Electrochemical Anodization Treatment Research Articles

FORMATION AND STRUCTURE OF MESOPOROUS SILICON

This article presents research results on the formation kinetics and structure of mesoporous silicon layers synthesized by electrochemical anodic treatment in an electrolyte based on a 12 % aqueous solution of hydrofluoric acid. The electrolyte consisted only of deionized water and hydrofluoric acid and contained no organic additives thus avoiding carbon contamination of the porous silicon during anodic treatment. Another distinguishing feature of the work is that all the experiments were conducted for whole silicon wafers 100 mm in diameter rather than for small size samples often used to save silicon. The initial substrates were single crystal silicon wafers brand IES −0,01 cut from Czochralski grown ingots. The thickness of the porous silicon layers, its growth rate and the bulk porosity of porous silicon were estimated as functions of anodic current density and anodic treatment time. The structure of the porous silicon layers and the size and the density of the pore channels investigated using SEM. We found optimum treatment modes allowing one to obtain homogeneous porous silicon layers for subsequent use as buffer layers for epitaxy.

Ni-doped TiO2 nanotubes for wide-range hydrogen sensing

Doping of titania nanotubes is one of the efficient way to obtain improved physical and chemical properties. Through electrochemical anodization and annealing treatment, Ni-doped TiO2 nanotube arrays were fabricated and their hydrogen sensing performance was investigated. The nanotube sensor demonstrated a good sensitivity for wide-range detection of both dilute and high-concentration hydrogen atmospheres ranging from 50 ppm to 2% H2. A temperature-dependent sensing from 25°C to 200°C was also found. Based on the experimental measurements and first-principles calculations, the electronic structure and hydrogen sensing properties of the Ni-doped TiO2 with an anatase structure were also investigated. It reveals that Ni substitution of the Ti sites could induce significant inversion of the conductivity type and effective reduction of the bandgap of anatase oxide. The calculations also reveal that the resistance change for Ni-doped anatase TiO2 with/without hydrogen absorption was closely related to the bandgap especially the Ni-induced impurity level.

Surface nanotopography of an anodized Ti–6Al–7Nb alloy enhances cell growth

The α/β-type Ti–6Al–7Nb alloy is a potential replacement for α/β-type Ti–6Al–4V alloy, which is widely used in biomedical implant applications. The biological response to implant material is dependent on the surface characteristics of the material. In the present study, a simple and fast process was developed to perform an electrochemical anodization treatment on Ti–6Al–7Nb alloy. The proposed process yielded a thin surface nanotopography, which enhanced cell growth on the Ti–6Al–7Nb alloy. The surface characteristics, including the morphology, wettability, and protein adsorption, were investigated, and the cytotoxicity was evaluated according to International Organization for Standardization 10993-5 specifications. Cell adhesion of human bone marrow mesenchymal stem cells on the test specimens was observed via fluorescence microscopy and scanning electron microscopy. The anodization process produced a surface nanotopography (pore size <100nm) on anodized Ti–6Al–7Nb alloy, which enhanced the wettability, protein adsorption, cell adhesion, cell migration, and cell mineralization. The results showed that the surface nanotopography produced using the proposed electrochemical anodization process enhanced cell growth on anodized Ti–6Al–7Nb alloy for implant applications.

Improvements in the corrosion resistance and biocompatibility of biomedical Ti–6Al–7Nb alloy using an electrochemical anodization treatment

The biocompatibility of an implant material is determined by its surface characteristics. This study investigated the application of an electrochemical anodization surface treatment to improve both the corrosion resistance and biocompatibility of Ti–6Al–7Nb alloy for implant applications. The electrochemical anodization treatment produced an Al-free oxide layer with nanoscale porosity on the Ti–6Al–7Nb alloy surface. The surface topography and microstructure of Ti–6Al–7Nb alloy were analyzed. The corrosion resistance was investigated using potentiodynamic polarization curve measurements in simulated blood plasma (SBP). The adhesion and proliferation of human bone marrow mesenchymal stem cells to test specimens were evaluated using various biological analysis techniques. The results showed that the presence of a nanoporous oxide layer on the anodized Ti–6Al–7Nb alloy increased the corrosion resistance (i.e., increased the corrosion potential and decreased both the corrosion rate and the passive current) in SBP compared with the untreated Ti–6Al–7Nb alloy. Changes in the nanotopography also improved the cell adhesion and proliferation on the anodized Ti–6Al–7Nb alloy. We conclude that a fast and simple electrochemical anodization surface treatment improves the corrosion resistance and biocompatibility of Ti–6Al–7Nb alloy for biomedical implant applications.

Abnormal conductivity behavior in porous lead telluride films

We report the experimental observation of the novel phenomenon of the resistivity decrease in porous PbTe layers during the pore formation process. Investigations were performed on the n-PbTe films with 2.3-μm thickness, which were near the point of the conductivity-type inversion at room temperature. Anodic electrochemical treatment for the porous layers with 41% to 52% porosity fabrication was performed using a KOH-based Norr electrolyte solution. For the porous lead telluride layers, the resistivity value at 300 K decreased 2.5 to 3 times. For the explanation of the observed phenomenon, a physical model is proposed which takes into account the Pb/Te ratio change during the anodic treatment.

Novel Method for Controllable Fabrication of a Superhydrophobic CuO Surface on AZ91D Magnesium Alloy

A novel method for controllable fabrication of a superhydrophobic CuO surface on AZ91D magnesium alloy is reported in this paper. Hierarchical structure composed of micro/nano-featherlike CuO was obtained by electrodeposition of Cu-Zn alloy coating and subsequently an electrochemical anodic treatment in alkaline solution. After modification with lauric acid, the surface became hydrophobicity/superhydrophobicity. The formation of featherlike CuO structures was controllable by varying the coating composition. By applying SEM, ICP-AES, and water contact angle analysis, the effects of coating composition on the surface morphology and hydrophobicity of the as-prepared surfaces were detailedly studied. The results indicated that at the optimal condition, the surface showed a good superhydrophobicity with a water contact angle as high as 155.5 ± 1.3° and a sliding angle as low as about 3°. Possible growth mechanism of featherlike CuO hierarchical structure was discussed. Additionally, the anticorrosion effect of the superhydrophobic surface was studied by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) measurements. The interface model for anticorrosion mechanism of superhydrophobic surface in corrosive medium was proposed. Besides, the mechanical stability test indicated that the resulting superhydrophobic surfaces have good mechanical stability.

Investigations of the pore formation in the lead selenide films using glacial acetic acid- and nitric acid-based electrolyte

We report a novel synthesis of porous PbSe layers on Si substrates by anodic electrochemical treatment of PbSe/CaF2/Si(111) epitaxial structures in an electrolyte solution based on glacial acetic acid and nitric acid. Electron microscopy, X-ray diffractometry, and local chemical microanalysis investigation results for the porous layers are presented. Average size of the synthesized mesopores with approximately 1010 cm−2 surface density was determined to be 22 nm. The observed phenomenon of the active selenium redeposition on the mesopore walls during anodic treatment is discussed.

3D surface topography study of the biofunctionalized nanocrystalline Ti–6Zr–4Nb/Ca–P

In this work surface of the sintered Ti-6Zr-4Nb nanocrystalline alloy was electrochemically biofunctionalized. The porous surface was produced by anodic oxidation in 1 M H{sub 3}PO{sub 4} + 2%HF electrolyte at 10 V for 30 min. Next the calcium-phosphate (Ca-P) layer was deposited, onto the formed porous surface, using cathodic potential - 5 V kept for 60 min in 0.042 M Ca(NO{sub 3}){sub 2} + 0.025 M (NH{sub 4}){sub 2}HPO{sub 4} + 0.1 M HCl electrolyte. The deposited Ca-P layer anchored in the pores. The biofunctionalized surface was studied by XRD, SEM and EDS. In vitro tests culture of normal human osteoblast (NHOst) cells showed very good cells proliferation, colonization and multilayering. Using optical profiler, roughness and hybrid 3D surface topography parameters were estimated. Correlation between surface composition, morphology, roughness and biocompatibility results was done. It has been shown by us that surface with appropriate chemical composition and topography, after combined electrochemical anodic and cathodic surface treatment, supports osteoblast adhesion and proliferation. 3D topography measurements using optical profiler play a key role in the biomaterials surface analysis. - Highlights: Black-Right-Pointing-Pointer Nanocrystalline Ti-6Zr-4Nb/Ca-P material was produced for hard tissue implant applications. Black-Right-Pointing-Pointer Calcium-phosphate results in surface biofunctionalization. Black-Right-Pointing-Pointer The biofunctionalized surfacemore » shows good in-vitro behavior.« less

Blood responses to titanium surface with TiO2 nano‐mesh structure

The goal of this study was to enhance the blood responses to titanium (Ti) surfaces used for dental implant application through the formation of a TiO2 nano-mesh surface layer produced by a fast electrochemical anodization treatment. Electrochemical anodization treatments with different anodization currents and temperatures in an alkaline solution were used to create a nano-mesh oxide layer on polished Ti surface. Surface characterizations of the mesh structure were carried out using thin-film X-ray diffractometer, field-emission scanning electron microscope, and atomic force microscope. The blood responses, including the blood-clotting ability and platelet adhesion morphology, to the test Ti surfaces were evaluated. The blood-clotting ability, in terms of optical density of blood, was statistically analyzed using a nonparametric method, Kruskal-Wallis test, for the factor of anodization treatment. A multilayer TiO2 nano-mesh structure was rapidly formed on the polished Ti surface using a simple electrochemical anodization treatment in an alkaline solution. The TiO2 nano-mesh had an average mesh size between 34 and 93 nm, depending on the anodization current and temperature. The features on the TiO2 nano-mesh structure on the anodized Ti surface were of a similar size scale as blood proteins, giving the material better blood clot ability (P<0.05) and improved platelet activation and aggregation as compared with an untreated polished Ti surface. The formation of TiO2 nano-mesh on the Ti surfaces was shown to enhance blood responses, which we expect to promote cell growth in the application of dental implants.

Fabrication and study of porous PbTe layers on silicon substrates

AbstractFabrication of porous PbTe layers on Si substrates using a developed technique based on anodic electrochemical etching of PbTe/CaF2/Si(111) heteroepitaxial structures in a Norr electrolyte with anodizing current density 2‐4 mA/cm2 is reported. The structural and morphological parameters of such layers are investigated with x‐ray reflectometry and diffractometry methods and with high‐resolution scanning electron microscopy. The influence of anodizing conditions on the parameters of the layers is discussed, as well as the morphological peculiarities of the anodized structures. The presence of cylindrical mesopores with diameter of 7‐26 nm inclined at the angle of ∼35° to the surface normal is shown. The value of the porosity for the near‐surface layer of lead telluride films is in the interval of 41‐68% and depends on the anodic electrochemical treatment conditions. (© 2011 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Microplasma electrochemical deposition of aluminum oxide-polyethylene composite coatings on iron surface

Composite coatings containing aluminum oxide and polyethylene are deposited using microplasma electrochemical anodic treatment of the iron surface in an aluminate bath at a voltage of 260–360 V. Using scanning electron microscopy, microprobe analysis, Fourier transform infrared spectroscopy, and electrochemical polarization measurements, the composition, structure, and corrosion characteristics of the coatings are determined. Adding 0.5–1.0 wt % polyethylene dispersion to the electrolyte is shown to substantially facilitate the origination of microplasma conditions, prevent the strong warming of electrolyte during anodizing, and obtain coatings with substantially higher corrosion resistance compared to those produced in an aluminate bath containing no polymer dispersion.

Improving the biocompatibility of titanium surface through formation of a TiO 2 nano-mesh layer

This study was to evaluate the biocompatibility, as determined by corrosion resistance and cell responses, of TiO 2 nano-mesh layer on polished Ti surface. Results showed that a TiO 2 nano-mesh layer was formed on the anodized Ti surface through electrochemical anodization treatment. In comparison to the polished Ti surface, the presence of TiO 2 nano-mesh layer on the anodized Ti surface increased the corrosion potential and decreased the corrosion rate and passive current in simulated body fluid. The nano-mesh layer also caused better cell adhesion and spreading, as well as faster cell proliferation and initial differentiation. Overall, this TiO 2 nano-mesh layer improved the biocompatibility of Ti surface.

Formation of porous nanostructured lead telluride films by an anodic electrochemical etching method

Comprehensive research of the structural, optical and electrical properties of a PbTe/CaF2/Si(1 1 1) epitaxial system after anodic electrochemical treatment in a Norr solution electrolyte with a low current density of 6 mA cm−2 was carried out. It is shown that the anodizing results in the increase of the band gap and resistivity and in the decrease of the refractive index of lead telluride. Using secondary ion mass spectrometry, a specific change of the C, K, H element distribution in depth of PbTe films after electrochemical treatment was detected. It is demonstrated that the set of presented experimental results can be explained from the standpoint of the formation of a mesoporous structure of lead telluride with a porosity value of about 50%. The effective radius of PbTe nanoparticles is equal to 13 nm. Triple-crystal x-ray diffractometry results analysis showed that the pores have spherical voids with an average dimension of 40 nm.

Effects of "P-N" Terminations on the Initial Stages of Pore Growth onto n-InP in HCl Aqueous Solution

In this paper we report, for the first time, a galvanostatic control in 1M HCl aqueous solution onto a InP surface that had been previously entirely nitrogenated. The surface nitrogenation required an anodic electrochemical treatment in acidic liquid ammonia (NH3 liq.). An homogeneous covering film with " P-N " terminations was obtained onto the InP surface properly deoxidized. This thin film is notable for its lack of air ageing and also for its chemical stability in HCl. A galvanostatic control at different current density (10 mA.cm-2, 100mA.cm-2 and 300 mA.cm-2) in 1M HCl was used to identify the effect of this " P-N " terminations on the porosification process. In comparison to a bare surface, a contrasted evolution of the interfacial potential was clearly observed for low current density. As expected, a crystal oriented pore morphology (CO) is obtained onto a bare InP surface whereas "oscillating" current line oriented pore morphology (CLO) is kept onto a surface entirely recovered by a " P-N " film. The presence of the nitrogenated film can therefore be significant on the pore growth evolution in 1M HCl aqueous solution.

Formation of TiO 2 nano-network on titanium surface increases the human cell growth

Objectives This study was to improve human cell growth on titanium (Ti) used for dental implants through formation of a nano-network surface oxide layer created by an electrochemical anodization treatment. Methods An electrochemical anodization treatment was used to produce a network oxide layer on Ti surface. Surface characterization of the network layer was carried out using thin film X-ray diffractometer and field emission scanning electron microscopy. Human bone marrow mesenchymal stem cells (hMSCs) were made to express green fluorescent protein (GFP) by retroviral transduction. The GFP signal was measured in situ to assess in vitro and in vivo cell growth on Ti surfaces. In vivo experiments on Ti-supported cell growth were carried out on the back skin of nude mice. Alizarin red staining and immunofluorescent staining were used to observe cell differentiation. Results A multilayer TiO 2 nano-network was produced rapidly on Ti surface using a simple electrochemical anodization treatment. The TiO 2 nano-network layer on the anodized Ti surfaces significantly improved in vitro and in vivo hMSC growth, as assessed by measurement of GFP fluorescence, relative to hMSC growth on untreated Ti surface. The TiO 2 nano-network layer on the anodized Ti surfaces can also induce the differentiation of hMSCs after 28-day in vivo test. Significance The formation of TiO 2 nano-network on the Ti surfaces can increase the hMSC growth in vitro and in vivo.

Nano/submicron-scale TiO 2 network on titanium surface for dental implant application

In this study, a fast electrochemical anodization treatment, applying different anodic currents, was used to produce a nano/submicron-scale network oxide layer on Ti metal surface for biomedical implant application. The anodized Ti surface was analyzed using thin film X-ray diffractometer, X-ray photoelectron spectrometer, and field emission scanning electron microscope. The whole blood coagulation and human bone marrow stem cells (hBMSCs) adhesion on the anodized Ti surface were evaluated. Results showed that a nano/submicron-scale TiO 2 network layer with a lateral pore size of 20–160 nm could be rapidly produced on Ti surface through electrochemical anodization treatment. Increasing the applied anodic current led to an increase in pore size of TiO 2 network. The nano/submicron-scale TiO 2 network layer significantly enhanced the whole blood coagulation and hBMSCs adhesion on Ti surface.

Synthesis of effective titania nanotubes for wastewater purification

In order to synthesize a self-organized, TiO2 nanotubular layer for wastewater purification, anodizations were performed at constant applied potential in hydrofluoric acid and the anodic TiO2 layer was heat treated. The anodic nanotube arrays were also influenced by the applied anodic potentials and HF concentrations. The anodic TiO2 nanotubular structured film with various morphologies and crystal structures can be synthesized by proper electrochemical anodization and additional annealing treatment. The photocatalytic efficiencies were maximized for the anatase-type, TiO2 nanotubular layer which was prepared by annealing at 550°C.

A Significant Anodic Passivation of n and p-InP Surfaces in Liquid Ammonia: First Evidence of Stable Phosphorus-Nitrogen Bonds

The anodic electrochemical treatment in liquid ammonia of InP (n- and p-) leads to a simultaneous oxidation of both semiconductor and solvent. The oxidation of InP takes place through a passivating layer revealed as well by electrochemistry as by XPS. The chemical composition of InP surface is therefore gradually modified according the anodic charge. The composition of the film layer is supposed to be close to HN=P-NH2, a promising compound stable as well in liquid ammonia as in water.

Evaluation of the corrosion resistance of phosphate coatings obtained by anodic electrochemical treatment

The corrosion resistance of phosphate coating obtained by anodic electrochemical treatment at 4–6 mA/cm 2 is addressed in this paper. The corrosion performance of these coatings is also compared with the coatings obtained by chemical treatment. The regenerated phosphoric acid under the influence of anodic current causes a large variation in morphological features of the coatings. Immersion and salt spray tests indicate the ability of these coatings to act as a barrier film on mild steel. Polarization and electrochemical impedance spectroscopic (EIS) studies indicate that the corrosion resistance of phosphate coatings obtained by anodic treatment decreases with increase in current density employed for deposition. In spite of their higher coating weight, the corrosion resistance of phosphate coatings obtained by anodic treatment is inferior to those obtained by chemical treatment. The porosity or discontinuities created due to the dissolution of the coating under the influence of anodic current are considered responsible for the inferior corrosion resistance of these coatings. The study concludes that anodic treatment has only a limited scope for preparing phosphate coatings with improved corrosion resistance.

Nanocrystalline structure and nanopore formation in modified thermal TiO 2 films

The anodic TiO 2 films on Ti 0 substrates were synthesized using different electrochemical techniques including potential step, potentiodynamic, and galvanostatic technique, from a 1 M Na 2 SO 4 + 10 mM NaF solution. The AFM imaging of film surfaces revealed that thin films ( h < 20 nm ) are composed of small spherical-shaped nanocrystals, up to 20 nm in size. In thicker TiO 2 films ( h > 20 nm ) , cylindrical nanopores with diameter of ca. 30 nm, are formed. In contrast to the nanocrystalline nature of anodic TiO 2 films, thermally grown TiO 2 films at 850 °C are composed of oriented large pyramidal crystallites (200–500 nm in size), which are transformed into even larger moulds (2– 3 μ m in size) at 1050 °C. Thermal films of this type have been known to show inferior surface properties leading to large reflectance losses and the presence of surface states, which promote the electron–hole recombination. In this paper, we propose a new way to remedy these disadvantages of thermal films by special low temperature electrochemical anodic treatment. We have found that by the anodic treatment of thermally grown TiO 2 films, it is possible to control the surface properties, such as the nanocrystalline structure and nanopore formation. These features are desirable for solar energy conversion devices and solar hydrogen production, where the enhancement of electrocatalytic activity by increasing real surface area, reduction of reflectance losses, and removal of surface states created by thermal growth, are of primary importance. The tested electrochemical treatment included program waveforms inducing nanocrystallinity and nanopore formation. The pulse-voltammetric procedures are proposed to control surface non-stoichiometry of TiO 2 films and surface-states density of the photoelectrodes.