Forms of Carbon

1
Forms of Carbon
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Diamond

• Covalent crystals C, Si, Ge, SiC
• Strong sp3s bonds form tetrahedral structure
• Face Centered Cubic lattice (fcc)
• 8 C atoms at the vertices of the cube, 6 C
  atoms in the face center, and 4 more
  within the unit cell
• Each C is tetrahedrally bonded to four others
• All C-C bonds 1.54 ?
• Properties
• Extremely hard
• Strong rigid structure (macromolecule)
• Insulator
• No delocalized e (p bonds)
• High index of refraction and strong dispersion of
  light

Diamond film (CVD)
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Diamond
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Graphite

• Parallel sheets of graphene
• Hexagonal, aromatic, benzene ring arrays
• sp2s bonds stronger than in diamond
• Delocalized p e between sheets
• Covalent-metal bond
• Van der Walls forces between sheets
• Randomly oriented graphite grains
• Properties
• Anisotropic
• Electrical conductivity along sheets
• Graphene zero gap semi-conductor
• Soft, greasy and lubricating
• Strong absorption of light
• On p e

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Graphite
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Fullerene

• Richard Buckminster Fuller (1895 - 1993)
• Bulk solid state Fullerite
• Closed cage C molecule
• Pentagons in hexagonal structure
• Isolated Pentagon Rule IPR (stress)
• Spheroidal curvature
• Admixture of sp3 hybridization
• C60
• Diameter 7 ?
• With ?e 10 ?, cavity 4 ?
• Hexagons (20)
• Single bonds (red) 1.40 ?
• Double bonds (yellow) 1.46 ?
• Pentagons (12)
• Single
• Delocalized p e
• Mostly outside the cage
• Higher density on double bonds
• Influence of sp3 and curvature

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Nanotube

• Cylindrical C nanostructure
• Graphene sheets wrapped into a cylinder
• Armchair (1), zigzag (2), chiral (3)
• sometimes capped by fullerene-like structure
• Diameter 1 to several nm
• Length 101 mm
• Single-walled carbon nanotubes SWCNT
• Bundles (ropes) of tens SWCNT stuck in triangular
  lattice
• Multi-walled carbon nanotubes MWCNT
• Few to few tens of concentric cylinders
• Spacing close to graphite 3.35 ?
• Toughest materials ever known
• High elastic modulus of graphene sheets

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Forms of Carbon