Silver containing sol–gel derived silica thin films: effect of aluminum incorporation on optical,microstructural and bactericidal properties

Silver containing silica (Ag–SiO₂) thin films with and without aluminum (Al) were prepared on soda-lime-silica glass by spin coating of aqueous sols. The coating sol was formed through mixing tetraethyl orthosilicate [Si(OC₂H₅)₄]/ethanol solution with aqueous silver nitrate (AgNO₃) and aluminum nitrate nonahydrate [(AlNO₃)₃·9H₂O] solutions. The deposited films were calcined in air at 100, 300 and 500 °C for 2 h and characterized using x-ray diffraction, UV-visible and x-ray photoelectron spectroscopy. The effect of Al incorporation and calcination treatment on microstructure and durability of the films, and chemical/physical state of silver in the silica thin film have been reported. The bactericidal activity of the films was also determined against Staphylococcus aureus via disk diffusion assay studies before and after chemical durability tests. The investigations revealed that the optical, bactericidal properties and chemical durability of Ag–SiO₂ films can be improved by Al addition. The Al-modified Ag–SiO₂ thin films do not exhibit any coloring after calcination in the range of 100–500 °C, illustrating that silver is incorporated within the silica gel network in ionic form (Ag⁺). Al incorporation also improved the overall durability and antibacterial endurance of Ag–SiO₂ thin films.     

Preparation of Silicates Using HSi(OC2H5)3 and Their NO x -Adsorption Behavior

The preparation and NO-adsorption/desorption behavior of Li, Ca and Ba silicates were investigated aiming at the application to a NO_x-absorbent. Li silicate was prepared by reaction of HSi(OC₂H₅)₃ with aqueous lithium silicate solution (LSS). Ca and Ba silicates were prepared from gels obtained using CH₃Si(OC₂H₅)₃, Si(OC₂H₅)₄, HSi(OC₂H₅)₃ and alkaline-earth alkoxides. The surface of these silicates indicated the solid basicity of H₀ = 9 and adsorbed the acidic gas of NO. FT-IR spectra of the silicates adsorbing NO showed the absorption peaks in the range of 1300–1600 cm^{– 1} corresponding to ionic and covalent nitrate NO₃^–. The complete desorption of adsorbed NO species occurred above 500°C in the Li silicate, above 500°C in the Ca and Ba silicates prepared using CH₃Si(OC₂H₅)₃, and above 700°C in the Ba and Ca silicates prepared using Si(OC₂H₅)₄. Regarding the Ca and Ba silicates, the difference in siloxane structure is thought to cause the difference in adsorption state and desorption behavior of NO.     

Chemical Solution Deposition of ZnO Thin Films by an Aqueous Solution Gel Precursor Route

An aqueous chemical solution deposition method was used to prepare thin films of ZnO on SiO₂/Si (1 1 1) substrates. Starting from an aqueous solution of Zn acetate, citric acid and ammonia, very thin films could be deposited by spin coating. Heating parameters, necessary for thin film annealing, were determined using FTIR experiments on dried gel precursors, heated up to different temperatures. The morphology and the thickness of the films were investigated by SEM. It is found that homogeneous thin films with grain sizes of about 20 nm are formed. XRD experiments show that there is an indication that the films, crystallized at 500°C, exhibit preferential grain growth along the c-axis.     

Preparation and optical properties of Bi2S3 microcrystallite doped glass and thin film by the sol-gel process

The Bi₂S₃ microcrystallite doped thin films and glass lumps have been successfully prepared by the sol-gel process from the hydrolysis of a complex solution of Si(OC₂H₅)₄ Bi(NO₃)₃ · 5H₂O and SC(NH₂)₂, and the size of the microcrystallites in glass heated for different times at 400°C was decided by the method of HRTEM. The optical transmission valley shifted towards longer wavelengths with longer heat-treatment time at 500°C in the Bi₂S₃ doped thin films, showing the experimental evidence of quantum size effects. The red-shift of emission peaks in luminenscence spectrum excited with longer wavelength is attributed to the broad distribution of particle size in Bi₂S₃ doped glass.     

Structural and IR Spectroscopic Analysis of Sol-Gel Processed CuFeMnO4 Spinel and CuFeMnO4/Silica Films for Solar Absorbers

Black colored CuFeMnO₄ spinel powders and films were prepared using sol-gel process from Mn-acetate and Fe- and Cu-chloride precursors. Films were deposited by dip-coating technique and heat-treated at 500°C. For CuFeMnO₄/silica films 3-aminopropyl-triethoxysilane (3-APTES) or tetraethoxysilane (TEOS) were used in molar proportion (Mn : Cu : Fe) : silica = 1 : 1. Films and powders were prepared by heating at 500°C. IR spectroscopic measurements were employed to follow the hydrolysis-condensation reactions in (Mn : Cu : Fe)/3-APTES sols hydrolysed with water, and (Mn : Cu : Fe)/TEOS sols hydrolysed with (NH₃)_aq (Stöber processing). The resulting coatings were examined with transmission electron microscopy (TEM) combined with electron dif-fraction analyses, Rutherford back scattering (RBS) and proton induced X-ray emission (PIXE) techniques. Results revealed that (Mn : Cu : Fe)/3-APTES films had a composite structure consisting of the upper Cu_1.4Mn_1.6O₄ spinel and the lower amorphous SiO₂ layer. RBS measurements confirmed the composite structure, showing also that the composition of the film was Mn : Cu : Fe = 1 : 0.96 : 0.29, i.e. close to the precursors ratio Mn : Cu : Fe = 3 : 3 : 1. (Mn : Cu : Fe)/TEOS films prepared from sols which were catalysed with (NH₃)_aq consisted of amorphous monodispersed spherical SiO₂ particles with a size of about 400–420 nm. Solar absorbance (a _s) and thermal emittance (e _T) values of CuFeMnO₄ (500°C) and (Mn : Cu : Fe)/TEOS films (500°C) showed that CuFeMnO₄ films could be used as potential selective coatings for solar absorbers in solar collector systems.     

Single-step sol-gel deposition and dielectric properties of 0.4 μm thick, (001) oriented Pb(Zr,Ti)O<Subscript>3</Subscript> thin films

Single-step sol–gel deposition was attempted for realizing submicron thick, (001) oriented Pb(Zr_0.53Ti_0.47)O₃ (PZT) thin films, using an alkoxide solution containing polyvinylpyrrolidone (PVP). A solution of molar composition, Pb(NO₃)₂:Zr(OC₃H₇ ⁿ)₄:Ti(OC₃H₇ ⁱ)₄:PVP:H₂O:CH₃COCH₂COCH₃:CH₃OC₂H₄OH:C₃H₇ ⁿOH = 1.1:0.53:0.47:0.5:5:0.5:22:0.98, was prepared as a coating solution. Gel films were prepared on Pt(111)/TiO₂/SiO₂/Si(100) substrates by spin-coating, and calcined at 350 °C and annealed at 650 °C either in an electric furnace or in a near-infrared (IR) furnace. When calcined in the near-IR furnace, the films became (001) oriented on annealing. When calcined in the electric furnace, on the other hand, the films became randomly oriented on annealing. These observations indicate that the heating the gel films from the substrate side in the calcination step at 350 °C induces crystallographic orientation in the annealing step at 650 °C. The effects of the heating methods on the thermal decomposition of the gel films, and the microstructure and dielectric properties of the fired films were studied. Finally 0.4 μm thick, (001) oriented PZT films could be successfully prepared by non-repetitive, single-step deposition. The oriented film thus obtained had the remnant polarization 2P _r of 39 μC/cm² and the dielectric constant ε′ of 960 ± 169.     

Sol-gel synthesis of nanocomposite materials based on lithium niobate nanocrystals dispersed in a silica glass matrix

With the final goal to obtain thin films containing stoichiometric lithium niobate nanocrystals embedded in an amorphous silica matrix, the synthesis strategy used to set a new inexpensive sol-gel route to prepare nanocomposite materials in the Li₂O-Nb₂O₅-SiO₂ system is reported. In this route, LiNO₃, NbCl₅ and Si(OC₂H₅)₄ were used as starting materials. The gels were annealed at different temperatures and nanocrystals of several phases were formed. Futhermore, by controlling the gel compositions and the synthesis parameters, it was possible to obtain LiNbO₃ as only crystallizing phase. LiNbO₃-SiO₂ nanocomposite thin films on Si-SiO₂ and Al₂O₃ substrates were grown. The LiNbO₃ average size, increasing with the annealing temperature, was 27 nm for a film of composition 10Li₂O-10Nb₂O₅-80SiO₂ heated 2 h at 800 °C. Electrical investigation revealed that the nanocrystals size strongly affects the film conductivity and the occurrence of hysteretic current-voltage curves.     

Bi4Ti3O12 Thin Films from Mixed Bismuth-Titanium Alkoxides

Bi₄Ti₃O₁₂ thin films were obtained by the sol-gel method. The precursor solution was prepared by allowing the two metallic alkoxides, Bi(OC₂H₄OCH₃)₃ and Ti(OC₂H₄OCH₃)₄, to react in 2-methoxy-ethanol to form the mixed alkoxide. This stable sol was deposited by spin-coating onto platinized silicon substrates. X-Ray diffraction patterns indicate that the perovskite initial crystallization temperature is 460°C for powder samples and it ranges between 400 and 500°C, for thin films, as a function of the number of coating layers. Dense, smooth and crack free thin films with grain sizes ranging from 20 nm to 500 nm are obtained, depending on the number of coating layers and on the post-deposition temperature annealing.     

Preparation,dielectric and ferroelectric properties of (Na<Subscript>0.5</Subscript>Bi<Subscript>0.5</Subscript>)<Subscript>0.94</Subscript>Ba<Subscript>0.06</Subscript>TiO<Subscript>3</Subscript> thin films by a sol–gel process

(BiFeO₃)_1−x –(BaTiO₃) _x solid solution thin films are grown on Pt/Ti/SiO₂/Si substrates by chemical solution deposition method. Films with x = 0.00, 0.05 and 0.10 were prepared by annealing at 500°C. X-ray diffraction patterns indicate that the pure BiFeO₃ film adopts random orientation while the solid solution films are highly (100) preferentially oriented. Improved electric property at room temperature was observed in the BaTiO₃ incorporated BiFeO₃ films. The remanent polarization of the film with x = 0.0, 0.05 and 0.10 are 76.6, 51.9 and 19.7 μC/cm² respectively under a measuring electric field of 0.94 MV/cm. The BaTiO₃ incorporated BiFeO₃ films show improved fatigue endurance. By the solid solution with BaTiO₃, the leakage current density is reduced effectively.     

Structural Changes in Sol-Gel Derived SiO2 and TiO2 Films by Exposure to Water Vapor

Structural changes in sol-gel derived thin films by exposure to water vapor were investigated using Fourier transform infrared absorption spectroscopy, ellipsometry and x-ray diffraction. We found that SiO₂ gel films were densified with a decrease in OH groups by the exposure at 60°–180°C. The shrinkage and the peak frequency of ₄ (TO) for the exposed films were comparable to those heated in a dry atmosphere at temperatures above 500°C. However, OH groups in the films were not completely removed by the water exposure. A subsequent annealing above 300°C changed the structure of the water-exposed SiO₂ films with condensation of the remaining OH groups. Although the exposed SiO₂ gel films were amorphous, TiO₂ gel films were transformed to anatase with a decrease in OH groups by the treatments at 80°–180°C.     

Sol-Gel Synthesis of Ge Nanocrystals-Doped Glass and Its Photoluminescence

Ge nanocrystal-embedded SiO₂ glasses were prepared by a sol-gel process. The glasses synthesized through the hydrolysis of Si(OC₂H₅)₄ and GeCl₄ were heated in H₂ gas atmosphere at 500 to 800°C, in which Ge⁴⁺ ions were reduced to precipitate nanosized Ge crystals with the size smaller than 10 nm diameter. Glasses doped with Ge nanocrystals of diameter of ≈5 nm showed the optical absorption edge at ≈2.8 eV and a broad photoluminescence exhibiting the peak at around 2.2 eV. Large Ge crystals precipitated by heating above 800°C showed no photoluminescence.     

Preparation of Ba(Ti,Sn)O<Subscript>3</Subscript> thin films by PVP-assisted sol–gel method and their dielectric properties

Ba(Ti_1−x Sn _x )O₃ (x = 0.10 or 0.15) thin films were deposited on Si(100) and Pt(111)/TiO _x /SiO₂/Si(100) substrates via sol–gel spin-coating. Crack-free thin films could be obtained by single-step deposition, where the thickness was about 0.46 and 0.29 μm at 1000 and 2000 rpm, respectively. Circular delaminated parts 100 μm in diameter, however, tended to appear in thicker films deposited at 1000 rpm. On both kinds of substrates, the films were crystallized between 500 and 600 °C, where the perovskite phase emerged as the primary phase, and the formation of single-phase perovskite was basically achieved between 700–800 °C. The films deposited on Pt(111)/TiO _x /SiO₂/Si(100) substrates, however, tended to have small SnO₂ and BaCO₃ diffraction peaks, which decreased with increasing spinning rate. The dielectric properties were evaluated on the films deposited on Pt(111)/TiO _x /SiO₂/Si(100) substrates at 2000 rpm. The films prepared by single-step depositions had dielectric constants of 350 and 230, and dielectric loss of 0.30 and 0.10 at x = 0.1 and 0.15, respectively. The films prepared by two time deposition had dielectric constants of 450 and 250, and dielectric loss of 0.21 and 0.19 at x = 0.10 and 0.15, respectively.     

Preparation and characterization of epoxy/SiO2 nanocomposites by cationic photopolymerization and sol–gel process

Epoxy/SiO₂ nanocomposite materials were prepared by cationic photopolymerization and sol–gel process using a novel epoxy oligomer (EP‐Si(OC₂H₅)₃) prepared by 3‐isocyanatopropyltriethoxysilane (IPTS)‐grafted bisphenol A epoxy resin and tetraethyl orthosilicate as inorganic precursor. The chemical structures of EP‐Si(OC₂H₅)₃ were characterized by Fourier transformed infrared spectroscopy. Transmission electron microscopy showed that the in situ generated nano‐SiO₂ dispersed uniformly in the EP matrix, and its average diameter is around 40 nm. The relationship between nanocomposite materials' thermal/mechanical properties and nano‐SiO₂ introduced were studied by thermogravimetric analysis, dynamic mechanical analysis, and impact strength test. The results showed that the nanocomposite materials' thermal and mechanical properties improved a lot with increase of the SiO₂ content. Copyright © 2013 John Wiley & Sons, Ltd.     

Low temperature preparation and electric properties of highly (100)-oriented Pb<Subscript>0.8</Subscript> La<Subscript>0.1</Subscript>Ca<Subscript>0.1</Subscript>Ti<Subscript>0.975</Subscript>O<Subscript>3</Subscript> thin films prepared by a sol–gel route

Highly (100)-oriented Pb_0.8La_0.1Ca_0.1Ti_0.975O₃ (PLCT) thin films deposited on Pt/Ti/SiO₂/Si substrate were successfully achieved by a sol–gel route. The influence of annealing temperature on microstructures and electric properties was investigated; it was found that the PLCT film could be crystallized only at 450 °C. When the annealing temperature increased to 500 °C, the PLCT film exhibited highly (100)-oriented, which also possessed higher remnant polarization Pr (27 μC/cm²) and better pyroelectric figure of merit (F _d = 205 μC/m²k) at room temperature. It was also found too high annealing temperature (625 °C) could lead to recrystallization of film, and the small grains caused by recrystallization could make polarization reversal difficult and disturbed the preferred crystal growth in film, which was not benefit to obtain enhanced electric properties.     

X-ray and Raman study of spray pyrolysed vanadium oxide thin films

Vanadium oxide thin films were prepared by spray pyrolysis using solutions of vanadium chloride (VCl₃) with different concentrations on glass substrates heated at 200 and 250 °C. The influence of substrate temperature (T_s) and solution concentration (molarity) on structural and vibrational properties is discussed by using X-ray diffraction and Raman spectroscopy. The results revealed that at 0.05 M and T_s = 200 °C, V₄O₉ thin films are obtained. At 250 °C, V₂O₅ phases with preferential orientation are observed and the films become polycrystalline when the molarity increases.     

Rectifying Properties of Oxide Semiconductor Heterostack Films at Elevated Temperatures

Heterostack films of p-type NiO and n-type TiO₂ semiconductors were deposited by a method of chemical solution deposition on a glass substrate having a sputtered ITO (In₂O₃ doped with Sn) electrode. Transparent films with total thickness of about 280 nm were obtained by heat treatments at 600°C. NiO reacted with TiO₂ to give a NiTiO₃ thin layer between them. The films exhibited a typical rectifying I-V behavior and this property was maintained at 300°C. The thickness of the NiTiO₃ intermediate layer increase with the heating time at 600°C and leading to a decrease of the current density at low voltage.     

The influence of film thickness and process temperature on <Emphasis Type="Italic">c</Emphasis>-axis orientation of Bi<Subscript>3</Subscript>TiTaO<Subscript>9</Subscript> thin films

Bi-layered ferroelectric Bi₃TiTaO₉ (BTT) thin films with different thickness (ranging from 100 to 400 nm) were successfully fabricated on Pt(111)/TiO₂/SiO₂/(100)Si substrates using chemical solution deposition (CSD) technique at different annealing temperatures. The c-axis orientation of the films was affected by film thickness and process temperature. The thinner the film and the higher the process temperature, the higher the c-axis orientation. With the increase of film thickness, the stress decreased but the film roughness increased, which led to the decrease of c-axis orientation of films. BTT films annealed at 800°C were found to have much improved remament polarization (P _r ) than that of films annealed at 650 and 750°C. The P _r and coercive field (E _c ) values were measured to be 2 μC/cm² and 100 kV/cm, respectively. BTT films showed well-defined ferroelectric properties with grain size larger than 100 nm.     

Radiative Striations of Spin-Coating Films: Surface Roughness Measurement and in-situ Observation

Silica gel films were prepared by spin-coating from Si(OC₂H₅)₄-HNO₃-H₂O-ROH solutions and heated at 200°C where ROH = CH₃OH, C₂H₅OH, CH₃OC₂H₄OH and CH₃CH(OH)CH₂OH. Striations were observed with an optical microscope, and quantitatively evaluated by surface roughness measurement. A decrease in height and an increase in spacing of the striations were observed when alcohols of high boiling points were used. However, even when the boiling point of the alcohols was high, an evolution of the striations did occur on spin-coating films, which disappeared while keeping the film in the ambient atmosphere. Convections, which might be the source of the striations, were observed in sol layers placed on a stationary substrate irrespective of the boiling point of the alcohols.     

Chemical solution processing and characterization of Ba(Zr,Ti)O<Subscript>3</Subscript>/LaNiO<Subscript>3</Subscript> layered thin films

Ba(Zr,Ti)O₃/LaNiO₃ layered thin films have been synthesized by chemical solution deposition (CSD) using metal-organic precursor solutions. Ba(Zr,Ti)O₃ thin films with smooth surface morphology and excellent dielectric properties were prepared on Pt/TiO _x /SiO₂/Si substrates by controlling the Zr/Ti ratios in Ba(Zr,Ti)O₃. Chemically derived LaNiO₃ thin films crystallized into the perovskite single phase and their conductivity was sufficiently high as a thin-film electrode. Ba(Zr,Ti)O₃/LaNiO₃ layered thin films of single phase perovskite were fabricated on SiO₂/Si and fused silica substrates. The dielectric constant of a Ba(Zr_0.2Ti_0.8)O₃ thin film prepared at 700°C on a LaNiO₃/fused silica substrate was found to be approximately 830 with a dielectric loss of 5% at 1 kHz and room temperature. Although the Ba(Zr_0.2Ti_0.8)O₃ thin film on the LaNiO₃/fused silica substrate showed a smaller dielectric constant than the Ba(Zr_0.2Ti_0.8)O₃ thin film on Pt/TiO _x /SiO₂/Si, small temperature dependence of dielectric constant was achieved over a wide temperature range. Furthermore, the fabrication of the Ba(Zr,Ti)O₃/LaNiO₃ films in alternate thin layers similar to a multilayer capacitor structure was performed by the same solution deposition process.