Structure and Bonding in Thiolate-Coated Au Nanostructures

Abstract

Structure and bonding properties of gold (Au) nanoparticles (NPs) are of great interest due to the unique size-dependent quantum-confinement effect exhibited by structures on the nanoscale. As such, Au NPs have demonstrated their potential use in a variety of fields (e.g. imaging, drug delivery, catalysis). The popularity of Au NPs is largely due to its versatility in synthesizing different NP compositions and surfaces. In this thesis, structure and bonding in Au NPs was examined from both surface functionalization/ligand and composition/metal bonding perspectives. Functionalization of Au-surface with model biomolecule ligands enables formation and electroless deposition of Au NPs onto a biocompatible Ti substrate. Through variation of model biomolecule size and concentration with respect to a Au precursor, insight was gained into the formation mechanisms of Au NPs, and the processes that lead to deposition upon the Ti substrate. Furthermore, using extended X-ray absorption fine-structure (EXAFS) with sample spinning and glancing angle setup allowed us to resolve small differences in coordination, leading to new findings on fine-tuning of peptide-coated Au NP size on Ti substrates. To explicitly analyze Au NP structure and bonding from a metallic perspective, NP model systems with precisely controlled compositions were studied with ab initio calculations to compare local environment and electronic character. It was determined that while surface features may be structurally similar, the effect of local environment and geometry can affect the electronic character of these features. Finally, small Au NP samples were studied to understand the alloying effect. The position of a heteroatom dopant Pt atom within Au25 has been a disputed issue, with no definitive means of determination. Using a combination of EXAFS spectra and ab initio calculations, it was possible to determine that the Pt atom resides in the central position of the icosahedral core. Furthermore, Pt doping in Au25 resulted in a contraction of the surface Au structure, an unobserved phenomenon until now. Through the careful and systematic comparison of Au NP systems, this thesis will contribute to a better understanding of Au local structure and bonding in ligand-functionalized substrate-supported Au NPs, as well as compositionally precise Au nanoclusters.