<p> β- and β"-gallates are analogs of β-Al2O3 family. K-β"-gallate was directly synthesized via solid state reaction with β-Ga2O3 (β-gallia) precursor. When α-Ga2O3 is used as starting material, K-β-gallate forms in spite of incorporation of aliovalent ions, i.e., Li+, Zn2+ and Cd2+. It is suggested that oxygen packing sequence in the Ga2O3 precursor plays an important role on the formation of K-β- or β"- gallates. β-Ga2O3 has the ABCABC oxygen packing sequence, similar to β"-gallate structure, thus β-Ga2O3 leads to form pure K-β"-gallate; α-Ga2O3 has the hexagonal structure with ABAB oxygen packing sequence. K-β-gallate forms around the α-Ga2O3 --> β-Ga2O3 phase transformation (≈700°C). This low reaction temperature negates the aliovalent ions to stabilize β"-structure when α-Ga2O3 precursor is employed.</p> <p> K-β- or β"-gallates show good ionic conductivity. Both can be fully ion-exchanged with Ba2+ and Sr2+. Sr-β-gallate is metastable and transforms to magnetoplumbite structure after annealing at 1200°C. But Ion-exchanged Ba-β-gallate is stable. Zn2+ doped Ba-β-gallate can be directly formed at 1300°C via solid state reaction.</p> <p> Mn2+ ion-exchanged K-β-or β"-gallates exhibit green photo luminescence. Mn2+ can also locate in the spinel block to confer green photo luminescence. Eu3+, Ce3+ and Eu2+ can not be ion-exchanged into the conduction plane of K-β-gallate. There is no luminescence observed for directly synthesized BaZnGa10O17 doped with Eu3+, Ce3+ and Eu2+ due to photoionization effect. When half Ga3+ is substituted by Al3+, directly formed BaZnAl5Ga5O17: Eu3+ shows red emission upon UV excitation (254nm). Blue emission of 485nm wavelength was observed for BaZnAl5Ga5O17: Eu2+.</p> <p> The structure of β- or β"-gallates was refined by Rietveld neutron powder diffraction. Zn2+ was detected on the Ga(2) site in β-K1.64Ga10.36Zn0.64O17. Extra K+ is balanced by Zn2+. K+ is distributed between BR (2(c)) and MO (6(h)) sites. Ba2+ was detected at MO sites, slightly shift from the BR sites in β-BaZnGa10O17. Extra K+ is also compensated by Zn2+ in β"-K1.67Ga10.33Zn0.67O17. In undoped K-β-gallate, VGa(1)Ga(5)i is introduced to balance extra K+. Extra K+ in undoped K-β"-gallate is supposed to be balanced by the formation of Ga+.</p> / Thesis / Master of Engineering (MEngr)

Optical and spectroscopic molecular properties are key to characterizing the behavior of molecules interacting with an applied electromagnetic field of light. Response theory has been used for a long time to calculate such properties in the frequency domain. Real-time (RT) methods solve for the frequency-dependent properties in the time domain by explicitly propagating the time-dependent wave function. Various quantum chemical methods can be incorporated with the RT formalism, including Hartree-Fock, density functional theory, configurational interaction, coupled cluster, etc. Among these, coupled cluster (CC) methods provide high accuracy for systems with strong electron correlation, making RT-CC implementations intriguing. All applications of CC methods face a substantial challenge due to their high-order polynomial scaling. For RT-CC methods, two aspects may be explored to improve the efficiency, the numerical techniques regarding the RT propagation and the reduced-scaling methods regarding CC itself. In this work, we start with the exploration of the hardware used for the calculations and the numerical integration methods for propagating the wave function parameters. Firstly, a GPU-enabled Python implementation has been developed by conducting the tensor contractions on GPUs utilizing PyTorch, a machine learning package, that has similar syntax as NumPy for tensor operations. A speedup of a factor of 14 is obtained for the RT-CCSD/cc-pVDZ absorption spectrum calculation of the water tetramer. Furthermore, to optimize the performance on GPUs, single-precision arithmetic is added to the implementation to achieve an additional speedup of a factor of two. Lastly, a group of integrators for solving differential equations are introduced to the RT framework, including regular explicit integrators, adaptive integrators, and a mixed-step-size approach customized for strong-field simulations. The optimal choice of the integrator depends on the requiring accuracy, stability and efficiency. In addition to being highly accurate, CC methods are also systematically improvable and provide a hierarchy of accuracy. Based upon the RT-CCSD implementation, the coupled cluster singles, doubles and approximate triples (CC3) method, favorable for calculating frequency-dependent properties, is tailored to the RT framework for high excitation and approximate orbital relaxation. The calculation is tested on both CPUs and GPUs, with a significant speedup gained from GPUs for the water cluster test cases. To further expand the range of applications of our RT-CC implementation, dynamic polarizabilities, first hyperpolarizabilities, and the G' tensor are calculated from induced electric and magnetic dipole moments using finite-difference methods. A discussion has also been conducted to compare RT-CC3 with RT-CCSD, and time-dependent nonorthogonal orbital-optimized coupled cluster doubles (TDNOCCD) method. Additionally, electron dynamics, including the Rabi oscillation and exited state to excited state transitions, have also been explored utilizing the well-developed RT-CC framework. / Doctor of Philosophy / Theoretical studies aim to match experiments, but more importantly, provide insights to interpret and predict experimental data. Calculating optical properties related to light-matter interactions is one of the most crucial tasks for characterizing molecular properties. In experiments, electromagnetic radiation in the form of light is applied to the system. The absorption or emission of light can be measured to identify, for example, the electronic structure of the molecule. In theoretical simulations, this applied radiation is represented by a perturbation operator that is added to the Hamiltonian in the Schrödinger equation. Quantum chemists are dedicated to developing methods that provide a better description of the spectroscopy. In the current work, the frequency, shape and the intensity of the radiation can all be finely-tuned, similar to experimental setups. The framework for extracting optical properties from time-dependent trajectories of induced dipole moments is established for accurate and efficient simulations. To improve efficiency and make the method feasible for real-world applications, a strong understanding of light-matter interactions on a quantum level and proper utilization of computational resources are both necessary. Improvements achieved and presented in this dissertation demonstrate a powerful tool for a better understanding of the nature of the interaction between the system and the electromagnetic radiation.

京都大学 / 新制・課程博士 / 博士(工学) / 甲第25015号 / 工博第5192号 / 新制||工||1991(附属図書館) / 京都大学大学院工学研究科合成・生物化学専攻 / (主査)教授 古川 修平, 教授 生越 友樹, 教授 杉安 和憲 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

In the search for nano-scale, highly customizable materials for next-generation electronic devices, two-dimensional (2D) materials have generated much interest. 2D materials have complex, layer-dependent optical and electronic properties of which many aspects remain yet to be explored and fully understood. The aim of this thesis was to investigate and explain optoelectronic properties of several 2D materials systems towards device design. This was accomplished using predictive physical modelling at the density functional theory level (DFT) as well as many-body theory (GW+BSE). The optical transitions of bulk ReS2 and ReSe2 were studied using DFT in comparison with experiment. We found that the orbital composition of the band edges determined the sign of the pressure coefficient of the optical gap. Our results provide a step towards understanding the perceived layer-independence of the optical properties of ReS2 and ReSe2. The exciton landscape of MoS2 monolayer was explored in detail using many-body theory (GW+BSE). We found dark excitons very close to bright excitons and even lower in energy. Our results help reverse the common assumption that the lowest-energy exciton in MoS2 is bright. The ideal band offset between recently predicted monolayers of the CaP3 family was predicted using GW theory. We observed chemical trends in the band offsets and explained their origin. Our results serve as indicators for heterojunction design with these novel materials. The effective mass of a test set of eighteen semiconductors including several 2D materials was calculated using DFT with semi-local and non-local hybrid exchange-functionals and compared for accuracy with respect to experimental data. Our analysis details the effect of the nonlocal exchange potential on the accuracy of the effective mass. Our results give guidelines for high-throughput calculations of the effective mass for different material classes, including 2D materials. / Thesis / Doctor of Philosophy (PhD)

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<p>Small animal imaging is a valuable tool in preclinical biomedical research which relies on the use of animal models to understand human disease. Newly emerging optical imaging techniques such as bioluminescence tomography offer an inexpensive and sensitive alternative to more established imaging technologies. These techniques are capable of non-invasively imaging a variety of cellular and molecular processes <em>in vivo</em>. As an emerging technology, current bioluminescence imaging methods suffer from several limitations, preventing them from reaching their full potential.</p> <p>In this work, we describe the design and characterization of an integrated imaging system capable of multispectral bioluminescence tomography (BLT), diffuse optical tomography (DOT), and X-ray computed tomography (CT). The system addresses many of the inherent problems encountered in planar bioluminescence imaging techniques, allowing for the recovery of more accurate and quantitative bioluminescence data. The integrated X-ray CT scanner provides anatomical information which aids in the visualization and localization of the recovered bioluminescence distributions and also helps to constrain the inverse reconstruction in the diffuse optical tomography system. It was found that the inclusion of spatial priors from X-ray CT improved the reconstructed image quality dramatically. Four image reconstruction algorithms were evaluated for their ability to recover the effective attenuation coefficients of a series of test phantoms. Two of the algorithms (a modified Levenberg-Marquardt method, and a single-step Tikhonov method) did not use any <em>a priori</em> spatial information. Two other algorithms (hard priors and soft priors) used <em>a priori </em>structural information from X-ray CT to constrain the reconstruction process. The two methods incorporating spatial prior information resulted in recovered optical property distributions with RMS errors ranging from 8 % to 15 % in a series of test phantoms versus errors of 11 % to 26 % for non-spatial methods. The soft priors method was shown to be more resilient to imperfect <em>a priori</em> information.</p> <p>The multispectral BLT component was used to recover accurate bioluminescence distributions in test phantoms using <em>a priori</em> background optical properties recovered from the DOT system. Multispectral measurements were shown to provide an accurate method for estimating the position of a bioluminescence source due to the wavelength dependent attenuation of tissue. Experimental measurements are presented which explore the importance of accurate estimates of background optical properties in BLT. The hard spatial prior method was found to provide the best overall recovery of total source strength, position, and fidelity at all source depths up to 12.5 mm. The total source strength was recovered to within 8 %, while the source position was recovered to within 0.16 mm in all cases. Errors in recovered power and position showed no dependence on depth up to the maximum of 12.5 mm.</p> / Doctor of Philosophy (PhD)

A knowledge of the fundamental optical properties of breast tissues is necessary in order to optimize transillumination imaging techniques for the diagnosis of breast disease. The optical absorption and scattering coefficients have been measured in normal and diseased breast tissues, over the range of wavelengths from 500 to 1100 nm. The tissues were obtained from surgical specimens, and consisted of normal glandular and adipose tissues, fibrocystic disease, fibroadenoma, and ductal carcinoma. Total attenuation coefficients were measured for thin slices of tissue obtained on a microtome. The diffuse reflectance and transmittance were measured for 1.0 mm thick samples of these tissues, using standard integrating sphere techniques. Monte Carlo simulations were performed to derive the scattering and absorption coefficients, as well as the mean cosine of the scattering angle. The results indicate that scatter exceeds absorption by at least two orders of magnitude. The absorption coefficients are strongly affected by the presence of blood, particularly at wavelengths below 600nm. The scattering coefficients lie in the range 30 mm to 90 mm-1 at 500 nm, and fall smoothly with increasing wavelength to between 10 mm and 50 mm at 1100 nm. The scatter coefficient for adipose tissue differs, in that it is invariant with wavelength over this spectral range. The scattered light, for all tissues examined, is highly forward peaked, with the mean cosine of the scattering angle in the range 0.945 to 0.985. This value remains constant with wavelength to within +/-0.01 for any given tissue. The absorption coefficients and scattering properties of each tissue type fall within distinct ranges at each wavelength. Fibrocystic disease and adipose tissue appear to be the most clearly distinguishable groups. The optical properties of carcinoma do not differ significantly from those of normal glandular tissues, although both groups differ from other tissue types. The implications of these results for imaging are yet to be determined. / Thesis / Master of Science (MS)

The reflectivity, transmissivity, and absorptivity of freshly evaporated silver and copper films were measured in vacuo and then in the presence of several gases. These measurements were performed, using the photoelectric method, with two photomultiplier tubes (931-A and 1P21), and were made at an angle of incidence of zero degrees for two different wavelengths (4047 A and 4358 A). The gases used were air, argon, nitrogen and oxygen. The use of oxygen required several changes in the evaporating system in order that the diffusion pump oil would not oxidize too rapidly and cause an explosion. Air was found to increase the transmissivity in two steps, first an initial change, and second a gradual change. The reflectivity decreased in two similar changes. Nitrogen and oxygen revealed to a greater or lesser extent the same changes as were observed for air. Argon produced only a gradual change in both reflectivity and transmissivity. The initial change in oxygen was attributed to oxidation, and the initial change in nitrogen attributed to chemisorption. The gradual change in all gases was due to physical adsorption. The possibility that chemisorption might have caused the initial change in oxygen was pointed out, but this experiment did not allow a definite choice to be made. / Master of Science