Titanium oxide xerogel films in porous aluminum oxide for photocatalytic application

We have used the sol–gel method to synthesize titanium dioxide in the pores of an anodic aluminum oxide membrane. The samples were used for the test reaction of degradation of the organic dye rhodamine B. The concentration of the dye rhodamine B was monitored from the change in the absorption spectra in the 554 nm region, for an aqueous solution containing the dye and exposed to the emission from a mercury lamp. The synthesized samples of titanium oxide xerogel in the porous anodic aluminum oxide membrane are efficient photocatalysts for decomposition of organic dyes in an aqueous medium.     

Luminescence of Eu3+ and Tb3+ Ions in the Structure Microporous Xerogel/Mesoporous Anodic Aluminum Oxide

We have investigated the luminescence, luminescence excitation, and transmittance of europium- and terbium-doped xerogel films formed on smooth, nanotextured surfaces and in the pores of anodic aluminum oxide. Some factors responsible for enhancement of luminescence in the structure lanthanide-doped xerogel/mesoporous anodic aluminum oxide have been analyzed. It is assumed that the optical excitation of lanthanide ions can be realized directly, through a xerogel matrix, and due to the multiple scattering of exciting radiation by the matrix of mesoporous anodic aluminum oxide.     

Luminescence in the 1.54 µm region for erbium in two-dimensional and three-dimensional mesoscopic structures

We have studied the luminescence and luminescence excitation spectra of erbium in the 1.54 μm region in titanium oxide and silicon oxide xerogels, formed in the mesoscopic pores of three-dimensional synthetic opals and two-dimensional porous aluminum oxide structures. For erbium-doped titanium oxide films formed in opal, in contrast to analogous films on porous aluminum oxide, in the luminescence excitation spectra we observe an intense broad band with a maximum in the ∼360 nm region. We discuss the possible nature of this band. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 5, pp. 622–626, September–October, 2007.     

Investigating the composition of periodic nano-size column structures of anodic titanium oxide by the method of IR spectroscopy

Periodic column structures of anodic tantalum oxide (ATO), formed by anodizing in different regimes a Ta—Al two-layer thin-film composition in an oxalic-acid solution as well as the films of dense anodic oxide and thermal tantalum oxide, are investigated by the methods of scanning electron microscopy and reflection IR spectroscopy. It is established that the ATO nano-size columns are composed of at least three known oxide phases from a Ta—O system: TaO, TaO₂ and Ta₂O₅. The structure of tantalum oxide compounds is amorphous with the near order (inclusions) of TaO₂ rutile, rhombic Ta₂O₅, and α- and β-modifications of tantalum pentoxide. The dense-ATO films are distinguished by a more disordered structure of the oxygen compounds of tantalum and an increased content of amorphous tantalum pentoxide. The thermal-ATO films have the most ordered structure of all the oxide phases that enter in their composition and increased relative contents of α- and β-Ta₂O₃. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 6, pp. 850–856, November–December, 1998.     

Thermodepolarization Analysis of Aluminum — Anodic Aluminum Oxide Electret Systems

Aluminum — anodic aluminum oxide electret systems prepared under widely varying oxidation conditions are studied in the present work by the methods of thermodepolarization analysis in combination with oxide partitioning. Energy spectra of polarization oxide state, volumetric charge distribution with the oxide thickness, total and partial charges transferred by the thermostimulated depolarization current, and the charge distribution with the activation energy of the thermostimulated depolarization current are examined. Contributions of the dipole relaxation and volumetric charge polarization decays to the total charge transferred by the thermostimulated depolarization current and the fundamental role of the negative volumetric charge in the formation and relaxation of the electret aluminum oxide state are discussed. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 59–63, August, 2005.     

Luminescence of europium-doped anode oxide films on titanium-aluminum composites

The luminescence of europium in anode oxide films (AOF) on titanium-aluminum film composites is investigated. It is shown that the intensity distribution in the continuous and line luminescence spectra of europium introduced into the AOF directly in the process of anodic oxidation essentially depends on the sequence of arrangement of the layers of metal films and on the temperature of their heat treatment preceding the process of anodic oxidation. It is established that the nature of the luminescence spectrum of the AOF correlates with the chronovoltammetry diagrams of anodic oxidation. Composites with a high degree of europium doping are found and methods of searching for composites for creating new materials of electronic technology are outlined. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 2, pp. 270–272, March–April, 2000.     

Electro-optical response due to mixed conduction electrodes, compared to ferroelectric ones, in asymmetric nematic liquid crystal cells

The usual liquid crystal cells show an electro-optical response symmetric to the applied voltage. On the contrary, when mixed conduction films such as tungsten trioxide or vanadium pentoxide are inserted on one side of the cell, the electro-optical response is asymmetric with respect to the applied voltage. Depending on the structural phase of the inserted film the electro-optical response is in phase (transmission ON during the anodic polarization on metal oxide electrode, transmission OFF during the cathodic one) or in opposition of phase (reverse combination). The first case has been explained by the formation of a double charge layer at the interface metal oxide–liquid crystal, because of migration of protons contained in the oxide films. The other case has been found after high-temperature treatments of metal oxides deposited on glass–ITO substrates, and it appears quite similar to the response collected by using films of ferroelectric materials such as lead zirconium titanate (PZT). This fact suggests a possible interpretation in terms of dielectric response, when the mixed conduction films undergo high-temperature treatments. A comparative study of films of WO₃, V₂O₅, and PZT is carried out in this work as a function of the annealing temperature. Paper presented at the 11th EuroConference on the Science and Technology of Ionics, Batz-sur-Mer, Sept. 9–15, 2007.     

X-ray fluorescence analysis of Ni–Fe–Mn/Cr systems

We have developed a procedure for x-ray fluorescence determination of the constituent composition and thickness of two-layer Ni–Fe–Mn/Cr films deposited on Polikor, an aluminum oxide ceramic. We have calculated correction coefficients taking into account interelement interference effects in this system. We have experimentally determined the density of the materials making up the composition of the films. We have established and present the metrological characteristics of the procedure developed.     

Effects of heat treatment on optical absorption properties of?Ni–P/AAO nano-array composite structure

Ni–P/AAO nano-array composite structure assemblies with Ni and P grown in the pores of anodic aluminum oxide (AAO) membranes were prepared by electroless deposition. The results of SEM, TEM and SAED show that as-deposited Ni–P nanowires have an amorphous structure and a few nanocrystallites form after annealing. The optical absorption spectra reveal that, as the annealing temperature increases, the absorption band edge of the Ni–P/AAO composite structure is obviously blue shifted, which is attributed to a decrease of the internal pressure after heat treatment. Meanwhile, the annealed Ni–P/AAO nano-array composite structure exhibits the absorption behavior of a direct band gap semiconductor. Details of this behavior are discussed together with the implications for potential device applications.     

Electrical and optical properties of reactive dc magnetron sputtered silver-doped indium oxide thin films: role of oxygen

Silver-doped indium oxide thin films have been prepared on glass and quartz substrates at room temperature (300 K) by a reactive dc magnetron sputtering technique using an alloy target of pure indium and silver (80:20 at. %). During sputtering, the oxygen flow rates are varied in the range 0.00–2.86 sccm keeping the magnetron power constant at 40 W. The resistivity of these films is in the range 10⁰–10^-3 Ω cm and they show a negative temperature coefficient of resistivity. The films exhibit p-type conductivity at an oxygen flow rate of 1.71 sccm. The work function of these silver–indium oxide films has been measured by a Kelvin probe technique. The refractive index of the films (at 632.8 nm) varies in the range 1.13–1.20. Silver doping in indium oxide narrows the band gap of indium oxide (3.75 eV). PACS 73.30.+y; 81.15.Cd; 78.20.Ci; 73.61.Le     

Vibrational and electronic properties of painting lakes

Naturally occurring dyes have been used to produce painting pigments, called lakes, by precipitation or adsorption of an organic dyestuff onto an insoluble inorganic substrate. Most natural dyes link to metal cations, by means of coordination bonds. The stable complexes formed precipitate together with solid amorphous hydrous aluminum oxide in alkaline solutions, yielding a hybrid material called a lake. Conventional chromatographic methods for lake analysis require dye extraction from the substrate; as a consequence, they do not provide any information about the organo-metallic complexes. In this work a comprehensive investigation based on X-ray fluorescence, Fourier transform infrared and UV–visible absorption and emission spectroscopies was carried out on 13 organic pigments derived from eight different natural sources. Three different kinds of substrate containing aluminum hydroxide were distinguished dependent on different preparation procedures. Information concerning the recipe and the dye composition was obtained by UV–visible spectroscopies. Dyes from different sources (animal or vegetal) could be distinguished. This study shows that the combined use of different spectroscopic techniques provides complementary information to high-performance liquid chromatography and therefore can be proposed for a molecular non-invasive investigation of these materials on works of art. PACS  87.64.Ni; 87.64.Je     

Electrosynthesis of TiO2 oxide film on ITO substrate and electrochemical comparative study of the oxide with its hydrated gel

Thin TiO₂ films obtained by cathodic electrosynthesis from an acidic aqueous bath containing TiOSO₄, H₂O₂ and KNO₃ on conductive glass indium tin oxide have been physically and electrochemically characterised. Secondary ion mass spectroscopy profile of the crystallised gel after heat treatment at 400 °C shows the presence of TiO₂ with traces of TiO and oxygen. X-ray patterns confirm the presence of anatase nanocrystallites for the annealed film and an amorphous structure for the non-annealed gel. Scattering electron microscopy surface micrographies reveal an opened porous nanostructure of the deposits. Cyclic voltammetry and impedance spectroscopic measurements reveal the different behaviour of the films obtained before and after the annealing, showing an important electrical activity of the non-annealed films. The dependence of capacitance values with potential in the anodic domain of depletion is obviously remarked from impedance plots for both gel and crystal forms of the film, which confirmed the fact that films obtained in this way have n-type properties. The potential of flat band equals −0.6 V/Ag/AgCl in pH range of 6.5 has been estimated according to Mott–Shottky curves for the crystallised oxide; meanwhile, the Mott–Shottky curve for the hydrated gel was nonlinear.     

Dielectric properties of anodic films on sputter-deposited Ti-Si porous columnar films

For electrolytic capacitor application of the single-phase Ti alloys containing supersaturated silicon, which form anodic oxide films with superior dielectric properties, porous Ti-7 at% Si columnar films, as well as Ti columnar films, have been prepared by oblique angle magnetron sputtering on to aluminum substrate with a concave cell structure to enhance the surface area and hence capacitance. The deposited films of both Ti and Ti-7 at% Si have isolated columnar morphology with each column revealing nanogranular texture. The distances between columns are ∼500 nm, corresponding to the cell size of the textured substrate and the gaps between columns are 100-200 nm. When the porous Ti-7 at% Si film is anodized at a constant current density in ammonium pentaborate electrolyte, the growth of a uniform amorphous oxide film continues to ∼35 V, while it is limited to less than 6 V on the porous Ti film. The maximum voltage of the growth of uniform amorphous oxide films on the Ti-7 at% Si films is similar for both the flat and porous columnar films, suggesting little influence of surface roughness on the amorphous-to-crystalline transition of growing anodic oxide under the high electric field. Due to the suppression of crystallization to sufficiently high voltages, the anodic oxide films formed on the porous Ti-7 at% Si film shows markedly improved dielectric properties, in comparison with those on the porous Ti film.     

Improved electrical properties of silicon-incorporated anodic niobium oxide formed on porous Nb-Si substrate

In the present study, porous Nb-Si alloy films with isolated nano-column morphology have been successfully developed by oblique angle magnetron sputtering on to aluminum substrate with concave cell structure. The deposited films are amorphous with the 15 at% silicon supersaturated into niobium. The porous Nb-15 at% Si films, as well as niobium films with similar morphology, are anodized at several voltages up to 50 V in 0.1 mol dm⁻³ ammonium pentaborate electrolyte. Due to the presence of sufficient gaps between neighboring columns, the gaps are not filled with anodic oxide, despite the large Pilling-Bedworth ratio (for instance, 2.6 for Nb/Nb₂O₅) and hence, a linear correlation between the reciprocal of capacitance and formation voltage is obtained for the Nb-15 at% Si. From the comparison with the anodic films formed on porous niobium films, it has been found that silicon addition improves the thermal stability of anodic niobium oxide; the change in capacitance and increase in leakage current become small for the Nb-Si. The findings indicate the potential of oblique angle deposition to tailor porous non-equilibrium niobium alloy films for high performance niobium-base capacitor.     

Synthesis and Optical Properties of Films Formed by the Sol‐Gel Method in Mesoporous Matrices

The main laws governing the formation of films by the solgel method in the mesopores of anodic aluminum oxide, porous silicon, and synthetic opals have been considered. Investigations of the luminescence at 1.5 m in the structure porous silicon–gel, doped with erbium, have been analyzed. Special features of the synthesis of the film structure microporous xerogel–mesoporous anodic aluminum oxide, doped with erbium, terbium, and europium, and the possible factors that enhance the photoluminescence of lanthanides in the structure are shown.     

Transient ionic space charges in thin oxide films

The initial step of anodic growth of thin oxide films (1 to 100 nm) on Al and Ta is the simultaneous emission of metal cations from the interface metal/oxide and oxygen ions from the interface oxide/electrolyte. These ions represent mobile space charges which migrate through the oxide film to the opposite interfaces. This process requires times from μs to 10⁴ s, depending on the field strength and the film thickness and was monitored in the time domain (current transients of potential steps, 10⁻⁶ s to 10⁴ s). The movement of the ionic space charges can be used to determine the concentration of mobile ions, the film thickness, the thickness distribution of nonhomogeneous films and the temperature of extreme thin films. Paper presented at the 2nd Euroconference on Solid State Ionics, Funchal, Madeira, Portugal, Sept. 10–16, 1995     

Investigation of the interaction of evaporated aluminum with vapor deposited Teflon AF films via X-ray photoelectron spectroscopy

The interfacial bonding and mixing between evaporated aluminum and a vapor deposited Teflon AF (abbreviated to AF) film have been investigated with X-ray photoelectron spectroscopy. Graphite carbon (C–C), and aluminum carbide (Al–C), oxide (Al–O–C) and fluoride (Al–F) are formed when aluminum atoms are deposited on to the AF film. With increasing deposition of aluminum, the concentrations of these newly formed components increase gradually. Moreover, in situ annealing results in remarkable increases in the C–C, Al–C, Al–O–C and Al–F configurations and a decrease in metallic aluminum. No significant diffusion of aluminum into the AF film was observed during the annealing. The Al compounds form a layer at the Al/AF interface that acts as an adhesion promoter and diffusion barrier. Received: 21 October 2002 / Accepted: 22 October 2002 / Published online: 15 January 2003 RID="*" ID="*"Corresponding author. Fax: +49-431/880-6229, E-mail: sjding@yahoo.com     

Optically passive cerium containing counter-electrodes for electrochromic devices

Electrochemical and optical behavior of sputter deposited CeO₂, Ce-Zr mixed oxide and Ce-V mixed oxide thin films are reported. The films were deposited starting from a target prepared by mixing and weakly pressing the oxide powders in the desired molar ratio. Li intercalation was accomplished from a liquid electrolyte. CeO₂ and Ce-Zr mixed oxide thin films are transparent in the visible range and behave as passive material upon oxidation/ reduction. During the cyclic voltammetries performed on the thin films a charge of few mC was reversibly cycled. The diffusion coefficient was evaluated from galvanostatic intermittent titration technique (GITT) experiments. Ce-V mixed oxide thin films showed a mixed anodic/cathodic behavior passing through a transparent state. The charge reversibly inserted during cyclic voltammetry at 10 mV/s was as high as 22 mC/cm² for a 107 nm thick film and ranks Ce-V mixed oxide among the most promising materials for electrochromic devices. Paper presented at the 5th Euroconference on Solid State Ionics, Benalmádena, Spain, Sept. 13–20, 1998.     

Spectral properties of thin films of modified polycyclohexadiene

Light-sensitive thin films with n-phenylene chains in their structure are formed by deposition from a solution and by thermal vacuum deposition of bromine-modified polycyclohexadiene (Br-PCHD). It is found that the Br-PCHD films possess photoluminescence properties. Using IR-, UV-, and x-ray photoelectron spectroscopy methods, it is shown that during storage and exposure to UV irradiation in air the Br-PCHD films undergo structuring because of having been photooxidized by the molecular oxygen adsorbed on the surface. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 6, pp. 722–726, November–December, 2005.     

Electronic properties of electrolyte/anodic alumina junction during porous anodizing

The growth of porous oxide films on aluminum (99.99% purity), formed in 4% phosphoric acid was studied as a function of the anodizing voltage (23-53 V) using a re-anodizing technique and transmission electron microscopy (TEM) study. The chemical dissolution behavior of freshly anodized and annealed at 200 °C porous alumina films was studied. The obtained results indicate that porous alumina has n-type semiconductive behavior during anodizing in 4% phosphoric acid. During anodising, up to 39 V in the barrier layer of porous films, one obtains an accumulation layer (the thickness does not exceed 1 nm) where the excess electrons have been injected into the solid producing a downward bending of the conductive and valence band towards the interface. The charge on the surface of anodic oxide is negative and decreases with growing anodizing voltage. At the anodizing voltage of about 39 V, the charge on the surface of anodic oxide equals to zero. Above 39 V, anodic alumina/electrolyte junction injects protons from the electrolyte. These immobile positive charges in the surface layer of oxide together with an ionic layer of hydroxyl ions concentrated near the interface create a field, which produces an upward bending of the bands.