Reflectant photonic crystals produced via porous-alumina-assisted-anodizing of Al/Nb AND Al/Ta systems

The development of new nanomaterials with controlled characteristics for nanophotonics is of great relevance. In this work, photonic crystals with re°ectance at the wavelength of 690 nm and the value of 28% were formed by porous-alumina-assisted-anodizing of system Al/Ta on Si wafer. By selecting improved anodizing modes of system Al/Nb on glass, the re°ectance was increased to 42% at the wavelength of 340 nm. This result shows the high promise of the proposed methods and in the future will signi cantly improve the result by trying two- or three-stage methods of porous-alumina-assisted-anodizing, nanoimprint stamps and optimization of the anodizing modes for any wavelengths

Optical Properties of Porous Alumina Assisted Niobia Nanostructured Films–Designing 2-D Photonic Crystals Based on Hexagonally Arranged Nanocolumns

Three types of niobia nanostructured films (so-called native, planarized, and column-like) were formed on glass substrates by porous alumina assisted anodizing in a 0.2 M aqueous solution of oxalic acid in a potentiostatic mode at a 53 V and then reanodizing in an electrolyte containing 0.5 M boric acid and 0.05 M sodium tetraborate in a potentiodynamic mode by raising the voltage to 230 V, and chemical post-processing. Anodic behaviors, morphology, and optical properties of the films have been investigated. The interference pattern of native film served as the basis for calculating the effective refractive index which varies within 1.75–1.54 in the wavelength range 190–1100 nm. Refractive index spectral characteristics made it possible to distinguish a number of absorbance bands of the native film. Based on the analysis of literature data, the identified oxide absorbance bands were assigned. The effective refractive index of native film was also calculated using the effective-medium models, and was in the range of 1.63–1.68. The reflectance spectra of all films show peaks in short- and long-wave regions. The presence of these peaks is due to the periodically varying refractive index in the layers of films in two dimensions. FDTD simulation was carried out and the morphology of a potential 2-D photonic crystal with 92% (wavelength 462 nm) reflectance, based on the third type of films, was proposed

Formation features, morphology and optical properties of nanostructures via anodizing Al/Nb on Si and glass

Using the method of niobia electrochemical anodizing via the porous alumina, three types of nanostructures: skittle-, medusa- and goblet-like niobia embryos were formed. Their morphology and formation boundary conditions were investigated. Established up to 37 V embryos are formed like skittles, in the region from 53 to 100 V medusa-like are formed, and above 150 V – goblet-like. To research the optical column-like niobia nanostructure properties inside porous alumina, embryos 53 V like medusa were formed on a glass substrate and re-anodized to a voltage of 230 V not to leave the metallic niobium. Investigations have shown the complete absorbance of the ultraviolet range and the presence of transmittance, reflectance and absorbance in the visible and infrared range with significant oscillations, which indicates the presence of Fabry-Perot interference

Anodic aluminum oxide formed in aqueous solutions of chelated complex zinc and cobalt compounds

The galvanostatic anodizing results of specially prepared high-purity aluminum in aqueous solutions of complex compounds K3[Co(C2O4)3] and K2[Zn(edta)] of various concentrations in the current density ranges 1.5−1.10 · 102 and 1.5−30 mA · cm−2, respectively. The kinetic features of anodizing have been established, indicating the occurrence of an oscillatory electrochemical process. Morphological features of a flaky and loose nature for K2[Zn(edta)] and monolithic for K3[Co(C2O4)3], uncharacteristic for anodic aluminum oxide, were revealed. The elemental composition, IR spectroscopic and photoluminescent characteristics of the formed oxides are shown

Anodizing of Hydrogenated Titanium and Zirconium Films

Magnetron-sputtered thin films of titanium and zirconium, with a thickness of 150 nm, were hydrogenated at atmospheric pressure and a temperature of 703 K, then anodized in boric, oxalic, and tartaric acid aqueous solutions, in potentiostatic, galvanostatic, potentiodynamic, and combined modes. A study of the thickness distribution of the elements in fully anodized hydrogenated zirconium samples, using Auger electron spectroscopy, indicates the formation of zirconia. The voltage- and current-time responses of hydrogenated titanium anodizing were investigated. In this work, fundamental possibility and some process features of anodizing hydrogenated metals were demonstrated. In the case of potentiodynamic anodizing at 0.6 M tartaric acid, the increase in titanium hydrogenation time, from 30 to 90 min, leads to a decrease in the charge of the oxidizing hydrogenated metal at an anodic voltage sweep rate of 0.2 V·s−1. An anodic voltage sweep rate in the range of 0.05–0.5 V·s−1, with a hydrogenation time of 60 min, increases the anodizing efficiency (charge reduction for the complete oxidation of the hydrogenated metal). The detected radical differences in the time responses and decreased efficiency of the anodic process during the anodizing of the hydrogenated thin films, compared to pure metals, are explained by the presence of hydrogen in the composition of the samples and the increased contribution of side processes, due to the possible features of the formed oxide morphologies

Anodic Niobia Column-like 3-D Nanostructures for Semiconductor Devices

Two types of anodic niobia (niobium oxide) column-like three-dimensional (3-D) nanostructures were synthesized by anodization in 0.4 mol•dm -3 oxalic acid aqueous solution at 37 V, reanodizing in 1% citric acid aqueous solution up to 300 and 450 V, and chemical etching of magnetron sputter-deposited Al/Nb metal layers. The dependence of the synthesized niobia column-like 3-D nanostructures' morphological properties on formation conditions were defined by scanning electron microscopy. The niobia column-like 3-D nanostructures' electrophysical characteristics were investigated in two measurement schemes. Aluminum layers of 500-nm thickness were used as contact pads. The current-voltage characteristic (I-V) has nonlinear and nonsymmetrical character. The nonsymmetrical I-V reached ~10 V. The breakdown voltages were 80 and 125 V, self-heating begins at voltage direct connection 33 and 60 V, initial resistance at 23 °C was 60 and 120 kΩ, specific resistance to the height of the columns was 87 and 116 Ω•nm -1 , and the calculated temperature coefficient of resistance in the range 20-105 °C appeared to be negative and rather low, -1.39•10 -2 and -1.28•10 -2 K -1 , for the niobia column-like 3-D nanostructures reanodized at 300 and 450 V, respectively

Porous Alumina Films Fabricated by Reduced Temperature Sulfuric Acid Anodizing: Morphology, Composition and Volumetric Growth

The volumetric growth, composition, and morphology of porous alumina films fabricated by reduced temperature 280 K galvanostatic anodizing of aluminum foil in 0.4, 1.0, and 2.0 M aqueous sulfuric acid with 0.5–10 mA•cm−2 current densities were investigated. It appeared that an increase in the solution concentration from 0.4 to 2 M has no significant effect on the anodizing rate, but leads to an increase in the porous alumina film growth. The volumetric growth coefficient increases from 1.26 to 1.67 with increasing current density from 0.5 to 10 mA•cm−2 and decreases with increasing solution concentration from 0.4 to 2.0 M. In addition, in the anodized samples, metallic aluminum phases are identified, and a tendency towards a decrease in the aluminum content with an increase in solution concentration is observed. Anodizing at 0.5 mA•cm−2 in 2.0 M sulfuric acid leads to formation of a non-typical nanostructured porous alumina film, consisting of ordered hemispheres containing radially diverging pores

Peculiar Porous Aluminum Oxide Films Produced via Electrochemical Anodizing in Malonic Acid Solution with Arsenazo-I Additive

The influence of arsenazo-I additive on electrochemical anodizing of pure aluminum foil in malonic acid was studied. Aluminum dissolution increased with increasing arsenazo-I concentration. The addition of arsenazo-I also led to an increase in the volume expansion factor up to 2.3 due to the incorporation of organic compounds and an increased number of hydroxyl groups in the porous aluminum oxide film. At a current density of 15 mA·cm−2 and an arsenazo-I concentration 3.5 g· L−1, the carbon content in the anodic alumina of 49 at. % was achieved. An increase in the current density and concentration of arsenazo-I caused the formation of an arsenic-containing compound with the formula Na1,5Al2(OH)4,5(AsO4)3·7H2O in the porous aluminum oxide film phase. These film modifications cause a higher number of defects and, thus, increase the ionic conductivity, leading to a reduced electric field in galvanostatic anodizing tests. A self-adjusting growth mechanism, which leads to a higher degree of self-ordering in the arsenazo-free electrolyte, is not operative under the same conditions when arsenazo-I is added. Instead, a dielectric breakdown mechanism was observed, which caused the disordered porous aluminum oxide film structure

Columnar Niobium Oxide Nanostructures: Mechanism of Formation, Microstructure, and Electrophysical Properties

The morphology and microstructure of columnar niobium oxide nanostructures are studied and the dependences of their morphological sizes on anodizing voltages (100–450 V) and anodic alumina pore diameters (40–150 nm) are established. The features of ion transport during local anodization of niobium are studied and the transport numbers of electrolyte anions and niobium cations are calculated; a mechanism of formation and growth is proposed and the phase composition and electrophysical properties of columnar nanostructures are studied

Controlled integrated vacuum elements on niobium field cathodes for microdisplays

The paper presents the methods of creation and research results of matrices of electronic elements on field cold cathodes with given geometric and electrophysical parameters. The developed controlled matrices are small-sized, highly efficient sources of electron beams with low energy consumption for microelectronic devices, such as microdisplays. Field emission elements with nanostructured cathodes in the triode and diode configurations are implemented based on original structural and technological methods for the electrochemical formation of vertically oriented arrays of metal oxide niobium nanostructures, compatible with the latest nanotechnologies used in the manufacture of promising optoelectronic and nanoelectronic products