Single-step Anodization Research Articles

Single Step Formation of C-TiO2Nanotubes: Influence of Applied Voltage and Their Photocatalytic Activity under Solar Illumination

Self-aligned and high-uniformity carbon (C)- titania (TiO2) nanotube arrays were successfully formed via single step anodization of titanium (Ti) foil at 30 V for 1 h in a bath composed of ethylene glycol (EG), ammonium fluoride (NH4F), and hydrogen peroxide (H2O2). It was well established that applied voltage played an important role in controlling field-assisted oxidation and field-assisted dissolution during electrochemical anodization process. Therefore, the influences of applied voltage on the formation of C-TiO2nanotube arrays were discussed. It was found that a minimal applied voltage of 30 V was required to form the self-aligned and high-uniformity C-TiO2nanotube arrays with diameter of ~75 nm and length of ~2 μm. The samples synthesized using different applied voltages were then subjected to heat treatment for the conversion of amorphous phase to crystalline phase. The photocatalytic activity evaluation of C-TiO2samples was made under degradation of organic dye (methyl orange (MO) solution). The results revealed that controlled nanoarchitecture C-TiO2photocatalyst led to a significant enhancement in photocatalytic activity due to the creation of more specific active surface areas for incident photons absorption from the solar illumination.

In situ fabrication of ultrathin porous alumina and its application for nanopatterning Au nanocrystals on the surface of ion-sensitive field-effect transistors

In situ fabrication in a single step of thin films of alumina exhibiting a thickness of less than 100 nm and nanopores with a highly regular diameter distribution in order to pattern nanostructures over field-effect devices is a critical issue and has not previously been demonstrated. Here we report the fabrication in situ of 50 nm thick ultrathin nanoporous alumina membranes with a regular pore size directly over metal-free gate ion-sensitive field-effect transistors. Depositing thin films of aluminum by an electron beam at a relatively low rate of deposition on top of chips containing the transistors and using a conventional single-step anodization process permits the production of a well-adhering nanoporous ultrathin layer of alumina on the surface of the devices. The anodization process does not substantially affect the electrical properties of the transistors. The small thickness and pore size of ultrathin alumina membranes allow them to be sequentially employed as masks for patterning Au nanocrystals grown by an electroless approach directly on the top of the transistors. The patterning process using a wet chemical approach enables the size of the patterned crystals to be controlled not only by the dimensions of the pores of alumina, but also by the concentration of the reactants employed. Surface modification of these nanocrystals with alkanethiol molecules demonstrates that the electrostatic charge of the functional groups of the molecules can modulate the electrical characteristics of the transistors. These results represent substantial progress towards the development of novel nanostructured arrays on top of field-effect devices that can be applied for chemical sensing or non-volatile memories.

Robust Superhydrophilic/Hydrophobic Surface Based on Self-Aggregated Al2O3 Nanowires by Single-Step Anodization and Self-Assembly Method

Superhydrophilic and superhydrophobic surfaces were studied with an eye to industrial applications and use as research tools. Conventional methods involve complex and time-consuming processes and cannot feasibly produce large-area three-dimensional surfaces. Here, we report robust and large-area alumina nanowire structures with superhydrophobic or superhydrophilic properties, generated by an inexpensive single-step anodization process that can routinely create arbitrary three-dimensional shapes. This process is expected to open up diverse applications.

Formation of TiO2–WO3 nanotubular composite via single-step anodization and its application in photoelectrochemical hydrogen generation

A nanotubular composite of TiO2–WO3 was synthesized via anodic oxidation of titanium in a single-step process using phosphotungstic acid as the tungsten source. The composite material was evaluated for photoelectrochemical water splitting and demonstrated a 46% increase in conversion efficiency by incorporating WO3 compared to TiO2 nanotubes prepared under similar conditions.

Fabrication of Porous Anodic Alumina by Single-Step Anodization: Influence of the Molar Concentration and effect of the Chemical Etching

Porous anodic alumina (PAA) films have been fabricated by single-step anodization for different concentrations of oxalic acid. The influence of the molar concentration on their average pore diameter was investigated and chemical etching processes for different times on the as-etched layer was performed in order to study its effect on the formation of self-organized nanopores. The experimental results show that controlling both, molar concentration and chemical etching times after anodization pores with different diameters can be easily prepared. This procedure leads to form porous alumina layers with high-quality two-dimensional hexagonal lattices and provide an ideal template for preparation of many one-dimensional nanomaterials.

Fabrication of Nanoporous Alumina Membranes by Single Step Anodization and Their Microscopic Characterization

Fabrication of Nanoporous Alumina Membranes by Single Step Anodization and Their Microscopic Characterization

Novel structure formation at the bottom surface of porous anodic alumina fabricated by single step anodization process

A simple approach for the growth of long-range highly ordered nanoporous anodic alumina film in H2SO4 electrolyte through a single step anodization without any additional pre-anodizing procedure is reported. Free-standing porous anodic alumina film of 180μm thickness with through hole morphology was obtained. A simple and single step process was used for the detachment of alumina from aluminum substrate. The effect of anodizing conditions, such as anodizing voltage and time on the pore diameter and pore ordering is discussed. The metal/oxide and oxide/electrolyte interfaces were examined by high resolution scanning transmission electron microscope. The arrangement of pores on metal/oxide interface was well ordered with smaller diameters than that of the oxide/electrolyte interface. The inter-pore distance was larger in metal/oxide interface as compared to the oxide/electrolyte interface. The size of the ordered domain was found to depend strongly upon anodizing voltage and time.

Detection of Cyclic Volatile Organic Compounds Using Single-Step Anodized Nanoporous Alumina Sensors

Conventional methods of fabricating anodic aluminum oxide (AAO) materials have utilized a multistep anodization process to manufacture sensor substrates and templates for nanostructured materials. The multistep anodization produces structured, highly ordered hexagonal nanopores. In this paper, it is demonstrated that a single-step anodization process employed in the manufacturing of moisture sensors produces a nanoporous AAO material suitable for the detection and discrimination of low molecular weight volatile organic compounds. Electrical impedance methods have been employed to analyze the electrical response of the single-step anodized AAO materials in the presence of cyclic organic vapors. The sensor exhibits an impedance response that discriminates cyclohexane, cyclohexene, benzene, toluene, and the three isomers of xylene. The impedance measurements have a direct correlation with the relative permittivity, polarizability, and dipole moments of the organic analytes.

Inside Front Cover: Fabrication of Ideally Ordered Nanoporous Alumina Films and Integrated Alumina Nanotubule Arrays by High‐Field Anodization (Adv. Mater. 17/2005)

AbstractA simple, low‐cost approach to fabricating large‐area highly ordered nanoporous alumina films in sulfuric acid solutions through a single‐step high‐field anodization, without the assistance of any additional process, is reported on p. 2115 by Chu and co‐workers. The critical high anodizing potential in the adopted electrolyte system increases with the ageing of solutions after a long period of anodization. Correspondingly, the applicable current density for stable anodization rises significantly, thus leading to high‐speed film growth. Uniform porous anodic alumina films in sulfuric acid solutions under a high electric field of 40–70 V and 1600–2000 A m–2 are achieved.

The fabrication of high-quality periodic porous alumina templates

Porous alumina films can be achieved by anodizing an ultra pure aluminum sheet in proper conditions. Both the distribution and the size of the pores are regular. The depths of the pores are uniquely limited by the anodization time thus very deep pores can be obtained, in the order of mm. Such a porous structure can be employed to serve as the templates for nanosized materials. The Oxalic acid of 0.3mol/L was used in our experiments with the applied DC voltage 40 V. The two-step method was involved to fabricate the templates. The resultant templates exhibit regular porous section. The pore size is ～40—70 nm and the pore-pore spacing is～110 nm. The depth is～0.4 mm. The dependence of the template quality on the solution (oxalic acid) temperature was analyzed and the comparison between the single-step and two-step anodization was made. The results indicate that low solution temperature and two-step method are necessary.

Buffer layer influence on guiding properties of oxidized porous silicon waveguides

We studied the influence of the thickness and porosity of the buffer layer on the guiding properties of oxidized porous silicon waveguides (OPSWG). It is demonstrated how a modified anodization process acts on the porosity of the final oxidized porous silicon. In this way, it is possible to control the refractive index jump between the core of OPSWG made of compact silicon dioxide and the bottom buffer layer made of porous silicon dioxide. The adoption of a double-step anodization process decreases the propagation losses to 0.5 dB/ cm against the 8 dB/ cm measured for the waveguide realized using a single-step anodization. The main reason seems not to be the increase of the difference of refractive index values but the more homogeneous buffer layer obtained along the core of the waveguide. This homogeneous layer permits a better lateral confinement of the light as demonstrated by spatial refractive index profile measurement.

Characterization of anodic porous alumina by AFM

The topography of supported and unsupported anodic aluminum oxide (AAO) films was measured by AFM under different testing modes. The supported film, attached onto an aluminum substrate, is mechanically stable and the contact mode shows good resolution for imaging the intrinsic features of the surface. Additionally, the non-contact mode can detect the presence of adsorbed species on the surface, which are not detected by the contact mode. On the contrary, for the unsupported alumina film, the non-contact mode shows better resolution, even for surface pore detection. These results are discussed in view of the different mechanical properties of both types of alumina films, and the magnitude of the sample–tip interaction for each operation mode. In relation with the pore arrangement, a single-step anodization process results in a dense but non-regular pore pattern. Regular pore arrays was obtained with a two-step anodization method using both oxalic and sulfuric acid as oxidation agents. AFM characterization allows the evaluation of the order of the pore array, the pore density and the external shape of AAO films obtained under different experimental approaches. A reliable determination of the internal diameter and shape of the pores is not well accomplished under the present experimental conditions.

Time and orientation dependence of ordering in anodized aluminum for self-organized magnetic arrays

Anodization experiments to create alumina pores were performed using pure Al and hard disk Al–Mg substrates. A single step anodization was employed for up to 40 h to determine the time dependence of pore ordering. The pores formed from the Al–Mg substrate were unordered, while ordered-pore domains as large as 3 μm form in both the as-rolled and annealed pure Al samples. The effect of the aluminum grain crystallographic orientation was investigated via orientation-imaging microscopy for the pure Al surface with both order and disordered pores. It was found that neither heat treatment nor crystallographic orientation played a large role in the pore ordering.