In this study, the characteristics of atomic layer deposited TiO2 films on Gallium Arsenide substrate were investigated. The physical and chemical properties were measured and surveyed. And an Al/ALD-TiO2/GaAs MOS structure was used for the electrical characterizations. For the electrical property improvements, we investigated the atomic layer deposited TiO2 films by the (NH4)2Sx treatments for GaAs substrate. The leakage currents and the hysteresis loop flatband voltage shift can be improved for ALD-TiO2 films on S-GaAs. Furthermore, in order to resist the leakage current from the grain boundary of the polycrystalline TiO2 films, amorphous-like structure of TiO2 thinner films are investigated. The combination of sulfur passivation and amorphous-like structure thinner films is sufficient to improve the electrical properties effectively.

Using liquid phase deposition (LPD) fluorine nitrogen altogether doping porous titanium dioxide nanoparticle, general has not doped the titanium dioxide to be able the step to be 3~3.2eV, is opposite to the absorption spectrum for ultraviolet ray 380nm about, but sunlight energy only then 6% in ultraviolet ray, but the visible light has occupied about 52% energy, because grows the titanium dioxide which comes out mainly is applies in the light catalyst and the solar cell, all hoped may enhance to the luminous energy absorption, therefore only then dopes the fluorine, the nitrogen in the titanium dioxide, the goal is in order to adjust the titanium dioxide the light to absorb the boundary (optical absorption edge), at present dopes the method can dope the impurity only then minority produces the key with the titanium dioxide to binding thus result not well, penetrates ammonium hexafluorotitanate and the boric acid by the liquid phase sedimentation mixes under 40 degrees grows ammonium oxofluorotitanate discoid crystal, in the middle of this forerunner fills the very many fluorine nitrogen, after annealing and then produces the titanium dioxide to penetrate the fluorine nitrogen which the ESCA analysis contains compared to, again applies in the solar cell when can observe the annealing temperature differently when remains the fluorine nitrogen which and the key ties to the solar cell efficiency. At present the titanium dioxide light absorbs the boundary to be possible to reach the blue light region, applies the porous titanium dioxide in the dye sensitization solar cell anode, present fill factor may reach about 29.6%.

Due to the high electron mobility compared with Si, III-V compound semiconductors (GaAs) has been applied widely for high-speed devices. The titanium oxide (TiO2) has not only has high dielectric constant but has well lattice match with GaAs substrate. Therefore, the high-k material TiO2 was chosen to be the gate oxide in this study. The major problem of III-V compound semiconductors is known to have poor native oxide on it and leading to the Fermi level pinning at the interface between oxide and semiconductor. The C-V stretch-out phenomenon can be observed and the leakage current is high. The surface passivation of GaAs with (NH4)2Sx treatment (S-GaAs) can prevent it from oxidizing after cleaning and improve the interface properties. In order to passivate the grain boundary of polycrystalline ALD-TiO2 film and the interface state, the fluorine from liquid-phase- deposited SiO2 solution can achieve the goal effectively. In addition, the post-metallization annealing (PMA) is another efficiency way to improve the ALD-TiO2 film quality. The mechanism of PMA process is the reaction between the aluminum contact and hydroxyl groups existed on TiO2 film surface. Then the active hydrogen is produced to diffuse through the oxide and passivate the oxide traps.

TiO2 nanoparticles were successfully synthesized by a wet impregnation method using SBA-15 or AP-SBA-15 as the template for confining the growth of TiO2 nanocrystals followed by acclimation at 550 ¢J in muffle furnace for 6 hrs. These uniform nano-sized TiO2 particles are difficult to prepare using the conventional sol-gel process since the decomposition of the Ti precursor proceeds rapidly to form large aggregates, resulting in a wide particle size distribution. The as-synthesized samples were characterized with powder X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectra (FTIR), and nitrogen adsorption isotherm. Results from TEM reveal that the TiO2 nanoparticles are highly dispersed in the channels of SBA-15; subsequent removal of the SBA-15 channels with HF gives the pure TiO2 nanoparticles having a diameter of ~ 9 nm. On the other hand, the bulk TiO2 outside the SBA-15 channels mainly forms aggregated large TiO2 particles. Prior treatment of SBA-15 surface with the coupling agent APTS (AP-SBA-15) enhances the easy chemosorption of a great number of titanium. Subsequent hydrolysis of the anchored Ti complexes and calcinations of the amorphous TiO2, anatase TiO2 nanocrystals yields uniform TiO2 nanoparticles having diameter of ~ 5 nm, as compared to the unconfined bulk TiO2 of 15~50 nm in diameter.

No description available.

Photocatalysis is a promising technology that can effectively convert the solar energyinto sustainable green energy. However, theoretical studies on the molecular mechanisms of photocatalytic reactions are rare. This thesis is devoted to investigate several typical photocatalytic reactions on the surfaces of the most popular photocatalysis TiO2 with density functional theory. We start our study with the characterization of both the free and trapped hole on the surface generated by the light. The oxidation of physisorbed H2O molecule by the hole trapped at bridge oxygen on rutile TiO2(110) surface has been studied. The hole is found to transferto the molecule via the anti-bonding orbital as a result of the hybridization between the hole orbital and the HOMO of the molecule. The energy and symmetry mismatching between the trapped hole orbital and the HOMO of the molecule explains why the trapped hole cannot directly transfer to the chemisorbed H2O molecule. On the other hand, we have found that the chemisorbed H2O moleculecan be more efficiently oxidized by the free hole with a lower barrier and higher reaction energy compared to the oxidation by the trapped hole. In this reaction, the free hole is transferred to the chemisorbed H2O after the dissociation. This is different from the oxidation of chemisorbed H2O on anatase TiO2(101) surface by free hole, in which the hole is transferred concertedly with the dissociation of themolecule.     In order to understand the hole scavenger ability of organic molecules, the oxidation of three small organic molecules (CH3OH, HCOOH and HCOH) onanatase TiO2(101) surface has been systematically investigated. The concerted hole and proton transfer is found for all these molecules. The calculations suggestthat both kinetic and thermodynamic effects need to be considered to correctly describe the hole transfer process. The order of hole scavenging power is found tofollow: HCOH &gt; HCOOH &gt; CH3OH &gt; H2O, which agrees well with experiments.     Photo-selective catalytic reduction of the NO by NH3 and the photooxidationof CO by O2 are closely related to the environment application. Both reactionsinvolve the formation and/or breaking of non R–H bonds. The mechanism for the photoreduction of NO proposed by experiment has been verified by our calculations.The role of the hole is to oxidize the adsorbed NH3 into ·NH2 radical, which canform a NH2NO complex with a gaseous NO molecule easily. The photooxidation of CO by O2 is the first multi-step photoreaction we ever studied. By combining thepotential energy surfaces at the ground and excited state we have found that thehole and electron both take part in the reaction. A molecular mechanism which is in consistent with various experiments is proposed.     These studies show that density functional theory is a powerful tool for studying the photocatalytic reaction. Apparently, more work needs to be done in orderto improve the performance of the existing materials and to design new ones thatcan take advantage of the solar light more efficiently / <p>QC 20140522</p>

TiO2 films have attracted much attention because of their photoactivity and superhydrophilcity. For the superhydrophilicity studies, most research focused mainly on enhancing superhydrophilicity of Ti02 film under UV illumination. A hydrothermal-dip-coating superwetting TiO2 film was synthesised and found to preserve its superhydrophilicity up to 6 months. This non-UV superwetting TI02 film potentially opens an alternative application as bioactive layer for growing hydroxyapatite (HAP) coating, used extensively as prosthetic device medically. In this research, a systematic study was carried out, aiming to understand and optimise the hydrophilicity and superwetting properties of Ti O2 film without UV illumination. The effect of (i) PEG concentration, (ii) film thickness and (iii) agglomerate size of TiO2 on the wettability of TiO2 film was investigated. Although the presence of PEG does affect the porosity of the film, PEG concentration does not play significant role in retaining superhydrophilicity of the film. The evidence from AFM showed that surface roughness is the key parameter to control in order to retain the superhydrophilic wetting and antifogging behavior of the synthesised films, which can be tuned by simple manipulation of the multilayer assembled of TiO2 nanoparticles through varying the film thickness and agglomerate size. A film thickness of (????140nm) yielded the optimum roughness (rms =23nm) for the creation of the best superhydrophilic wetting behavior. Thicker films smoothened the film roughness, and therefore causing detrimental effects on their superhydrophilic wetting properties. Smaller agglomerate size was also found to be important in retaining the roughness film. The photoactivity of the "non UV illuminated"superhydrophilic film was found that be comparable with a Pilkington Activ??? in degrading methyl blue. The growth of Hydroxyapatite (HAP), synthesised via organic-inorganic hybrid method, and the mechanical stability of the HAP coating on the TiO2 films applied on titanium foil were studied. Homogenous HAP coating was found to grow only on the T O2 film with superhydrophilic properties. However the coating was of poor mechanical stability. Surface -OH was found to play an important role in aligning the phosphonate groups in HAP recursor during dip-coating.

L’objective est d’améliorer l’activité photocatalytique de TiO2 sous irradiations UV et Visible. Pour contourner les limites de TiO2 intrinsèque nous envisageons une fabrication de nanocomposite plasmonique à base de nanofils de TiO2 périodiquement organisés et assemblés avec des nanoparticules plasmoniques. Pour la fabrication des nanofils de TiO2 mécaniquement stables, deux approches ont été réalisées. La première approche est basée sur la croissance sélective en phase vapeur, la deuxième approche consiste en l’utilisation d’un moule de membranes AAO et d’un dépôt de films conformes par ALD. En parallèle les films de TiO2déposés par ALD sont assemblés avec les nanoparticules plasmoniques d’or. Les différentes architectures de TiO2 sont valorisées par des tests photocatalytiques (UV et Visible) sur les polluants modèles. Une nouvelle approche de la fabrication des films mesoporeux d’H-TiO2 avec efficacité photocatalytique à la fois sous irradiation UV et Visible est développée. / The objective of this thesis is to improve the photo-response of well-known photocatalytic material such as TiO2, which is usually only active in the UV range. The basic idea is to assemble several approaches within one device to improve the photocatalytic properties: fabrication of periodically-organised TiO2 nanostructures and their assembly with plasmonic nanoparticles. Two fabrication strategies were investigated for these purposes. The first approach consists of selective vapour phase growth. The second approach implements the use of an AAO template. In parallel, TiO2 films deposited by ALD and assembled with plasmonic gold nanoparticles are investigated. The photocatalytic measurements on various TiO2 architectures were performed in both irradiation ranges UV and Vis. A new fabrication approach of mesoporous H-TiO2 films was developed giving promising results of photocatalytic efficiency improvement in both UV and Visible ranges.

Ce travail décrit la synthèse et le comportement de nouveaux photocatalyseurs à base de dioxyde de titane utilisés pour des applications environnementales. Dans la première partie, la pertinence des composés modèles testés, le colorant acide orange 7 (AO7) et le 4-Chlorophénol (4-CP), pour des traitements photocatalytiques à base de TiO2 a été étudiée et validée. Cette étude a été centrée sur l’effet de la concentration initiale en composé et sur la vitesse d’agitation pendant la réaction photocatalytique. La deuxième partie est consacrée principalement à la synthèse et la caractérisation des suspensions de particules colloïdales de TiO2. Leur séparation puis leur récupération après le traitement étant pratiquement impossible l’immobilisation de ces particules sur des supports de type hydroxydes doubles lamellaires (HDL) a été étudiée afin de préparer un matériau composite TiO2/HDL présentant une activité photocatalytique comparable à celle du dioxyde de titane pur. Un deuxième type de composite basé sur des mélanges de TiO2/SiO2 a également été envisagé et utilisé dans la préparation de fines couches efficaces pour la photodégradation de l’hexane. Enfin, le comportement photocatalytique d’HDL pur à base de zinc et de chrome, sans addition de TiO2, a également été étudié et est présenté dans la partie finale de cette thèse. Les matériaux préparés ont été caractérisés par différentes analyses chimiques, diffraction et fluorescence des rayons X, microscopie électronique à transmission et à balayage, spectroscopie IR à transformé de Fourier, analyse thermogravimétrique, mesure du potentiel Zeta, diffusion de la lumière, mesure d’adsorption N2. Les différents matériaux ont été testés photocatalytiquement via la photo-Oxydation en solution aqueuse de l’acide orange 7 (AO7), du 4-Chlorophénol (4-CP) ou du bleu de méthylène à différents pH. L’activité photocatalytique du matériau composite à base de TiO2/SiO2 sous forme de film fin a été évaluée en phase gaz en présence d’hexane. / This work describes the behaviour and fabrication of new photocatalysts based on titaniumdioxide for the purpose of environmental applications. It consists of five closely connectedparts. In the first part the suitability of chosen model compounds, azo dye Acid Orange 7(AO7) and 4-Chlorophenol (4-CP), for photocatalytic activity assessment of TiO2 was studied.This study was focused on the effect of different initial concentrations of model compoundand different rates of stirring during photocatalytic reaction. The second part then focusedmainly on the synthesis and characterization of aqueous colloidal suspensions of TiO2. Theseparation of TiO2 particles in the form of colloidal suspensions and their regeneration afterthe reaction, while keeping the same photocatalytic properties, is almost not possible.Therefore, it was necessary to find an appropriate method how to immobilize these particleson the support or in the form of composite. The layered double hydroxides (LDH) werechosen as one of suitable supports for TiO2 photocatalyst. The focus was kept on thepreparation of TiO2/LDH composites with the same or higher photocatalytic activity as purecolloidal titanium dioxide. The second chosen type of composite was based on twocomponentTiO2/SiO2 material and these composites were used for the preparation of thinlayers. Photocatalytic behaviour of pure LDHs and their possible use as photocatalyst withoutTiO2 addition was also studied and described in a final part of this work. Prepared materials were characterized by chemical analysis, X-Ray diffraction andflorescence, transmition electron microscopy, scanning electron microscopy, Fouriertransform infrared spectroscopy, thermogravimetric analysis, dynamic light scattering, zetapotential measurement and N2 adsorption. As another step, materials were tested asphotocatalyst by the photooxidation of Acid Orange 7, 4-Chlorophenol and Methylene Blue indifferent pH in aqueous medium. Photocatalytic activity of TiO2/SiO2 composites in the formof thin films was tested in gaseous phase using hexane as a model pollutant. It was found that quantum yields of 4-CP degradation for all prepared alkaline colloidalsuspensions of TiO2 were lower than those obtained for acidic TiO2 colloidal suspensions. Inthe contrary to the quantum yield of acidic TiO2, the quantum yield of alkaline suspensionsdecreased during the aging. Prepared TiO2/Mg2Al1.5 nanocomposites exhibited higherphotocatalytic activity than the original TiO2 in basic conditions and also it was much easierto recover the photocatalyst after reaction by simple sedimentation. In the case of TiO2/SiO2composites, it was found that composite prepared with TiO2:SiO2 ratio 1:1 has higherphotocatalytic activity in aqueous media than starting pure TiO2 but with increasing SiO2content reaction rate of AO7 degradation decreases. Thin layers of TiO2:SiO2 compositeprepared from simultaneously co-Precipitated particles (they have improved crystallinity inrelation to pure TiO2) are able to photocatalyticaly degrade hexane. In the case of pure LDH,it was proved that even noncalcined Zn2CrCO3 LDH can produce HO• radicals. However,mixed oxides (containing ZnO) prepared by LDH calcination at temperatures higher than500°C, showed higher efficiency.

Filmes finos de TiO2 e N:TiO2, e multicamadas TiO2/N:TiO2 foram crescidos sobre substratos de aço AISI 316 e Si(100), por meio da técnica de deposição química de organometálicos em fase vapor (MOCVD). Foram produzidos filmes com diferentes espessuras, nas temperaturas de 400 e 500°C. Os filmes foram caracterizados utilizando-se técnicas de difração de raios X (DRX), espectroscopia de fotoelétrons excitados por raios x (XPS) e microscopia eletrônica de varredura (MEV). A resistência à corrosão foi avaliada por meio de testes de polarização potenciodinâmica em eletrólito 3,5%p NaCl. Filmes não dopados, crescidos a 400°C, apresentaram TiO2 anatase, enquanto que os crescidos a 500°C apresentaram a fase rutilo, além de anatase. Nos filmes dopados com nitrogênio (7,29 e 8,29 at% a 400 e 500°C, respectivamente), em ambas as temperaturas, houve a formação de TiO2 anatase, bem como de fases contendo nitrogênio. Os filmes de TiO2 crescidos a 400°C ofereceram melhor proteção contra a corrosão que os crescidos a 500°C. Filmes crescidos a 500°C apresentaram estrutura colunar, que representa alto nível de porosidade, enquanto que os filmes crescidos a 400°C apresentaram estrutura mais densa. A dopagem não foi eficiente para proteger o substrato contra corrosão, provavelmente devido à formação das fases contendo nitrogênio. Os resultados para os testes com filmes compostos por multicamadas sugerem que aqueles com mais interfaces apresentam melhor resistência à corrosão. O processo de corrosão das amostras se inicia na superfície do filme, que está em contato com o meio agressivo, originando pites, que permitem ao meio corrosivo acessar o substrato metálico. O metal é atacado e dissolvido sob o filme, e resulta na delaminação do filme. / TiO2 and N-doped TiO2 (N:TiO2) thin films, and TiO2/N:TiO2 multilayered films were grown on AISI 316 steel substrates, and Si (100) by using metallorganic chemical vapor deposition (MOCVD) technique. The growth of the films was carried out at 400 and 500°C, and films with different thicknesses and structures were obtained. Titanium dioxide films were produced by using only titanium isopropoxide IV as both titanium and oxygen sources. In order to obtain N:TiO2 films, NH3 was also added to the system. The films were characterized by using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) The corrosion resistance was evaluated by potentiodynamic polarization tests in a 3.5wt% NaCl electrolyte. TiO2 undoped films, grown at 400°C, presented anatase, while those grown at 500°C showed the rutile phase, besides anatase. For nitrogendoped films (7.29 and 8.29 at% at 400 and 500°C, respectively), at both temperatures, TiO2 anatase was formed, as well as nitrogen-containing phases. TiO2 films grown at 400°C provided better protection against corrosion than those grown at 500°C. Films grown at 500°C showed a columnar structure, which represents a high level of porosity, while the films grown at 400°C presented a denser structure. Doping was not efficient to protect the substrate against corrosion, probably due to the formation of nitrogen containing phases. The corrosion results for tests with multilayered films suggest that those with more interfaces present better resistance to corrosion. The corrosion of the samples starts at the surface of the films, which is in contact with the aggressive medium, causing pitting in this film, which allows the corrosive medium to reach the metallic substrate. The metal is attacked and dissolved under the film, and results in film delamination.