Titanium oxide (TiO2) films have been actively investigated as many applications because of the mechanical and chemical durability, high refractive index and high transparency. In catalytic and electrochemical applications, it has been utilized as a stable semiconductor electrode for the conversion of solar energy into chemical or electrical energy. Uniform TiO2 films were deposited on conductive glass substrate (ITO/glass) by liquid phase deposition (LPD) with the aqueous solutions of ammonium hexafluoro-titanate and boric acid. Niobium oxide powder and Hydrofluoric acid which add deionized water were used to be Niobium doping solution. Undoped LPD-TiO2 has hydroxyl related defects and Li+ ions will be trapped to degrade the electrochromic durability. For niobium doping, the electrochromic characteristics were enhanced. Niobium doping in TiO2 can reduce hydroxyl related defects. The electrochromic durability was enhanced from 5¡Ñ103 to 1¡Ñ104 times. The transparency ratio was enhanced from 61 % to 70 % at the wavelength of 550 nm. In our experiment, TiO2 films morphology and thickness was characterized by scanning electron microscopy (SEM), structure was characterized by X-ray diffraction (XRD) and surface roughness was measured by atomic force microscopy (AFM), chemical properties was characterized by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR), optical properties was characterized by spectrophotometer (MP-100), and electrochromic characterized by cyclic voltammetry (CHI627C).

In this study, SiO2 and TiO2 films were deposited on GaN, their physical and chemical properties were measured. An Al/SiO2/GaN and Al/TiO2/GaN MOS structures were used for the electrical measurements. To improve the electrical properties, we investigated the characteristics of SiO2 and TiO2 films after annealing in nitrogen, oxygen, and nitrous oxide ambient. The highest dielectric constant of 3.91 and 28.68, and lowest leakage current density of 8.97¡Ñ10-5 A/cm2 at 2 MV/cm and 2¡Ñ10-2 A/cm2 at 1 MV/cm for the N2O-annealed SiO2 film and TiO2 film can be obtained.

When the size of display panel increased, the RC delay of TFTs became serious. High dielectric (high-k) materials used as the gate oxide can increase the gate oxide capacitance Co, which can induce a higher drain current, and higher aperture ratio. Therefore, low-k materials are used for inter-metal dielectrics. Thus, it can improve the RC delay. LPD-TiO2 film on a-Si and poly-Si technology and characterization of films were described in detail in this thesis. The highest dielectric constant of 11.76 and 29.54, and lowest leakage current density of 5.45¡Ñ10-7A/cm2 at -0.45 MV/cm and 3.11¡Ñ10-1 A/cm2 at 0.45 MV/cm for the O2-annealed of LPD-TiO2film on a-Si and poly-Si can be obtained.

abstract: As the 3rd generation solar cell, quantum dot solar cells are expected to outperform the first 2 generations with higher efficiency and lower manufacture cost. Currently the main problems for QD cells are the low conversion efficiency and stability. This work is trying to improve the reliability as well as the device performance by inserting an interlayer between the metal cathode and the active layer. Titanium oxide and a novel nitrogen doped titanium oxide were compared and TiOxNy capped device shown a superior performance and stability to TiOx capped one. A unique light anneal effect on the interfacial layer was discovered first time and proved to be the trigger of the enhancement of both device reliability and efficiency. The efficiency was improved by 300% and the device can retain 73.1% of the efficiency with TiOxNy when normal device completely failed after kept for long time. Photoluminescence indicted an increased charge disassociation rate at TiOxNy interface. External quantum efficiency measurement also inferred a significant performance enhancement in TiOxNy capped device, which resulted in a higher photocurrent. X-ray photoelectron spectrometry was performed to explain the impact of light doping on optical band gap. Atomic force microscopy illustrated the effect of light anneal on quantum dot polymer surface. The particle size is increased and the surface composition is changed after irradiation. The mechanism for performance improvement via a TiOx based interlayer was discussed based on a trap filling model. Then Tunneling AFM was performed to further confirm the reliability of interlayer capped organic photovoltaic devices. As a powerful tool based on SPM technique, tunneling AFM was able to explain the reason for low efficiency in non-capped inverted organic photovoltaic devices. The local injection properties as well as the correspondent topography were compared in organic solar cells with or without TiOx interlayer. The current-voltage characteristics were also tested at a single interested point. A severe short-circuit was discovered in non capped devices and a slight reverse bias leakage current was also revealed in TiOx capped device though tunneling AFM results. The failure reason for low stability in normal devices was also discussed comparing to capped devices. / Dissertation/Thesis / M.S. Materials Science and Engineering 2011

É crescente o interesse, dentre os diversos tipos de dispositivos fotovoltaicos, nas células solares com corantes (dye-sensitized solar cell, DSCC). Isto é devido não só aos menores custos de produção (química molhada), mas também ao grande número de combinações orgânico/semicondutor que podem ser utilizadas, buscando as propriedades de interesse de cada dispositivo. Em uma DSSC a absorção de luz é realizada pelo material orgânico, que injeta o elétron no semicondutor para sua extração como corrente. A neutralidade da molécula é recuperada através de um eletrólito transportador de carga a partir do outro terminal. Este problema é de difícil investigação experimental, devido ao grande número de variáveis envolvidas, já que qualquer defeito ou mudança na deposição pode alterar o processo de transferência de carga. Da mesma forma, também o estudo teórico apresenta grande dificuldade, sendo necessária a adoção de modelos simplificados para o estudo, buscando um entendimento mais profundo dos processos que ocorrem durante a absorção de luz. Neste trabalho investigamos uma combinação de materiais de alta relevância, ácido retinóico sobre óxido de titânio na fase anatase, a mais importante para nanoestruturas. Realizamos uma investigação detalhada da aplicabilidade de diferentes metodologias ao problema, focalizando as características eletrônicas e óticas, e buscando evidências de transferência de carga. Para tal, analisamos modelos simples (materiais isolados, e outros sistemas diferentes de mesmas características), utilizando métodos vindos de diferentes postulações iniciais, como Hartree-Fock e Funcional da Densidade, e também partindo tanto de implementações ab initio (primeiros princípios) como de formulações semi-empíricas. Por fim, escolhida uma metodologia ideal, estudamos sistemas mais realistas de interfaces orgânico/óxido. Nossos resultados indicam a influência das dimensões nanoscópicas da matriz inorgânica nas propriedades de fotocolheita, assim como a grande importância da ligação covalente, presente na montagem quimissorvida molécula/superfície, que altera as propriedades óticas de ambos os componentes. / There is growing interest, among the many types of photovoltaic devices, in dye-sensitized solar cells (DSSC). The reasons for that are not only the lower costs of production (wet chemistry), but also the large number of organic/semiconductor combinations that can be made, depending on the properties that are interesting for each device. On a DSSC the light absorption occurs in the organic material, from which the electron is transferred to the semiconductor for current generation. The molecule regains its neutrality through an electrolyte that carries charge from the opposing terminal. The experimental investigation of this problem is very difficult, due to the large num- ber of variables involved, as any defect or change on the deposition can affect the charge transfer process. Similarly, the theoretical study is also difficult, making necessary the use of simplified models for the system to gain deeper understanding of the processes of light absorption. In this work we have studied a combination of large relevancy, retinoic acid over titanium oxide, at the anatase phase, the most important for nanostrucutres. We have thoroughly investigated the applicability of several methodologies, focusing at electronic and optical characteristics, and searching for evidences of charge transfer. For this we analyzed sim- ple models (isolated materials, and other systems that share the same characteristics), using methodologies from different starting theories, as Hartree-Fock and Density Functional The- ory, and also applying both ab initio and semi-empirical approaches. Once chosen the best methodology, we studied a more realistic system, true organic/oxide interfaces. Our results show the influence of the nanoscopic dimensions of the inorganic substrate on the properties of the photoharvest, and also the fundamental role played by the covalent bond that exists on the chemisorbed deposition of molecule/surface, that alters the optical properties of both components.

Un dispositif de dépôt chimique en phase vapeur à l’air libre, utilisant une torche à injection axiale (TIA), a été développé pour l’élaboration de couches minces de TiO2 et TiO2/SiO2. Les effets des paramètres de dépôt comme la distance torche-substrat (d), la puissance micro-onde incidente et le débit de précurseur de titane (TTIP) sur (i) la morphologie et (ii) la structure cristalline des couches ont été étudiés. Dans la mesure où ces couches sont appliquées dans le domaine de la photocatalyse hétérogène, l’optimisation du procédé vise dans un premier temps à permettre l’obtention d’une grande surface spécifique et à favoriser la croissance de la phase anatase. En plus de l’étude de la phase plasma (par spectroscopie d’émission optique) et des interactions thermiques plasma – surface, une caractérisation complète du matériau obtenu dans les conditions optimisées ont permis de proposer un mécanisme de croissance de la couche en mode statique. Ce dernier met en évidence une croissance par réaction de surface dans la zone centrale du dépôt et une croissance par agglomération de nanoparticules préalablement formées en phase plasma, dans sa zone périphérique. Enfin, la potentialité du dépôt d’oxydes mixtes TiO2/SiO2 a été explorée sur une large gamme de ratio Si/Ti. Il a été montré que quelle que soit la distance torche – substrat, trois phases sont détectées : SiO2, TiO2 et TixSiyOz. Lorsque d=10 mm, la phase de TiO2 est cristallisée sous la forme anatase, alors que lorsque d=30mm, l’ensemble de la couche est amorphe. L’addition d’une faible quantité de silice (environ 3%) au TiO2 cristallisé permet d’augmenter l’activité photocatalytique du matériau d’environ 15%. Une étude préliminaire a de plus permis d’obtenir un dépôt sur de larges surface grâce à la mise en mouvement du substrat, ouvrant la voie à de plus larges applications. / An open air chemical vapour deposition process, using an axial injection torch (TIA) was developed for the deposition of TiO2 and TiO2 / SiO2 thin films. The effects of deposition parameters such as the torch-to-substrate distance (d), the incident microwave power and the titanium precursor (TTIP) flow rate on (i) the morphology and (ii) the crystalline structure of the layers were investigated . Since these layers are applied in the field of heterogeneous photocatalysis, the process optimization aimed to obtain a high surface area and to promote the growth of anatase phase. Besides the study of the plasma phase (by optical emission spectroscopy) and the plasma - surface interactions, a complete characterization of the film deposited in the optimized conditions enabled to provide a growth mechanism in the static mode. It was suggested that (i) the central zone of the deposit results from surface reactions and (ii) the peripheral zone results from the surface agglomeration of nanoparticles previously formed in plasma phase. Finally, the deposition of mixed oxides TiO2 / SiO2 was investigated over a wide range of Si / Ti ratios. It has been shown that whatever the torch-to-substrate distance, three phases were detected: SiO2, TiO2 and TixSiyOz. When d = 10 mm, the TiO2 layer is crystallized in the anatase form, whereas when d = 30 mm, the entire layer is amorphous. The addition of a small amount of silica (about 3%) to the anatase TiO2 increased the photocatalytic activity of about 15%. A preliminary study consisting in the deposition on large areas by moving the substrate, opens the way for wider applications.

京都大学 / 0048 / 新制・課程博士 / 博士(人間・環境学) / 甲第20475号 / 人博第825号 / 新制||人||197(附属図書館) / 28||人博||825(吉田南総合図書館) / 京都大学大学院人間・環境学研究科相関環境学専攻 / (主査)教授 吉田 寿雄, 教授 内本 喜晴, 教授 田部 勢津久, 教授 加藤 立久 / 学位規則第4条第1項該当 / Doctor of Human and Environmental Studies / Kyoto University / DFAM

Continuous population growth and rapid industrial advancement and development have paved the way for ever increasing environmental pollution. At present, water pollution is a serious global issue that threatens environmental sustainability. The contamination of aquatic bodies with potentially toxic organic and inorganic substances are the result of world-wide anthropogenic activities. These pollutants can have detrimental health consequences on humans and ecosystems. Over the past decades, techniques such as chemical precipitation, ion-exchange, adsorption, membrane filtration, and electrocoagulation-flocculation have been developed and employed for the treatment of drinking and wastewater. Among the currently available techniques, pollutant removal by adsorption is most promising due to its cost-effectiveness, simplicity in operation, environmental friendliness, and abundance of adsorbents. This study emphasized the utilization of biochar (BC), after appropriate surface modification, for the removal of potentially toxic contaminants. In the first study, a base activated biochar was synthesized by treating the biochar with potassium hydroxide (KOH) at 700 ℃ in a muffle furnace for 1 h. The resulting high surface area biochar (KOHBC) was used for the removal of Cr(VI), Pb(II) and Cd(II). In the second study, a biochar-supported polyaniline hybrid was synthesized for aqueous chromium and nitrate adsorption. Introduction of amine and imine groups to the biochar facilitated the removal of these contaminants. In the final study, a composite containing Fe-Ti oxide/biochar (Fe2TiO5/BC) was synthesized for sorptive removal of metal cations, oxy anions, inorganics, and organic contaminants from aqueous solutions. Additionally, this composite was used as a photocatalyst towards aqueous methylene blue (MB) degradation. The surface chemistry and composition of these adsorbents were examined by PZC SEM, TEM, XPS, FTIR, TGA, elemental analysis, and surface area measurements.

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