Surface chemical control over the valence electronic structure of gold nanoparticles
Open Access
- Author:
- Cirri, Anthony
- Graduate Program:
- Chemistry
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- May 24, 2016
- Committee Members:
- Benjamin James Lear, Dissertation Advisor/Co-Advisor
- Keywords:
- gold nanoparticle
surface chemistry
electron spin resonance
ligand
thiolate - Abstract:
- Control over the electronic properties of metallic and semiconducting nanoparticles is critical for the development of new technologies in photocatalysis, solar energy conversion, quantum computing, and nanosensing. Size, shape, crystal structure, and dielectric environment are common parameters that are used to tune the electronic structure of nanomaterials. However, a less explored but equally promising parameter is modification of surface chemistry. The chemisorption of small molecules onto the surface of nanoparticles introduces a wide array of chemical functionality that allows for discrete modification of electronic structure at the metal/molecule interface. Specifically in monolayer-protected gold nanoparticles (AuNPs), previous work suggests that a stark change in surface chemistry (i.e., alkylthiol vs. alkylamine) is required to observe a modification of the electrical, optical, thermal, and magnetic properties of the metal core -- each of which is dependent upon the interfacial electronic structure. Conduction electron spin resonance (CESR) spectroscopy is a valuable technique which has gone unexplored for observing how surface chemistry influences electronic structure. The utility of CESR lies in its selectivity and sensitivity to electronic structure at the Fermi level of the metal. Herein, I show how para-substituted aromatic thiolate and alkanethiolate ligands are capable of modifying the electronic structure through analysis of the measured g-factor -- a parametrization of spin-orbit coupling that comes from the electron spin resonance energy. In conjunction with quantum chemical calculations, we demonstrate that the sigma-bonding strength of the ligand is capable of controlling the degree of interfacial mixing between the metal and adsorbent, and correlate this with changes in the AuNPs' surface potential.