Transcript Chemical Bonding of Carbon Nanotubes

Chemical Bonding of Carbon
Nanotubes
Doug Wylie 04/20/04
2 Types of Bonding related to Nanotubes
• Covalent Bonding – Strong bond between individual
neighbouring carbon atoms in a single tube
• Bonding found along the 2-D plane in a hexagonally close
packed sheet of graphite
• Van der Waal Forces – Weak bond between the individual
nanotubes themselves
• Bonding between separate layers of graphite
• (Reason why graphite is an excellent lubricant, and why talcum
powder feel so smooth!)
• Nanotubes are composed entirely of sp2
bonds, similar to graphite. Stronger than the sp3
bonds found in diamond. This bonding structure
provides them with their unique strength.
• Nanotubes naturally align themselves into
"ropes" held together by Van Der Waal Force.
• Under high pressure, nanotubes can merge
together, trading some sp2 bonds for sp3 bonds,
giving great possibility for producing strong,
unlimited-length wires through high-pressure
nanotube linking.
Typical Values of a Single Walled Carbon Nanotube
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Equilibrium Structure
Average Diameter of SWNT's
Distance from opposite Carbon Atoms
Analogous Carbon Atom Separation
Parallel Carbon Bond Separation
Carbon Bond Length
C - C Tight Bonding Overlap Energy
Lattice Constant
1.2-1.4 nm
2.83 Å
2.456 Å
2.45 Å
1.42 Å
~ 2.5 eV
17 Å
Comparison between Diamond and
Graphite
Comparison showing Diamond and Graphite
bonding along the cube body-diagonal direction
ie: perpendicular to the planes of packing
Conclusions
• Covalent bonding is a very strong bond (can often be
stronger than Ionic bonding)
• Weak VdW forces allow rolling up of indivitual graphite
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sheets into tubes.
Electrons are shared between Carbon atoms so as to fill
outer electron shells.
Covalent bonds are highly directional (unlike Ionic)
therefore only a few characteristic shapes are found.
Carbon Nanotubes exhibit quite different properties
related to size and width of tube but the bonding type
remains the same.