Solution and Substrate Assembly of Noble Metal Nanoparticles

Abstract

The plasmon phenomenon is the driving force behind noble metal nanoparticle research. While some work synthesizing new kinds of particles is still performed, a wider range of opportunities is available if these nanoparticles’ self-assembly in solution and on substrates can be controlled. This text presents several such methodologies, describing each assembly process and characterizing the resulting structures. The selective, aqueous dimerization of gold bipyramids is the first study. These novel antennae are created by stabilizing the gold biypramid’s ligand shell, then linking the particles with amino acids. Because of the gold bipyramids’ monodispersity and the precision of the reaction, the assembly can be monitored to ensure high dimer yield. Gold nanorod alignment on, and by, a shallowly corrugated diblock copolymer thin film demonstrates the power of template assisted assembly. Controlling the alignment of the underlying film controls the gold nanorods’ alignment, yielding mesoscale structures with orientation dependent optical properties. With intentional design, other polymer substrates are used to construct gold bipyramid – silver nanosphere plasmonic heterostructures. With proper ligand-polymer interaction tailoring, this result demonstrates how this technique can rationally create almost any noble metal nanoparticle based structure. The nonlinear optical properties of these heterostructures are currently being investigated. These assemblies are all unique, and barely represent a fraction of what plasmonic nanoparticle assembly research can entail. Given polymer templates’ efficacy in controlling these particle’s deposition and alignment, a study of a diblock copolymer thin film’s swelling behavior is also contained in this work. By understanding and controlling the film’s surface morphologies, its efficacy for noble metal nanoparticle alignment can be determined. Gold nanoparticles are used to probe the chemical nature of diblock’s swollen surface, and concurrently demonstrate that it can align small, highly charged, plasmonic nanoparticles. Several attempts to synthesize solution-based plasmonic antennae and fluorophore hybrids are also described, resulting in an introduction to the realm of semiconductor nanocrystal synthesis. Although these gold bipyramid – water soluble quantum dot systems have not yet been achieved, with some refinement, such systems should be possible. Finally, following the theme of unexpected research directions, two collaborations are presented that utilized the nanoparticle synthesis and characterization skills required to perform the rest of this research.