presented by:
Shishir Rai

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Carbon Nanotubes
What is a Carbon Nanotube?
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.
A CNT is characterized by its Chiral Vector: Ch = n â1 + m â2,
q ® Chiral Angle with respect to the zigzag axis.
Why do Carbon Nanotubes form?
Carbon Graphite (Ambient conditions)
sp2 hybridization: planar
Diamond (High temperature and pressure)
sp3 hybridization: cubic
Nanotube/Fullerene (certain growth conditions)
sp2 + sp3 character: cylindrical
Finite size of graphene layer has dangling bonds. These dangling
bonds correspond to high energy states.
Eliminates dangling bonds
Nanotube formation + Total Energy
Increases Strain Energy decreases
Types of CNTs
 Single Wall CNT (SWCNT)
 Multiple Wall CNT (MWCNT)
 Can be metallic or semiconducting depending on their geometry
CNT Properties
CNT: Implications for electronics
 Carrier transport is 1-D.
 All chemical bonds are
satisfied Þ CNT Electronics not bound to use SiO2 as an insulator.
 High mechanical and thermal stability and resistance to electromigration Þ Current densities upto 109 A/cm2 can be sustained.
 Diameter controlled by chemistry, not fabrication.
 Both active devices and interconnects can be made from semiconducting and metallic nanotubes.
Nanotube Growth Methods
) Arc Discharge
b) Laser Abalation
 Involve 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 mm 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.
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
Controlled Growth by CVD
a) SEM image of aligned nanotubes.
B) SEM image of side view of towers. Self-alignment due to Van der Walls interaction.
c) High magnification SEM image showing aligned nanotubes.
d) Growth Process: Base growth mode.