Nanostructured Materials for Solar Energy Applications

Abstract

The work presented in this thesis focuses on nanostructures, and what effect parameters like size, material, and surroundings have on their physical properties, with special emphasis on optical properties. The motivation for this thesis has been to provide foundational work, both experimentally and theoretically, for the exploration of metal nanoparticles for solar energy applications. The devices were fabricated using electron beam lithography and electron beam evaporation. Characterization and imaging were done with scanning electron microscopy and atomic force microscopy. Optical performance was measured using thin film analyzer, dark field microscopy and integrating spheres. Numerical analysis of optical behavior was done using the software Lumerical. The experimental work was done at the University of Bergen NanoStructures laboratory and at Rice University Halas Nanophotonics laboratory. The thesis consists of six articles, which can be divided into three categories. The first, main category focuses on the optical and electrical properties of metal nanoparticles and metal nanostructures, and contains four articles. The first three articles cover theoretical investigations of the absorption properties of a nanofluid, experimental investigations of the effect of annealing on the optical properties, and the influence of fabrication methods on optical properties of metal nanoparticles. The fourth article presents a novel bimetallic metal-insulator-metal (MIM) device, where two metals with different work functions have been used to create a bias for hot-electron extraction. To the best of the authors knowledge this is the first MIM-device that does not require an external bias. The second category concerns non-optical effects of nanosized features. It contains one article, which describes how wetting can be affected by surface treatment. The third category has a more conceptual theme, and contains one article. It describes how to build an affordable nanoscience laboratory, which might help motivate people and local industry to develop nanotechnology in Norway and elsewhere.