Obtained Oxide Films Research Articles

Optical Properties of Valve Metals Functional Thin Films Obtained by Electrochemical Anodization on Transparent Substrates

Nanostructured aluminum, tantalum, and vanadium oxide layers on glass substrates were obtained by electrochemical anodizing in oxalic and sulfuric–oxalic electrolytes. The morphological and optical properties of the obtained structures were investigated experimentally by scanning electron microscopy and transmission spectroscopy. Obtained oxide coatings are quasi-ordered arrays of vertical (aluminum oxide/tantalum oxide, aluminum oxide/vanadium oxide, and aluminum oxide obtained in the oxalic electrolyte) or non-ordered tree-like (aluminum oxide obtained in the sulfuric–oxalic electrolyte) pores depending on the initial film metal and anodizing technology. The light transmission in the range of 750–1200 nm is up to 60% for aluminum oxide/tantalum oxide/glass (annealed) and quasi-ordered aluminum oxide/glass structures, and around 40% for aluminum oxide/tantalum oxide/glass (not annealed) and aluminum oxide/vanadium oxide. Non-ordered aluminum oxide is characterized by low transmission (no more than 8%) but has a developed surface and may be of interest for the formation of films with poor adhesion on smooth substrates, for example, photocatalytic active xerogels. The refractive indices of dispersion of the obtained layers were calculated from the transmission spectra by the envelope method. The dispersion of the refractive indices of the obtained oxide films is insignificant in a wide range of wavelengths, and the deviation from the average value is assumed to be observed near the intrinsic absorption edges of the films. The glasses with proposed semi-transparent nanostructured oxide layers are promising substrate structures for subsequent sol–gel coating layers used in photocatalytic purification systems or up-conversion modules of tandem silica solar cells with forward and reverse illumination.

Ultra-thin anodized aluminium dielectric films: the effect of citric acid concentration and low-voltage electronic applications

Anodically oxidized, ultra-thin (d < 10 nm) aluminium films emerge as the dielectric of choice for low-cost thin film capacitors (TFCs), thin film transistors (TFTs), and bio- and chemical sensors. In this work, the dielectric properties of ultra-thin aluminium oxide films grown by anodization in aqueous solutions of citric acid (CA) have been studied. It is observed that the electrolyte strength variation from 0.1 mM to 1000 mM has virtually no influence on the chemical composition, surface morphology and the dielectric properties of the fabricated alumina films. The anodized films are very smooth having RMS area roughness around ∼5 Å. This was further improved after deposition of n-octadecyltrichlorosilane (OTS) self-assembled monolayer (SAM) to ∼4 Å. Also, the XRD and elemental analysis using EDS and XPS unambiguously confirms that the obtained oxide films are amorphous, stoichiometric Al2O3 without any carbon contamination. The fabricated Al/Al2O3/Al MIM capacitors show almost ideal capacitor characteristics from 10 Hz to 100 kHz. It has been found that the OTS coating does not only improve the capacitor frequency response further but also reduces the leakage current through the dielectric layer by passivating reactive dangling bonds on the oxide surface. As a result of the favourable properties of the anodized Al2O3/OTS films, high-performance, low threshold voltage organic thin film transistors (OTFTs) operating below 1 V are successfully demonstrated.

Influence of light incident angle on reflectance spectra of metals processed by color laser marking technology

A comparison of oxide films formed on the stainless steel surface during laser and furnace heating is presented. Obtained samples were examined by optical and scanning electron microscopy. In order to characterize the optical properties, reflection spectra within the wavelength range 190–900 nm were measured with a spectrophotometer equipped with the integrating sphere for incidence angles from 0° to 60°. The topology of obtained oxide films was characterized by scanning probe microscopy. Due to light interference in produced films, the coloration of treated area is observed. It was found that there is no change in the characteristic appearance of reflectance spectra at different light incidence angles, but a blue-shift occurs especially for the case of laser-induced films, which results in a visible change of surface color. This effect is associated with an interference character of originating color and features of surface relief under an oxide film.

Synthesis, electrochemical impedance spectroscopy study and photoelectrochemical behaviour of as-deposited and annealed WO3 films

WO3 films have been obtained by anodization of tungsten in the different acidic electrolytes (HCl, H2SO4, H3PO4, H3PO4+NH4F) and at various applied potentials. Electrochemical impedance spectroscopy was used to investigate film formation and to characterize the obtained oxide films. The equivalent electric circuits modelling reactive and blocking behaviour are provided and discussed. It was found, that oxide film capacitance decreases linearly with increasing anodization potential. The relative permittivity of tungsten oxide films varies from 31 to 56 depending on the acid used. A relatively high rate of the film formation (1.87nmV−1) and increased resistance against oxide breakdown can be achieved for tungsten oxide obtained from 0.3M oxalic acid bath. Compact oxide films are formed at the potentials ranged from 10V to 30V, whereas increasing of anodization voltage to 60V resulted in the formation of disordered, porous structures due to surface etching. Semiconductor properties were determined by Mott-Schottky analysis. Photoelectrochemical properties of as-deposited and annealed at 600°C WO3 films were determined in a Na2SO4 solution under pulsed and constant UV irradiation. It was determined that annealed WO3 films in comparison to as-deposited films are more stable and generate substantially higher photelectrochemical currents.

Anodic luminescence, structural, photoluminescent, and photocatalytic properties of anodic oxide films grown on niobium in phosphoric acid

This article reports on properties of oxide films obtained by anodization of niobium in phosphoric acid before and after the dielectric breakdown. Weak anodic luminescence of barrier oxide films formed during the anodization of niobium is correlated to the existence of morphological defects in the oxide layer. Small sized sparks generated by dielectric breakdown of formed oxide film cause rapid increase of luminescence intensity. The luminescence spectrum of obtained films on niobium under spark discharging is composed of continuum radiation and spectral lines caused by electronic spark discharging transitions in oxygen and hydrogen atoms. Oxide films formed before the breakdown are amorphous, while after the breakdown oxide films are partly crystalline and mainly composed of Nb2O5 hexagonal phase. The photocatalytic activity of obtained oxide films after the breakdown was investigated by monitoring the degradation of methyl orange. Increase of the photocatalytic activity with time is related to an increase of oxygen vacancy defects in oxide films formed during the process. Also, higher concentration of oxygen vacancy defects in oxide films results in higher photoluminescence intensity.

Investigation of anodic oxide coatings on zirconium after heat treatment

Abstract Herein, results of heat treatment of zirconium anodised under plasma electrolytic oxidation (PEO) conditions at 500–800 °C are presented. The obtained oxide films were investigated by means of SEM, XRD and Raman spectroscopy. The corrosion resistance of the zirconium specimens was evaluated in Ringer's solution. A bilayer oxide coatings generated in the course of PEO of zirconium were not observed after the heat treatment. The resulting oxide layers contained a new sublayer located at the metal/oxide interface is suggested to originate from the thermal oxidation of zirconium. The corrosion resistance of the anodised metal was improved after the heat treatment.

Hydrothermal Surface Modification of a Low Modulus Ti-Nb Based Alloy

Abstract A low modulus near β type titanium alloy (Ti-25Nb-3Zr-2Sn-3Mo, or TLM alloy) was subjected to hydrothermal treatments with a urea solution at different temperatures followed by heat treatment. The surface structure, the chemical composition, adhesion and hydrophilicity of the treated TLM alloy were investigated by SEM, XRD, XPS, Rockwell-C indentation test and contact angle measurement. The results show that nanosheet films of ammonium titanate can be formed at 105 and 120 °C, while the nanoparticle film of anatase TiO2 containing Nb2O5 is formed at 150 °C on the alloy surface. The subsequent annealing heat treatment at 400 °C can decompose the ammonium salts and crystallize titania. The obtained oxide films have a good adhesion. The duplex treatment has enhanced the hydrophilicity of the TLM alloy, and it would be good for its biocompatibility.

Characterization of low-temperature microwave loss of thin aluminum oxide formed by plasma oxidation

We report on the characterization of microwave loss of thin aluminum oxide films at low temperatures using superconducting lumped resonators. The oxide films are fabricated using plasma oxidation of aluminum and have a thickness of 5 nm. We measure the dielectric loss versus microwave power for resonators with frequencies in the GHz range at temperatures from 54 to 303 mK. The power and temperature dependence of the loss are consistent with the tunneling two-level system theory. These results are relevant to understanding decoherence in superconducting quantum devices. The obtained oxide films are thin and robust, making them suitable for capacitors in compact microwave resonators.

Pulsed Laser Assisted Polycrystalline Growth of Oxide Thin Films for Efficient Processing

ABSTRACTWe have investigated the polycrystalline growth by means of an excimer laser assisted metal organic deposition process and the strategy for the efficient growth. It was revealed that the pulsed photo thermal heating properties must be controlled by changing the laser fluence according to the substrate properties, such as thermal diffusivity. The threshold of the teff value for initial crystal nucleation is approximately 70 ns for oxide thin films. For the fabrication of good quality films with high crystallinity and without a laser ablation of the film surface, it is necessary that the irradiated laser fluence is adjusted to the conditions of teff (efficient annealing time) &gt; 70 ns and Tmax (maximum temperature) &lt; Tm (melting point). Obtained oxide films by using the pulsed UV laser has large crystallite size, and it well functioned to enhance physical properties of films. For further efficient growth for polycrystalline growth of the oxide films, the starting solution containing nanoparticles is very useful: it is named as photo-reaction of nanoparticles process.

Studies on Electrochromism of Chemically Deposited Nickel Oxide Thin Films

In this work, nickel oxide (NiO x ) thin films were prepared from aqueous solution of nickel nitrate and carbamide. Those films were deposited onto fluorine doped tin oxide (FTO) coated glass substrates. An electrochromic test device (ECTD) was constructed by using these films as working electrodes, and FTO coated glass as an opposite electrode in alkaline medium of 0.1 M NaOH aqueous solution. The obtained nickel oxide films exhibited anodic electrochromism, changing color from transparent to dark brown. Various techniques were used for characterization of the films as x-ray diffraction (XRD), visible spectroscopy and electrochemical methods. The dependence of the optical density on the charge density was examined and the coloration efficiency was calculated from the optical density change. The time response was also determined.

Characterisation of titanium oxide films by potentiodynamic polarisation and electrochemical impedance spectroscopy

Titanium is used for many applications, ranging from chemical, biomedical, and decorative. Its versatility is due to its excellent mechanical properties, high corrosion resistance and biocompatibility. Moreover, its oxides, grown by anodising techniques, can have different colourations, which make them useful for applications related to art and architecture; in their crystalline form, they show excellent photochemical properties, which are widely used in chemical synthesis and in the cleansing of pollutants. The aim of this work is to characterise the titanium dioxide films, grown anodically in sulphuric acid 0·5 M at three different anodising potentials, by potentiodynamic polarisation and electrochemical impedance spectroscopy (EIS). When comparing the obtained oxide films, a progressive increment in their crystallinity and electrical resistance was observed with the increase of the anodising potential.

Anodic oxide films on silicon carbide

AbstractAnodic oxide films were grown on SiC using various electrolytes. The obtained oxide films were compared and some of their electrophysical properties were investigated. Anodic oxidation of SiC was shown to be useful for precise removal of layers as well as for identification of the polar faces of SiC crystals. (© 2007 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

The role of passivation in titanium oxidation: thin film and temperature effects

Through the combined application of Auger electron spectroscopy (AES) and factor analysis (FA), we have studied the oxidation process of titanium under different regimes: bulk and thin film at room temperature (RT) and high temperature (HT). While the saturation regime at RT is produced by the formation of a passivated TiO 2 film at the surface of bulk and thick oxide films, the saturation is governed by the substrate/titanium film interactions in the case of thinner films. The stoichiometry of the obtained oxide films also depends on the oxidation process. We found only TiO 2 for RT bulk oxidation, Ti 2O 3 and TiO 2 for HT, and TiO and TiO 2 for thin films. Heating the sample, once the RT saturation was achieved, produces additional oxidation (post-oxidation), but the stoichiometry of the oxide films remains unchanged. For the thinner films, the post-oxidation produces almost no effect.

Electron cyclotron resonance microwave discharge for oxide deposition using tetramethylcyclotetrasiloxane

Results of the dielectric oxide films deposited at 300 °C using tetramethylcyclotetrasiloxane/oxygen chemistry in a reactor with electron cyclotron resonance microwave discharge are presented. We have found that quality oxide is deposited with an O2/tetramethylcyclotetrasiloxane flow-rate ratio of greater than 3. The properties of the deposited films are characterized by prism coupler, infrared spectroscopy, Auger electron spectroscopy, Rutherford backscattering spectrometry, and triangular voltage sweep measurements. The deposition rate using tetramethylcyclotetrasiloxane is found to be about four times higher than tetraethylorthosilicate under similar processing conditions. We have obtained oxide films with superior quality (both material and electrical properties) at a deposition rate of 5000 Å/min. The step coverage of oxide is found to be excellent when rf bias is applied on the substrate during the deposition. We have demonstrated that trenches with aspect ratios ≥1.50 can be filled without voids. Details of reaction chemistries for oxide deposition in the electron cyclotron resonance reactor and the effect of ion bombardment on the oxide profile are discussed.