Synthesis and optical characterization of template mediated plasmonic metal nanocrystal assembly

Abstract

Recent years, many researchers have focused their interest in synthesizing plasmonic metal nanocrystal assemblies with controlled morphologies due to their exceptionally strong local field enhancement that manifests when the structures satisfy the condition for hot spots generations. Endeavors to prepare various shapes for nanoparticle assembly, many methods have been developed with each method utilizing different tools, such as ligands, patterning, templates, and lithography, to form different assembly structures. Of all the methods available, template mediated methods have chosen for this study due easy manipulation of structural features, and stability of the assembled structure. The first chapter of thesis delineates basic characteristics of plasmonic metal nanocrystals, properties of plasmonic nanocrystal assembly, and the preparation methods for the nanocrystal assembly. In chapter 2, the preparation method for 1-D chain assembly of AuOh NCs and AuOh@AgAu peapod structure with anodized aluminum oxide (AAO) as hard template, the role of $H_2O_2$ surface treatment, the effect of solvent, and the role of silver shells on the final structure were explained in details. In chapter 4, synthesis methods for cholesteric liquid crystal (CLC) mediated chiral AuNRs assembly was introduced. The chirality of CLC template and AuNRs-CLC composite were verified with the appearance of grandjean texture in POM. The optical behavior of AuNR-CLC composite was studied with metal enhanced fluorescence (MEF) and the chiroptical property was studied with CD spectroscopy. Lastly, the manipulation of chiral pitch with chiral dopant content was observed and it was shown that addition of chiral dopant content could indeed cause change in the chiral pitch of the CLC template. These studies are expected to expand our knowledge on optical behaviors of template mediated plasmonic NCs assembly and become a stepping stone for their future applications as high performance sensors.