Using an improved heat sink from the barrier layer, the voltage of anodic electrochemical oxidation of aluminum in sulfuric electrolytes is successfully increased from the conventional limit of about 40 to 200 V. This is done by localization of the anodized regions within the windows in the niobium thin film masks with the diameters of 0.3 μm to 2.5 mm. High‐voltage anodization in water solutions of sulfuric acid is observed to be accompanied by a reproducible formation of densely packed alumina nanotubes and intense gas propulsion from the pores of the forming alumina. The latter is proposed and experimentally confirmed for use as an efficient driving agent in micro‐ and nanoengines. Test samples are accelerated to the velocities up to 1 cm s −1 , demonstrating a thrust‐to‐weight ratio of about 1000.

The anodic growth conditions of titania with a tubular structure are investigated. We propose a mechanism of anodic growth of tubular titania, which presupposes that electrochemical oxidation of titanium is predominantly confined to the bottom of pores in a barrier layer, i.e., where the anodic current density is higher, which causes a temperature rise in these regions. As the barrier layer temperature exceeds a certain threshold, the structure of growing oxide changes from the commonly obtained porous honeycomb-like structure to a tubular one. The proposed mechanism is supported by experimental results.

The conditions for the formation of anodic titanium oxide with a tubular structure were studied. The mechanism for the formation of tubular titanium oxide based on the localization of the electrochemical oxidation of titanium in the places of the barrier layer at the bottom of the pore, where the density of the flowing anodic current is increased, as a result of which the temperature of these regions increases. With an increase in the temperature of the barrier layer above the threshold value, a transition from the traditional «honeycomb-like» porous structure to the tubular structure takes place. The proposed mechanism is confirmed by the results of experimental research.

Local porous aluminum anodizing with a photolithography mask has been carried out at anodic voltages varying from 15 to 200 V in sulfuric acid electrolytes. Record anodic voltages at room temperature have been achieved leading to new parameters of porous alumina such as interpore distance up to 320 nm, forming cell factor up to 1.2 nm/V, thickness expansion factor up to 3.5, porosity up to 1%, sulfur concentration up to 7.7 at.%. A central angle of porous alumina cells has been measured in concave points as well as in peak points of porous alumina cells at the border with aluminum. The measurements have shown that central angles can reach 90 degrees at anodic voltages larger than 100 V. The electric field distribution in porous alumina cells has been simulated for different central angles. It is found that the electric field reaches 2.7x10(10) V/m in the layers with a porosity of 1% in growing alumina.

A fabrication of porous alumina films by electrochemical anodization of aluminium foils and aluminium films deposited on silicon wafers is presented. Anodization process was held in the 2 % sulphuric acid aqueous solution at different forming voltages. It was shown that thermal treatment at 450 °С and 950 °С leads to increase of anodic alumina film porosity and decrease of volume expansion factor. It was also defined that embedding of electrolyte components in anodic alumina during anodization in sulphuric acid solutions intensifies with the increase of forming voltage value.

The formation conditions of anodic alumina with a tubular structure have been investigated. It is shown that alumina has the self-ordered tubular structure at temperature of barrier oxide layer to be several tens of degrees more than electrolyte temperature in cases of viscous electrolytes (viscosity more than 10-2 Pa·s at 20 °C) and hundred degrees more in cases of low viscous electrolytes (viscosity less than 10-2 Pa·s at 20°C). It is assumed that temperature of the barrier layer during the formation of the self-ordered tubular alumina can reach several hundred degrees because of the presence of spherical structures in the pores mouths. These spheres are expected to be formed due to the melting of an aluminum substrate during the anodizing process.

Physics, Chemistry and Applications of Nanostructures, pp. 587-590 (2015) No AccessNANOSTRUCTURED SILICON FOR ANODES OF LITHIUM-ION BATTERIESA. A. LESHOK, D. A. SASINOVICH and V. E. BORISENKOA. A. LESHOKBelarusian State University of Informatics and Radioelectronics, P. Browka 6, 220013 Minsk, Belarus, D. A. SASINOVICHBelarusian State University of Informatics and Radioelectronics, P. Browka 6, 220013 Minsk, Belarus and V. E. BORISENKOBelarusian State University of Informatics and Radioelectronics, P. Browka 6, 220013 Minsk, Belarushttps://doi.org/10.1142/9789814696524_0142Cited by:0 PreviousNext AboutSectionsPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack CitationsRecommend to Library ShareShare onFacebookTwitterLinked InRedditEmail Abstract: Nanostructured silicon films have been fabricated on stainless steel by magnetron sputtering of an Al+Si composite target with a subsequent selective etching off the aluminum from the deposited film. They have been used as anodes in prototype Li-ion cells and subjected to cycling lithiation at high current densities. The fabricated films demonstrate an efficient Li accumulation/release during charging/discharging cycles combined with high mechanical durability. FiguresReferencesRelatedDetails Physics, Chemistry and Applications of NanostructuresMetrics History PDF download

Double-walled TiO2 nanotubes have been fabricated by electrochemical anodization of Ti foil in 0.3% ammonium fluoride solution in ethylene glycol with 2 vol.% of water at the low temperature of electrolyte and the subsequent annealing at 450 °C. The double-walled titania nanotubes structure with an upper honeycomb layer could be modified by sonication to the cone like tips.

The porous titania growth during electrochemical anodization of titanium films and foils in the 0.1M ammonium fluoride (FNH4) solution in ethyleneglycol has been studied in the temperature range from −5°C to +20°C. Titania films with a smooth tubular morphology was found to be formed at the electrolyte temperatures below 0°C. The growth rate was as high as 1.5μm/min provided that the tube diameters were up to 300nm and the film porosity was less than 1%. Porous titanium anodization at the electrolyte temperature of 0°C and below induces formation of porous titania with a structure close to ideal packed hexagonal prisms with a smooth tubular surface. The mechanism of the appearance of such structure is discussed.

Titania (TiO2) exhibiting semiconducting behaviour (Eg ~ 3.2 eV) is a promising material for various photocatalytic applications. Thanks to its high stability to corrosion it is widely used as a cathode in photoelectrochemical systems for oxygen and hydrogen generation by water splitting and in electrolytic solar cells [1]. In addition, the ability to be fabricated in a porous form with a high specific surface makes titania to be a privileged candidate for electrochromic [2] and liquid crystal displays [3] as well as for efficient air and water purification through photo-oxidation of contaminants (organic molecules, bacteria). The electrochemical anodization of titanium is found to be a simple method for fabrication of porous titania. The anodization in water based electrolytes allows formation of porous titania films with a thickness up to 1 μm. 100 μm thick or even thicker films can be obtained in organic based electrolytes [4,5]. Meanwhile, anodic current density is one of the limiting factors to perform high rate anodization due to heating up of the anodized samples. Many research groups [6,7] studied the anodic formation of titania at room temperature whereas anodization of titanium below 0 o C has not been tested yet. This paper presents results for that temperature regimes.

The alumina waveguide with a nanocomposite Al2O3/TiO2 core has been developed and fabricated. The refractory index of the nanocomposite was about 1.8. It allowed decreasing the optical losses in the multilayer waveguide up to 0.6 dB/cm.

A method to fabricate tubular nanoporous alumina layers by anodization of aluminum at current densities up to 1400 mA/cm2 and anodization rates up to 70 μm/min has been developed. It implies anodization in the meniscal region of the sample dipping into an electrolyte. The formed porous alumina has been found to be selforganized nanotube cells when the anodization current excides 100 mA/cm2. The formation of nanotubes is supposed to be controlled by the increased volume expansion factor (more than 2) at high forming current densities. The meniscal anodization allows fabrication of porous alumina nanotubes with desired tilt angles in the range of 0°–16°.

A simple method to fabricate a porous alumina layer at high forming current densities has been developed. This method allows carrying an anodic process of aluminium film dipping into the electrolyte in the meniscal part with forming current density up to 1500 mA/cm2 and anodising rate up to 70 mum/min. The structure of the porous alumina formed has been found to be self-organized nanotube cells for anodizing current densities more than 100 mA/cm2.

A facile method to fabricate a porous alumina layer at high forming current densities has been developed. This method allows to carry an anodic process of alummium film dipping into the electrolyte in meniscal region with forming current density up to 1500 mA/cm(2) and anodising rate up to 70 mu m/min. The structure of the porous alumina formed has been found to be selforganized nanotube cells for anodizing current densities more than 100 mA/cm(2).

A new approach to fabrication of nanoporous oxides of refractory metals is presented. It is based on the magnetron co-sputtering of aluminum and refractory metal (titanium, niobium or tungsten) followed by porous electrochemical anodization of the composite film and selective etching of alumina. The nanoporous oxide films with a thickness up to 5 µm were fabricated and studied. The porosity of the oxide films characterized by the surface area of 230 – 460 m2/cm3 can betuned by the aluminum content in the as-deposited composite films. The pore diameters are found to be varied in nanometer and subnanometer ranges. The parameters of porous titania within porous alumina matrix for different titanium concentrations are presented. The fabricated porous composite oxide films are characterized by the refractive index in the range from 1.45 to 1.77. The dielectric permeability for these films is found to be varied from 6.7 to 24. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

An electroluminescent structure based on nanostructured porous silicon embedded in a layer of anodic alumina has been suggested and fabricated. The heat conductivity of the alumina matrix markedly exceeds that of the silicon-containing insulators. The effective heat removal makes it possible to attain an 0.5% quantum efficiency of electroluminescence, which is comparable with the best parameters of silicon-based light-emitting devices. The physical phenomena responsible for the emission of light by the structure under study are considered.

Magnetron deposited Al-Nb nanocomposite films were selectively etched for fabrication of nanoporous niobium. Atomic force and scanning electron microscopy investigations have shown that the fabricated nanostructures include interconnected nanowires of 20-50 nm in diameter and 100-150 nm plates. Annealing at 450 °C in air transformed porous niobium into the porous niobia, which can be as thick as 3 μm.