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.     

Understanding and improving the deposition conditions of SiO2 thin films obtained by ultrasonic sol-gel procedure

Sol-gel deposition of an ultrasonically atomized aerosol has been proven to be a convenient thin film deposition method. Flexibility of the ultrasonic process allows the use of a large range of source solutions. In this paper we describe and discuss the deposition conditions of SiO₂ films. The chemical parameters are contemplated and we discuss the influence of ultrasonic waves on the reliability of our process. Source solutions and SiO₂ film properties are studied by viscosimetry, Fourier Transform IR spectroscopy and spectroscopic ellipsometry.     

Patterned Deposition of Sol-Gel Thin Films Using an Airbrush

ABSTRACT

In this article, we present a method to pattern glass substrates with sol-gel derived thin films. This method is based on the aerosol deposition of sol-gel precursor solutions using an inexpensive, commercially available airbrush. The technique was demonstrated using Cy5-doped sol-gel thin films for the creation of wavelength conversion devices. The films deposited were mechanically and chemically rigid, and patterns could be achieved with a resolution limit of approximately 250 μm. Constructing channel waveguides was also attempted using both zirconium- and titanium-based sol-gel thin films. Deposited thin films of these materials showed graininess that limited the ability to couple light into the films and increased the observed scatter. However, light was successfully coupled into the titanium-based sol-gel film using small lens-like structures created on the glass surface.     

Atmospheric Pressure Plasma Discharge for Polysiloxane Thin Films Deposition and Comparison with Low Pressure Process

An atmospheric pressure dielectric barrier plasma discharge has been used to study a thin film deposition process. The DBD device is enclosed in a vacuum chamber and one of the electrodes is a rotating cylinder. Thus, this device is able to simulate continuous processing in arbitrary deposition condition of pressure and atmosphere composition. A deposition process of thin organosilicon films has been studied reproducing a nitrogen atmosphere with small admixtures of hexamethyldisiloxane (HMDSO) vapours. The plasma discharge has been characterized with optical emission spectroscopy and voltage-current measurements. Thin films chemical composition and morphology have been characterized with FTIR spectroscopy, atomic force microscopy (AFM) and contact angle measurements. A strong dependency of deposit character from the HMDSO concentration has been found and then compared with the same dependency of a typical low pressure plasma enhanced chemical vapour deposition process.     

Plasma enhanced aerosol–gel method: a new way of preparing ceramic coatings

The sol–gel process is widely used for the production of powders, coatings and bulk materials. However, being a wet-chemical technique, it has certain limitations related to properties of aqueous colloidal solution, especially when applied as a coating. The most frequently used methods, such as dip- and spin-coating, are difficult to apply onto more complex substrates. In these cases, the aerosol–gel deposition method can be regarded as the solution of this problem. In the present article, a novel plasma enhanced aerosol–gel method of coatings production is presented. A novelty of this method is based on an integration of the aerosol–gel deposition of thin films and their low temperature plasma treatment. Owing to the above, all stages of the coatings production process—substrate preparation, film deposition, and its plasma treatment, can be carried out in a single reactor. The design and operational scheme of such device is presented in this work. Using this device, thin coatings were first deposited on substrates and then plasma treated. The effect of deposition and plasma discharge conditions on morphology and chemical structure of the films has been studied. It was found that plasma treatment had a substantial influence on all the examined properties of the aerosol–gel deposited coatings.     

Thin films of functionalized amorphous silica for immunosensors application

Within the framework of the development of an optical immunosensor, the sol-gel process has been used to prepare a thin film of amorphous silica, deposited by spin coating on a gold-coated glass slide, and possessing chemically active functional groups (SH, NH₂...). After activation of the sol-gel film in aqueous buffers by a bifunctional coupling agent, biological molecules such as antibodies could be covalently bonded on or inside the sol-gel film. Therefore, the behavior in aqueous solutions of the functionalized silica thin films has been analysed by Surface Plasmon Resonance (SPR) and guided wave propagation. Results show a modification of the thickness and of the refractive index of the silica film. Pore size range has been deduced by the infiltration of different molecular weight dextran molecules diluted in water into the sol-gel material. Immunosassays have demonstrated biological activity of antibodies which are covalently linked to or entraped in the sol-gel film.     

Vapor-Gel Deposition Method for Oxide Thin Films

In this paper, we attempt to formally establish the chemistry of a vapor-gel process for the low temperature deposition of thin films. A number of applications of such a process will be discussed mostly on a theoretical basis, with the exception of one or two particular aspects that we have experimentally demonstrated so far. The essential components of the deposition apparatus will be described in detail along with some discussions on their operation conditions. Finally, we conclude this paper by systematically comparing the vapor-gel method to other well-known thin film fabrication techniques including the sol-gel method.     

Photostability Study of Nanoporous TiO2 Film Electrodes in Basic Solutions

The nanoporous TiO2 film electrodes have been prepared by a sol-gel deposition process The photostability of the electrodes in basic solutions has been studied. The results show that the photostability of the electrodes decreases rapidly in strong basic solutions with or without methanol. The reaction of holes to O^2- produces active O^2- atoms and the products O^2- atomsoxidize Ti^3 to Ti^4 on TiO2 film surface and subsurface. This results in the TiO2 film electrodes unstable in basic solutions both without methanol and with too low concentration.     

Evaporated thin films of insulating poly-(tetrabromo-p-phenylenediselenide)

It has been shown that thin insulating film at the interface transparent conductive oxide/organic electroluminescent film could improve the performance of organic electroluminescent diodes (OLED). Such insulating film can be inorganic or organic. Poly-(tetrabromo-p-phenylenediselenide) (PBrPDSe) has been proved to be an efficient insulating film in OLED. The properties of these evaporated PBrPDSe thin films have been systematically studied by IR absorption, X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, electron spin resonance and optical transmission measurements. It is shown that, when the deposition temperature is kept below the decomposition temperature of the polymer, tetrabromo-p-phenylenediselenide molecule is preserved during the deposition process. However the polymer, which is insoluble in powder form, becomes soluble after deposition. It can be concluded that films are mainly composed of oligomers of tetrabromo-p-phenylenediselenide.The electrical properties of SnO₂/PBrPDSe/Al thin films structures have been studied. The current-voltage characteristics exhibit a rectifying behaviour with a forward direction corresponding to a positive bias of the transparent conductive oxide film, the SnO₂.     

Low-temperature preparation of nanocrystalline anatase films through a sol-gel route

Nanocrystalline anatase (TiO₂) films were prepared at very low temperature through a sol-gel route using titanium isopropoxide and hydrogen peroxide in ethanol. Crystallization occurred after film deposition at 35°C in an atmosphere saturated with water vapor. Both thin and thick films of nanocrystalline anatase were prepared. Observed particle size in crystallized films is approximately 20–40 nm as measured with AFM. No residual organic material was apparent through FTIR after crystallization occurred. Dynamic light scattering studies performed on this system indicate that particle size measured in solution is strongly dependent on the amount of agitation samples received prior to measurement.     

In-situ fluorescence imaging of sol-gel thin film deposition

Pyranine was used as a fluorescence probe to monitor the chemical evolution in-situ during thin film deposition by the dip coating process. The sensitivity of the pyranine luminescence to protonation/deprotonation effects was used to quantify changes in the water/alcohol ratio in real time within the depositing film as the substrate was withdrawn from the coating reservoir. The spatially resolved spectral results clearly showed that preferential evaporation of alcohol occurred with increasing distance from the reservoir and that the maximum water content reached rather high values near the drying line. Correlation of the luminescence results with the interference pattern of the drawn films allows the solvent composition in the film to be mapped as a function of film thickness. These experiments demonstrate for the first time that luminescent organic molecules may be applied to the processing science of sol-gel thin film deposition.     

Stable PZT sol for preparing reproducible high-permittivity perovskite-based thin films

Results are reported on the development of high-K dielectric material using sol-gel chemistry. High permittivity thin film capacitor have been developed based on lead-zirconate-titanate (PbZr _x Ti_1−x O₃, PZT) ferroelectric ceramic layers deposited on to 6″ platinized silicon wafer using the spin-coating technique. Selecting a diol-based solvent as diluting medium, a PZT solution with remarkable shelf life up to 1 year has been prepared. To synthesize such a reproducible and time-stable solution, a ripening step before dilution has been introduced. The deposition process has been also optimized to reduce the required number of coatings and to avoid intermediate high-temperature annealing. By carefully controlling environmental parameters, the as-developed PZT solution leads to reproducible high-performance thin film capacitor, enabling an industrial use. Thus, 200-nm thick PZT layers with permittivity as high as 900, capacitance as high as 40 nF/mm2 and breakdown voltage up to 30 V have been obtained.     

Structure evolution in the PbO-ZrO2-TiO2 sol-gel system: Part II—Pyrolysis of acid and base-catalyzed bulk and thin film gels

The pyrolysis behavior of acid and base-catalyzed bulk and thin film Pb(Zr, Ti)O₃, or PZT, gels as well as their components have been studied using Thermo-Gravimetric Analysis (TGA), Differential Thermal Analysis (DTA), and Dynamic Mass Spectrometric Analysis (DMSA). The TGA/DTA data reflected the structural differences of the acid and base-catalyzed gels. Gels obtained using an acid catalyst were less cross-linked, denser, and more homogeneous than base-catalyzed gels. Based on the understanding of structure evolution in the silica system, the various events in the TGA/DTA studies of acid-catalyzed PZT gels were attributable to specific mechanisms. The DMSA showed that primarily water, 2-methoxyethanol, acetone, and carbon dioxide were evolved for both acid and base catalyzed PZT gels. The presence of the latter two volatiles was associated with the decomposition of the acetate group via the carbonate route. Acetate and carbonate groups were determined by Fourier Transform Intrared Spectroscopy (FTIR) to be present in the gel structure prior to pyrolysis. Differences in the synthesis of the prehydroiyzed solution were found to affect the amount of residual alkoxy groups, gel structure, pyrolysis behavior, and therefore, the resulting microstructures of sol-gel derived PZT thin films. Finally, some suggestions for improving the processing of sol-gel PZT thin films are given.     

基于酚藏花红掺杂有机改性溶胶-凝胶膜的亚硝酸盐光学传感器

利用溶胶-凝胶法,研制出基于有机改性溶胶-凝胶膜的亚硝酸盐光学传感器.以甲基三乙氧基硅烷为有机交联剂,与正硅酸乙酯进行水解和缩聚,制备了酚藏花红包埋的有机-无机硅酸盐杂化材料,并采用旋涂法将其涂抹在显微镜载玻片上,形成薄膜.在酸性条件下,NO<'-><,2>与酚藏花红掺杂的溶胶-凝胶膜发生作用,使溶胶-凝胶膜从红色变为...     

ATR-SEIRAS study of the adsorption of acetate anions at chemically deposited silver thin film electrodes

The adsorption of acetate anions at silver thin film electrodes has been studied by in-situ infrared spectroscopy experiments with a Kretschmann internal reflection configuration. Stable silver thin films were chemically deposited on germanium substrates. Ex-situ STM images show mean grain sizes ranging from ca. 20 to 90 nm for deposition times between 2 and 20 min, respectively. The thickness of the silver film, measured by AFM, is typically around 10 nm for a deposition time of 10 min and increases up to 50 nm for a deposition time of 20 min. Roughness factors around 2.3 have been obtained for the silver films from the charge involved in lead underpotential deposition (UPD). A noticeable enhancement of the infrared absorption of adsorbed species (SEIRA effect) is observed when the silver films are used as electrodes under internal total reflection conditions. Maximum intensities of the adsorbate bands were observed for a deposition time of 10 min and an angle of incidence around 65 degrees . The potential-dependent infrared spectra of acetate and interfacial water are consistent with previously proposed models involving the existence of weakly hydrogen-bonded water molecules at potentials below the potential of zero charge and the reorientation of water molecules at potentials above the potential of zero charge. Results reported in this work suggest a weak interaction between acetate and water molecules adsorbed at the silver thin film electrodes.     

Kinetic Study of the Maillard Reaction in Thin Film Generated by Microdroplets Deposition

The Maillard reaction kinetics in the confined volume of the thin film produced by ESI microdroplet deposition was studied by mass spectrometry. The almost exclusive formation of the Amadori product from the reaction of D-xylose and D-glucose toward L-glycine and L-lysine was demonstrated. The thin film Maillard reaction occurred at a mild synthetic condition under which the same process in solution was not observed. The comparison of the thin film kinetics with that of the reaction performed in solution showed strong thin film rate acceleration factors.     

Early Stages of CeO2 Thin-film Nucleation and Growth with Photo Irradiation

In this paper, the early stages of nucleation and photoirradiation growth of CeO₂ thin films have been studied. Cyclic voltammetry, chronoamperometry and scanning electron microscopy were used to analyze the nucleation process of CeO₂ thin films deposited on the anode with photo irradiation. Experimental results show that the anodic deposition process with photo illumination is controlled by diffusion. Compared with the dark state, photo illumination mainly contributed to increase the current density of the three-dimensional nucleation process, because photo illumination is helpful to create active sites and accelerate the nucleation progress on the surface that a thin ceria film has been formed. Two-dimensional nucleation process mainly exists within the initial 2 s, and then only three-dimensional instantaneous nucleation process continues, which may be the main reason why the thickness of the CeO₂ film can continue to grow with photo illumination but not in the dark state. Increasing the deposition overpotential can promote two-dimensional nucleation and growth rate, whilst when the potential exceeds 0.65 V, three-dimensional current density decreases. The li-miting factor at that time may be the diffusion rate of cerium ions in the solution towards the electrode substrate.     

In situ FTIR investigation of MMA plasmas,plasma-polymerized films,and reaction mechanisms

Methyl methacrylate (MMA) plasmas and plasma-polymerized methyl methacrylate (PPMMA) films were studied in situ with FTIR and FTIR/ATR (attenuated total reflection) in an r.f. capacitively coupled glow discharge. A statistically designed experiment was conducted by varying the r.f. power, process pressure, and MMA flow rate. MMA plasma fragments were identified from the gas-phase FTIR measurements. They include the intermediate species such as dimethylketene, formaldehyde, allene, and propene; small hydrocarbons such as acetylene, methane, and ethylene; and oxygenates such as carbon dioxide, carbon monoxide, and methanol. Statistical analysis techniques (correlation analysis, analysis of variance and regression analysis) were used on both gas and film data. Gas-phase reaction mechanisms are proposed, and the relationship between the gas and film data is investigated to understand the film deposition chemistry. The deposition rate is positively correlated to the relative concentrations of MMA fragments which are identified as the major film precursors in the deposition process. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 587–602, 1998     

Influence of Precursor Chemistry on the Formation of MTiO3 (M = Ba,Sr) Ceramic Thin Films

Thin films of BaTiO3 and SrTiO3 were prepared by a chemical solution deposition method. The impact of the precursor on the processing, on the microstructure, and on the dielectric properties has been studied by systematically varying the alkyl chain length of the used Ba- and Sr-carboxylates. In addition, the effect of stabilizing the Ti-alkoxide precursor by acetylacetone has been investigated. The decomposition process, the crystallization behavior, and the film morphology were analyzed by glancing incidence XRD, reflectance FT-IR and field emission SEM. Distinct precursor effects on the thin film morphology and properties were revealed. Part of this influence can be attributed to an intermediate complex carbonate phase which forms for selected carboxylates with short alkyl chains. The high transformation temperature of this intermediate phase to the perovskite obviously has a marked influence on the crystallization and densification process of the alkaline earth titanate thin films. We correlate the morphological differences of the films to their dielectric properties.