Aging of ITO anodes treated by supercritical CO<Subscript>2</Subscript>/H<Subscript>2</Subscript>O<Subscript>2</Subscript> fluids for OLEDs

The aging behaviors of indium tin oxide (ITO) anodes treated by supercritical CO₂/H₂O₂ (SCCO₂/H₂O₂) fluids were investigated. As the SCCO₂/H₂O₂-treated ITO anodes were aged, the contact angle and surface energy were analyzed and compared with those of the ITO anodes treated by oxygen plasma. The SCCO₂/H₂O₂ pretreatment yielded a stable polar component of the ITO surfaces after 48 h of aging. The energy reduction in the polar component of the oxygen-plasma-treated ITO due to aging was 20 %, as compared with the 1.1 % decrease in ITO treated with the SCCO₂/H₂O₂ fluids at 4000 psi for 15 min. The X-ray photoelectron spectroscopy analysis revealed that the oxygen content of the ITO surfaces with the SCCO₂/H₂O₂ pretreatment was significantly higher than that of the ITO treated by oxygen plasma. This could result from the formation of hydroxyl products that functioned as a stable buffer layer against further contamination during aging. In addition, the correlated dependence of the OLED performance on the aged ITO anodes was also studied. The OLEDs with the SCCO₂/H₂O₂ pretreatment showed an improved degradation of I–V characteristics and brightness in comparison with those of the devices treated with oxygen plasma after aging the treated ITO anodes for 6 and 12 h. The obtained results suggested that the ITO anodes treated by the SCCO₂/H₂O₂ fluids exhibited a stable surface chemistry and could be useful for OLED applications.     

General aspects of the growth of In-In<Subscript>2</Subscript>O<Subscript>3</Subscript> films

Transformations in indium nanolayers have been studied by optical spectroscopy, microscopy, and gravimetry in relation to the thickness of the layers (2–147 nm) and heat treatment temperature (473–873 K) and time (0–120 min). The kinetic curves for the degree of conversion are adequately described by a linear, inverse logarithmic, parabolic, or logarithmic law, depending on the thickness of the indium film and heat treatment temperature. We have measured the contact potential difference across the In and In₂O₃ films and the photovoltage in the In-In₂O₃ system. The results have been used to derive the energy band diagram of the In-In₂O₃ system. A model has been proposed for the thermal transformation of indium films, which involves oxygen adsorption steps, charge carrier redistribution in the In-In₂O₃ interfacial field (positive on the In₂O₃ side), and In₂O₃ formation.     

Electrophysical parameters and composition of a DC glow discharge plasma in HBr/H<Subscript>2</Subscript> mixtures

Model investigations of the effect of the initial composition of a HBr/H₂mixture on the stationary parameters of a dc glow discharge plasma (p = 30−250 Pa, i _p = 20 mA) have been carried out. Calculation data on energy distributions of electrons, integral characteristics of the electron gas, and concentrations of neutral and charged particles have been obtained.     

Formation and growth studies of the (Bi,Pb)<Subscript>2</Subscript>Sr<Subscript>2</Subscript>Ca<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>10</Subscript> phase in Ag sheathed tapes

The formation and the thickness growth of the (Bi,Pb)₂Sr₂Ca₂Cu₃O₁₀ phase in Ag-sheathed tapes have been investigated by scanning electron microscopy on samples sintered at 840°C in a flow of 8.5% O₂ (rest N₂) and quenched in air after sintering for 1 to 50 h. The thickness of the (Bi,Pb)₂Sr₂Ca₂Cu₃O₁₀ grains was measured statistically after different sintering times. The experimental results show that the average thickness of these grains increases during the entire sintering period, while the average thickness growth rate decreases exponentially with sintering time. The volume fractions of the various phases present during the heat treatment were also measured from micrographs. Detailed studies of the microstructure and phase formation kinetics support the view that the formation of the (Bi,Pb)₂Sr₂Ca₂Cu₃O₁₀ phase proceeds via a nucleation and growth process. Based on the present observations, a model describing the microstructure evolution is presented.     

Formation of solid solutions in the TiO<Subscript>2</Subscript>-Cr<Subscript>2</Subscript>O<Subscript>3</Subscript> system

The phase formation and reaction kinetics in the TiO₂-Cr₂O₃ system have been studied by x-ray diffraction and electron microscopy. The Cr₂O₃ solubility in TiO₂ has been accurately determined, and the rate parameters of the formation of solid solutions in this system have been evaluated. The results demonstrate that Cr₂O₃ dissolves in rutile and not in anatase. Cr₂O₃ markedly reduces the temperature of the anatase-rutile phase transition.     

Dissolution of UO<Subscript>2</Subscript> in the N<Subscript>2</Subscript>O<Subscript>4</Subscript>-H<Subscript>2</Subscript>O system

The kinetics of the UO₂ dissolution in the N₂O₄-H₂O system was studied. At 25°C, the process is kinetically controlled, whereas at 55°C the process occurs initially under kinetic control (3 min) and then under diffusion-kinetic control. At 80°C, the process occurs exclusively under diffusion-kinetic control. The apparent activation energy was estimated at ∼39 kJ mol⁻¹.     

Solvothermal synthesis of CoFe<Subscript>2</Subscript>O<Subscript>4</Subscript> hollow spheres

Hollow CoFe₂O₄ spheres consisted of CoFe₂O₄ nanoparticles were synthesized by a facile solvothermal treatment of an ethylene glycol solution of FeCl₃ · 6H₂O, CoCl₂ · 6H₂O, and NaAc at 200 °C in the presence of polyethylene glycol and oleic acid. The products were characterized by powder X-ray diffraction, transmission electron microscopy, selected area electron diffraction, high-resolution transmission microscopy, scanning electron microscopy. The magnetic properties were evaluated using a vibrating sample magnetometer. The probable mechanism of the formation of Hollow CoFe₂O₄ spheres was discussed. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Luminescence studies on Eu<Superscript>2+</Superscript> and Tb<Superscript>3+</Superscript> doped Ca<Subscript>2</Subscript>MgSi<Subscript>2</Subscript>O<Subscript>7</Subscript> phosphors

Eu²⁺ and Tb³⁺ doped Ca₂MgSi₂O₇ phosphors were synthesized by conventional solid-state reaction. The phase formation was confirmed by X-ray powder diffraction technique and refined lattice parameters were calculated by rietveld refinement process using Celref v3. The photoluminescence (PL) excitation and emission spectra were investigated. The phosphors exhibited broaden green emitting luminescence peaking at 520 nm when excited at 374 nm source. Morphological studies were carried out using Scanning electron microscopy (SEM) images of the sample with optimum PL emission. The dependence of photoluminescence intensity on co-dopant concentration and the kinetic parameters were also reported. Time resolved fluorescence spectroscopy (TRFS) is used to investigate the decay in luminescence signals with respect to time. The sample proved to be a good long lasting material, which makes it useful in emergency signs, textile printing, textile exit sign boards and electronic instrument dial pads etc.     

Thermal oxidation of InP with V<Subscript>2</Subscript>O<Subscript>5</Subscript> + PbO nanolayers of different compositions

Data are presented on the thermal oxidation of (V₂O₅ + PbO)/InP structures which demonstrate that the combined effect of the oxides deposited by magnetron sputtering does not follow the additivity rule and that this behavior is due to the formation of a quasi-liquid phase (maximum) and lead vanadate (minimum) (IR spectroscopy, Auger electron spectroscopy). The effective activation energy for the oxidation of the (V₂O₅ + PbO)/InP structures is shown to systematically decrease with increasing initial vanadium oxide content. The oxidation of the structures follows a partially catalytic mechanism, with V₂O₅ acting as a catalyst (oxidation kinetics, IR spectroscopy, ultrasoft X-ray emission spectroscopy).     

Enhanced photocatalytic activity of Bi<Subscript>12</Subscript>O<Subscript>17</Subscript>Cl<Subscript>2</Subscript> preferentially oriented growth along [200] with various surfactants

In this study, Bi₁₂O₁₇Cl₂ nanosheets preferentially oriented growth along [200] were successfully synthesized through a facile hydrothermal method in the presence of various surfactants, including PVP, CTAB and CTAC. The crystallization behavior, band gap structure and morphology of Bi₁₂O₁₇Cl₂ could be modulated by the addition of surfactants. Bi₁₂O₁₇Cl₂ with surfactants displays superior visible light photocatalytic performance than pristine sample for photodegrading RhB and 2-chlorophenol. Moreover, Bi₁₂O₁₇Cl₂ preferentially oriented growth along [200] maintained stable and recyclable in the photocatalytic process, demonstrating their promising application in environment remediation.     

Effect of Y<Subscript>2</Subscript>O<Subscript>3</Subscript> on the crystallization behavior of SiO<Subscript>2</Subscript>–MgO–B<Subscript>2</Subscript>O<Subscript>3</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> glasses

A series of glass comprising of SiO₂–MgO–B₂O₃–Y₂O₃–Al₂O₃ in different mole ratio has been synthesized. The crystallization kinetics of these glasses was investigated using various characterization techniques such as differential thermal analysis (DTA), thermo gravimetric analysis (TGA), X-ray diffraction (XRD), and scanning electron microscopy (SEM). Crystallization behavior of these glasses was markedly influenced by the addition of Y₂O₃ instead of Al₂O₃. Addition of Y₂O₃ increases the transition temperature, T _g, crystallization temperature, T _c and stability of the glasses. Also, it suppresses the formation of cordierite phase, which is very prominent and detrimental in MgO-based glasses. The results are discussed on the basis of the structural and chemical role of Y³⁺ and Al³⁺ ions in the present glasses.     

Influence of C<Subscript>4</Subscript>F<Subscript>8</Subscript>/Ar/O<Subscript>2</Subscript> plasma etching on SiO<Subscript>2</Subscript> surface chemistry

The plasma assisted etching of SiO₂ in a commercial RF reactor with a variety of C₄F₈/Ar/O₂ chemistries has been studied by XPS, SIMS and FTIR. A simple model of surface reactions is proposed. In particular, the role of oxygen in the etch process has been investigated. According to our experiments, oxygen inhibits the formation of CFH based polymeric films on the surface. As the etching process is due to an exchange reaction between the oxygen in the SiO₂ and the gaseous fluorine species in the plasma, the presence of oxygen in the etch hinders this process by occupying adsorption sites on the surface. The results would confirm that argon does not participate in chemical reactions with the SiO₂ substrate but provides energy for reactions in which F, C and O are involved. The results also indicate that a thick fluorocarbon layer only forms on the surface in the absence of oxygen, regardless of the oxygen source. Consequently, only when the SiO₂ layer has been substantially removed does this film form.     

Mechanochemical Synthesis of Crystalline Compounds in the Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>–GeO<Subscript>2</Subscript> System

Crystalline mechanochemical synthesis products in the Bi₂O₃–GeO₂ system are studied by x-ray diffraction. The results indicate the formation of sillenite (Bi₁₂GeO₂₀), eulytite (Bi₄Ge₃O₁₂), and Aurivillius (Bi₂GeO₅) phases. The Aurivillius phase is shown to be in mechanochemical equilibrium with the sillenite phase in the 2Bi₂O₃ + GeO₂ system and with the eulytite phase in the Bi₂O 3 + GeO 2 system. The structural parameters of the synthesized metastable solid solutions are determined. The three phases contain high concen-trations of vacancies. In addition, the sillenite and Aurivillius phases are characterized by compositional disordering. Structural and ESR data point to partial reduction of the oxides, which accounts for the formation of the Aurivillius phase. According to x-ray photoelectron spectroscopy results, mechanical activation of bismuth oxide produces reduced binding energy states of Bi and O, which is tentatively attributed to clustering and the formation of complex radicals.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 6, 2005, pp. 711–719.Original Russian Text Copyright © 2005 by Zyryanov, Smirnov, Ivanovskaya.     

Preparation and magnetic properties of the CoFe<Subscript>2</Subscript>O<Subscript>4</Subscript> thin films on Si substrate by sol-gel technique

A stable precursor for CoFe₂O₄ thin film was prepared by sol-gel technique from the aqueous solution of FeCl₃·6H₂O and CoCl₂·6H₂O. Sol was deposited on a naturally oxidized silicon-substrate by spinning technique (2000 rpm) and heat treated at different temperatures ranging from 700 to 1100 °C. Thickness of the films was controlled in the range of 400–500 nm and all the films were characterized by using XRD and SEM. The effects of temperature and the composition on the formation of CoFe₂O₄ thin film were also studied. Films obtained at relatively lower temperature showed multi-phases of α-Fe₂O₃, CoFe₂O₄ and CoO while the formation of CoFe₂O₄ phase increases with increasing temperature. Furthermore, the composition of the solution in mol% has great role on the formation of CoFe₂O₄ films and the film containing 50 mol% of Co²⁺ exhibited CoFe₂O₄ mono-phase. Surface morphology of the films was studied by scanning electron microscope (SEM). Magnetic properties of the films, studied by using vibrating sample magnetometer (VSM), showed relatively high saturation magnetization (8.04–22.21 kWb/m²) as well as high coercivity (44.59–63.30 kA/m). Saturation magnetization also increases with increasing heat treatment temperature.     

Formation of YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>6 + <Emphasis Type="Italic">x</Emphasis></Subscript> clusters in laser-generated plasma

We have studied the influence of YBa₂Cu₃O_{6 + x} clusters formed in the plasma generated by laser ablation of a YBa₂Cu₃O_{7 ? δ} target on the optical transmission spectra of amorphous YBaCuO films deposited on glass substrates arranged along the direction of predominant plasma expansion in the laser plume. It is established that intense cluster formation begins in the region of rapid decrease in the film thickness, where the temperature of plasma decreases to a level at which stable atomic complexes characteristic of the target composition can form (under the experimental conditions studied, this was observed at as distance of L > 6 cm from the target). As the amount of clusters in the deposit increases, the magnitude of the interference fringes, which are characteristic of optically homogeneous media, gradually decreases and eventually almost vanishes. At the same time, features typical of the electron structure of YBa₂Cu₃O_{7 ? δ} appear and grow in the optical transmission spectra of the YBaCuO films, including the absorption due to free charge carriers at ?ω < 1.2 eV (characteristic of “metallic” clusters) and the minima at ?ω = 1.4 and 1.75 eV (characteristic of a dielectric state).     

Redox behavior and reduction mechanism of Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>–CeZrO<Subscript>2</Subscript> as oxygen storage material

Fe₂O₃–CeZrO₂ is a suitable oxygen storage material for the production of pure hydrogen by a cyclic water gas shift (CWGS) process which is based on the reduction of the material by syngas followed by the re-oxidation of the reduced material with water vapor. For identification of the reduction kinetics H₂-temperature programmed reduction experiments were performed. Several kinetic models were tested and the activation energy of reduction was calculated by the Kissinger method, by model-based curve fitting and by the isoconversional analysis method. The reduction of Fe₂O₃–CeZrO₂was found to occur in a four-step process including the reduction of Fe₂O₃,Fe₃O₄, and CeZrO₂. The overall process can be interpreted as phase-boundary controlled reduction of Fe₂O₃ to Fe₃O₄, and two-dimensional nucleation controlled reduction of Fe₃O₄ to Fe and of CeO₂ to Ce₂O₃. At higher oxygen conversion, the reduction of Fe₃O₄ and CeO₂ are significantly influenced by volume-diffusion in the solid bulk.     

Simulation of the adsorption of CaCl<Subscript>2 </Subscript>on Mg(OH)<Subscript>2</Subscript> planes

The adsorption behavior of Ca²⁺ and Cl⁻ on Mg(OH)₂ planes was simulated using Universal Force Field method. The energy, the capacity and the configuration involved in the adsorption process were estimated. The results showed that Ca²⁺ was easier to be adsorbed and incorporated on the (001) plane than other planes such as (100), (101) and (110) planes. The incorporation of Cl⁻ in Mg(OH)₂ was difficult since the radius for Cl⁻ is much bigger than that of OH⁻. The adsorption of Ca²⁺ on (001) plane at elevated temperature may inhibit the growth along [001] direction, leading to occurrence of the (001) plane, the shrinkage of the (101) and (110) planes and the formation of Mg(OH)₂ plates with bigger ratios of diameter to thickness. Project supported by the National Natural Science Foundation of China (No. 50574051).     

Thermochemical and luminescent properties of the K<Subscript>2</Subscript>MgV<Subscript>2</Subscript>O<Subscript>7</Subscript> and M<Subscript>2</Subscript>CaV<Subscript>2</Subscript>O<Subscript>7</Subscript> (M = K,Rb, Cs) vanadates

We have studied the compounds K₂MgV₂O₇ and M₂CaV₂O₇ with M = K, Rb, and Cs. These vanadates melt incongruently in the range 635–717°C. Cooling their decomposition products to room temperature leads to the formation of nonequilibrium phase assemblages characteristic of the corresponding oxide systems. The compounds offer broadband photo- and radioluminescence with an essentially white (to the human eye) emission spectrum. A model is proposed for luminescence centers in the vanadates, which involves the formation of defects in vanadium-oxygen groups, and an energy level diagram of the emission centers is constructed in the form of configuration curves in the harmonic oscillator approximation. The luminescent properties of these compounds suggest that they can be used as basic components of cathodo- and roentgenoluminescent screens and white-light-emitting diodes with improved color performance.     

Preparation of magnetic composites through SrO-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-B<Subscript>2</Subscript>O<Subscript>3</Subscript> glass crystallization

Glasses with nominal compositions 11SrO · 5.5Fe₂O₃ · 4.5Al₂O₃ · 4B₂O₃ (1) and 15SrO · 5.5Fe₂O₃ · 4.5Al₂O₃ · 4B₂O₃ (2) were prepared by rapidly quenching oxide melts between counterrotating steel rollers. The glasses were then heat-treated in the range 650–950°C to produce glass-ceramic samples. The samples were characterized by X-ray diffraction, electron microscopy, and magnetic measurements. The phase composition of the glass-ceramics was determined, and their microstructure and magnetic properties were studied. The annealing temperature was shown to have a strong effect on the coercivity of the materials, which reaches 650 and 570 kA/m for compositions 1 and 2, respectively.     

K<Superscript>+</Superscript> ion conducting properties in the R<Subscript>2</Subscript>O<Subscript>3</Subscript>-KNO<Subscript>3</Subscript> (R: Rare earths) solid solution series

A new type of polycrystalline potassium ion conducting solid electrolyte doped with potassium nitrite as the starting material, was developed. Since cubic rare earth oxides hold reasonably enough interstitial space for bulky K⁺ ion migration in the crystal lattice, an extraordinary high K⁺ ion conductivity was successfully achieved by forming a polycrystalline (1 − x)R₂O₃-xKNO₃ solid solution, which was realized by doping KNO₂ as the KNO₃ state into the interstitial site of cubic rare earth oxide crystal lattice. The potassium ion conductivity of the (1 − x)R₂O₃-xKNO₃ (R: rare earths) solid solution linearly increased with expanding the R₂O₃ crystal lattice and the highest K⁺ ion conductivity was obtained for the 0.653Gd₂O₃-0.347KNO₃ solid solution, which is three orders of magnitude higher than that of a well-known polycrystalline K⁺ ion conducting K₂SO₄ solid and the value exceeds that in the ab conducting plane of a K⁺-β ”-Al₂O₃ single crystal.