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Stability of silicon-doped heterofullerenes

Stability of silicon-doped heterofullerenes. Carlo Massobrio. Institut de Physique et de Chimie des Matériaux de Strasbourg, 23 Rue du Loess BP 43 F-67034 Strasbourg Cedex 2, France ( Carlo.Massobrio@ipcms.u-strasbg.fr ). Here: substitutional doping. Why to dope fullerenes ??. C 40 Si 20.

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Stability of silicon-doped heterofullerenes

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  1. Stability of silicon-doped heterofullerenes Carlo Massobrio Institut de Physique et de Chimie des Matériaux de Strasbourg, 23 Rue du Loess BP 43 F-67034 Strasbourg Cedex 2, France (Carlo.Massobrio@ipcms.u-strasbg.fr) Here: substitutional doping Why to dope fullerenes ?? C40Si20 Create new nanostructures from a very stable one Enhance chemical reactivity Other doping exist: endohedral (encapsulation inside) coating (addition on the cage) C: yellow, Si: black

  2. Stability of silicon-doped heterofullerenes Carlo Massobrio Institut de Physique et de Chimie des Matériaux de Strasbourg, 23 Rue du Loess BP 43 F-67034 Strasbourg Cedex 2, France (Carlo.Massobrio@ipcms.u-strasbg.fr) Here: substitutional doping Why to dope fullerenes ?? C40Si20 Create new nanostructures from a very stable one Enhance chemical reactivity Other doping exist: endohedral (encapsulation inside) coating (addition on the cage) C: yellow, Si: black

  3. Research context: atomic-scale materials at IPCMS Tools: first-principles molecular dynamics (FPMD) (Car-Parrinello) to optimize and follow temporal evolution or (large metallic systems) Classical n-body potentials (CMD) Liquid and glasses (intermediate range order) (FPMD) Lamellar hybrid organic-inorganic solids (FPMD) Nanosystems: Stability of unsupported (free) clusters (FPMD) GeSe2 Cu2(OH)3NO3 Diffusion on metallic surfaces (Au(111)) (CMD)

  4. Si-doping of fullerenes: experimental facts C2n-qSiq 2n=32-100, q<4 Fullerene geometry preserved Si atoms close to each other Concerning the upper limit of Si for doping, what else is known..?? Si60 is not stable as a cage, It relaxes to a “puckered” ball (M.Menon, K. R. Subbaswamy,CPL 219, 219 (1994)) From J. Chem. Phys 110, 6927 (1999) “…for Si, a value close to 12 seems to be the upper limit” (M. Pellarin, C. Ray, J. Lermé, J. L. Vialle, M. Broyer X. Blase, P. Kéghelian, P. Mélinon, A. Perez)

  5. Basics of structural properties and bonding in C59Si and C58Si2 (I.M.L. Billas, C.Massobrio, M. Boero, M. Parrinello, W. Branz, F. Tast, N. Malinowski, M. Heinebrodt, T. P. Martin, JCP 111, 6787 (1999)) HOMO LUMO

  6. C59Si: Localized orbitals (Wannier functions) and electron localization function (ELF) Si bonds to the neighbors C in a distorted or “weak” sp2 manner Si ELF= 0.8 ELF= 0.9472

  7. Toward highly Si-doped fullerenes: the case of C54Si6 (Masahiko Matsubara and CM, JCP 122, 084304 (2005)) From T=0K to T=3000K in 12 ps (stepwise) The four most stable isomers Thermal behavior highlights weaker connections, likely to break at high temperatures (see Si-Si hh in isomer A)

  8. Highly silicon-doped fullerenes… Geometry optimization for C40Si20, C36Si24, C30Si30 (Masahiko Matsubara and CM, JPhysChem 109, 4415 (2005)) Increased doping: decrease of binding energy (C60: 8.17 eV/atom, C40Si20: 6.81 eV/atom, C30Si30: 6.13 eV/atom)

  9. A fully half-doped substitutional fullerene retains a cage-like structure ..!! Si atoms cap the fullerene via Si-Si-Si triads (angles scattered around the tetrahedral value) Probability isodensty surface associated with the total valence charge density “forced “ sp2 bonding

  10. Stability of the cage vs increased doping content: issues to be addressed Threshold value for the number of Si-C replacements FPMD on structures vibrationally stable From T=0K to T=5000K 24 ps Mechanism of instability with increasing Si content To ensure adiabaticity, Nosé-Hoover thermostat on electronic degrees of freedom at the higher temperatures

  11. Topological analysis and charge pattern Si atoms can be classified as outer (neighbors of C) and inner (not neighboring C) Ionic interaction prevails at the Si-C frontier, but not inside (Si-Si interactions) With increased doping, the number of Si outer does not exceed 12: instability due to Si inner and triggered by temperature Our proposal: threshold for Si inner = Si outer (C40Si20): is it consistent with dynamics?

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