In this work, we report the effect of annealing temperature on the properties of epitaxial PbZr_0.52Ti_0.48O₃ (PZT) films deposited using sol-gel techniques on (001) Si substrates with a thin, epitaxial SrTiO₃ (STO) interlayer. The STO is grown on silicon using molecular beam epitaxy (MBE) and acts as the template for PZT growth. We report the values for stress, density, thickness, and refractive index vs. anneal temperatures for a thin PZT film. AFM surface roughness values of less than 0.4 nm are typical for this film. XRD patterns show the film to be c-axis orientated, with PHI scans demonstrating that the [100] PZT is orientated along the [110] Si direction. SEM cross-sections show the film morphology is free of gain boundaries and are clear of interfacial layers from the multiple spin/bake/anneal deposition technique, thereby making this material an excellent candidate for electro-optic applications.

Typical characteristics of BaTiO₃ thin films, such as hysterisis behavior, spontaneous polarization below the Curie temperature, faster switching speed etc., are particularly of much attention for high capacitance integrated elements, dynamic random access memories (DRAMs), phase conjugation, holographic optical data storage, two-beam coupling and optical computing. Several techniques have been employed for the fabrication process of such ferroelectric thin films. Among other methods, Sol-Gel and MOD prove to be a powerful and inexpensive means to deposit thin films. The main advantages of these deposition techniques are good homogeneity, ability to precisely control the stoichiometry of the film, lower temperature processing, and the ability to produce high-purity materials for electronics and optics without much investment in equipment. We report the structural characterization of BaTiO₃ films deposited on single crystal Si (100) and MgO (100) substrates by sol-gel process. The films were prepared by the sol-gel process and annealed at different temperatures. In this method the sol-gel polymerization is initiated by adding water to a solution of alkoxide in methanol. The chemical conditions are generally chosen in such a way that nearly complete hydrolysis occurs. A series of experiments ranging from X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), were conducted on the spin-coated films and their correspondingly annealed films at different temperatures.

The paper focuses on a systematic study of the influence of water on the electrochemical and optical properties of CeO₂-TiO₂ amd WO₃ sol-gel coatings as well as devices made with these layers. The coatings were studied electrochemically in 1 M LiC1O₄ in propylene carbonate electrolyte with water content up to 3 wt%. The intercalculated and deintercalated charge was measured during Cyclic Voltammetry (CV) and Chronoamperometric (CA) cycles up to 500 cycles (TiO₂-CeO₂) and 7000 cycles (WO₃). For CeO₂-TiO₂ it was found to increase from 3mC/cm² (dry electrolyte) up to 11 mC/cm² (3 wt% water). This increase is important for the coloration of EC-devices because the charge capacity of this counter electrode is known to be a limiting factor for the transmission change of the EC-devices. For WO₃ coatings, the transmission change (T_colored-T_bleached)is higher in wet electrolytes (1 wt% water) than dry electrolyte and above all remains constant (74%). These improvements are essentially due to an increase of the kinetics of the intercalation and deintercalation of Li⁺ ions. The electro-optical behavior of solid state EC-devices with and without incorporation of water in the solid electrolyte measured up to 500000 CA cycles is also presented and discussed.

CeO₂-TiO₂ sol-gel coatings are well known as Li-ion storage electrode in electrochromic (EC) devices of the form glass/ TE /WO₃/ electrolyte/ CeO₂-TiO₂/ TE/ glass (TE: transparent electrode, e.g. SnO₂:F, FTO). The charge capacity of the CeO₂-TiO₂ coating is a limiting factor to get a high coloration intensity of such devices. In order to improve the charge capacity of these electrodes, new routes for the preparation of thick porous CeO₂-TiO₂ sol-gel layers were tested. One route was the preparation of thick porous TiO₂ coatings on a conducting glass support (FTO) using a solution of colloidal TiO₂ particles. After heat treatment at temperatures up to 550°C the coatings were soaked in a solution of a cerium-IV (Ce(NH₄)₂(NO₃)₆) or a cerium-III salt (Ce(NO₃)₃ 6H₂O) and heat treated again. Another route was the preparation of sols by mixing a solution of the cerium-IV or cerium-III salt or a colloidal CeO₂-sol with the colloidal solution of TiO₂. After dip coating on FTO-glass the coatings were also heat treated at temperatures up to 500°C. ALl these coatings were studied electrochemically in 1 M LiC1O₄ in propylene carbonate electrolyte. Although thick porous single coatings could be obtained, typically 450 nm for TiO₂ and 600 nm for cerium-titanium oxide, the intercalated and deintercalcated Li⁺ charges remain small and lie in the range of 2 mC/cm² to 3 mC/cm². The reasons for such low charge capacity is discussed.

The impedance spectra of non-sensitized and Ru(II)-sensitized Nb₂O₅ nanoporous coatings have been measured in the dark and under solar illumination using an electroactive electrolyte. All the Nyquist plots consist of a high and a low frequency depressed semicircle. The results have been modeled and fitted by an equivalent electric circuit consisting of a resistor R_s in the series with two parallel RC circuits containing both a constant phase element (CPE). The resistor R_s describes the total resistance of the electrolyte and conducting electrodes (SnO₂:F). The high frequency semicircule (f<1kHz) describes the capacitance and resistance of the semiconducting materials (grain boundaries and interfaces). The low frequency cycle (f < 1 kHz) is related to the formation of a double charge layer capacitance at the nanoparticle/electrolyte interface and a charge transfer resistance. Both values are strongly dependant of the experimental conditions, in particular of the applied potential and the state of illumination. The evolution of the electric elements is presented and discussed. It is shown in particular that the measurements in the dark cannot be directly compared to those under illumination as in teh latter all the Nb₂O₅-film is accessed.

Micrometer-sized spherical particles containing laser dyes such as Rhodamine 6G, DCM and Pyridine 1 have been fabricated by the vibrating orifice technique for the spherical cavity micro-laser. A cylindrical liquid jet of diluted hybrid raw materials passing through an orifice breaks up into equal-sized droplets by mechanical vibration. Then the solvent of these droplets was evaporated during flying with carrier gas and subsequently solidified into dye-doped hybrid-microspheres in ammonium water trap. The microspheres of different dye contents were pumped by second harmonic pulses of Q-switched Nd: YAG laser (532 nm wavelength, repetition rate is 10 Hz) and their photodegradation of lasing intensities were measured against shot number of pumping pulses. Degree of the degradation strongly depended on the pumping power and the dye content incorporated in the microsphere. Suitable pumping power and dye content gave the best date for the photostability: Laser out-put energy was consumed 50% of the initial value after 100,000 pulses for R6G and Pyridine 1, and 240,000 pulses for DCM.

YETO (Y_2-xEr_xTi₂O₇) thin films of good optical quality have been successfully deposited using the Aerosol-gel process. Strong photoluminescence (PL) emission centered at 1.53 μm was detected when pumping in a waveguiding configuration at 980 nm. Different heat-treatment procedures have been used in order to study the relationship between the spectroscopic properties and the thin films microstructure. A clear correlation between microstructure and spectroscopic properties was observed, when passing from amorphous to crystallized YETO. A single exponential PL decay with a lifetime of 7.5 ms was found for crystalline YETO films. The erbium quenching concentration in crystalline YETO is 10²¹ ions/cm³ and the corresponding PL lifetime is 3.5 ms. Our work shows that the dilution of the erbium ions within a Y₂Ti₂O₇ (YTO) matrix allows to prevent short range distance interactions between the active Er³⁺ ions and therefore improves the spectroscopic properties with respect to pure ETO.

The effects of heat treatment on the optical quality of organic-norganic hybrid spherical particles were investigated. The spherical particles with a diameter of 6μm were prepared via sol-gel process from phenyl-tetraethyl-silane(PTES) using the vibrating orifice technique, and they showed strong oscillation signals based on the spherical resonance mode with low power threshold of the incident CW-Ar⁺ laser. Against the heat treatment on the slide glass plate, there were some particles which remained their spherical shape after 400°C heating depending on the condition of sol preparation. The survived particles were also found to have high photo-stability that they were not damaged from the laser irradiation of 514.5nm Ar⁺ light with a power >120mW/particle, while as-prepared particles were bursted by the irradiation <20mW/particles. From the measurements of micro Raman scattering spectroscopy, optical and secondary electron microscope and thermal analysis, the thermal stability of hybrid materials was considered.

The interest of the antireflective coatings applied onto large-area glass components increases everyday for the potential application such as building or shop windows. Today, because of the use of large size components, sol-gel process is a competitive way for antireflective coating mass production. The dip-coating technique commonly used for liquid-deposition, implies a safety hazard due to coating solution handling and storage in the case of large amounts of highly flammable solvent use. On the other hand, spin-coating is a liquid low-consumption technique. Mainly devoted to coat circular small-size substrate, we have developed a spin-coating machine able to coat large-size rectangular windows (up to 1 x 1.7 m²). Both solutions and coating conditions have been optimized to deposit optical layers with accurate and uniform thickness and to highly limit the edge effects. Experimental single layer antireflective coating deposition process onto large-area shielding windows (1000 x 1700 x 20 mm³) is described. Results show that the as-developed process could produce low specular reflection value (down to 1% one side) onto white-glass windows over the visible range (460-750 nm). Low-temperature curing process (120°C) used after sol-gel deposition enables antireflective-coating to withstand abrasion-resistance properties in compliance to US-MIL-C-0675C moderate test.

The conventional dip coating techinques, as it is used for flat surfaces, cannot be applied to deposit homogeneous coatings in optical quality inside tubes. The resulting coatings exhibit large variations in thickness and roughness over the length of the tube and show a morphology with a network of cracks. The main reason for these problems seem to be a delayed and restricted solvent evaporation due to the impediment of a laminar flow and the progressive saturation of the atmosphere in the tube. A modified dip coating technique was therefore developed to allow forced flow conditions inside the tubes by an additional exhausting tube. By means of this modification transparent conducting coatings of sol-gel SnO₂:Sb (antimony-doped tin oxide - ATO) could be deposited on both sides of borosilicate glass tubes (300 mm, inner diamters down to 11 mm) with excellent thickness uniformity and low roughness (Ra≈1nm). After a heat treatment at temperatures up to 500°C, the prepared ATO coatings are mechanically stable and highly transparent (>85% transmission) with a sheet resistance down to 10 kΩ. The coatings can be used as electrodes for electronic devices and electrical heaters or to give antistatic properties to the substrate.

Binary oxide solid products and glasses in the ZrO₂-GeO₂ system with the Ge:Zr molar ratio ranged from 1:1 to 3:1 were synthesized from inorganic precursors in aqueous medium by ammonia stimulated hydrolysis and coprecipitation. The latter were formed due to reaction of Zr(IV)+Ge(IV) solution with precipitating agent. The precipitated xerogels covered a color spectrum from white to red, and the color was more intense with increase of GeO₂ content in the binary ZrO₂-GeO₂ composition. DTA, XRD, IR, and XPS were used for examination of crystalline structure and phase transformations in the coprecipitated amorphous xerogels and thermally treated ZrO₂-GeO₂ products. In samples with excess of germania in the binary ZrO₂-GeO₂ system both tetrahedral and octahedral coordination of Ge occur, resulting in different crystallization behaviors. In line with the stable ZrGe0₄ phase with scheelite structure we have established an appearance of new crystalline phase (called X-phase) for thermally treated (1000°C) samples with Ge:Zr = 2:1 and 3:1 rather than the hexagonal GeO₂ phase.

Sol-gel films doped with MeS (Me=Cd or Pb) nanocrystals or with M_xO_y (M=Ni or Co) nanocrystals have been fabricated. Two different strategies were used: for the sulfides a colloidal doping sol was prepared at room temperature and then mixed with the matrix sol. For the oxides a bifunctional ligand was used, bearing either an amine group capable of coordinating the M ions and hydrolysable siloxane groups for anchoring the metal complex moiety to the silicate matrix. In this case the oxide nanocrystals precipitate at 500°C. Films containing MeS nanocrystals showed both non-linear and active optical properties. Nanocomposite films doped with MxOy showed optical gas sensing properties.

Biomolecules encapsulated in porous silicate glass using the sol-gel process form optically transparent materials capable of biorecognition. We are working to design biosensors from these materials for the detection of glutamate, the major excitatory neurotransmitter in the central nervous system. Previously we demonstrated the ability of glutamate dehydrogenase (GDH)-doped sol-gel bulk materials to measure glutamate at varying concentrations. Here we show that GDH can be encapsulated in a thin film while retaining its enzymatic activity. The films are likely to be reaction limited rather than diffusion limited, as the reaction rate at saturating glutamate concentrations varies linearly with enzyme loading. At a given enzyme loading, the film reaction rate increases with increasing glutamate concentration, demonstrating its potential as a glutamate sensor material. In addition we have shown that the enzyme-doped sol-gel glass can be deposited onto the tip of an optical fiber. The fiber is active and responds to the presence of glutamate.

We report on the fabrication of transparent, conductive and directly photopatternable, pure and Sb-doped tin dioxide thin films. Precursors used were antimony(III)isopropoxide and a photo-reactive tin alkoxide synthesized from tin(IV)isopropoxide and methacrylic acid. The synthesis of methacrylic acid modified tin alkoxide was monitored in-situ using IR- and ESI-TOF mass spectroscopic techniques. Sb-doped organo-tin films were deposited via single layer spin coating. After deposition the films were patterned via photopolymerization, using a mercury I-line UV-lamp. All investigated materials could be patterned with 3 μm features. After development in isopropanol, the films were annealed in air, in order to obtain crystalline and conductive films. The electrical conductivities of the annealed thin films with, and without, UV-irradiation were determined using a linear four-point method. The direct photopatterning process was found to increase the film conductivity for all the Sb-doping levels tested. The mechanisms for the increased conductivity were characterized using AFM, XPS and XRD techniques.

Al₂O₃-SiO₂ glasses doped with Sm³⁺ ions were prepared using sol-gel method, in which the Sm³⁺ ions were reduced into Sm²⁺ by heaing in H₂-gas or irradiating with x-ray. When heated in H₂ gas, the H₂ molecules react with oxygen ions to form H₂O. Removal of the generated H₂O causes the number of oxygen ions surrounding Sm³⁺ to decrease, resulting into the resuction of the Sm³⁺ ions. in contrast, in the x-ray irradiated glass, it is concluded that the Sm³⁺ ions are reduced into Sm²⁺ by electron transfer from the oxygen defect center. The hole defect centers are trapped in oxygen ions boound with Al³⁺ ions. The spectral hole burning of the x-ray irradiated glasses could be burned by the reverse reaction of the reduction of Sm³⁺ ions, that is, the electron transfer from the excited Sm²⁺ into the surrounding oxygen. A short distance between the Sm²⁺ and oxygen defect centers brings fast hole burning. On the other hand, the hole burning in the H₂-treated glasses was performed by the electron transfer between the Sm²⁺ and the trapping center such as Sm³⁺.

Monodisperse spheres of silica and latex were obtained by a surfactant free styrene polimerization and the Stoeber method respectively. Controlling settling either by centrifugation or by dip-coating colloidal crystals could be obtained. Silica inverse opals were prepared by using the latex colloidal crystals as templates and TEOS/ethanol solution. Eu³⁺ containing silica spheres were obtained dispersing silica spheres in Eu(NO₃)₃ isopropanol solutions. Emission spectra suggest the formation of an amorphous Eu³⁺ containing phase well adhered at the spheres surface. The utilization of solutions of trifluoroacetates salts of Pb²⁺ and Eu³⁺ was observed to destroy the silica spherical pattern when samples are treated at 1000°C. In that case nanocrystals of PbF₂ and amorphous silica were obtained after heat treatment