Plenarvorträge - DPG-Tagungen

Oberflächenphysik Mittwoch
O 28 Postersitzung (Elektronische Struktur, Grenzfläche fest-flüssig,
Halbleiteroberflächen und -grenzflächen, Magnetismus und Symposium SYXM,
Methodisches, Nanostrukturen, Oberflächenreaktionen, Teilchen und Cluster,
Zeitaufgelöste Spektroskopie)
Zeit: Mittwoch 16:00–19:00 Raum: Bereich C
O 28.1 Mi 16:00 Bereich C
Bulk and surface sensitive photoemission on 1T-TiS2 — •M.
Garbrecht, O. Seifarth, M. Skibowski, and L. Kipp — Institut
für Experimentelle und Angewandte Physik, Universität Kiel, D-24098
Kiel, Germany
The bulk and surface sensitive electronic structure of the layered transition
metal dichalcogenide 1T-TiS2 is investigated by means of angle
resolved photoemission spectroscopy with VUV and XUV photons. At
photon energies around 50 eV where ARPES is extremely surface sensitive
we observe a semiconducting band structure. This is contrasted
by more bulk sensitive photoemission data obtained at 150 eV where a
semimetallic behavior is found. The results are discussed in the context
of recent band structure calculations performed within the density functional
theory. The experiments have been performed with the ASPHERE
spectrometer at the HASYLAB beamlines W3.2 and BW3. Work supported
by the BMBF project no. 05 KS1 FKB and DFG Forschergruppe
FOR 353
O 28.2 Mi 16:00 Bereich C
Excited state UPS of C60 — •Arne Rosenfeldt, Klaus Finsterbusch,
and Helmut Zacharias — AG Zacharias, Physikalisches
Institut, Westfälische Wilhelms-Universität
A 200 layer C60 film is prepard by growth on an annealed C60 monolayer
on Cu(111). This system is pumped with tunable 351 to 415nm radiation
of 100ps pulse duration and probed with delayed 263, 211 and 150nm
photons. Using the time-of-flight technique photo-electrons are observed
from LUMO+1, LUMO, and singlet exciton states. The excitation probability
of these states as a function of photon energy is measured. A
maximum is found for hν = 3.16eV (λ ∼ 392nm). Further, the electron
dynamic is analyzed and will be discussed.
O 28.3 Mi 16:00 Bereich C
Geometric and electronic structure of epitaxial PbS on HfS2 —
•J. Iwicki, A. Kamenz, O. Seifarth, S. Habouti, M. Kalläne,
and L. Kipp — Institut für Experimentelle und Angewandte Physik,
Universität Kiel, D-24098 Kiel, Germany
Misfit layer compounds like (PbS)NbS2 form a special class of layered
heterostructures. Due to 4-fold symmetries of the PbS layers which contrast
the 6-fold symmetry of the NbS2 layers a misfit is constituted. Up to
now, bulk crystals of misfit compounds could only be grown with metallic
hexagonal layers like e.g. NbS2 or TiS2. Here we show first steps of epitaxial
growth of PbS on semiconducting HfS2 with corresponding STM
images and angle resolved photoemission spectra for different coverages
of PbS on HfS2. The photoemission results are compared with data of
clean HfS2 and PbS bulk crystals. The experiments have been performed
with the ASPHERE spectrometer at HASYLAB.
Work supported by the BMBF proj. 05 KS1 FKB and DFG Forschergruppe
FOR 353
O 28.4 Mi 16:00 Bereich C
High energy conduction band states in layered materials — •M.
Marczynski, K. Rossnagel, M. Kalläne, E. E. Krasovskii, M.
Skibowski, W. Schattke, and L. Kipp — Institut für Experimentelle
und Angewandte Physik, Universität Kiel, D-24098 Kiel, Germany
Employing angle resolved photoemission in the constant initial state
mode we investigate the conduction band states of layered materials up
to about 100 eV above the Fermi level. The layered materials HfS2 and
TiTe2 serve as model systems showing distinct features even for higher
conduction bands. The experimentally observed structures are discussed
in the context of theoretical results obtained by ab initio calculations. In
particular, photoemission final states are treated within ELAPW based
scattering theory.
The experiments have been performed at HASYLAB (BW3 beamline)
and the Advanced Light Source (beamline 7).
Work supported by the BMBF project no. 05 KS1 FKB and DFG
Forschergruppe FOR 353.
O 28.5 Mi 16:00 Bereich C
Angle resolved measurement of the (1π) 1 photoemission cross
section of CO adsorbed on Pt(111) — •Sebastian Wegner,
Grigorios Tsilimis, Jörg Kutzner, and Helmut Zacharias —
Physikalisches Institut, Westfälische Wilhelms Universität Münster,
Wilhelm-Klemm-Straße 10, D-48149 Münster
High order harmonic radiation is generated by focussing femtosecond
Ti:sapphire pulses into a noble gas. The pulsed radiation is tunable in
the range of 20 − 110 eV in steps of 3.1 eV. At an energy of 32.4 eV we
measured the CO(1π) −1 photoemission of the c(4 ×2)-2CO/Pt(111) surface.
In contrast to experiments on oriented molecules in the gas phase
we observe emission parallel as well as perpendicular to the axes of the
adsorbed CO. We fitted the angular distribution by Legendre polynomials
Pl(cosθ). It is best fitted by l = 3 and l = 4 polynomials indicating a
large contribution of d and f partial waves.
O 28.6 Mi 16:00 Bereich C
Fermi-Surface-Mapping an Übergangsmetallen — •M. Krause,
S. Dreiner, M. Schürmann, U. Berges und C. Westphal — Universität
Dortmund, Experimentelle Physik I, 44221 Dortmund
Die Kenntnis der elektronischen Struktur von Metallen ist grundlegend
für das Verständnis vieler physikalischer Phänomene. Die elektronischen
Zustände an der Fermikante bedingen z.B. die elektrische
Leitfähigkeit, die Temperaturabhängigkeit des Ferromagnetismus, die Supraleitung
und die Hochtemperatursupraleitung. Durch Aufnahme winkelaufgelöster
Photoemissionsspektren über dem Halbraum der Probe
mit HeI Strahlung wurden Schnitte durch die Fermiflächen gemessen. Zur
Interpretation wurden Vergleichsrechnungen der Dichtefunktionaltheorie
(LKKR) durchgeführt.
Die Meßergebnisse für Cu, Ni, Pd und Rh werden gezeigt und mit den
jeweiligen Rechnungen verglichen. Diese Ergebnisse bilden die Grundlage
für zukünftige Experimente.
O 28.7 Mi 16:00 Bereich C
Surface state as local sensor for single magnetic impurities —
•Daniel Wegner, Andreas Bauer, and Günter Kaindl — Freie
Universität Berlin, Institut für Experimentalphysik, Arnimallee 14, 14195
Berlin-Dahlem
The (0001)-surface of Lu metal exhibits a highly localized surface state
directly at the Fermi energy, EF [1]. It appears as a sharp peak in the tunnelling
spectra measured by low-temperature scanning tunnelling spectroscopy
(STS) at 10 K. We have used this surface-state peak as a sensor
for single magnetic impurities of Gd and Ho atoms embedded in the
film surface. Within a radius of about 15 ˚A around such an impurity,
the surface-state appears as a double-peaked structure in the tunnelling
spectra with a narrow dip in between; this dip is only a few meV wide
and is located within less than 1 meV at EF. The results are discussed
on the basis of the Kondo effect.
This work was supported by the DFG, Sfb-290.
[1] A. Bauer, A. Mühlig, D. Wegner, and G. Kaindl, Phys. Rev. B 65,
75421 (2002).
O 28.8 Mi 16:00 Bereich C
Correlation of electronic transport and structural properties of
Cs layers on Si(001) — •Hong Liu, A.A. Shklyaev, V. Zielasek,
and H. Pfnür — Universität Hannover, Institut für Festkörperphysik,
Appelstr. 2, 30167 Hannover
Combining LEED, EELS, and conductivity measurements we have
studied the correlation of electronic transport with structural properties
of Cs layers on Si(001). Depending on the substrate temperature T
during Cs deposition we find three different growth regimes. Only for
T