Tunable plasmonic properties of nanostructures fabricated by shadow nanosphere lithography

Abstract

In this thesis we investigate the structural as well as optical properties of our by means of nanosphere lithography fabricated nanostructures. We can thereby control the fabrication process to get arrays of nanostructures such as quasitriangular shaped nanoislands, subwavelength holes, as well as grating like oriented nanowires. The various structural characterization methods presented here revealed a crucial dependence of the sample preparation process on the final form of the structure. It could be demonstrated that by changing the sphere size of the mask building polystyrene latex spheres and by altering the material deposition angle, the geometry of the structure could be controlled. As deposition materials, however, we carefully chose three metals: Gold for its well known and desired plasmonic response, aluminum as a “lossy” metal, and iron for its magnetic properties. The optical characterization of the samples was carried out in the far as well as in the near field. We used therefore standard spectroscopic techniques and near-field optical microscopy. The studies revealed that the optical response of the gold samples was mainly due to the coupling of the light to surface plasmons. This excitation of surface plasmon polaritons was responsible for the measured enhanced transmission of the light through, e.g., our subwavelength hole arrays. Furthermore we could show that the plasmonic response can be controled by judicious choice of structure morphology.