In recent years, electro-optic polymers have been used to make various optical devices in the telecommunication field due to several advantages, such as large and fast electro-optic (EO) response. Semiconductor nano-crystals promise even higher response speed due to the unique quantum confinement mechanism, and they also show very high EO response because of surface and quantum size effects. Many investigative efforts have been made in the area of semiconductor nano-clusters. These efforts mainly focus on synthesizing high quality particles, and their physical and chemistry properties (luminescence spectra, nonlinear optical, and other effects), but their electro-optic properties and potential uses in devices have not been fully investigated, so there is still much work to do in this aspect. For application of electro-optic polymers in electro-optic devices, the challenges are to develop more stable electro-optic polymers with higher electro-optic coefficients. The electrostatic self-assembly (ESA) technique has many advantages over traditional polymer electro-optic film synthesis processes, such as spin coating. For ESA-generated EO films, no poling field is needed, high orientation of the EO polymer can be obtained which does not degrade with time, so the films can be very stable, and this processing is easily compatible with semiconductor VLSI technology. This is a very attractive technique. The goal of this research is to develop new electro-optic materials by means of ESA techniques and to use them to form improved performance next generation electro-optic devices, with emphasis on two kinds of electro-optic materials: nano-sized II-VI semiconductors (CdS, CdSe), and electro-optic active polymers (chromophores), and their potential use in electro-optic devices. In this research work, II-VI semiconductor nano-clusters have been synthesized, with particle diameters ranging from 4 nm to several tens of nanometers. There is a difference in peak positions of absorption and photo luminescence spectra, related to defects in nano-crystals. Larger CdS particles have larger differences than small CdSe particles. Particle sizes measured by absorption spectrum and by HRTEM methods are very close. Based on quantum mechanical theory, peak spectral shifts as a function of particle size can be predicted, but the theoretical results are typically far from the experimental results, because many complicating factors should be considered. Films fabricated by ESA have much stronger absorption than spin coated films, and exhibit a slight blue shift in peak position wavelength. Photo luminescence spectra also show a blue shift for ESA films with respect to spun films. Polymeric electro-optic films were also fabricated by the ESA technique. Effects due to applying an external electrical field during the ESA process on film growth and properties have also been investigated. Peak position, optical density and wavelength at maximum absorption, all increase with the number of bilayers, and films made under external fields have lower absorption and peak wavelength than those of films fabricated without an external field. These results are related to the order parameter, and indicate that molecule alignment can be improved by the application of an external field during the process of ESA film growth. CdSe nano-clusters have a much higher electro-optic coefficient than their bulk crystal counterparts. In comparison with polymers, they have totally different origins in their electro-optic effects. For both nano-cluster-and chromophore based ESA films, electro-optic coefficients are hi gher than those of spin-coated films, and no poling voltage is needed. The reasons have been fully discussed. This result means that the ESA technique is effective to align and hold the dipoles in films and to intensify the electro-optic effect. CdSe quantum dots need 17. 5 ms to complete their physical orientation due to a rotation of the permanent dipole moment. Therefore, at lower frequencies (<100Hz), electro-optic modulation mainly stems from the orientation of the permanent dipole moment. At frequencies higher than 100 Hz, the electro-optic modulation mainly arises from the induced dipole moment orientation and pure electron movement. The ratio of the electro-optic coefficients r333/r113 > 3. This means that ESA films cannot be treated as an ideal isotropic system with the C v symmetry, and interactions should be considered. Quadratic Kerr electro-optic coefficients have a similar frequency dependence to that of the linear electro-optic coefficients r333 and r113. This indicates that the orientational distribution of the CdSe quantum dots particularly contributes to the quadratic electro-optic modulation. From the FT-IR measurement of the films, proton irradiation can break the N=N double bonding in pi-conjugated bridges, leading to damage of the conjugating structure, so causing a decrease of the EO coefficient. But the thermal and temporal stability of ESA films are much better than those of spin coated films; this is a significant feature of ESA technique. The effect of an external field and film thickness on the optical and electro-optic properties of ESA films has been investigated. Electro-optic coefficient decreases with thickness. Electrical field influences the electronic states of the chromophores. Based on the properties of electro-optic films, the applications of polymer and nano-cluster electro-optic films are discussed. A nano-cluster CdSe electro-optic film has a higher refractive index than the PS-119 polymer film, and these values they are much lower than that of semiconductor wafers, but slightly higher than optical silica glasses. Accordingly optical silica glasses are the ideal substrates for those films. By analysis, the cutoff thickness was determined, which defines the minimum film thickness required for light propagation. For channel waveguides, the aspect ratio w/t, w, and t are determined versus the refractive index of the electro-optic films. Modulator beam length and modulation index were discussed, for high speed operation. Modulator beam length should be carefully chosen to obtain high modulation index; similarly important is the refractive index match between core, substrate, and cladding layers. For high speed operation, traveling wave electrode designs were considered, based on effective refractive index and impedance matching. The effective dielectric constant and characteristic impedance as a function of electrode configuration (sizes) were diagramed, and this served as a basic design suggestion for traveling wave electrodes. / Ph. D.

Thin nanoporous films are attractive for many potential uses for example gas separation, catalysis, filtration of viruses, ore flotation, or as low-dielectric-constant materials. Zeolite and mesoporous materials are the two important nanoporous material classes. In this thesis, we synthesized and characterized two different thin nanoporous films; (i) mesostructured films at the mica-solution interface; (ii) mechanical exfoliated zeolites. The mesoporous materials are well-defined pore shoe and size, and exhibit various morphologies, such as thin films, etc. In contrast, zeolites are a kind of perfect crystal and the morphologies are strongly related to their structures and are difficult to control. Therefore, first we synthesis mesostructured films at mica-solution interface in acidic solution. In-situ Atomic Force Microscopy (AFM) has been used to reveal the formation process of organic and inorganic mesophase films at the molecular level. Then, we synthesized two-dimensional zeolite structures via mechanical exfoliation process that does not involve any chemical intervention and can be applicable to a wide variety of structures with different chemical makeup. Three different zeolite structure nanosheets related to the structure code MWW, UTL, and MFI have been prepared. AFM and TEM have been used to characterized the exfoliated single nanosheet. In order to broaden the application of the single zeolite nanosheet, platinum nano-clusters are encapsulated within mechanical exfoliated zeolite MFI nanosheets by ion exchange from aqueous solution of [Pt(NH3)4](NO3)2. High-angle annular dark field scanning transmission electron microscopy has been used to indicate the Pt clusters in the zeolite MFI structures. Because of the property of the mechanically as-synthesised exfoliated MFI nanosheets that is the long hydrocarbon chains are essentially intact on both sides of the inorganic layer, and can prevent thickening of the zeolite MFI nanosheets along b-axis, we use the mechanically exfoliated MFI as seeds for further growth to form large scale MFI membrane with uniform nano-thickness. Encapsulating noble metals within the channels or cavities of zeolites has already drawn numerous attentions because the well-defined zeolite structure is able to constrain the metal nanoparticle (NPs) aggregation size and enhance the diversity and activity for catalysis. We use the organic surfactant (C22-6-6Br2) and [Pt(NH3)4](NO3)2 as the structure and metal precursor to form Pt-containing nanowires; and use F- to inhibit the premature precipitation of Pt precursors. After involving F-, the Pt-containing nanowire structures were generated.

Les aciers ODS (Oxide Dispersed Strengthened Steels), renforcés par des dispersions de nano-oxydes métalliques (à base d'éléments Y, Ti et O), sont des matériaux prometteurs pour les réacteurs nucléaires de génération IV. La compréhension fine des mécanismes mis en jeu lors de la précipitation de ces nano-oxydes permettrait d'améliorer la fabrication et les propriétés mécaniques de ces aciers ODS, avec un fort impact économique en vue de leur industrialisation. Pour étudier expérimentalement ces mécanismes, une approche analytique par implantation ionique est utilisée dans cette étude, permettant de contrôler différents paramètres de synthèse de ces précipités comme la température et leur concentration. Ce projet a permis de démontrer la faisabilité de cette méthode et d'étudier le comportement d'alliages modèles (à base d'oxyde d'aluminium) sous recuit thermique. Des alliages Fe-10Cr de haute pureté ont été implantés avec des ions Al et O à température ambiante. Les observations de microscopie électronique en transmission ont montré que des nano-oxydes apparaissent dans la matrice de Fe-10Cr dès l'implantation à température ambiante, sans recuit subséquent. Les défauts créés lors de l'implantation ionique sont à l'origine de la mobilité des éléments introduits, permettant la nucléation de ces nanoparticules, de quelques nm de diamètre. Ces nanoparticules sont composées d'aluminium et d'oxygène, et également de chrome. Les examens en haute résolution montrent que leur structure cristallographique correspond à celle d'un composé hors équilibre de l'oxyde d'aluminium (de type γ-Al₂O₃). Les traitements thermiques effectués après implantation induisent une croissance de la taille de ces nano-oxydes, et un changement de phase qui tend vers la structure d'équilibre (de type α-Al₂O₃). Ces résultats sur des alliages modèles s'appliquent entièrement aux matériaux industriels : en effet l'implantation ionique reproduit les conditions du broyage, et les traitements thermiques sont à des températures équivalentes à celles des traitements d'élaboration thermo-mécaniques. Un mécanisme de la précipitation de nano-oxydes dispersés dans des alliages ODS est proposé dans ce manuscrit. / ODS (Oxide Dispersed Strengthened) steels, which are reinforced with metal dispersions of nano-oxides (based on Y, Ti and O elements), are promising materials for future nuclear reactors. The detailed understanding of the mechanisms involved in the precipitation of these nano-oxides would improve manufacturing and mechanical properties of these ODS steels, with a strong economic impact for their industrialization. To experimentally study these mechanisms, an analytical approach by ion implantation is used, to control various parameters of synthesis of these precipitates as the temperature and concentration. This study demonstrated the feasibility of this method and concerned the behaviour of alloys models (based on aluminium oxide) under thermal annealing. High purity Fe-10Cr alloys were implanted with Al and O ions at room temperature. Transmission electron microscopy observations showed that the nano-oxides appear in the Fe-10Cr matrix upon ion implantation at room temperature without subsequent annealing. The mobility of implanted elements is caused by the defects created during ion implantation, allowing the nucleation of these nanoparticles, of a few nm in diameter. These nanoparticles are composed of aluminium and oxygen, and also chromium. The high-resolution experiments show that their crystallographic structure is that of a non-equilibrium compound of aluminium oxide (cubic γ-Al₂O₃ type). The heat treatment performed after implantation induces the growth of the nano-sized oxides, and a phase change that tends to balance to the equilibrium structure (hexagonal α-Al₂O₃ type). These results on model alloys are fully applicable to industrial materials: indeed ion implantation reproduces the conditions of milling and heat treatments are at equivalent temperatures to those of thermo-mechanical treatments. A mechanism involving the precipitation of nano-oxide dispersed in ODS alloys is proposed in this manuscript based on the obtained experimental results, and the existing literature.