Plenarvorträge - DPG-Tagungen

Oberflächenphysik Dienstag
The interplay between structure and quantum effects in atomic
nanocontacts is investigated. Our approach is based on density functional
theory and the Korringa-Kohn-Rostoker Green’s function method.
Atomic relaxations of nanocontacts and electrodes are calculated with ab
initio based many body potentials for low-dimensional systems. We concentrate
on Cu, Fe, Co, Rh and Pd atomic bridges. The quantum size
effect is found to be dominated by unoccupied electronic states and leads
to an enhancement of the LDOS at the Fermi level as the number of atoms
in the contact increases. We show that the atomic bridges constructed
from non-magnetic in bulk Rh and Pd can be magnetic.
O 24.6 Di 17:00 H38
Nanostructuring by Erosion Sputtering: transition from dots
to ripples — •Tobias Allmers, Georgi Rangelov, and Markus
Donath — Physikalisches Institut, Westfälische Wilhelms-Universität
Münster, Wilhelm-Klemm-Str. 10, 48149 Münster
Self-organization plays an important role for massive parallel production
of nanostructures. One way of producing self-organized structures is
erosion sputtering.
The generation of ripples by oblique ion impact on certain material
surfaces has been known since the seventies [1]. In recent studies, selforganized
patterns of hexagonal ordered quantum dots have been found
after ion bombardment perpendicular to the sample surface [2].
For this contribution, we investigated the transition from dots to ripples
for GaSb as a function of the incidence angle of the argon ions. The
structures obtained were characterized by microscopic and spectroscopic
methods.
Dots appeared up to an incidence angle of 10 ◦ relative to the surface
normal. We observed that the transition between dots and ripples is not
abrupt - first the hexagonal order is lost and then ripples begin to appear.
[1] Bradley and Harper, J. Vac. Sci. Technol. A 6, 2390 (1988)
[2] Facsko et al., Science 285, 1551 (1999)
O 24.7 Di 17:15 H38
STM-based nanolithography in diamond-like carbon layers —
•Thomas Mühl — IFW Dresden, Helmholtzstr. 20, D-01069 Dresden
The spatially localized emission current of a scanning tunneling microscope
tip leads to a local graphitization of diamond-like carbon thin
films. Using this technique, lines and dots smaller than 10 nm in size
can be written. Due to the widely different properties of diamond-like
and graphite-like carbon, there are a lot of possible applications of these
graphite nanostructures on the diamond film. Systematic investigations
of the current, voltage, and charge dependence combined with analytical
methods like tunneling spectroscopy lead to some preliminary conclusions
about the underlying modification mechanism on the atomic scale.
O 24.8 Di 17:30 H38
Gold clusters in nanopits: growth process and morphology —
•T. Irawan, I. Barke, and H. Hövel — Universität Dortmund, Experimentelle
Physik I, D-44221 Dortmund
The geometric structure and the growth process of gold clusters on
graphite was investigated with scanning tunneling microscopy and transmission
electron microscopy. Gold was evaporated on the surface with
preformed nanometer sized pits at a temperature of 350 ◦ C with rates of
3 × 10 −3 . . .1.4 × 10 −2 ML/s. Here we present a study for a broad range
of cluster sizes; starting from small clusters (N ≈ 10 2 atoms) without
facets [1] up to large clusters (N ≈ 10 4 atoms) with (111) facets on top of
the clusters [2]. The cluster shape is described with different geometric
models. The position of the clusters at the edge of the pits is determined
using STM images before and after a tip induced cluster displacement.
O 25 Epitaxie und Wachstum II
[1] H. Hövel, Appl. Phys. A 72, 295 (2001).
[2] H. Hövel, I. Barke, New J. Phys. 5, 31 (2003).
O 24.9 Di 17:45 H38
Stability of Au nanoparticles on fully oxidized TiO2 substrates.
An AFM/XPS study of Au/TiO2 model systems — •Stefan
Kielbassa, Markus Kinne, and Rolf-Jürgen Behm — Abt.
Oberflächenchemie und Katalyse, Univ. Ulm, 89069 Ulm
The stability of nm-sized gold particles deposited on fully oxidized
TiO2(110) substrates under ultra-high vacuum (UHV) conditions, in an
O2 atmosphere and in air was examined with atomic force microscopy
(AFM) and x-ray photoelectron spectroscopy (XPS). Au/TiO2 model
systems were prepared by evaporating submonolayers of gold on fully
stoichiometric and atomically smooth TiO2 rutile (110) substrates. The
thermal stability of the particles is found to strongly depend on the reaction
atmosphere. Under UHV conditions, the particles are stable even
after annealing at 400 ◦ C and only minor changes are detected after annealing
at 500 ◦ C. In an O2 atmosphere, the particles are stable at room
temperature, but grow dramatically after annealing to 400 ◦ C. In air, particle
growth is observed already at RT, accompanied by the formation
of Au-OH species. Possible mechanisms underlying these effects are discussed.
O 24.10 Di 18:00 H38
Ferroelectric Nano-Rods Grown in Porous Alumina Template
— •Dung Le Quang Tien 1 , J. Yekecheva 2 , F. Müller 1 , A.-D.
Müller 1 , V.D. Dan 3 , and H. Hietschold 1 — 1 Chemnitz University
of Technology, Institute of Physics, Solid Surfaces Analysis Group, D-
09107 Chemnitz, Germany — 2 On leave from Nowosibirsk State Technical
University-Russia — 3 Physics Department, Hue University,77 Nguyen
Hue street, Hue City - Vietnam
We have investigated the structural and electrical properties of ferroelectric
nano-rods of lead zirconate-titanate PbZr1-xTixO3 (PZT) grown
in a porous alumina template. Porous alumina membranes with pores
ranging from 50 to 400 nm were obtained by an electrochemical etching.
We have seen a clear dependency of the voltage and the electrolyte on the
size and shape of these pores. The morphology was characterized using
SEM and AFM. The perfect cylindrical porous alumina samples were
used to grow the PZT nanotubes by dipping in PZT precursor using
vacuum to promote penetration into the pores.
O 24.11 Di 18:15 H38
Imaging of self-assembled organic adsorbates - STM and
STS measurements under ambient conditions — •Sebastian
Hohenstein, Florian Buchner, Stefan Griessl, and Wolfgang
M. Heckl — LMU Muenchen, Department fuer Geo- und
Umweltwissenschaften, Theresienstr. 41, 80333 Munich
A host-guest structure of trimesic acid molecules (TMA) was investigated
under ambient conditions at the liquid-solid interface.
The organic TMA molecules self assemble into two different, nondense-packaged
phases induced by directed hydrogen bonding on a crystalline
surface. In this way a two-dimensional grid architecture with
molecular caves is formed in both cases. These two structure variants
have been imaged by STM with sub-molecular resolution.
It was found that the preparation method is crucial for the resulting
structure of the TMA-grid-network. Therefore further investigation of
the preparation method specifics is in progress.
Furthermore this grid network is now being used as a host system to
store guest molecules. Different molecules are introduced into the solution
to investigate their interaction with the network and to find new
applications and technological uses for such a system.
Zeit: Dienstag 15:45–18:15 Raum: H39
O 25.1 Di 15:45 H39
Influence of cluster mobility and fault energy on stacking-fault
formation — •Andreas Lammerschop 1 , Carsten Busse 1,2 , Celia
Polop 1 , and Thomas Michely 1 — 1 I. Physikalisches Institut, RWTH
Aachen — 2 Present Address: Institute of Physics and Astronomy, University
of Aarhus, 8000 Aarhus C, Denmark
We have applied a mean field rate equation approach to the formation
of stacking faults in thin film growth. Here, we discuss the influence of
cluster mobility and stacking-fault energy on the probability for the formation
of a fault is found. As expected, the fault energy has a strong
influence on the formation probability. The higher the fault energy, the
lower the probability to find an island in the wrong stacking. Our key
finding is, however, the unexpected importance of cluster mobility on
the stacking fault probability. For a fixed fault energy, cluster mobility
may change the nucleation probability for fault islands by several orders
of magnitude; the formation of stacking faults is favored for low clus-