Two-step Anodization Process Research Articles

Rapid and Sensitive Detection of Lung Cancer Biomarker Using Nanoporous Biosensor Based on Localized Surface Plasmon Resonance Coupled with Interferometry

We propose a nanobiosensor to evaluate a lung cancer‐specific biomarker. The nanobiosensor is based on an anodic aluminum oxide (AAO) chip and functions on the principles of localized surface plasmon resonance (LSPR) and interferometry. The pore‐depth of the fabricated nanoporous AAO chip was 1 µm and was obtained using a two‐step electrochemical anodization process. The sensor chip is sensitive to the refractive index (RI) changes of the surrounding medium and also provides simple and label‐free detection when specific antibodies are immobilized on the gold‐deposited surface of the AAO chip. In order to confirm the effectiveness of the sensor, the antibodies were immobilized on the surface of the AAO chip, and the lung cancer‐specific biomarker was applied atop of the immobilized‐antibody layer using the self‐assembled monolayer method. The nanoporous AAO chip was used as a sensor system to detect serum amyloid A1, which is a lung cancer‐specific biomarker. The specific reaction of the antigen‐antibody contributes to the change in the RI. This in turn causes a shift in the resonance spectrum in the refractive interference pattern. The limit of detection (LOD) was found to be 100 ag/mL and the biosensor had high sensitivity over a wide concentration range.

A Facile Method for Controllable Fabrication of Porous Anodic Aluminum Oxide Templates with Multiple-Scale Structures

Porous anodic aluminum oxide (AAO) templates with diverse nano/submicron/micron multiple-scale structures have been fabricated by a facile and controllable two-step anodization process. The first step anodization has been achieved by using a simple competitive growth process with high anodization voltage (Ua) in ethanol-oxalic acid mixture electrolytes. The effects of Ua (300–600 V), anodization current density (Ja, 100–200 A m−2), and the proportion of ethanol adding (0.3 M oxalic acid : ethanol = 1 : 1, 3 : 2, V/V) on the submicron/micron structures of AAO templates have been investigated in detail. The second step anodization has been conducted under relatively lower Ua of 30 V and 40 V, respectively. The effects of Ua, etching process, and anodization time on the nanostructures of as-fabricated porous AAO templates have been studied carefully. In addition, related intrinsic formation mechanisms have also been investigated. Based on these quantitative experimental results, the fabrication of multiple-scale porous AAO films with diverse nano/submicron/micron structures can be more controllable and designable, facilitating their practical applications in simple template synthesis of complex multiple-scale functional materials.

Highly ordered hierarchical TiO2nanotube arrays for flexible fiber-type dye-sensitized solar cells

Highly ordered hierarchical TiO2 nanotube (HTNT) arrays are obtained with a facile and low-cost approach, which can be applied in flexible fiber-type dye-sensitized solar cells (DSSCs). To achieve the HTNT arrays, smooth TiO2 nanotube (STNT) arrays are fabricated by a two-step anodization process followed by hydrothermal treatment in the presence of the aqueous solution of NH4F. Both STNT and HTNT arrays can serve as photoanodes in the flexible fiber-type DSSCs. We demonstrate that the conversion efficiency of the HTNT array-based flexible fiber-type DSSC (8.6%), which has increased by more than 30% compared with that of the STNT array-based flexible fiber-type DSSC. Moreover, the conversion efficiency is highly stable, even when the flexible fiber-type DSSC is subjected to extreme mechanical deformation, such as 180° bending. This promising conversion efficiency may originate from the significant dye loading capability of the photoanode, which has an enormous surface area benefited from the hierarchical nanostructures.

Control of nanotube shape and morphology on Ti–Nb(Ta)–Zr alloys by varying anodizing potential

Different applied potentials have been employed in a two-step anodization process, utilizing a 1M H3PO4 electrolyte and a solution containing this electrolyte and 0.8wt.% NaF, to control the shape and morphology of oxide nanotubes on coatings for ternary Ti–30Ta–xZr alloys. The ternary alloys were manufactured using an arc furnace, and corrosion testing was carried out using a potentiostat. The microstructures of the Ti–30Ta–xZr alloys had a needle-like structure, and the lath thickness of the α′ phase increased as the Zr content increased. The microstructures of Ti–30Nb–xZr alloys had equiaxed grains. The Ti–30Nb–xZr alloys showed smaller micropores and nanotubes compared to the Ti–30Ta–xZr alloys. The Ti–Nb(Ta)–Zr alloys tended to have improved corrosion resistance with increasing Zr content.

Enhanced light-harvesting of the conical TiO2 nanotube arrays used as the photoanodes in flexible dye-sensitized solar cells

ABSTRACT Free-standing conical TiO2 nanotube arrays with various lengths were prepared directly on the Ti foil by adjusting the applied voltage during the two-step anodic oxidation process. Then the as-grown TiO2 nanotube arrays were transferred onto the flexible ITO/PEN substrates by using titania slurries without any organic binder, which were used as the photoanodes to fabricate the front-illuminated flexible DSSCs. SEM image showed that the conical TiO2 nanotube arrays were successfully obtained. UV–vis spectra were used to explore the enhanced optical absorption compared with the regular cylinder TiO2 nanotube arrays. The photovoltaic properties for incident photon to current efficiency (IPCE) and photovoltaic conversion efficiency was also studied under AM 1.5 illumination, which showed that the conical TiO2 nanotube arrays with 14 μm have the higher photovoltaic performance (3.78%) than that of the regular cylinder TiO2 nanotube arrays (2.79%). The reason of the enhanced photovoltaic performance is due to the enhanced light-harvesting ability of the conical TiO2 nanotube arrays.

Mechanical properties and interface toughness of metal filled nanoporous anodic aluminum oxide coatings on aluminum

The mechanical properties and coating/substrate interface toughness of nanoporous anodic aluminum oxide thin films, both unfilled and metal-filled, are investigated in the current study. A two-step anodization process is used to grow the porous oxide, which is subsequently filled with Ni. The mechanical properties of the coating are probed using nanoindentation and the micro-cantilever deflection technique is used to study the interface toughness. The results are discussed and suggestions for improving the interface toughness are made.

Different TiO2 nanotubes for back illuminated dye sensitized solar cell: fabrication, characterization and electrochemical impedance properties of DSSCs

In the present work we reported the fabrication of different TiO2 nanotube arrays (TiO2 NTs) by anodization method. When used in dye-sensitized solar cells, the TiO2 NTs prepared in the two-step anodization process (2-step TiO2 NTs) showed better efficiency than those of TiO2 NTs prepared in one step anodization process (1-step TiO2 NTs). The 2-step TiO2 NTs show a remarkable efficiency of 1.56 %. This is higher than those of TiO2 NTs prepared in one step anodization process. Electrochemical impedance spectroscopy has been performed for qualitative analysis of charge transport process in dye-sensitized solar cells.

에칭용액의 인산 첨가량에 따른 양극산화 알루미늄 템플레이트의 제작 및 특성

Anodic aluminum oxides (AAO) fabricated by the two-step anodizing process have attracted much attention for the fabrication of nano template because of pore structure with high aspect ratio, low cost process and ease of fabrication. AAOs are characterized by a homogeneous morphology of parallel pores that grow perpendicular to the template surface with a narrow distribution of diameter, length and inter-pores spacing, all of which can be easily controlled by suitably choosing of the anodizing parameters such as pH of the electrolyte, anodizing voltage and duration of anodizing. In this study, AAO templates were characterized by X-ray diffraction and field-emission scanning electron microscope (FE-SEM). The dependence of the pore size change according to the amount of addition of phosphoric acid, which was used to remove the initial alumina oxide layer, was not observed.

Fabrication of 3D-Hybrid Nanostructure for Surface-Enhanced Raman Scattering Substrate: Effect of Applied Voltage on Porous Size of AAO Template

Three-dimensional (3D)-hybrid surface-enhanced Raman scattering (SERS) substrates have been achieved via simultaneous assembled silver nanoparticles (AgNPs) onto the anodic aluminum oxide (AAO) templates. The AAO templates were prepared from the UHV aluminum foil in 0.3 M oxalic acid using the two-step anodization process at 0°C. The effect of applied voltage ranging from 30 to 50 V on the porous diameter and the inter-porous distance of the AAO templates was investigated and observed with filed-emission scanning electron microscope (FE-SEM). The results showed that the porous distance and the inter-porous distance were linearly increased with the increase in the voltage potentials. To investigate the pore-size effect on the SERS activities, the AgNPs were deposited on the AAO nanoporous templates. The SERS activities of these nanostructures were demonstrated with the methylene blue (MB) as the probing molecules.

Self-Ordering Behavior of Anodic Porous Alumina via Selenic Acid Anodizing

The self-ordering behavior of anodic porous alumina that was formed by anodizing in selenic acid electrolyte (H2SeO4) at various concentrations and voltages was investigated with SEM and AFM imaging. A high purity aluminum foil was anodized in 0.1-3.0M selenic acid solutions at 273K and at constant cell voltages in the range of 37 to 51V. The regularity of the cell arrangement increased with increasing anodizing voltage and selenic acid concentration under conditions of steady oxide growth without burning. Anodizing at 42-46V in 3.0M selenic acid produced highly ordered porous alumina. By selective dissolution of the anodic porous alumina, highly ordered convex nanostructures of aluminum with diameters of 20nm and heights of 40nm were exposed at the apexes of each hexagonal dimple array. Highly ordered anodic porous alumina with a cell size of 102nm from top to bottom can be fabricated by a two-step selenic acid anodizing process, that includes the first anodizing step, the selective oxide dissolution, and the second anodizing step.

Preparation and Antimicrobial Properties of Surface Antibacterial Layer of Aluminum

Antibacterial layer was prepared on the aluminum surface by anodizing pure Al and electrodepositing Cu in the pores of the anodic aluminum oxide (AAO) membrane. The AAO membrane was generated by a two-step anodization process in oxalic acid solution. The electrodeposition of Cu was conducted in copper sulfate solution using alternating current. The structural characterizations by scanning electron microscopy (SEM), X-ray diffractometer (XRD) and energy-dispersive spectrometer (EDS) show that Cu nanowires with an average diameter of 70 nm are assembled in the pores of the AAO membrane. The tests of antimicrobial properties against two typical bacteria of Escherichia coli (E. Coli) and Staphylococcus aureus (S. Aureus) indicate that surface antibacterial layer of aluminum possesses excellent antimicrobial properties and the maximum value of the antibacterial rate can reach 99.9% both for E. coli and S. aureus.

Direct detection and speciation of trace explosives using a nanoporous multifunctional microcantilever.

We have developed a highly selective and sensitive nanomechanical infrared (IR) calorimetric spectrometer for use in the direct detection of ultralow concentrations of explosive vapors using a nanoporous TiO2 cantilever. These cantilevers were fabricated using a two-step anodization and photolithography process. By patterning nanoscale wells onto a cantilever, its surface area is increased by 2 orders of magnitude and the surface is converted into a preconcentrator. Resonant excitation of adsorbed molecules using IR radiation causes the cantilever to bend due to temperature changes originating from the nonradiative decay process. The porous structure of the cantilever increases its thermomechanical sensitivity as well as the number of adsorbed molecules. The system performance was demonstrated by detecting binary explosive mixtures under ambient conditions. The TiO2 sensor surface also allows regeneration through the photocatalytic decomposition of adsorbates under UV irradiation.

A transparent nanostructured optical biosensor.

Herein we report a new transparent nanostructured Fabry-Perot interferometer (FPI) device. The unique features of the nanostructured optical device can be summarized as the following: (i) optically transparent nanostructured optical device; (ii) simple and inexpensive for fabrication; (iii) easy to be fabricated and scaled up as an arrayed format. These features overcome the existing barriers for the current nanopore-based interferometric optical biosensors by measuring the transmitted optical signals rather than the reflected optical signals, thereby facilitating the optical testing significantly for the arrayed biosensors and thus paving the way for their potential for high throughput biodetection applications. The optically transparent nanostructures (i.e., anodic aluminum oxide nanopores) inside the FPI devices are fabricated from 2.2 microm thick lithographically patterned Al thin film on an indium tin oxide (ITO) glass substrate using a two-step anodization process. Utilizing the binding between Protein A and porcine immunoglobulin G (IgG) as a model, the detection of the bioreaction between biomolecules has been demonstrated successfully. Experiments found that the lowest detection concentration of proteins is in the range of picomolar level using current devices, which can be easily tuned into the range of femtomolar level by optimizing the performance of devices.

Transparent TiO2 nanotube array photoelectrodes prepared via two-step anodization.

Two-step anodization of transparent TiO2 nanotube arrays has been demonstrated with aid of a Nb-doped TiO2 buffer layer deposited between the Ti layer and TCO substrate. Enhanced physical adhesion and electrochemical stability provided by the buffer layer has been found to be important for successful implementation of the two-step anodization process. With the proposed approach, the morphology and thickness of NT arrays could be controlled very precisely, which in turn, influenced their optical and photoelectrochemical properties.

The Application of Anodizing for Hybrid Capacitor

Introduction Anodizing is widely studied because of its good advantages such as low cost and tractability in over a wide industrial area as one of the surface treatment processing technologies. Thus the anodized metal electrode is used as anode electrode of an electrical circuit. Consequently this process is named anodizing. Recently this process has the limelight to fabricate nano-scale structure with aluminum and titanium metals, etc. For these reasons anodizing have been used for fabrication of nano-scale linear materials and this linear type materials are applied to functionality inorganic membrane, photonic crystals, bio sensor, and electrode in energy storage devices Experimental The template was prepared by anodizing of 99.99% pure aluminum template of 0.2 mm thickness at 40V in 0.3 mol dm-3 sulfuric acid electrolyte at 20 ̊C. It was used as working electrode, and an aluminum sheet was also used as a counter electrode. After anodizing, pore-widening treatments were conducted by immersing the anodic alumina template obtained in 5wt% phosphoric acid at room temperature for 2 hours.Then, the mixture of anodic porous templates and carbon resource was heated in argon at 300 ̊C and kept at this temperature for 30min. After that, the temperature increased up to 600 °C and kept for 1 hour. In this heat treatment, the carbon resource was decomposed to liquefy into porous structure of template. And templates were dissolved in 10% NaOH solution and the CNFs formed were filtered. The morphologies and structures were examined using SEM, Tem, Impedance analysis, Cyclic-voltammetry and Charge-discharge analysis. Result & Discussion Figure shows SEM images of the AAO templates after pore-expansion treatment with 2nd anodized AAO templates. The effects of the two-step anodizing process can be seen clearly, and we can confirm that the AAO template shows a well-ordered pore distribution and increase of pore diameter according to pore-expansion time after the second anodizing step.

Preparation of Porous Alumina Template for Nanostructure Fabrication

Porous alumina films are widely used as templates for fabricating one-dimensional (1-D) nanostructures such as nanowires or nanotubes. Using a two-step anodisation process, we have successfully optimized the growth conditions for fabricating highly ordered porous alumina films with pore diameters ranging from 20 to 150 nm, to be used as templates for 1-D nanostructure synthesis. The effects of the anodisation conditions on pore structure and the formation rate of the films were systematically studied. It was found that low electrolyte temperatures and agitations decreased the growth rate of the films but favored the process of pore ordering. Removal of oxide layer formed from first anodisation process and removal of barrier oxide at pore ends had an important bearing on pore morphology. Besides the stand-alone porous alumina films, we have also fabricated porous alumina films on rod-shaped Al substrates.

TiO2Nanotube Arrays Composite Film as Photoanode for High-Efficiency Dye-Sensitized Solar Cell

A double-layered photoanode made of hierarchical TiO2nanotube arrays (TNT-arrays) as the overlayer and commercial-grade TiO2nanoparticles (P25) as the underlayer is designed for dye-sensitized solar cells (DSSCs). Crystallized free-standing TNT-arrays films are prepared by two-step anodization process. For photovoltaic applications, DSSCs based on double-layered photoanodes produce a remarkably enhanced power conversion efficiency (PCE) of up to 6.32% compared with the DSSCs solely composed of TNT-arrays (5.18%) or nanoparticles (3.65%) with a similar thickness (24 μm) at a constant irradiation of 100 mW cm−2. This is mainly attributed to the fast charge transport paths and superior light-scattering ability of TNT-arrays overlayer and good electronic contact with F-doped tin oxide (FTO) glass provided from P25 nanoparticles as a bonding layer.

Fabrication of nanoporous alumina by two-step anodization and studyof their structural properties

Anodic nanoporous alumina (NPA) is known to be a low cost material suitable for fabrication of templates for the growth of a variety of nanostructured materials, membranes and sensors. In this work, nanoporous alumina was prepared in 0.4 M oxalic acid by a two-step anodization process. The properties of nanoporous alumina film grown on aluminum foil were studied by atomic force microscopy (AFM), scanning electron microscopy (SEM) and optical microscopy. The microscopy investigations confirm the pore formation in the produced layers and the process of anodization allows consistent fabrication of nanoporous alumina. The effect of anodization process parameters on the size of the nanopores and the distance between them were studied and good agreement with published data was found. Hence a desired diameter of the pores and the distance between of it can be obtained by adjusting the electrolyte and oxidation voltage.

Chemical Synthesis, Characterisation, and Biocompatibility of Nanometre Scale Porous Anodic Aluminium Oxide Membranes for Use as a Cell Culture Substrate for the Vero Cell Line: A Preliminary Study

In this preliminary study we investigate for the first time the biomedical potential of using porous anodic aluminium oxide (AAO) membranes as a cell substrate for culturing the Cercopithecus aethiops (African green monkey) Kidney (Vero) epithelial cell line. One advantage of using the inorganic AAO membrane is the presence of nanometre scale pore channels that allow the exchange of molecules and nutrients across the membrane. The size of the pore channels can be preselected by adjusting the controlling parameters of a temperature controlled two-step anodization process. The cellular interaction and response of the Vero cell line with an in-house synthesised AAO membrane, a commercially available membrane, and a glass control were assessed by investigating cell adhesion, morphology, and proliferation over a 72 h period. The number of viable cells proliferating over the respective membrane surfaces revealed that the locally produced in-house AAO membrane had cells numbers similar to the glass control. The study revealed evidence of focal adhesion sites over the surface of the nanoporous membranes and the penetration of cellular extensions into the pore structure as well. The outcome of the study has revealed that nanometre scale porous AAO membranes have the potential to become practical cell culture scaffold substrates with the capability to enhance adhesion and proliferation of Vero cells.

In-situ polymerization of styrene in AAO nanocavities

One of the most promising aspects of the anodic aluminium oxide (AAO) template is the ability to generate a variety of different hierarchical one-dimensional (1D) polymer morphologies with structural definition on the nanometric scale. In-situ polymerization of monomers in reduced space of porous AAO template nanocavities can give rise to the direct production of versatile polymer nanostructures. In this work, porous AAO devices of 35 nm of diameter have been obtained by a two-step electrochemical anodization process and used as a nanoreactor to study the radical polymerization kinetics of styrene (St) in confinement and the results compared to those of polymerization in bulk. SEM morphological study has been conducted to establish the final structure of obtained polymer nanostructures. Confocal Raman microscopy has been performed to study the formation of the polymer through the AAO cavities as a function of time and with this methodology it has been possible to establish the monomer conversion for styrenic polymerization in AAO devices. Polystyrene obtained in the nanoreactor was characterized by SEC, NMR, TGA and DSC and the properties compared with those of bulk polymer. It was found that both the average molecular weights and polydispersity index of nanostructured polymer are lower than those obtained for bulk polymer. NMR studies have shown that the use of a reactor with nanometric size dimensions gave the obtained polystyrene greater stereospecificity than that obtained in bulk. Thermal stability and glass transition temperature (Tg) values are higher for nanostructured than bulk polymers. Moreover, the methodology proposed in this work, using AAO nanocavities as nanoreactors for polymerization reaction, can be generalized and applied to obtain polymer nanostructures of very different chemical nature and morphology by choosing the appropriate monomer or monomer reactants and by tailoring the dimension of AAO cylindrical nanocavities, that is, diameter from 20 to 400 nm and length from a few to hundreds of microns.