FRD - Investigación - Ciencia y Tecnología

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Author: search.filters.author.Bragas, Andrea

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    High resolution imaging using nanoparticle based probes
    (2018) Scarpettini, Alberto; Bragas, Andrea
    New plasmonic probes, based on silica microspheres decorated with metal nanoparticles (Figure 1), are built and used to confine and enhance the electric field in their interaction with the sample, giving ultra-high optical resolution in a wide variety of samples [1]. The coverage and aggregation processes of nanoparticles on plane and spherical substrates were systematically studied [2]. These probes present red shifted resonances, dominated by the formation of small nanoparticle clusters [3]. Approach curves with the new probes show clearly field enhancement at very short probe-sample distances, and depend strongly on the incoming wavelength and polarization. Optical contrast was achieved in flat samples composed by materials of different dielectric constants, and images were obtained using optical feedback.
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    Monitoring the Photothermal Reshaping of Individual Plasmonic Nanorods with Coherent Mechanical Oscillations
    (2018-12-03) Scarpettini, Alberto; Della Picca, Fabricio; Gutierrez, Marina; Bragas, Andrea
    Light absorption in gold nanoparticles leads to metal heating that induces photothermal reshaping because of atomic surface diffusion at temperatures well below the gold melting point. In this work, we perform time-resolved experiments to measure the frequencies of the extensional coherent mechanical mode in single gold nanorods, as a monitor of the changes in their aspect ratio produced by this photoinduced reshaping. We show that photothermal reshaping always occurs in typical pump–probe experiments conducted in air even at low-excitation light irradiance and usually long measuring times. The reshaping effect can be reduced by a polymer coating, which allows faster heat dissipation from the nanoparticle to the environment.
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    Plasmon-induced photochemical synthesis of silver triangular prisms and pentagonal bipyramids by illumination with light emitting diodes
    (2013) Scarpettini, Alberto; Roldán, Virginia; Bragas, Andrea; Bordenave, Martín; Pellgri, Nora
    We have grown silver prisms and pentagonal bipyramids, induced by plasmon excitation on a colloidal solution under the irradiation of light emitting diodes of different colors. Two methods of synthesis of the seeds were tested and their growth evolution recorded, in order to analyze the effect of the chemical synthesis and the color of the irradiation on the morphology and size of the final product. We show that the conversion rate into anisotropic nanoparticles is determined by the chemical environment and the shift of the irradiation wavelength with respect to the plasmon resonance of the seeds. The conversion rate defines the final morphology of the nanoparticles, whereas the size of the nanoparticles is univocally determined by the wavelength of irradiation, irrespective of the method to prepare the seed solution.