Plenarvorträge - DPG-Tagungen

Oberflächenphysik Donnerstag
messer 100 ˚A beträgt und ein geschlossener Co Film gewachsen ist. Nach
Deposition von 7 ˚A zeigt der Co Film erstmals ein magnetisches Verhalten.
Anlassen der Probe über 500 K führt zur Koaleszenz der Cluster und
einer fortschreitenden Diffusion von Co Atomen durch das Oxid in das
Substrat, wobei nach dem Anlassen auf 1000 K Co vollständig diffundiert
ist.
O 39.6 Do 17:00 H39
Kinetic lattice Monte-Carlo simulations of stacking fault nucleation
on Ir(111) — •Michael Müller and Karsten Albe — TU
Darmstadt, FB Materialwissenschaft, Petersenstraße 23, 64289 Darmstadt
A prominent fault during epitaxial growth of face-centered-cubic (111)
metal surfaces is the formation of adatom islands that nucleate and
grow in the hexagonal-close-packed stacking. For sub-monolyer growth
on Ir(111) detailed experimental data on the temperature dependence of
the probability of stacking fault island formation is available from scanning
tunneling microscopy. Here, we present kinetic lattice Monte-Carlo
(KLMC) simulations of homoepitaxial island growth on Ir(111) that are
able to reproduce the experimentally observed shape and distribution of
stacking fault islands over a wide temperature range. In our simulations,
atomic positions are not restricted to perfect fcc lattice sites, as it is the
case in conventional KLMC. Therefore, an effective method to implement
a refined lattice that includes fcc as well as hcp sites is presented. Also,
the diffusion behavior of small adatom clusters plays a central role for
the formation of stacking fault islands on Ir(111). Our KLMC simulations
identify adatom clusters on the surface. In addition to single adatoms,
these clusters are also treated as mobile species.
O 39.7 Do 17:15 H39
Epitaxial growth of thin Alumina on a Cr2O3(0001) substrate
— •Karifala Dumbuya 1 , Sven L. M Schroeder 2 , and Klaus
Christmann 1 — 1 Freie Universität Berlin, Institut für Chemie, Takustrasse
3, 14195 Berlin, Germany — 2 Molecular Materials Centre, Department
of Chemical Engineering, UMIST, PO Box 88, Manchester, M60
1QD, UK
The growth of vapour-deposited Al and aluminium oxide on chromia
Cr2O3(0001) has been studied by auger electron spectroscopy (AES), low
energy electron diffraction (LEED), ion scattering spectroscopy (LEIS),
and x-ray photoelectron spectroscopy (XPS). If aluminium is deposited
in the absence of oxygen, aluminium LVV auger signals are found in the
40-56 eV region, indicative of aluminium in the oxidised state (Metallic
Al appears at 67 eV). This led us to conclude that the phenomenon of aluminothermy
must have occured. Controlled evaporation of aluminium in
an oxygen milieu, however, resulted in the growth of well ordered Al2O3
films up to a thickness of 30 ˚A, whereby the epitactic growth could be
monitored by LEED. These films were conducting enough to be subjected
to electron spectroscopy. A gradual attenuation of the XP signals
of Cr indicates layer-by-layer growth. A parallel and recently concluded
investigation of the Cr2O3/Al2O3 system using LEIS and XPS has corroborated
our assumption that alumina grows on the Cr2O3 substrate
in an oriented manner. In addition, LEIS indicated that the uppermost
Al2O3 layers are Cr-free, and from XPS we deduced that Al actually
exists in the Al 3+ valence state.
O 39.8 Do 17:30 H39
Atomic structure of ultrathin Fe films on Cu(100) and Cu(111)
prepared by pulsed laser deposition (PLD) — •Hannes
Schiechl, Albert Biedermann, Michael Schmid, and Peter
Varga — Institut für Allgemeine Physik, Technische Universität Wien,
Wiedner Hauptstrasse 8-10/134, A-1040 Vienna, Austria
O 40 Halbleiteroberflächen und -grenzflächen
Ultrathin Fe films up to 10 ML were grown on Cu(100) and Cu(111)
using pulsed laser deposition (PLD) and analyzed by scanning tunneling
microscopy (STM). We present a survey of the local atomic structure
of these films, which show enhanced layer-by-layer growth compared to
films grown by thermal deposition (TD). At laser intensities near the ablation
threshold we observe a bcc-like Fe phase between 2 and 5 ML film
thickness on Cu(100), similar to our previous results on TD-films, where
this structure can be correlated to the interesting magnetic properties
of these films. Regarding Fe films grown on the Cu(111) surface using a
laser wavelength of 532 nm, we observe a transition of the growth mode
by increasing the laser fluence per pulse. The bilayer growth mode, which
we find on TD-films, changes to layer-by-layer growth.
O 39.9 Do 17:45 H39
Growth and structure of pulsed laser deposited Pd films on
Cu(100) — •Y. Lu, H.L. Meyerheim, W. Wang, J. Barthel,
M. Przybylski, and J. Kirschner — MPI für Mikrostrukturphysik,
Weinberg 2, 06120 Halle
Pd films in the coverage regime between 0.2 to 8 monolayers
(ML, 1ML=1.53×10 15 atoms/cm 2 ) were grown at room temperature on
Cu(001) using pulsed laser deposition (PLD) and studied by scanning
tunneling microscopy (STM), low energy electron diffraction (LEED) and
Auger-electron spectroscopy (AES). Up to a Pd coverage of θ = 4 ML a
well defined layer-by-layer growth mode is observed, at higher coverage
the strain due to the large mismatch (7.6 %) relaxes by formation of
a two-dimensional ordered array of dislocations running parallel to the
〈100〉 directions of the Cu-substrate. In the coverage regime below 4ML,
LEED images do not indicate the formation of any ordered superstructure
such as the c(2x2), which was previously observed at 0.5 ML for
thermally deposited Pd [1]. The two-dimensional misfit dislocation network
formed at θ > 4ML gives rise to the appearance of diffuse lines of
satellite reflections between the (1x1) substrate reflections. For deposition
at 500 K, Pd-growth proceeds by the step flow mode and a better
ordering of the dislocation network is observed. [1] P.W. Murray et al.,
PRB 52, R14404 (1995)
O 39.10 Do 18:00 H39
Self-healing of stacking faults in homoepitaxial growth on
Ir(111) — Carsten Busse 1,2 , •Arne Thoma 1 , and Thomas
Michely 1 — 1 I. Physikalisches Institut der RWTH Aachen, 52056
Aachen, Germany — 2 Present address: Institute of Physics and
Astronomy, University of Aarhus, 8000 Aarhus C, Denmark
The growth of a thin film is studied from the nucleation phase to the
closure of the first monolayer in the face-centered cubic (fcc) system
Ir/Ir(111) using temperature-variable scanning tunneling microscopy.
The island that nucleate in the hexagonal close-packed (hcp) stacking
cannot coalesce with regular islands. Instead, an assimilation process is
observed, where material is transported from the metastable hcp to the
energetically favourable fcc sites. The atomic mechanisms governing this
transfer are identified. Furthermore, the influence of adsorbates on nucleation
of stacking-faults is investigated by exposing the surface to different
gases prior to evaporation.
Zeit: Donnerstag 15:45–18:45 Raum: H45
O 40.1 Do 15:45 H45
Optische Charakterisierung ultradünner Siliziumoxid-Filme mit
der Brewster-Winkel Analyse (BWA) — •Michael Lublow
und H. J. Lewerenz — Hahn-Meitner-Institut Berlin Abteilung Solare
Energetik (SE5) Glienicker Str. 100 14109 Berlin
Die optische Charakterisierung ultradünner Filme mit Schichtdicken
d < 8 nm wird durch den Einfluß rauher Grenzflächen erschwert: die
ermittelten Werte weichen von denen anderer oberflächensensitiver Me-
thoden wie Auger Elektronenspektroskopie oder Photoelektronenspektroskopie
ab. Für das natürliche Oxid auf Si(111) wird die Oberflächeninformation
mittels dynamischer Anpassung des Einfallswinkels
durch eine symmetrische Messung des Reflektivitätssignals um den
Brewster-Winkel des SiOx/Si-Systems herum erfaßt. Charakteristische
Unterschiede gegenüber phasenoptimierter Ellipsometrie werden für naßchemische
Ätzungen des Oxids untersucht. Es wird gezeigt, daß die BWA
die einzelnen Stufen der Oxidabtragung sowie die anschließende Rauhig-