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Oldenburg, Germany

Kolny-Olesiak J.,Carl von Ossietzky University | Weller H.,University of Hamburg
ACS Applied Materials and Interfaces | Year: 2013

Semiconductor nanocrystals possess size-dependent properties, which make them interesting candidates for a variety of applications, e.g., in solar energy conversion, lighting, display technology, or biolabelling. However, many of the best studied nanocrystalline materials contain toxic heavy metals; this seriously limits their potential for widespread application. One of the possible less toxic alternatives to cadmium- or lead-containing semiconductors is copper indium disulfide (CIS), a direct semiconductor with a bandgap in the bulk of 1.45 eV and a Bohr exciton radius of 4.1 nm. This Review gives an overview of the methods developed during the last years to synthesize CIS nanocrystals and summarizes the possibilities to influence their shape, composition and crystallographic structure. Also the potential of the application of CIS nanocrystals in biolabellling, photocatalysis, solar energy conversion, and light-emitting devices is discussed. © 2013 American Chemical Society. Source

Greskowiak J.,Carl von Ossietzky University
Geophysical Research Letters | Year: 2014

This study investigated the stability of the upper saline plume (USP) within shallow tide-affected submarine groundwater discharge (SGD) zones. In contrast to earlier studies, numerical modeling revealed a number of realistic hydrological and hydrogeological conditions where the USP becomes unstable and salt-fingering flow occurs. These conditions were reasonably well identified in a stability diagram based on two dimensionless numbers that characterize the system. If fingering flow occurs, the SGD pattern is distinctly different from that of stable flow conditions: (i) freshwater discharge zones along the beach face are manifold and change their location with time, (ii) undulating freshwater/seawater interface that is extended along the groundwater flow path, and (iii) the total tide-averaged fresh SGD rate varies considerably in an irregular pattern. This has presumably important implications on reactive transport processes in the subterranean estuary, as well as on the interpretation of field data on water and solute fluxes during SGD. Key Points Identification of unstable tide-induced upper saline plumes in beach zonesThey lead to moving freshwater springs and varying freshwater discharge ratesDimensionless instability diagram predicts the onset of salt-fingering flow ©2014. American Geophysical Union. All Rights Reserved. Source

Pisarchik A.N.,Technical University of Madrid | Feudel U.,Carl von Ossietzky University
Physics Reports | Year: 2014

Multistability or coexistence of different attractors for a given set of parameters is one of the most exciting phenomena in dynamical systems. It can be found in different areas of science, such as physics, chemistry, biology, economy, and in nature. The final state of a multistable system depends crucially on the initial conditions. From the viewpoint of applications, there are two major issues related to the emergence of multistability. On one hand, this phenomenon often can create inconvenience, as for instance, in the design of a commercial device with specific characteristics, where multistability needs to be avoided or the desired state has to be stabilized against a noisy environment, and on the other hand, the coexistence of different stable states offers a great flexibility in the system performance without major parameter changes, that can be used with the right control strategies to induce a definite switching between different coexisting states. These two examples alone illustrate the importance of multistability control in applied nonlinear science. For the last decade a lot of research has been devoted to the development of control techniques of multistable systems. These methods cover several strategies, going from feedback control methods to nonfeedback, such as periodic or stochastic perturbations capable of changing the coexisting states stability and driving the system from multistability to monostability. We review the most representative control strategies, discuss their theoretical background and experimental realization. © 2014 Elsevier B.V. Source

Copper sulphide is a material with low toxicity and high application potential. Colloidal synthesis allows its incorporation into hybrid nanostructures, which not only combine the properties of different materials within one nanocrystal, but also exhibit new features due to the interaction of the building blocks connected on the nanometer scale. Starting with copper sulphide seeds, such hybrid nanocrystals composed of copper sulphide and semiconductors like CuInS2, CuInxGa1-xS2, Cu2ZnSnS4, ZnS, CdS, and PbS have been synthesized. In some of these reactions the main focus lies on the formation of new hybrid nanocrystals; in others copper sulphide plays the role of a catalyst, and copper sulphide containing hybrid nanoparticles are only intermediates in the synthesis and shape control of other semiconductor materials. Both possibilities and the underlying growth mechanisms are discussed in this article. This journal is © the Partner Organisations 2014. Source

Borchert H.,Carl von Ossietzky University
Energy and Environmental Science | Year: 2010

Semiconductor nanoparticles are promising for use as electron acceptors in polymer-based bulk heterojunction solar cells. Potential advantages over fullerene derivates that are widely used in organic photovoltaics are tuneable absorption properties and the possibility to use elongated nanoparticles for more efficient electron transport. Despite these advantages, efficiencies obtained with hybrid polymer/nanoparticle solar cells are still below those of state-of-the-art polymer/fullerene solar cells. This Perspective summarises the achievements in the field of hybrid solar cells, compares the knowledge on elementary processes in hybrid and organic systems and points out the most recent trends in research. The design of the polymer nanoparticle/interface by the choice of capping ligands and development of appropriate surface treatments for the nanoparticles plays an important role, and recent progress opens new perspectives for the future improvement of hybrid solar cells. © 2010 The Royal Society of Chemistry. Source

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