Carbon Fullerenes

1
Carbon Fullerenes
2
Formation

• Basic model
• Clustering
• Chains, rings, tangled poly-cyclic structures or
  graphite sheets
• Annealing (no collisions)
• Random cage, open cage, closed cage structures
• Elimination of dangling bonds
• Fullerenes
• Stone-Wales transformation
• Migration of pentagons
• Rearrangement to lower energy
• Critical parameters
• Annealing time
• Annealing temperature
• 10-1 ms 1000-1500 K for the laser method
• 100 s 1000 K for the arc discharge method

3
Formation

• Picture models
• Pentagon road (1)
• Addition of dimers and trimers leaving pentagons
  as a deffect
• Reduction of dangling bonds, adjacent pentagons
  too much stress
• Ring pentagon road (2)
• Stacking of proper size of C rings
• Pentagon annealing
• Fullerene road (3)
• Linear chains up to C10
• Rings C10 to C20, fullerene from C30,
• Addition of C2 at two neighboring p-s
• Ring annealing (4)
• Big rings, bi/tri-cyclic structures (C60) anneal
  under high T conditions
• Chain annealing (5)
• Long chain with spiral structure
• Graphite road (6)
• C10 clusters, graphite sheet, curling
• Nanotube road (7)
• Chips of carbon nanotubes

1
4
Formation

• Molecular dynamics (MD) simulations
• Many-body potential function
• Kinetic energy of clusters
• Classical mechanics
• translation, vibration and rotation
• Clustering
• Collisions of atoms or clusters grow and
  fragmentation of cluster
• Cooling collisions with buffer gas and radiation
• Annealing between collisions

T 3000 K
5
Formation

• Temperature dependence of cluster structures
• Collision-free annealing of C60
• Stone-Wales transformation

6
Formation

• Fullerene-like cage structures 2500ltTlt3500
• Extrapolation roughly agrees with experimental
  conditions

7
Formation
C24 flat cluster, 0 s

• Model of charges at bonds
• Molecules classical dynamics
• Electrons quantum mechanics
• Ground and excited states
• Interaction potentials
• Covalent bonds, rotation, torsional vibration
• Interaction between atoms and electrons
• bonding electron pairs at the centers of the
  covalent bonds
• unshared electrons at approximately the same
  distance from the carbon atoms
• Classical equations of motion for both
• Folding of flat carbon clusters
• Unshared e rearrange and form symmetrical sphere
  layer outside the fullerene

Semispheroid, 50 ps
Fullerene, 150 ps
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Formation

• Another QM and MD simulation
• Density functional theory
• Ring fusion spiral zipper mechanism
• C atoms combine to C2 and C3
• nlt10 linear chain Cn
• sp hybrid prefer linear geometry
• 10ltnlt30 ring
• Energy gain in killing dangling bonds
  overcompensates for strain energy caused by
  folding
• ngt30 ring structure can grow in fullerene

9
Synthesis

• Graphite vaporization or ablation
• Laser
• Resistive heating
• AC or DC arc
• Pyrolysis of hydrocarbons
• Flame combustion
• Laser
• Torch or tube furnace
• Ion implantation
• Temperature of condensation and annealing
• 10001500 K
• C60 30/gram

The first published mass spectrum of carbon
clusters in a supersonic beam produced by laser
vaporization of a carbon target in a pulsed
supersonic nozzle operating with a helium carrier
gas.
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Synthesis
Fullerenes are made wherever carbon condenses. It
just took us a little while to find out. Smalley

• Laser vaporization of graphite
• laser-vaporization supersonic cluster beam
  technique (Rice Univ., Texas)
• 1985 H. W. Kroto (Sussex Univ., Brighton) R.
  E. Smalley (Rice)
• Experiment
• NdYAG
• 300 mJ, 535 nm, 5ns
• Rotating graphite disk
• Plasma of vaporized carbon atoms
• 10 000 K
• High-density helium pulse
• Condensation and transport
• Integration cup
• Adjusts the time of clustering
• Supersonic expansion
• Frizzing out the reactions
• Ionization by excimer laser
• Mass spectrometer

11
Synthesis

• Laser evaporation of doped carbon

12
Synthesis

• Resistive heating of graphite
• Carbon rod in 100 torr helium
• Kratschmer-Huffman 1990
• First macroscopic quantities of C60
• Carbon arc
• AC or DC arc in 100 torr helium
• 60 Hz, 100200 A, 1020 V rms
• Continuous graphite rod feedeing

The generator design based on the
Kratschmer-Huffman apparatus.
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Synthesis

• Pyrolysis of hydrocarbons
• Benzene, acetylene, toluene
• Polycyclic aromatic hydrocarbons PAH
• Naphtalene
• Mechanism
• Removal of hydrogen
• Curling of joined rings
• Optimum conditions
• Very low pressure and high temperature
• Examples
• Combustion of benzene
• Premixed flame of benzene and oxygen with argon
• 20 torr, C/O 0.995, 10 Ar, 1800 K
• Acetylene/oxygen/argon flame
• Adding Cl2 increases fullerene yield
• Torch heating of naphtalene
• Heating torch
• Pyrolysing torch propane/oxygen 1000 ºC
• Laser pyrolysis

Pyrolysis apparatus
Mechanism of formation of a partial C60 cage from
naphthalene
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Synthesis

• Low-pressure benzene/oxygen diffusion flame
• p 12 40 torr, Tmax 1500 1700 K
• Precursor PAH
• Elimination of CO from oxidized PAH thought to be
  a source of C pentagons
• Highest yield of fullerenes
• High soot formation
• High dilution with argon

15
Synthesis

• Atmospheric pressure combustion

Oxy-acetylene torch (Ferrocene (C10H10Fe)
Fe_at_C60)
Syringe injector Benzene, Dicyclopentadiene,
Pyridine (C5H5N), Thiophene (C4H4S)
Stainless steel plate on water-cooled brass block
(lt 800 K)
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Synthesis

• DC arc torch dissociation of C2Cl4
  (tetrachlorethylene)

Operating conditions Torch power 56 kW He flow
rate 225 slm C2Cl4 feed rate 0.29 mol/min
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Synthesis

• Ion implantation
• Carbon ions 120 keV
• Copper substrates 7001000 ºC
• Thin film (diamond, fullerenes, onions)
• Endohedral fullerenes
• Evaporation of fullerene (C60) onto a substrate
• Ions of dopant

N_at_C60
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Solid State C60 - Fullerite

• Face-centered cubic (fcc)
• The most densely packed structure
• Lattice constant a 14.17 ?
• Weak Van der Waals bonds
• Soft
• Molecules spin nearly freely around centers
• Simple cubic (sc)
• Tlt261 K
• Fixed rotational axis
• 4 C60 molecules arranged at vertices of
  tetraeder, spinning around different but fixed
  axis
• Weak coulombic interaction
• Fixed orientation of molecules
• Tlt90 K molecules entirely frozen
• Polymeric
• Covalent bonds
• Photo-excitation, molecular collisions,
  high-pressure/temperature, ionization
• Insolvable in toluene

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Purification

• Extraction from carbon soot
• Cnlt100 solvable in aromatic solvents
• Toluene, benzene, hexane, chloroform
• C60 magenta
• C70 dark red
• Cngt100 high boiling-solvents
• trichlorbenzene
• Separation by chromatograph

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Derivatives

• Intercalation (fullerides)
• Octahedral or tetrahedral inter. sites
• Alkali or alkaline-earth metal atoms
• Na, K, Rb, Cs, Ca, Sr and Ba)
• Charge transfer to the cage
• Superconductors
• Polymers

Ba6C60 7 K
K3C60 19 K
Rb3C60 29 K
Cs3C60 30 K
Cs2RbC60 33 K
Polymerized Rb1C60
C60-Fullerene tetrakis(dimethylamino)ethylene -
ferromagnet
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Derivatives

• Heterofullerenes
• Substitution of an impurity atom with a different
  valence for C on the cage
• B, N, BN Nb
• C59X (XB,N) nonlinear optical properties
• Deformation of the electronic structure, strong
  enhancement of chemical activity
• Radicals which can be stabilized by dimerization

Azafullerenes (a) C59N, (b) C59HN, and (c)
(C59N)2
C48N12
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Derivatives

• Exohedral
• Covalent addition of atom or molecule
• Hydrogenation
• C60H18, C60H36
• Fluorination
• C60F36, C70F34, C60F60 (teflon balls)
• Oxidation
• Organic groups and complexes

(eta2-C70-Fullerene)-carbonyl-chloro-bis(triphenyl
phosphine)-iridium
C60Cl6
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Derivatives

• Endohedral
• Synthesis
• Evaporation of doped carbon
• Arc, laser
• Ion implantation
• M_at_C60
• Noble gases
• without overlap of Van der Waals radii
• Metallofullerenes
• B, Al, Ga, Y, In, La
• Stabilize cages not fulfilling isolated
  pentagons rule (nlt60)
• With permanent dipole moment form di/trimers and
  large aggregates on metal surfaces and C60 films
• Alkali metals
• Lanthanide metals
• N, P (Group V)

Synthesis of microcapsules for medical
applications
N_at_C60
He_at_C60
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Properties

• C60 electron affinity EA 2.65 eV (Cl 3.62, )
• more electronegative than hydrocarbons
• Dissolves in common solvents like benzene,
  toluene, hexane
• Readily sublimes in vacuum around 400C
• Low thermal conductivity
• Pure C60 is an electrical insulator
• C60 doped with alkali metals shows a range of
  electrical conductivity
• Insulator (K6 C60) to superconductor (K3 C60) lt
  30 K
• Interesting magnetic and optical properties
• Ferromagnetism
• At high pressure C60 transfoms to diamond
• C60 soft and compressible brown/black odorless
  powder/solid
• Flexible chemical reactivity

breathing vibrational mode
Pentagonal pinch mode
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Properties

• Simulation of C60-C240 collision
• Simulation of C60 melting

Kinetic energy 10 eV
Kinetic energy 100 eV
Kinetic energy 300 eV
David Tomanek Theoretical Condensed Matter
Physics Michigan State University
26
Potential applications

• Lubrication
• Molecular-sized ball bearing
• Not economical
• Superconductors
• Intercalation metal fullerides
• (Semi)Conductors
• Excellent conductors when compressed
• Photoconductors
• add conducting properties to other polymers as a
  function of light intensity
• Optical Limiters
• C60 and C70 solutions absorb high intensity
  light protection for light-sensitive optical
  sensors
• Atom Encapsulation
• Radioactive waste encapsulation
• Ho_at_C82

Rh-C60 polymer with vacancies Excess spin
density Dipole moment of magnitude 2.264 Debye
per C60 unit
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Potential applications

• Diamond films
• Smoother than vaporizing graphite
• Novel polymers
• Optoelectronic nanomaterials and buliding blocks
  for nanotechnology
• Endohedral fullerenes
• Nanobots
• Medical applications
• Magnetic Resonance Imaging markers
• Metal organic complex (toxic Ga)
• contrast agents, tracers
• anti-viral (even anticancer) agents
• neuroprotective agents
• fullerene-based liposome drug delivery systems
• deployment of fullerene therapeutics to targeting
  vehicles

MRI fullerene contrasting agent

• Water soluble tail (red gray)
• Encapsulates 2 gadolinium metal atoms (purple)
  and 1 scandium (green) attached to central
  nitrogen atom
• H2O molecules (red yellow)

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Potential applications

• Potential AIDS inhibitor
• HIV reproduces by growing long protein chains
• Protein is cut in the active site of enzyme
  HIV-protease
• Derivative of C60 has been synthesized that is
  soluable in water

Model of C60 docked in the binding site of HIV-1
protease