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

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

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)

Lang et al notation Miller index f Edge geometry Unit cell (2D) p(111) x (100) step A 8(111) x (100) step A (p+1,p-1,p-1) (9,7,7) 2/3 nn p odd : PR p even : CR p(111) x (-111) step B 8(111) x (-111) step B (p-2,p,p) (6,8,8) 1/3 p odd : CR p even : PR p(100) x (111) 8(100) x (111) (1,1,2p-1) (1,1,15) 1/2 CR p(100) x (010) 8(100) x (010) (0,1,p-1) (0,1,7) nnn (kinks)

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

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

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

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

Surface morphology 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). Au(110) Growth of CoO on Ag(001)

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

Ag(977) surface geometry and reciprocal space

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

Experimental and theoretical details 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.

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

Theory 19.3 Å dbulk = 0.3061 Å 17 Å slab with 56 atoms 9 phase shifts 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

Results so far... -x +x +z Δx, Δz : deviation from bulk position 1 2 3 Atom nr. Δ x [Å] Δ z [Å] 1 -0.10 +0.125 2 -0.01 +0.08 3 - -0.02 4 +0.01 5 6 7 8 -0.14 -0.09 9 +0.11 10 +0.02 11 14 15 16 17 +0.04 18 -x +x +z 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 d1-2 = - 15% d2-3 = - 33% d8-9 = +65% d9-10 = -29% RP=0.32

d1-2 = - 15% - d2-3 = - 33% - d8-9 = +65% - d9-10 = -29% - RP=0.32 Atom nr. Δ x [Å] Δ z [Å] 1 -0.10 +0.125 2 -0.01 +0.08 3 - -0.02 4 +0.01 5 6 7 8 -0.14 -0.09 9 +0.11 10 +0.02 11 14 15 16 17 +0.04 18 1 2 3 8 9 4 10 16 17 18 d1-2 = - 15% - d2-3 = - 33% - d8-9 = +65% - d9-10 = -29% - RP=0.32

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

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.