Anodic porous alumina, –AAO– (also known as nanoporous alumina, nanohole alumina arrays, –NAA– or nanoporous anodized alumina platforms, –NAAP–) has opened new opportunities in a wide range of fields, and is used as an advanced photonic structure for applications in structural coloration and advanced optical biosensing based on the ordered nanoporous structure obtained and as a template to grow nanowires or nanotubes of different materials giving rise to metamaterials with tailored properties. Therefore, understanding the structure of nanoporous anodic alumina templates and knowing how they are fabricated provide a tool for the further design of structures based on them, such as 3D nanoporous structures developed recently. In this work, we review the latest developments related to nanoporous alumina, which is currently a very active field, to provide a solid and thorough reference for all interested experts, both in academia and industry, on these nanostructured and highly useful structures. We present an overview of theories on the formation of pores and self-ordering in alumina, paying special attention to those presented in recent years, and different nanostructures that have been developed recently. Therefore, a wide variety of architectures, ranging from ordered nanoporous structures to diameter changing pores, branched pores, and 3D nanostructures will be discussed. Next, some of the most relevant results using different nanostructured morphologies as templates for the growth of different materials with novel properties and reduced dimensionality in magnetism, thermoelectricity, etc. will be summarised, showing how these structures have influenced the state of the art in a wide variety of fields. Finally, a review on how these anodic aluminium membranes are used as platforms for different applications combined with optical techniques, together with principles behind these applications will be presented, in addition to a hint on the future applications of these versatile nanomaterials. In summary, this review is focused on the most recent developments, without neglecting the basis and older studies that have led the way to these findings. Thus, it gives an updated state-of-the-art review that should be useful not only for experts in the field, but also for non-specialists, helping them to gain a broad understanding of the importance of anodic porous alumina, and most probably, endow them with new ideas for its use in fields of interest or even developing the anodization technique.

/pdf/revisiting-anodic-alumina-templates-from-fabrication-to-2fqw97iqp4.pdf

Revisiting anodic alumina templates: from fabrication to applications

Magnetic behaviour of densely packed hexagonal arrays of Ni nanowires: Influence of geometric characteristics

Corrosion is a major problem for high strength aluminium alloys Thickening of the naturally formed oxide layer through anodizing is one of the main approaches to improve the corrosion resistance of these materials Chromate anodizing is extremely efficient to produce anodized layers with good corrosion resistance and painting adhesion, however chromate based surface treatments must be banished from industrial use The corrosion resistance of aluminium alloy 2524 (AA2524) anodized in tartaric/sulphuric acid (TSA) bath and protected with a hybrid sol-gel coating was evaluated by means of electrochemical impedance spectroscopy (EIS) and salt-spray tests The morphologies of the obtained layers were characterized by SEM-FEG while the chemical in depth distribution of the hybrid layers was evaluated by means of Rf-GDOES The effect of anodizing voltage on the sol-gel impregnation and the protection afforded by the layers was evaluated Electrical equivalent circuit fitting of the EIS data has shown that the anodized layer thickness plays an important role in the protection mechanism of the sol-gel layer Salt-spray tests highlighted the significant contribution of the sol-gel distribution in the anodized layer

Corrosion resistance of 2524 Al alloy anodized in tartaric-sulphuric acid at different voltages and protected with a TEOS-GPTMS hybrid sol-gel coating

Influence of electrodeposition techniques on Ni nanostructures

Two series of self-organized hexagonal arrays of uniaxial Permalloy nanowires are grown by electroplating, filling of nanopores in anodic alumina films. Nanowires with periodicities of 65 and 105nm and wire diameter of 25–60nm were investigated by magnetization and ferromagnetic resonance (FMR) measurements. The length of the wires is 2.5μm, the volume ratio 0.13⩽v⩽0.43. A crossover transition from a one-dimensional easy axis “wire” behavior of weakly interacting uniaxial nanowires to a two-dimensional behavior of strongly coupled “wire film” having an easy plane anisotropy is determined from FMR measurements. The crossover occurs at v=0.27 for 105nm periodicity, and v=0.43 for 65nm periodicity. The system of the thinnest nanowires corresponds to a statistical ensemble of weakly interacting uniaxial particles, characterized by the highest coercivity of 1276Oe, the highest switching field distribution, and highest FMR linewidth, resulting from the broad distribution of individual wires. The coercivity mono...

Interaction effects in Permalloy nanowire systems

Systematic study of magnetic nanowire arrays grown in anodic alumina membranes (AAM) has been done by means of Rutherford backscattering spectroscopy (RBS). The AAM used as templates were morphologically characterized by using high resolution scanning electron microscopy (HRSEM), fast Fourier transform (FFT) and atomic force microscopy (AFM). The highly ordered templates with a mean pore diameter size of 30 nanometers, a mean inter-pore spacing of 100 nm and lengths ranging from 4 to 180 microns were obtained through two-steps anodization process, and the Ni and Co nanowire arrays were grown by electrodeposition techniques. The main attention is addressed to Ni nanowire arrays. RBS results allowed us to determine the real depth profile of atomic composition of the obtained nanowire arrays. In addition, the RBS spectra fitting showed that the porosity increased from the top to the bottom of the samples. Two phenomenological models are proposed to understand the apparition of that secondary porosity and a linear relation between the total amount of electrodeposited Ni and the electrodeposition time was obtained. As an example, it is also reported the relation between RBS results and magnetic properties, such as coercive field and remanence/saturation magnetization ratio of the samples. Particularly, for Ni nanowires arrays obtained by using voltage pulses, it is demonstrated that the larger the nanowires, the higher the definition for easy axis parallel to the nanowire length is possible.

Magnetic nanowire arrays in anodic alumina membranes: Rutherford backscattering characterization

Self-ordering degree of anodic alumina nanopores is related to the volume expansion of the aluminum oxide. However, little is known about how the ionic species derived from electrolyte affect parameters inducing self-ordering of the nanopores. The influence of sulfur incorporation into nanoporous anodic aluminum oxide (AAO) films on volume expansion and self-ordering degree has been investigated under potentiostatic conditions (14–25 V) in different sulfuric acid electrolytes (3–20 wt %), the average current densities of each anodization being in the range of 0.1–10 mA cm–2. Rutherford backscattering spectroscopy (RBS) reveals that the incorporation of sulfur species into AAO, as well as the volume expansion factor (VEF), follows a logarithmic dependence on the average current density regardless of the applied voltage and sulfuric acid concentration. The relationship between volume expansion and the S/Al ratio is linear for each concentration of acid in the electrolyte. Furthermore, self-ordering regimes ...

/pdf/influence-of-sulfur-incorporation-into-nanoporous-anodic-2dlzfw8u6y.pdf

Influence of Sulfur Incorporation into Nanoporous Anodic Alumina on the Volume Expansion and Self-Ordering Degree

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Magnetic nanowire arrays in anodic alumina membranes: Rutherford backscattering characterization

Influence of Sulfur Incorporation into Nanoporous Anodic Alumina on the Volume Expansion and Self-Ordering Degree