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Plasmonic nanostructures are good candidates for refractive index sensing applications through the surface plasmon resonance due to their strong dependence on the surrounding dielectric media. However, typically low quality-factor limits their application in sensing devices. To improve the quality-factor, we have experimentally and theoretically investigated two-dimensional gold nanoparticle gratings situated on top of a waveguide. The coupling between the localized surface plasmon and waveguide modes results in Fano-type resonances, with high quality-factors, very similar to plasmonic surface lattice resonances. By combining plasmonic surface lattice resonance and waveguide theory, we present a theoretical framework describing the structures. By immersing the fabricated samples in three different media we find a sensitivity of ∼50 nm/RIU and figure of merit of 8.9, and demonstrate good agreement with the theory presented. Further analysis show that the sensitivity is very dependent on the waveguide parameters, grating constant and the dielectric environment, and by tuning these parameters we obtain a theoretical sensitivity of 887 nm/RIU.

This thesis work focuses on nanostructured optical elements for light and matter waves that have been fabricated using helium ion beam lithography and electron beam lithography. The motivation of this thesis has been to develop new optical elements and to contribute with foundational work to instrumentation and characterization of nanostructures. The work has been carried out at the University of Bergen, Nanostructure Laboratory and at the Massachusetts Institute of Technology, Nanostructure Laboratory. The thesis is based on five papers published in international, peer reviewed, Web of science journals. The thesis defender is sole first author on paper I-IV and shared first author on paper V. Paper I presents the first helium ion beam lithography patterning on a non-horizontal surface. Such patterning is possible because of the large field of depth in a helium ion beam instrument. Comparable writing cannot be performed with standard electron beam lithography. Patterning on curved or tilted surfaces is potentially very useful in a range of devices e.g. optical lenses, and is fundamentally an attractive property. Paper II presents a systematic scanning-electron-microscopy study of the charging effect in metal nanostructures on insulating surfaces. Negative charging is found to induce a measurement error in the measured dimensions of the nanostructures comparable to a de-magnified image. In paper III, the optical response of metal nanoparticles mediated by the localized surface plasmon resonance effect are studied using integrating spheres, and the influence of the fabrication method on the optical properties is discussed. Paper IV and V describe optical elements for matter waves. In Paper IV a high-transmission atom sieve for focusing neutral helium atoms is fabricated, showing that focusing below 10 nm should in principle be possible. Paper V demonstrates fast resolution change in the focusing neutral helium microscope by inserting collimating apertures. Without changing the properties of the neutral helium beam and without breaking the vacuum a resolution change by a factor of 4.4 is demonstrated.

Metal nanoparticles (MNPs) are of key interest in many research fields due to their unique optical properties, which are largely dominated by the localized surface plasmon resonance (LSPR) effect. The LSPR effect gives rise to intense light absorption by the MNP at certain wavelengths of incident light. The LSPR wavelength can be manipulated by changing the size and shape of the MNPs as well as by changing the surrounding medium, opening for a variety of applications such as optical- and biological sensing and solar energy conversion. The company EnSol AS has patented a novel thin- film solar cell technology based on the LSPR effect in MNPs. The University of Bergen, in collaboration with EnSol, has started a project of investigating and optimizing the production parameters of the EnSol solar cell with the ultimate aim of producing model solar cells. As a step in the optimization process, the optical properties of large arrays of nanoparticles need to be investigated theoretically and experimentally. This has been the aim of this thesis work. Large arrays (9 mm2 - 16 mm2) of disk-shaped aluminum, gold or nickel NPs fabricated on non-conductive glass substrates have been fabricated by the means of electron beam lithography (EBL). MNP disks of diameter down to 20 nm have been fabricated. The optical properties of MNP arrays are analyzed for disk diameters in the range 30 nm - 45 nm with a constant height of 25 nm. EBL suffer from low throughput, but offer high control of particle size, shape and orientation which is of prime importance in the development of reliable model system where size- and shape dependent properties are investigated. The large size of the arrays allows optical investigation using spectroscopy techniques, making it possible to mimic realistic operation conditions of the solar cell. The LSPR wavelengths are found experimentally using an integrating sphere set-up. The experimental results are tested and supported by theoretical calculations based on an electrostatic model developed by I. Simonsen and R. Lazzari, where the disk-shaped metal nanoparticles are approximated as spheroids truncated by a glass substrate. Despite the discrepancies in particle shape between the model and experimental system, good qualitative agreement is found. The LSPR wavelength is also found to be in good agreement with published literature that in most cases is based on much smaller arrays. MAMN-NANO NANO399