Effects of UV-irradiation on the formation of oxide thin films from chemically modified metal-alkoxides

The effects of UV-irradiation on the properties of ZrO₂ and TiO₂ gel films prepared from corresponding metal-butoxides modified with acetylacetone (AcAc) or benzoylacetone (BzAc) have been studied. It was found that the chelate bonds of -diketones remaining in the gel films were dissociated by the UV-irradiation. The UV-irradiation also changed the properties of the gel films such as solubility; the solubility in acidic solutions was decreased for ZrO₂ gel films modified with AcAc and TiO₂ gel films modified with BzAc became insoluble in alcohol. Based on these findings, a new fine-patterning process has been established, which enables us to make fine-patterns of ZrO₂ and TiO₂ films on a variety of substrates.     

The effect of composition variables on precursor degradation and their consequence on Nb2O5 film properties prepared by the Pecchini Method

The calcination of Nb₂O₅ prepared by the Pecchini method was investigated using thermal analysis. The polymer precursor was prepared with different citric acid/ethylene glycol (CA/EG) and citric acid/niobium precursor (CA/Nb) molar ratios. The results suggest a strong influence of the CA/EG molar ratio, mainly on the polymerization degree. The CA/Nb ratio also modifies the degradation process of the precursor solution. The effect of the precursor compositional variation was also observed in the oxide structure, as well as in its electrochemical and electrochromic behavior. Films prepared using high CA/EG and a Nb salt precursor amount have the highest values of charge density and coloration efficiency. Moreover XRD data for this sample show a crystalline structure while the samples prepared with low CA/EG ratio are amorphous.     

Thick Fe2O3, Fe3O4 films prepared by the chemical solution deposition method

Fe₂O₃, Fe₃O₄ films have been prepared from Fe(OCH₂CH(CH₃)₂)₃–(CH₃)₂CHCH₂OH–2.2′-diethanola- mine (DEA)–poly(vinylpyrrolidone) (PVP) solutions by the spin-(SC) and dip-coating (DC) technique on SiO₂ and Si substrates. The maximum film thickness achieved without crack formation has been increased by incorporation of PVP (relative molecular weights 40000 and 360000) into the precursor solution. The stability of the precursor solutions was remarkably increased by addition of DEA. Compact, dense, and crack-free Fe₂O₃ films with thicknesses 900 nm (DC), 450 nm (SC), have been obtained via single-step deposition cycle. Higher-molecular-weight PVP has been more effective in increasing the thickness. The minimum concentration of DEA, which results in pronounced increase of solutions stability, is about R _P (n(DEA)/n(Fe) = 0.1). The high content of carboneous residue in the pyrolysed Fe₂O₃ films promotes the formation of Fe₃O₄ films via reduction in a gas flow of H₂/N₂ gas mixture. Microstructure, surface morphology, and magnetic properties of the films have been also investigated using SEM, AFM, and SQUID, respectively.     

Surface modification of thermoplastics by atomic layer deposition of Al2O3 and TiO2 thin films

Al₂O₃ and TiO₂ thin films were deposited by atomic layer deposition at 80-250 °C on various polymeric substrates such as polymethylmethacrylate (PMMA), polyetheretherketone (PEEK), polytetrafluoroethylene (PTFE) and ethylenetetrafluoroethylene (ETFE). The films were studied with FESEM, EDX, XRD, contact angle measurements and adhesion tests. The film growth rates on the thermoplastics were close to the corresponding growth rates on Si substrates. The adhesion of the films was good on PEEK and poor on PTFE. All coated surfaces showed lower water contact angles than the uncoated thermoplastics. Furthermore, the water contact angles on all TiO₂-coated surfaces decreased upon UV illumination, most efficiently with crystalline TiO₂ coatings.     

Capacitance and photocurrent study of electronic properties of anodic oxide films on Nb and Ta. Evaluation of the ionized donor concentration profile in Nb2O5 film

Electronic properties of electrochemically formed oxide films on Nb were studied by photocurrent and differential capacitance measurements in 0.025 M KH₂PO₄+0.025 M Na₂HPO₄ electrolyte, pH 6.9. Oxide films of n-type conductivity were formed galvanostatically for final potentials ranging from 4 to 230 V. Measurements were performed in two potential regions, which correspond to formation of a depleted layer of variable thickness at relatively low potentials, and to complete depletion of oxide films of electronic charge carriers at higher potentials. In the first potential region the behavior of both capacitance and photocurrent, was governed by a build up of a depleted layer of potential dependent thickness. In the second, high potential, region, which extends up to the oxide film formation potential, the photocurrent and capacitance of oxide films in most features followed the trends typical of dielectric films containing defects and traps. The photocurrent and capacitance measurements on presumably dielectric oxide films formed on Ta were staged for comparison. The capacitance–potential measurements performed in the first potential region enabled us to construct the ionized donor concentration profile across the Nb₂O₅ film width. The limitations on the use of the C–E profiling method for electrochemically formed oxide layers are considered.     

Refinement of the cation distribution in Nb-Mo double oxide

The structure of Nb₂Mo₃O₁₄ double oxide is refined from powder data using synchrotron radiation and the anomalous scattering effect; space group P $ \bar 4 The structure of Nb₂Mo₃O₁₄ double oxide is refined from powder data using synchrotron radiation and the anomalous scattering effect; space group P 2₁ m is found for the material. It is demonstrated that in the tetragonal unit cell with parameters a = 23.173 ?, c = 4.0027 ? Nb⁵⁺ and Mo⁶⁺ ions are stochastically distributed in MO₆ octahedra and MO₇ pentagonal bipyramids of the polygonal network structure of the Mo₅O₁₄ type. Original Russian Text Copyright ? 2008 by T. Yu. Kardash, L. M. Plyasova, V. M. Bondareva, and A. N. Shmakov __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 49, No. 4, pp. 729–735, May–June, 2008.     

High photocatalytic activity and stability for decomposition of gaseous acetaldehyde on TiO2/Al2O3 composite films coated on foam nickel substrates by sol-gel processes

A set of anatase titanium dioxide (TiO₂) films coated on foam nickel that modified by Al₂O₃ films as transition layer (indicated as TiO₂/Al₂O₃ films) were synthesized via sol-gel route. The bulk and surface properties of the TiO₂/Al₂O₃ films were characterized by thermal gravimetric and differential scanning calorimetry (TG-DSC), X-ray diffraction (XRD), field-emission scanning electron microscope (FE-SEM), and BET. The photocatalytic activities of TiO₂/Al₂O₃ films were investigated based on the degradation of gaseous acetaldehyde under ultraviolet (UV) irradiation. The foam nickel is a promising substrate material in practical applications because of its excellent hydrodynamic properties for gas passing. The TiO₂/Al₂O₃ composite films showed much higher photocatalytic activity and stability for degradation of gaseous acetaldehyde than the onefold TiO₂ films. The significant enhancement in photocatalytic activity and stability can be ascribed to the coating of Al₂O₃ transition layer, which concentrates the target substances around TiO₂ particles and increases the specific surface area (SSA) of the substrate (the SSAs of bare foam nickel and Al₂O₃ modified foam nickel are 0.12 and 113.7 m²/g, respectively) to provide more sites for TiO₂ loading.     

Influence of the crystallinity on the Li+ intercalation process in Nb2O5 films

Nb₂O₅ thin films were prepared by the Pechini method. The effect of the film crystallinity on the electrochemical and electrochromic properties was investigated. A relationship between the crystalline structure and the Li⁺ intercalation/extraction process, stability and kinetics was observed. A significant decrease in the electrochemical response was observed as a function of the number of cycles for films treated at 400 and 450 °C. However, as the calcination temperature increases this effect disappears. XRD studies shown that at 400 °C, the material is amorphous, evolving to orthorhombic phase. The transmittance variation as well as the coloration efficiency increases as the temperature is increased. In the initial cycles the intercalation charge is higher for the amorphous oxide than for the orthorhombic phase. However, the variation in the optical density is small. On the other hand, the charge of the orthorhombic phase oxide does not change. These results suggest that there are two different processes associated with Li⁺ intercalation, but only one of them leads to the coloration process.     

Evolution and characterization of fluorite-like nano-SrBi2Nb2O9 phase in the SrO-Bi2O3-Nb2O5-Li2B4O7 glass system

Transparent glasses of various compositions in the system (100−x)Li₂B₄O₇−x(SrO-Bi₂O₃-Nb₂O₅) (where x=10, 20, 30, 40, 50 and 60, in molar ratio) were fabricated via splat quenching technique. The glassy nature of the as-quenched samples was established by differential thermal analyses. X-ray powder diffraction (XRD) and transmission electron microscopic studies confirmed the amorphous nature of the as-quenched and crystallinity in the heat-treated samples. Fluorite phase formation prior to the perovskite SrBi₂Nb₂O₉ phase was analyzed by both the XRD and high-resolution transmission electron microscopy. Dielectric and the optical properties (transmission, optical band gap and Urbach energy) of these samples have been found to be compositional dependent. Refractive index was measured and compared with the values predicted by Wemple-Didomemenico and Gladstone-Dale relations. The glass nanocomposites comprising nanometer-sized crystallites of fluorite phase were found to be nonlinear optic active.     

The impact on the magnetic field growth of half-metallic Fe3O4 thin films

Half-metallic Fe₃O₄ films grown on a Si (100) substrate with a tantalum (Ta) buffer layer were prepared by DC magnetron reactive sputtering. Primary emphasis was placed on magnetic field growth of Fe₃O₄ thin film. The experiment's results showed that applying an external magnetic field to the samples during the growth was efficient to promote the polycrystalline Fe₃O₄ growth along certain directions. The magnetoresistance (MR) was also tested for comparison of the samples prepared with and without an external magnetic field, and showed that applying an external magnetic field can promote the MR values.     

An EQCM investigation of charging RuO2 thin films prepared by the polymeric precursor method

An electrochemical quartz crystal microbalance (EQCM) study of RuO₂ thin films, prepared by the sol-gel precursor method, is presented. The X-ray diffraction (XRD) analysis demonstrates that RuO₂ films were crystallized in the rutile phase and scanning electron microscopy investigations indicated the formation of a smooth surface. Cyclic voltammetry and EQCM studies were performed simultaneously in order to investigate the charging processes of the RuO₂ films in 0.1 M HClO₄. The voltammetric and mass versus potential responses present three well-defined regions associated with the RuO₂ redox couples. Based on these results and on the mass-charge relationships, the corresponding charging mechanisms are proposed. In the potential region governed by the Ru³⁺/Ru⁴⁺ redox couple, the mass-charge relation can be associated with the double-injection of protons and electrons. The other regions correspond to water release and oxyhydroxide species formation during charging.     

Process optimization and characterization of thin films of SrFeO3-x by the pechini method

Nanostructured coatings have recently attracted increasing interest because of the possibilities of synthesizing materials with unique physical-chemical properties. Highly sophisticated surface related properties, such as optical, magnetic, electronic, catalytic, mechanical, chemical and tribological properties can be obtained by advanced nanostructured coatings, making them attractive for various industrial applications. In this report we describe our efforts at developing methodology for the fabrication of SrFeO_3-x based thin films using a modified Pechini method. Thin films of SrFeO_3-x were fabricated using spin coating and a drop coating method developed in-house on Al₂O₃ and Si- substrates. The films annealed at 600°C for one hour show a perovskite phase. The grain size increases with increase in annealing temperature. The influence of various variables such as metal to chelant ratio, drying control reagents, calcination conditions, substrate type and mode of film formation were studied using XRD, optical microscopy, SEM and AFM.     

Growth of semiconducting iron sulfide thin films by chemical vapor deposition from air-stable single-source metal organic precursor for photovoltaic application

Semiconducting nanostructured iron sulfide thin films were prepared by aerosol chemical vapor deposition at 673 and 723?K from newly synthesized iron complex of dithiocarbo-1,2,3,4-tetrahydroquinoline [Fe(S₂CNC₉H₁₀)₂]. The degree of film surface roughness was determined by atomic force microscopy. The nature of the deposited thin films formed was determined by a combination of EDX analysis and glancing angle X-ray diffraction.     

Morphology control and luminescence properties of BaMgAl10O17:Eu phosphors prepared by spray pyrolysis

Starting from the aqueous solutions of metal nitrates with citric acid and polyethylene glycol (PEG) as additives, BaMgAl₁₀O₁₇:Eu²⁺ (BAM:Eu²⁺) phosphors were prepared by a two-step spray pyrolysis (SP) method. X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence spectra were used to characterize the resulted BAM:Eu²⁺ phosphors. The obtained BAM:Eu²⁺ phosphor particles have spherical shape, submicron size (0.5-3 μm). The effects of process conditions of the spray pyrolysis, such as molecular weight and concentration of PEG, on the morphology and luminescence properties of phosphor particles were investigated. Adequate amount of PEG was necessary for obtaining spherical particles, and the optimum emission intensity could be obtained when the concentration of PEG was 0.03 g/ml in the precursor solution. Moreover, the emission intensity of the phosphors increased with increasing of metal ion concentration in the solution. Compared with the BAM:Eu²⁺ phosphor prepared by citrate-gel method, spherical BAM:Eu²⁺ phosphor particles showed a higher emission intensity.     

Metal-organic deposition of YBa2Cu3Ox and Bi2Sr2Ca1Cu2Ox films on various substrates starting from different fluorine-free metallorganic compounds

YBa₂Cu₃O_x (Y-123) and Bi₂Sr₂Ca₁Cu₂O_x (Bi-2212) films on various substrates have been prepared by Metal-Organic Deposition starting from different metallorganic fluorine-free compounds and using a very simple instrumentation. The processing conditions include a rapid pyrolysis step in air and an annealing step in oxygen for Y-123 and in air for Bi-2212. The films obtained have been characterized by X-ray diffraction (XRD) and the formation of a superconducting phase of Y-123 or Bi-2212 was confirmed measuring the critical temperature (T _c) with Ac-susceptibility and resistive measurements. Microstructure and final cationic ratios have been studied by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS).     

Dielectric and tunable properties of highly (110)-oriented (Ba<Subscript>0.65</Subscript>Sr<Subscript>0.35</Subscript>)TiO<Subscript>3</Subscript> thin films deposited on Pt/LaNiO<Subscript>3</Subscript>/SiO<Subscript>2</Subscript>/Si substrates

Highly (110)-oriented Ba_0.65Sr_0.35TiO₃ films were deposited on Pt/LaNiO₃/SiO₂/Si substrates by a sol–gel method. It was found that the (110)-preferred Pt film was very effective for growing (110)-oriented ferroelectric films with perovskite structure. The as-grown Ba_0.65Sr_0.35TiO₃ films showed good dielectric properties with dielectric constant and loss tangent tan δ = 0.026. Excellent dielectric tunability was also achieved in the (110)-oriented films. With applying an electric field of 230 kV/cm at 100 kHz, the dielectric tunability and the figure of merit can reach up to 63.4% and 16, respectively. These results indicate that the highly (110)-oriented Ba_0.65Sr_0.35TiO₃ film is a promising candidate for the applications in microwave tunable devices.     

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.     

Microstructure and properties of sol-gel derived Pb(Zr<Subscript>0.3</Subscript>Ti<Subscript>0.7</Subscript>)O<Subscript>3</Subscript> thin films on GaN/sapphire for nanoelectromechanical systems

Highly (111) oriented, phase-pure perovskite Pb(Zr_0.3Ti_0.7)O₃ (or PZT 30/70) thin films were deposited on single-crystal, (0001) wurtzite GaN/sapphire substrates using the sol-gel process and rapid thermal annealing. The phase, crystallinity, and stoichiometry of annealed PZT films were evaluated by X-ray diffraction and Rutherford backscattering spectroscopy. The atomic force microscopy revealed a smooth PZT surface (rms roughness ∼1.5 nm) with striations and undulations possibly influenced by the nature of the underlying GaN surface. The cross-sectional field-emission scanning electron microscopic images indicated a sharper PZT/GaN interface compared to that of sol-gel derived PZT on (111) Pt/TiO₂/SiO₂/(100) Si substrates. The capacitance-voltage (C-V) characteristics for PZT in the Pt/PZT/GaN (metal-ferroelectric-semiconductor or MFS) configuration were evaluated as a function of annealing temperature and applied voltage. The observed C-V hysteresis stemmed from trapped charge at defect sites within PZT. Also, the lower capacitance density (C/A = 0.35 μF/cm², where A is the area of an electrode) and remnant polarization (P _r ∼ 4 μC/cm²) for PZT in the MFS configuration, compared to the values for PZT in the MFM configuration (Pt/PZT/Pt), were attributed to the high depolarization field within PZT.     

Photodegradation of 2,4-D over PdO/Al2O3-Nd2O3 photocatalysts prepared by the sol-gel method

The photocatalytic activity of 1.0 wt% PdO supported on Al₂O₃-Nd₂O₃ binary oxides prepared by the sol-gel method was studied in the photodegradation of 2,4-dichlorophenoxyacetic acid (2,4-D). The photocatalysts were characterized by N₂ physisorption, XRD and UV-vis spectroscopy. PdO supported on γ-Al₂O₃ photo-degrades the 2,4-D, however the addition of Nd₂O₃ to γ-Al₂O₃ notably improves the photocatalytic activity. As the concentration of Nd₂O₃ in the binary oxide increases from 2 to 10 wt%, the photodegradation of 2,4-D is highly enhanced. The catalytic test for PdO supported on pure Nd₂O₃ showed scarce photocatalytic activity. Total organic carbon (TOC) analysis showed that the 2,4-D has been completely destroyed on the PdO/Al₂O₃-Nd₂O₃ photocatalysts after 6 h under irradiation.     

Investigation on the catalytic activity of doped low-percentage oxide catalysts Mn/ZnO obtained from oxalate precursor

The precursors with a low manganese content ≤ 0.07% Mn were synthesized by spontaneous crystallization from Zn²⁺, Mn²⁺ and C₂O₄ ²⁻-containing solutions. The initial ratio Zn²⁺:C₂O₄ ²⁻ = 1:1 and 1:2 influences the morphology and prevailing orientations of the crystallites in the oxalate samples. The presence of such small Mn content in the samples does not change the morphology or size of the crystals. The ZnO and Mn/ZnO oxides with manganese content from 0.51×10⁻² to 15.1×10⁻² Wt % are obtained after thermal decomposition of the oxalates. The oxides preserved the morphology of the precursors. The catalytic tests show that the pure ZnO has a poor activity for CO oxidation reaction. Its doping with Mn promotes the catalytic activity (up from twice to five times) in spite of the very low contents of the dopants. The observed increase of the activity depends on both dopant concentration and Zn²⁺:C₂O₄ ²⁻ ratio, probably due to the different mechanism of the manganese inclusion and different morphology of the oxides. The catalysts of the 1:2 series are more active in CO oxidation reaction.