Deutsche Tagung f ¨ur Forschung mit ... - SNI-Portal

Nanostrukturen und Grenzflächen Poster: Do., 13:00–15:30 D-P299
Interface properties and electronic structure of ultrathin manganese oxide
Mathias Nagel 1 , Indro Biswas 1 , Heiko Peisert 1 , Thomas Chassé 1
1 Institut für Physikalische und Theoretische Chemie, Universität Tübingen, Auf der
Morgenstelle 8, 72076 Tübingen
Transition metal oxides reveal interesting properties due to their high electronic correlation.
Besides their electronic properties magnetic phenomena are of particular interest
in layer systems which are already utilised in technical applications. As a consequence
of the trend in miniaturising devices questions about the influence of the specific interface
and the reduced dimensionality on the properties arise. The MnO/Ag(001) system
is an interesting model system due to the high lattice mismatch (9 %). By choosing
the optimal preparation method either pseudomorphic or relaxed growth of ultrathin
MnO on Ag(001) can be obtained. This defined growth method gives the possibility
to separately study the interface strain, the effect of the reduced dimensionality and
the influence of the substrate. Ultrathin, epitaxial layers of MnO were prepared at
Ag(001) with thicknesses of a few monolayers. The samples were characterised in situ
by means of XPS, XES and XAS measurements. By combining these techniques a detailed
understanding of the local geometry and the electronic structure of the evolving
film can be obtained. The Mn L2,3 absorption edges of bulk and thin film samples were
measured polarisation-dependent at ANKA. Atomic multiplet-ligand field simulations
of the absorption edges were conducted using a code provided by F. de Groot. The
parameters of the cubic and tetragonal distorted crystal field, respectively, were varied
until a good correlation between experiment and theory was achieved. In pseudomorphically
grown samples a tetragonal distortion of the MnO lattice is observed which
decreases with increasing film thickness. In relaxed films the distortion is reduced but
does not vanish completely. The valence band spectra of the films show significant
differences compared to bulk samples as a consequence of the tetragonal distortion.
Additionally a prominent difference between bulk and thin film samples appears in
XES measurements.
We gratefully acknowledge the support by E. Pellegrin, P. Nagel and S. Schuppler
at the WERA beamline.