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. 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)

5. 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

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

7. 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

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

9. 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)

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

11. Ag(977) surface geometry and reciprocal space

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

13. 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.

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

15. 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

16. 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

17. 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

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

22. 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.