Extreme Near-Field Enhancement for Gaseous Plasma Generation and Fundamental Plasma Chemistry
Abstract
In this project, plasmon-driven surface reactions and other gas phase reactions involving ions have been investigated experimentally and theoretically. The experimental effort has been focused on mechanistic understanding of plasmon-driven photochemistry. Before the publication of our results from this project, the mechanism of plasmon-driven reactions has been discussed mainly in terms of hot electron transfer. Our results obtained in this project indicate that photochemistry on plasmonic nanoparticles can be induced by hot electron transfer from the nanoparticle to an unoccupied orbital of the adsorbate and/or by plasmon-pumped electron transitions from occupied molecular orbitals to unoccupied molecular orbitals of the adsorbate. The branching photochemical reaction of para-amino thiophenol on plasmonic gold surfaces depending on the presence of cetyltrimethylammonium bromide surface ligands that influence the hot electron concentration is used to highlight reactions driven by hot carriers. The importance of plasmon-pumped electronic excitation of adsorbates in initiating surface photochemistry is demonstrated based on the N-demethylation of methylene blue (MB) on gold nanostructures depending on excitation wavelengths. At excitation wavelength that overlaps with the resonances of MB and the gold nanoparticles, conversion of MB to thionine is observed in the presence of oxygen in the atmosphere and water in the surface-molecule complex. Considering that MB is a well-known photosensitizer, this observation suggests that the photochemical N-demethylation reaction involves singlet oxygen molecules that can be generated via energy transfer from MB triplet excited state to O2 triplet ground state. Theoretical work has been mostly focused on a deeper understanding of ion-molecule reactions and other processes involving ions. Several levels of theory have been carried out.
Document Details
- Document Type
- Technical Report
- Publication Date
- May 07, 2019
- Accession Number
- AD1086093
Entities
People
- Terefe G Habteyes
Organizations
- University of New Mexico