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  1. I.A.E.A. Vienna CRP Atomic and Molecular Data for Plasma Modelling Coordination Meeting 17-20 November, 2008 INTERACTION OF SLOW IONS WITH SURFACES: ION SURVIVAL PROBABILITY ON CARBON, TUNGSTEN AND BERYLLIUM SURFACES (ROOM TEMPERATURE AND HEATED) ZDENEK HERMAN and JANŽABKA J. Heyrovský Institute of Physical Chemistry, v.v.i. Academy of Sciences of the Czech Republic, Prague IAEA, Vienna, 17-20 Novermber, 2008

  2. EXPERIMENT • ION SURVIVAL PROBABILITY • percentage of incident ions • surviving a surface collision as product ions • SA = 100 ΣIprod/ Iinc (%) • ( Iinc = Itarg,m + ΣIprod ) • Experimental determination • Direct measurement of projectile ion current incident on the target (Itarg,m) • Determination of total current of product ions from ion current to the detector, collecting efficiency of the apparatus, and angular distributions

  3. PERCENTAGE OF SURVIVING IONS, Sa(%) • CARBON (HOPG), INC. ANGLE 300 (w.r. to the surface)

  4. PERCENTAGE OF SURVIVING IONS C3Hn+, Sa (%) (room-temperature carbon (HOPG) surfaces) incident angle: 300 with respect to the surface

  5. ION SURVIVAL PROBABILITY, Sa (%) CONCLUSION: survival probability on W or Be usually about 5-10x smaller than on HOPG

  6. 1.COLLISIONS OFCDn+ (n=3-5) WITH CARBON(HOPG), ROOM TEMPERATURE, Φs = 300 VERY LOW ENERGY 3 – 11 eV ION SURVIVAL PROBABILITY Sa(%) SA decreases below Einc. = 10 eV to zero

  7. PROBABILITY OF ION SURVIVAL • DEPENDENCE ON INCIDENT ANGLE IONS FROM ETHANOL (SS SURFACE COVERED BY HYDROCARBONS) C2H5OH+• C2H5OH2+, C2H5O+ CONCLUSIONS - survival probability depends strongly on incident angle: lower for steep collisions - survival much higher for ions of low ionization energy (usually closed-shell ions), for ions of IE> ~10.5 eV about an order of magnitude lower

  8. ION SURVIVAL PROBABILITY vs. IONIZATION ENERGY OF PROJECTILES (Carbon (HOPG) surface at room temperature, Einc = 30 eV, inc. angle 300 w.r. to the surface) correctly should be recombination energy (RE) of the projectile ion, but RE values little known, replaced by well-known ionization energies of the projectile ions (IE) in most cases RE = IE, sometimes RE<IE (CH4+) SURFACES HYDROCARBONS C-chain IE (eV) n-alkanes olefins (C-C=C-….) C4 10.53 9.1 C5 10.35 9.04 C6 10.138.97 C7 9.928.84 C8 9.868.91 C9 9.728.90 C10 9.658.90 ____________________________________ n-alkanes (pump oil) crack to form olefins

  9. ION SURVIVAL PROBABILITY vs. IONIZATION ENERGY OF PROJECTILES (Carbon (HOPG) surface HEATED, Einc = 30 eV, inc. angle 300 w.r. to the surface)

  10. ION SURVIVAL PROBABILITY vs. IONIZATION ENERGY OF PROJECTILES (Carbon (HOPG) surface, room temperature Einc = 30 eV, inc. angle 300 w.r. to the surface) SEMILOG PLOT *) data from A.Somogyi..(V.H.Wysocki),JACS 13(2002)1151

  11. ION SURVIVAL PROBABILITY vs. IONIZATION ENERGY OF PROJECTILES (Carbon (HOPG) surface, Einc = 30 eV, inc. angle 300 w.r. to the surface) SEMILOG PLOT COMPARISON: - ROOM-TEMPERATURE (hydrocarbon-covered) -HEATED (“naked”) SURFACES RT: slope -0.39 ± 0.04 HEATED: slope -0.5 ± 0.1 log SA = a - b (IE) Analogy with the Arrhenius equation? (dependence of rate constant of a chemical reaction on temperature T) log k = a – b/T k = A exp (- E / RT)

  12. ION SURVIVAL PROBABILITY vs. IONIZATION ENERGY OF PROJECTILES Einc = 30 eV, inc. angle 300 w.r. to the surface TUNGSTEN • ROOM-TEMPERATURE SURFACE • HEATED ( 6000C) SURFACE

  13. ION SURVIVAL PROBABILITY vs. IONIZATION ENERGY OF PROJECTILES Einc = 30 eV, inc. angle 300 w.r. to the surface TUNGSTEN SEMILOG PLOT • ROOM-TEMPERATURE SURFACE • HEATED ( 6000C) SURFACE • CONCLUSION • Very similar slopes (-0.35 – 0.36) on both RT and HEATED W- surface

  14. ION SURVIVAL PROBABILITY vs. IONIZATION ENERGY OF PROJECTILES Einc = 30 eV, inc. angle 300 w.r. to the surface SEMILOG PLOTS COMPARISON OF ROOM-TEMPERATURE SURFACES • CARBON (HOPG) • TUNGSTEN (W) • BERRYLIUM (Be) • CONCLUSION • Similar slopes (-0.35- 0.39), similar behavior of surfaces covered by a hydrocarbon layer

  15. ION SURVIVAL PROBABILITY vs. IONIZATION ENERGY OF PROJECTILES SEMILOG PLOT log SA = a - b (IE) ____________________________________ surface ab ____________________________________ C (HOPG) - H 5.4 ±0.1 0.5 ± 0.1 C (HOPG)-RT 3.9 ± 0.5 0.39 ± 0.04 W – H 2.5 ±0.4 0.36 ± 0.04 W – RT 2.9 ± 0.20.35 ± 0.02 Be – RT (3.9 ± 0.5) (0.39?) Be – H ?? _____________________________________

  16. CONCLUSIONS • Survival probability of ions in collisions with surfaces, SA, changes over several orders of magnitude (from ~10% to 10-3% ) depending on the type of ion, type of surface and incident angle. • SA for even-electron ions (low ionization energies) appears to be much higher than for radical cations (open-shell ions, higher ionization energies) • A dependence of SAvs. IE of the projectile ion shows a drastic change (from ~10 % to less than 1%) at IE ~ 9 - 10 eV. For surfaces covered with hydrocarbons this correlates well with the IE of C4-C10 olefins with non-terminal C=C. • A dependence log SAvs. IE shows a good correlation over many orders of magnitude • log SA = a – b (IE) • with „a“ dependent on the type of the surface, and b = - 0.35 - 0.4 for room-temperature (hydrocarbon-covered surfaces)