Fullerenes; discovery, properties and applications

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Fullerenes discovery, properties and applications

• Physics 790 presentation by
• Mustapha Habibi
• UNR Fall 2007

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Outline

• History
• Introduction
• What are fullerenes?
• Bonds in the sp2 hybridization.
• How are fullerenes made?
• Properties
• Photo-ionization of fullerenes
• Ion-photon merged-beams end station at ALS
• Photo-ionization process
• Photo-ionization of C60
• Photo-ionization of C84
• Comparison between the two spectra
• Applications of fullerenes
• Summary

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How did we get to know about fullerenes?

• Nuclear physics researchers Hahn Strassman in
  Germany noticed that carbon cluster ions up to
  C15 were produced in a high frequency arc with a
  graphite electrode in the 1943.
• A Japanese physical organic chemist E. G. Osawa
  had perceived that carbon in the single layer
  closed cages structure would be aromatic and
  therefore stable, in early 1970.
• Galpern (Russian scientist) had completed the
  first of many Hückel calculations showing that it
  would be a closed shell molecule with a large
  HOMO-LUMO gap in 1973.
• Fullerenes were discovered experimentally for the
  first time by a group of scientists at Rice
  University, Houston, Texas, in September of 1985.

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Photograph of the research group that discovered
the fullerenes at Rice University in September of
1985. standing Curl, kneeling (left to right)
OBrian, Smalley, Kroto and Heath
Nobel Prize in chemistry in 1996
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What are fullerenes?

• Fullerenes are closed hollow cages consisting of
  carbon atoms interconnected in pentagonal and
  hexagonal rings.
• Each carbon atom on the cage surface is bonded to
  three carbon neighbors therefore is sp2
  hybridized.
• The most famous fullerene is C60, known also by
  buckyball ".
• Other relatively common clusters are C70, C72,
  C74, C76, C80, C82 and C84 (plenty of others,
  higher or lower than C60, exist too but less
  abundant in the experimentally produced mixture
  fullerene soot).

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Mass spectrum of carbon clusters
R. E. Smalley, Nobel Prize lecture, December 7,
1996
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What are fullerenes? (continued)
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Carbon-carbon bonds in the sp2 hybridization
configuration.

• Hybridization The mixing of atomic orbitals,
  such as s and p orbitals, to form a new, hybrid
  orbital for use in bonding.
• Carbon virtually never uses a pure s orbital to
  bond.
• Carbon has three different ways to hybridize
  sp3, sp2, and sp.
• sp3 all three p orbitals are mixed in with the s
  orbital.
• sp2only two of the p orbitals are mixed in.
• Sp only one p atomic orbital is mixed with an s
  orbital.
• The designation spm is intended to be a
  shortened form of s1pm.

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How are fullerenes made?

• Fullerenes can be made by vaporizing carbon
  within a gas medium.
• (they could form spontaneously in a condensing
  carbon vapor)

R. E. Smalley, Nobel Prize lecture, December 7,
1996
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Outline

• History
• Introduction
• What are fullerenes?
• Bonds in the sp2 hybridization.
• How are fullerenes made?
• Properties
• Photo-ionization of fullerenes
• Ion-photon merged-beams end station at ALS
• Photo-ionization process
• Photo-ionization of C60
• Photo-ionization of C84
• Comparison between the two spectra
• Applications of fullerenes
• Summary

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Properties of fullerenes

• No other element has such wonderful properties as
  carbon.
• Buckyballs are relatively cheap carbon is
  everywhere!
• Even though each carbon atom is only bonded with
  three other carbons (they are most comfortable
  with four bonds) in a fullerene molecule,
  dangling a single carbon atom next to the
  structure is not strong enough to break the
  structure of the fullerene molecule.

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Properties of fullerenes (continued)

• In fullerenes, 12 pentagonal rings are necessary
  and sufficient to effect the cage closure.
• Fullerenes contain carbon atoms arranged as a
  combination of 12 pentagonal rings and n
  hexagonal rings. The chemical formula is C202n.
• Fullerene cages are about 7-15 Å in diameter, and
  are one carbon atom thick.

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Properties (continued)

• Quite stable from chemical and physical points of
  view (breaking the balls requires temperatures of
  about 1000 C).
• Highest tensile strength of any known 2D
  structure or element.
• Highest packing density of all known structures.
• Impenetrable to all elements under normal
  circumstances, even to a helium atom with an
  energy of 5 eV.

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Outline

• History
• Introduction
• What are fullerenes?
• Bonds in the sp2 hybridization.
• How are fullerenes made?
• Properties
• Photo-ionization of fullerenes
• Ion-photon merged-beams end station at ALS
• Photo-ionization process
• Photo-ionization of C60
• Photo-ionization of C84
• Comparison between the two spectra
• Applications of fullerenes
• Summary

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Ion-photon merged-beams endstation at the
Advanced Light Source
Beamline 10.0.1






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Direct (non-resonant) Photoionization
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e-
e-
e-
Ion A
Ion A
Photon A (atom, ion or molecule)
? A free electron
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Indirect (resonant) Photoionization
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e-
e-
e-
Ion A
Final charge 1
Photon A
? Inner shell e- of ion A jumps to an upper
energy level ( A)
? The excited e- decays back to its initial
energy level giving its excess energy to another
e- from the same upper level
? The latter gets enough energy to get away and
be free
? e- A
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Giant Resonances

• A giant resonance in general describes a
  collective excitation of the nucleons or
  electrons of an atom or ion.
• Giant resonances may be excited by
  photo-absorption or by collisions.
• The term giant resonance in atoms has also been
  applied to describe a dominant excitation that
  accounts for a significant fraction of the total
  oscillator strength.

M. Ya Amusia and J. P. Connerade, Rep. Prog.
Phys. 63, 41-70 (2000).
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Surface Plasmon
e-
e-
1
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Volume Plasmon
e-
1
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Photoionization of C60 ions
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Photoionization of C60 (continued)
Localized Molecular Excitations

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Two distinct modes of collective oscillations of
the 239 valence electrons of the C60 molecule
due to photo-excitation are evident.
S.W.J. Scully et al., Phys. Rev. Lett. 94, 065503
(2005).
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Fullerene ions in initially higher charge states
photoionize less readily.
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Photoionization of C84 molecular ion.
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(No Transcript)
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C60 and C84 photoionization cross sections
scale with the number of C atoms.
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Outline

• History
• Introduction
• What are fullerenes?
• Bonds in the sp2 hybridization.
• How are fullerenes made?
• Properties
• Photo-ionization of fullerenes
• Ion-photon merged-beams end station at ALS
• Photo-ionization process
• Photo-ionization of C60
• Photo-ionization of C84
• Comparison between the two spectra
• Applications of fullerenes
• Summary

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Applications of fullerenes.

• Due to their extremely resilient and sturdy
  nature, fullerenes are being considered for use
  in combat armor.
• Researchers have found that water-soluble
  derivates of fullerenes inhibit the HIV-1
  protease (enzyme responsible for the development
  of the virus) and are therefore useful in
  fighting the HIV virus that leads to AIDS.
• Elements can be bonded with C60 or other
  fullerenes to create more diverse materials,
  including superconductors and insulators.

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Summary

• Giant dipole resonances dominate the
  photoionization of fullerene molecular ions in
  the low energy range 17- 50 eV.
• Contributions due to localized and collective
  electron excitations of fullerenes are readily
  distinguishable in photoion-yield spectra.
• Fullerenes have many applications and are very
  useful in military, medicine, nano-technology and
  many other fields .

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Any Questions?
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Fullerenes discovery, properties and applications

• Physics 790 presentation by
• Mustapha Habibi
• UNR Fall 2007