Toward a quantitative understanding of the shape-controlled synthesis of colloidal noble-metal nanocrystals

Abstract

This dissertation is focused on the development of a quantitative analysis of the thermodynamic and kinetic factors responsible for the mechanisms and pathways during the nucleation and growth of noble-metal nanocrystals. With the chemisorption of Br− ions on Pd{100} facets as an example, I demonstrate the capability of quantitatively analyzing the coverage density of this capping agent using a combination of inductively coupled plasma mass spectrometry and X-ray photoelectron spectroscopy. I further apply the collision model that has long been established in surface science to seed-mediated growth of cubic seeds with or without chemisorbed Br− ions on their side facets in an effort to account for the deposition probability of atoms on the surface of a seed and thus its growth pattern in the presence or absence of surface capping. In a third project, with the polyol synthesis of Pd nanocrystals as an example, I demonstrate that the kinetic parameters, including rate constant and activation energy of a reaction can be derived from spectroscopic measurement and then used to calculate the initial reduction rate and further confirm that this parameter can be a quantitative knob for controlling the internal structure of a nanocrystal. Finally, the symmetry breaking phenomenon involved in the seed-mediated growth of Pd nanocrystals was investigated by quantitatively correlating the growth modes (symmetric vs. asymmetric) with the reaction kinetics simulated based on experimental parameters. The quantitative understanding achieved in this dissertation lays the foundation for the rational design and deterministic synthesis of nanocrystals with desired and controlled structures, shapes, and related properties.