Aerosol-gel Process Research Articles

Up-conversion emission in rare earth-doped Y 2Ti 2O 7 sol–gel thin films

Yttrium titanate (YTO) thin films doped with rare earth elements have been deposited using the aerosol–gel process. The up-conversion emission (UPE) of films doped with erbium and/or thulium has been studied with respect to the film crystallization degree and rare earth concentration. The effects of ytterbium codoping have been considered as well. Mechanisms that control UPE of YTO films are discussed with respect to the experimental conditions. It is shown that films, which selectively emit in the blue ( 1G 4→ 3H 6 transition of thulium ions), green ( 2H 11/2→ 4I 15/2 and 4S 3/2→ 4I 15/2 transitions of erbium ions), or red ( 4F 9/2→ 4I 15/2 transition of erbium ions), can readily be achieved.

Luminescence properties of ORMOSIL films doped with terbium complexes

Luminescence properties of sol–gel SiO2–TiO2 ORMOSIL films doped with various terbium complexes were studied. 3-(Trimethoxysilyl) propyl methacrylate and tetraisopropyl-orthotitanate complexed with methacrylic acid were used as sol–gel precursors for film deposition. In situ rare earth complexation was performed through the direct incorporation of TbCl3 and 1,10-phenanthrolin (Phen), phthalic acid (Phta), or 2,2′-bipyridyl (Bipy) ligand in the sol–gel precursor solution. ORMOSIL coatings were deposited using the aerosol–gel process, which is an original deposition method based on the sol–gel polymerization of a liquid film produced from an ultrasonically sprayed aerosol. ORMOSIL films containing terbium complexes exhibited a strong green emission, which was intensified through post-treatment temperature optimization. The highest photoluminescence intensities were measured on films doped with Tb(Phen)3+ complex and heat treated at 150°C, while films doped with Tb(Bipy)3+ complex and heat-treated at the same temperature exhibited the longest lifetimes.

Photoinduced processes in Aerosol-gel deposited ormosil films

Photopolymerizable ormosil films have been deposited using the Aerosol-gel process. Methacryloxypropyl-trimethoxysilane (MTPS) and tetraisopropyl-orthotitanate (TIPT) complexed with methacrylic acid (MAA) were used as sol-gel precursors. Photoinduced processes were sensitized using commercially available photoinitiators. Fourier transform infrared (FTIR) characterization as well as thickness and refractive index measurements have been performed to study photoinduced polymerization and densification mechanisms in ormosil films. Particular attention is paid to the interactive effects of titanium species and photoinitiator on the photoinduced processes.

Microstructure and photoluminescence properties of sol–gel Y2−xErxTi2O7 thin films

Abstract Optically active Y2−xErxTi2O7 (YETO) thin films have been successfully deposited using the aerosol–gel process. The effects of post-deposition rapid thermal annealing and conventional thermal annealing heat-treatments have been investigated. The corresponding thin film microstructure is described and discussed in terms of crystallisation degree, mean crystallite size, and porosity. Strong photoluminescence (PL) at 1.53 μm is observed under 980 nm excitation. PL properties are found to depend closely on the film crystallisation degree. PL emission spectra exhibit sharp peaks for crystalline films and a wide band for amorphous ones. PL decay curves are also very closely related to the film microstructure and the corresponding lifetimes range between 2 and 7 ms for a similar erbium concentration.

Characterization of optically active and photocurable ORMOSIL thin films deposited using the Aerosol process

Aerosol-gel process is a deposition method based on the sol-gel polymerization of a liquid film produced from an ultrasonically sprayed aerosol. This process offers an attractive alternative for the deposition of photocurable SiO2—TiO2 ORMOSIL films. 3-(trimethoxysilyl) propylmethacrylate and tetraisopropyl-orthotitanate complexed with methacrylic acid were used as sol-gel precursors. Doping with a terbium:sulphosalicylic acid complex was also studied to test the deposition of spectroscopically active photocurable films. FTIR spectroscopy has been used to study the precursor solutions and ORMOSIL films. It is shown that titanium precursor incorporation enhances the solution reactivity, which yields optical quality thin films. Photopolymerization and photoluminescence properties of the films are reported and discussed with respect to the experimental parameters. The results allow envisaging the UV-imprinting fabrication of Aerosol-gel-derived active waveguides.

Aerosol–gel deposition of photocurable ORMOSIL films doped with a terbium complex

Photocurable SiO 2 –TiO 2 ORMOSIL films have been deposited using the aerosol–gel process. 3-(trimethoxysilyl) propylmethacrylate and tetraisopropyl-orthotitanate complexed with methacrylic acid were used as sol–gel precursors. Doping with a terbium:sulphosalicylic acid complex was also studied to test the deposition of optically active photocurable films. Photopolymerization and photoluminescence properties of the films are reported. The results demonstrate the potential of UV-writing of aerosol–gel deposited active thin films.

Aerosol–gel deposition and spectroscopic characterization of pyrochlore films heavily doped with erbium ions

Abstract Optically active films in the Y2Ti2O7–Er2Ti2O7 (YETO) system have been deposited using the aerosol–gel process. Photoluminescence properties closely depend on the film crystallization degree. Dilution of erbium ions within a crystalline Y2Ti2O7 matrix (YETO solid solution) allows preventing photoluminescence concentration quenching induced by short range distance interactions. Consequently, heavily doped films with good photoluminescence properties can be obtained. First studies of a YETO-derived microcavity demonstrate the potential of YETO films for integrated optics applications.

Influence of crystallisation on the photoluminescence properties of Y2-xErxTi2O7 sol-gel thin films

Optically active Er2Ti2O7 (ETO) and Y2-xErxTi2O7 (YETO) films have been successfully deposited using the aerosol-gel process. Several heat-treatment procedures are investigated in the 600–850 °C range. ETO and YETO films start to crystallise in the pyrochlore phase at about 750 °C, depending on the heat-treatment time. Crystalline YETO films form a solid solution where the erbium ions are well diluted. Up-conversion emission (UPE) in the visible wavelength range and infrared photoluminescence (PL) at 1.53 μm are investigated. PL spectra are composed of several sharp peaks. Stark splitting of the 4I13/2 and 4I15/2 erbium levels is analysed. A clear correlation between spectroscopic properties and film microstructure is evidenced. YETO films exhibit strong PL compared to ETO films. PL lifetimes of up to 8.6 ms were measured on YETO films at an erbium concentration of 2×1020 ions/cm3. The YETO compound is found to be a suitable material, improving the erbium active properties.

Functionality of aerosol-gel deposited TiO2 thin films processed at low temperature

TiO2 thin films have been deposited using the Aerosol-gel process and heat-treated at low temperature. Functional coatings necessitate reasonably good abrasion resistance in order to support possible damages related to a targeted application. Besides, specific applications of TiO2 films require additional criteria, e.g. a tailored refractive index, a controlled chemical composition or a suitable crystallization degree. In this paper, we present several low temperature preparation procedures that answer the different criteria and allow to envisage applications on thermally sensitive substrates.

Aerosol-gel deposition of optically active thin films in the system Y2Ti2O7-Er2Ti2O7

Optically active thin films in the system Y2Ti2O7-Er2Ti2O7 (YETO) have been deposited using the Aerosol-gel process. Depending on the heat-treatment temperature, amorphous or crystalline films could be prepared in the range 600–950°C. The study shows that dilution of erbium ions within a Y2Ti2O7 (YTO) matrix allows to prevent short range distance interactions between those ions and to promote good photoluminescence properties of YETO films. These properties are discussed and compared with those of sol-gel derived silica films doped with erbium.

Calcium phosphate coatings prepared by aerosol-gel

The aerosol-gel process has been assayed for the deposition of calcium phosphate (CaP) coatings. The deposition conditions have been preliminarily studied in order to obtain polycrystalline hydroxyapatite (HAP) coatings. The evolution of composition, structure and morphology was monitored by FTIR, XRD and SEM techniques as a function of the sintering temperature. HAP coatings deposited on TiAlV substrates were further characterized by Auger and indentation techniques in order to measure their quantitative composition and adhesive strength, respectively. The results corroborate the high quality of aerosol-gel derived HAP coatings.

Aerosol-gel-derived Microcrystalline Hydroxyapatite Coatings

Highly porous microcrystalline hydroxyapatite (HAP) coatings have been prepared from calcium nitrate and phosphoric acid based sols by the aerosol-gel process. The coatings were studied after sintering at different temperatures with the use of Fourier transform infrared spectroscopy, x-ray diffraction, energy disperse x-ray microanalysis, scanning electron microscopy, and transmission electron microscopy. The composition, structure, and morphology of the coatings sintered at 650 °C fit fairly well highly porous HAP. These coatings were reproduced onto TiO2/Si substrates and studied by Rutherford backscattering. It is shown that even after chemical etching, an adherent calcium phosphate phase remains attached to the TiO2/Si substrate.

Surface Modification of Cyclic Olefinic Copolymers for Bio-Mems Microfluidic Devices

AbstractCyclic Olefin copolymers (COC) are a new class of polymers that may prove to be extremely useful in injection molding of micron scale fluidic devices. In microfluidic devices it is desirable to have a hydrophilic surface such as in flow driven by capillary action. However, such hydrophilic surfaces tend to display protein deposition when contacted with blood unlike hydrophobic surfaces. Alternatives to capillary action are then needed to control fluid flow for hydrophobic surfaces. Our goal in this research is to tune the slightly hydrophobic COC surfaces through simple surface modifications that are amenable to injection molding and other processing methods. In this study, the surface of an injection molded microfluidic component made from COC was modified in order to change the surface properties important to bio-fluidic devices. Some of the techniques used in this study were plasma treatments and ASG (aerosol gel) coating. Plasma treatments were conducted by using O2, CF4 and their combination gas. O2 treated surfaces became hydrophilic with increasing time of treatment. Combining O2 and CF4 made the surfaces more hydrophobic compared to CF4 only. The structural changes after the plasma treatments were examined by ATR (Attenuated Total Reflectance) spectroscopy. Titania and silica particles from the ASG process were synthesized from titanium iso-propoxide and tetraethoxysilane, respectively. Titania coated surfaces became more hydrophilic and the silica coated surfaces did not have much change in their surface characteristics. The hydrophobicity of the plastic surfaces was measured by their contact angle with water. The implication of these treatments on bio-fluidic devices and their adaptation to the injection molding process will also be discussed.

Mechanical and in vitro testing of aerosol–gel deposited titania coatings for biocompatible applications

The biocompatible properties of sol–gel titania have increased the interest in the mechanical properties of this material in the form of functional coatings for prosthetic applications. In the present work, titania coatings with thicknesses of 1 μm have been prepared using the aerosol–gel process. The main objective has been to evaluate the mechanical properties of the coatings and to prove their in-vitro biocompatibility. For this purpose, the hardness and Young's modulus of the coatings were measured by nanoindentation with loads in the 6–30 m n range. A continuous increase of these magnitudes was observed for the coatings treated at increasing sintering temperatures (150–800°C). The hardness and the Young's modulus ranged between 15.8–19.5 GPa and 142–186 GPa, respectively. This behaviour has been confirmed by measurements of the plastic energy of deformation in 10 m n full loading–unloading tests and by determination of the mean indentation creep under 30 m n loads. The films were additionally characterised by XRD, FTIR and ellipsometry to study the chemical and structural changes produced by sintering. Biocompatibility tests are very conclusive. Cells seeded on aerosol–gel titania coatings grow while adhered onto the surface. These coatings are thus of potential interest for the enhancement of the properties of prosthetic TiAlV alloys.

Optically active coatings deposited from an ultrasonically generated aerosol

Two deposition techniques, based on the ultrasonic pulverisation of a metal–organic liquid solution, have been developed and tailored for the preparation of optical oxide coatings. Both techniques are low-cost deposition processes, fully compatible with in-line technologies for mass production. The ultrasonic pulverisation leads to the formation of an aerosol that is deposited on a substrate surface either by pyrolysis in the vapour phase (Pyrosol process) or by sol–gel transformation of a liquid film deposited at room temperature (Aerosol–gel process). The preparation and properties of thin films deposited using these techniques for applications in integrated active optics are described.

Photoluminescence of terbium-organic complex in aerosol–gel-derived planar waveguides

This work deals with the low-temperature preparation of optically active silica-based materials. Tb3+-doped silica monolithic gels were elaborated at 40 °C. Tb3+–SSA-doped SiO2–TiO2 thin films were deposited by an original sol–gel approach, the aerosol–gel process, and heat-treated at 150 °C. Organic complexation of terbium ions was used to improve the active properties of doped silica gels and thin-film samples. Spectroscopic characterisations are reported for these samples. Photoluminescence increase by a factor two was observed for complexation by sulphosalicylic acid.

Aerosol–gel preparation of optically active layers in the system Er/SiO 2–TiO 2

Er-doped silica–titania multilayer coatings have been successfully deposited using an original sol–gel deposition technique: the Aerosol–gel process. This study is the first step toward Aerosol–gel preparation of active planar wave guides. In this paper, we report on the physical, chemical, optical, microstructural and spectroscopic properties of the multilayer coatings. A new optically active crystalline phase, Er 2Ti 2O 7 (ETO), has been identified. This study shows that, depending on the experimental conditions (titanium and erbium content, heat treatment temperature), ETO can be obtained in the form of nanocrystallites dispersed in a transparent amorphous matrix.

Aerosol-gel deposition and low temperature heat-treatment of SiO 2 layers

Aerosol-gel deposited SiO 2 layers were obtained after heat-treatment in air at 80°C. The layers were produced from reactive solutions specially designed for Aerosol-gel process implementation. A two-step solution preparation procedure was used, in order to control separately hydrolysis and condensation reactions. An effective reactivity control was achieved by adjusting the pH value from two during the first preparation step to four during the second step. The solutions appeared very stable in the diluted state, and very reactive during the post-deposition drying stage, producing a well developed and densified SiO 2 network at low temperature. A competition mechanism between condensation and reesterification was put in evidence during aging of the solution at room temperature or at 60°C. Layers were characterized by FTIR spectroscopy, 29SI-NMR, ellipsometry and by using simple mechanical quality evaluation tests. The results show that a good film mechanical resistance is the consequence of a suitable adjustment of the solution reactivity. Depending on the reactivity, mechanically resistant layers can be produced after a heat-treatment at only 80°C.

Doped TiO 2 coatings made by aerosol-gel process

Doped TiO 2 coatings made by aerosol-gel process

Elaboration at 80°C of SiO2 Layers Deposited by Aerosol-Gel Process

The aerosol-gel process is a thin film deposition technique based on the sol-gel polymerization of a liquid film deposited from an ultrasonically sprayed aerosol. SiO2 layers have been deposited by aerosol-gel process from TEOS solutions prepared using a two-step procedure. After a post-treatment at 80°C, the layers have a remarkable abrasion resistance and a high refractive index. In this paper, the chemical mechanisms involved in the formation of SiO2 layers at low temperature are studied by FTIR spectroscopy and related to the processing conditions.