Plenarvorträge - DPG-Tagungen

Oberflächenphysik Donnerstag
O 37.4 Do 16:30 H36
Image-potential states on stepped Cu(11l) surfaces —
•Manfred Roth, Martin Weinelt, and Thomas Fauster
— Lehrstuhl für Festkörperphysik, Universität Erlangen-Nürnberg,
Staudtstr. 7/A3, 91058 Erlangen
The dynamics of image-potential states on stepped Cu(11l) surfaces
has been studied with time- and angle-resolved two-photon photoemission.
In comparison to the Cu(001) surface the image-potential states
on the stepped surfaces show increased decay and dephasing rates [1].
A direction-dependent resonant scattering process with large momentum
transfer was observed [2], which leads to strong interband scattering from
the n = 2 to the n = 1 image-potential state band. The intensity of this
scattering depends on the regularity and the mean terrace width of the
step arrangement [3]. Further the anisotropic scattering leads to an asymmetric
behavior of the lifetime in the n = 1 image-potential-state band.
This can be explained by a direction-dependent reflection at the step
edges, found by scanning tunneling spectroscopy [4]. The dependence of
the mentioned effects on the step density will be discussed.
[1] M. Roth, M. Pickel, J. Wang, M. Weinelt, and Th. Fauster, Appl.
Phys. B 74, 661 (2002)
[2] M. Roth, M. Pickel, J. Wang, M. Weinelt, and Th. Fauster, Phys.
Rev. Lett. 88, 096802 (2002)
[3] M. Roth, M. Pickel, M. Weinelt, and Th. Fauster, Appl. Phys. A 78,
149 (2004)
[4] M. Roth, M. Weinelt, Th. Fauster, P. Wahl, M. A. Schneider, L.
Diekhöner, and K. Kern, Appl. Phys. A 78, 155 (2004)
O 37.5 Do 16:45 H36
Treatment of many-body effects in sodium clusters by means of
GW theory — •Yaroslav Pavlyukh and Wolfgang Hübner —
FB Physik, TU Kaiserslautern, D-67663 Kaiserslautern, Germany
The GW approximation for the calculation of electronic properties
of systems without translational invariance like clusters or molecules is
presented. In our implementation of the GW approximation we use the
expansion of all quantities in gaussian type basis functions. The Green
function, screened interaction, and self-energy are represented on the real
axis of the frequency domain. The dielectric function is treated without
any simplifications, such as the plasmon pole approximation. Convolutions
are performed using fast Fourier transforms to the real time and
back. We apply our approach to the range of Nan clusters (n=9-25).
We present ionization potentials, electron affinities, band-gaps, plasmon
energies, and life-times of quasiparticle states and collective excitations,
which shows exellent agreement with experiments and other theories,
such as TDLDA. A partially self-consistent GW calculation on Na + 9 cluster
enables us to improve the HOMO-LUMO gap (4.5 eV – HF, 3.7 eV
– G0W0, 3.37 eV GW) and to determine the plasmon width and lifetime
(2 eV and 4.1 fs, respectively).
O 38 Adsorption an Oberflächen III
O 37.6 Do 17:00 H36
Fs-Laserpulspropagation in Single-Mode Glasfasern —
•Georgios Ctistis, Jan Podsiadly, Jens J. Paggel und Paul
Fumagalli — Institut für Experimentalphysik, Freie Universität
Berlin, Arnimallee 14, 14195 Berlin
Die Ausbreitung von Kurzzeitpulsen in dispersiven Medien ist ein nicht
nur für die Telekommunikation wichtiges Gebiet. Bisher wurde intensiv
an ps-Laserpulsen experimentell wie theoretisch geforscht. Der Übergang
zu fs-Pulsen führt nun zu noch größeren Übertragungsraten in der Telekommunikation,
jedoch scheint das Verhalten von fs-Pulsen in den dispersiven
Medien erst jetzt in das Interesse der Forschung zu rücken.
Es werden erste Experimente zum Durchgang von fs-Laserpulsen durch
SM-Glasfasern bei einer Wellenlänge von 820 nm gezeigt. Der Einfluss
der Faserlänge auf die Pulsverbreiterung wurde ebenso geprüft wie die
Abhängigkeit von der eingestrahlten Leistung des benutzten Ti:Sa-Lasers
bei einer Pulsbreite von etwa 150 fs. Die beobachtete Pulsbreite hängt dabei
nichtlinear von der Laserleistung ab und ist um ein vielfaches größer
als theoretisch erwartet.
Gefördert durch die DFG über SPP 1133.
O 37.7 Do 17:15 H36
Femtosecond electron dynamics in amorphous and crystalline
ice layers on Ru(001) — •Martin Wolf, Cornelius Gahl, Julia
Stähler, Panagiotis Loukakos, and Uwe Bovensiepen — Freie
Universität Berlin, Fachbereich Physik, Arnimallee 14, 14195 Berlin
The ultrafast electron transfer and solvation dynamics in D2O layers on
Ru(001) have been studied by time-resolved two-photon-photoemission
(2PPE) spectroscopy. Structural characterization of the ice layers were
carried out by simultaneous measurements of the electronic structure,
work function and the D2O desorption rate as a function of temperature.
Hereby, amorphous and crystalline multilayers as well as the bilayer can
be prepared with high accuracy. We find that the electron dynamics differ
significantly for amorphous and crystalline ice. In amorphous layers,
electron solvation, characterized by a time-dependent shift of the electron
binding energy by 1 eV/ps, as well as the population decay, occurs much
faster compared to the dynamics observed previously in amorphous D2O
layers on Cu(111) [1]. This is attributed to structural differences of the
first bilayer and more efficient electron backtransfer to the Ru substrate.
Moreover, the binding energy of the solvated state increases at a higher
rate on the Ru substrate suggesting a more mobile hydrogen bonded network
than on Cu. In the crystalline ice layers electron solvation is not
been observed, however, trapping of extremly long-lived electrons into
structural defects formed by thermal activation.
[1] Phys. Rev. Lett. 89, 107402 (2002); J. Phys. Chem. B 107, 8706
(2003).
Zeit: Donnerstag 15:45–18:15 Raum: H38
O 38.1 Do 15:45 H38
Electronic and geometrical structure of adsorbed small organic
molecules: formate, 3-thiophene carboxylate and glycinate on
Cu(110) surface — •Nicolae Atodiresei, Kurt Schroeder, and
Stefan Blügel — Institut für Festkörperforschung, Forschungszentrum
Jülich, D-52425 Jülich, Germany
The attachment of carboxylic acids and biological molecules to metal
surfaces has very important applications like molecular recognition and
biosensor development. One interest is focused in the property of chirality
which can be induced by the absorption of organic molecules on surfaces.
We performed ’ab initio’ calculations based on density functional theory
(DFT) using a projector augmented plane wave (PAW) method to
obtain the equilibrium geometry of formate, 3-thiophene carboxylate and
glycinate adsorbed on the Cu(110) surface. All molecules contain a carboxylate
functional group (COO-) which binds to Cu atoms of the first
layer via the oxygen atoms. In the case of formate and 3-thiophene carboxylate
the functional group is sitting perpendicular to the Cu(110)
surface. The relative energies of formate on Cu(110) with different coverages
in (2x2) unit cell are discussed. For the saturation coverage of
3-thiophene carboxylate on Cu(110) ((2x1) unit cell) the thiophene ring
is sitting perpendicular to the metal surface but rotated with 23 0 relative
to the [110] direction. The glycinate molecules form a (3x2) unit cell
with 2 flat-lying molecules. They bind to the Cu surface also via amino
group ( H2N-). The heterochiral arrangement is found to be energetically
more stable than the homochiral one because two hydrogen bonds per
molecule can be formed.
O 38.2 Do 16:00 H38
Atomically resolved diffusion processes of hydrogen on Si(001)
induced by nanosecond heating pulses — •C. Schwalb, M.
Lawrenz, M. Dürr, and U. Höfer — Fachbereich Physik, Philipps-
Universität, D-35032 Marburg
The rearrangement of silicon dangling bonds following pulsed laser
heating of monohydride-covered Si(001) surfaces has been studied with
scanning tunneling microscopy (STM). Laser-induced thermal desorption
(LITD) of small amounts of H2 via the so-called interdimer pathway
leads to the creation of isolated pairs of dangling bonds at two adjacent
dimers [1]. Hydrogen diffusion causes this arrangement of dangling bonds
- which represents an excited state of the surface - to change quickly into
the equilibrium configuration consisting of dangling bonds paired up at a
single dimer. By using multiple nanosecond heating pulses we were able
to freeze the surface at various stages of the equilibration process and
take snapshots with the STM. In this way we were able to monitor hydrogen
diffusion processes with atomic resolution which are associated