Transcript Carbon Nanotubes - ROYAL MECHANICAL

Carbon Nanotubes
CARBON NANOTUBES
• Discovered in 1991 by Sumiyo Iijima, a Japanese
scientist working at the NEC Corporation.
• Is a tubular form of carbon with a diameter as small
as 0.4 nm and length from a few nanometers up to a
millimeter.
• Length-to-diameter ratio of a carbon nanotube can
be as large as 28,000,000:1, which is unequalled by
any other material.
• Carbon exists in several forms; graphite and
diamond are the most familiar.
• A CNT is characterized by its Chiral Vector: Ch = n â1
+ m â2,
Formation of CNT
• Process which is used to form these Nanotubes,
is called Chemical Vapor Deposition.
• Can be made in a standard chemistry laboratory.
• A quartz tube about 1 inch in diameter serves as
the growth reactor and is inserted inside a tube
furnace.
Scanning electron microscopy of nanofibers covered with nanotubes
• Tube furnace is a standard
heating device for
conducting, syntheses and
purifications.
• Nanotube grows on a silicon
wafer that is placed at a
central location inside the
quartz tube.
• A thin layer of iron or nickel
or cobalt is applied to the
silicon wafer to serve as a
catalyst to grow the
nanotubes.
• In a few minutes, the silicon
wafer appears black,
indicating that it is covered
with nanotubes.
Types of CNTs
1. Single Wall CNT (SWCNT)
2. Multiple Wall CNT (MWCNT)
Can be metallic or semiconducting depending
on their geometry.
Single Walled CNT’s
Single-walled carbon nanotubes
• Made by a single layer of a graphite sheet,
cutting it into a small piece of any size, and
rolling it.
SWCNT….
• Characterized by a set of two integers (n, m) called
the Chirality vector.
• When (n-m)/3 is an integer (for example when n is 8
and m is 2), then the nanotube has metallic
properties.
• If (n-m)/3 is not an integer, the corresponding
nanotube behaves like it is a semiconductor.
• Ability to create tubes of either metallic or
semiconductor nature is of great practical
importance.
Conti..
• Single wall carbon nanotubes exhibit
extraordinary mechanical properties.
• Hundred times stronger than steel at one-sixth
of its weight.
• Ability to carry current and heat along the axial
direction is extraordinary.
• Has the potential to replace copper wires as
conductors.
• Scientists and engineers envision all carbonbased electronics using semiconducting and
metallic carbon nanotubes of different values of
n and m.
Types of Single-Walled Carbon Nanotubes
n and m can be counted
at the end of the tube
Zigzag (n,0)
Types of Single-Walled Carbon Nanotubes
Armchair (n,n)
Chiral (n,m)
Armchair (n,m) = (5,5)
 = 30
Zig Zag (n,m) = (9,0)
 = 0
Chiral (n,m) = (10,5)
0 < < 30
MWCNT
A tower of multiwalled carbon Nanotubes
• Take multiple
layers of a graphite
sheet and roll them
in the form of a
cylinder.
Fig. 2. (a). Band structure of
a graphene sheet (top) and
the first Brillouin zone
(bottom).
(b) Band structure of a
metallic (3,3) CNT. (c) Band
structure of a (4,2)
semiconducting CNT. The
allowed states in the
nanotubes are cuts of the
graphene bands indicated
by the white lines. If the cut
passes through a K point,
the CNT is metallic;
otherwise, the CNT is
semiconducting.
CNT Properties
CNT Properties (cont.)
Nanotubes Growth Methods
a) Arc Discharge
Abalation
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b) Laser
Involves condensation of Catoms generated from
evaporation of solid carbon
sources. Temperature ~
3000-4000K, close to melting
point of graphite.
Both produce high-quality
SWNTs and MWNTs.
MWNT: 10’s of m long, very
straight & have 5-30nm
diameter.
SWNT: needs metal catalyst
(Ni,Co etc.).
Produced in form of ropes
consisting of 10’s of
individual nanotubes close
packed in hexagonal crystals.
Nanotubes Growth Methods
c) Chemical Vapor
Deposition:
Hydrocarbon + Fe/Co/Ni catalyst
550-750°C
CNT
Steps:
• Dissociation of hydrocarbon.
• Dissolution and saturation
of C atoms in metal
nanoparticle.
• Precipitation of Carbon.
Choice of catalyst material?
Base Growth Mode or Tip Growth
Mode?
• Metal support interactions
Application
Electrical
1.
Field emission in vacuum electronics
2.
Building block for next generation of VLSI
3.
Nano lithography
Energy storage
1.
Lithium batteries
2.
Hydrogen storage
Biological
1.
Bio-sensors
2.
Functional AFM tips
3.
DNA sequencing
Challenges & Future..
Future applications:
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Already in product: CNT tipped AFM
Big hit: CNT field effect transistors based nano
electronics.
Futuristic: CNT based OLED, artificial
muscles…
Challenges:
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Manufacture: Important parameters are hard
to control.
Large quantity fabrication process still missing.
Manipulation of nanotubes.
Conclusion
• Their phenomenal mechanical properties, and
unique electronic properties make them both
interesting as well as potentially useful in future
technologies.
• Significant improvement over current state of
electronics can be achieved if controllable
growth is achieved.
• Growth conditions play a significant role in
deciding the electronic and mechanical
properties of CNTs.
• Growth Mechanisms yet to be fully established.
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