Subsequent Anodization Research Articles

Electroluminescence from aluminum-porous silicon reverse-biased Schottky diodes formed on the base of highly doped n-type polysilicon

The fabrication and the properties of light-emitting aluminum-porous silicon Schottky diodes, formed on the base of highly doped n-type polysilicon are presented.The polysilicon layer was formed on a crystalline silicon substrate by low-pressure chemical vapour deposition. Highly doped n+-poly-Si was then formed by phosphorous thermal diffusion. On this material the porous layer was obtained by electrochemical anodization using process parameters between electropolishing and pore formation regimes. The structure of the formed layer was investigated using the transmission electron microscopy technique. Photoluminescence spectra obtained after anodization are reported.The aluminum electrodes (pads) were obtained by standard photolithography and subsequent electrochemical aluminum anodization process. Electroluminescence (EL) was observed in reverse biased junctions. EL emission spectrum was broad and covered the whole visible range with a maximum at 770–800 nm. Current-voltage characteristics were determined at different temperatures. The optical and electrical characteristics of the developed light emitting diodes are promising for display device applications.

Photoelectrochemical studies of oxide film of PbO n + SnO n obtained by potentiodynamic anodisation of Pb + Sn alloy electrode in alkaline medium

Thin film semiconducting oxides are synthesised by potentiodynamic anodisation of Pb + Sn alloy electrodes of various Sn content in hot alkaline sodium sulfate solution. The effect of Sn on the photoelectrochemical behaviour in Fe(CN) 4− 3− 6 (pH 9.2, buffer) of lead oxide thin film prepared by this method is investigated. It has been concluded that the incorporation of tin into Pb + Sn alloy and its subsequent anodisation decreases the growth of photoactive α-PbO (tetragonal) phase and introduces a relatively very low photoactive SnO phase. The oxide layer formed after 20 min of anodisation of Pb-0.1wt.%Sn electrode shows the best photoresponse (conversion efficiency 0.23%), but it is lower than that obtained with undoped lead oxide (0.86%). The reasons for obtaining a low efficiency are discussed. The oxide layer is characterised by various physical and photoelectrochemical techniques. The growth of oxide film is found to be maximal in the potential range −1.25 to +2.35 V(vs. SCE).

Oxidation of copper and mobility of copper ions during anodizing of an Al—1.5 wt.% Cu alloy

AbstractThe mechanism of oxidation of copper at the alloy/film interface, and the subsequent migration of copper ions in barrier‐type films, has been examined for anodizing of an Al—1.5 wt.% Cu alloy with a prior chemical polishing treatment. Both chemical polishing and anodizing result in formation of a thin layer of alloy at the alloy/film interface, of ∼2 nm thick, that is highly enriched in copper. The layer is present immediately beneath the different types of film formed by chemical polishing and subsequent anodizing, and contains in both cases ∼6 × 1019 Cu atoms m−2. The amount of copper contained within the enriched layer of alloy is not significantly dependent upon the anodizing voltage. During anodic film growth, both aluminium and copper ions are incorporated into the film at the alloy/film interface, on average in their alloy proportions. However, the film is depleted in copper relative to the alloy because copper ions in the film migrate faster than Al3+ ions and, on reaching the film/electrolyte interface, are ejected directly to solution. The mechanism of oxidation of copper is proposed to depend upon the formation, through prior oxidation of aluminium, of copper‐rich clusters in the enriched layer of alloy at the alloy/film interface. Individual clusters are oxidized only on achieving a critical size. Consequently, copper is incorporated into the film discontinuously both in time and in position along the alloy/film interface. The films contain a high population density of flaws, which affects the film composition, the uniformity of ionic current, the faradaic efficiency of film growth, and the detailed distributions of copper ions within the films. However, the general features of film growth are compatible with the usual growth mechanism of anodic alumina, with transport numbers of Al3+ and O2−/OH− ions of ∼0.4 and ∼0.6, respectively.

A sims investigation of hydrogen penetration of titanium electrodes

The corrosion of titanium in acidic solution leads to the accumulation of substantial amounts of hydrogen in the metal, modifying the subsequent voltammetric behaviour of the electrode. SIMS has been used to show that hydrogen penetrates into the metal to a depth of several microns during prolonged exposure to acid solutions and the SIMS images obtained suggest that crystalline platelets of titanium hydride are formed in a titanium matrix under these conditions. The hydride is only partially oxidised during subsequent anodisation of the titanium, so that successive passivation/activation cycles lead to the progressive build up of hydride.

Anodic Oxide Growth on Aluminum in the Presence of a Thin Thermal Oxide Layer

The presence of a thin film of thermal oxide on the surface of aluminum promotes the growth of additional crystalline oxide during subsequent anodization in an aqueous phosphate solution. It was shown through the use of phosphorus‐32 tracer and chemical thinning procedures that the anodic crystalline oxide is formed beneath a discrete, continuous layer of amorphous oxide, and that the original thermal oxide is incorporated in the anodic crystalline film. The concentration of phosphorus in the amorphous layer is greater than that which occurs in the absence of crystalline oxide. Evidence is given that the occluded phosphorus species has some ionic mobility in both oxides.

Crystalline Anodic Oxide Growth on Aluminum Foil in an Aqueous Ammonium Dihydrogen Phosphate Anodization Electrolyte

The parameters affecting the growth of small crystallites within the anodic oxide film formed on aluminum during anodization in an 85°C aqueous ammonium dihydrogen phosphate electrolyte have been investigated. The degree of crystallinity of the anodic oxide was observed to increase with decreasing anodization current density and increasing voltage. The more crystalline films had a higher capacitance, were thinner, and contained less phosphorus than largely amorphous films anodized to the same voltage. A short thermal treatment of the aluminum foil at 600°C produced tiny platelets of , which acted as effective nucleation sites for the growth of crystalline anodic oxide. Nucleation of crystalline anodic oxide also occurred on electropolished foil; however, the deposition of a thin amorphous oxide film on the electropolished aluminum prevented crystal growth during subsequent anodization. The crystalline anodic oxide has the crystal structure and shows a strong preferred orientation related to the orientation of the aluminum substrate. A much smaller number of crystal growth sites was observed in the anodic oxide grown on (100) aluminum grains than in the oxide grown on any other substrate orientation.

アルミニウムの各種前処理により生成する表面皮膜に関する研究 ＩＩ 交流インピーダンス法による皮膜構造の解析およびアノード酸化挙動に及ぼす前処理の影響

AC impedance analysis was carried out on the surface oxide films formed on aluminum by three surface treatments:1) electropolishing, 2) chemical polishing, and 3) immersion in H3PO4/CrO3 solution. The pretreated specimens were anodized in a neutral phosphate solution to examine the effects of the initial surface films on the subsequent formation of anodic oxide.It was found that the equivalent circuits for the surface films were all expressed as parallel combinations of resistance (Rox) and capacitance (Cox) components. The value of Rox decreased in the order of pretreatments (1)>(3)>(2); the order was reversed for Cox. Dielectric constant and specific resistivity of the films were estimated and the relationship between the electrical properties and the chemical composition is discussed.The Cl- ions incorporated in the surface film formed by treatment 1) led to the formation of anodic oxide films with a relatively large number of defects. The inner layer of the anodic oxide films was composed of pure Al2O3, and it was thinner for films with pretreatment 3) than those with 1) and 2). This is explained in terms of the effects of pre-existing films on ion transport during subsequent anodizing.

Study of oxygen transport processes during plasma anodization of Si between room temperature and 600 °C

Studies of oxygen transport mechanisms during plasma anodization of Si have been carried out using a combination of 18O tracing techniques and nuclear microanalysis. A thin 18O-enriched ZrO2 overlay film has been used as a source of oxygen tracers during subsequent plasma anodization of Si. The enhancement effect of the zirconia layer on the kinetics of Si anodization allows one to study the mechanisms of Si anodization between room temperature and 600 °C. Results of the 18O depth distributions show that the order of oxygen atoms is largely preserved in the SiO2 and that oxygen ions migrate during film growth. For the temperature range (25–600 °C) studied the microscopic mechanism of oxygen transport during plasma anodization of Si involves a short-range oxygen ion migration, in contrast to the case of high-temperature thermal oxidation. The contribution of a pure thermal process via the diffusion of neutral oxygen species is negligible compared to the high-field-assisted oxygen ion migration in these plasma anodization experiments.

Corrosion Protection of at Alloys by Solution Cast Ta2O5

AbstractA newly developed amorphous, corrosion resistant Ta2O5 coating in saturated H2/H2O/Cl2 environment was studied by scanning and transmission electron microscopy and surface spectroscopy. Although Ta2O5 films formed on polished Al single crystal surfaces by sputter deposition of Ta and subsequent anodization effectively prevent the Al from corrosion by water saturated with chlorine, Al alloy surfaces are not protected, since the anodic film formed over grain boundaries, processing lines, and emergent Precipitates is poorly adherent, thus providing loci for corrosion. This problem was eliminated by casting a 400Å layer of tantalum oxyhydroxide polymer from ethanol solution onto the Al alloy substrate and curing to a Ta2O5 layer that effectively resisted attack by wet chlorine.

On the Inhibition of the Reaction Between Anodic Aluminum Oxide and Water

The reaction between anodic aluminum oxide and several passivating solutions of citric acid and ammonium dihydrogen phosphate (ADP) is studied by capacitance measurements. In addition, the passivating effect of the above solutions has been evaluated by the reaction of the oxide with pure boiling water and subsequent anodization. The results show a strong passivating effect of the ADP solution which is partially diminished by the addition of citrate ions.

Post-breakdown anodization of aluminium

The sparking and its influence over subsequent (post-breakdown) anodization was studied for the galvanostatic anodic-film formation on Al in electrolytes in which the film is insoluble. A constancy both of the breakdown voltage and the frequency of breaking down was observed during prolonged sparking without change of the electrolyte. The fact that broken down anodic film can continue to grow in an electrolyte with characteristically higher breakdown voltage, known for other metals, was confirmed for Al as well. In other words, the breakdown characteristics are independent of the presence of previous breakdowns. Contrary to the existing concepts, it turned out that the greater the number of the previous breakdowns, the higher the rate of the post-breakdown anodization. An empirical equation and a plausible interpretation of this dependence are suggested.

Nickel Oxide Interface for Xerographic Selenium Photoreceptors on Flexible Nickel Foils

The paper reports on a method to produce a nickel oxide interface for xerographic selenium alloy photoreceptors on flexible nickel foils. The process consists of an etching treatment in phosphoric acid catalyzed by small amounts of Pd or Pt on the surface and a subsequent electrochemical treatment in a Na2Cr207 solution. The catalytic effect of Pd and Pt on the nickel dissolution in phospheric acid is investigated and explained on the basis of electrochemical principles. The etched nickel surface provides excellent adhesion of the photoconducting layer to the nickel substrate. In the subsequent electrochemical anodization treatment, a several hundred A thick nickel oxide layer is formed which reduces electron injection from the interface.

Hydrogen Induced Damage in Pickled and Anodized Ti-6Al-4V Alloy Surfaces

Abstract A study was undertaken to investigate a possible relationship between pickling time and the amount of hydrogen introduced in the pickling process. This paper describes the results of surface and bulk hydrogen analysis of Ti-6Al-4V alloy specimens which were pickled according to a predetermined schedule. Hydrogen content in the alloy increased with pickling time, but the rate of absorption was higher for shorter time tests (less than 2 minutes) than for longer time tests (greater than 5 minutes). Alkaline etching significantly reduced the hydrogen pick-up. Sufficient hydrogen in the alloy resulted in failure of the adhesively bonded oxide coating formed during a subsequent anodization treatment.