Nucleation, growth, and etching of noble-metal nanocrystals

Abstract

Colloidal noble-metal nanocrystals have tremendous potential in applications ranging from medicine to sensing to catalysis. The ultimate utility of these nanomaterials relies on our ability to precisely control their size, shape, and structure, since many of the relevant physiochemical properties emerge as a consequence of these parameters. This dissertation is focused on the roles of nucleation and growth processes in noble-metal nanocrystal synthesis, guided by kinetic considerations and the presence of appropriate capping agents, as well as the impact of oxidative etching. I begin by demonstrating the synthesis of well-defined Ag nanocubes with sub-15 nm edge lengths, achieved through the overgrowth of Ag2S clusters coupled with the capping of the {100} facets by Br− ions. In the second project, I conduct a quantitative analysis of the synthesis of Pd decahedra in order to ascertain the impacts of reduction kinetics and post-nucleation coalescence process on the formation and growth of the decahedral nanocrystals, respectively, and in an attempt to maximize both the precursor conversion and morphology yields. With the insights gained during this study, I proceed to demonstrate the synthesis of Pd penta-twinned nanowires, achieved through a combination of precisely tuned reduction kinetics and the capping of {100} facets by I− ions. Finally, I carry out a systematic study to understand the impact of oxidative etching by the O2/I– pair on the morphology of Pd decahedral nanocrystals. The mechanistic understanding achieved in this dissertation helps lay the foundation for the rational design and deterministic synthesis of nanocrystals with desired and controlled size, shapes, and structures.