PROBING GOLD NANOROD SURFACE PLASMON-MEDIATED METAL DEPOSITION AND RESHAPING DYNAMICS USING LIQUID PHASE TRANSMISSION ELECTRON MICROSCOPY

Abstract

Coupling of plasmonic nanostructures to optical radiation via localized surface plasmon resonance (LSPR) enables converting incident light energy into excited charge carriers (i.e. “hot” electrons and holes) and thermal energy at the nanostructure surface, making plasmonic photocatalysis a promising alternative to conventional chemical production methods. Although hot carriers can promote redox reactions at the surface of plasmonic nanostructures, incomplete understanding of spatially-dependent plasmon-mediated reaction dynamics impels further investigation with high spatiotemporal resolution experimental techniques. In this work, we explore application of in situ liquid-phase transmission electron microscopy (LP-TEM) to studying shell deposition dynamics from secondary metal precursors. During LP-TEM, the electron beam concurrently served as a broadband LSPR excitation stimulus while enabling nanoscale visualization of secondary metal deposition rates and locations during shell growth, availing exploration of plasmonic hot carrier-mediated reaction dynamics. First, we examine dynamics of silver deposition onto plasmonic gold nanorods (AuNRs) from aqueous silver nitrate (AgNO3) precursor solution. During LP-TEM, we observed deposition of faceted bipyramidal shells or tip-preferential lobes. Through companion ex situ experiments and simulations, we assessed individual and combined impacts of chemical reduction, white-light illumination, and surfactant concentration on Ag deposition patterns. Among these features of the LP-TEM sample environment, we found surfactant-mediated, radiolytic radical-induced chemical reduction of Ag dominated the observed deposition behaviors, while plasmonic hot electrons (HE’s) had no appreciable contribution. This work indicates suppressing radiolysis is crucial to isolate and observe plasmonic hot carrier-mediated reaction dynamics. Next, we transition study of Ag shell deposition dynamics into a radiolysis-resistant toluene/isopropanol solvent environment. Collectively, resulting particle morphologies, spatially-dependent shell deposition rates, and growth dynamics relative to incident electron beam flux and AuNR orientation were consistent with plasmonic hot carrier-driven surface metal redox. Moreover, we found the reaction efficiency of generated AuNR HE’s to be ~1 in 107 – 1010. Subsequently, we discuss efforts to probe the energetic distribution of AuNR HE’s via dynamics of shell deposition from metal-acetylacetonate complexes with varying redox potential. Finally, we summarize the work performed in this dissertation and recommend future research directions, including exploration of other Au nanoparticle morphologies and in situ nanothermometry to elucidate plasmonic photothermal heating dynamics.