Degree
Doctor of Philosophy (PhD)
Department
Chemistry
Document Type
Dissertation
Abstract
The first part of this dissertation presents calculations of the extinction spec- tra of gold-silver/silver-gold core-shell nanospheres. The goal of this projectsis to get a deeper understanding of surface plasmonic resonance in metal nanospheres with core-shell geometry. Here, we used the finite-difference time-domain (FDTD) method and total-field/scattered-field (TFSF) framework to compute the extinction spectra of nanoparticles to determine the geometry of gold-silver/silver-gold core-shell nanoparticles. This supported experimental work on monitoring the growth dynamics of colloidal gold- silver/silver-gold core-shell nanoparticles using in situ second harmonic generation (SHG) and extinction spectroscopy.
The second and main project involved simulating attosecond transient spectra for understanding the electron dynamics after excitation. The overall goal of this project is to develop and validate a first-principals methodology for computing X-ray attosecond transient absorption (ATA) and to develop simple rules for interpret the spectra. In one study, we used real-time time-dependent density functional theory (RT-TDDFT) to sim- ulate ultraviolet-pumped electron dynamics in a range of molecules (carbon monoxide, molecular oxygen, 4-aminophenol, and a tetracyanoethylene dimer). Our results showed that the oxygen and nitrogen K-edge transient X-ray spectra were correlated with the lo- cal density around the atom. Specifically, the optical density (OD) decreases with increas- ing electron density around the atom. In another study, we generalized this to the case of soft X-ray triggered dynamics in 4-aminophenol, where a nitrogen or oxygen 1s core- hole induces valence dynamics. Likewise, the results demonstrate a pronounced modula- tion of the OD due to electron density changes. These results suggest that X-ray ATA is a promising method for probing attosecond dynamics in molecules, with first-principles simulations for interpretation.
Date
7-11-2023
Recommended Citation
Chen, Min, "First-principles Simulations of Attosecond Transient X-ray Absorption" (2023). LSU Doctoral Dissertations. 6233.
https://repository.lsu.edu/gradschool_dissertations/6233
Committee Chair
Lopata, Kenneth