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Atomic structure of Ag(977) vicinal surface by low energy electron diffraction

Atomic structure of Ag(977) vicinal surface by low energy electron diffraction. Edmar A. Soares, Rosa M.C. Marques, Vagner E. de Carvalho, Hans-D. Pfannes, Roberto Paniago Departamento de Física - ICEx – UFMG Wolfgang Moritz Department of Earth and Environmental Sciences, University of Munich.

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Atomic structure of Ag(977) vicinal surface by low energy electron diffraction

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  1. Atomic structure of Ag(977) vicinal surface by low energy electron diffraction Edmar A. Soares, Rosa M.C. Marques, Vagner E. de Carvalho, Hans-D. Pfannes, Roberto Paniago Departamento de Física - ICEx – UFMG Wolfgang Moritz Department of Earth and Environmental Sciences, University of Munich

  2. Outline • What are vicinal surfaces? • Motivation • Ag(977) surface geometry and reciprocal space • Experimental and theoretical details • Results • Conclusions

  3. What are vicinal surfaces? • Regularly spaced low Miller index terraces separated by monoatomic steps; • Obtained by cutting the crystal at an angle “slightly” off the low Miller index. Au(788)

  4. SC – atoms in the step chain TC – atoms in the terrace chains (TC1, TC2, ...) CC – atoms in the corner chain BNN – nearest neighbour of the corner atom in the bulk W – terrace width r– surface registry

  5. Cu(111) Si(111) -7x7, 15nm x 15nm Si(111) -7x7, 50nm x 50nm Motivation Steps exist in any kind of surfaces

  6. Self-organized growth Co on Pt(997) Co on Au(788) Co on Au(11,12,12) Science, 416 (2002) 301 J.Phys: Condens. Matter 15 (2003) S3363-S3392

  7. Pt induced facet formation on W(111) Stability with respect to faceting

  8. Au(110) Atomic-force microscopy shows calcite growth with no amino acids (a); with an achiral, or neutral-handed, amino acid, glycine (b); with left-handed aspartic acid (c); and with right-handed aspartic acid (d). Growth of CoO on Ag(001) Surface morphology

  9. Electronic states J.Phys: Condens. Matter 15 (2003) S3281-S3310

  10. Ag(977) surface geometry and reciprocal space

  11. Motivation: • Relaxation of step atoms • Comparison with DFT-calculation • Adsorption at steps • Steps separated by 19.3 Å • → relaxation of a single step

  12. Experimental and theoretical details Experiment • Ag(977) from Surface Lab. Preparation (Netherlands) best polished and aligned to 0.1°; • Sputtering (Ar+, 500 eV, 25min); • Annealing (693K, 20 min); • Cooling down (5K/min); • 15 non-equivalent beams collected at 155K and nearly normal incidence.

  13. Ag(977) LEED patterns Ep=76eV Ep=44eV

  14. 19.3 Å 17 Å Theory dbulk = 0.3061 Å LEEDFIT code slab with 56 atoms 9 phase shifts energy range 30 – 260 eV optimised parameters: z1 – z18, x1,x2,x7,x8,x9 θD-surf = 160 K θD-bulk = 225 K

  15. 1 2 3 4 5 5 6 7 8 9 13 10 14 11 15 16 12 17 18 Results so far... Δx, Δz : deviation from bulk position -x +x +z d1-2 = - 15% d2-3 = - 33% d8-9 = +65% d9-10 = -29% RP=0.32

  16. 1 2 3 4 8 9 10 16 17 18 d1-2 = - 15% - d2-3 = - 33% - d8-9 = +65% - d9-10 = -29% - RP=0.32

  17. DFT: Cu - p(111)x(11-1) – (p,p,p-2) Surf. Sci. 600 (2006) 3008-3014 Experimental J.Phys: Condens. Matter 15 (2003) S3197-S3226

  18. Conclusions and future work • Reasonable agreement between experiment-theory; • Large inward relaxation of the step atoms; • Large outward relaxation of the corner atoms; • Finish the structural determination of the Ag(977) and compare the results with DFT and ECT calculations; • Study of the electronic structure of Ag(977)(1x1) by ARUPS and STM; • Adsortion of large molecules and transition-metal atoms on Ag(977); • Structure determination on other p(111)x(100) Ag vicinal surfaces to better understand the relation between surface relaxations and the number of atoms p on the terrace.

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