Plenarvorträge - DPG-Tagungen

Oberflächenphysik Montag
O 4.7 Mo 12:45 H43
Electronic Structure of Self-Assembled Bacterial S-Layers
— •Serguei Molodtsov 1 , Denis Vyalikh 1 , Steffen
Danzenbächer 1 , Michael Mertig 2 , Alexander Kirchner
2 , Wolfgang Pompe 2 , and Yuriy Dedkov 3 — 1 Inst. f.
Festkörperphysik, TU Dresden — 2 Inst. f. Werkstoffwissenschaft, TU
Dresden — 3 II. Physikalisches Institut, RWTHA
The discovered possibility to grow thin self-organized biological films
on appropriate substrates is one of the mostly important recent achievements
of materials science. Various branches of microelectronics already
advance by this unique possibility. To make further progress in these
fields, thorough information about electronic structure of grown layers is
required. The corresponding data are lacking, however, since the biological
substances are quite sensitive to exposure and can easily be destroyed
by irradiation as necessary for spectroscopic techniques usually used to
study electronic structure of solids.
We present first results of photoemission and x-ray absorption study of
ordered films of bacterial cell well proteins (S-layer) of Bacillus sphaericus
and Sporosarcina ureae. The films under study are found to be wide-gap
semiconductors. Similar to organic materials both the occupied and the
unoccupied electron densities of states represent series of peaks, which
O 5 Epitaxie und Wachstum I
can be related to the molecular-like electron orbitals.
O 4.8 Mo 13:00 H43
Calculation of the optical constants of thin films from just one
spectral measurement and its application to organic films —
•Robert Nitsche, Holger Pröhl, Thomas Dienel, and Torsten
Fritz — Institut für Angewandte Photophysik, TU Dresden
The interpretation of optical thin film spectra is usually not straight
forward since the shape of the spectra is strongly influenced by the substrate.
Therefore, one has to extract the optical constants of the film,
namely the index of refraction n and the absorption coefficient k. Here,
we present a new method which allows to determine the optical constants
from just one spectral measurement. The algorithm makes explicit use of
the fact that n and k are connected by a Kramers-Kronig transformation.
The successful application of the method is demonstrated on both, analytically
generated and experimentally recorded examples. For this contribution
we chose a Differential Reflectance Spectrum (DRS) of a thin film
of the organic semiconductor PTCDA (3,4,9,10-perylenetetracarboxylic
dianhydride) on HOPG (Highly Oriented Pyrolytic Graphite). This example
has been selected since its optical spectrum does not resemble the
material’s absorption at all.
Zeit: Montag 11:15–13:15 Raum: H44
O 5.1 Mo 11:15 H44
Growth dynamics of Ge islands on high index Si surfaces
— •Marcel Himmerlich 1,2 , Woochul Yang 1 , Robert J. Nemanich
1 , and Juergen A. Schaefer 2 — 1 Department of Physics,
North Carolina State University, Raleigh, NC 27695 — 2 Institut für
Physik and Zentrum für Mikro- und Nanotechnologien, TU Ilmenau,
98684 Ilmenau
The growth dynamics of Ge islands on Si substrates with surface orientation
close to (113) has been studied in situ by photoelectron emission
microscopy (PEEM) at 450 ◦ -550 ◦ C and during annealing up to 700 ◦ C.
The growth rate was varied between 0.1 and 0.6 ML/min. Photoelectrons
were excited by UV-light generated by the UV free electron laser at Duke
University. First, up to 3-4ML, uniform emission was observed indicating
the growth of a strained wetting layer. Then 3D-growth occurred with
different island shapes. Low growth rates result in elongated islands in
[332] direction, indicating anisotropical strain. At higher deposition rates
round islands were created. There, during continuous deposition, islands
enlargement was observed with no further nucleation. During annealing,
the density of round islands decreased while the average size increased
(ripening), whereas the elongated structures undergo a shape transformation
leading to indentations.
O 5.2 Mo 11:30 H44
Nucleation in the presence of adatom insertion: Co/Pt(111) —
•Philipp Buluschek, Stefano Rusponi, Mehdi El Ouali, Emmanuel
Vargoz, Klaus Kern, and Harald Brune — Institut de
Physique des Nanostructures, Ecole Polytechnique Fédérale de Lausanne,
CH-1015 Lausanne, Switzerland
We used variable temperature STM to study submonolayer nucleation
of Co/Pt(111). The Pt(111) surface is under tensile stress and undergoes
a reconstruction above 1330 K, or upon Pt deposition at 400 K. For Co
deposition, adatom incorporation into the first atomic plane has been reported
upon deposition at 300 K. We show that conventional on-surface
diffusion and nucleation takes place up to 180 K. Above this temperature
the island density continues to decrease but with a smaller slope
in its Arrhenius representation. Our experiments demonstrate that this
coincides with the onset of inclusion.
We present kinetic Monte-Carlo simulations revealing that insertion
leads to the creation of repulsive point and line defects. The comparison
between simulations and experiment enables access to the energy barriers
for surface diffusion, insertion and the repulsion at the defects.
O 5.3 Mo 11:45 H44
Untersuchungen des Wachstums von Mn-Filmen auf Si(100) —
•Holger Lippitz, Kai Schwinge, Jens J. Paggel und Paul Fumagalli
— Institut für Experimentalphysik, Freie Universität Berlin,
Arnimallee 14, 14195 Berlin
Die bisherigen Untersuchungen von Mn und Mn-Verbindungen kon-
zentrierten sich häufig auf die magnetischen und strukturellen Eigenschaften
relativ dicker Mn-Filme. Hier werden die Strukturen dünner
Mn-Schichten (von 1/10 ML bis zu 5 ML) auf Si(100) und 4 ◦ fehlorientierten
Si(100) Substraten im UHV untersucht. Die Ausheiltemperaturen
und Schichtdicken werden variiert. Zur Untersuchung der Proben stehen
STM, RHEED, LEED und AES zur Verfügung. Es werden mehrere Arten
der Inselbildung (temperatur- und schichtdickenabhängig), aber keine
atomar glatten und geschlossenen Filme beobachtet. Es treten Strukturen
auf, die auf eine Bildung von MnSi oder Mn5Si3 hindeuten. Generell
wird eine Zunahme der Defektdichten auf dem Substrat gefunden. Die
beobachtete Inselgröße wird von der Stufendichte des Substrats beeinflusst.
Alle Ergebnisse weisen auf ein Filmwachstum in Form eines Silizids
anstatt eines Mn-Filmes hin. Gefördert von der Deutschen Forschungsgemeinschaft
durch den SFB 290.
O 5.4 Mo 12:00 H44
Hochempfindliche Messung von Oberflächenverspannung — Peter
Kury, Michael Horn-von Hoegen, •Peter Kury und Michael
Horn-von Hoegen — Inst. f. Laser- und Plasmaphysik, Universität
Duisburg-Essen
Die Verspannung von Oberflächen (surface stress) ist eine der wichtigsten
physikalischen Größen für das Verständnis von Phänomenen im
Bereich der Epitaxie. Eine Messung der Verspannung kann mit optischen
Biegebalkenmethoden wie SSIOD (surface stress induced optical
deflection) erfolgen, wobei ohne großen Aufwand eine Auflösung von etwa
0.2N/m erreichbar ist. Eine Steigerung der Empfindlichkeit, um Verspannungen
ab 0.05N/m sicher detektieren zu können, erfordert aufwändige
Änderungen des Meßaufbaus im Bereich des Detektors, des Lasersystems
und der Probe. Diese Modifikationen und ihre Auswirkungen werden anhand
von neuen Adsorptions- und Filmwachstumsmessungen auf Si Substraten
vorgestellt.
O 5.5 Mo 12:15 H44
Growth of Vanadiumoxide and Niobiumoxide on Cu3Au(100)
— •Jürgen Middeke, Ralf-Peter Blum, and Horst Niehus —
Humboldt-Universität zu Berlin, Institut für Physik, ASP, Newtonstr.
15, 12489 Berlin
Thin crystalline 2-dim vanadiumoxide films can be prepared with controlled
stoichiometry by implantation of oxygen into Cu3Au(100) and
deposition of vanadium, followed by annealing [1]. The keystep of this
procedure is the formation of an amorphous vanadiumoxide layer during
the deposition of vanadium that locally has the desired ratio of vanadium
to oxygen. With no mass transport necessary, annealing to 700K is sufficient
for crystallisation. Depending on the amount of oxygen implanted
into the Cu3Au(100)-surface, VO2, V2O3 and VO can be obtained.
As a check if this growth method can be applied also to other transition
metal oxides, we exchanged vanadium by niobium. The result is that also
flat 2-dim Niobiumoxide films can be prepared. As an example, we get a