Optical Approaches to Study Nanoscale Electrochemical Processes

Abstract

In this work, we use optical approaches to study and provide mechanistic insight into electrochemical reactions occurring at the surface of single nanoparticles. Correlated optical-electrochemical studies offer several advantages over single nanoparticle electrochemical studies including, higher spatial resolution, the ability to interrogate many nanoparticles at the same time and identify populations of inactive nanoparticles. Throughout this dissertation, two optical techniques are discussed in detail, dark-field scattering and super-localization imaging. In the first set of experiments, we describe calcite-assisted localization and kinetics (CLocK) microscopy, a multiparameter super-localization imaging technique. By placing a rotating birefringent calcite crystal in the infinity space of an optical microscope, CLocK provides immediate polarization and orientation information while still maintaining the ability to localize a single nanoparticle with < 10 nm resolution. Additionally, we demonstrate that the CLocK point spread function encodes kinetic information that we quantified to be an order of magnitude shorter than the integration time of the camera. In this work, CLocK provides new mechanistic insight into dynamic processes such as the dissolution of single gold nanorods as well as single-molecule surface-enhanced Raman scattering. In the second work, dark-field scattering was employed to monitor a proposed post-synthesis silver nanoparticle surface cleaning strategy to improve homogeneity across a population. Here, a sacrificial silver-sulfide sulfide shell is chemically grown on single silver nanoparticles to outcompete surface impurities. We demonstrate that upon electrochemical removal of the shell, a more reactive and reproducible silver surface can be achieved as revealed by enhanced electrodissoluion of the freshly cleaned silver nanoparticles. In these experiments, we additionally found a sulfide-dependent formation of multiple sulfide-species as well as mixed character sulfide shells on single nanoparticles themselves, thus demonstrating the sensitivity provided by optical microscopy at identifying multiple surface chemistries. Overall, the work in this dissertation highlights the ability of optical tools at revealing heterogeneity in single particle studies providing insight into structure-function relationships.