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Klinkhammer J.,University of Cologne | Forster D.F.,University of Cologne | Schumacher S.,University of Cologne | Oepen H.P.,Institute For Angewandte Physik | And 2 more authors.
Applied Physics Letters | Year: 2013

We present a straightforward and reproducible method to grow stoichiometric and single phase (100) textured EuO thin films on epitaxial graphene. Depending on coverage, either separated EuO grains or fully closed layers can be prepared. Room temperature preparation followed by annealing in Eu vapor leads to a random distribution of the in-plane orientation, whereas growth under distillation conditions at 720 K induces a fixed orientation with respect to the substrate. Magneto-optical Kerr effect (MOKE) shows that the films are ferromagnetic with an enhanced Curie temperature. © 2013 AIP Publishing LLC.

Heyn C.,Institute For Angewandte Physik
Physical Review B - Condensed Matter and Materials Physics | Year: 2011

The self-organized in situ drilling of nanoholes into semiconductor surfaces by using liquid metallic droplets during conventional molecular beam epitaxy represents a new degree of freedom for the design of heterostructure devices. A model of this local droplet etching is presented that is based on a core-shell droplet structure. With the model, the evolution of the droplet and substrate morphology is calculated. We demonstrate quantitative agreement between model results and measured morphologies. Furthermore, also the influence of the process temperature is correctly reproduced by the model. © 2011 American Physical Society.

Hu D.Z.,Paul Drude Institute for Solid State Electronics | Hu D.Z.,Institute For Angewandte Physik | Trampert A.,Paul Drude Institute for Solid State Electronics | Schaadt D.M.,Paul Drude Institute for Solid State Electronics | Schaadt D.M.,Institute For Angewandte Physik
Journal of Crystal Growth | Year: 2010

The post growth annealing of InAs quantum dots (QDs) at relatively high temperature was investigated by an in-situ stress cantilever beam setup. For samples annealed at 500 {ring operator} C, stress accumulated during QD formation relaxes below the value which was built-up during wetting-layer growth. AFM images taken at different annealing stages reveal that QDs ripen first and then dissolve within 10 min of annealing. These observations are explained by a combination of In desorption, especially at the beginning of annealing, and interdiffusion between Ga and In. © 2009 Elsevier B.V. All rights reserved.

Ostermann R.,Justus Liebig University | Zieba R.,BASF | Rudolph M.,Institute For Angewandte Physik | Schlettwein D.,Institute For Angewandte Physik | Smarsly B.M.,Justus Liebig University
Chemical Communications | Year: 2011

Nanoparticles of ATO (antimony doped tin oxide) were used to produce thick conductive, free standing mats of nanofibers via electrospinning. These fibrous mats were incorporated into polymer films to produce a transparent conducting polymer foil. Moreover, the fiber mats can serve as porous electrodes for electrodeposition of Prussian Blue and TiO2 and were tested in dye-sensitized solar cells. © The Royal Society of Chemistry 2011.

Purwins H.-G.,Institute For Angewandte Physik | Bodeker H.U.,Institute For Angewandte Physik | Amiranashvili S.,Institute For Angewandte Physik | Amiranashvili S.,Weierstrass Institute for Applied Analysis And Stochastics
Advances in Physics | Year: 2010

The present review summarizes experimental and theoretical work dealing with self-organized solitary localized structures (LSs) that are observed in spatially extended nonlinear dissipative systems otherwise exhibiting translational and rotational symmetry. Thereby we focus on those LSs that essentially behave like particles and that we call dissipative solitons (DSs). Such objects are also solutions of corresponding nonlinear evolution equations and it turns out that they are rather robust with respect to interaction with each other, with impurities, and with the boundary; alternatively they are generated or annihilated as a whole. By reviewing the experimental results it turns out that the richest variety of DS phenomena has been observed in electrical transport systems and optical devices. Nevertheless, DSs show up also in many other systems, among which nerve pulses in living beings are of uppermost importance in practice. In most of these systems DSs behave very similarly. The experimental results strongly suggest that phenomenon of DSs is universal. On the background of the experimental findings models for a theoretical understanding are discussed. It turns out that in a limited number of cases a straightforward quantitative description of DS patterns can be carried out. However, for the overwhelming number of systems only a qualitative approach has been successful so far. In the present review particular emphasis is laid on reaction-diffusion systems for which a kind of 'normal form' can be written down that defines a relatively large universality class comprising e.g. important electrical transport, chemical, and biological systems. For the other large class of DS carrying systems, namely optical devices, the variety of model equations is much larger and one is far away, even from a universal qualitative description. Because of this, and due to the existence of several extensive reviews on optical systems, their theoretical treatment has been mentioned only shortly. Finally, it is demonstrated that in terms of a singular perturbation approach the interaction of DSs and important aspects of their bifurcation behaviour, under certain conditions, can be described by rather simple equations. This is also true when deriving from the underlying field equations a set of ordinary differential equations containing the position coordinates of the individual DSs. Such equations represent a theoretical foundation of the experimentally observed particle-like behaviour of DSs. Though at present there is little real practical application of DSs and related patterns in an outlook we point out in which respects this might change in future. A systematic summary of a large amount of experimental and theoretical results on reaction-diffusion systems, being rather close to the subject of the present review, can also be found on the website http://www.uni-muenster.de/Physik.AP/Purwins/Research- Summary. © 2010 Taylor & Francis.

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