Nanoporous Alumina Films Research Articles

铝表面形貌对纳米孔氧化铝膜生长的影响

铝表面形貌对纳米孔氧化铝膜生长的影响

X-ray study of anisotropically shaped metal halide perovskite nanoparticles in tubular pores

Recently, we have reported that metal halide perovskite nanoparticles formed in nanoporous alumina and silicon thin films exhibit blue shifted photoluminescence due to spatial confinement, thus allowing for color tuning of the emission by varying the pore size. While perovskite nanoparticles grown in nanoporous alumina films have been integrated into LEDs, similar approaches have failed with silicon. Here, we report the results of investigating the structure of the alumina pore system and the perovskite crystallites forming within. We use two x-ray diffraction techniques, namely, small-angle x-ray scattering (SAXS) and high-energy microbeam wide-angle x-ray scattering (WAXS). SAXS reveals that the alumina pore system diffracts like regularly arranged tubes with the average diameter and nearest neighbor distance of 12 nm and 20 nm, respectively. High-energy microbeam WAXS shows that perovskite nanoparticles within the nanoporous alumina have a distinctly anisotropic shape with the average particle length along and perpendicular to the pore axis of 26 nm and 13 nm, respectively. In contrast, no shape anisotropy has been detected for nanoparticles inside the silicon pores in a previous study. This suggests that utilizing nanoporous alumina has a twofold advantage. First, the tubular alumina pores, spanning the entire insulating film, offer percolated paths for the perovskite to fill. Second, the elongation of the nanoparticles in the tubular alumina pores can be expected to aid device performance as the length of the nanoparticles approaches the active layer thickness (ca. 40 nm) of LEDs, while the small diameter of the crystallites accounts for the observed blue shifted emission.

Evaluation of Optical Anisotropy of Nanoporous Alumina Films by Stokes-Polarimetry and Matrix Coherence Methods

The effect of amplitude anisotropy of nanoporous alumina films and depolarization of the transmitted radiation on the phase shift between orthogonally polarized components of the transmitted radiation was studied using Stokes-polarimetry and matrix coherence methods. The test samples were illuminated by linearly polarized radiation with the polarization azimuth of 45° in the wavelength range from 400 to 1000 nm. The systematic error introduced into the phase shift between the orthogonally polarized components of the transmitted radiation as a result of neglecting the material amplitude anisotropy and the depolarization of the transmitted radiation was established.

Metallized nanoporous anodic alumina films and their applications

The optimal conditions of the aluminum electrochemical anodization and electrochemical and chemical metallization were determined. Metallized nanoporous anodic alumina (NAA) films with ultrahigh/average/low density of pores were obtained using the optimal conditions. The physical and chemical properties of the obtained NAA films were studied by high-resolution scanning electron microscopy and the reflective interference spectra in a wavelength range of 235–735 nm. Possible applications of the obtained NAA films are in micro/nanoscale lasers with indirect electrical pumping by laser diodes; optical interferometric chemical nanosensors; and the selective interference coloration and protection of the metal surface.

IR Scattering by Optically Inhomogeneous Nanoporous Anodic Alumina Films

This paper presents results of thermographic studies of nanoporous alumina films having different geometric parameters of their porous layer (thickness and average pore diameter), which were exposed to thermal radiation. The films have been shown to shield thermal radiation. The present results suggest that nanoporous alumina membranes can be used as heat shields for reducing the thermal contrast of an object and the surrounding background in the IR spectral region.

Generation of laser radiation by nanostructured solid active elements with selective optical nanoresonators formed in nanoporous aluminum oxide films

Generation of laser radiation by nanostructured solid active elements with selective optical nanoresonators formed in nanoporous aluminum oxide films

Anodization of Au thin film on Al in oxalic acid

An Au thin film, which was sputter-deposited on an Al substrate, was potentiostatically anodized in oxalic acid. The Au film was first anodized and a spongelike nanoporous film grew down to the interface between Au and Al. Then, the Al was anodized and a very thin and fine nanoporous alumina film was formed underneath the nanoporous Au. Under the same anodization conditions, the current density for Al was ~40μAcm−2, less than 1% of that for Au (~30mAcm−2). The growth rates of the nanoporous films were ~0.7nm/min for Al and 26nm/min for Au, indicating that the growth rate of nanoporous alumina was less than 3% of that of nanoporous Au. Al is suitable as the substrate for preparing nanoporous Au films because the electrochemical reactions of both the electrolyte and the substrate are significantly suppressed when the nanopores penetrate Au and the electrolyte reaches the substrate.

Flexural Properties and Fracture Behavior of Nanoporous Alumina film by Three-Point Bending Test.

This study investigated the influence of porosity on the flexural property of a nanoporous alumina film. When the porosity of the alumina film increased, both bending strength and modulus declined. The results from the bending test revealed that the setting of the film during the bending test had significant influence on the flexural property. Fracture only occurred when the porous side of the alumina film suffered tensile stress. The ability to resist fracture in the barrier layer was higher than in the porous side; the magnitude of the bending strength was amplified when the barrier layer sustained tensile stress. When the porous layer suffered a tensile stress, the bending strength decreased from 182.4 MPa to 47.7 Mpa as the porosity increased from 22.7% to 51.7%; meanwhile, the modulus reduced from 82.7 GPa to 17.9 GPa. In this study, the most important finding from fractographic analysis suggested that there were a localized plastic deformations and layered ruptures at the porous side of the alumina film when a load was applied. The fracture behavior of the nanoporous alumina film observed in the present work was notably different from general ceramic materials and might be related to its asymmetric nanostructure.

Corrosion Behavior of Aluminum Oxide Film Growth by Controlled Anodic Oxidation

Due to the light weight and good corrosion resistance, nowadays aluminum and its alloys are used in different industries in order to decrease the maintenance costs and also to increase the equipments lifetime cycle. When aluminum and its alloys are exposed to the extreme environments, the native aluminum oxide film lose the anticorrosive properties that lead to the damage of equipments and increasing the costs. In order to improve the anticorrosive and mechanical performances of aluminum and its alloys, different techniques are used: organic coatings, the growth of a thick aluminum oxide film through different methods, etc. The most used method for aluminum oxide growth is anodic oxidation. Anodic oxidation is an electrochemical method that allows to growth an aluminum oxide film with controllable characteristics. The aim of present paper was to growth on 1050 aluminum alloy surface nanoporous aluminum oxide films with improved anticorrosive properties. The obtained nanoporous aluminum oxide films were characterized morphological and structural by scanning electron microscopy coupled with X-ray energy dispersive analyzer. The anticorrosive properties were evaluated by electrochemical methods such as: open circuit potential, electrochemical impedance spectroscopy and cyclic voltammetry. The results showed that anodic oxidation treatment improve the anticorrosive performances of 1050 aluminum alloy.

Generation of laser radiation by nanostructured solid active elements based on nanoporous aluminum oxide films activated with rhodamine 6G

The generation of laser radiation by a solid active element based on a nanoporous aluminum oxide film activated with rhodamine 6G has been obtained for the first time in the geometry to reflection. The lasing is characterized by high-quality radiation with the absence of a spontaneous component. It is found that the application of silicone oil as the immersion substance reduces the generation threshold more than two times. The optimal concentration of rhodamine 6G molecules in the impregnation solution for mirror films of nanoporous aluminum oxide is determined, at which the dye fluorescence intensity has the maximum value. The generation by a nanoporous aluminum oxide film activated with rhodamine 6G in the continuous mode has been obtained for the first time.

Surface characterization of nanoporous aluminium oxide films synthesized by single-step DC and AC anodization

Nanoporous alumina films were synthesized on commercial grade aluminum substrates using single-step anodization technique in 0.3M phosphoric acid at room temperature. Effect of applied voltage (100–130V) on surface characteristics of anodized aluminum oxide (AAO) film was investigated. Surface topography parameters and regularity ratio of nanopores arrangement were characterized using power spectral density (PSD) and fast Fourier transform (FFT) profiles. While DC anodization suffered from filament-like cavities at 130V owing to thermally enhanced dissolution of oxide, AC anodization produced localized flower-like morphology for all the applied voltages. The intensity of localized flower-like morphology was increased monotonically with applied voltage. Evolution of flower-like morphology was discussed on the basis of Pashchanka-Schneider model.

Wetting characteristic of nanoporous aluminum oxide films

Nanoporous aluminium oxide film template has been widely used over the last decade for development of numerous functional nanostructures such as nano sensors and nanophotonic devices. In this study, the nanoporous aluminum oxide film on silicon substrates were prepared from a 500 nm-thick aluminum film by low-temperature anodization process in a mixed solution of phosphoric and oxalic acids at different anodization voltage (10-50 Voltage). The morphology and wettability of nonporous aluminum oxide films were investigated by field emission scanning electron microscope and contact angle measurement, respectively. The result shown that the interpore of AAO template increase with anodization voltage increases. In addition, the wettability of the template depends on the pore size on the film surface.

Surface Plasmon-Polaritons and Transverse Spin Angular Momentum at the Boundary of Hyperbolic Metamaterials

Conditions for the existence of localized surface waves (plasmon-polaritons) at the boundary of hyperbolic metamaterials are found for the case when the optical axis is perpendicular to the boundary. It is shown that a surface wave localized at the boundary between an isotropic dielectric and a hyperbolic type II metamaterial has a transverse spin which can be controlled by varying the wavelength of the exciting radiation. The results obtained here are illustrated with the example of a hyperbolic metamaterial based on a nanoporous aluminum oxide film with pores filled with silver.

Characteristic Resonance Reflection Spectra of Nanoporous Alumina Films and Its Application to Precise Thickness Measurement

In this article, we investigate the thicknesses effect on the characteristic resonance reflection spectra of nanoporous anodic aluminum oxide (AAO) films and its potential application to nondestructive precise thickness measurement. The resonance spectrum of AAO was linked to the film thickness and pore diameter. Different thicknesses of AAO were prepared by changing anodization time. As a result, the amplitude of reflection peaks reduced at short wavelength and decreased with increasing thickness over a wavelength of 350∼850 nm. The pore diameter was also enlarged by pore widening to examine the evolution of reflection spectra. The relationship between the reflection peak and thickness was identified through equal inclination interference formula and potentially used for the nondestructive inspection of film thickness. The thickness of AAO films measured by the low-cost UV-vis reflection spectrophotometer was in a wide range from sub-μm to about 7 μm compared to that less than 1.3 μm by a complex and expensive ellipsometric method. The accuracy of thickness measured by resonance spectrum method was about 1.0 ± 0.4% uncertainty that was verified by scanning electron microscope measurement.

Investigation of roughness and specular quality of commercial aluminum (6061 alloy) for fabrication of nanoporous anodic alumina films

Nanoporous anodic alumina (NAA), obtained via aluminum anodization, have been used as template for fabrication of nanostructure materials and photonic devices. In order to promote the formation of regular porous and to control the desired properties, high-purity aluminum and pretreatment of Al surfaces are mandatory. This procedure consists in electrochemically removing the external irregular layer of the metal promoting a flat, bright and smooth metallic surface. In this study, the effect of electropolishing parameters on commercial aluminum samples (6061 alloy, 97%) was investigated. This procedure was performed at constant potential in a mixture of perchloric acid and ethyl alcohol solution in different experimental conditions. A factorial design was used to investigate the effect of applied potential, electropolishing time and electrolyte temperature on roughness and specularity of Al substrates. These samples were characterized by Atomic Force Microscopy (AFM) and Diffuse Reflectance Spectroscopy (DRS). All variables presented significant effects on roughness of Al substrates, although electropolishing time presented the most important effect on specularity of these samples. After galvanostatic anodization in oxalic acid solution, the results showed the influence of Al surface roughness on morphology of NAA films. Since all Al samples were anodized under same conditions, the differences observed in micrographs of NAA films were related to roughness of Al substrates, which was affected by electropolishing parameters, mainly the applied potential and electropolishing time.

Self-Ordering Regimes of Porous Anodic Alumina Layers Formed in Highly Diluted Sulfuric Acid Electrolytes

Nanoporous anodic alumina films with long-range hexagonal order have been obtained from a series of highly diluted sulfuric acid electrolytes. A simple linear relationship was established between the self-ordering voltages and acid concentrations (28, 29, and 30 V for 0.2, 0.1, and 0.05 M electrolytes, respectively). Besides establishing new self-ordering regimes, our experimental work sheds new light on some fundamental principles of honeycomb anodic alumina formation. It suggests that the spontaneous self-organization of a stable nanoscale structure originates from the electrohydrodynamic (EHD) convection rather than from Marangoni-type instability at the anode surface. Theoretical analysis displays a decreasing exponential functional relationship between electrolyte concentration and the critical values of the earlier found electrochemical analogue of Rayleigh number, which can be used for prediction of hexagonal cell pattern in currently unexplored anodizing electrolytes.

Effect of continuous magnetic field on the growth mechanism of nanoporous anodic alumina films on different substrates

The effects induced by an external homogeneous magnetic field on the oxide film growth on aluminum in aqueous solutions of oxalic and sulfuric acid and on surface morphology of the alumina films were studied. Aluminum films of 100 nm thickness were prepared by thermal evaporation on SiO2/Si and glass-ceramic substrates. The pore diameter for oxalic acid alumina films on the SiO2/Si substrate decreased by 0.8 nm, the interpore distance by 5.9 nm, and cell diameter by 6.9 nm if a magnetic field of 0.5 T was applied. When aluminum was anodized in sulfuric acid on the same substrate, the significant changes in parameters of porous structure of alumina, which were similar to the ones in oxalic acid, are firstly observed in stronger magnetic fields (of 0.7 T). On the basis of data obtained in this study and of previous investigation on the negative space charge and thermally activated defects in anodic alumina, we concluded that the intensity of the magnetic field is associated with energy of electron traps and that the changes of cell diameter characterize the trap concentration. The energy of electron traps in oxalic acid alumina films was proved to be smaller than the one in films formed in sulfuric acid, but the concentration of traps was of the same order of magnitude. When the substrate was replaced with the glass-ceramic one, the pore diameter in oxalic acid alumina films increased to ca. 17.6 nm.

Enhanced Reflective Interference Spectra of Nanoporous Anodic Alumina Films by Double Electrochemical Deposition of Chemical Metal Nanoparticles

The effect of selective color reflection enhancement from a double metalized nanoporous anodic alumina (NAA) film surface under proper conditions of electrochemical and chemical metal (Cu—Ag, Cu—Au) deposition has been observed. Selective coloration of the NAA films with high index of the reflection and wide range of the color tones was achieved. The additional chemical deposition of the noble metal leads to the enhancement of the selective reflection ability and the interference contrast of the reflected light. The distribution of the chemically deposited silver nanoparticles on the top surface of electrochemically copper metalized pores of anodized aluminum has been shown by the electron microscopy method. The optical reflection spectra at different angles (10°-85°) of metalized NAA film have been measured, and the effective index of refraction (n ≈ 1.6) and film thickness have been calculated. The effect of the reflected light interference contrast enhancement has been explained as being a result of the more effective separation of the two reflecting surfaces air/Al2O3 in the structure of the film similar to a Fabry-Perot interferometer.

The effect of anodization temperature on optical properties of nanoporous anodic alumina (NAA) films

Nanoporous anodic alumina (NAA), produced by aluminum anodization presents interesting optical effects in luminescence property exhibiting waveguides or Fabry–Pérot interference. This phenomenon, which is used as transducer response in optical sensors, depends on morphological characteristics of the NAA films, such as pore diameter, inter-pore distance and film thickness. In this work, the effect of electrolyte temperature on NAA morphology was investigated and, consequently, how this effect shaped the interference property. For this, all anodizing experimental conditions were kept constant while the electrolyte temperature was changed (5, 10, 15, 20 and 25°C). It was observed an increase in the minimum and stationary current density values during anodization as the electrolyte temperature increased, which were correlated to enlargement of porous oxide layer, since pore diameter, inter-pores distance and porosity remained constant for all studied temperatures. The photoluminescence (PL) spectra showed an increase in the number of fringes and an amplitude decrease with the increase of electrolyte temperature. NAA film thickness was evaluated using optical and morphological parameters and compared to values in the literature. A brief discussion of the results regarding the ratio of film thickness and pore diameter (L/dp) was performed to validate the NAA films with better waveguides property to be used as a platform for optical sensing applications.

Facile Fabrication of Ordered Multi-Tiered Hierarchical Porous Alumina Nanostructures with Multiple and Fractional Ratios of Pore Interval toward Multifunctional Nanomaterials

Conventional nanoporous anodic alumina films are composed of one-tiered pore arrays that can only render to one-dimensional (1D) nano-structures if they are used as nano-templates. Hence, three-dimensional (3D) nanoporous alumina films are desirable to dramatically increase the variety of nanostructures by template-fabrication for various potentially enhanced performances. Herein we report a facile approach to fabricate a variety of ordered multi-tiered 3D porous alumina nanostructures with multiple integer (m = 2, 3, 4, 5, 7, 9, and 10) and fractional ratios (n = 1/2 and 1/3) of the pore interval and pore diameter among different tiers on ITO/glass and Al sheets. The multi-tiered nanostructures and the pore interval ratios of the neighboring tiers can be accurately and independently controlled by a tailored multiple stepwise anodization, successively in appropriate acidic electrolytes of sulfuric, oxalic, and/or phosphoric solutions at designed voltages of 15–180 V, corresponding to the multiple or fractional ratios of pore interspacing. Moreover, the multi-tiered hierarchical nanoporous alumina films on ITO/glass substrates exhibited a lower transmittance compared with that of the single-tiered films with ordered cylindrical pores, which can be attributed to the diffusive reflection from the tier interface with different pore intervals.