Metal and Semiconductor Nanoparticle Self-Assembly.

Abstract

The field of nanotechnology is rapidly growing and faces numerous challenges to its further growth and development. Many new types of nanomaterials and applications for these materials have been developed recently; however, most of the processes by which nanomaterials and nanodevices are produced are top-down processes that are time consuming, expensive, and not practical for scale-up and commercialization. These top-down processes work by creating smaller assemblies and structures from larger ones, or physically manipulating nanomaterials using external forces. On the other hand, bottom-up synthesis and assembly techniques rely on smaller interactions between nanomaterials to guide their self-assembly. These bottom-up techniques, once properly mastered, allow for the economic scale-up of nanomaterial synthesis and nanodevice production. The present thesis focuses on two areas of nanoparticle self-assembly, the first is the spontaneous self-assembly and subsequent recrystallization of semiconductor nanoparticles into nanowires. The self-assembly and recrystallization of CdTe nanoparticles into CdTe nanowires, as well as the effect of the solution properties on the mechanism governing this process, is investigated. Specifically, the effect of dimethyl sulfoxide on the CdTe nanoparticle reorganization into pearl necklace agglomerates, and its effect on Ostwald ripening, which triggers the recrystallization of the pearl necklace agglomerates into nanowires, is studied. The decomposition of CdTe and CdSe nanoparticles into Te and Te/Se nanowires is also studied with particular emphasis on the effect of Se on the aspect ratio and tortuosity on the Te nanowire formation. Finally, the placement of Au nanoparticles and coatings on twisted CdTe nanoribbons by soaking the nanoribbons in HAuCl4 is studied with the objective of creating metallic chiral structures for use in negative index materials. There is a particular emphasis on the effect of crystallinity of the CdTe nanoribbons and the soak time on the type of Au deposition. The second area of this thesis is the spontaneous self-assembly of various types of nanomaterials for applications; namely, the electrostatically driven self-assembly of large, positively charged Au nanoparticles and small, negatively charged CdSe/ZnS quantum dots into higher ordered core/shell assemblies whose structure and photoluminescent properties are responsive to the environment.