Doctor of Philosophy (PhD)
Ultrafast and nonlinear spectroscopies are implemented in the investigation of excited-state dynamics and structural properties of materials and nanomaterials. In the first study, the excited-state dynamics of size-dependent colloidal TiO2-Au nanocomposites are investigated using ultrafast transient absorption spectroscopy. The dynamics corresponding to the plasmon depletion band are characterized by electron-phonon and phonon-phonon coupling lifetimes that are observed to be independent of the gold nanocluster shell thickness. The excited-state dynamics corresponding to the interband transition of gold is also spectrally overlapped with the interfacial electron transfer lifetime, which is shown to decrease as the nanocluster shell thickness increases. In the second study, in-situ second harmonic generation (SHG), a nonlinear spectroscopic technique, is coupled with extinction spectroscopy to monitor the growth of colloidal gold nanoparticles in real time. The in-situ SHG results capture an early stage of the growth process where a large enhancement in the SHG is observed due to the formation of plasmonic hot spots attributed to a rough and uneven nanoparticle surface. In a third project, the ultrafast carrier dynamics of self-assembled La1-xSrxTiO3-δ (LMSO) is studied using ultrafast reflectivity experiments. The measured long-lived phonon-phonon coupling lifetime for the oxygen deficient LSMO thin film indicates that the phonons are the major energy carrier in the system. Residual oscillations of two distinct phonon frequencies are also observed and are superimposed on a biexponential decay. Both oscillatory signals are fit with an exponentially damping sine function in which both frequency and damping times are obtained. In a fourth project, our ultrafast reflectivity setup is modified with an added microscopy component for our work with the Consortium for Innovation in Manufacturing and Materials (CIMM) to investigate heating and melting dynamics of metals, semiconductors, and metal alloys. Finally, in the last portion of this dissertation, electronic sum-frequency generation spectroscopy is utilized to study the azimuthal angular dependence in α-quartz (0001). This dissertation describes the versatility of these ultrafast and nonlinear spectroscopic techniques through fundamental research on different types of materials and nanomaterials in colloidal suspension and at surfaces.
Khoury, Rami Anthony, "Ultrafast and Nonlinear Spectroscopy of Nanomaterials" (2018). LSU Doctoral Dissertations. 4682.