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fabrication, structure, and chemical properties of surface confined alloys

Andreas Bergbreiter, Albert Engstfeld, Ralf Rötter, Markus Mauksch, Otávio Brandão Alves, Harry E. Hoster, R. Jürgen Behm

 

 

motivation

 

         surface alloys as model system for structural and catalytical investigations

         catalytic properties: strongly related to catalyst structure

         metal-metal interactions: responsible for the atomic arrangement

         knowledge of structure and energetics are important to understand catalytic properties

         linking experiment with theory by comparing

- effective interaction deduced from atomically resolved STM images

- DFT calculations

 

example: fabrication of a PtRu/Ru(0001) surface alloy:

(a) vapor deposition of Pt onto Ru(0001)

(b) annealing to 1350 K

 

 

proposed mechanism of surface alloying for guest metal with negative segregation energy

(i) exchange between adatoms and underlying rest atoms

(ii) guest metal overgrown by islands with little probability due negative segregation energy, i.e. also lower surface energy

*    conservation of initial foreign metal amount despite changes in surface morphology.

 

        

 

 

example: conservation of Pt during PtRu/Ru(0001) surface alloy formation due to local equilibrium

 

generic classes of surface alloys: lateral atom distribution

A. phase separation

B. dispersed intermixing

 

approach for quantitative description:


2D lattice gas Hamiltonian with pairwise potentials

* resulting Hamiltonian

z(r): coordination number of the corresponding coordination shell

Si: occupation operator at site i  (+1 for atom A, -1 for atom B)

*      model only distinguishes between like and unlike pairs

interaction model:

 

Veff > 0: effective attraction between unequal atoms

Veff < 0: effective attraction between equal atoms

 

additive interaction model: suitable for Monte-Carlo simulations

 

measured

simulated

 

algorithm scheme to deduce effective cluster interactions - inverse Monte-Carlo (IMC) simulation

 

EPI calculation from DFT calculated mixing energies of ordered surface alloys

 

 

 

further development: Monte-Carlo simulation of atom distribution and thermal desorption behavior based on DFT calculations

left: simulation;                                        right: experiment

example: PtAu/Pt(111) surface alloys; atom distribution and thermal desorption of CO (Hoster, Eyrich, Bergbreiter, Sakong, Gross, Behm, unpublished results)

 

 

 

 

Related Literature:

"Pt Promotion and Spill-over Processes during Deposition and Desorption of upd-Had and OHad on PtxRu1-x/Ru(0001) Surface Alloys", H.E. Hoster, M.J. Janik, M. Neurock, R.J. Behm, PCCP 12, in press

"Entropy effects in atom distribution and electrochemical properties of AuxPt1-x/Pt(111) surface alloys", A. Bergbreiter, O.B. Alves, H.E. Hoster, ChemPhysChem, in press

From Bilayer to Monolayer Growth: Temperature Effects in the Growth of Ru on Pt(111)”, A. Bergbreiter, A. Berkó, H.E. Hoster, R.J. Behm, Surface Science 603 (2009), 2556-2563  

On the Origin of Ru Bilayer Island Growth on Pt(111)”, A. Bergbreiter, A. Berkó, P.M. Erne, H.E. Hoster, R.J. Behm,
Vacuum 84, 13-18 (2009)

Surface alloy formation, short-range order, and deuterium adsorption properties of monolayer PdRu/Ru(0001) surface alloys” H. Hartmann, T. Diemant, A. Bergbreiter, J. Bansmann, H.E. Hoster, R.J. Behm, Surf. Sci. 603 (2009) 1439

PtxRu1-x/Ru(0001) surface alloysformation and atom distribution”, H. E. Hoster, A. Bergbreiter, P. Erne, T. Hager, H. Rauscher, and R. J. Behm, PCCP 10 (2008) 3812

“Interaction of CO with atomically well-defined PtxRuy/Ru(0001)surface alloys”, H. Rauscher, T. Hager, T. Diemant, H. Hoster, F. Buatier de Mongeot, R.J. Behm, Surface Science 601 (2007) 4608

Energetics driving the short-range order in CuxPd1-x/Ru(0001) monolayer surface alloys”, A. Bergbreiter, H.E. Hoster, S. Sakong, A. Groß, R.J. Behm, PCCP 9 (2007) 5127

Formation and short-range order of two-dimensional CuxPd1-x monolayer surface alloys on Ru(0001)”, H.E. Hoster, E. Filonenko, B. Richter, R.J. Behm, Phys. Rev. B 73 (2006) 165413

Catalytic influence of Pt monolayer islands on the hydrogen electrochemistry of Ru(0001) studied by Ultrahigh Vacuum Scanning Tunneling Microscopy and Cyclic Voltammetry”, H. E. Hoster, B. Richter, R.J. Behm, Journal of Physical Chemistry B 108 (2004) 14780-14788

Hydrogen adsorption and H2/CO coadsorption on well-defined bimetallic PtRu surfaces – A model study on the CO tolerance of bimetallic PtRu anode catalysts in low temperature Polymer Electrolyte Fuel Cells”, T. Diemant, T. Hager, H.E. Hoster, H. Rauscher, R.J. Behm,
Surf. Sci. 541(2003) 137-145

Pt-Ru-model catalysts for anodic methanol oxidation: Influence of structure and composition on the reactivity”, Harry Hoster, Teresa Iwasita, Hermann Baumgärtner, Wolf Vielstich, Physical Chemistry Chemical Physics 3 (2001) 337-346

CO adsorption and oxidation on bimetallic Pt/Ru(0001) surfaces – a combined STM and TPD/TPR study“, F. Buatier de Mongeot, M. Scherer, B. Gleich, E. Kopatzki and R. J. Behm, Surf. Sci., 1998, 411, 249.

Correlation between local substrate structure and local chemical properties: CO adsorption on well-defined bimetallic Au/Pd(111) surfaces”, Surf. Sci. 386(1997) 48

 

S. Müller, J. Phys.: Condens. Matter, 2003, 15, R1429

B. Sadigh, M. Asta, V. Ozolins, A. K. Schmid, N. C. Bartelt, A. A. Quong and R. Q. Hwang, Phys. Rev. Lett., 1999, 83, 1379

A. Christensen, A. V. Ruban, P. Stoltze, K. W. Jacobsen, H. L. Skriver, J. K. Nørskov and F. Besenbacher, Phys. Rev. B: Condens. Matter Mater. Phys., 1997, 56, 5822

A. V. Ruban, H. L. Skriver, and J. K. Nørskov, Phys. Rev. B, 1999, 59, 15990

 

 

 

 

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