부산대학교 도서관

This Thesis introduces a new chemistry methodology to synthesize in situ metallic nanocomposites thin films, made of Au and Ag nanoparticles embedded in solid dielectric matrices of TiO2 and SiO2. By this methodology, it is possible to control the size, shape and filling factor of the nanoparticles, being corroborated by different electronic microscopy techniques (SEM, TEM, HAADF-STEM) and surface characterization (AFM). Moreover, the optical properties of these layers were measured using different techniques, like extinction, transmittance and reflectance, as well as the indices of refraction were determined by means of ellipsometry, confirming the typical localized surface plasmon resonance of these metallic nanoparticles. These properties were explained using the Maxwell-Garnett effective medium approximation within the picture of Fresnel equations in order to explain the origin of reflectance and extinction spectra. Using these layers in combination with a controlled wet chemical etching, we obtain antireflectance layers by means of the formation of a porous inside the layer that allows the formation of a gradient-index multilayer, which traduces in a dramatic diminution of the reflectance in samples deposited over Si, showing a minimum in the spectral region dominated by the plasmon resonance. This gradual diminution of the reflectance with the etching time is explained with calculations in a multilayer structure. When the layers are doped with Ag nanoparticles, we observe the interaction with the organic molecule 2-mercaptoethanol in aqueous medium. This interaction provokes the diminution in the intensity of the optical extinction, as well as a shift in the wavelength of the plasmon resonance to larger energies. This opens the path to the development of potential applications in the field of chemical sensors. Colloidal quantum dots with diameters between 3-8 nm were synthesized and their optical properties were characterized by means of absorption and photoluminescence in the regimes of low temperature and high hydrostatic pressures. Taking into account the linear dependence of the effective masses with the temperature and the successfully applied finite potential wall model to explain the confinement energy alongside the non-parabolicity of the bands, a similar model has been employed in order to explain the ecotonic dynamics at high pressure regime and compared with the measurements in the spectral region of the infrared for the bulk material. We have obtained a good agreement with the experimental data, comparing with the differences obtained using a simplified model with the mechanical diminution of quantum dot’s size. Three different kind of bilayer nanocomposites have been fabricated containing metallic nanoparticles and quantum dots based on CdSe, observing in all these samples an photon-plasmon coupling, resulting in a enhancement or quenching in the emission of the quantum dots, that could be controlled by adding a dielectric spacer layer.