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京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第20383号 / 工博第4320号 / 新制||工||1669(附属図書館) / 京都大学大学院工学研究科電子工学専攻 / (主査)教授 川上 養一, 教授 藤田 静雄, 教授 木本 恒暢 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

Pulsed laser ablation ¡]PLA¡^in single shot on polycrystalline Ti thin foil ca. 20

The H-type Nb2O5 powders (monoclinic structure with (101) crystallographic shear plane) submicron to micrometers in size were subjected to pulsed laser ablation fragmentation in water (PLAL) with optional NaCl addition in order to study the structure change of the resultant Nb2O5 nanoparticles by x-ray diffraction and electron microscopy. The Nb2O5 nanoparticles via such a dynamic PLAL fragmentation process turned out to be H-type relic and newly formed T-type (an orthorhombic high-pressure phase), TT-type (a pseudohexagonal high-pressure phase) and a nonstoichiometric amorphous phase which coexist within a faceted nanoparticle (down to ca. 5 nm) or coalesced with each other. The composite Nb2O5 nanoparticles were protonated and imposed with a considerable internal compressive stress to modify the structure units and band structure as indicated by vibrational (Raman and FTIR) spectra and uv-visible absorption spectrum of the darkened colloidal solution indicating a stepwise minimum band gap lowering down to stepwise 3.0¡Ó0.1 eV and 2.5¡Ó0.1eV. NaCl spiking in water did not cause appreciable change on the phase behavior of Nb2O5 powders upon PLAL.

Soot aerosols are well known to be atmospheric constituents, but the hydrophobic nature of fresh soot likely prohibits them from encouraging cloud development. Soot aged through contact with oxygenated organic compounds may become hydrophilic enough to promote water uptake. In this study, the tandem differential mobility analyzer (TDMA) and differential mobility analyzer?aerosol particle mass analyzer (DMA?APM) were employed to measure the changes in morphology and hygroscopicity of soot aerosol particles upon coating with succinic and glutaric acids. The effective densities, fractal dimensions and dynamic shape factors of fresh and coated soot aerosol particles have been determined. Significant size-dependent increases of soot particle mobility diameter, mass, and effective density (?eff) were observed upon coating of aggregates with succinic acid. These properties were restored back to their initial states once the acid was removed by heating, suggesting no restructuring of the soot core had occurred. Coating of soot with glutaric acid, on the other hand, leads to a strong size shrinking with a diameter growth factor ~0.60, even after the acid has been removed by heating suggesting the strong restructuring of the soot agglomerate. The additional 90% RH cycle can evidently enhance the restructuring process. The extinction and scattering properties at 532 nm of soot particles internally mixed with dicarboxylic acids were investigated experimentally using a cavity ring-down spectrometer and an integrating nephelometer, respectively, and the absorption is derived as the difference between extinction and scattering. It was found that the organic coatings significantly affect the optical and microphysical properties of the soot aggregates. The size-dependent amplification factors of light scattering were as much as 3.8 and 1.7 with glutaric and succinic acids coatings, respectively. Additional measurements with soot particles that are first coated with glutaric acid and then heated to remove the coating show that both scattering and absorption are enhanced by irreversible restructuring of soot aggregates to more compact globules. These results reveal the microphysical state of soot aerosol with incomplete restructuring in the atmosphere, and advance the treatment of atmospheric aged soot aerosol in the Mie theory shell-and-core model.

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Optical spectroscopy is an essential tool for characterization of materials’ optical properties. Quantitatively understanding material absorption, scattering and emission properties is challenging with existing spectrometric and fluorometric techniques. The direct Polarized Resonance Synchronous Spectroscopy (PRS2) is a breakthrough to the existing spectroscopic techniques for differentiation and quantification of material absorption, scattering and emission properties including their light depolarizations and optical cross-sections. However, there are some limitations and unchecked assumptions in the direct PRS2 technique that need to be addressed during my PhD study. We first examined the effect of light scattering and absorption on their innerilter-effect (IFE) and validated that sample UV-vis extinction can be approximated as absorption extinction for IFE correction in the PRS2 data processing due to the high sensitivity of PRS2 to light scattering. In the case where such approximation may produce large error, iteration PRS2 can be included to decompose the UV-vis extinction into absorption and scattering components. Compared to the direct PRS2 that must rely on several assumptions, the recent developed Bandwidth Varied PRS2 (BVPRS2) and Polarized Anti-Stokes’, On-resonance, Stokes’-shifted (PAOS) spectroscopic techniques are self-contained methods universally amenable to all kinds of fluorescent materials. BVPRS2 or PAOS is necessary for fluorescent materials that possess non-zero scattering depolarization and wavelength dependent fluorescence depolarization. Furthermore, BVPRS2 and PAOS prove that not only off-resonance fluorescence also contributes to the fluorescence signal detected in PRS2 measurement. BVPRS2 offers indirect observation that fluorescence intensity increases quadratically, while scattering signal increases linearly as wavelength bandwidth expands. More importantly, PAOS allows direct visualization of the contribution from anti-Stokes’-shifted fluorescence, ORF and Stokes’-shifted fluorescence in the detected signals, revealing the origins of the off-resonance contribution. Finally, it is illustrated that different PRS2 methods should be applied to different types of optical materials to ensure accuracy and efficiency. Direct PRS2 was readily used to study gold nanoparticles, which are light absorbers and scatterers. In contrast, PAOS-assisted PRS2 was performed on fluorescent quantum dots, which are simultaneously light absorbers, scatterers and emitters. The presented PRS2 methodology and the new insights acquired from the materials investigated should be of great significance to material design and characterization.

Polymer dispersed liquid crystal (PDLC) films, consisting of micro-sized domains of a liquid crystal dispersing in a polymer matrix, serve as the basis of a variety of high-efficiency electro-optical effects. The thermo-optical properties of the PDLCs were investigated in this thesis. The thermal properties and the morphologies of four low molar mass mesogens were studied by DSC and polarized optical microscope (POM). There were significant super cooling/heating effects on the first order phase transitions but not on the mesophase transitions. The structural effects on the transition temperature were investigated. Between the two 4-alkoxybenzoic acids mesogens, the clearing temperature of 4-(octyloxy)benzoic acid was higher than 4-(decyloxy)benzoic acid because of the increasing chain length. Trans-4-methoxycinnamic acid had the highest melting temperature among the four mesogens despite the molar mass because the carboxylic acid termini of trans-4-methoxycinnamic acid gave rise to strong intermolecular attractions. The smectic phases of 4-(octyloxy)benzoic acid were classified as head-to-head bilayer orientational smectic structures, SmA2 and SmC2, respectively, by wide angle X-ray diffraction through measuring the d spacing of the liquid crystal. The total solubility parameter was used to evaluate matching a polymer-LC-solvent combination. PDLC films were prepared by the solvent induced phase separation method and suitable morphologies were achieved by thermal induced phase separation. The phase transition temperatures of PDLCs were shifted to a lower temperature due to the polymer dispersion effects. Different mesophases were observed in PDLC films when LC exhibited different mesophases. The LC fractions in the droplets were calculated from the nematic to isotropic enthalpies through the Smith equation. Two factors, thermal cooling rate and the LC concentration, which affect the size of the droplet dispersed in the polymer matrix, were investigated in the PVC dispersed 4,4'-azoxyanisole. The phase transitions of pHEMA dispersed 4-(octyloxy)benzoic acid and PVC dispersed 4,4'-azoxyanisole were investigated by TMDSC and quasi-isothermal TMDSC. The TMDSC results were analysed by the two approaches, reversing and non-reversing heat flow and complex heat capacity. The results of the phase transitions of the two PDLCs illustrated that in the PDLCs it involved both non-reversing, melting, and reversing, clearing and the transition between two mesophases. In the non-reversing transition, the transition temperature would be affected by super cooling/heating and the results obtained in the experiments were dependent on the experimental conditions, such as the heating or cooling rate, sample size and purge gas flow rate. However, in the reversing transition process, there were no super cooling/heating effects observed and it seemed that the experimental conditions were not so critical. Results could be monitored by Lissajous figures obtained from the quasi-isothermal TMDSC. The plots of modulated heat flow versus the derivative of modulated temperature can be used to alert to unfavorable experimental conditions where loss of system linearity could be seen.

This thesis presents a theoretical study on optical properties of molecular materials. Special emphasis has been put on the influence of solvent environment, nuclear vibrations, and aggregation effects on molecular properties like linear and nonlinear polarizabilities, one- and two-photon absorption probabilities. All calculations have been performed by means of time independent and dependent quantum chemical methods at the Hartree-Fock and density functional theory levels. Solvation models that include both long range and short range interactions have been employed for calculations of optical properties of molecules in solutions. Pure vibrational and zero-point vibrationally averaged contributions have been taken into account for linear and nonlinear polarizabilities. The linear coupling model is applied to simulate vibronic profiles of optical absorption spectra. The computational strategies described in this thesis are very useful for the design of efficient molecular photonic materials. More specifically, the nonmonotonic behavior of the solvatochromic shifts and the first hyperpolarizability of para-nitroaniline (pNA) with respect to the polarity of the solvents have been theoretically confirmed for the first time. The significant contributions of the hydrogen bonding on the electronic structures of pNA are revealed. Vibrational contributions to the linear and nonlinear polarizabilities of methanol, ethanol and propanol have been calculated both at the static limit and in dynamic optical processes. The importance of vibrational contributions to certain nonlinear optical processes have been demonstrated. A series of end-capped triply branched dendritic chromophores have been studied with the result that their second order nonlinear optical properties are found strongly dependent on the mutual orientations of the three chromophores, numbers of caps and the conjugation length of the chromophores. Several possible mechanisms for the origin of the Q-band splitting of aluminum phthalocyanine chloride have been examined. Calculated vibronic one-photon absorption profiles of two molecular systems are found to be in very good agreement with the corresponding experiments, allowing to provide proper assignments for different spectral features. Furthermore, effects of vibronic coupling in the nonradiative decay processes have been considered which helps to understand the aggregation enhanced luminescence of silole molecules. The study of molecular aggregation effects on two-photon absorption cross sections of octupolar molecules has highlighted the need to use a hybrid method that combines density functional response theory and molecular dynamics simulations for the design of molecular materials. / QC 20100820

An onset coarsening-coalescence event based on the incubation time of cylindrical mesopore formation and a significant decrease of specific surface area by a certain fraction relative to the dry pressed samples was determined by N2 adsorption-desorption hysteresis isotherm for amorphous SiO2 nanoparticles (ca. 40 nm in size). In the temperature range of 1150-1300oC, the nanoparticles with binder (PVA) additive underwent onset sintering coupled with coarsening-coalescence without appreciable crystallization. The apparent activation energy of such a rapid process for amorphous SiO2 nanoparticles was estimated as 177 ¡Ó 31.5 kJ/mol, based on 30% change of specific surface area. As a comparison, in much lower temperature range of 600-900oC, the amorphous Zn2SiO4 nanoparticles underwent onset sintering coupled with coarsening-coalescence accompanied more or less with the formation of ZnO The apparent activation energy of such a rapid process for a amorphous Zn2SiO4 was estimated as 105 ¡Ó 3.8 kJ/mol based on 50% change of specific surface area. The minimum temperatures for sintering/coarsening/coalescence of the amorphous SiO2 and Zn2SiO4 are 1120¢J and 635oC, respectively based on the extrapolation of steady specific surface area reduction rates to null. PLA fragmentation of amorphous and nearly spherical SiO2 nanoparticles (40 nm in size) in water (i.e. PLAL process) with optional NaCl addition was conducted under Q-switch mode (532 nm, 400 mJ per pulse) having laser focal point fixed at ca. 10 mm beneath the water level for an accumulation time of 20 and 30 min at 10 Hz. The 532 nm laser incidence suffered little water absorption and was effective to produce irregular shaped amorphous nanocondensates as small as 10nm~20nm in diameter with accompanied change of medium range order (MRO) as indicated by single rather than two broad x-ray diffractions at low 2theta angle. Whereas the Na+ uptake in the amorphous silica from the salty water account for a lower wave number of FTIR bands. The combined effects of nanosize, MRO change and H+ -signature may cause a lower minimum band gap of the amorphous products (analogous to opal-A) which become partially crystallized as £]-cristobalite (analogous to opal-CT) with additional £\-tridymite when Na+ is present.