| dc.description.abstract | As nanofabrication has become more advanced over the last few decades, nanomaterials have received increased interest. One particular aspect of nanosized structures made of noble materials such as gold, is the peculiar interaction they demonstrate when illuminated by electromagnetic radiation. These structures show a strong absorption of certain energies, which has been found to relate to a phenomena known as localized surface plasmon resonance. These interactions have yet to be fully understood. This study is aimed at both nanofabrication techniques for plasmon structures, and analyzing the electromagnetic interaction between the plasmonic nanostructure and light with a spectroscopic Mueller-matrix ellipsometer.For the fabrication process, focused ion beam (FIB) microscopy was used to mill out nanostructures from substrates coated with with a thin gold film. The gold was evaporated onto the UV-grade fused silica substrates and a TEM-grid substrate with an electron beam evaporator. In addition to this physical deposition method, a recently developed chemical method for growing single-crystalline gold nanoflakes has also been tested in order to see if these were better suited for plasmonic nanostructuring by FIB than the polycrystalline gold film. The size and shape of the milled structures were characterized with a scanning electron microscope (SEM) and an atomic force microscope (AFM). A spectroscopic Mueller matrix ellipsometer was used to measure the surface plasmon resonance (collective response) of the structures, while a transmission electron microscope (TEM) was used to detect the electron energy loss specter of individual particles and for high resolution imaging.The FIB fabrication provided highly ordered nanostructures with good accuracy and reproducibility, consisting of particles $approx$SI{50}{nanometre} in diameter and bow ties with dimensions measuring $approx$SI{200}{nanometre}. The single-crystalline gold flakes gave higher resolution structures, but were difficult to work with, and too small for ellipsometric measurements. The optical behavior of the nanostructures was modeled with both isotropic- and uniaxial Bruggeman effective medium theory, and with the software GRANFILM which is based on the Bedeaux-Vlieger model. For the smallest structures (where the plasmon resonance occur around 2.2 eV), the ellipsometric measurements agreed with the Bruggeman theory and the GRANFILM simulations to a certain extent. However, neither model could describe the off-diagonal Mueller matrix elements in the ellipsometer data, nor the red shift for larger particles. Also, both models failed to describe the measurements at higher energies, where new symmetries were observed in the azimuth rotational spectroscopic Mueller matrices. It is believed that a rigorous coupled wave analysis is needed to fully understand the interaction of the highly ordered nanostructures. | nb_NO |
