Sol-gel synthesis of nickel oxide thin films and their characterization

Sol-gel method has been employed for the synthesis of nanocrystalline nickel oxide (NiO). The NiO powders were sintered at 400-700 °C for 1 h in an air. Thin films of sintered powders were prepared on glass substrate using spin coating technique and changes in the structural, morphological, electrical and optical properties were studied. The structural and microstructural properties of nickel oxide films were studied by means of X-ray diffraction and field emission scanning electron microscopy. Structural analysis shows that all the films are crystallized in the cubic phase and present a random orientation. Surface morphology of the nickel oxide film consists of nanocrystalline grains with uniform coverage of the substrate surface with randomly oriented morphology. The electrical conductivity showed the semiconducting nature with room temperature electrical conductivity increased from 10^− 4 to 10^− 2 (Ω cm) ^− 1 after sintering. The electron carrier concentration (n) and mobility (μ) of NiO films annealed at 400-700 °C were estimated to be of the order of 1.30 to 3.75 × 10¹⁹ cm^− 3 and 1.98 to 4.20 × 10^− 5 cm² V^− 1 s^− 1.The decrease in the band gap energy from 3.86 to 3.47 eV was observed for NiO sintered between 400 and 700 °C. These mean that the optical quality of NiO films is improved by sintering.     

Sol-gel preparation and properties of TiO2-P2O5 bulk glasses

Monolithic transparent and colorless, or Ti³⁺-free TiO₂-P₂O₅ glasses containing very large amounts of TiO₂ (up to 93 mol%) were successfully prepared by heat-treating the xerogels, which were made from titanium tetraisopropoxide and triethyl phosphate, through the sol-gel reaction. The density and refractive index n_632.8 nm of the sol-gel-derived glasses were higher than the melt-derived glasses of the corresponding compositions. The glasses of TiO₂ content of larger than 80 mol% seemed somewhat porous, but n_632.8 nm of these glasses was very high as 2.2-2.3. Higher density and higher n_632.8 nm than the melt-derived glasses were considered to be due to more abundance of six-fold coordinated Ti⁴⁺ ions.     

Effects of Mg Incorporation on Microstructure and Optical Properties of ZnO Thin Films Prepared by Sol-gel Method

Well-crystallized MgZnO alloy thin films with hexagonal wurtzite structure were fabricated by sol-gel method. With the band gap increases, the surface roughness and the grain size reduces. It is worth noting that the intensity of the band-edge luminescence of Mg doped films enhances with the increase of the Mg content. The microstructure and photoluminescence mechanism have been discussed based on X-ray diffraction patterns, atomic force microscopy images, ultraviolet-visible absorption spectra, photolumine...     

Properties of Gd2O3:Eu, Tb nanopowders obtained by sol-gel process

A significant practical application for nanostructured materials is X-ray medical imagery, because it is necessary to use dense materials in order to enable absorption of high energy photons. An important requirement of these materials is UV-vis range emission produced by X-ray excitation, which can be influenced by the particle size. Europium doped gadolinium oxide is a well known red phosphor. Moreover, nanophosphors of Gd₂O₃ codoped with Tb³⁺, Eu³⁺ increase their light yield by energy transfer between Tb³⁺ and Eu³⁺. In this study, Gd₂O₃ nanopowders codoped with Eu³⁺ and Tb³⁺ (2.5 at.% Eu³⁺, and 0.005 and 0.01 at.% Tb³⁺) were obtained via a sol-gel process using gadolinium pentanedionate as precursor and europium and terbium nitrates as doping sources. In this paper, we report the influence of annealing temperature on the structure, morphology and luminescent properties of Gd₂O₃:Eu³⁺, Tb³⁺ by means of TGA, XRD, TEM and X-ray emission measurements.     

Microstructure Control of Nanoporous Silica Thin Film Prepared by Sol-gel Process

Nanoporous silica films were prepared by sol-gel process with base, acid and base/acid two-step catalysis.Transmission electron microscope （TEM） and particle size analyzer were used to characterize the microstructure and the particle size distribution of the sols. Scanning electron microscopy （SEM）, atomic force microscopy （AFM） and spectroscopic ellipsometer were used to characterize the surface microstructure and the optical properties of the silica films. Stability of the sols during long-term storage was investigated. Moreover,the dispersion relation of the optical constants of the silica films, and the control of the microstructure and properties of the films by changing the catalysis conditions during sol-gel process were also discussed.     

Sol-gel synthesis and green upconversion luminescence in BaGd2(MoO4)4:Yb,Er phosphors

Yb³⁺/Er³⁺ codoped BaGd₂(MoO₄)₄ phosphor powders were prepared by the Sol-gel method and the upconversion luminescence properties were investigated in detail. Under 980 nm semiconductor laser excitation, BaGd₂(MoO₄)₄:Yb³⁺,Er³⁺ phosphor exhibits green upconversion luminescence with peaks at 530 and 550 nm, which are due to the transitions of Er³⁺ (²H_11/2) → Er³⁺ (⁴I_15/2) and Er³⁺ (⁴S_3/2) → Er³⁺ (⁴I_15/2), respectively. Both of the two green emission lines are produced by populating Er³⁺ ions to the excited state through a two-photon process. By monitoring the intensities of the green upconversion luminescence, the optimum conditions for the Sol-gel synthesis were determined when the molar ratio of citric acid to total chelate metal cations was 2:1 and the sintering temperature was at 1073 K. The concentration quenching effect for Er³⁺ was found at the optimum doping concentration of 6 mol%, and the critical distance for the neighboring Er³⁺ was determined to be about 21.5 Å.     

Sol-gel derived fluoridated hydroxyapatite films

Fluoridated hydroxyapatite [Ca₅(PO₄)₃(OH)_xF_1−x] films have reasonably good bioactivity and stability in the body, they could behave better than hydroxyapatite films in medical applications. In this work, a sol-gel method was adopted to prepare fluoridated hydroxyapatite films on titanium alloy. Three kinds of fluorine-containing reagents CF₃COOH, HPF₆ and NH₄PF₆ were selected to add into mixed Ca(NO₃)₂-P₂O₅ ethanol solutions to form dipping sols. The dipping sol with CF₃COOH led to an apatite film in which fluorine could not be detected in EDS. While the dipping sol, with HPF₆ or NH₄PF₆, could result in fluoridated hydroxyapatite films. The incorporation of fluorine could be attributed to the reactions of both HPF₆ or NH₄PF₆ with the mixed Ca(NO₃)₂-P₂O₅ ethanol solution to form nano-sized CaF₂ particles, which in turn, react with other species to form fluoridated hydroxyapatite during the film formation at 600 °C. Among the three fluorine-containing reagents, HPF₆ was the best because its dipping sol was more stable and the resulting films had better morphology.     

One-step construction of silver nanowires in hexagonal mesoporous silica using the polyol process

An original one-step preparation of single-crystal silver nanowires in hexagonal mesoporous silica is presented. The silver precursor, silver nitrate, is reduced in ethylene glycol (EG). This procedure avoids thermal treatments which can lead to phase segregation. The absorbance spectrum of the resulting hybrid material exhibits a transverse resonance plasmon peak near 360 nm whereas the longitudinal oscillation is shifted to the near-infrared region at about 1500 nm.     

Characterization of Bi-substituted Dysprosium Iron Garnet Films Prepared by Sol-gel Process

Bi-substituted dysprosium iron garnet films were prepared by sol-gel process, and were annealed for crystallization. The crystallographic structures of garnet films annealed at different temperatures were analyzed by XRD, the film annealed at 650℃ was polycrystalline garnet with no preferred orientation and no impurity crystalline phase. Magnetic and magneto-optical properties were investigated, the film had magnetic anisotropy perpendicular to the film plane, and exhibited strong coercivity of 1100-1600 Oe and high squareness. These films had large figures of merit applicable to magneto-optic storage, with 2 deg. at λ=430 nm and 1.5 deg. at λ=520 nm respectively.     

Synthesis and Structure Transformation of Orthorhombic LiMnO2 Cathode Materials by Sol-gel Method

Orthorhombic LiMnO2 cathode materials were synthesized successfully at lower temperature by sol-gel method. When LiMnO2 precursor prepared by sol-gel method was fired in air, the product was a mixture of spinel structure LiMn2O4 and rock-salt structure Li2MnO3, whereas in argon single-phase orthorhombic LiMnO2 could obtain at the range of 750℃ to 920℃. The substitution of Mn by Zn2+ or Co3+ in LiMnO2 led to the structure of LiMnO2 transiting to Qα-LiFeO2. The results of electrochemical cycles indicated that the discharged capacity of orthorhombic-LiMnO2 was smaller at the initial stages, then gradually increased with the increasing of cycle number, finally the capacity stabilized to certain value after about 10th cycles. This phenomenon reveals that there is an activation process for orthorhombic LiMnO2 cathode materials during electrochemical cycles, which is a phase transition process from orthorhombic LiMnO2 to tetragonal spinel Li2Mn2O4. The capacity of orthorhombic LiMnO2 synthesized at lower te     

The optical properties of Bi3.25La0.75Ti3O12 thin films with different thickness prepared by chemical solution deposition

Bi_3.25La_0.75Ti₃O₁₂(BiLT) thin films with different thickness were successfully deposited onto fused quartz by chemical solution deposition. X-ray diffraction analysis shows that BiLT thin films are polycrystalline with (0 0 2)-preferred orientation. The dispersion of refractive indices of the BiLT thin films was investigated by the optical transmittance spectrum. The optical band gap energy was estimated from the graph of (hνα)² versus hν. The results show that the refractive index and band-gap energy of the BiLT thin films decrease with the films thickness.     

Development and Characterization of Sol-gel Derived Al Doped ZnO/p-Si Photodiode

The effect of Al doping on the J-V characteristics sol-gel derived of ZnO/p-Si photodiodes was investigated.The resistivity of Si was 0.1Ω·cm.ZnO films annealed at 500℃ were of the best quality.To investigate the spectral response of the photodiodes,the J-V characteristics were measured under different monochromatic lights at wavelength 420,530,570 and 630 nm.The diodes exhibit strong responsivity in the blue region at 420 nm.The responsivity is 0.22 A/W for Al doped (0.8 wt pct) photodiode,whereas for the undoped photodiode,it was much lower.An estimate of the responsivity as a function of wavelength has been made in terms of the width of depletion region of photodiodes.     

Sol-gel dry spinning of mullite fibers from AN/TEOS/AIP system

Continuous mullite ceramic fibers were fabricated by a sol-gel dry-spinning technique. The sol was prepared from an aqueous solution of aluminum nitrate, aluminum isopropoxide and tetraethylorthosilicate. The sol-gel transition was investigated by measuring the volume, the solid content, the viscosity and the rheological properties of the solution. Shear viscosity η of the mullite sol varied dynamically with concentrating time and temperature of the sol. Combined with size analysis of sol particles and TEM analysis, the growth characteristics of sol particle agglomeration and its structural evolution were examined. By adjusting the temperature, the gelation degree could be stabilized at a certain value, and the sol-gel transition could be transferred to the spinning line. Continuous fibers were obtained from such sols using a laboratory dry-spinning apparatus. Sintering of the precursor fibers at 1100 °C yielded crack-free mullite ceramic fibers when the solid content of spinnable sol was above 50%.     

Sol-gel preparation of transparent zinc oxide films with highly preferential crystal orientation

ZnO films highly orientated along the (0 0 2) plane were obtained by preheating the films at different temperatures for 10 min after each coating and postheating at 600 °C for 1 h. The pre-heat treatment conditions were found to strongly affect the crystallographic orientation, morphology and the optical properties of the resultant ZnO films. The more the films were oriented preferentially along (0 0 2) direction, the greater became their optical properties. By applying the preheating temperature of 300 °C, the grain size of films was increased and the average optical transmittance became about 80% in the visible range. The films showed smooth surface with a fine microstructure without cracks and voids.     

Sol-gel planar waveguides for improved fluorescence microarrays

The real-time monitoring of the hybridization signal, giving access to the reaction kinetics, can widen the results of a microarray experiment. Nevertheless, the presence of a strong fluorescent mix often degrade the experimental sensitivity, limiting the interest of this technique: the implementation of an evanescent wave excitation scheme can represent in this case a real advantage. In this paper, we propose high refractive index waveguides fabricated by sol-gel process for evanescent wave microarray applications. The influence of the sol composition and annealing parameters on materials microstructure are carefully studied to obtain good optical properties and high refractive index (n = 1.8-2.1) using thermal treatments below 250 °C. Monomode TiO₂ planar waveguides chelated by acetic acid are used as substrates for waveguide-based microarray in real-time experiments, demonstrating a significant increase of the signal to noise ratio.     

Synthesis and characterization of nanocrystalline CdZnO thin films prepared by sol-gel dip-coating process

Nanocrystalline Cd_xZn_1 − xO thin films with different Cd volume ratios in solution (x = 0, 0.25, 0.50, 0.75 and 1) have been deposited on glass substrate by sol-gel dip-coating method. The as-deposited films were subjected to drying and annealing temperatures of 275 °C and 450 °C in air, respectively. The prepared films were characterized by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, UV-vis spectroscopy and dc-electrical measurements. The results show that the samples are polycrystalline and the crystallinity of the films enhanced with x. The average grain size is in the range of 20-53 nm. The atomic percent of Cd:Zn was found to be 9.50:1.04, 6.20:3.77 and 4.42:6.61 for x = 0.75, 0.50 and 0.25, respectively. It was observed that the transmittance and the band gap decreased as x increased. All the films exhibit n-type electrical conductivity. The resistivity (ρ) and mobility (μ) are in the range of 3.3 × 10² − 3.4 × 10^− 3 Ω cm, and 1.5 − 45 cm² V^− 1 s^− 1 respectively. The electron density lies between 1.26 × 10¹⁶ and 0.2 × 10²⁰ cm^− 3.     

Water soluble cellulose acetate: a versatile polymer for film coating

The objective of this study was to investigate the use of water soluble cellulose acetate (WSCA) as a film coating material for tablets. Aspirin (ASA) tablets were prepared by direct compression and coated with either WSCA or HPMC (hydroxypropyl methylcellulose) dispersions. Coatings of 1-3%, depending on the intended application, were applied to the model drug (ASA) tablets employing a side-vented coating pan. Free films of WSCA, prepared by cast method, are crystal clear and, depending on the viscosity grade, are flexible, strong and durable. WSCA has the capability of forming free films without plasticizers and the films dry at room temperature. Glass transition temperature, Tg, was determined by differential scanning calorimetry. The Tg of WSCA is significantly higher relative to HPMC. Inclusion of plasticizer lowers the Tg of WSCA and effective plasticizers were PEG 400 and glycerin. Low viscosity WSCA was more soluble in water (25-30%) relative to medium viscosity WSCA (10-15%). WSCA solutions exhibited no increase in viscosity with an increase in temperature. Samples of coated (WSCA and HPMC) tablets and uncoated ASA cores were packaged for stability studies at room and elevated temperature storage. Physical stability of ASA tablets coated with 2:1 LV: MV (low viscosity: medium viscosity) WSCA formulations was better when compared to tablets coated with HPMC. Dissolution stability of WSCA coated ASA was similar to the physical stability results. After three months at elevated temperature (35 and 45°C), the WSCA coated tablets complied with USP dissolution requirements for ASA, while the HPMC coated tablets did not. There was no difference in moisture (weight) gain of ASA tablets coated with either WSCA or HPMC. The WSCA coated tablets were not sticky or tacky, while the HPMC coated tablets were tacky and stuck together.     

Water Soluble Cellulose Acetate: A Versatile Polymer for Film Coating

ABSTRACT

The objective of this study was to investigate the use of water soluble cellulose acetate (WSCA) as a film coating material for tablets. Aspirin (ASA) tablets were prepared by direct compression and coated with either WSCA or HPMC (hydroxypropyl methylcellulose) dispersions. Coatings of 1–3%, depending on the intended application, were applied to the model drug (ASA) tablets employing a side-vented coating pan. Free films of WSCA, prepared by cast method, are crystal clear and, depending on the viscosity grade, are flexible, strong and durable. WSCA has the capability of forming free films without plasticizers and the films dry at room temperature. Glass transition temperature, Tg, was determined by differential scanning calorimetry. The Tg of WSCA is significantly higher relative to HPMC. Inclusion of plasticizer lowers the Tg of WSCA and effective plasticizers were PEG 400 and glycerin. Low viscosity WSCA was more soluble in water (25–30%) relative to medium viscosity WSCA (10–15%). WSCA solutions exhibited no increase in viscosity with an increase in temperature. Samples of coated (WSCA and HPMC) tablets and uncoated ASA cores were packaged for stability studies at room and elevated temperature storage. Physical stability of ASA tablets coated with 2:1 LV: MV (low viscosity: medium viscosity) WSCA formulations was better when compared to tablets coated with HPMC. Dissolution stability of WSCA coated ASA was similar to the physical stability results. After three months at elevated temperature (35 and 45°C), the WSCA coated tablets complied with USP dissolution requirements for ASA, while the HPMC coated tablets did not. There was no difference in moisture (weight) gain of ASA tablets coated with either WSCA or HPMC. The WSCA coated tablets were not sticky or tacky, while the HPMC coated tablets were tacky and stuck together.     

Sol-gel fabrication of compact, crack-free alumina film

Compact, crack-free alumina film was fabricated using an alumina sol with a high Al₂O₃ content. With the addition of ethylacetoacetate (CH₃COCH₂COOC₂H₅, EAcAc), the stable sol could be prepared with a molar ratio of aluminum sec-butoxide (Al(O-sec-Bu)₃, ASB) to water up to 1:25. It was found that EAcAc could notably decrease the surface tension of the liquid in the gel pores. The EAcAc modification layer on the colloidal particle retarded greatly the densification of the Al₂O₃ gel film and provided a long-lasting structural relaxation during heating. Therefore, the formation of cracks was effectively prevented in this alumina material. The alumina gel film contained a high Al₂O₃ content and there was a rather small mass loss during sintering. The critical thickness of Al₂O₃ sol-gel film was eight times higher than that could be achieved via the general sol-gel route and a film thicker than 0.8 μm was prepared by a single-step dipping operation.     

Preparation and hydrophilicity of TiO2 sol-gel derived nanocomposite films modified with copper loaded TiO2 nanoparticles

In this study, TiO₂ nanocomposite films with 10 g/L of TiO₂ and copper loaded TiO₂ nanoparticles as nanofillers were deposited on the glass substrates using the sol gel dip-coating method. FE-SEM and UV-vis spectrophotometer were used to evaluate morphological and optical properties of copper loaded titania nanoparticles. In addition, XPS and water contact angle techniques were used to study the surface properties and superhydrophilicity of titania nanocomposite films, respectively. The results indicated that copper loaded TiO₂ nanoparticles had a significant effect on the hydrophilicity of nanocomposite film and maintaining it in a dark place for a long time (6.2 degree for titania nanocomposite films with copper loaded nanoparticle and 23.7 degree for nanocomposite film with titania nanoparticles).