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

electron diffractionelectron diffraction

Edmar A. Soares, Rosa M.C. Marques, Vagner E. de Carvalho, Edmar A. Soares, Rosa M.C. Marques, Vagner E. de Carvalho, Hans-D. Pfannes, Roberto PaniagoHans-D. Pfannes, Roberto Paniago

Departamento de Física - ICEx – UFMGDepartamento de Física - ICEx – UFMG

Wolfgang MoritzWolfgang MoritzDepartment of Earth and Environmental Sciences, University Department of Earth and Environmental Sciences, University

of Munich of Munich

OutlineOutline

What are vicinal surfaces?What are vicinal surfaces? MotivationMotivation Ag(977) surface geometry and reciprocal Ag(977) surface geometry and reciprocal

spacespace Experimental and theoretical detailsExperimental and theoretical details ResultsResults ConclusionsConclusions

What are vicinal surfaces?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 Lang et al et al notationnotation Miller indexMiller index ff

Edge Edge geometrygeometry Unit cell (2D)Unit cell (2D)

p(111) x (100) step p(111) x (100) step AA

8(111) x (100) step 8(111) x (100) step AA

(p+1,p-1,p-1)(p+1,p-1,p-1)(9,7,7)(9,7,7) 2/32/3 nnnn p odd : PRp odd : PR

p even : CRp even : CR

p(111) x (-111) step p(111) x (-111) step BB

8(111) x (-111) step 8(111) x (-111) step BB

(p-2,p,p)(p-2,p,p)(6,8,8)(6,8,8) 1/31/3 nnnn p odd : CRp odd : CR

p even : PRp even : PR

p(100) x (111)p(100) x (111)8(100) x (111)8(100) x (111)

(1,1,2p-1)(1,1,2p-1)(1,1,15)(1,1,15) 1/21/2 nnnn CRCR

p(100) x (010)p(100) x (010)8(100) x (010)8(100) x (010)

(0,1,p-1)(0,1,p-1)(0,1,7)(0,1,7) 00

nnnnnn(kinks)(kinks)

p odd : CRp odd : CRp even : PRp even : PR

SC – atoms in the step chainTC – atoms in the terrace chains (TC1, TC2, ...)CC – atoms in the corner chainBNN – nearest neighbour of the corner atom in the bulkW – terrace widthr – surface registry

MotivationMotivation

Cu(111) Si(111) -7x7, 15nm x 15nm Si(111) -7x7, 50nm x 50nm

Steps exist in any kind of surfaces

Self-organized growth

Co on Pt(997)Science, 416 (2002) 301

Co on Au(788) Co on Au(11,12,12)J.Phys: Condens. Matter 15 (2003) S3363-S3392

Pt induced facet formation on W(111)

Stability with respect to faceting

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)

Au(110)

Surface morphology

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

Ag(977) surface geometry and Ag(977) surface geometry and reciprocal spacereciprocal 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 Experimental and theoretical detailsdetails

ExperimentExperiment

Ag(977) from Surface Lab. Preparation Ag(977) from Surface Lab. Preparation (Netherlands) best polished and aligned to 0.1(Netherlands) best polished and aligned to 0.1°;°;

Sputtering (ArSputtering (Ar++, 500 eV, 25min);, 500 eV, 25min); Annealing (693K, 20 min);Annealing (693K, 20 min); Cooling down (5K/min);Cooling down (5K/min); 15 non-equivalent beams collected at 155K and 15 non-equivalent beams collected at 155K and

nearly normal incidence.nearly normal incidence.

Ep=44eV Ep=76eV

Ag(977) LEED patterns

Theory

17 Å

19.3 Å

slab with 56 atoms9 phase shiftsenergy range 30 – 260 eV

optimised parameters:z1 – z18,x1,x2,x7,x8,x9

θD-surf = 160 KθD-bulk = 225 K

dbulk = 0.3061 Å

LEEDFIT code

Atom Atom nr.nr.

ΔΔ x [ x [ÅÅ]] ΔΔ z [ z [ÅÅ]]

11 -0.10-0.10 +0.125+0.125

22 -0.01-0.01 +0.08+0.08

33 -- -0.02-0.02

44 -- +0.01+0.01

55 -- 00

66 -- 00

77 -- 00

88 -0.14-0.14 -0.09-0.09

99 -0.02-0.02 +0.11+0.11

1010 -- +0.02+0.02

1111 -- 00

1414 -- 00

1515 -- 00

1616 00 -0.02-0.02

1717 00 +0.04+0.04

1818 00 +0.01+0.01

1 2 3 4 55 6 7 8 9 10 11 12 1314 15 16 17 18

-x +x

Results so far...Results so far...

d1-2 = - 15%d2-3 = - 33%d8-9 = +65%d9-10 = -29%

RP=0.32

+z

Δx, Δz : deviation from bulk position

d1-2 = - 15% - d2-3 = - 33% - d8-9 = +65% - d9-10 = -29% - RP=0.32

1 2 38 9

4

10

16 17 18

Atom Atom nr.nr.

ΔΔ x [ x [ÅÅ]] ΔΔ z [ z [ÅÅ]]

11 -0.10-0.10 +0.125+0.125

22 -0.01-0.01 +0.08+0.08

33 -- -0.02-0.02

44 -- +0.01+0.01

55 -- 00

66 -- 00

77 -- 00

88 -0.14-0.14 -0.09-0.09

99 -0.02-0.02 +0.11+0.11

1010 -- +0.02+0.02

1111 -- 00

1414 -- 00

1515 -- 00

1616 00 -0.02-0.02

1717 00 +0.04+0.04

1818 00 +0.01+0.01

Surf. Sci. 600 (2006) 3008-3014

DFT: Cu - p(111)x(11-1) – (p,p,p-2)

J.Phys: Condens. Matter 15 (2003) S3197-S3226

Experimental

Conclusions and future workConclusions and future work

Reasonable agreement between experiment-theory;Reasonable agreement between experiment-theory; Large inward relaxation of the step atoms;Large inward relaxation of the step atoms; Large outward relaxation of the corner atoms;Large outward relaxation of the corner atoms;

Finish the structural determination of the Ag(977) Finish the structural determination of the Ag(977) and compare the results with DFT and ECT and compare the results with DFT and ECT calculations;calculations;

Study of the electronic structure of Ag(977)(1x1) by Study of the electronic structure of Ag(977)(1x1) by ARUPS and STM;ARUPS and STM;

Adsortion of large molecules and transition-metal Adsortion of large molecules and transition-metal atoms on Ag(977);atoms on Ag(977);

Structure determination on other p(111)x(100) Ag Structure determination on other p(111)x(100) Ag vicinal surfaces to better understand the relation vicinal surfaces to better understand the relation between surface relaxations and the number of between surface relaxations and the number of atoms p on the terrace.atoms p on the terrace.