Structural Characteristics of Metal Oxide Thin Films Grown by Pulsed Laser Deposition: Fluorescence Excitation Spectroscopy of NH₂, HCF, HCCI under Jet-Cooled Condition and Measurement of Fluorescence Lifetime
Date of Award
Dissertation - Restricted
Doctor of Philosophy (PhD)
Thin films of metal oxide have been extensively synthesized by PLD. The component and microstructure of the film are dependent on the ablation laser fluence, film thickness, annealing temperature and conditions of substrates. For SnOx thin films grown by PLD, the formation of Litharge phase of SnO and Orthorhombic phase of Sn02 during annealing has been fascinated. This present dissertation will be found useful in controlling the conditions of formation of Litharge phase of SnO and Orthorhombic phase of Sn02, such as ablation laser fluence, wavelength, film thickness and by using metal target followed by the annealing in the air. Ga203 thin films have also been grown by PLD under vacuum or in the oxygen ambient gas. The film characteristics and the comparison between vacuum and in oxygen environment were described in detail in this dissertation. It is found that the initial component of thin films has strong correlation with the component of neutral gas phase produced in ablation. Time-of-flight mass spectroscopy was used to analyze the components of ablation plume, their dependence on laser fluence and their velocity distribution. We studied the laser fluence dependencies in the 532 nm ablation of Ga20 3 target and the velocity distribution was described with shifted or unshifted, single or multi component Maxwell-Boltzmann distribution. Fluorescence excitation spectroscopy provides useful information on the electronic structure of free radicals and carbenes, such as rotational constants, band origins, perturbation analysis, and geometry change of molecule from ground states to excited states. In this dissertation, a total 14 pure bending bands of NH2 were scanned and the transition frequencies were fit with a linear least-squares routine to a modified Hill and Van Vleck equation. Combining the previous work, the effect of orbital angular momentum was studied in detail. pure bending bands (0, v2', 0) (v2' =0-7) and combination bands (0, Vz', I) and (I, v2', 0) of HCF were probed and the spectra were fit to an asymmetric top Hamiltonian. Renner-Teller effect was extensively observed especially with the splitting of Ka'=l sub-band for higher bending levels (v2' <'. 4). In the case of HCC!, only Ka'=O bending sub-bands and C-Cl stretching containing combination bands (0, v/-1, 1) and (0, V2'-2, 2) caused by Fermi resonance were observed. The forbidden band "formula" is also present in spectrum as the result of axis-switching effect. The disappearance of K.'=1,2 subbands are mainly due to the Renner-Teller effect. Fluorescence lifetime is another important indicator for the dynamics of free radicals and carbenes. The lengthening of lifetime indicates the occurrence of perturbation while the drastically shortened lifetime stands for the nonradiative relaxation or occurrence of decomposition for small molecules. With the resolution of our laser, we can measure the lifetime for a specific rovibronic line. Fluorescence lifetimes for "formula" L bands (v2'=9-25) were measured and in reasonably agreement with the three dimension theoretical calculation .. Lifetimes of HCF showed a strong dependence on Ka' value, which was dominated by Renner-Teller effect. The lengthening of lifetime was commonly observed for Ka' >0 sub-bands, which indicates the occurrence of perturbation. However the lengthening of lifetime itself cannot tell what kind of perturbation is involved in the specific situation.