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Author: Kraus, Tobias × End date: 2019 × Start date: 2000 × DDC: 530 × WGL Institute: INM ×

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Now showing 1 - 4 of 4
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    Ageing of alkylthiol-stabilized gold nanoparticles
    (Hoboken, NJ : Wiley, 2015) Lacava, Johann; Weber, Anika; Kraus, Tobias
    The ageing of spherical gold nanoparticles having 6-nm-diameter cores and a ligand shell of dodecanethiol is investigated under different storage conditions. Losses caused by agglomeration and changes in optical particle properties are quantified. Changes in colloidal stability are probed by analytical centrifugation in a polar solvent mixture. Chemical changes are detected by elementary analysis of particles and solvent. Fractionation occurs under all storage conditions. Ageing is not uniform but broadens the property distributions of the particles. Small-number statistics in the ligand shell density and the morphological heterogeneity of particles are possible explanations. Washing steps exacerbate ageing, a process that could not be fully reversed by excess ligands. Dry storage is not preferable to storage in solvent. Storage under inert argon atmosphere reduces losses more than all other conditions but could not prevent it entirely.
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    Self-assembly of gold nanoparticles at the oil-vapor interface: from mono- to multilayers
    (Washington D.C. : American Chemical Society, 2014) Born, Philip; Schön, Volker; Blum, Susanne; Gerstner, Dominik; Huber, Patrick; Kraus, Tobias
    Alkylthiol-coated gold nanoparticles spontaneously segregate from dispersion in toluene to the toluene-vapor interface. We show that surface tension drops during segregation with a rate that depends on particle concentration. Mono- and multilayers of particles form depending on particle concentration, time, and temperature. X-ray reflectometry indicates fast monolayer formation and slow multilayer formation. A model that combines diffusion-limited segregation driven by surface energy and heterogeneous agglomeration driven by dispersive van der Waals particle interactions is proposed to describe film formation.
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    Dense arrays of uniform submicron pores in silicon and their applications
    (Washington D.C. : American Chemical Society, 2015) Brodoceanu, Daniel; Elnathan, Roey; Prieto-Simón, Beatriz; Delalat, Bahman; Guinan, Taryn M.; Kroner, Elmar Karsten; Voelcker, Nicolas H.; Kraus, Tobias
    We report a versatile particle-based route to dense arrays of parallel submicron pores with high aspect ratio in silicon, and explore the application of these arrays in sensors, optics, and polymer micropatterning. Polystyrene (PS) spheres are convectively assembled on gold-coated silicon wafers and sputter-etched, resulting in well-defined gold disc arrays with excellent long-range order. The gold discs act as catalysts in Metal-Assisted Chemical Etching (MACE), yielding uniform pores with straight walls, flat bottoms and high aspect ratio. The resulting pore arrays can be used as robust antireflective surfaces, in biosensing applications, and as templates for polymer replica molding.
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    Multivalent bonds in self-assembled bundles of ultrathin gold nanowires
    (Cambridge : Royal Society of Chemistry, 2016) Reiser, Beate; Gerstner, Dominik; González-García, Lola; Maurer, Johannes H.M.; Kanelidis, Ioannis; Kraus, Tobias
    Ultrathin gold nanowires are unusual colloidal objects that assemble into bundles with line contacts between parallel wires. Each molecule in the contact line interacts with many ligand and solvent molecules. We used X-ray scattering and electron microscopy to study how these interactions control assembly.