Plenarvorträge - DPG-Tagungen

Oberflächenphysik Dienstag
Variation of both the I − and the I2 concentrations enables the identification
of the respective emission features (by their electron binding
energies), and hence allows us to quantitatively follow the evolution of
the relative intensities in accordance with the equilibrium of complex
formation: I − + I2 ⇀↽ I − 3 . The experiments were performed at the MBI
undulator beamline at BESSY in the 50-120 eV photon energy range,
using a 6 µm diameter liquid jet.
O 19.3 Di 11:45 H39
Magnetism of mass selected, deposited, small Gadolinium and
Gadolinium oxide clusters — •Matthias Reif, Leif Glaser,
Michael Martins, and Wilfried Wurth — Institut für Experimentalphysik,
Universität Hamburg, Luruper Chaussee 149, 22761 Hamburg
Results of XMCD (X-Ray Circular Magnetic Dichroism) measurements
of small deposited Gadolinium- and Gadolinium oxide clusters are presented.
The clusters are supported by a magnetized ultrathin iron film
epitaxially grown on Cu(100) and showing an easy magnetization axis
perpendicular to the crystal surface. The clusters are generated by high
energy sputtering of a Gd-target with Xe-ions. After mass selection using
a dipole magnet, the clusters are deposited on the iron surface. In
order to prevent fragmentation of the clusters, the process of softlanding
is applied. Here, some multilayers of Argon consume the kinetic energy
during deposition of the clusters.
Focusing on the 3d→4f and 4d→4f excitations, dichroism spectra measured
at beamline UE56/1PGM at BESSYII are shown and different
contributions to the dichroism signal are discussed. The different Gdn
clusters show similar dichroism patterns as Gd thin films, whereas for
the oxidized GdnOm clusters different features are found in the spectra.
This project is supported by BMBF under contract KS1 GUB/5.
O 19.4 Di 12:00 H39
Lasergestützte Methode zur Einengung der Größen- und Formverteilung
von Gold-Nanoteilchen — •C. Hendrich, H. Ouacha,
T. Vartanyan, F. Hubenthal und F. Träger — Experimentalphysik
I, Institut für Physik und Center for Interdisciplinary Nanostructure
Science and Technology - CINSaT, Universität Kassel, Heinrich-Plett-
Straße 40, D-34132 Kassel
Auf dielektrischen Oberflächen können durch selbstorganisiertes
Wachstum metallische Nanoteilchen (NT) hergestellt werden. Die Teilchenensembles
weisen in der Regel eine gewisse Größen- und Formverteilung
auf. Durch den Wachstumsprozess ist außerdem die Teilchenform
fest mit der Teilchengröße verknüpft. Wir haben diese Parameter nach
dem Wachstum künstlich durch Laserbestrahlung verändert. Ausgenutzt
wurde hierbei die Interaktion des Laserlichts mit den für metallische
NT typischen Oberflächen-Plasmon-Resonanzen (OPR). Ensembles von
Gold-NT wurden in systematischen Untersuchungen mit Nanosekunden-
Laserpulsen bestrahlt. Die resonanten NT wurden durch das resultierende
selektive Heizen kugelähnlicher, die OPR wurde entsprechend zu höheren
Plasmonenergien verschoben. Auf diese Weise wird die durch das Wachstum
vorgegebene Abhängigkeit zwischen Form und Größe verhindert.
Durch sukzessive Bestrahlung bei verschiedenen Laser-Wellenlängen ist
es außerdem möglich, die Größen- und Formverteilung einzuengen. Die
so veränderten NT-Ensembles wurden mit Rasterkraftmikroskopie und
optischer Spektroskopie untersucht.
O 19.5 Di 12:15 H39
Spectroscopy of gold clusters on graphite for a broad range of
cluster sizes — •I. Barke, T. Irawan, and H. Hövel — Universität
Dortmund, Experimentelle Physik I, D-44221 Dortmund
Gold clusters grown on nanostructured highly oriented pyrolytic
graphite (HOPG) have been investigated by Scanning Tunneling
Spectroscopy (STS) and Ultraviolet Photoelectron Spectroscopy (UPS).
The evolution of the d electron UPS spectra for increasing cluster size
is consistent with corresponding Scanning Tunneling Microscopy (STM)
results. The combination of these methods allows a semi quantitative
analysis of the cluster growth process. The main emphasis lies on the
change of the cluster morphology from small clusters without facets to
large faceted clusters. In addition, we present STS results for a wide
variety of cluster sizes. On the (111) facets of large Au clusters (N ≈ 10 4
atoms) STS and UPS spectra revealed a two dimensional cluster surface
state confined to the cluster facet [1, 2]. Further on, we measured dI/dV
spectra for about 70 different smaller clusters (N ≈ 10 1 . . . 10 3 atoms).
Though these series of STS curves look more complicated, we observed
spectral features changing systematically with the cluster size.
[1] I. Barke, H. Hövel, Phys. Rev. Lett. 90, 166801 (2003).
[2] H. Hövel, I. Barke, New J. Phys. 5, 31 (2003).
O 19.6 Di 12:30 H39
Luminescence from gold nanoparticles mediated by plasmon
emission — •T. A. Klar 1 , E. Dulkeith 1 , T. Niedereichholz 1 ,
J. Feldmann 1 , G. von Plessen 2 , D. I. Gittins 3 , S. Mayya 3 ,
and F. Caruso 3,4 — 1 Photonics and Optoelectronics Group, Department
of Physics and CeNS, Ludwig-Maximilians-Universität München
— 2 1. Physikalisches Institut, RWTH Aachen — 3 Max-Planck-Institut
für Kolloid- und Grenzflächenforschung — 4 Department of Chemical and
Biomolecular Engineering, The University of Melbourne, Australia
We observe photoluminescence emission at the particle plasmon frequency
from gold nanoparticles when the nanoparticles are excited above
the d-sp interband transition threshold. Estimates of quantum yields for
direct emission from d-sp interband recombination in bulk metals have
given quantum efficiencies of 10 −10 [1]. In contrast, here we observe a
quantum efficiency of 10 −6 , which is essentially independent of the particle
size. This increased quantum efficiency is explained by a two step
process: Instead of a direct emission of a photon, the d-sp band recombination
excites a particle plasmon which in turn decays radiatively,
emitting a photon.
[1] Mooradian, Phys. Rev. Lett. 5, 185 (1969)
O 19.7 Di 12:45 H39
TEM and STM Study of Gold Nanoparticles — •M. Smetanin 1 ,
S. Schulze 1 , F. Müller 1 , D. Piasta 2 , S. Spange 2 , and M.
Hietschold 1 — 1 Chemnitz University of Technology, Institute of
Physics, Solid Surfaces Analysis Group, D-09107, Chemnitz, Germany
— 2 Chemnitz University of Technology,Institute of Chemistry, D-09107
Chemnitz, Germany
Metal nanoclusters are interesting candidates for nanostructured materials
and nanoelectronic digital circuits. We have investigated the structure
of chemicaly synthesized gold nanoparticles of different sizes with
and without thiol coating. Gold nanoparticles with a diameter of 3 nm
and 10 nm were studied using transmission electron microscopy (TEM)
and scanning tunneling microscopy (STM). TEM investigations show the
crystalline structure of gold nanoparticles in all cases. High energy electron
difraction (HEED) shows that the lattice structure of nanoparticles
of 10 nm average diameter corresponds to fcc independently from
coating. But for smaller clusters with an average diameter of 3 nm the
coexistence of bcc and fcc seems to be possible. Moreovere we have observed
a dependency of the thiol coating for these phases. Furthermore
we have investigated the shapes of gold clusters by STM for comparison
with TEM experiment.
O 19.8 Di 13:00 H39
Shaping silver nanoparticles with cw laser light — •M.
Alschinger, N. Borg, F. Hubenthal, and F. Träger — Institut
für Physik and Center for Interdisciplinary Nanostructure Science and
Technology - CINSaT, Universität Kassel, Heinrich-Plett-Str. 40, 34132
Kassel
Nanoparticles and systems in the nanometer size regime have been
studied intensively in recent years. These systems have e.g. electronic,
optical and catalytic properties which differ considerably from those of
the corresponding bulk material and depend strongly on the size and
morphology of the structures under investigation. For many applications
it is very important to prepare nanoparticles on surfaces with well-defined
sizes and shapes, e.g. for optical filters which selectively block radiation in
narrow wavelength intervals. A widely used method to prepare nanoparticles
on surfaces is to deposit metal atoms on substrates followed by
Volmer-Weber growth. However, this usually produces nanoparticle ensembles
with a broad distribution of sizes and shapes. To overcome this
disadvantage our group has developed a laser-based method to tailor
nanoparticles with well defined dimensions. We showed that, irradiating
the particles with ns pulsed laser light during growth systems of reduced
dimensions can be prepared with a predetermined axial ratio independent
of size [1]. This method has been extended to the use of cw laser
irradiation of different wavelength. For silver particles on quartz we have
observed a strong dependence of the process of nanoparticles shaping on
the intensity of the cw laser light.
[1] T. Wenzel et al., Appl. Phys. B. 69, 513 (1999)