Development, synthesis and characterization of multifunctional nanomaterials

To achieve the societal and technological ambitions set for nanotechnology in general, multifunctional magnetic-plasmonic nanostructures can be a great asset. Such multifunctional materials, in which magnetic and plasmonic functionalities are combined at the nanoscale, can be used to unravel fundamental interactions between light and magnetism at that same scale. Further, they can also be applied in e.g. biomedicine for cancer therapy, catalysis for improved reaction rates at lower temperatures, sensors for magnetic field strength and miniaturized optical components such as optical isolators.In the first part of this work we present the calculated optical properties of core-shell magnetic-plasmonic nanospheres and nanorods as a function of nanostructure composition, size, and shape with a focus on biomedical applications. With this knowledge it is possible to rationally design and synthesize structures that possess a plasmon band in the advantageous biomedical near-infrared spectral window region and other optical properties such as scattering and absorption cross sections as desired for potential application in life sciences.To deal with the disadvantages of previously used synthesis protocols for nanoparticle-based thin film magnetic-plasmonic materials, a novel synthetic protocol was devised. The protocol itself, the resulting materials and their linear, nonlinear and magneto-optical properties are described in the second part of this work.Using short bifunctional molecular linkers, we produced magnetic-plasmonic nanoparticle multilayers by a novel layer-by-layer (LbL) synthesis on glass substrates. No polymers or polyelectrolytes were required during synthesis. Resulting nanocomposites, incorporating gold, silver and magnetite nanoparticles were homogeneous over a large area, had large nanoparticle filling fractions and showed tunability of the plasmon wavelength over a very broad spectral range by changing composite thickness through the number of added nanoparticle layers.Theoretical calculations were performed to verify and explain the observed optical properties of these magnetic-plasmonic assemblies. The calculations and the comparison with experimental observations lead us to a more nuanced view of the LbL self-assembly process as a function of layers. Nonlinear optical microscopy images confirmed homogeneity of the sample and the generated nonlinear optical signals. Spectral nonlinear optical measurements showed that gold-magnetite nanoparticle multilayers combine and simultaneously enhances second and third order nonlinear optical processes. Large magneto-optical responses were measured for gold-magnetite composites and the influence of the plasmonic gold nanoparticles was established.These results show that the developed layer-by-layer synthesis protocol can be used to produce homogeneous thin films of good quality. Advantageous and tuneable optical properties, large magneto-optical responses and the observed nonlinear optical resonance enhancements of such thin films make them attractive candidates for further fundamental research into e.g. magnetoplasmonics and for application in sensors or optical components.status: publishe