Conventional Sol-gel Technique Research Articles

Eu-doped indium tin oxide thin films fabricated by sol–gel technique

We have fabricated Eu-doped indium tin oxide thin films via the conventional sol–gel technique, and confirmed that the doped Eu atoms were chemically incorporated into the indium tin oxide lattice by substituting the In sites. Optical spectra indicated that the Eu-doped films were free of any impurities leading to additional vibrational effects. Valence states of Eu ions in our Eu-doped indium tin oxide films were discussed in connection with Eu concentration.

On the etching of silica and mesoporous silica films determined by X-ray reflectivity and atomic force microscopy

X-ray reflectometry and atomic force microscopy were used to characterize the etching effect of 0.1 mol dm − 3 NaOH solution on mesoporous silica films < 100 nm thick produced by the evaporation induced self assembly route using a nonionic triblock co-polymer as the template. The effect of this treatment on films that had been partly condensed at 80 °C or fired at 400 °C in air are compared to non-porous films produced using conventional sol–gel technique. The evolution of film structure was monitored by atomic force microscopy and X-ray reflectometry. Thicknesses obtained from these measurements were used as an order parameter to determine the etch rate. For the mesoporous films, distinct stages corresponding to (a) film compression; (b) removal of the weakly organised caplayer; (c) progressive removal of bilayers of pores/silicated layres; and finally film collapse were revealed.

An organically modified silicate molecularly imprinted solid-phase microextraction device for the determination of polybrominated diphenyl ethers

An organically modified silicate (ORMOSIL) SPME stationary phase molecularly imprinted with BDE-209 has been successfully fabricated by conventional sol–gel technique from phenyltrimethoxysilane and tetraethoxysilane. The thickness of the ORMOSIL-SPME stationary phase, on fused-silica optical fibres, was measured to be ca. 9.5 μm with a volume of ca. 0.12 μL. Rebinding assays and Scatchard analysis revealed that the imprinted ORMOSIL-SPME stationary phase possessed a binding affinity, K B , of 7.3 ± 1.7 × 10 10 M −1 for BDE-209, with a receptor site density, B max, of 1.2 × 10 −3 pmol per SPME device. Besides its molecular template, the ORMOSIL-SPME stationary phase also showed good affinity (log K B ≥ 9.5) for smaller BDE congeners commonly found in the natural environment. The density of receptor sites within the imprinted matrix for those smaller BDE congeners was even higher than that for BDE-209. This may be attributable to the binding site heterogeneity of the imprinting process that creates deformed binding sites that are suitable for the accommodation of the smaller BDE congeners. Compared to the commercially available polyacrylate and polydimethylsiloxane SPME stationary phases, the imprinted ORMOSIL-SPME devices showed much higher pre-concentration ability towards polybrominated diphenyl ethers (PBDEs), even in direct immersion sampling at room temperature. Coupled with GC–NCI-MS and GC-μECD, the imprinted ORMOSIL-SPME device was able to achieve detection sensitivity of 0.2–3.6 pg mL −1 and 1–8.8 pg mL −1, respectively, for commonly occurring BDE congeners, including medium to high molecular weight PBDEs. The imprinted ORMOSIL-SPME device has been successfully applied to monitor PBDE contents in municipal wastewaters.

Micro- and Macroscopic Observations of the Microtexture, the Dielectric and Piezoelectric Properties in Bulk and Multilayer Pb (Zr, Ti)O&lt;sub&gt;3&lt;/sub&gt;

The objective of the present paper is to give an insight of the fundamental properties strongly depended on the crystallizing phase, grain size, thickness, including stoichiometry of material. The subject of this work is the lead zirconate titanate [Pb(Zr,Ti)O3, PZT] with its composition located at the morphotropic phase boundary (MPB) that were prepared by a solid state method [1] and a conventional sol-gel technique [2,3]. The samples prepared by the first methods are in a bulk form while the latter the multilayer. The physical property and the dielectric and piezoelectric properties of the PZT samples have been discussed comparatively when the sample size decreasing from the bulk to the thin-film scale.

Local structural environment and photoluminescence of Er 3+ ions doped in indium tin oxide nanopowder

It has been experimentally demonstrated that the indium tin oxide can be doped with rare earth element through the conventional sol–gel technique. Erbium in its trivalent state replaces the indium site in the indium tin oxide lattice. Homogeneously distributed and optically activated Er 3+ ions then allow a strong photoluminescence emission at ∼1.5 μm. Reduced particle size and the existence of Sn are believed to affect the local structural environments of doped Er 3+ ions, thus contributing to the radiative emission properties: Large spectral bandwidth without concentration quenching is useful for practical applications.

The effect of sputter-deposited TiO 2 passivating layer on the performance of dye-sensitized solar cells based on sol–gel derived photoelectrode

The aim of this work is to prevent short-circuits in the solar cells and back transfer of electrons due to direct contact between the electrolyte and the conductive substrate. A thin passivating TiO 2 under layer was deposited on SnO 2:F coated glass substrate by facing target sputtering technique with different sputtering pressures: 0.1, 1.0 and 2.0 Pa. An upper nanoporous TiO 2 layer was deposited by conventional sol–gel technique with 2.0 g of polyethylene glycol. The variation of photoelectric conversion efficiency of the solar cells with different TiO 2 passivating layers is discussed with the analysis of crystallographic and microstructural properties of passivating and upper nanoporous TiO 2 layers.

Carbon supports for methanol oxidation catalyst

Highly mesoporous carbon was synthesized employing conventional sol–gel technique using resorcinol and formaldehyde. The porous carbon electrodes were characterized by X-ray powder diffraction, N 2 adsorption isotherm, atomic absorption spectroscopy (AAS). Platinum was anchored on support by the incipient wetness method and reduced to its metallic form using sodium formate as a reducing agent. The electrocatalysis for methanol oxidation on carbon supported Pt in acid and alkaline solutions were investigated. It was found that the activity of Pt for methanol oxidation was higher in alkaline than in acid medium. High mesopore surface area of carbon can significantly increase the metal dispersion and affect particle size, which favoured the progress of the electrochemical processes occurring during methanol oxidation.

Microwave synthesis of yttria stabilized zirconia

Yttria stabilised zirconia (YSZ) nanocrystals, with a mean size between 5 and 10 nm, were prepared by microwave flash synthesis. Flash synthesis was performed in alcoholic solutions of yttrium, zirconium chloride and sodium ethoxide (EtONa) using a microwave autoclave (RAMO system) specially designed by authors. Energy dispersive X-ray analysis (EDX), X-ray powder diffraction (XRD), BET adsorption technique, photon correlation spectroscopy (PCS) transmission and scanning electron microscopy (TEM and SEM) are used to characterized these nanoparticles. Compared with conventional synthesis, nanopowders can be produced in a short period (e.g. 10 s), both high purity and stoechiometric control are obtained. Nevertheless, this mean of production is more cheaper and much faster than the ones commonly used to produce yttria stabilized zirconia (YSZ) by conventional sol–gel techniques.

Synthesis of strontium bismuth niobate (SrBi 2Nb 2O 9) using an aqueous acetate–citrate precursor gel: thermal decomposition and phase formation

An aqueous solution–gel route was developed for the preparation of the ferroelectric material strontium bismuth niobate (SrBi 2Nb 2O 9, SBN). Starting from aqueous Bi 3+-acetate and Sr 2+-acetate solutions and an aqueous peroxo-citrato-Nb 5+-precursor solution, this method offers a low-cost and environmentally friendly alternative to the conventional sol–gel techniques. With regard to the deposition of thin films, it is important to gain insight in the behaviour of the precursor during thermal treatment. For this reason the thermal decomposition mechanism of the precursor gel was studied: weight loss and evolved gases were characterized by (hyphenated) TGA–MS and TGA–FTIR, while changes in the solid state during heating were detected using high temperature diffuse reflectance infrared fourier transform spectroscopy (HT-DRIFT). The decomposition in dry air can be divided in four temperature regions. The first two steps are ascribed to the drying of the sample and to the decomposition of the organic matrix, not coordinated to the metal ions. During the third step the coordination sphere of the metal ions is decomposed and finally the residual organic matter is combusted in the fourth region. TEM experiments on freestanding thin films showed that the precursor homogeneity was maintained throughout the entire thermo-oxidative decomposition of the gel. The phase formation of SBN was studied by means of high temperature X-ray diffraction (HT-XRD). At about 425 °C the intermediate fluorite phase is crystallized out of the amorphous precursor. The phase transformation into the desired ferroelectric perovskite phase seems to be dependent on the Bi-content: an excess of Bi lowers the onset temperature of perovskite formation.

Deposition of nanocrystalline diamond and titanium oxide coatings onto pyrolytic carbon using CVD and sol–gel techniques

In this paper, we report the deposition of freestanding nanocrystalline diamond (NCD) films and dense nanocrystalline titanium oxide (nc-TiO 2) coatings onto pyrolytic carbon (PyC) using advanced chemical vapour deposition (CVD) and sol–gel techniques, respectively. The micro-structural properties, such as surface morphology and crystallinity, of PyC, NCD and nc-TiO 2 were characterised using XRD, Raman spectroscopy and SEM analysis. Freestanding NCD films were prepared using our newly introduced time-modulated CVD (TMCVD) process. Furthermore, conventional sol–gel technique was used to uniformly coat PyC with dense nc-TiO 2 coatings. The as-grown nc-TiO 2 coatings were found to display smooth surface profiles and the average crystallite size was in the range approximately 30–50 nm.

Nano-architectural silica thin films with two-dimensionally connected cagelike pores synthesized from vapor phase.

Novel mesostructured silica thin films were prepared on a Si substrate by a vapor-phase synthesis. Vapor of tetraethoxysilane (TEOS) was infiltrated into a surfactant film consisting of a poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer. Nanophase transition from a lamellar structure to a two-dimensional cage structure of a silica-surfactant nanocomposite was found under vapor infiltration. The rearrangement into the cage structure implies high mobility of the silica-surfactant composites in solid phase. The silica thin films have two-dimensionally connected cagelike mesopores and are isotropic parallel to the film surface. The structure of pores of the films is advantageous for next-generation low-k films. The mesoporous structure has a large lattice parameter d of approximately 102 A, silica layer thickness of approximately 58 A, pillar diameter in the middle of approximately 60 A, pore size of approximately 72 A, BET surface area of approximately 729 m(2)/g, and pore volume of approximately 1.19 cm(3)/g. The films synthesized by the vapor infiltration show a lower concentration of residual Si-OH groups compared to the films prepared by a conventional sol-gel method. The films show high thermal stability up to 900 degrees C and high hydrothermal stability. This method is a simpler process than conventional sol-gel techniques and attractive for mass production of a variety of organic-inorganic composite materials and inorganic porous films.

膜リアクタ・デバイス 半導体層間絶縁膜としての周期構造ポーラスシリカ膜の合成

Low-k dielectric materials have been in demand in order to solve the physical limits of interconnects for a new LSI technology system. Ordered mesoporous silica films are promising materials as low-k dielectrics because of their high porosity and high mechanical strength. Here, we show two preparation methods for thermally stable mesoporous silica films.First, a mesoporous silica film was prepared on a silicon substrate using a spin-coating process followed by a vapor treatment using tetraethyl orthosilicate (TEOS). The TEOS-treated mesostructured silica film did not contract during calcination, showing high structural stability. A flat mesoporous silica film about 250 nm thick was grown from the silicon substrate. No silica particle was deposited on the surface of film. FTIR studies suggested that the Si-OH groups in the film significantly decreased after the TEOS treatment. TEOS molecules penetrate into an originally deposited silicate film and react with the silanol groups. The densified silica wall has high structural stability and hardly contracts under a calcination process.Vapor-phase synthesis is another promising method for the preparation of thermally stable mesoporous silica film. We found nano-phase transition of an organic-inorganic nanocomposite under vapor infiltration of TEOS. The rearrangement into a hexagonal periodic structure implies high mobility of the surfactant-silicate composites in solid phase. The vapor infiltration method is a simpler process than conventional sol-gel techniques and attractive for mass production of a variety of organic-inorganic composite materials and inorganic porous films.

Ferroelectrics Templated in Nanoporous Silicon Membranes

A new method is proposed of fabrication of ferroelectric nanostructures using porous silicon as a template. It is shown that with the pore size of about 20 nm conventional sol-gel technique provides embedding of guest material only into the top layer of the host. Optical second harmonic generation is used as a probe to distinguish between paraelectric and ferroelectric phases of embedded nanoparticles.

Ordered Mesoporous Silica Films Synthesized from Vapor Phase

AbstractA novel synthesis route for mesostructured silica films is reported. Nano-phase transition from lamellar phase of surfactant to hexagonal phase of silica-surfactant nanocomposite was found under vapor infiltration. Vapor infiltration was performed using HCl as catalyst source and tetraethoxysilane (TEOS) as framework source. Highly ordered mesostructured silica films are obtained using alkyltrimethylammonium bromide CnTAB (the carbon number in the alkyl chain; n = 8, 10, 12, 14, 16, 18) as templating agent. The d values of the mesostructured silica films increase with increasing the length of the alkyl chain and are controllable by the synthetic temperature. The vapor infiltration synthesis is a simpler process compared to conventional sol-gel techniques and attractive for mass production of a variety of organic-inorganic composite materials and inorganic porous materials. This novel synthetic method provides opportunities for the creation of new materials technologies.

Synthesis and microstructural control of nanocrystalline titania powders via a stearic acid method

Nanocrystalline titania powders doped with alumina with good dispersity were prepared by a novel method, the so-called stearic acid method (SAM). The preparative process was studied by Fourier transform infrared spectroscopy (FTIR). The influence of the alumina dopant concentration on the microstructure of resulting TiO 2 powder was investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Compared with the conventional sol-gel technique, SAM is faster and convenient, and can be used to prepare various mixed metal oxides.

Charge transport mechanism and the effect of poling on the current-voltage characteristics of conducting polyaniline–BaTiO 3 composites

Conducting polyaniline–barium titinate (PANI–BaTiO 3) composites have been synthesized by `in situ' deposition technique by placing the fine grade powder of BaTiO 3 (prepared by conventional sol–gel technique) in the polymerization reaction mixture of aniline — finally yielding the Polyaniline–BaTiO 3 composites. The charge transport process in these composites have been studied by sandwiching the pellets of these composites between the silver and platinum electrodes. It presumably suggests presence of a nonlinear space charge controlled charge transport process. Also, a large hysteresis in the I– V characteristics of these composites has been observed which also supports the space charge controlled conduction. The samples were poled by applying a constant voltage for a fixed time and the I– V characteristics were traced before and after poling. Some striking differences have been observed in the I– V characteristics before and after poling. These have been explained on the basis of creation of an internal electric field due to poling which in turn opposes the externally applied electric field.

Titanium ion substitution ranges for zirconium ion in the Na 1 + xZr 2Si xP 3 − xO 12 system

Ti 4+ ion substitution ranges for Zr 4+ ion have been investigated in the Na 1 + x Zr 2Si x P 3 − x O 12 (NASICON) system synthesized by a conventional solid state reaction using inorganic compounds at the reaction temperatures of 1000, 1100 and 1200 °C. The Ti 4− ion substitution rate was greater in the phosphate-rich region than in the silicate-rich region. In the silicate end member, the Ti 4− ion substitution rate and the melting temperature decreased with increasing Ti 4− ion content of the starting materials. In the narrow range around x ~ 2.5, at low Ti 4− ion content and at low temperatures, the Na 2ZrSi 2O 7 phase segregated. Essentially the same results, except for the Na 2ZrSi 2O 7 phase, have been shown when the NASICON compounds were synthesized by a conventional sol-gel technique using metal alkoxides.

Impregnated SiO 2 gels used as dye laser matrix hosts

Long longevity has been obtained for doped SiO 2 gel samples used in a laser cavity by combining the conventional sol-gel technique with a new process: impregnation with a sol. Results of laser action several months after preparation and storage of the samples are presented.