Plenarvorträge - DPG-Tagungen

Oberflächenphysik Dienstag
O 18.5 Di 12:15 H38
Re-oxidation of MoO3 and V2O5 systems: Cluster DFT calculations.
— •Malgorzata Witko 1 , Renata Tokarz-Sobieraj 1 ,
Robert Grybos 1 , and Klaus Hermann 2 — 1 Institute of Catalysis
and Surface Chemistry, PAS, ul. Niezapominajek 8, 30-239 Krakow,
Poland — 2 Fritz-Haber-Institut der MPG, Faradayweg 4-6, D-14195
Berlin, Germany
Vanadia and molybdena based systems represent important classes of
materials due to their role in technology, catalysis and environmental
protection. The goal of the present theoretical research is to examine
re-oxidation of V2O5(010) and MoO3(010) surfaces reduced in processes
where surface oxygen vacancies are created. All electronic and energetic
parameters are obtained by the DFT method using embedded clusters
V10O30H12 and Mo15O56H22 clusters as surface models. It is shown that
re-oxidation proceeding via O2 adsorption is a very localized process.
Oxygen adsorbs at any surface vacancy with binding energies EB(O2)
depending on the specific vacancy site (O(1-3)) where the calculations
yield an energetic order O(1) < O(2) < O(3) for MoO3 and O(2) < O(1)
< O(3) for V2O5. Molecular oxygen becomes adsorbed at the surface and
can replace the surface O occupying a specific lattice site with almost no
change in the electron distribution of its vicinity. Thus, the reduced oxide
surface is able to incorporate large amounts of (weakly bound) oxygen
species. The activated oxygen molecule can undergo dissociation yielding
reactive products.
O 18.6 Di 12:30 H38
Surface Strain versus Substrate Interaction in Heteroepitaxial
Metal Layers: Pt on Ru(0001) — •Peter Jakob 1,2 , Andreas
Schlapka 2 , Ulrich Käsberger 2 , Markus Lischka 2 , and
Axel Groß 2 — 1 Fachbereich Physik, Philipps Universität Marburg,
35032 Marburg, Germany — 2 Physik-Department, Technische Universität
München, 85747 Garching, Germany
Using STM, FT-IRAS and TDS, the effect of strain at an epitaxially
grown Pt/Ru(0001) overlayer on the adsorption of various adsorbates
has been studied. These effects are of strong current interest since they
might provide a means of manipulating adsorption properties quite significantly.
For pseudomorphic bimetallic layers the residual influence of
the substrate and of the lattice strain within the deposited film produce
a combined effect on the adsorbed species and it is difficult to uniquely
separate their consequences. By studying the adsorption of CO on increasingly
thicker layers of Pt deposited on Ru(0001), the influence of
surface strain on the adsorption energy has now been disentangled from
the residual chemical interaction with the substrate: whereas the electronic
influence of the substrate dominates for thin films (1-2 layers) and
vanishes for >3 Pt layers, strain related effects due to the 2.5% lattice
mismatch of Pt and Ru remain active for thicker pseudomorphic overlayers
and are only gradually released for n ≥ 5 Pt layers by means of
formation of dislocation networks. Electronic structure calculations confirm
the experimental observations, in particular, the dramatic decrease
of the CO adsorption energy on a single Pt layer which is caused by the
strong Pt-Ru interlayer coupling.
O 19 Teilchen und Cluster II
O 18.7 Di 12:45 H38
Circular dichroism in core-level photoemission from butanediol
on Si(100) — •JeongWon Kim 1 , Massimo Tallarida 1 ,
Hugo Dil 1 , Karsten Horn 1 , Marilena Carbone 2 , Maria
Pia Casaletto 3 , Roberto Flammini 4 , and Maria Novella
Piancastelli 2 — 1 Fritz-Haber-Institut der MPG, 14195 Berlin —
2 Dip. Di Scienze e Tecnologie Chimiche, Universita Tor Vegata, 00133
Roma, Italia — 3 Istituto per lo Studio di Materiali Nanostrutturati,
CNR, I-90146 Palermo — 4 Istituto di Metod. Inorganiche, 00016
Monterotondo
Molecules which possess a chiral center are of great importance in
chemistry and biology. In search of a method to control enantioselectivity
in chemical reactions, recent interest has turned to adsorbed chiral
molecules. The detection of chirality in adsorbed molecules is difficult,
however, having so far been mostly demonstrated in scanning tunnelling
microscopy. Here we report on a study of an adsorbed chiral molecule,
i.e. 2,3 butanediol on Si(100), using circular dichroism in core level photoemission.
Butanediol is well suited for such studies since it contains
two chemically different sets of carbon atoms, only one of which is in a
chiral center. We observe clear dichroism in the carbon 1s emission signal
from R,R and S,S butanediol. In our analysis of the results we aim at distinguishing
between circular dichroism from the chiral center itself, and
that induced by the chiral nature of the experimental geometry, through
a comparison of dichroism observed under different experimental geometries,
as well as by a comparison with data from the achiral enantiomer
of butanediol.
O 18.8 Di 13:00 H38
SERS and infrared spectra of NO on cold-deposited Cu —
•Matthias Lust 1 , Andreas Priebe 1 , Andreas Otto 2 , and Annemarie
Pucci 1 — 1 Kirchhoff-Institut für Physik, Universität Heidelberg,
Im Neuenheimer Feld 227, D-69120 Heidelberg, Germany —
2 Lehrstuhl für Oberflächenwissenschaft, Universität Düsseldorf, Universitätsstr.
1, D-40225 Düsseldorf, Germany
SERS-spectra of nitric oxide (NO) on cold-deposited (