Plenarvorträge - DPG-Tagungen

Dünne Schichten Dienstag
oscillations. Increased ion dosages result in a complete loss of exchange
bias properties which is supported with loss in inter-layer definition by
ion irradiation.
DS 22.36 Di 14:30 Poster B
TEM Investigation of the Structure and Geometry of Nanotunnels
formed upon Cu Deposition on VSe2 Surfaces — •E.
Spiecker, S. Hollensteiner, and W. Jäger — Technische Fakultät
der Christian-Albrechts-Universität zu Kiel
Linear nanostructures formed in the early stages of Cu deposition onto
VSe2 crystal surfaces have been studied in detail by TEM in plan-view
geometry. The nanostructures are found to be made up of two parallel
strands each of them consisting of a linear array of VSe2 platelets. Combining
diffraction analyses with tilt experiments the platelets of the two
strands are shown to be symmetrically inclined by ∼ 30 o with respect
to the surface, thus forming a roof-like nanotunnel with triangular crosssection.
Along the strands the platelets show only minor misorientations
with respect to each other. No gaps are observed at the substrate-platelet
interfaces and at the interfaces along the ridges. The symmetry of the
configuration and the sharpness of these interfaces indicate the presence
of linear structure modifications with lateral dimensions of only few
nanometers. These structures might be composed of special structural
units, such as the topological defects discussed for caps of MoS2 nanotubes.
Our observations of the presence of substrate dislocations which
are spatially correlated with the nanoroofs indicate that the nanoroof formation
is connected with dislocation injection, thus providing a mechanism
for strain relaxation during the early deposition stages. A formation
model will be presented which extends earlier suggestions attributing the
formation of nanotunnels to the relaxation of compressive surface strain.
DS 22.37 Di 14:30 Poster B
Heteroepitaxial growth of cubic boron nitride films on Single
Crystalline (001) Diamond Substrates — •H. Yin, X.W. Zhang,
H.-G. Boyen, and P. Ziemann — Abteilung Festkörperphysik, Universität
Ulm, D-89069 Ulm
In addition to hard coating applications, cubic boron nitride (c-BN)
is also considered as a starting material for high-temperature electronic
devices. In order to use c-BN for such a purpose, a high structural quality
of the corresponding samples appears necessary. To approach this goal,
heteroepitaxial c-BN films were grown by ion beam assisted deposition
(IBAD) on highly oriented (100) diamond substrates at high temperatures
(∼1000 ◦ C). Combination of several characterization techniques
showed that 100% pure c-BN films prepared at elevated temperatures
on top of (100) diamond nucleate and grow directly on this substrate
without an interfering hexagonal BN layer. Atomic force microscopy of
such high quality c-BN films shows a well-defined square pattern with
an average lateral grain size of 3 µm reflecting the grain boundaries of
the underlying diamond substrate. As opposed to c-BN growth on top of
heteroepitaxially prepared CVD diamond films delivering typical rocking
widths of ∆Ω = 4.6 ◦ , c-BN films deposited on single crystalline (001)
diamond substrates exhibit significantly improved values of 0.2 ◦ . The
smooth surface and extremely high hardness and Young’s modulus are
further indications of the high quality epitaxial growth of c-BN films on
single crystalline diamond substrates.
DS 22.38 Di 14:30 Poster B
Adjusting Wettability, Adhesion, and Residual Stress of Hard
Carbon Coatings — •Nicolas Wöhrl, Stephan Reuter, Oleksiy
Filipov, and Volker Buck — Thin Film Technology Group, Dept.
of Physics, University of Duisburg-Essen, Universitätsstr. 3-5, 45141 Essen,
Germany
In this work hard carbon coatings are grown with a dc-arc. As a carbon
source, graphite electrodes are used and the films are deposited on
double-side polished (100) Si-Substrate in a hydrogen atmosphere. The
variation of process-parameters like gas flow, pressure, or gas-mixture
is used to influence the properties of the films. Nitrogen, Argon and
Tetramethyl-Silane is used as gas admixture. Properties like mechanical
stress in the film, adhesion of the film on the substrate and wettability
can be adjusted in a wide range. The adhesion of the films to the substrate
is tested by cavitation erosion tests. The cavitation erosion test is
a quantitative measurement system for adhesion, in which the ablation
of the film as a function of measuring time is used to characterize the
adhesion of the film. The advantage of this method compared to conventional
adhesion tests (such as nanoindenter scratch tests) is the lack
of wear of the test-equipment. The mechanical stress is analysed by an
optical setup, measuring the substrate curvature. The films are also analysed
by Fourier-transformed infrared spectroscopy (FTIR), micro-Raman
measurements, and scanning electron microscopy (SEM).
DS 22.39 Di 14:30 Poster B
Growth and Thermal (In-)Stability of Mulitlayers and
Nanowires on Facetted Alumina Templates — •Carsten
Herweg 1 , Jörg Hoffmann 2 , and Herbert C. Freyhardt 1,2 —
1 Institut für Materialphysik, Universität Göttingen, Tammannstr. 1,
D-37077 Göttingen — 2 Zentrum für Funktionswerkstoffe ZFW gGmbH,
Windausweg 2, D-37073 Göttingen
Annealing of α-Al2O3 (10¯10), (m-plane) at ∼ 2
3 · Tm (Tm: melting temperature)
in air results in the formation of a highly ordered facetted
alumina surface. Investigation by Atomic Force Microscopy (AFM) and
cross-section ransmissionelectronmicroscopy (TEM) reveal a periodicity
of ∼300 nm at a hill-to-valley hight of ∼50 nm. In such a way prepared
alumina surfaces were utilised as substrate for the deposition of multilayers
and nanowires. Metallic multilayers consisting of two immiscible
components are known to be transformable into a nanostructered system
of non-statistically distributed nearly spherical particles in a surrounding
matrix of the complementary component by an annealing process. The
influence of the underlying substrate structure, i.e. local curvature, on the
film growth and on the microstructural transformation during the heat
treatment is analysed by means of XRD, AFM, TEM and electrical transport
measurement. AFM analysis and MOKE of nanowires prepared by
grazing incident sputter deposition show, dependent on deposited material
either overgrowing of the facets or well-defined, separated wires
with a width of ∼100–150 nm, whereas the length is limited only by the
macroscopic substrate dimensions.
DS 22.40 Di 14:30 Poster B
Eigenschaften magnetischer Tunnelelemente mit ECWR-
Plasma oxidierten Barrieren — •Rainer Kaltofen, Ingolf
Mönch, Joachim Schumann, Dieter Elefant und Hartmut
Vinzelberg — IFW Dresden, Postfach 270116, 01171 Dresden
Für die Verwendung von magnetischen Tunnelelementen als Sensoren
oder Speicher sind Tunnelbarrieren mit unterschiedlichen Widerständen
erforderlich. Die chemisch-strukturelle und morphologische Perfektion
der eingesetzten Tunnelbarrieren bestimmt den Tunnelwiderstand, das
magnetische Schaltverhalten und die Stabilität der Elemente. In dieser
Arbeit wird die Herstellung von AlOx-Barrieren durch Oxidation von Al-
Schichten unterschiedlicher Dicke in einem Elektron-Zyklotron-Wellen-
Resonanz angeregten Sauerstoffplasma untersucht. In Abhängigkeit von
den Betriebsbedingungen der Plasmaquelle variiert die Dissoziation der
Sauerstoffmoleküle in O-Atome und -Ionen zwischen 20 und 80%, die kinetische
Energie der Ionen beim Auftreffen auf die Al-Schicht zwischen
20 und 50 eV. Es wurden Tunnelwiderstände zwischen 100kΩµm 2 und
100MΩµm 2 eingestellt, und aus den Tunnelkennlinien Parameter der Barriere
ermittelt. Der Tunnelmagnetowiderstand wurde für ungetemperte
und zur Bildung der antiferromagnetischen NiMn-Phase bis 700K getemperte
NiMn/CoFe/AlOx/CoFe/FeNi Schichtstapel bestimmt.
DS 22.41 Di 14:30 Poster B
Die Heusler-Basislegierung Co2CrAl als Elektrodenmaterial für
Dünnschicht-TMR-Elemente — •Joachim Schumann, Alexander
Burkov, Jochen Werner, Günter Behr, Hartmut Vinzelberg,
Dieter Elefant und Rainer Kaltofen — Leibniz-Institut
für Festkörper- und Werkstoffforschung Dresden, Helmholtzstr. 20, D-
01069 Dresden
Magnetische Tunnelelemente mit großem Magnetowiderstand (≥ 40%)
benötigen Elektroden mit hoher Spinpolarisation. Halbmetallische Heuslerlegierungen
erfüllen dank ihrer Bandlücke in nur einem Spinkanal diese
Anforderung, wobei jedoch die Schichtdarstellung sicherstellen muß, daß
der halbmetallische Charakter der Heuslerschichten unmittelbar an den
inneren Grenzflächen der Tunnelstrukturen keine Degradation erfährt.
Untersuchungen zur Struktur- und Phasenbildung an den für die Targetpräparation
und die Einkristallzüchtung erforderlichen polykristallinen
Ausgangsmaterialien verdeutlichen, daß nur durch eine definierte
Wärmebehandlung die Heuslerphase zu stabilisieren ist, was durch Transportmessungen
in Abhängigkeit von der Temperatur bestätigt wurde. An
Sputterschichten konnte gezeigt werden, daß die Targetzusammensetzung
in den Schichten reproduziert werden kann. Für die Ausprägung eines
optimalen magnetischen Verhaltens erweist sich eine Temperbehandlung
als notwendig. Eine Präparationstechnologie für Heusler-basierte Tunnel-