Enhanced electrochemical properties of fluoride-coated LiCoO<Subscript>2</Subscript> thin films

The electrochemical properties of fluoride-coated lithium cobalt oxide [LiCoO₂] thin films were characterized. Aluminum fluoride [AlF₃] and lanthanum fluoride [LaF₃] coating layers were fabricated on a pristine LiCoO₂ thin film by using a spin-coating process. The AlF₃- and LaF₃-coated films exhibited a higher rate capability, cyclic performance, and stability at high temperature than the pristine film. This indicates that the AlF₃ and LaF₃ layers effectively protected the surface of the pristine LiCoO₂ film from the reactive electrolyte.     

Structure and electrical properties of sputtered TiO<Subscript>2</Subscript>/ZrO<Subscript>2</Subscript> bilayer composite dielectrics upon annealing in nitrogen

The high-k dielectric TiO₂/ZrO₂ bilayer composite film was prepared on a Si substrate by radio frequency magnetron sputtering and post annealing in N₂ at various temperatures in the range of 573 K to 973 K. Transmission electron microscopy observation revealed that the bilayer film fully mixed together and had good interfacial property at 773 K. Metal-oxide-semiconductor capacitors with high-k gate dielectric TiO₂/ZrO₂/p-Si were fabricated using Pt as the top gate electrode and as the bottom side electrode. The largest property permittivity of 46.1 and a very low leakage current density of 3.35 × 10^-5 A/cm² were achieved for the sample of TiO₂/ZrO₂/Si after annealing at 773 K.     

Enhanced photocatalytic oxidation properties in Pt-TiO<Subscript>2</Subscript> thin films by grounding

The rates of formaldehyde and toluene photocatalytic oxidation with different initial concentrations over a Pt-TiO₂ film were analyzed at both the grounded and non-grounded states. The photocatalytic oxidation rates at the grounded states were faster than in the non-grounded states under similar reaction conditions. The enhanced photocatalytic oxidation rates in the grounded state were attributed to the effective splitting of the electron-hole pairs as a result of the scavenging of photoexcited electrons through the ITO (indium tin oxide) glass to earth. The pseudo first order model showed good agreement with the experimentally obtained heterogeneous photocatalytic oxidation rates of formaldehyde and toluene.     

Electronic and magnetic properties of SnO<Subscript>2</Subscript>/CrO<Subscript>2</Subscript> thin superlattices

In this article, using first-principles electronic structure calculations within the spin density functional theory, alternated magnetic and non-magnetic layers of rutile-CrO₂ and rutile-SnO₂ respectively, in a (CrO₂) _n (SnO₂) _n superlattice (SL) configuration, with n being the number of monolayers which are considered equal to 1, 2, ..., 10 are studied. A half-metallic behavior is observed for the (CrO₂) _n (SnO₂) _n SLs for all values of n. The ground state is found to be FM with a magnetic moment of 2 μ_B per chromium atom, and this result does not depend on the number of monolayers n. As the FM rutile-CrO₂ is unstable at ambient temperature, and known to be stabilized when on top of SnO₂, the authors suggest that (CrO₂) _n (SnO₂) _n SLs may be applied to spintronic technologies since they provide efficient spin-polarized carriers.     

Structural,electrical and optical properties of pure and NaLaF<Subscript>4</Subscript> doped PEO polymer electrolyte films

A Sodium ion conducting polymer electrolyte based on Polyethylene oxide (PEO) complexed with Sodium lanthanum tetra fluoride (NaLaF₄) was prepared using solution cast technique. The complexation of the salt with PEO was confirmed by X-ray diffraction (XRD) and Fourier Transform Infrared spectroscopic (FTIR) studies. Differential Scanning Calorimetry (DSC) is carried out to determine the melting temperature of these electrolyte films. Electrical conductivity was measured in the temperature range 300–370 K as a function of dopant concentration as well as temperature. Optical absorption studies were made in the wavelength range 200–600 nm on pure and NaLaF₄ doped PEO film. The absorption edge was observed at 4.62 eV for undoped PEO while it ranged from 3.16 to 3.5 eV for NaLaF₄ doped films. The direct band gaps for undoped and NaLaF₄ doped PEO films were found to be, respectively, 4.54 and 3.44, 3.24 and 3.12 eV while the indirect band gaps were 4.43 and 3.25, 3.05 and 2.9 eV, respectively. It was found that the energy gaps and band edge values shifted to lower energies on doping with NaLaF₄ salt.     

Characterization of thermally aged AlPO<Subscript>4</Subscript>-coated LiCoO<Subscript>2</Subscript> thin films

The electrochemical properties and stability during storage of pristine and AlPO₄-coated LiCoO₂ thin films were characterized. The wide and smooth surface of the thin film electrode might provide an opportunity for one to observe surface reactions with an electrolyte. The rate capability and cyclic performance of the LiCoO₂ thin film were enhanced by AlPO₄ surface coating. Based on secondary ion mass spectrometry analysis and scanning electron microscopy images of the surface, it was confirmed that the coating layer was successfully protected from the reactive electrolyte during storage at 90°C. In contrast, the surface of the pristine sample was severely damaged after storage.     

Detection of CO<Subscript>2</Subscript> and O<Subscript>2</Subscript> by iron loaded LTL zeolite films

Detection of oxygen and carbon dioxide is important in the field of chemical and biosensors for atmosphere and biosystem monitoring and fermentation processes. The present study reports on the preparation of zeolite films doped with iron nanoparticles for detection of CO₂ and O₂ in gas phase. Pure nanosized LTL type zeolite with monomodal particle size distribution loaded with iron (Fe-LTL) was prepared under hydrothermal condition from colloidal precursor suspensions. The zeolite was loaded with iron to different levels by ion exchange. The Fe-LTL suspensions were used for preparation of thin films on silicon wafers via spin coating method. The reduction of the iron in the zeolite films was carried out under H₂ flow (50% H₂ in Ar) at 300 °C. The presence of iron nanoparticles is proved by in situ ultra-violet-visible spectroscopy. The properties of the films including surface roughness, thickness, porosity, and mechanical stability were studied. In addition, the loading and distribution of iron in the zeolite films were investigated. The Fe-LTL zeolite films were used to detect O₂ and CO₂ in a concentration dependent mode, followed by IR spectroscopy. The changes in the IR bands at 855 and 642 cm^–1 (Fe?O?H and Fe?O bending vibrations) and at 2363 and 2333 cm^–1 (CO₂ asymmetric stretching) corresponding to the presence of O₂ and CO₂, respectively, were evaluated. The response to O₂ and CO₂ was instant, which was attributed to great accessibility of the iron in the nanosized zeolite crystals. The saturation of the Fe-LTL films with CO₂ and O₂ at each concentration was reached within less than a minute. The Fe-LTL films detected both oxygen and carbon dioxide in contrast, to the pure LTL zeolite film.

Open image in new window

     

Synthesis,characterization and electrical properties of polypyrrole/V<Subscript>2</Subscript>O<Subscript>5</Subscript> composites

Polypyrrole (PPy) and its composites with vanadium pentoxide (V₂O₅) were synthesized in aqueous medium by chemical oxidation polymerization using FeCl₃·6H₂O as an oxidant. The materials were characterized by Fourier transform infrared (FT-IR) spectroscopy, X-ray diffractometry (XRD), thermogravimetry analyzer (TGA), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), UV/visible spectroscopic techniques and LCR-meter. The FT-IR results confirmed the successful synthesis of PPy and PPy/V₂O₅ composites. The XRD study showed the amorphous and crystalline nature of PPy and PPy/V₂O₅ composites, respectively. The TGA analysis showed slight increase in the thermal stability of the composites. The SEM data verified the porous nature of PPy and the composites. The UV/visible spectrometry confirmed the doping of PPy in composites. The electrical properties of the materials displayed their semiconducting nature. The resistance of the samples was found to be dependent on temperature and the contents of V₂O₅ in the composites.     

Effect of rapid thermal annealing on the structural and electrical properties of TiO2 thin films prepared by plasma enhanced CVD

Titanium oxide thin films were deposited on p-type Si(100), SiO₂/Si, and Pt/Si substrates by plasma enhanced chemical vapor deposition using high purity Ti(O-i-C₃H₇)₄ and oxygen. As-deposited amorphous TiO₂ thin films were treated by rapid thermal annealing (RTA) in oxygen ambient, and the effects of RTA conditions on the structural and electrical properties of TiO₂ films were studied in terms of crystallinity, microstructure, current leakage, and dielectric constant. The dominant crystalline structures after 600 and 800 ‡C annealing were an anatase phase for the TiO₂ film on SiO₂/Si and a rutile phase for the film on a Pt/Si substrate. The dielectric constant of the as-grown and annealed TiO₂ thin films increased depending on the substrate in the order of Si, SiO₂/Si, and Pt/ Si. The SiO₂ thin layer was effective in preventing the formation of titanium silicide at the interface and current leakage of the film. TEM photographs showed an additional growth of SiO_x from oxygen supplied from both SiO₂ and TiO₂ films when the films were annealed at 1000 ‡C in an oxygen ambient. Intensity analysis of Raman peaks also indicated that optimizing the oxygen concentration and the annealing time is critical for growing a TiO₂ film having high dielectric and low current leakage characteristics.     

Effect of annealing temperature on the evolution of structural,microstructural, and optical properties of spin coated ZnO thin films

Zinc oxide (ZnO) thin films were sol-gel spin coated on glass substrates and annealed at various temperatures from 300–500 °C. Zinc acetate dihydrate (ZAD), monoethanolamine (MEA), and 2-methoxyethanol were used as the starting materials, stabilizer and solvent, respectively. The effect of annealing temperature on the structural and optical properties of the ZnO thin films was investigated by X-ray diffractometer (XRD), atomic force microscope (AFM), UV–VIS spectrophotometry and ellipsometry. The XRD results showed the films to have a preferential c-axis orientation, whereas the AFM results confirmed a columnar structure. The surface roughness increased with the increase in annealing temperature. Parameters such as ratio of free charge carrier concentration to effective mass (N/m*) and plasma frequency (ω_p) were determined from the transmittance graph using the Wemple di Domenico model. Both N/m* and ω_p were noticed to reduce with the increase in annealing temperature. Band gap decreased with the increase in the annealing temperature indicating absorption edge shift towards the red region.     

Dependence of the optical properties of the 30.5K<Subscript>2</Subscript>O · 8.3Al<Subscript>2</Subscript>O<Subscript>3</Subscript> · 3.6SiO<Subscript>2</Subscript> · 57.6P<Subscript>2</Subscript>O<Subscript>5</Subscript> glass on the trivalent titanium content

An optical material, namely, the potassium aluminosilicophosphate glass activated with trivalent titanium ions, is synthesized and studied. The optimum concentration range (0.2–10.0 wt % Ti₂O₃) that provides the best physical, luminescent, and kinetic properties of glasses is determined. This makes it possible to use the sensitizing properties of Ti³⁺ ions to the greatest extent.Original Russian Text Copyright © 2004 by Fizika i Khimiya Stekla, Batyaev, Leonov.     

Scanning Probe Microscopy on heterogeneous CaCu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript> thin films

The conductive atomic force microscopy provided a local characterization of the dielectric heterogeneities in CaCu₃Ti₄O₁₂ (CCTO) thin films deposited by MOCVD on IrO₂ bottom electrode. In particular, both techniques have been employed to clarify the role of the inter- and sub-granular features in terms of conductive and insulating regions. The microstructure and the dielectric properties of CCTO thin films have been studied and the evidence of internal barriers in CCTO thin films has been provided. The role of internal barriers and the possible explanation for the extrinsic origin of the giant dielectric response in CCTO has been evaluated.     

Electrolytic properties of sulfide-conducting phases based on the BaLn<Subscript>2</Subscript>S<Subscript>4</Subscript> and CaLn<Subscript>2</Subscript>S<Subscript>4</Subscript> compounds of different structural types

The criteria for the choice of objects of investigation that possess sulfide-ion conduction, have the general formula MeLn₂S₄, and crystallize in different structural types are considered. The data obtained on the electrolytic properties of phases based on BaLn₂S₄(Ln = Nd, Sm, Tm); CaFe₂O₄ structural type), CaLn₂S₄(Ln = Y, Yb); Yb₃S₄ structural type), and CaLn₂S₄(Ln = Pr, Nd, Gd); Th₃P₄ structural type) are generalized. The performed comparative analysis of the properties of the synthesized electrolytes has demonstrated that the properties of solid electrolytes depend on the configuration of the f state of lanthanides to a greater extent than on the structure of the electrolytes under investigation. The vacancy mechanism of defects formation and sulfide-ion transfer in phases based on thiolanthanates is proposed reasoning from the data on the dependence of the electrolytic and thermodynamic properties on the composition.     

Structure of an atmospheric-pressure H<Subscript>2</Subscript>/O<Subscript>2</Subscript>/N<Subscript>2</Subscript> flame doped with iron pentacarbonyl

This paper presents the measurement and simulation data on the thermal and chemical structure of an atmospheric-pressure premixed H₂/O₂/N₂ flame doped with iron pentacarbonyl Fe(CO)₅. Soft ionization molecular beam mass spectrometry was used to measure concentration profiles of the combustion products of iron pentacarbonyl: Fe, FeO₂, FeOH, and Fe(OH)₂. A comparison of experimental and simulated concentration profiles showed that they are in satisfactory agreement for FeO₂ and Fe(OH)₂ and differ significantly for Fe and FeOH. Thus, the previously proposed kinetic model for the oxidation of iron pentacarbonyl was tested and it was shown that the mechanism needs further elaboration.     

Selective oxidation of H<Subscript>2</Subscript>S to sulfur over CeO<Subscript>2</Subscript>-TiO<Subscript>2</Subscript> catalyst

The catalytic oxidation of hydrogen sulfide (H₂S) to elemental sulfur was studied over CeO₂-TiO₂ catalysts. The synthesized catalysts were characterized by various techniques such as X-ray diffraction, BET, X-ray photoelectron spectroscopy (XPS), temperature-programmed desorption of ammonia, and scanning electron microscopy (SEM). Catalytic performance studies of the CeO₂-TiO₂ catalysts showed that H₂S was successfully converted to elemental sulfur without considerable emission of sulfur dioxide. CeO₂-TiO₂ catalysts with Ce/Ti=1/5 and 1/3 exhibited the highest H₂S conversion, possibly due to the uniform dispersion of metal oxides, high surface area, and high amount of acid sites.     

Effect of mixed solvent on structural,morphological, and optoelectrical properties of spin-coated TiO2 thin films

Nanocrystalline TiO₂ anatase thin films have been synthesized from alkoxide solution via sol–gel spin coating method. The effects of different solvents of methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, and tert-butanol as well as those of mixed solvents on crystal structure, thermal behavior, morphology, and optoelectrical properties were investigated. It was found that not only the occurrence of rutile with anatase phase was solvent dependent, but also the morphology and optoelectrical properties of the films were strongly affected by solvent type. However, using two different types of alcohols as a single solvent brings the advantages of both solvents. Also, some unique properties in mixed solvent samples could be achieved. The viscosity, gel time, boiling point, possible complexes, dipole moment, and chain length of the solvent affect the packing density, lattice distortion, interfaces, thickness, optical band gap, refractive index, and extinction coefficient.     

Structural,electrical and optical properties of molybdenum-doped TiO2 thin films

Molybdenum doped TiO₂ (MTO) thin films were prepared by radio frequency (RF) magnetron sputtering at room temperature and followed by a heat treatment in a reductive atmosphere containing 90% N₂ and 10% H₂. XRD and FESEM were employed to evaluate the microstructure of the MTO films, revealing that the addition of molybdenum enhances the crystallization and increases the grain size of TiO₂ films. The optimal electrical properties of the MTO films were obtained with 3 wt% Mo doping, producing a resistivity of 1.1×10^?3 Ω cm, a carrier density of 9.7×10²⁰ cm^?3 and a mobility of 5.9 cm²/Vs. The refractive index and extinction coefficient of MTO films were also measured as a function of film porosity. The optical band gap of the MTO films ranged from 3.28 to 3.36 eV, which is greater than that of the un-doped TiO₂ film. This blue shift of approximately 0.14 eV was attributed to the Burstein–Moss effect.     

Surface modified nanostructured-TiO<Subscript>2</Subscript> thin films for removal of Congo red

We synthesized nanostructured TiO₂ thin films by the modified sol-gel template method using the polyethylene glycol as filler media. The TiO₂ surface modification for both the thin films, i.e., template and non-template, was done with the ascorbic acid. All the four thin film samples, S1 (TiO₂ (non-template), TiO₂ (template), S3 (S1 modified with ascorbic acid) and S4 (S2 modified with ascorbic acid), were characterized by various analytical methods. Phase evaluation was monitored by the X-Ray diffraction analysis. Moreover, the thin films particle sizes were obtained to be 22.32, 21.20, 14.52 and 16.77 nm, respectively for the samples S1, S2, S3 and S4. The changes in particle size and morphology due to the PEG and ascorbic acid were determined by scanning electron microscopy (SEM). Similarly, thermal gravimetric (TG) and differential scanning calorimetry (DSC) were performed to determine the decomposition behavior of organic compound present in the solid samples. The functional groups were determined by infrared (IR) analysis. The photocatalytic efficiency, as a reference of Congo red, was conducted using all the four samples of TiO₂ thin films. Complete photocatalytic degradation of Congo red was achieved by these samples within 130, 80, 40 and 30 mins of UV illumination.     

Structure and electrical conductivity of glasses in the Na<Subscript>2</Subscript>O-Na<Subscript>2</Subscript>SO<Subscript>4</Subscript>-P<Subscript>2</Subscript>O<Subscript>5</Subscript> system

The temperature-concentration dependence of the electrical conductivity of glasses in the Na₂SO₄-NaPO₃ and Na₂O-P₂O₅ systems has been investigated. Based on the obtained experimental data (IR spectra, density, microhardness, sound velocity, and paper chromatography), it has been demonstrated that SO₄²⁻ ions form terminal groups through the incorporation into polyphosphate fragments of the structure of glasses in the Na₂SO₄-NaPO₃ system. An increase in the electrical conductivity of glasses in this system by a factor of ∼1000 (as compared to NaPO₃) at 25°C and a decrease in the activation energy for electrical conduction from 1.40 to 1.10 eV have been interpreted from the viewpoint of the decrease in the dissociation energy E _d of polar sulfate phosphate structural chemical fragments formed in the glass bulk upon introduction into sodium metaphosphate Na₂SO₄. This leads to an increase in the number of dissociated sodium ions, which are charge carriers, and to a decrease in the energy (E _a) of their activation shift in the sublattice formed by sulfate phosphate fragments of the structure.