Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第16866号 / 工博第3587号 / 新制||工||1542(附属図書館) / 29541 / 京都大学大学院工学研究科材料化学専攻 / (主査)教授 平尾 一之, 教授 田中 勝久, 教授 三浦 清貴 / 学位規則第4条第1項該当

Gallium arsenide is piezoelectric, so it is possible to generate coupled mechanical and electrical surface acoustic waves (SAWs) by applying a high-frequency voltage to a transducer on the surface of GaAs. By combining SAWs with existing low-dimensional nanostructures one can create a series of dynamic quantum dots corresponding to the minima of the travelling electric wave, and each dot carries a single electron at the SAW velocity (~ 2800 m/s). These devices may be of use in developing future quantum information processors, and also offer an ideal environment for probing the quantum mechanical behaviour of single electrons. This thesis describes a numerical and theoretical study of the dynamics ofan electron in a range of geometries. The numerical techniques for solving thetime-dependent Schrödinger equation with an arbitrary time-dependent potential will be described in Chapter 2, and then applied in Chapter 3 to calculate the transmission of an electron through an Aharonov-Bohm (AB) ring. It will be seen that an important property of the techniques used in this thesis is that they can be easily adapted to study realistic geometries, and we will see features in the AB oscillations which do not arise in simplified analytic descriptions. In Chapter 4, we will then study a device consisting of two parallel SAW channels separated by a controllable tunnelling barrier. We will use numerical simulations to investigate the effect of electric and magnetic fields upon the electron dynamics, and develop an analytic model to explain the simulation results. From the model, it will be apparent that it is possible to use this device to rotatethe state of the electron to an arbitrary superposition of the first two eigenstates. We then introduce coherent and squeezed states in Chapter 5, which are ex-cited states of the quantum harmonic oscillator. Coherent and squeezed electronicstates may be of use in quantum information processing, and could also arise dueto unwanted perturbations in a SAW device. We will discuss how these statescan be controllably generated in a SAW device, and also discuss how they couldthen be detected. In Chapter 6 we describe how to use the motion of a SAW to create a rapidly-changing potential in the frame of the electron, leading to a nonadiabatic excita-tion. The nonadiabatically-excited state oscillates from side to side within a 1Dchannel on a few-picosecond timescale, and this motion can be probed by placing a tunnelling barrier at one side of the channel. Numerical simulations will beperformed to show how this motion can be controlled, and the simulation resultswill be seen to be in good agreement with recent experimental work performed by colleagues. Finally, we will show that this device can be used to measure the initial state of an electron which is an arbitrary superposition of the first twoeigenstates.

The nature of the calcium-silicate-hydrate phase in hydrated Portland cement has been the subject of considerable debate for decades. Various nanostructural models have been proposed including those constructed from colloidal-based particulate systems and those formulated on the basis of layered calcium-silicate-hydrates. These are examined in detail in the literature review section of the thesis. Relatively recent composition-based models have been proposed by Taylor and Richardson-Groves. These models contain structural elements comprised of 1.4 nm tobermorite and jennite. Details are also provided in the literature review. There is however a paucity of data on the engineering properties of pure calcium-silicate-hydrate phases and virtually none on the mechanical performance of 1.4 nm tobermorite and jennite. The global objective of this thesis was to examine the compatibility of the composition-based models with the engineering behaviour of the pure tobermorite and jennite phases. Pure phases of a variety of layered calcium-silicate-hydrates were synthesized and novel techniques developed to determine their engineering characteristics in a variety of test environments. The silicate phases investigated included high temperature silicates e.g. gyrolite as these layered structures are known to be cross-linked. Investigation of the role of ‘structural’ water in layered silicates was also a part of these studies. The thesis is based on a series of twelve refereed journal papers by the candidate (eight are published or accepted and four have been submitted for publication). The research is reported in four parts with each part comprised of three papers. Each part provides insight into the nanostructure of C-S-H in hydrated cement. The arguments developed evolve from an assessment of various factors including aging and the state of water in the layered silicates. The first part of the thesis focuses on the development and application of dynamic mechanical thermo-analysis methods that are sensitive to phase changes and are useful for assessing the compatibility of engineering behaviour with model composition based on 1.4 nm tobermorite and jennite. The second part represents a study of volume stability and mechanical property-porosity relationships for the pure silicate phases that are germane to these studies. The third part focuses on prolonged aging and role of structural water in cement paste hydrated for 45 years. The fourth and final part attempts to address the role of layer structure e.g. cross-linking of silicate sheets on engineering behaviour. The non-uniqueness of modulus of elasticity with respect to equilibrium moisture content is demonstrated. Structurally related irreversible effects that are dependent on drying history are rationalized. A summary chapter is provided wherein the evidence for a composition-based model with tobermorite and jennite structural units is rationalized in terms of the experimental evidence provided in this study and suggestions for future research are discussed.

This thesis describes the formation of and applications of self-assembled structures on metals. Primarily the focus of this PhD project is on the formation of surfaces structures on stainless steel (AISI 304) but other metals have been studied. Laser generated surface structures have been applied to the modification of wettability and reflectivity with a view towards developing these processes for industrial applications. Compared to conventional techniques for the modification of wettabililty, lasers offer the advantage of being a relatively simple technique for the modification of surface structure, reducing the need for complex processes. It is hoped that investigations into the reduction of surface reflectivity will have applications in the conversion of solar energy into useable power in the form of solar thermal energy. The production of self assembled structures is demonstrated using diode pumped solid state (DPSS) Nd:YVO4 lasers operating at wavelengths of 532 and 1064 nm. It is shown that the production of surface microstructures is highly dependant on the correct laser fluence and requires multiple pulses and processing passes. At 1064 nm wavelengths, it has been found highly reproducible surface structures can be formed by carefully controlling laser fluence and scanning speed while keeping the optical arrangement relatively simple. In addition to microstructure formation, the use of ultrafast femtosecond lasers, operating at 400 and 800 nm wavelengths has verified the production of laser induced periodic surface structures. Additionally, the stationary method used to produce these surfaces has been adapted to cover large surface areas with sub wavelength ripple structures with periods of ~295nm and 600nm. Applications of laser surface microstructures on metals have been studied in an effort to produce hydrophobic and superhydrophobic surfaces on metals. It has been found that the roughness change produced by laser processing induces composite wetting when water droplets are introduced to the surface. Contact angle measurements and small angle XRD analysis of laser processed stainless steel (AISI 304) have shown that surface wettability decreased over a period of approximately one month, leading to steady contact angles of over 140°. This is attributed to the formation of a magnetite (Fe3O4) oxide layer in the period after laser processing. The effect of surface microstructure on surface reflectivity has also been studied. It was found that laser induced surface microstructures on copper can decrease surface reflectivity by almost 90%. A comparative study of the effects of surface roughness and chemistry on the optical absorption of copper is given, finding that these surfaces are competitive with contemporary coatings.

Thesis (M. Sc. (Physics)) -- University of Limpopo, 2016 / Titania is a cheap and nontoxic polymorphic material of current interest for a variety of technological applications like in gas sensing and photovoltaic cells. Generally, TiO2, with a band gap of 3.2 eV, can only be excited by a small UV fraction of solar light, which accounts for only 3-5% of the solar energy. Various strategies have been pursued including doping with metallic elements (e.g. Fe) or nonmetallic elements (e.g. N) with the aim of shifting the absorption into the visible range. Since the properties and performance of devices, particularly for high-temperature applications, may be affected by the transformation from one phase to another, it is of significant interest to understand the conditions that affect phase transitions. In the present work TiO2 was doped with platinum (Pt), palladium (Pd), silver (Ag) and gold (Au) at doping levels of 5% weight, following the standard sol-gel methods. Structural characterization was carried out using scanning electron microscopy, Raman Spectroscopy and X-ray diffraction. Optical properties were studied using the Diffused reflectance Spectroscopy (DRS). Doping with Pt and Pd resulted in a lower anatase to rutile phase transformation temperature while doping with Au and Ag did not affect the transformation temperature. SEM micrographs show that the surface contains irregular shaped particles which are the aggregation of tiny crystals at lower temperature range, whereas at higher temperatures (900 °C), spheroids are observe.The reflectance spectra of the metal loaded TiO2 reveal substantial strong spectral cut-off starting from roughly 400 nm to the entire visible region (i.e. they show enhanced absorption).

京都大学 / 新制・課程博士 / 博士(工学) / 甲第23502号 / 工博第4914号 / 新制||工||1768(附属図書館) / 京都大学大学院工学研究科機械理工学専攻 / (主査)教授 平方 寛之, 教授 北條 正樹, 教授 嶋田 隆広, 教授 井上 康博 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

abstract: Solar energy has become one of the most popular renewable energy in human’s life because of its abundance and environment friendliness. To achieve high solar energy conversion efficiency, it usually requires surfaces to absorb selectivity within one spectral range of interest and reflect strongly over the rest of the spectrum. An economic method is always desired to fabricate spectrally selective surfaces with improved energy conversion efficiency. Colloidal lithography is a recently emerged way of nanofabrication, which has advantages of low-cost and easy operation. In this thesis, aluminum metasurface structures are proposed based on colloidal lithography method. High Frequency Structure Simulator is used to numerically study optical properties and design the aluminum metasurfaces with selective absorption. Simulation results show that proposed aluminum metasurface structure on aluminum oxide thin film and aluminum substrate has a major reflectance dip, whose wavelength is tunable within the near-infrared and visible spectrum with metasurface size. As the metasurface is opaque due to aluminum film, it indicates strong wavelength-selective optical absorption, which is due to the magnetic resonance between the top metasurface and bottom Al film within the aluminum oxide layer. The proposed sample is fabricated based on colloidal lithography method. Monolayer polystyrene particles of 500 nm are successfully prepared and transferred onto silicon substrate. Scanning electron microscope is used to check the surface topography. Aluminum thin film with 20-nm or 50-nm thickness is then deposited on the sample. After monolayer particles are removed, optical properties of samples are measured by micro-scale optical reflectance and transmittance microscope. Measured and simulated reflectance of these samples do not have frequency selective properties and is not sensitive to defects. The next step is to fabricate the Al metasurface on Al_2 O_3 and Al films to experimentally demonstrate the selective absorption predicted from the numerical simulation. / Dissertation/Thesis / Masters Thesis Mechanical Engineering 2019

Research was conducted on broadband, anti-reflective coatings for fused silica and chalcogenide substrates in the infrared region of light. Using chemical preparation to create nano-porous through nano-particle based sol-gel solutions, the alteration of optical properties including refractive index and optical thickness was conducted. The nano-particles can modify the coating surface to allow only zero-order diffracted wave propagation reducing scattering while a partially graded profile of refractive index due surface evaporation lessened the precise phase relations of typical homogeneous coatings. My study of silica and titania sol-gel, and hybrid mixtures of the two were used to obtain the optical properties of the materials. The choice of experiments were rooted in theoretically calculated values, and parameters were selected based on quarter wavelength thickness and square root of refractive index theories of destructive cancellation of rebound waves for reduction of reflection. The fused silica system required anti-reflection in the region of 1.0-1.6 micrometer wavelength of the near-infrared. The base, uncoated transmission in this region is ~91%. A maximum transmission of 98% and no less than 97.3% over the entire region of interest was achieved. The chalcogenide system required anti-reflection in the regions of 1.0-1.6 and 3.5-5.0 micrometers of the near- and mid-infrared. The base, uncoated transmission of these regions is 61.9%. A maximum of 95% transmission was achieved for the 1.0-1.6 region and 87% for the 3.5-5.0 region. Solutions and coatings were characterized by Scanning Electron Microscope, Atomic Force Microscopy, X-ray Photoelectron Spectroscopy, particle size, elipsometry, UV-Vis-NIR, and FTIR to reveal the science behind the development and synthesis of nano optical coatings.

<p>Carbon nanotubes (CNTs) are arguably the most widely studied material within the field of nanotechnology. The impressive physical and electronic properties of these materials have led to their investigation in a diverse range of applications. In recent years, the deposition of inorganic nanoparticles upon the surface of CNTs has received much attention. Research within this field has been driven by the desire to develop new composite materials exhibiting novel electronic, optical, and catalytic properties. In addition to the decoration of individual nanotubes, several groups have also investigated the use of CNT thin films as scaffolds for the assembly of inorganic nanostructures as well as other secondary components, including polymers and biomaterials. Nanotube films exhibit a number of physical properties that make them suitable for such applications, displaying impressive electrical conductivity, flexibility, and thermal stability while also possessing a high surface area upon which chemical modification can be conducted.</p><p>This thesis presents work that demonstrates the potential of CNT thin films as flexible conductive scaffolds for the support of a variety of inorganic nanostructures. Procedures are described for the preparation of SWNT -Au nanoparticle composite films that, as subsequently demonstrated, are suitable substrates for the growth of III-V semiconductor nanowires using gas-source molecular beam epitaxy. At the time of writing, the majority of published research within this field focused upon the preparation of SWNT composite films containing spherical metallic or semiconductor nanoparticles. In contrast, the growth of semiconductor nanowires upon nanotube thin films had not been explored. The work described in this thesis therefore represents the development of a novel composite material that combines the flexibility of CNT films with the unique optoeletronic properties exhibited by semiconductor nanowires. The development of functional electronic devices incorporating these materials is also discussed, as is the extension of the methods developed to investigate novel composite materials that combine other inorganic nanostructures with carbon based substrates.</p> / Thesis / Doctor of Philosophy (PhD)

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