The major difference between semiconductor quantum dots and bulk semiconductors is in the quantum confinement effect. It results the controllable exciton¡¦s absorption and emission spectra by tuning the size of the quantum dot. Moreover, multi-exciton states are reported to be observed in the highly symmetric quantum dot systems. In this dissertation, we use the single molecule fluorescence measurement to study the power dependence of multi-exciton state in single CdSe/ZnS semiconductor quantum dots. At low excitation fluence, anti-bunching behavior, and nearly single exponential relaxation dynamics are observed. By increasing the laser power, bi-exponential fluorescence decay dynamics as well as bunching behaviors from the same QD indicate the fast PL dynamics due to the relaxation from multi-exciton. The results indicate certain threshold energy level for multi-exciton generation. In addition, the multiple step cascade radiative relaxation processes are observed. Besides, we modulate linear polarization light to study the excitation orientation dependence. The results indicate the emission dipole of multi-exciton is similar to the single exciton, having a two dimensional transition dipole plane with c-axis symmetry. However, the absorption dipole of multi-exciton exhibits different orientation dependence from the single exciton.

Nanostructures often possess unique properties, which may lead to the development of new microelectronic and optoelectronic devices. They also provide an opportunity to test fundamental quantum mechanical concepts such as the role of quantum confinement. Considerable effort has been made to understand the electronic and structural properties of nanostructures, but many fundamental issues remain. In this work, the electronic and structural properties of nanostructures are examined using several new computational methods. The effect of dimensional confinement on quantum levels is investigated for hydrogenated Ge <110> using the plane-wave density-functional-theory pseudopotential method. We present a real-space pseudopotential method for calculating the electronic structure of one-dimensional periodic systems such as nanowires. As an application of this method, we examine H-passivated Si nanowires. The band structure and heat of formation of the Si nanowires are presented and compared to plane wave methods. Our method is able to offer the same accuracy as the traditional plane wave methods, but offers a number of computational advantages such as the ability to handle large systems and a better ease of implementation for highly parallel platforms. Doping is important to many potential applications of nano-regime semiconductors. A series of first-principles studies are conducted on the P-doped Si <110> nanowires by the real-space pseudopotential methods. Nanowires of varied sizes and different doping positions are investigated. We calculate the binding energies of P atoms, band gaps of the wires, energetics of P atoms in different doping positions and core-level shift of P atoms. Defect wave functions of P atoms are also analyzed. In addition, we study the electronic properties of phosphorus-doped silicon <111> nanofilms using the real-space pseudopotential method. Nanofilms with varied sizes and different doping positions are investigated. We calculate the binding energies of P atoms, band gaps of the films, and energetics of P atoms in different doping positions. Quantum confinement effects are compared with P-doped Si nanocrystals and as well as nanowires. We simulate the nanofilm STM images with P defects in varied film depths, and make a comparison with the experimental measurement. / text

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Esta tese de doutorado tem por objetivo aprofundar as pesquisas realizadas no mestrado, a saber, da caracterização e estudo das propriedades estruturais e ópticas de filmes de oxinitreto de silício (SiOxNy:H) ricos em silício depositados pela técnica de deposição química a vapor assistida por plasma a baixa temperatura (PECVD). Os resultados obtidos no mestrado indicaram que os filmes de SiOxNy:H ricos em silício apresentam emissão luminescente na faixa do visível cuja intensidade e freqüência de emissão estão em correlação com o excesso de silício. Os resultados sugeriram que o excesso de silício na matriz do SiOxNy:H estava disposto na forma de aglomerados de silício de dimensões nanométricas responsáveis por efeitos de tamanho quântico bem como a estados radiativos na interface dos aglomerados com a matriz isolante. Neste trabalho a fim de avaliar o efeito da separação de fases, do tamanho quântico, e da interface, foram produzidos sistemas nanoestruturados a base de silício com total e parcial separação de fases para caracterizar e analisar suas propriedades ópticas e estruturais e compará-las com as dos filmes ricos em silício. Assim foram produzidas multicamadas de a-Si:H de poucos nanômetros de espessura com materiais dielétricos. Em algumas destas multicamadas foi promovida a mistura parcial das camadas por meio de bombardeamento iônico. O estudo nas estruturas de multicamadas permitiu caracterizar e analisar as propriedades estruturais e ópticas de materiais nanoestruturados com total e parcial separação de fases para posteriormente contrastá-los com as características dos filmes de oxinitreto de silício ricos em silício. A fim de analisar a influência da interface nas propriedades ópticas destes sistemas as multicamadas foram fabricadas com dois dielétricos diferentes: o óxido de silício e o ni treto de silício. A espessura das camadas dielétricas foi mantida fixa entanto que a das camadas de silício foi variada para avaliar efeitos de confinamento no silício. A caracterização foi feita utilizando técnicas de absorção óptica no UV-Vis, absorção no infravermelho (FTIR), espectroscopia Raman, fotoluminescência (PL), espectroscopia de absorção de raios X próximos 7 à borda do silício (XANES), e microscopia eletrônica de transmissão de alta resolução (HRTEM). Da análise dos resultados concluiu-se que o confinamento é fundamental para a existência da emissão luminescente embora o tipo de interface influencie a energia e a intensidade da emissão. A análise comparativa com as multicamadas permitiu verificar que os filmes de oxinitreto de silício ricos em silício apresentam, separação parcial de fases já como depositados, os tratamentos térmicos promovem a segregação do silício aumentando conseqüentemente a separação de fases. / The aim of this doctorate thesis is to enhance the knowledge in the research conducted along the Master degree based on the characterization and study of the structural and luminescent properties of silicon rich silicon oxynitride films (SiOxNy:H) deposited at low temperature by Plasma Enhanced Chemical Vapor Deposition (PECVD). The results of this study indicated that silicon rich SiOxNy:H films present luminescence in the visible spectra range with intensity and frequency in correlation with the silicon excess. The results suggested that the silicon excess in the SiOxNy:H matrix is confined in nanometric silicon clusters responsible for the to quantum size effects as well as for radiactive states at the interface of the silicon clusters with the insulating matrix. In the present work in order to evaluate the effect of phase separation, quantum size and interface effects si licon based nanostructured systems presenting total and partial phase separation were produced and their structural and optical properties were characterized in order to correlate them with the silicon rich films ones. In this way multilayers with few nanometers thick a-Si layers with dielectric materials were produced. The mixture of the layers was promoted by ion bombardment in some of these multilayers. The study of these structures permitted the characterization of structural and optical properties of materials with total and partial phase separation with the purpose of comparing them to the silicon-rich silicon oxynitride films characteristics. In order to analyze the interface influence in the optical properties, multilayers systems with two different dielectric materials, silicon oxide and silicon nitride, were fabricated. The dielectric layer thickness was kept constant while the silicon layer was varied in order to study the confinement effect. The characterization was done utilizing UV-Vis optical absorption, infrared absorption (FTIR), Raman spectroscopy, Photoluminescence (PL), X-ray absorption near edge spectroscopy (XANES) and high-resolution transmission electron microscopy (HRTEM) techniques. From the results analysis it was concluded that confinement is essent ial for the existence of luminescent 9 emission although the type of interface also influences the energy and intensity of the emission. The comparative analysis with the multilayers permitted to verify that the silicon-rich silicon oxynitride films present, as deposited, partial phase separation and that the thermal treatments promotes silicon aggregation thus increasing the phase separation.

Esta tese de doutorado tem por objetivo aprofundar as pesquisas realizadas no mestrado, a saber, da caracterização e estudo das propriedades estruturais e ópticas de filmes de oxinitreto de silício (SiOxNy:H) ricos em silício depositados pela técnica de deposição química a vapor assistida por plasma a baixa temperatura (PECVD). Os resultados obtidos no mestrado indicaram que os filmes de SiOxNy:H ricos em silício apresentam emissão luminescente na faixa do visível cuja intensidade e freqüência de emissão estão em correlação com o excesso de silício. Os resultados sugeriram que o excesso de silício na matriz do SiOxNy:H estava disposto na forma de aglomerados de silício de dimensões nanométricas responsáveis por efeitos de tamanho quântico bem como a estados radiativos na interface dos aglomerados com a matriz isolante. Neste trabalho a fim de avaliar o efeito da separação de fases, do tamanho quântico, e da interface, foram produzidos sistemas nanoestruturados a base de silício com total e parcial separação de fases para caracterizar e analisar suas propriedades ópticas e estruturais e compará-las com as dos filmes ricos em silício. Assim foram produzidas multicamadas de a-Si:H de poucos nanômetros de espessura com materiais dielétricos. Em algumas destas multicamadas foi promovida a mistura parcial das camadas por meio de bombardeamento iônico. O estudo nas estruturas de multicamadas permitiu caracterizar e analisar as propriedades estruturais e ópticas de materiais nanoestruturados com total e parcial separação de fases para posteriormente contrastá-los com as características dos filmes de oxinitreto de silício ricos em silício. A fim de analisar a influência da interface nas propriedades ópticas destes sistemas as multicamadas foram fabricadas com dois dielétricos diferentes: o óxido de silício e o ni treto de silício. A espessura das camadas dielétricas foi mantida fixa entanto que a das camadas de silício foi variada para avaliar efeitos de confinamento no silício. A caracterização foi feita utilizando técnicas de absorção óptica no UV-Vis, absorção no infravermelho (FTIR), espectroscopia Raman, fotoluminescência (PL), espectroscopia de absorção de raios X próximos 7 à borda do silício (XANES), e microscopia eletrônica de transmissão de alta resolução (HRTEM). Da análise dos resultados concluiu-se que o confinamento é fundamental para a existência da emissão luminescente embora o tipo de interface influencie a energia e a intensidade da emissão. A análise comparativa com as multicamadas permitiu verificar que os filmes de oxinitreto de silício ricos em silício apresentam, separação parcial de fases já como depositados, os tratamentos térmicos promovem a segregação do silício aumentando conseqüentemente a separação de fases. / The aim of this doctorate thesis is to enhance the knowledge in the research conducted along the Master degree based on the characterization and study of the structural and luminescent properties of silicon rich silicon oxynitride films (SiOxNy:H) deposited at low temperature by Plasma Enhanced Chemical Vapor Deposition (PECVD). The results of this study indicated that silicon rich SiOxNy:H films present luminescence in the visible spectra range with intensity and frequency in correlation with the silicon excess. The results suggested that the silicon excess in the SiOxNy:H matrix is confined in nanometric silicon clusters responsible for the to quantum size effects as well as for radiactive states at the interface of the silicon clusters with the insulating matrix. In the present work in order to evaluate the effect of phase separation, quantum size and interface effects si licon based nanostructured systems presenting total and partial phase separation were produced and their structural and optical properties were characterized in order to correlate them with the silicon rich films ones. In this way multilayers with few nanometers thick a-Si layers with dielectric materials were produced. The mixture of the layers was promoted by ion bombardment in some of these multilayers. The study of these structures permitted the characterization of structural and optical properties of materials with total and partial phase separation with the purpose of comparing them to the silicon-rich silicon oxynitride films characteristics. In order to analyze the interface influence in the optical properties, multilayers systems with two different dielectric materials, silicon oxide and silicon nitride, were fabricated. The dielectric layer thickness was kept constant while the silicon layer was varied in order to study the confinement effect. The characterization was done utilizing UV-Vis optical absorption, infrared absorption (FTIR), Raman spectroscopy, Photoluminescence (PL), X-ray absorption near edge spectroscopy (XANES) and high-resolution transmission electron microscopy (HRTEM) techniques. From the results analysis it was concluded that confinement is essent ial for the existence of luminescent 9 emission although the type of interface also influences the energy and intensity of the emission. The comparative analysis with the multilayers permitted to verify that the silicon-rich silicon oxynitride films present, as deposited, partial phase separation and that the thermal treatments promotes silicon aggregation thus increasing the phase separation.

Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第15612号 / 工博第3301号 / 新制||工||1498(附属図書館) / 28139 / 京都大学大学院工学研究科電子工学専攻 / (主査)教授 木本 恒暢, 教授 藤田 静雄, 准教授 山田 啓文 / 学位規則第4条第1項該当

Catalytic conversion of methanol to hydrocarbons (MTH) provides an alternative route to the production of fuels and important industrial chemicals that are currently mainly produced from the refinery of petroleum. The ability to control the product distribution of MTH according to the demands of specific applications is of crucial importance, which relies on the thorough understanding of the reaction pathways and mechanisms. Despite the significant research efforts devoted to zeolite-catalyzed MTH, it remains a challenge to establish a firm correlation between the physicochemical properties of zeolites and their catalytic activity and selectivity. In this dissertation, we designed a series of experiments to gain fundamental understanding of how the structural and compositional parameters of zeolites influence their catalytic performances in MTH. We investigated different types of zeolites, covering large-pore Beta, medium-pore ZSM-5, and small-pore DDR zeolites, and tune their crystallite size/diffusion length, hierarchical (mesoporous) structure, and Si/Al ratio (density of acid sites) by controlled synthesis or post-synthesis treatments. The influence of mesoporosity of a zeolite catalyst on its catalytic performance for MTH, with zeolite Beta, was first investigated. The shorter diffusion length associated with the hierarchical structure results in a lower ethylene selectivity but higher selectivity towards C4-C7 aliphatics. Then we investigated the correlation between the Al content and the ethylene selectivity by ZSM-5 zeolites with similar crystal sizes but varied Si/Al ratios. We realized that ethylene selectivity is promoted with the increase of aluminum content in the framework. These two observations can be explained by the same mechanistic reason: the ethylene selectivity is associated with the propagation degree of the aromatics catalytic cycle and essentially determined by the number of the acid sites that methylbenzenes would encounter before they exit the zeolite crystallite. Last we explored how to maximize the propylene selectivity by tuning the physicochemical properties of DDR zeolites. Due to the confined pore space in DDR, the propagation of olefins-based catalytic cycle can be preferentially promoted in a tunable manner, which cannot be realized with zeolites having larger pores. Thus, the propylene selectivity increases with increasing the Si/Al ratio and decreasing the crystallite size.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第18286号 / 工博第3878号 / 新制||工||1595(附属図書館) / 31144 / 京都大学大学院工学研究科電子工学専攻 / (主査)教授 木本 恒暢, 教授 白石 誠司, 准教授 浅野 卓 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

Yes / Recycled aggregate concrete filled stainless steel tube (RAC-FSST) is a new type of composite member combining the advantage of stainless steel and RAC. In this paper, a total of twenty-four RAC-FSST stub columns were tested under axial load, considering the influences of coarse recycled aggregate (CRA) content, steel ratios and compressive strengths of RAC. The obtained results, including the failure patterns, responses of axial load vs. deformation, stress states of external stainless steel tube and inner RAC and confinement effects, were systematically analyzed. Results indicated that all specimens presented good ductility and high residual strengths after reaching the maximum axial load. The elastic stiffness of RAC-FSSTs obviously declined with the increasing CRA content, while the strain at the ultimate load was larger. The inclusion of CRA could advance the occurrence of the confinement and lead to lower confining stress. Based on the experimental results, an analytical model with consideration of confinement action was developed to predict the axial response of RAC-FSST stub columns. Besides, the current design provisions for the normal CFST and RAC-FST members were employed to evaluate their applicability to RAC-FSSTs. In general, the design rules EN 1994-1-1:2004, GB 50936-2014 and T/CECS 625-2019 gave a conservative and relatively accurate prediction on ultimate strength of RAC-FSST stub columns. / This work was supported by the National Natural Science Foundation.

The basis of mixing ventilation is the airflow supply to the room by means of jets initiatedfrom the ventilation diffusers. To avoid the draught problem, the design of mixing ventilationmakes uses the throw term, which is defined as the distance to the supply air terminal inwhich the jet centreline mean velocity is decreased to a given value. Traditionally, the throw ismeasured by the supply air device manufacturer. The throw is applied by designers to estimatethe velocity levels in the occupied zone. A standard for determining the throw is the CENstandard CEN/TC156/WG4 N86 "Draft Standard. Air terminal Devices. AerodynamicsTesting And Rating For Mixed Flow Application".The measurement of the throw is very time consuming even with the free jets and theinfluence of the room (the effect of confinement) is not considered. The objective of thepresent study is to give a basis for modifying the existing design and testing method used topredict the velocities in the occupied zone during the design process. A new method whichmay probably be more easier than the existing methods and at the same time give a betterprecision by including the confinement effect.In this thesis two methodological systems of experiment and numerical simulations have beenused. The numerical predictions are used in comparison with the measurements. Thereasonable agreement of the above mentioned methods is implemented to numerical study ofthe other room configurations which are not experimentally studied. This examining methodallows the possibility of studying a lot of configurations and in this manner generalising of theresults. Although the experimental part was made for both model-scale and full-scale testrooms, a large amount of data was obtained for a new test room whose dimension aresystematically varied. All of studies have been made for the isothermal case and themeasurements of velocities and pressures conducted along the room perimeters. The effect ofshort and deep rooms on the properties of the jet ( velocities, pressure, integral scale, jetmomentum, the rate of spreading of jet and turbulence intensities) have been carried out.Some old and recent investigations have been examined. Specially the concept of correlationsfrom open to closed rooms is criticised. It is also shown that the flow field in a confined roomis affected by many other factors than the Reynolds number. The surface pressure on theperimeters was used to calculate the reaction forces at the corners which causes recirculatingbubbles at corners. A study of the turbulent axisymmetric jet which is the basic element inturbulent shear flows and some restrictions of the traditional measurement techniques at theregion of interest in ventilation applications are discussed. The jet momentum is measured byweighing on a balance. Also a study of jets which collide with a wall , that is impinging jet,the effect of walls and confinement on the jet momentum have experimentally andnumerically been carried out. A new momentum balance model was developed for both thefree jet and confined one. An empirical relation has been found for estimation of the room’srotation centre which is used for validation of CFD results.Finally, it is found that the jets in a ventilated room which are a combination of free jet, walljet and impinging jet differ from the traditional wall jets. The rate of spreading of the jet andthe maximum velocity decay in a ventilated room are also different depending on the roomsize and its confinement.