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Carbon Fullerenes

Carbon Fullerenes. 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

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Carbon Fullerenes

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  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 2500<T<3500 • 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

  8. Formation • Another QM and MD simulation • Density functional theory • Ring fusion spiral zipper mechanism • C atoms combine to C2 and C3 • n<10: linear chain Cn • sp hybrid prefer linear geometry • 10<n<30: ring • Energy gain in killing dangling bonds overcompensates for strain energy caused by folding • n>30: 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 • 1000÷1500 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.

  10. Fullerenes are made wherever carbon condenses. It just took us a little while to find out. Smalley Synthesis • 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 • Nd:YAG • 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, 100÷200 A, 10÷20 V rms • Continuous graphite rod feedeing The generator design based on the Kratschmer-Huffman apparatus.

  13. 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 • Photosensitizer SF6 + C2H4 • CO2 laser 100÷180 W, 300 torr Pyrolysis apparatus Mechanism of formation of a partial C60 cage from naphthalene

  14. 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 Syringe injector Benzene, Dicyclopentadiene, Pyridine (C5H5N), Thiophene (C4H4S) Oxy-acetylene torch (Ferrocene (C10H10Fe) – Fe@C60) Stainless steel plate on water-cooled brass block (< 800 K)

  16. 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

  17. Synthesis • Ion implantation • Carbon ions 120 keV • Copper substrates 700÷1000 ºC • Thin film (diamond, fullerenes, onions) • Endohedral fullerenes • Evaporation of fullerene (C60) onto a substrate • Ions of dopant N@C60

  18. Solid State C60 - Fullerite • Face-centered cubic (fcc) • The most densely packed structure • Lattice constant a = 14.17 Ǻ • Weak Van der Waals bonds • Soft • Molecules spin nearly freely around centers • Simple cubic (sc) • T<261 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 • T<90 K: molecules entirely frozen • Polymeric • Covalent bonds • Photo-excitation, molecular collisions, high-pressure/temperature, ionization • Insolvable in toluene

  19. Purification • Extraction from carbon soot • Cn<100 solvable in aromatic solvents • Toluene, benzene, hexane, chloroform • C60 magenta • C70 dark red • Cn>100 high boiling-solvents • trichlorbenzene • Separation by chromatograph

  20. 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 Polymerized Rb1C60 C60-Fullerene tetrakis(dimethylamino)ethylene - ferromagnet

  21. Derivatives • Heterofullerenes • Substitution of an impurity atom with a different valence for C on the cage • B, N, BN Nb • C59X (X=B,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

  22. 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(triphenylphosphine)-iridium C60Cl6

  23. Derivatives • Endohedral • Synthesis • Evaporation of doped carbon • Arc, laser • Ion implantation • M@C60 • Noble gases • without overlap of Van der Waals radii • Metallofullerenes • B, Al, Ga, Y, In, La • Stabilize cages not fulfilling isolated pentagon’s rule (n<60) • 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@C60 He@C60

  24. 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 400°C • 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) < 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

  25. 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@C82 Rh-C60 polymer with vacancies Excess spin density Dipole moment of magnitude 2.264 Debye per C60 unit

  27. 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)

  28. 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

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