AFM
probes for the purpose of increased resolution as well as decreased wear on
sample and probe tip.
• Flat panel display screens. When a nanotube is put into an electric field,
it will emit electrons from the end of the nanotube like a small cannon. If those
electrons are allowed to bombard a phosphor screen then an image can be
created. When scientists instead use millions of carbon nanotubes as tiny
electron guns, the required dimensions change and the creation of a flat panel
display becomes possible. Advertising billboards have already been made and
are being used.
OTHER APPLICATIONS

23. • Nanoscale electronics/nanocomputing Scientists have exploited the
mechanical and electrical properties of carbon nanotubes to produce
molecular electronic devices. When nanotubes are placed in a grid, the
intersections of the nanotubes become bits of information that can be stored
non-volatilely.
Semiconducting nanotubes also can be used as single molecule transistors.
• Nanothermometer. A carbon nanotube can be partially filled with gallium
metal.
When the temperature is changed, the gallium metal expands or contracts to fill
or empty the carbon nanotube. The gallium level in the carbon nanotube varies
almost linearly with temperature. This new device may find use in certain
microscopies.
• Flash photography and carbon nanotubes. Scientists have discovered
that as grown
single-walled carbon nanotubes can be ignited by holding a conventional
camera flash a few centimeters away and flashing the sample.

24. • Actuators/Artificial muscles. An actuator is a device that can induce
motion. In
the case of a carbon nanotube actuator, electrical energy is converted to
mechanical energy causing the nanotubes to move. Two small pieces of
"buckypaper," paper made from carbon nanotubes, are put on either side of a
piece of double-sided tape and attached to either a positive or a negative
electrode. When current is applied and electrons are pumped into one piece of
buckypaper and the nanotubes on that side expand causing the tape to curl in
one direction. This has been called an artificial muscle, and it can produce 50
to
100 times the force of a human muscle the same size. Applications include:
robotics, prosthetics.

25. • Microelectro mechanical devices.
Dr. Morinobu Endo at Shinshu University mixed nylon with carbon fibers (not
nanotubes) 100-200 nm in diameter creating a nanocomposite materials that
could be injected into the world’s smallest gear mold. The carbon fibers have
good thermal conductivity properties that cause the nanocomposite material to
cool more slowly and evenly allowing for better molding characteristics of the
nanocomposite. The "improved" properties of the nanocomposite allow it more
time to fill the tiny micron-sized mold than nylon would by itself. The tiny gears
currently are being made in collaboration with Seiko for use in watches.
• Hydrogen storage. When oxygen and hydrogen react in a fuel cell,
electricity is produced and water is formed as a byproduct. If industry wants to
make a hydrogen-oxygen fuel cell, scientists and engineers must find a safe
way to store hydrogen gas needed for the fuel cell. Carbon nanotubes may be
a viable option. Carbon nanotubes are able to store hydrogen and could
provide the safe,