Design, synthesis and characterization of Au and Ag nanoshells and Au semishells with tunable localized surface plasmon resonance

• Design, Synthese und Charakterisierung von Au- und Ag-Nanoschalen und Au-Halbschalen mit einstellbarer lokalisierter Oberflächenplasmonresonanz

Mann, Daniel; Möller, Martin (Thesis advisor); Palkovits, Regina (Thesis advisor)

Aachen (2018)
Dissertation / PhD Thesis

Dissertation, RWTH Aachen University, 2018

Abstract

Metal nanoparticles are of huge interest due to their wide range of possible applications ranging from catalysis to medicine, chemical and biological sensing, SERS and sunlight harvesting as well as light trapping. For many applications their plasmonic properties are the property of interest. To extend the possibility to tune the optical absorption and scattering over a wide range of the electromagnetic spectrum a dielectric core particle can be introduced creating a metal nanoshell. When this shell covers the core particle only on one side a metal semishell is created that introduces an angle dependency into the optical properties, further increasing the application possibilities. To date the quality of metal nanoshells synthesized is rather poor and the match between theoretically predicted optical properties and what is experimentally available is unsatisfying. For semishells the synthetic methods available have many drawbacks resulting in poor quality or poor scalability. For experimentalists who want to apply metal nanoshells it is very important to be able to synthesize particles with distinct optical properties. But a systematic study how deviations from a perfect model that are inherent to synthetic procedures, like a size distribution or a rough surface structure, influence the optical properties is lacking. Therefore in this thesis we present a systematic study on the optical properties of Ag and Au nanoshells. The optical simulations that are part of this study have been performed by Daniel Nascimento-Duplat and Dr. Aurèle Adam at the Department of Imaging Physics at Delft University of Technology in the Netherlands. We develop synthetic procedures to realize high quality nanoshells with surface coverage and roughness as close to the perfect model as possible. We synthesize nanoshells with various shell thicknesses and core diameters and study the influence of these parameters on the optical properties. Additional we calculate extinction cross sections of these particles and compare them to the experimentally obtained spectra. We identify differences and implement these into the calculations to get a better fit. Therefore we generate a tool to successfully predict optical properties of nanoshells and synthesize these exact particles. Additionally we develop a new synthetic procedure to create Au semishells that eliminates the drawbacks from previously reported procedures. Therefore we develop a colloidal protecting patch that can be easily removed after metal plating. We analyze the optical properties of these particles experimentally and theoretically. Additionally we analyze the scope of the newly developed method and study the reaction mechanism of the synthesis of the protecting patch. Afterwards we use our gained knowledge about the reaction mechanism to make slight changes to the reaction procedure that result in various patchy particles.