Carbon Nanotubes
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Transcript of Carbon Nanotubes
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Carbon Nanotubes
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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,
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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
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• 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.
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Types of CNTs
1. Single Wall CNT (SWCNT)2. Multiple Wall CNT (MWCNT)
Can be metallic or semiconducting depending on their geometry.
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Single Walled CNT’s
• Made by a single layer of a graphite sheet, cutting it into a small piece of any size, and rolling it.
Single-walled carbon nanotubes
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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.
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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 carbon-
based electronics using semiconducting and metallic carbon nanotubes of different values of n and m.
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Types of Single-Walled Carbon Nanotubes
n and m can be counted at the end of the tube
Zigzag (n,0)
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Types of Single-Walled Carbon Nanotubes
Chiral (n,m)
Armchair (n,n)
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Armchair (n,m) = (5,5) = 30
Zig Zag (n,m) = (9,0) = 0
Chiral (n,m) = (10,5)0 < < 30
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MWCNT
A tower of multiwalled carbon Nanotubes
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• Take multiple layers of a graphite sheet and roll them in the form of a cylinder.
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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.
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CNT Properties
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CNT Properties (cont.)
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Nanotubes Growth Methodsa) Arc Discharge b) Laser
Abalation• Involves condensation of C-
atoms 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.
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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
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Application Electrical1. Field emission in vacuum electronics2. Building block for next generation of
VLSI3. Nano lithography
Energy storage4. Lithium batteries5. Hydrogen storage
Biological6. Bio-sensors7. Functional AFM tips8. DNA sequencing
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Challenges & Future..Future applications:• Already in product: CNT tipped AFM• Big hit: CNT field effect transistors based
nano electronics.• Futuristic: CNT based OLED, artificial
muscles…
Challenges:• Manufacture: Important parameters are
hard to control.• Large quantity fabrication process still
missing.• Manipulation of nanotubes.
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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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