Porous Alumina Films Research Articles

Blind reconstruction of atomic force microscopy tip morphology by using porous anodic alumina membrane

An atomic force microscopy (AFM) image of a surface is a convolution of the tip geometry and sample features. It is important to develop tip characterisers and estimate the tip shape for a more accurate AFM image. With the traditional characterisers with special microstructures it is difficult to accurately determine tip shape because of their dimensional uncertainty. Combined with tip blind reconstruction algorithms, some nanomaterials with arrayed nanostructures are often used to estimate the AFM tip morphology. However, the blind reconstruction algorithms are sensitive to image noise. To solve such problems, the porous anodic alumina (PAA) film with well-ordered porous nanostructures was fabricated and used as a new tip characteriser. By setting the appropriate scanning routine and scanning mode, the two-dimensional and three-dimensional tip morphology was accurately calculated. PAA film as the AFM tip characteriser can effectively reduce the influence of AFM image noise and sample-dimensional uncertainty of tip blind estimation results, especially avoiding tip wear and damage.

Continuous and Nanostructured TiO2 Films Grown by dc Sputtering Magnetron

The growth of Anatase nanostructured films using dc reactive magnetron sputtering and post-annealing treatment is reported. TiO2 has been deposited on Porous Anodic Alumina Films used as templates which were previously grown in phosphoric acid solution and etched to modify their pore diameters. This synthesis via results in the formation of vertically aligned and spatially ordered TiO2 nanostructures replicating the underlying template. Previously, the growth optimization of TiO2 thin films deposited by dc magnetron sputtering on flat silicon substrates was done. The crystalline structure and Ti in-depth concentration profile were determined by grazing incidence X-ray diffraction and Rutherford backscattering spectrometry, respectively. The surface morphology of the samples was explored by mean of a Field Emission Gun scanning electron microscope. Optical properties of the nanostructured samples were studied by using the reflectance spectra received in the UV-visible range. In these spectra different band gap values and complex light absorption features were observed.

Preparing nano-hole arrays by using porous anodic aluminum oxide nano-structural masks for the enhanced emission from InGaN/GaN blue light-emitting diodes

We report on the achievement of the enhanced cathodoluminescence (CL) from InGaN/GaN light-emitting diodes (LEDs) by using roughening surface. Nanoporous anodic aluminum oxide (AAO) mask was utilized to form nano-hole arrays on the surface of InGaN/GaN LEDs. AAO membranes with ordered hexagonal structures were fabricated from aluminum foils by a two-step anodization method. The average pore densities of ∼1.0 × 1010 cm−2 and 3.0 × 1010 cm−2 were fabricated with the constant anodization voltages of 25 and 40 V, respectively. Anodic porous alumina film with a thickness of ∼600 nm has been used as a mask for the induced couple plasma etching process to fabricate nano-hole arrays on the LED surface. Diameter and depth of nano-holes can be controlled by varying the etching duration and/or the diameter of AAO membranes. Due to the reduction of total internal reflection obtained in the patterned samples, we have observed that the cathodoluminescence intensity of LEDs with nanoporous structures is increased up to eight times compared to that of samples without using nanoporous structure.

Relationship between microstructure and optical properties of a novel perovskite C12PbI4 embedded in matrix of porous alumina

In this study, organic–inorganic hybrid perovskite multiple quantum wells (PbI QWs) embedded in porous anodic alumina (PAA) thin films on glass and aluminum substrates are investigated in detail. The pore height and diameter of the nanoscale structure of porous anodic alumina (PAA) film produced by the anodization technique are controllable. The synthesized films are characterized morphologically using the atomic force microscopy (AFM). Scanning electron microscopy (SEM) study showed granular surface. The structural and optical properties were investigated by X-ray diffraction (XRD), photoluminescence (PL) and UV–Vis–NIR spectrophotometer. The effect of the two different substrates on the impregnation of the PbI QW in the PAA is presented. Both PL and AFM studies show a better penetration of the PbI QW in the case of the Al substrate providing a wider pore diameter. Remarkable enhancement of quantum confinement is demonstrated.

Cavity-type hypersonic phononic crystals

We report on the engineering of the phonon dispersion diagram in monodomain anodic porous alumina (APA) films through the porosity and physical state of the material residing in the nanopores. Lattice symmetry and inclusion materials are theoretically identified to be the main factors which control the hypersonic acoustic wave propagation. This involves the interaction between the longitudinal and the transverse modes in the effective medium and a flat band characteristic of the material residing in the cavities. Air and filled nanopores, therefore, display markedly different dispersion relations and the inclusion materials lead to a locally resonant structural behavior uniquely determining their properties under confinement. APA films emerge as a new platform to investigate the rich acoustic phenomena of structured composite matter.

Capacitive humidity sensor with a coplanar electrode structure based on anodised porous alumina film

A simple and new relative humidity (RH) capacitive sensor with a two-layer planar structure based on anodic aluminium oxide (AAO) film serving as a sensing layer has been fabricated. A pair of separated tantalum thin films under the AAO layer served as two coplanar electrodes. AAO film was fabricated by anodising deposited aluminium thin film in oxalic acid. The influence of the pore size and thickness of the AAO film, and the electrode spacing, on the performance of the sensor was investigated. The RH sensor with a thicker AAO film and narrower electrode spacing was more sensitive. By pore widening, the sensitivity of the sensor can be improved. The achieved average sensitivity as high as ∼3.57 pF/RH% was obtained for sensors with an AAO layer of 2 µm thickness and 80 nm pore size. These results were explained using the partial capacitance method and parallel-serial model. In addition, under the humidity range of 20–80%, sensors with 70 nm pores had the highest sensitivity, which was interpreted in terms of effective permittivity and anion concentration. This study provides an easy method to fabricate high-performance humidity sensors with very simple structures for practical applications.

Stable Lipid Bilayers Based on Micro- and Nano-Fabrication as a Platform for Recording Ion-Channel Activities

In this review, we will discuss our recent approaches for the formation of mechanically stable bilayer lipid membranes (BLMs) by combining with BLM formation and micro- and nano-fabrication techniques. BLMs were prepared across a microaperture fabricated in silicon (Si) chips or nanoporous alumina films using a minimized amount of organic solvent. Although BLMs spanned over the porous alumina film showed better electrical properties, such as background current noise and current transient, BLMs suspended in a thin Si(3)N(4) septum showed a much superior BLM stability. The BLMs showed tolerance to a high voltage of ±1 V, a membrane lifetime of >40 h, and tolerance to repetitive solution exchanges. Application to a drug screening system has been examined by using the human ether-a-go-go-related gene (hERG) potassium channel as an illustrative example. The potentiality of the present system as a platform of the high-throughput analysis for ion-channel protein is also discussed.

Deposition of Polyelectrolyte Multilayer Film on a Nanoporous Alumina Membrane for Stable Label-Free Optical Biosensing

The stabilization of inorganic nanostructures is a key challenge in developing label-free optical biosensors using inorganic nanoporous films. In the present study, a polyelectrolyte multilayer film (PMF) composed of poly(acrylic acid) and poly(allylamine hydrochloride) was deposited on porous anodic alumina (PAA) film (pore diameter = 40 nm) by the layer-by-layer technique. The characteristics of the PMF as a protective coating layer against dissolution of the PAA film were examined by means of in situ optical waveguide spectroscopy (OWS), ex situ scanning electron microscope/energy-dispersive spectroscopy (SEM/EDS), and infrared reflection–adsorption spectroscopy (IR-RAS). The results obtained by OWS and SEM/EDS indicated the formation of PMF at both the alumina pore surface and the PAA film surfaces. Processing the PMF-deposited PAA (PMF–PAA) film at 180 °C to promote thermal cross-linking allowed PMF to act as a strong protective coating layer in aqueous buffer solutions (pH 2.5–8.7) but also in common alumina matrix etchant. Residual amino groups in the cross-linked PMF could also be used to conjugate single-probe DNA at the PMF–PAA film for OWS-based DNA–DNA hybridization assay. From the results obtained in this study, it was concluded that the deposition of PMF followed by thermal cross-linking is potentially useful not only as a protective coating and but also for immobilizing biorecognition elements in the PAA film.

Ultrathin highly porous alumina films prepared by alucone ABC molecular layer deposition (MLD)

Highly structured porous alumina thin films have many practical uses, including membrane applications and catalyst encapsulation. One route to synthesizing these films that offers exceptional control over film thickness to several angstroms starts with the molecular layer deposition (MLD) of an aluminum alkoxide (alucone) film. Oxidizing the alucone film removes the organic component and produces the desired nanoporous alumina. The pore size can be controlled by selection of the length of the carbon chain in the polymer film. In this study, 500nm silica nanoparticles were coated with 10–40cycles of alucone using a three-step ABC MLD process. Trimethylaluminum, ethanolamine, and maleic anhydride were used as precursors. The organic component of the alucone films was removed in air by calcination at elevated temperature or in water at room temperature. It is shown that the pore size of the porous films can be increased from 0.6 to 0.8nm by depositing an alucone film having longer carbon chains. Film surface area, composition, thickness, and pore size were measured, confirming that the ABC MLD process can produce high quality porous alumina films and provide a pathway to tune nanopore size in these films.

Influence of the humidity on dielectric characteristics of porous aluminum oxide with inclusions of triglycine sulfate

The temperature dependences of the capacitance and conductance measured for samples of porous aluminum oxide films with inclusions of triglycine sulfate have been investigated. The character of these dependences obtained for the films treated in a humid atmosphere differs from that of the corresponding dependences measured for the initial porous Al2O3 matrix, bulk triglycine sulfate, and dried Al2O3 + triglycine sulfate composite. The observed changes are determined by the influence of the water adsorbed on the surface of the film and the water structured in pores of the composite.

Effect of solvent on the structural features and the degree of ordering of pore arrays in porous anodic alumina

Porous anodic alumina (PAA) films are usually fabricated in aqueous solutions. In this work, ethylene glycol (EG) as an organic solvent, is chosen to replace the conventional aqueous media. The anodization behaviors of aluminum in the EG solutions and the nanostructural characteristics of the as-fabricated PAA films were reported. In phosphoric and oxalic acid EG solutions, the ordered PAA films can be formed at room temperature by conventional low-field anodization. A fracture mode through the cell boundaries was found for the PAA films fabricated in the oxalic acid EG solution. These findings demonstrate that the solvents employed play a key role in the formation and self-ordering of PAA. Based on a model of field-induced plastic flow, a reasonable explanation of the experimental phenomena is proposed. The present results shed a new light on the formation mechanisms of PAA. The change of solvent also offers a novel tunability of morphology and cell size of PAA templates.

Microstructural and Optical Properties of Porous Alumina Elaborated on Glass Substrate

A transparent porous anodized aluminum oxide (AAO) nanostructure was formed on a glass substrate using the anodization of a highly pure evaporated aluminum layer. A parametric study was carried out in order to achieve a fine control of the microstructural and optical properties of the elaborated films. The microstructural and surface morphologies of the porous alumina films were characterized by x-ray diffraction and atomic force microscopy. Pore diameter, inter-pore separation, and the porous structure as a function of anodization conditions were investigated. It was then found that the pores density decreases with increasing the anodization time. Regular cylindrical porous AAO films with a flat bottom structure were formed by chemical etching and anodization. A high transmittance in the 300-900 nm range is reported, indicating a fulfilled growth of the transparent sample (alumina) from the aluminum metal. The data showed typical interference oscillations as a result of the transparent characteristics of the film throughout the visible spectral range. The thickness and the optical constants (n and k) of the porous anodic alumina films, as a function of anodizing time, were obtained using spectroscopic ellipsometry in the ultravioletvisible-near infrared (UV-vis-NIR) regions.

Nanoporous α-Alumina Membrane with High Chemical Resistance Prepared by Anodizing

not Available.

Fabrication of Highly Ordered Gold Nanorods Film Using Alumina Nanopores

A simple method for fabrication of highly ordered gold nanorod film is introduced in this article. The procedure is based on thermal evaporation of gold into a porous anodic alumina film (PAA). The PPA film was fabricated by combining the hard and mild anodization. This combination effectively decreases the processing time of fabrication of highly ordered porous anodic alumina film with controlled pore diameter and length. It was found that gold nanorods configuration affected by the porous anodic alumina film structure such as pore diameter and length. Furthermore the evaporation process change the rods diameter along the nanopores via the decreasing the pore mouth during the gold deposition.

Electrochemical deposition of lead and tellurium into barrierless nanoporous anodic aluminium oxide

Electrochemical deposition of Pb and Te into barrierless nanoporous aluminium oxide films on Ti substrates was studied. Porous anodic alumina on Ti was prepared by two-step anodization in oxalic acid of Al layer sputtered on Ti. The barrier layer was eliminated by the controllable acidic treatment of anodized samples. The effectiveness of the barrier layer dissolution was studied electrochemically using lead deposition-oxidation test reaction. Electrodeposition of Te into porous anodic alumina films was found to proceed with overvoltage related both to nucleation barrier and diffusion limitation in the pores. Lead underpotential deposition on Te particles electrodeposited in anodic alumina films was considered. It is characterized by high irreversibility due to the effective chemical interaction between Te nanoparticles and lead adatoms resulting in PbTe nanoparticles formation.

Controllable synthesis of well‐aligned CuO nanotube arrays using porous alumina templates

AbstractIn order to further enhance the performance of CuO in currently existing applications, well‐aligned CuO nanotube arrays with different diameters were fabricated. During the synthesis process, porous anodic alumina films were fabricated, and then the synthesis of CuO nanotube arrays was realized by using the obtained porous anodic alumina films as templates. The morphology and structure of the obtained products has been confirmed by field‐emission scanning electron microscopy, transmission electron microscopy and X‐ray diffraction measurements. Due to the large surface area of the synthesized products, the prepared CuO nanotube arrays may have potential applications in catalyzing and gas sensing area.

Inhomogeneous nanostructured honeycomb optical media for enhanced cathodo- and under-x-ray luminescence

Photo-, radio-, and pulse cathodoluminescence spectra from sol-gel derived titania, doped with strontium and terbium, deposited on porous anodic alumina (PAA) films are reported. The morphology and qualitative elemental depth distributions have been examined by transmission electron microscopy, scanning electron microscopy, and radio-frequency glow discharge optical emission spectroscopy. PAA films with pore and cell sizes ranging from 170 to 190 and 240 to 270 nm, respectively, have been generated on aluminum and monocrystalline silicon substrates followed by spin-on sol-gel derived coating with the subsequent thermal treatment. The resultant PAA surface is not coated with a continuous xerogel film; the xerogel is mainly distributed near the pore bases, leaving much of the pore volume unfilled. The xerogel/PAA structures reveal terbium-related luminescence under x-ray excitation and cathodoluminescence. The same xerogels generated on monocrystalline silicon revealed no cathode- or under-x-ray luminescence. Thus, PAA enhances strongly the cathode- and under x-ray luminescence from terbium and strontium-doped titania xerogels confined in the porous matrix. The fabricated structures are considered as a type of low-cost, thin-film convertor of x-rays, and cathode ray irradiation into visible light, with an average cell size of the convertor of about 250 nm.

Energy transfer in porous anodic alumina/rhodamine 110 nanocomposites

We have used porous anodic alumina (PAA) films as templates for embedding rhodamine 110 (Rh110) molecules and examined their photoluminescence (PL) properties in detail. The analysis of the polarization memory (PM) of PL strongly suggests that there is a significant energy transfer from PAA to Rh110 molecules. The effect of annealing the PAA layer on the PL properties of the nanocomposite has been studied. The results show that the energy transfer becomes more efficient in annealed PAA.

Preparation of calcium chloride-anodized aluminum composite for water vapor sorption

In the present study, we propose a novel solid sorbent, which is composed of anodized aluminum and calcium chloride, for water sorption chillers and heat pumps. Aluminum is electrolyzed in acid baths with the result that a thin and porous aluminum oxide film is formed on its surface. The anodic alumina films prepared using an electrolytic bath of sulfuric acid have an average thickness from 8 to 100 μm and mean pore diameter from 6 to 22 nm. The physical properties of anodized aluminum can be controlled by electrolytic conditions such as current density, processing time and temperature. A calcium chloride-anodized aluminum composite sorbent has been prepared by a solution impregnating method. The amount of calcium chloride impregnated on the alumina films reaches up to 16.1 wt%, and the deposition of calcium chloride in the alumina layer has been confirmed by X-ray analysis. The experimental results shows that bare anodized aluminum adsorbs very little water vapor, but the prepared calcium chloride-anodized aluminum composite is active against water vapor even in the low pressure range. Hence, this composite is a promising sorbent for adsorption chillers and heat pumps using water as working fluid.

Mechanism of aluminium and oxygen ions transport in the barrier layer of porous anodic alumina films

Aluminium was anodised in oxalic acid electrolyte at concentrations 0.125–0.5 M, current densities 25–100 A m−2 and low temperatures 0 and 5 °C. The efficiencies of Al consumption and oxide production in the metal|oxide interface and the transport numbers of Al3+ and O2− in the barrier layer of porous anodic alumina films were determined. The Al consumption efficiency essentially coincides with that by Faraday’s law while that of oxygen evolution, visually detected at these temperatures, is negligible. The oxide production efficiency and O2− transport number decrease with temperature, increase with current density and are almost independent of electrolyte concentration. The transport numbers combined with literature ones for oxalate and sulphuric acid electrolytes were treated by high field kinetic equations describing independent Al3+ and O2− transport to penetrate its mechanism. The half jump activation distances were found comparable to ions radii. This mechanism embraces two steps, equilibrium established between ordinary oxide lattice hardly allowing transport and locally emerging transformed structure dispersed in barrier layer consisting of pairs of Al3+ and O2− clusters enabling transport and the rate-controlling step of actual ion transport within clusters. The transformed structure then returns to ordinary while it emerges at other sites. The real activation energy of Al3+ transport is higher than that of O2−, e.g. by ≈ 19 kJ mol−1 at low current densities, but the fraction of really mobile Al3+ is ≈ 103–104 times larger than that of O2− justifying the not excessively different values of O2− and Al3+ transport numbers.