Angle resolved photoemission study of Sn/Pd(111) surface alloy

phases

Mgr. Jiří Libra, Ph.D.

KFPP MFF UK, Prague, Czech Republic

French-Czech seminar, Giens, 20-27 June 2009

Sn/Pd system investigation

- KFPP, Prague:- XPS, LEED, ISS- Angle resolved photoelectron spectroscopies: ARUPS, XPD- Kateřina Veltruská, Slavomír Nemšák, Tomáš Skála, Miloš Cabala, Vladimír Matolín

- Elettra, Trieste:- SRPES, LEED- CO adsorption experiments- Jiří Libra, Peter Pira, Kateřina Veltruská, Miloš Cabala, Vladimír Matolín

CO adsorptions experiments - the strength of CO bonding to the surface depends on surface reconstruction - shifts of CO molecular orbitals

Model studies for catalytic applications

SRPES measurement of valence band with primary photon energy of 130 eV. Solid lines represent spectra before CO adsorption, dashed after adsorption.

The relative intensities of CO molecular orbitals normalised to the intensity of spectra obtained from clean Pd(111) surface after CO adsorption.

Pd(111)

Sn/Pd (√3x√3)R30° Sn/Pd p(2x2)

Angle resolved UPS

Our ISS measurement qualitatively confirmed surface model proposed by Lee

Structure models

A.F. Lee, C.J. Baddeley, M.S. Tikhov and R.M. Lambert 1997 Surf. Sci. 373 195

Sn/Pd (√3x√3)R30°surface alloy withno bulk equivalent

1/3 – 3 ML of Snannealing

Sn/Pd p(2x2)bulk Pd3Sn alloy

>3 ML of Snannealing

Pd

Sn

PdSn

p(2x2) (√3x√3)R30°

ISS experiment

Clean Pd(111) Sn/Pd (√3x√3)R30°

Sn deposition of 0.8 nmAnnealing to 400 C

Sn/Pd p(2x2)

Sn deposition of 4 nmAnnealing to 400 C

Surface preparation

XPD (X-ray photoelectron diffraction)

Pd(111), Pd 3d pattern

p(2x2)typical bulk pattern

(√3x√3)R30°similar like p(2x2)

XPD Sn 3d patterns

difference

XPD pattern calculations

em itte rs

3

4

S n/P d(111) (2x2)

em itte rs

2

5

1

Layer 1 Layer 2 Layer 3 Layer 4 Layer 5

sum of contributions experiment

Surface versus bulk structure

P d Sn layer

1st

2nd

3rd

S n/P d(111) (2x2)

Pd Sn layer

1st

2nd

3rd

Sn/Pd(111) (√3x√3)

?

?

? 4th

Comparison of scattering properties of Pd and Sn atoms

Sn/Pd Sn difference

2 x 2 √3 x √3

1+2 1+2+3 1+2+3+4 1+4 1+4+5

Layer 1 Layer 2 Layer 3 Layer 4 Layer 5

Experiment:

All (1-5)

Conclusions

Pd

Sn

Sn/Pd (√3x√3)R30° Sn/Pd p(2x2)

bulk Pd3Snalloy terminatedby p(2x2)

(√3x√3)R30°surface alloy

Pd3Sn-like alloyformed by rest ofdeposited Sn atoms

Sn/Pd (√3x√3)R30° surface consists of Pd2Sn surface alloyand some Sn atoms under surface, probably in layer 4 and deeper