Grupo de Nanofotonica
Permanent URI for this collectionhttp://48.217.138.120/handle/20.500.12272/1241
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Item Síntesis de nanopartículas híbridas dieléctrico-metal y estudio de sus propiedades ópticas(2018) Paredes, María; Scarpettini, AlbertoSe sintetizaron y estudiaron nanopartículas esféricas del tipo núcleo-cáscara de sílice y oro, con control de sus dimensiones. En una primera etapa se realizó la síntesis de esferas de SiO2 monodispersas de varios tamaños, seguido de la funcionalización de su superficie. Se prepararon semillas de oro de muy pocos nanómetros, que se adsorbieron sobre las esferas funcionalizadas. Se estudió la dinámica de crecimiento de una capa uniforme de oro sobre las nanoesferas de SiO2 decoradas. Se observó la coalescencia de los grupos adsorbidos en la superficie, y se comprobó que el agente reductor y las condiciones de reacción son esenciales para evitar la nucleación del metal fuera de la superficie del núcleo. La formación de una capa de oro cerrada nos permite obtener estructuras núcleo-cascara, con esferas dieléctricas y recubrimiento metálico, cuyas resonancias plasmónicas se correlacionan muy bien con la teoría de Mie.Item Kinetic and plasmonic properties of gold nanorods adsorbed on glass substrates(2019-09-19) Gutierrez, Marina; Scarpettini, Alberto FMonodisperse gold nanorods with different sizes were synthesized and adsorbed on chemically modified glass substrates. Influence of surfactant molar concentration on nanorod adsorption was studied and the optimum range was determined. During substrate coverages we monitored the growth of longitudinal localized Surface plasmon resonances at short times due to density increase of isolated nanorods and, at longer times, their subsequent decrease and a concurrent growth of coupling resonances owing to nanoparticle surface mobility andaggregation. Temporal evolution of amplitudes of resonance peaks in extinction spectra and nanorod counting statistics in electron micrographs were used to model both coverage and aggregation processes, as exponential- like functions of time. Their characteristic times and saturation values were analyzed and related to kinetic parameters, nanorod dimensions and extinction coefficients. This work can be used as a predictive tool to prepare plasmonic substrates with desired optical resonances.Item Determination of Nanoscale Mechanical Properties of Polymers via Plasmonic Nanoantennas(2020-06-02) Boggiano, Hilario D; Berté, Rodrigo; Scarpettini, Alberto F; Cortés, Emiliano; Maier, Stefan A.; Bragas, Andrea V.Nanotechnology and the consequent emergence of miniaturized devices are driving the need to improve our understanding of the mechanical properties of a myriad of materials. Here we focus on amorphous polymeric materials and introduce a new way to determine the nanoscale mechanical response of polymeric thin films in the GHz range, using ultrafast optical means. Coupling of the films to plasmonic nanoantennas excited at their vibrational eigenfrequencies allows the extraction of the values of the mechanical moduli as well as the estimation of the glass transition temperature via time-domain measurements, here demonstrated for PMMA films. This nanoscale method can be extended to the determination of mechanical and elastic properties of a wide range of spatially strongly confined materials.Item High resolution imaging using nanoparticle based probes(2018) Scarpettini, Alberto; Bragas, AndreaNew 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.Item Nanorod-based plasmonic substrates with predefined optical resonances(2018) Scarpettini, Alberto; Gutierrez, MarinaTo design and fabricate plasmonic substrates to be used in ultrasensitive chemical sensing or surfaceenhanced spectroscopies, it is important to achieve control on the morphology, dimensions and surface density of metallic nanostructures on the substrate, and therefore to achieve control on their optical resonances. In this direction, monodisperse colloidal gold nanorods were synthesized in a seed-mediated growth [1] with a longitudinal surface plasmon resonance tunable in wavelengths from 600 to 1000 nm. These nanorods with well-controlled size and aspect ratio were used as plasmonic building blocks. Glass substrates were chemically modified and the synthesized gold nanorods were adsorbed through a dipping process [2]. The nanostructured coverage dynamics of these substrates was characterized by spectrophotometry and electron microscopy (Fig. 1). A nanoparticle surface aggregation was observed during the coverage process at long times. This aggregation is dominated by the mobility of the isolated nanorods, which first join in dimers and, further in time, in clusters of higher number of nanorods, changing from well-defined longitudinal plasmons to more complex coupling resonances. Evolution of amplitudes of resonance peaks in extinction spectra and nanorod counting statistics were used to model both coverage and aggregation processes [3]. Their characteristic times and saturation values were analyzed and related with kinetic parameters and nanorod extinction coefficients. This work can be used as a predictive tool to prepare plasmonic substrates with desired optical resonances.Item Fabricación y Caracterización de Sustratos Plasmónicos Basados en Nanobastones de Oro(2015) Scarpettini, Alberto; Gutierrez, MarinaSe fabricaron sustratos plasmónicos mediante el recubrimiento controlado de superficies de vidrio y películas delgadas de oro con nanobastones de oro. Estos sustratos nanoestructurados poseen resonancias ópticas en el rango visible e infrarrojo cercano del espectro electromagnético, y producen grandes intensificaciones de campo, llamados puntos calientes, en regiones muy localizadas de su superficie. El control de estas propiedades ópticas y la posibilidad de sintonizar la respuesta espectral de un sustrato son fundamentales para el diseño y construcción de sensores moleculares ultrasensibles y de sondas de microscopía óptica de altísima resolución. Se sintetizaron nanobastones de oro utilizando métodos de crecimiento mediado por semillas, con un preciso control de sus dimensiones finales. Se obtuvieron suspensiones monodispersas y con alta eficiencia. Se modificaron químicamente superficies de vidrio y películas de oro para adsorber nanobastones de oro. Se controló la densidad de recubrimiento superficial mediante el tiempo de inmersión de los sustratos en la solución coloidal. Se caracterizaron los sustratos fabricados mediante espectros de extinción e imágenes de microscopía electrónica. Se obtuvieron recubrimientos homogéneos con bandas de absorción dadas por el acoplamiento de las resonancias de los nanobastones con el material del sustrato.Item Monitoring the Photothermal Reshaping of Individual Plasmonic Nanorods with Coherent Mechanical Oscillations(2018-12-03) Scarpettini, Alberto; Della Picca, Fabricio; Gutierrez, Marina; Bragas, AndreaLight 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.Item 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, NoraWe 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.Item Harmonic demodulation and minimum enhancement factors in field-enhanced near-field optical microscopy(2015-01) Scarpettini, Alberto; Bragas, Andrea VeronicaField enhanced scanning optical microscopy (FESOM) relies on the design and fabrication of plasmonic probes which had to provide optical and chemical contrast at the nanoscale. In order to do so, the scattering containing the near field information recorded in a FESOM experiment, has to surpass the background light, always present due multiple interferences between the macroscopic probe and sample. In this work, we show that when the probe-sample distance is modulated with very low amplitude, the higher the harmonic demodulation is, the better the ratio between the near field signal and the interferometric background results. The choice of working at a given n harmonic is dictated by the experiment when the signal at the n+1 harmonic goes below the experimental noise. We demonstrate that the optical contrast comes from the nth-derivative of the near field scattering, amplified by the interferometric background. By modeling the far and near field we calculate the probe-sample approach curves, which fit very well the experimental ones. After taking a great amount of experimental data for different probes and samples, we conclude with a table of the minimum enhancement factors needed to have optical contrast with FESOM.Item Recubrimiento controlado de sustratos de vidrio con nanobastones metálicos(2015-03-12) Gutierrez, Marina; Paredes, María Yanela; Scarpettini, AlbertoSe realizó la síntesis de nanobastones de oro monodispersos con una eficiencia superior al 80% sobre el total de nanopartículas, caracterizado por una resonancia plasmónica longitudinal cercana a los 800 nm. Se modi- ficaron superficialmente sustratos de vidrio y se los recubrió con los nanobastones sintetizados, con control de la densidad superficial. Se monitoreó la dinámica del recubrimiento a través de espectros de extinción, y se observó una densidad máxima de saturación dada por repulsión electrostática y un tiempo característico del proceso. Luego de alcanzada la saturación de nanobastones por unidad de área se observa un ensancha- miento de las resonancias hacia el infrarrojo, debido a interacciones entre los nanobastones por producirse agregaciones sobre la superficie. Estos resultados tienen aplicación inmediata en el diseño y fabricación de dispositivos plasmónicos, por ejemplo en el sensado molecular.