Pulsed lasers are studied as new tools to realize competitive nanomanufacturing. The capabilities of pulsed lasers as promising tools for research, design, manufacturing, and control rely on the flexibility due to the great variety of operation parameters, and the inherent precision in aspects of time, spatial resolution, and energy input. As new tools, the fundamental understanding and technological capabilities of pulsed laser-induced chemical synthesis were explored in this dissertation research. In order to study the capabilities of pulsed laser in controlled synthesis, a thermal model was developed to predict the local temperature change due to the very short period of irradiation by a pulsed laser. And combining with the classical Gibbs free energy theories, a set of guidelines were developed for precision control for pulsed laser-induced chemical synthesis. Zinc oxide crystals were studied as an example case, showing the relationship between the wide range variables of pulsed laser including repetition rate, energy area density, power density, irradiation duration, etc. and the material structures of deposited crystals in aspects of crystal density, size, shape, crystalline properties, surface morphologies, growth rate, etc. Mechanisms from thermodynamic and kinetic aspects were explored. Pulsed laser-induced different heating conditions were found to separate two crystallization processes with different energy barriers, one dominated by a burst of nucleation and the other dominated by crystal growth through particle aggregation. For the study of the fundamental mechanisms in crystallization, pulsed laser initiated and controlled the crystallization in its early stage, and the crystal evolution were observed and analyzed by transmission electron microscopy (TEM). Crystal growth from intermediate monomers was first studied by an electron beam under the condition without precursor solution environment, providing crucial process information of crystal evolution, indicating multistage processes by continuous mass and phase transfer among intermediate monomers. This dissertation shows the capabilities of pulsed laser in realizing precision control for the targeted synthesis in nanomanufacturing, providing unique insight to crystallization mechanisms, and extending prospects to scientific research of other energy beam induced processes.

Since the fortuitous discovery of the existence of quantum size effects on the band structure of colloidal semiconductor nanocrystals, the development of synthetic methods that can form nanoscale crystalline materials of controllable size, shape, and composition has blossomed as an empirical scientific achievement. The fact that the term “recipe” is commonly used within the context of describing these synthetic methods is indicative of the experimentally driven nature of the field. In this respect, the highly attractive photophysical properties of semiconductor nanocrystals—as cheap wavelength tunable and high quantum yield absorbers and emitters of light for various applications in lighting, biological imaging, solar cells, and photocatalysis—has driven much of the interest in these materials. Nevertheless, a more rigorously predictive first-principles-grounded understanding of how the basic processes of nanocrystal formation (nucleation and growth) lead to the formation of semiconductor nanocrystals of desired size and size dispersity remains an elusive practical and fundamental goal in materials chemistry. In this thesis, we describe efforts to directly study these dynamic nucleation and growth processes for lead chalcogenide nanoparticles, in many cases in-situ, using a mixture of X-ray scattering and UV-Vis/NIR spectroscopy. The lack of a rigorously predictive and verified mechanism for nanocrystal formation in solution for many material systems of practical interest is due both to the inherent kinetic complexity of these reactions, as well as the spectroscopic challenge of finding in-situ probes that can reliably monitor nanoscale crystal growth. In particular, required are direct time-resolved structural probes of metastable inorganic amorphous and crystalline intermediates formed under the high temperature inert conditions of nanocrystal synthesis. It is, at the very least, highly challenging to apply many of the standard spectroscopic tools of mechanistic inorganic and organic chemistry such as ¹H NMR spectroscopy, IR vibrational spectroscopy, and mass spectrometry to this task. A notable counterexample is, of course, UV-vis/NIR absorbance and emission spectroscopies, which are of great value to the studies described herein. Nevertheless, to address this relative dearth of conventional spectroscopic probes, here we explore the use of X-ray Total Scattering real space Pair Distribution Function (PDF) analysis and Small Angle X-ray Scattering (SAXS) techniques to directly probe the crystallization process in-situ. Time-resolved measurements of the small angle reciprocal space scattering data allow mapping of the time evolution of the colloidal size and concentration of the crystals during synthesis, while the Fourier transform of scattering data over a wide range of reciprocal space provides direct insight into the local structure. Through this approach, we compare direct observations of these nucleation and growth processes to the widely cited theoretical models of these processes (Classical Nucleation Theory and LaMer “Burst Nucleation”) and find a number of stark differences between these widely cited theories and our experiments. The first two chapters cover the results of these 𝘪𝘯-𝘴𝘪𝘵𝘶 diffraction studies. Chapter 1 focuses on small angle X-ray scattering data collection and modeling. Chapter 2 focuses upon lead sulfide and lead selenide real space PDF analysis of local structural evolution during synthesis. Finally, Chapter 3 discusses a project in which we examine the origins of emergent semiconducting electronic structure in an increasing size series of atomically precise oligomers of [Ru₆C(CO)₁₆]²⁻ bridged by Hg²⁺ and Cd²⁺ atoms. Using an atomically well-defined series of molecules that bridge the small molecule and nanoscale size regimes, we discuss the factors that give rise to controllable semiconductor electronic structure upon assembly into extended periodic structures in solution. In all these projects, we seek to highlight the value of applying concepts of molecular inorganic chemistry—ligand binding models, relative bond strengths, in addition to kinetics and thermodynamics—to explain our observations regarding nanocrystal nucleation and growth. Consideration of the chemistry of nanocrystal formation processes provides a valuable compliment to the physics-based classical models of nucleation and growth that do not explicitly consider the system specific molecular structure and bonding.

(1) Yoshikawa, S., Kida, H. & Sato, K. Promotional effects of new types of additives on fat crystallization. J. Oleo Sci. 63(4), 333–345, © 2014 Japan Oil Chemists’ Society, Tokyo., (2) Yoshikawa, S., Kida, H. & Sato, K. Fat crystallization with talc particles is influenced by particle size, concentration, and cooling rate. Eur. J. Lipid Sci. Technol. 117(6), 858–868, © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim., (3) Yoshikawa, S., Kida, H., Matsumura, Y. & Sato, K. Adding talc particles improves physical properties of palm oil-based shortening. Eur. J. Lipid Sci. Technol., DOI: 10.1002/ejlt.201500283 (in press), © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. / 京都大学 / 0048 / 新制・論文博士 / 博士(農学) / 乙第13044号 / 論農博第2837号 / 新制||農||1044(附属図書館) / 学位論文||H28||N5008(農学部図書室) / 33036 / (主査)教授 松村 康生, 教授 裏出 令子, 教授 安達 修二 / 学位規則第4条第2項該当 / Doctor of Agricultural Science / Kyoto University / DFAM

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Magnesium alloys are excellent material candidate to reduce mass of automotive structures, and as such to meet the Department of Energy's targets in fuel economy and clean energy. However, magnesium alloys show poor ductility at room temperature, which is one of the most important impediments to achieving cost-effective manufacturing of wrought alloys and insuring good energy absorption in crash structures. This Master thesis aims to identify the mechanisms behind the low ductility of magnesium. Therefore, non-destructive EBSD analyses upon tension of both a strong and weak textured magnesium alloy were conducted with a focus on the role of twinning in fracture initiation. This study revealed five mechanisms responsible for early fracture, all of which relate to twinning activity. These mechanisms were involved directly in the shear incompatibility arising from interactions between twin-twin, twin-slip, twin-grain boundary, and double twinning. Backstress played a major role in twin-grain boundary and twin-twin boundary interactions.

The automotive industry's search for stronger lighter materials has been hampered in its desire to make greater use of Magnesium alloys by their poor formability below 150°C. One current challenge is to identify the complex structure and deformation mechanisms at work and determine which of these are primary contributors to the nucleation of defects. Orientation Imaging Microscopy has been the most accessible tool for microstructural analysis over the past 15 years. However, using OIM to analyze defect nucleation sites requires prior knowledge of where the defects will occur because once the defects nucleate the majority of microstructural information is destroyed. This thesis seeks to contribute to the early detection of nucleation sites via three mechanisms: 1. Detection of cracks that have already nucleated, 2. Detection of surface topography changes that may indicate imminent nucleation and 3. Beam control strategies for efficiently finding areas of interest in a scan. Successive in-situ OIM scans of a consistent sample region while strain is increased, while using the three techniques developed in this thesis, will be employed in future work to provide a powerful defect analysis tool. By analyzing retrieved EBSD patterns we are able to locate defect / crack sites via shadowing on the EBSD patterns. Furthermore, topographical features (and potentially regions of surface roughening) can be detected via changes in intensity metrics and image quality. Topographical gradients are currently only detectable in line with the beam incidence. It is therefore suggested that the tensile specimens to be examined are orientated such that the resulting shear bands occur preferentially to this direction. The ability to refine the scan around these areas of interest has been demonstrated via an off-line adaptive scan routine that is implemented via the custom scan tool. A first attempt at a defect detection framework has been outlined and coded into MATLAB. These tools offer a first step to accessing the information about defect nucleation that researchers are currently seeking.

Quantum dots are semiconductor nanocrystals that have tunable emission through changes in their size. Producing bright, efficient quantum dots with stable fluorescence is important for using them in applications in lighting, photovoltaics, and biological imaging. This study aimed to optimize the process for coating CdSe quantum dots (which are colloidally suspended in octadecene) with a ZnS shell through the pyrolysis of organometallic precursors to increase their fluorescence and stability. This process was optimized by determining the ZnS shell thickness between 0.53 and 5.47 monolayers and the Zn:S ratio in the precursor solution between 0.23:1 and 1.6:1 that maximized the relative photoluminescence quantum yield (PLQY) while maintaining a small size dispersion and minimizing the shift in the center wavelength (CWL) of the fluorescence curve. The process that was developed introduced a greater amount of control in the coating procedure than previously available at Cal Poly. Quantum yield was observed to increase with increasing shell thickness until 3 monolayers, after which quantum yield decreased and the likelihood of flocculation of the colloid increased. The quantum yield also increased with increasing Zn:S ratio, possibly indicating that zinc atoms may substitute for missing cadmium atoms at the CdSe surface. The full-width at half-maximum (FWHM) of the fluorescence spectrum did not change more than ±5 nm due to the coating process, indicating that a small size dispersion was maintained. The center wavelength (CWL) of the fluorescence spectrum red shifted less than 35 nm on average, with CWL shifts tending to decrease with increasing Zn:S ratio and larger CdSe particle size. The highest quantum yield was achieved by using a Zn:S ratio of 1.37:1 in the precursor solution and a ZnS shell thickness of approximately 3 monolayers, which had a red shift of less than 30 nm and a change in FWHM of ±3 nm. Photostability increased with ZnS coating as well. Intense UV irradiation over 12 hours caused dissolution of CdSe samples, while ZnS coated samples flocculated but remained fluorescent. Atomic absorption spectroscopy was investigated as a method for determining the thickness of the ZnS shell, and it was concluded that improved sample preparation techniques, such as further purification and complete removal of unreacted precursors, could make this testing method viable for obtaining quantitative results in conjunction with other methods. However, the ZnS coating process is subject to variations due to factors that were not controlled, such as slight variations in temperature, injection speed, and rate and degree of precursor decomposition, resulting in standard deviations in quantum yield of up to half of the mean and flocculation of some samples, indicating a need for as much process control as possible.

<p> An experimental investigation is reported for water boiling at atmospheric pressure on a copper surface. Bubble nucleation at an artificial site was observed for five heat fluxes between 11,000 and 20,000 BTU/Hr Ft^2, and subcooling from 0° to about 30°F. Using Wiebe's correlation for heat flux and superheat layer thickness, four mathematical models were tested. The measured results are found to provide excellent agreement with the Han and Griffith model for bubble nucleation.</p> / Thesis / Master of Engineering (MEngr)

<p> An analysis of reported and theoretical methods of precipitating calcium carbonate from aqueous solution is presented, with emphasis on methods that generate the anion in the presence of Ca(++) ion.</p> <p> A new CaCO3 precipitation method referred to as precipitation from quasi-homogeneous solution and suitable for digital processor control is developed. This technique is then used to investigate the effects of ionic strength and Mg(++) ion on calcium carbonate nucleation.</p> <p> A minicomputer based interactive information system, capable of automatic data logging and processing of experimental results in studies using processor controlled precipitation of CaCO3 from quasi-homogeneous solution, is implemented and tested.</p> / Thesis / Master of Science (MSc)