Nanotube Nanoelectronics

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If you re-use any material in this presentation,
please credit Michael S. Fuhrer, University of
Maryland
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Why is Carbon Unique for Electronics?
Carbon
Graphite
Hexagonal lattice 1 pz orbital at each site
4 valence electrons
1 pz orbital
3 sp2 orbitals
Fundamental question Is graphite a metal or a
semiconductor?
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Solid State Physics in One Dimension
1 orbital (doubly degenerate)
1 atom 1 electron
Ten atoms
Energy Levels
Ground state Fill lowest five (doubly
degenerate) levels
Excited state Energy e above ground
state metallic
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Solid State Physics in One Dimension
1 orbital (doubly degenerate)
1 atom 1 electron
Dimerization can lower energy
Energy Levels
Dimerization creates two bands Electrons fill
lower band semiconducting
Excited state costs energy Eg
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Graphite Atoms or Dimers?
Graphite Metallic in some
directions, Semiconducting in others!
Atomic chain metallic
Dimer chain semiconducting
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Rolling up graphene into a tube
Graphics courtesy Rick Smalley

• Pick a lattice vector in graphite
• Cut out a strip perpendicular
• to that vector

• Roll up the strip
• to form a tube!

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Nanotubes Metallic or Semiconducting?
Metallic
Semiconducting
Whether nanotube is metallic or semiconducting
depends on how nanotube is wrapped.
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Nanotube Band Structure
Metal
E2 (hvFk)2
Semiconductor
E2 ?2 (hvFk)2