Forming of nanostructured anti-reflective coating on titanium elements of optical devises

Technological approach for anti-reflective coatings on refractory metal surfaces has been proposed. Specular reflection coefficient of anti-reflective coatings created on titanium samples was as low as 0,1–0,33 % for the visible range. Coatings with similar properties can be created using different refractory metals. Developed approach can be used to decrease unwanted reflection of the digital camera elements on earth imaging satellites.Антиотражающие покрытия представляют интерес для разработки и создания оптоэлектронных и дисплейных устройств. Одна из бурно развивающихся сфер применения данных покрытий – снижение светового загрязнения изображений отражениями от элементов оптоэлектронных систем и их носителей. Многие современные антиотражающие покрытия имеют органическую основу или созданы на основе массивов углеродных нанотрубок и, как следствие, неустойчивы в условиях высоких температур и механических нагрузок. Для создания наиболее бюджетных антиотражающих покрытий на металлических поверхностях применяются, как правило, методики микроструктурирования поверхности путем механической обработки (шлифовка, пескоструйная обработка и другие технологии абразивной обработки). Подобная обработка позволяет снизить коэффициент зеркального отражения поверхности титанового изделия до уровня полутора-двух процентов

Effect of anodic voltage on parameters of porous alumina formed in sulfuric acid electrolytes

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° 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 2.7×1010 V/m in the layers with a porosity of 1% in growing alumina

ВЛИЯНИЕ ТЕРМООБРАБОТКИ НА СТРУКТУРУ И СОСТАВ ПОРИСТЫХ ПЛЕНОК АНОДНОГО ОКСИДА АЛЮМИНИЯ, СФОРМИРОВАННЫХ ПРИ РАЗЛИЧНЫХ НАПРЯЖЕНИЯХ ФОРМОВКИ

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.Представлены результаты исследования электрохимического анодирования алюминиевой фольги и тонких алюминиевых пленок, осажденных на кремниевые пластины, в 2 % водном растворе серной кислоты при различных напряжениях формовки. Показано, что термообработка при температурах 450 °С и 950 °С увеличивает пористость пленки анодного оксида алюминия и приводит к снижению значения коэффициента увеличения объема. Также установлено, что встраивание компонентов электролита в анодный оксид при анодировании в растворах серной кислоты интенсифицируется с ростом напряжения формовки

ОСОБЕННОСТИ ФОРМИРОВАНИЯ АНОДНОГО ОКСИДА АЛЮМИНИЯ С ТРУБЧАТОЙ СТРУКТУРОЙ

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.Проведено исследование условий формирования пористого анодного оксида алюминия с трубчатой структурой. Показано, что самоупорядоченная трубчатая структура оксида алюминия формируется в том случае, если температура барьерного слоя превышает температуру электролита на несколько десятков градусов для вязких электролитов (вязкость более 10-2 Па·с при 20 °С) и на сто градусов и более для водных электролитов с низкой вязкостью (вязкость менее 10-2 Па·с при 20 °С). Сделано предположение, что температура барьерного слоя в процессе формирования самоупорядоченного трубчатого оксида алюминия может достигать нескольких сот градусов, что объясняет возникновение шарообразных структур в устьях пор, формируемых в результате оплавления алюминия в процессе анодирования

Formation of alumina nanotubes and jet effect during high voltage local anodization of aluminum

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

TERMAL TREATMENT IMPACT ON STRUCTURE AND COMPOSITION OF POROUS ALUMINA FILMS FORMED AT DIFFERENT VALUES OF FORMING VOLTAGE

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

Pecularities of tubular anodic alumina formation

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

Tubular alumina formed by anodization in the meniscal region

A method to fabricate tubular nanoporous alumina layers by anodization of aluminum at current densities up to 1400 mA/cm(2) and anodization rates up to 70 mu m/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/cm(2). 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 degrees-16 degrees

Anodizing technique for Liquid Crystal Displays

Specific self organized nanoscale structures, process of its formation by electrochemical treatment and its application for Liquid Crystal Displays (LCDs) are considered in this paper. Special pillar titania formation technology is proposed to overcome some restriction incidental to porous alumina alignment layers. Both materials allow designing extremely time-, ultraviolet (UV) - and temperature stable alignment layers. A new method based on anodizing in meniscus region at high current densities has been developed for adjustable tilt porous structures formation. Masking and changing of anodizing parameters can be used to control properties and shapes of the structures

Growth pecularities of anodic oxides of valve metals and their alloys

Проведено исследование основных закономерностей роста анодных оксидов вентильных металлов. В качестве материалов для исследования выбраны наиболее распространенные металлы: алюминий, титан и алюминиево-титановый сплав (содержание Ti 27%). Формирование плотных анодных оксидов проводилось в 1% растворе лимонной кислоты в комбинированном режиме при начальной плотности тока Jf=10 мА/см2 и установившемся значении напряжения формовки от 10 до 100 В. Установлено, что толщина пленки и коэффициент формовки анодного оксида исследуемых материалов определяются напряжением формовки анодного процесса и данная зависимость имеет нелинейный характер. Отклонение от линейной зависимости можно объяснить влиянием естественного оксида для малых толщин пленок и уменьшением эффективности анодного процесса по току при увеличении толщины анодного оксида. На основании результатов проведенных исследований была предложена формула, позволяющая установить соответствие между значением напряжения формовки и параметрами получаемых анодных оксидных пленок в достаточно широком диапазоне значений с учетом нелинейного характера данной зависимости.The growth mechanism of anodic oxides of valve metals and their alloys have been studied. Aluminium, titanium and Al-Ti alloy have been investigated in our study. The nonporous anodic oxide formation was carried out in the 1% citric acid solution at current density of 10 mA/cm2. The film thickness was measured at various forming voltages. The forming factor depends on the forming voltage and such dependence is found to be nonlinear. The deviation from the linear dependence can be explained by the influence of natural oxide on the valve metal surface and by reduction of anodic process efficiency for thick oxide films