Sol–gel chemistry of an aqueous precursor solution for YBCO thin films

A water based YBa₂Cu₃O_7−x (YBCO) precursor using a triethanolamine (TEA)/acetic acid complexing method to obtain YBCO thin films is described in detail. The influence of complexation behavior in the formation of transparent and homogenous sols and gels after the combination of Y, Ba and Cu—acetates, acetic acid and TEA has been studied by potentiometric titration and the results are compared with analytical simulations. The decomposition of the gel was studied by IR (infrared) and Thermal Gravimetric Analysis/Differential Thermal Analysis (TGA/DTA). The results in sol-gel chemistry can be used to decide on the necessities in the preparation of stable sol–gel precursors with a minimum amount of organic compounds. The sol–gel system was also used for the deposition of high textured superconducting thin films on STO substrates by dip coating. The synthesized YBCO showed a superconducting transition temperature of 90.95 K with narrow ΔT (2 K) for thin films. The results from X-ray diffraction show that the single phase YBCO was obtained. SEM pictures also indicate that the properties of the surface thin films are good.     

Effects of niobium doping on lead zirconate titanate films deposited by a sol–gel route

Niobium (Nb)-doped lead zirconate titanate (PZT) films have been prepared on platinized silicon substrates using a sol–gel method. The Zr/Ti ratios of the films are 53/47 and 40/60, and the Nb doping level ranges from 0 mol% to 3 mol%. Similar to the cases in bulk ceramics, after the doping with Nb, the remanent polarization P_r, effective transverse piezoelectric coefficients e_31,c and pyroelectric coefficient p of the PZT films increase; but the longitudinal effective piezoelectric coefficient d_33,c remains roughly unchanged. At the optimum Nb doping levels, the observed P_r, −e_31,c and p reach a maximum value of 30 μC/cm², 18 C/m² and 350 μC/m² K, respectively, for the PZT (53/47) films, and 37 μC/cm², 7.9 c/m² and 370 μC/m² K for the PZT (40/60) films. Our results also reveal that there exist linear relations between p, e_31,c/ε_r and P_r.     

Influence of the Plasma Chemistry on the Composition of ZrOx and NbOx Thin Films Deposited by Reactive Magnetron Sputtering

The plasma chemistry of magnetron sputtered Zr and Nb in an Ar/O₂ atmosphere has been measured as a function of the O₂ partial pressure. The previously reported composition of films deposited onto grounded non-intentionally heated substrates was correlated with the dominant positive and negative ion populations in the plasma. While the oxygen deficient films were grown in the Ar⁺ dominant mode, the close-to-stoichiometric films were grown in the O⁺/O⁻ dominant mode. The formation of close-to-stoichiometric ZrO_2.1 is observed in the compound mode (CM), while the formation of close-to-stoichiometric Nb₂O_4.7 thin films was reported in addition to the CM also in the transition mode (TM). This may be understood based on the 1.5–1.9 times higher power dissipated in the Nb–Ar–O₂ plasma as compared to the Zr–Ar–O₂ plasma. We suggest that at larger power O₂ dissociation may be more efficient and lead to the presence of sufficient atomic oxygen to fully oxidize the films. This finding may provide a pathway towards a deposition rate enhancement, since compound formation at the substrate is enabled in the TM of the higher power Nb–Ar–O₂ plasma and not only in the CM, as in the case of the lower power Zr–Ar–O₂ plasma.     

Effect of amine catalysts on preparation of nanometric SiO<Subscript>2</Subscript> particles and antireflective films via sol–gel method

SiO₂ sols were prepared by hydrolysis and condensation reactions of tetraethyl orthosilicate through a one step acid or a two step acid + base catalysis process, in the presence of nitric acid and four different base catalyzers, namely trimethylamine, triethylamine, tripropylamine and tributylamine. Hydrolysis of TEOS was followed by FT-IR analyses. Particle size distributions of the sols were evaluated after predetermined durations in 1–22 days. Particle growth was seen to be faster in amine catalyzed systems than in one step acid catalyzed system. The highest rate of growth was in triethylamine catalyzed system. Glass substrates were dip coated with the prepared SiO₂ sols. Effect of sol aging duration on film thickness and on light transmittance properties of the films was investigated with respect to type of base catalyst. Thicknesses of the films which were measured to be in the range of 100–400 nm, were seen to increase with aging duration of the sols. Triethylamine catalyzed system presented the highest film thickness. Films obtained from one step acid catalyzed system presented an increase of 4.8%; whereas acid + base catalyzed films provided an increase in the light transmittance of 5.7% in the first 4 days of aging. Surfaces of films were examined by FESEM and AFM. The antireflective character of the films was verified by diffuse reflectance analyses.     

Preparation of highly stable TiO<Subscript>2</Subscript> sols and nanocrystalline TiO<Subscript>2</Subscript> films via a low temperature sol–gel route

Highly stable TiO₂ sols were prepared by adjusting the water-to-titanium molar ratio to ~4 in the process of hydrolysis and condensation of titanium isopropoxide in ethanol with HNO₃. Particularly, long-term stable TiO₂ sols were prepared without adding any chemical additives. Anatase TiO₂ nanocrystallites with sizes of 3–5 nm in diameter were uniformly dispersed in the stable sol. Crystallized TiO₂ films were successfully deposited on Si (100) using the stable sol via a dip-coating process with low temperature curing at as low as 100 °C. The synthesized TiO₂ sols and films are promising for use in flexible or dye-sensitized solar cells.     

Thermochemistry of Bu<Subscript>4</Subscript>NBr solutions in binary solvents containing formamide

The heats of solution of tetrabutylammonium bromide have been measured in mixtures of formamide (FA) with methanol (MeOH) and ethylene glycol (EG) at 313.15 K by calorimetric method. The standard enthalpies of solution in binary mixtures have been extrapolated to infinite dilution by Redlich–Rosenfeld–Meyer type equation using the literary data at 298.15 K and the present paper data at 313.15 K. The Debye–Hückel limiting law slope A _H required for calculation of the ∆_sol H ⁰ value has been obtained with application the new additive scheme of determination of the physic-chemical characteristics of binaries. The scheme is tested on the example of Bu₄NBr solutions in FA–MeOH mixture at 298.15 K. Its application yields the ∆_sol H ⁰ value very closed on the ones determined with the real (non-additive) characteristics of binaries. The standard enthalpies of solution extrapolated by Redlich–Rosenfeld–Meyer type equation are in a good agreement with the ones computed in terms of the Debye–Hückel theory in the second approximation. The heat capacities characteristics of Bu₄NBr have been calculated in H₂O–FA, MeOH–FA and EG–FA mixtures using the literary and present data. The sequence of solvents H₂O > FA > EG > MeOH located on their ability to solvophobic solvation found by us earlier for enthalpic characteristics is confirmed by the ∆C _p ⁰ values. The comparison of thermochemical characteristics of Bu₄NBr solutions in aqueous and non-aqueous mixtures containing FA has been carried out. The own structure of water remains in the region of small additions of formamide to co-solvents. It considerably differs the H₂O–FA mixture from the investigated non-aqueous systems.     

Indoor 222Rn concentrations and the corresponding lung cancer risk in Celein region, west of Al Khums, Libya

Paramagnetic products stabilized in both 4,4′(5′)-di-(tert-butylcyclohexano)-18-crown-6 (DtBuCH18C6) and its solution in 1-octanol upon low temperature (77 K) X-rays irradiation were studied by ESR spectroscopy. Macrocyclic –O–ĊH–CH₂– radicals and acyclic O = C(H)–ĊH–O– radicals were found as main radiolysis products in neat DtBuCH18C6. Fraction of acyclic radicals resulting from the macrocycle cleavage was about 50%. No radical products resulted from t-Bu and cyclohexyl fragments were observed. It was concluded that the primary events were essentially concerned with ionization of the polyether moiety. Irradiation of frozen DtBuCH18C6 solutions in 1-octanol resulted in formation of radicals both from crown ether and alcohol.     

Sol–gel-derived titania-hydroxypropylcellulose hybrid thin films of high refractive indices: solution components affecting the refractive index and uncracking critical thickness

Optically transparent, ca. 200–800 nm thick TiO₂-hydroxypropylcellulose (HPC) hybrid thin films were prepared from Ti(OC₃H₇ⁱ)₄–HPC–HCl–H₂O–C₃H₇ⁱOH solutions by the sol–gel method, where the as-deposited films were dried at 120 °C. The effects of the amount of HPC, H₂O and HCl in the starting solutions on the refractive index and uncracking critical thickness of the films were studied, where the effects on the critical thickness was discussed on the basis of in situ stress measurements during heating. The increase in HPC content increased the critical thickness and lowered the refractive index. The increase in HCl content resulted in a decrease in critical thickness and an increase in refractive index. Larger H₂O contents gave rise to a maximum in critical thickness while the refractive index was unaffected. Such variation in critical thickness with varying solution compositions was demonstrated to result from the differences in in-plane stress generated during heating. By optimizing the processing parameters an 810 nm thick TiO₂–HPC hybrid film of a refractive index of 1.84 was obtained.     

Sol-Gel Chemistry of Tantala HR Coatings: Structure and Laser-Damage Resistance

Sol-gel processing of Ta(OC₂H₅)₅ to produce high reflective and high refractive index (HR) tantala coatings has been followed by infrared spectroscopy (FTIR), where in the presence of ethanoic acid, both chelation and hydrolysis reactions co-exist, depending on the preparative parameters. However, most of the precursor was found to convert into an amorphous tantala sol and finally a gel. Transmission electron microscopy (TEM) and light-scattering showed that the primary sol particles (whose size was about 5 nm) aggregated into clusters up to 60–80 nm via different linkages: ring-like, cross-linked and colloidal structures. Thermal analysis-X-ray diffraction (TGA-XRD) indicated that the gel did not crystallise below 700 K. Tantala films (0.3 μm thick; refractive index of 1.7) were prepared by spin-coating of these sols and had properties closely related to the sol structure.     

Effects of fused benzene rings on tautomerizations and inversions of benzo, azabenzo, and oxabenzocycloheptatrienes at theoretical levels

Biologically important bicyclic species, including 6H-, 6H-6-aza-, and 6-oxabenzocycloheptatrienes (in which the benzene moiety is fused meta with respect to the tetrahedral constituents: –CH₂–, –NH–, and –O–, respectively), show strong shifts of tautomerizations in favor of the corresponding tricyclic benzonorcaradienes (with ΔH values of −11.49, −14.55, and −19.20 kcal mol⁻¹, respectively), at B3LYP/6-311++G**//B3LYP/6-31G*, and MP2/6-311++G**//MP2/6-31G* levels, and at 298 K. In contrast, such shifts are strongly disfavored by the isomeric bicyclic species in which the benzene moieties are fused ortho or para with respect to –CH₂–, –NH–, and –O–, respectively. Hence for species with ortho benzene rings including 5H-, 5H-5-aza- and 5-oxabenzocycloheptatrienes, tautomerization ΔH values are 30.76, 31.89, and 25.27 kcal mol⁻¹, respectively, while for species with para fused benzene moieties including 7H-, 7H-7-aza-, and 7-oxabenzocycloheptatrienes, tautomerization ΔH values are 24.12, 26.00, and 19.55 kcal mol⁻¹, respectively. NICS calculations are successfully used to rationalize these results. The calculated energy barriers for inversion of the seven-membered rings of bicyclic species predict a dynamic nature for all the structures except for the virtually planar 6H-6-aza- and 6-oxabenzocycloheptatrienes. Finally, our theoretical data are compared to the experimental results where available. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

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 and characterization of TiO<Subscript>2</Subscript> hybrid sol for UV-curable high-refractive-index organic–inorganic hybrid thin films

In this study, UV-curable hybrid thin films were successfully prepared from TiO₂ and TiO₂ hybrid sols containing the acrylic monomer DPHA on PMMA substrates. The prepared TiO₂ and TiO₂ hybrid sols showed long-term storage stability and can provide operating control for the preparation of high-refractive-index hybrid thin films. The existence of interaction between the TiO₂ particle and the coupling agent was evidenced by FT-IR and UV–visible spectra. All hybrid thin films showed good adhesion to the PMMA substrate with refractive index falling over the range 1.64–1.77. These results suggested the potential application of present TiO₂ hybrid films in optical devices, such as anti-reflective coatings.     

Effects of diethanolamine on the evolution of silver/titanium dioxide sol–gel process

In order to clarify the effects of diethanolamine (DEA) in the silver (Ag)/titanium dioxide (TiO₂) sol–gel process, sols with and without DEA, and films derived from these sols were prepared. The samples were investigated by X-ray diffraction, transmission electron microscopy, electron diffraction and optical absorption spectra. The results showed that metallic Ag clusters were formed in the sol with DEA and was absent in the sol without DEA. This indicated that DEA worked not only as the stabilizer but also as the reduce agent in Ag/TiO₂ sol–gel process. After annealed, Ag metallic nanoparticles were generated in the films derived from both the sols with and without DEA. The particles in the films derived from the sol with DEA were smaller than those from the sol without DEA. This can be ascribed to the limitation of the growth of Ag cluster formed in the sol with DEA during heat treatment. Mechanisms for the formation of metallic Ag in the Ag/TiO₂ sols and films were discussed. The effects of DEA in the sols and films were studied in detail.     

Dielectric properties of sols of silver nanoparticles capped by alkyl carboxylate ligands

Sols of silver nanoparticles in toluene were studied by broadband dielectric spectroscopy (10⁻³–10⁵ Hz). The frequency dependences of the specific alternating current (ac) conductivity and the complex electric modulus were used to estimate the temperature/frequency intervals of long- and short-range charge transfer occurs, respectively. A considerable increase (by more than 30 °C) in the Vogel temperature T ₀ and the glass transition temperature T _g in sols compared with the pure solvent was found. It can be hypothesized that these cooperative effects reflect the initial stage of the superlattice formation. Although the dielectric characteristics of sols are generally controlled by the conductivity relaxation, the dielectric response was observed in the high-frequency range (1–10³ Hz) at low temperatures (from −50 to +10 °C). This response results from the presence of nanoparticles in solution. It is supposed that the relaxation is caused by the motion of ion impurities on the Ag nanoparticle surface within the carboxylate ligands shell. The dielectric properties of films strongly depend on both the characteristics of nanoparticles and the conditions of the film preparation. Like in sols, the direct current (dc) conductivity and the dielectric response of Ag nanoparticles in films are due to ion impurities.     

X-ray photoelectron spectroscopy study of neodymium niobate and tantalate precursors and thin films

Neodymium niobate NdNbO₄ (NNO) and tantalate NdTaO₄ (NTO) thin films (~100 nm) were prepared by sol-gel/spin-coating process on Al₂O₃ substrate with LaNbO₄/PbZrO₃ interlayer and annealing at 1000°C. Surface chemistry was investigated by X-ray photoelectron spectroscopy (XPS). The core-level XPS studies of sol-gel NNO and NTO were performed for the first time. The binding energy differences Δ(O―Nb) and Δ(O―Ta) were used to characterize average energies of Nb―O bonding in NNO (322.9 eV) and Ta―O bonding in NTO (504.2 eV). The XPS demonstrated single valence state of Nd (Nd³⁺) in precursors. Nd concentration (at. %) decreases from 22% in precursors to 7% in films considering the substrate contains C, Al, Si, Pb, and Zr elements (37%) at Nb or Ta (5%) and O (51%). The X-ray diffraction analyses verified formation of the monoclinic (M-NdNbO₄ or M′-NdTaO₄), orthorhombic (O-NdNbO₄) and tetragonal (T-NdTaO₄) phases in precursors and films. Single valence state of Nd³⁺ was confirmed in these films designed for the application in environmental electrolytic thin film devices.     

Electronic Properties and Chemical Bonding of O-Rich Clusters MM′O<Subscript>7</Subscript><Superscript>−</Superscript> (M,M′ = V,Nb, Ta)

Density functional theory (DFT) calculations are carried out to investigate the electronic and structural properties of a series of bimetallic oxygen-rich clusters, MM′O₇ ⁻ (M, M′ = V, Nb, Ta). Generalized Koopmans’ theorem is applied to predict the vertical detachment energies (VDEs) and simulate the photoelectron spectra (PES). Theoretical calculations at the B3LYP level yield dibridged structures with doublet state (C _s, ²A′′) as ground states for the anionic clusters. Intriguingly, an O₂ unit is found to be bonded to the metal atom which is inclined to donate electrons in the MM′O₇ ⁻ (M, M′ = V, Nb, Ta) species. The extremely high binding energies, above 5.50 eV, are due to oxygen 2p-based orbitals and suggest that these clusters are strong oxidizers. Chemical bonding analyses reveal superoxide in the oxygen-rich clusters, in excellent consistence with their structural characteristics.     

Synthesis and characterization of novel InVO<Subscript>4</Subscript>–TiO<Subscript>2</Subscript> thin films using the low temperature sol

The InVO₄ sol was obtained by a mild hydrothermal treatment (the precursor precipitation solution at 423 K, for 4 h). Novel visible-light activated photocatalytic InVO₄–TiO₂ thin films were synthesized through a sol–gel dipping method from the composite sol, which was obtained by mixing the low temperature InVO₄ sol and TiO₂ sol. The photocatalytic activities of the new InVO₄–TiO₂ thin films under visible light irradiation were investigated by the photocatalytic discoloration of methyl orange aqueous solution. The thin films were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and UV–Vis absorption spectroscopy (UV–Vis). The results revealed that the InVO₄ doped thin films enhanced the methyl orange degradation rate under visible light irradiation, 3.0 wt% InVO₄–TiO₂ thin films reaching 80.1% after irradiated for 15 h.     

Photocatalytic activity of (sulfur,nitrogen)-codoped mesoporous TiO<Subscript>2</Subscript> thin films

Nitrogen and sulfur co-doped mesoporous TiO₂ thin films were fabricated using thiourea as a doping resource by the combination of the sol–gel and evaporation-induced self-assembly (EISA) processes. Scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), N₂ adsorption–desorption, and UV–vis spectra were performed to characterize the as-synthesized mesoporous TiO₂ materials. The XPS result shows that O–Ti–N and O–Ti–S bonds in the (S, N)-codoped mesoporous TiO₂ were formed. The resultant mesoporous (S, N)-codoped TiO₂ exhibited anatase framework with a high porosity and a narrow pore distribution. After being illuminated for 3 h, methyl orange (MO) could be degraded completely by the co-doped sample under the ultraviolet irradiation, whereas mesoporous TiO₂ film without doping could only degrade 60% MO. After being illuminated by visible light, the water contact angles of the mesoporous co-doped TiO₂ samples decreased slightly, but the pure TiO₂ mesoporous film exhibited no change in the hydrophilicity.     

Synthesis,Characterization, and Crystal Structures of Metal Amide Cage Complexes Containing a M<Subscript>4</Subscript>O<Subscript>4</Subscript> (M = Nb,Ta) Core Unit

Metal cage complexes [(Me₂N)₃MO]₄ (M = Nb, 3; Ta, 4) have been prepared from the reactions of M(NMe₂)₅ (M = Nb, 1; Ta, 2) with water. Single crystal X-ray diffraction studies of 3 and 4 reveal that they adopt cubane-like structures with M–O bridges. Variable-temperature NMR studies of –NMe_AMe_B rotations in 3 and 4 have been performed to give the following activation parameters for the exchanges: ΔH ^≠ = −1.4(1.1) kJ/mol, ΔS ^≠ = −209(8) J/mol K, \Updelta G _{30 8  \textK} ¹ = 6 4( 2)  \textkJ/\textmol \Updelta G_{{_{{ 30 8\;{\text{K}}}} }}^{{^{ \ne } }} = 6 4\left( 2\right)\;{\text{kJ}}/{\text{mol}} for 3, and ΔH ^≠ = −0.9(1.2) kJ/mol, ΔS ^≠ = −2.1(0.2) × 10² J/mol K, \Updelta G _{30 8  \textK} ¹ = 6 3( 6)  \textkJ/\textmol \Updelta G_{{ 30 8\;{\text{K}}}}^{{^{ \ne } }} = 6 3\left( 6\right)\;{\text{kJ}}/{\text{mol}} for 4.     

Mechanistic study on the atmospheric formation of acid rain base on the sulfur dioxide

The reaction pathways of acid rain formation from reaction of sulfur dioxide vapor and water vapor on the singlet potential energy surface have been investigated theoretically. The calculated results show that the reactants are initially associated with the adduct SO₂–H₂O through a barrier less process. Subsequently, via a variety of transformations of isomer SO₂–H₂O, three kinds of products H₂SO₃, SO₃ + H₂, and H₂O₂ + ³SO are obtained. The cleavage and formation of the chemical bonds in the reaction pathways have been discussed using the structural parameters. Also, by means of the transition states and their connected intermediates or products at the CCSD(T)//B3LYP level, mechanism of H₂O + SO₂ reaction on the singlet potential energy surface are plotted. The calculation results show that the most suitable reaction pathways are the formation of H₂SO₃. Finally, the rate constants have been calculated only for these suitable pathways by the RRKM and TST theories at temperature range of 250–2500 K.