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End date: 2012 × Subject: Morphology ×

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    Methods to characterize the dispersability of carbon nanotubes and their length distribution
    (Weinheim : Wiley-VCH Verl., 2012) Krause, Beate; Mende, Mandy; Petzold, Gudrun; Boldt, Regine; Pötschke, Petra
    Two main properties of carbon nanotube (CNT) materials are discussed in this contribution. First, a method to characterize the dispersability of CNT materials in aqueous surfactant solutions in presented, which also allows conclusions towards the dispersability in other media, like polymer melts. On the other hand it is shown, how the length of CNTs before and after processing, e.g., after melt mixing with thermoplastics, can be quantified. Both methods are illustrated with examples and the practical relevance is shown. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
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    Towards deterministically controlled InGaAs/GaAs lateral quantum dot molecules
    (College Park, MD : Institute of Physics Publishing, 2008) Wang, L.; Rastelli, A.; Kiravittaya, S.; Atkinson, P.; Ding, F.; Bof Bufon, C.C.; Hermannstädter, C.; Witzany, M.; Beirne, G.J.; Michler, P.; Schmidt, O.G.
    We report on the fabrication, detailed characterization and modeling of lateral InGaAs quantum dot molecules (QDMs) embedded in a GaAs matrix and we discuss strategies to fully control their spatial configuration and electronic properties. The three-dimensional morphology of encapsulated QDMs was revealed by selective wet chemical etching of the GaAs top capping layer and subsequent imaging by atomic force microscopy (AFM). The AFM investigation showed that different overgrowth procedures have a profound consequence on the QDM height and shape. QDMs partially capped and annealed in situ for micro- photoluminescence spectroscopy consist of shallow but well-defined quantum dots (QDs) in contrast to misleading results usually provided by surface morphology measurements when they are buried by a thin GaAs layer. This uncapping approach is crucial for determining the QDM structural parameters, which are required for modeling the system. A single-band effective-mass approximation is employed to calculate the confined electron and heavy-hole energy levels, taking the geometry and structural information extracted from the uncapping experiments as inputs. The calculated transition energy of the single QDM shows good agreement with the experimentally observed values. By decreasing the edge-to-edge distance between the two QDs within a QDM, a splitting of the electron (hole) wavefunction into symmetric and antisymmetric states is observed, indicating the presence of lateral coupling. Site control of such lateral QDMs obtained by growth on a pre-patterned substrate, combined with a technology to fabricate gate structures at well-defined positions with respect to the QDMs, could lead to deterministically controlled devices based on QDMs. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.
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    The morphology of silver nanoparticles prepared by enzyme-induced reduction
    (Frankfurt, M. : Beilstein-Institut zur Förderung der Chemischen Wissenschaften, 2012) Schneidewind, H.; Schüler, T.; Strelau, K.K.; Weber, K.; Cialla, D.; Diegel, M.; Mattheis, R.; Berger, A.; Möller, R.; Popp, J.
    Silver nanoparticles were synthesized by an enzyme-induced growth process on solid substrates. In order to customize the enzymatically grown nanoparticles (EGNP) for analytical applications in biomolecular research, a detailed study was carried out concerning the time evolution of the formation of the silver nanoparticles, their morphology, and their chemical composition. Therefore, silvernanoparticle films of different densities were investigated by using scanning as well as transmission electron microscopy to examine their structure. Cross sections of silver nanoparticles, prepared for analysis by transmission electron microscopy were additionally studied by energy-dispersive X-ray spectroscopy in order to probe their chemical composition. The surface coverage of substrates with silver nanoparticles and the maximum particle height were determined by Rutherford backscattering spectroscopy. Variations in the silver-nanoparticle films depending on the conditions during synthesis were observed. After an initial growth state the silver nanoparticles exhibit the so-called desert-rose or nanoflower-like structure. This complex nanoparticle structure is in clear contrast to the auto-catalytically grown spherical particles, which maintain their overall geometrical appearance while increasing their diameter. It is shown, that the desert-rose-like silver nanoparticles consist of single-crystalline plates of pure silver. The surface-enhanced Raman spectroscopic (SERS) activity of the EGNP structures is promising due to the exceptionally rough surface structure of the silver nanoparticles. SERS measurements of the vitamin riboflavin incubated on the silver nanoparticles are shown as an exemplary application for quantitative analysis.