Plenarvorträge - DPG-Tagungen

Dielektrische Festkörper Dienstag
DF 4.12 Di 17:30 H23
A binary colloidal mixture in 2D: An ideal model system for the
glass transition — •Hans König — Fachbereich Physik, Universität
Konstanz, 78457 Konstanz
Investigating a binary 2D colloidal glass former with a repulsive (1/r 3 )
potential we have measured particle positions as a function of time by
video-microscopy. The local packing of the big and small particles as well
as the heterogeneous dynamics were analysed depending on the system
temperature. Finally, we could describe the amorphous 2D short-range
order by local density-optimized triangles. However, there is one triangle
DF 5 Poster
for each 3-particle combination of big and small colloids. Regions with
structural frustration occur between clusters of optimally packed triangles.
For decreasing system temperature the number of densely packed
triangles increased and they began to form clusters. For low system temperatures
such local density-optimized regions moved cooperatively resulting
in heterogeneous dynamics. By structural and dynamical investigations
we identify the 2D glass transition as a percolation of local
density-optimized triangles, which form a stable frame through the whole
glass former. At last, we call this glass description the concept of local
density-optimized crystallite clusters.
Zeit: Mittwoch 14:30–18:00 Raum: Poster C
DF 5.1 Mi 14:30 Poster C
Well-ordered arrays of ferroelectric BaTiO3 and SrBi2Ta2O9
nanostructures grown by pulsed laser deposition — Wenhui Ma,
•Dietrich Hesse, and Ulrich Gösele — Max-Planck-Institut für
Mikrostrukturphysik Halle
Monolayers of monodisperse latex spheres of micron and submicron size
were used as deposition masks to fabricate arrays of ferroelectric nanostructures
by pulsed laser deposition (PLD). First, arrays of well-ordered
BaTiO3 and SrBi2Ta2O9 amorphous structures were prepared on Nbdoped
SrTiO3 (100) substrates (STO:Nb) by PLD at room temperature.
These as-deposited structures were shown to have a pyramid-like shape
with lateral sizes between 100 and 200 nm, forming a hexagonal pattern.
Post-deposition annealing was used to crystallize these nanostructures.
The ferroelectric properties of the crystalline nanostructures were investigated
using scanning force microscopy in piezoresponse mode (PFM).
Depending on material and size of the nanostructures, piezoelectric hysteresis
loops of different shape and size were recorded, demonstrating
that BaTiO3 and SrBi2Ta2O9 nanostructures of 100 to 200 nm lateral
size have a remanent polarization and are switchable by an electric field,
i.e. they are indeed ferroelectric.
DF 5.2 Mi 14:30 Poster C
Properties of high-k dielectric materials studied by conducting
Atomic-Force Microscopy — •Harald Wurmbauer 1 , Sascha
Kremmer 1 , Christian Teichert 1 , Friedemar Kuchar 1 , and
Grazia Tallarida 2 — 1 Department of Physics, University of Leoben,
A-8700 Leoben — 2 Laboratorio MDM - INFM, I-20041 Agrate Brianza,
Milano
The steadily shrinking device dimensions in semiconductor devices demand
for advanced electrical characterization methods operating on the
nanometer scale. One suitable technique already used for the evaluation
of silicon gate oxide quality is Conducting Atomic-Force Microscopy (C-
AFM).
Here, C-AFM is used to study different high-k dielectric materials with
regard to their electric properties and homogeneity. Therefore, materials
like ZrO2 and HfO2, grown by atomic layer chemical vapor deposition on
a silicon substrate are studied by C-AFM in ultra high vacuum (UHV).
The UHV conditions are mandatory to avoid surface modifications during
the experiments. Local current-voltage measurements are used to obtain
a statistical distribution of the leakage current as a function of voltage.
This provides an insight into the influence of the amorphous or crystalline
structure of the films depending on their thickness and heat treatment.
Further, two-dimensional current scans with a positive voltage applied to
the sample are performed to obtain the local distribution of the leakage
current.
DF 5.3 Mi 14:30 Poster C
Wet chemical deposition of semiconducting materials into
porous Al2O3 — •L. Nosova 1,2 , A. Belaidi 1 , T. Guminskaya 1 , S.
Gavrilov 3 , R. Bayon 1 , I. Sieber 1 , V. Timoshenko 4 , I. Urban 5 ,
N. Grigorieva 1,6 , and Th. Dittrich 1 — 1 Hahn-Meitner-Institut,
Glienicker Str. 100, D-14109 Berlin, Germany — 2 permanent address:
Heat Physics Department, Uzbek Academy of Sciences, 700135
Tashkent, Uzbekistan — 3 Moscow Institute of Electronic Engineering
— 4 M. V. Lomonosov Moscow State University, Physics Department,
119899 Moscow, Russia — 5 Bundesanstalt für Materialforschung, Unter
den Eichen 87, D-12205 Berlin — 6 permanent address: St. Petersburg
State University, Department of Solid State Physics, Ulyanovskaya 1,
198504 St. Petersburg, Russia
Porous Al2O3 with ordered pores is prepared by two-step anodization.
Different deposition techniques (successive ion layer adsorption reaction,
chemical bath deposition, ion layer gas reaction, electrochemical
deposition) are used to deposit semiconducting materials as CdS, PbS,
CuO, CuxS, ZnO into pores with diameters between 20 and 200 nm.
The samples are characterized by secondary and transmission electron
microscopy, infrared spectroscopy, optical transmittance and photovoltage
techniques. The different deposition techniques are evaluated with
respect to the quality of the prepared nanocomposites.
DF 5.4 Mi 14:30 Poster C
Integrated electromagnetic bandgap structures for micro- and
millimeter waves — •Michael Schuster and Norbert Klein —
Forschungszentrum Jülich, 52428 Jülich
2dimensional EBG structures are most promising for a possible application
as integrated structure for microwave and optoelectronical devices
due to their advantages in terms of stability, EBG properties and applicable
machining processes. Combining microwave range sized models,
full electromagnetic field simulation software and silicon micromachining
processes it is feasible to built up an integrated circuit technology
based on EBG materials for frequencies from several 10 GHz up to the
millimeter wave range of several 100 GHz.
Starting from the investigation of modular structures for frequencies
as low as 10 GHz, we have been investigating the fabrication of EBG
structures for frequencies around 30 GHz employing a lost Mould technique.
We are investigating line and point defect structures in these 2
dimensional EBG lattices, Q factors of excited modes and the optimisation
of impedance matching between integrated EBG structures and
conventional external waveguiding devices.
For even higher frequencies around 100GHz and the lower Terahertz
regime, we are investigating the fabrication and the properties of high
resistive silicon 2D EBG structures fabricated by a chemically assisted
silicon etching process by frequency and time domain mmeasurements.
DF 5.5 Mi 14:30 Poster C
Holographische Datenspeicherung als Technik zur Langzeitarchivierung
— •Marcus Werner 1 , Theo Woike 1 und Mirco Imlau
2 — 1 Institut für Mineralogie, Universität zu Köln — 2 Universität
Osnabrück
Für die dauerhafte Konservierung elektronischer Daten existiert bis
jetzt kein zukunftssicheres System. Ein Lösungsansatz ist die holographische
Speicherung von Daten in ferroelektrischen Kristallen.
Im Poster werden die speziellen Anforderungen an ein holographisches
Langzeitspeichersystem aufgezeigt. Speziell für das Speichermedium Lithiumniobat
wird ein Versuchsaufbau vorgestellt, der sowohl hohe Datendichte
(10 GBit/qcm) als auch eine lange Speicherdauer (> 100 Jahre)
ermöglicht.
Das System ermöglicht die gemischte Aufzeichnung analoger und digitaler
Daten, wobei sich die Analogdaten (ähnlich wie beim Mikrofilm) mit
einfachsten Hilfsmitteln auslesen lassen. Die kombinierte Speicherung von
Analog- und Digitaldaten genügt daher einerseits den erhöhten Anforderungen
der Archivare bezüglich der Zukunftssicherheit eines Speichermediums,
andererseits ist die ständige digitale Verfügbarkeit der Daten
gewährleistet.