Plenarvorträge - DPG-Tagungen

Oberflächenphysik Dienstag
translates into generation of higher harmonics in the scattered far field
intensity when the tip-sample distance is varied sinusoidally. Detecting
the intensity and phase of these harmonics allows to obtain images of the
localized near field interactions essentially free of parasitic linear scattering
signatures from the surrounding area. The consideration of different
tip and substrate materials is important to interpret and optimize experiments.
O 23.9 Di 17:45 H36
Molecular Resolution Imaging of C60 on Au(111) by Dynamic
Force Microscopy — •R. Hoffmann 1,2 , J.M. Mativetsky 1 , S.A.
Burke 1 , Y. Sun 1 , and P. Grütter 1 — 1 Department of Physics,
McGill University, Montreal, Canada, H3A 2T8 — 2 Physikalisches Institut,
Universität Karlsruhe, 76128 Karlsruhe
Dynamic Force Microscopy (DFM) was used to study thin films and
clusters of C60 on Au(111). After observing the Au(111) 23 x √ 3 reconstruction,
2-3 molecular monolayers of C60 were deposited onto the Au
surface. The close-packed C60 surface was imaged by DFM with molecular
resolution. Enhanced corrugation contrast and an apparent contrast
inversion were observed at step edges. Based on a rough spring model
calculation, it is proposed that this may be the result of a tip-induced
displacement of edge molecules. While imaging small clusters of C60,
some molecules were removed by interaction with the tip, leading to
O 24 Nanostrukturen II
structural rearrangements in the clusters.
O 23.10 Di 18:00 H36
Manifestations of slow hysteretic atomic jumps in dynamic force
microscopy — •R. Hoffmann 1,2 , A. Baratoff 1 , H.J. Hug 1 und
H.-J. Güntherodt 1 — 1 Institut für Physik, Universität Basel, Klingelbergstr.82,
CH-4056Basel, Schweiz — 2 Physikalisches Institut, Universität
Karlsruhe, 76128 Karlsruhe
In dynamic force microscopy, the frequency shift and the excitation amplitude
necessary to keep the cantilever oscillation at a constant amplitude
can be measured simultaneously. The mechanisms leading to atomicscale
contrast in the excitation amplitude are currently the subject of
controversies. Several authors suggested that the energy dissipated into
hysteretic motion of atoms induced by the tip in every oscillation cycle
could cause the observed effects [1]. Site-specific force-distance measurements[2]
performed on KBr(001) provide insight into the relation between
the excitation amplitude and the force. Below a certain critical tip-sample
distance, the frequency jumps between two limiting curves on the timescales
of the order of seconds. The fact that these tip instabilities begin to
occur at the same tip-sample distance as the energy dissipation suggests
that the two are related.
[1] N. Sasaki and M. Tsukada, Jap. J. Appl. Phys. 39, L1334 (2000)
[2] M.A. Lantz et al., Science 291, 2580 (2001)
Zeit: Dienstag 15:45–18:30 Raum: H38
O 24.1 Di 15:45 H38
A Method to Generate Aligned Nanowires on Various Substrates
— •Rainer Adelung, O.C. Aktas, A. Biswas, R. Kunz,
J. Kanzow, U. Schürmann, M. Elbahri, U. Saeed, J. Kruse, and
F. Faupel — Lehrstuhl für Materialverbunde, Technische Fakultät der
CAU Kiel
New methods to prepare nanowires like shown in [1] are still of substantial
interest, as no general solution is found to produce nanowires in
arbitrary form on arbitrary substrates. Here we introduce a method that
allows us to produce aligned nanowires on almost any solid surface. The
method is based on the generation of cracks in thin films as template,
large sticking coefficient differences and long diffusion length. Examples
will be given in which metal deposition in vacuum is used to provide the
material for the nanowires. Those include magnetic nanowires on glass,
gold nanowires on polyimide and platinum nanowire networks on Nafion
surfaces. It will be shown how a precise control over the alignment, the
form of nanowire intersections or the type of nanowire (solid or ”dashed”)
is achieved. In addition, applications for the nanowire networks formed
in this manner will be discussed.
[1] N. A. Melosh, A. Boukai, F. Diana, B. Gerardot, A. Badolato, P.
M. Petroff and J. R. Heath, Science 300,112 (2003)
O 24.2 Di 16:00 H38
Low Electron Energy Microscopy and X-ray Photoemission
Electron Microscopy studies of Conducting Atomic-Force Microscopy
induced surface modifications on thermally grown
SiO2 — •Sascha Kremmer 1 , Stefan Heun 2 , Harald Wurmbauer
1 , Sven Peißl 1 , and Christian Teichert 1 — 1 Department
of Physics, University of Leoben, A-8700 Leoben — 2 Nanospectroscopy
Beamline, Synchrotron ELETTRA, I-34012 Trieste
The process of local anodic oxidation, where positive voltages are applied
between a conductive AFM tip and a silicon sample is well understood.
Here, C-AFM induced surface modification of thermally grown oxides
for opposite sample voltage is investigated. To obtain information on
the nature of the protrusions observed after C-AFM experiments, LEEM
and XPEEM experiments are performed. With LEEM it is found that
the protrusions are heavily charged after their formation. This charge
within the protrusions is annihilated after the exposure of the sample to
short pulses of synchrotron radiation. However, these short x-ray pulses
do not change the topography of the protrusions. After prolonged xray
exposure, a radiation induced desorption of the structures as well
as a desorption of the thermal oxide is observed. The spectra obtained
from XPEEM images at different kinetic electron energies reveal that the
structures formed by C-AFM consist of SiO2.
O 24.3 Di 16:15 H38
Imaging of self-assembled organic adsorbates, STMmeasurements
under UHV conditions — •Christian Gerl,
Lorenz Kampschulte, Stefan Griessl, and Wolfgang M.
Heckl — LMU Muenchen, Dept. Geo.- u. Umweltwissenschaften,
Theresienstr. 41, 80333 Muenchen
The adsorption of Trimesic acid (TMA) on single crystal surfaces
has been studied under Ultra High Vacuum conditions. For this purpose
Trimesic acid was evaporated on different substrates using an effusion
cell. For the UHV preparation of TMA monolayers additional TDS
(Thermal Desorption Spectroscopy) and LEED (Low Energy Electron
Diffraction) investigations were necessary. The structure is characterized
by periodic non-dense-packing of the molecules. Two coexisting phases
could be imaged by STM with sub-molecular resolution. Induced by directed
hydrogen bonding, in both cases the organic molecules built a
two-dimensional grid architecture with molecular caves, both able to
store guest molecules. As a first step TMA molecules themselves were
inserted as guest molecules into the host structure. The guest molecules
could be identified in different adsorption sites.
O 24.4 Di 16:30 H38
Behavior of quantum-well and surface states of Ag/Ni(111) —
•A. Varykhalov 1 , O. Rader 1 , C. Di Giacomo 1 , A. M. Shikin 1,2 ,
W. Gudat 1,3 , C. Grazioli 4 , and C. Carbone 4 — 1 BESSY, 12489
Berlin — 2 Institute of Physics, St. Petersburg State University, 198504
Russia — 3 Insitut für Physik, Universität Potsdam, 14415 Potsdam —
4 CNR-ISM, I-34012 Trieste
Ag films on Ni(111) are known to lead to quantum-well states in angleresolved
photoemission experiments [1]. We have improved the growth of
Ag/Ni(111) by low-temperature deposition and post-annealing. The dispersion
of quantum well states parallel to the film plane has been measured,
and the influence of the substrate on the dispersion is compared
for low (∼ 5 atomic layers) and high thickness (∼ 20 layers). Moreover,
a decrease of the intensity of the L-gap centered surface state of Ag(111)
with increasing Ag coverage is observed. The results are discussed in
connection to our recent data obtained from Ag films on W(110) and
Ge(111).
[1] T. Miller, A. Samsavar, and T.-C. Chiang, Phys. Rev. B 50, 17686
(1994).
O 24.5 Di 16:45 H38
Quantum effects in atom-sized contacts — •A.L. Klavsyuk 1 ,
A.N. Baranov 1 , V.S. Stepanyuk 2 , W. Hergert 1 , P. Bruno 2 , and
I. Mertig 1 — 1 Fachbereich Physik, Martin-Luther-Universität, Von-
Seckendorff-Platz 1, 06120 Halle, Germany — 2 Max-Planck-Institut für
Mikrostrukturphysik, Weinberg 2, D-06120 Halle, Germany