Porous Anodic Aluminum Oxide Template Research Articles

Fabrication of nanomaterials using anodic aluminum oxide and their properties

A porous anodic aluminum oxide (AAO) template on the aluminum plate was formed by two-step anodization. Vertically well aligned pores had the average pore sizes of 15–70 nm and the length of approximately 40 μm. CdS nanostructure materials have been fabricated in porous anodic aluminum oxide (AAO) template by using chemical bath deposition (CBD). These nanostructure materials had uniform diameters of about 15–200 nm, which correspond to the pore sizes of the templates used, and the length was up to 40 μm. X-ray diffraction (XRD) investigation demonstrates that CdS nanostructure materials were hexagonal polycrystalline in nature. As the pore diameter of AAO templates was enlarged, the preferential orientation of c-axis was improved. From PL analysis, the sulfur-deficient defects at the surfaces of CdS nanostructure materials were increased when the sample was synthesized in the template with larger pore diameter.

Photocatalytic Activity of F<sup>-</sup>/ SiO<sub>2</sub>/TiO<sub>2</sub> Nanowires

Titania nanowire arrays were synthesized in highly ordered porous anodic alumina template by sol-gel method. The samples were characterized by means of SEM, XRD. The photocatalytic property of TiO2, SiO2/ TiO2, F-/SiO2/TiO2 nanowire arrays were studied by methyl orange degradation. The results show that F-/ SiO2/ TiO2 nanowire arrays have higher photocatalytic activities than those of TiO2 and SiO2 /TiO2. Under the condition of 1 h irradiation, the degradation ratio of methyl orange exceeds 90%. At the same time, the higher photocatalytic activity and the smaller crystal size of F-/ SiO2/ TiO2 are related to the incorporation of F-.

A Novel Method for Fabricating the Surface-Enhanced Raman Scattering Substrates and Its Enhanced Properties

We have got large area surface-enhanced Raman scattering (SERS) substrates with uniform high enhancement factors by the so-called moulage method for the first time. A silver film (99.99%) with several millimeters thickness was thermally evaporated on the porous anodic alumina templates and the SERS substrate was got after moving off the templates. Surface-enhanced Raman scattering spectra of pyridine (0.01 Mol/L) were measured under 632.8 nm excitation. The experimental enhancement factors were more than 10(5) and S/N(p-p) around 100 was obtained. We have compared the SERS spectra of pyridine collected from different locations on the same SERS substrate and different substrates, which illustrate the well uniform enhance properties and the reproducibility of this method, respectively. The comparison of the SERS spectra, obtained from the SERS substrates and Ag film evaporated directly on glass slide, have proved that the electromagnetic coupling between two adjacent nanoparticles was important to the SERS effect. We also used rhodamine 6G as the probe molecules and found that the different molecules were very sensitive to the morphology of the SERS substrates.

Electrodeposition of Ni and Ni-Cu Nanowires in Rectified Porous Anodic Alumina Membrane

Highly ordered Ni and Ni-Cu nanowires were electrodeposited into the micropores of the porous anodic alumina (PAA) template which was fabricated by the method of two-step anodizing and the thickness of barrier layer which was formed during the anodizing process was rectified by applying current limited anodization steps. The X-ray diffration (XRD) was used to characterize the Ni and Ni-Cu nanowires and the morphology of these nanowires was examined by the way of scanning electron microscopy (SEM). The SQUID magnetometry was used to investigate the magetic properties of the nanowires. It is found that the coercivity and remanence ratio of Ni-Cu nanowire is larger than that of Ni nanowire.

End-closed NiCoFe-B nanotube arrays by electroless method

A novel approach is obtained during the fabrication of NiCoFe-B nanotube arrays via electroless method. Porous anodic aluminum oxide (AAO) templates fabricated by anodization of aluminum foil were sensitized using PdCl 2 solution and immersed into electroless plating baths at room temperature to produce nanotube arrays. Compositional and morphological properties of the nanotube arrays are characterized. Results indicates the formation of end-closed nanotubes with the dimension of 100–130 nm in outside diameter, which is determined by the pore size of the AAO template, and about 15 nm in thickness of tube walls. The possible formation mechanism of end-closed metallic nanotube arrays is discussed.

Diffusion-Controlled Growth Model for Electrodeposited Cobalt Nanowires in Highly Ordered Aluminum Oxide Membrane

This work studies the electrochemical growth behavior of cobalt nanowires in highly ordered aluminum oxide membrane. Considering the electrodeposition of metallic nanowires, cation concentration profile in each nano pore was calculated. With assumption of linear diffusion zone on the growing surface of nanowires, a modified Cottrell equation was evaluated. To confirm the model, the Co nanowires were electrodeposited into porous anodic aluminum oxide (AAO) templates and the mechanism of deposition was studied. Comparing the results of model and the experiments has proved the accuracy of the model. Also, it was observed that the growth of the Co nanowires was controlled mainly by diffusion process. With these considerations, the diffusion coefficient of the Co2+ cation in pore was determined about D = 2.14×10-5 cm2.s-1. SEM and TEM analysis showed high density and uniform nanowires that retained the shape of pores.

Porous anodic alumina membranes formed by anodization of AA1050 alloy as templates for fabrication of metallic nanowire arrays

The through-hole porous anodic aluminum oxide (AAO) membranes were fabricated by a two-step anodization of the aluminum alloy (AA1050) in 0.3M oxalic acid at 45V and 20°C followed by removal of Al and pore opening/widening procedures. The effect of duration of the second anodizing step on the porous oxide layer thickness and the influence of the pore opening time on structural features of as-prepared membranes were studied in detail. The prepared membranes with a thickness of about 60μm were used as templates for fabrication of dense arrays of Ag, Au, and Sn nanowires with various aspect ratios by a DC electrochemical deposition process. The successful synthesis of metallic nanowires by simple DC electrodeposition of metals inside the pores of AAO templates fabricated from the AA1050 alloy was reported for the first time. The fabrication costs of nanowire arrays can be reduced by about 500 times when AAO templates, prepared from the AA1050 alloy, are used instead of those usually formed from expensive high purity Al.

A study on the formation of titania nanopillars during porous anodic alumina through-mask anodization of Ti substrates

The formation of anodic titania during porous anodic alumina (PAA) through-mask anodization has been analysed for varying anodization conditions on mechanically polished bulk Ti surfaces. Titania nanopillars were formed through the porous masks in both oxalic and phosphoric acid electrolytes. For applied potentials above 40 V the titania formed along narrow channels through the alumina pore bottoms resulting in root-like attachments of the titania pillars to the Ti substrate. We further demonstrated that high-field anodization can be used for PAA through-mask anodization. The formation of titania changed with increased current density which resulted in more efficient oxide growth through the alumina pores. When the Al/Ti samples were immersed in the electrolyte without exclusively exposing the Al surface to the electrolyte the titania formed solely on top of the alumina pore bottoms which resulted in that the titania structures were detached from the Ti substrates during selective removal of the PAA templates.

Tuning the Composition and Nanostructure of Pt/Ir Films via Anodized Aluminum Oxide Templated Atomic Layer Deposition

AbstractNanostructured metal films have been widely studied for their roles in sensing, catalysis, and energy storage. In this work, the synthesis of compositionally controlled and nanostructured Pt/Ir films by atomic layer deposition (ALD) into porous anodized aluminum oxide templates is demonstrated. Templated ALD provides advantages over alternative synthesis techniques, including improved film uniformity and conformality as well as atomic‐scale control over morphology and composition. Nanostructured Pt ALD films are demonstrated with morphological control provided by the Pt precursor exposure time and the number of ALD cycles. With these approaches, Pt films with enhanced surface areas, as characterized by roughness factors as large as 310, are reproducibly synthesized. Additionally, nanostructured PtIr alloy films of controlled composition and morphology are demonstrated by templated ALD, with compositions varying systematically from pure Pt to pure Ir. Lastly, the application of nanostructured Pt films to electrochemical sensing applications is demonstrated by the non‐enzymatic sensing of glucose.

Tuning the Composition and Nanostructure of Pt/Ir Films via Anodized Aluminum Oxide Templated Atomic Layer Deposition

AbstractNanostructured metal films have been widely studied for their roles in sensing, catalysis, and energy storage. In this work, the synthesis of compositionally controlled and nanostructured Pt/Ir films by atomic layer deposition (ALD) into porous anodized aluminum oxide templates is demonstrated. Templated ALD provides advantages over alternative synthesis techniques, including improved film uniformity and conformality as well as atomic‐scale control over morphology and composition. Nanostructured Pt ALD films are demonstrated with morphological control provided by the Pt precursor exposure time and the number of ALD cycles. With these approaches, Pt films with enhanced surface areas, as characterized by roughness factors as large as 310, are reproducibly synthesized. Additionally, nanostructured PtIr alloy films of controlled composition and morphology are demonstrated by templated ALD, with compositions varying systematically from pure Pt to pure Ir. Lastly, the application of nanostructured Pt films to electrochemical sensing applications is demonstrated by the non‐enzymatic sensing of glucose.

Synthesis and properties of delafossite CuAlO2 nanowires

Ultra-long and uniform CuAlO2 nanowires were successfully synthesized within a porous anodic aluminum oxide template by means of sol–gel method at 900 °C. The results of X-Ray diffraction indicate that the obtained CuAlO2 nanowires have a single delafossite structure. The scanning electron microscopy and transmission electron microscopy show that the CuAlO2 nanowires have a uniform diameter with about 50 nm and a length up to 10 μm. Room-temperature photoluminescence measurement of nanowires exhibits an ultraviolet near-band-edge emission around 350 nm (3.54 eV).

Synthesis of AuNi/NiO Nanocables by Porous AAO Template Assisted Galvanic Deposition and Subsequent Oxidation

AbstractA facile and economic approach has been developed for the synthesis of coaxial nanocables with AuNi alloy nanowires as inner solid cores and NiO as outer shells by infiltrating a gold‐coated anodic aluminum oxide (AAO) template, with ring‐shaped Al foil on its outer edge, with a mixed aqueous solution of NiCl2 and HAuCl4 to form AuNi/Ni nanocables, and subsequent immersion in an aqueous NaOH solution to oxidize the Ni sheath during template removal. The formation of the AuNi/Ni nanocables in the channels of the AAO template could be ascribed to the reduction of the Ni2+ ion complexes adhering on the AAO channel walls and the redox reactions of two galvanic cells in which the surrounding Al foil acts as the anode. The approach enables excellent control over the shell thickness and the chemical composition of the AuNi/NiO nanocable by tuning the composition of the mixed solution. The AuNi/NiO nanocables have potentials in nanodevices and nanosystems.

Oriented cube-on-cube nanocrystal assembly ofSrTiO3 tubules

We report on an unusual crystallization phenomenon thatresults in the self-assembly of sub-micron tubules of crystallineSrTiO3. The deposition of the tubular structures was done in the pores ofanodized aluminum oxide templates by the electrophoretic deposition ofSrTiO3 sols and subsequent annealing. Homogeneous nucleation inside the pores produces a criticalnumber of crystallites leading to their self-organization when the nanocrystals reach sizesthat equal the mean free distances between the nuclei. Due to steric constraints the crystalsstart to organize in order to most efficiently fill the available surface of the pore walls. Thisprocess leads to the formation of domains containing a large number of idiomorphicSrTiO3 nano-cubes that are self-aligned into almost perfect cube-on-cube and cube-to-wall registry,which makes up the walls of the tubules. The described mechanism shows the ability ofnanocrystals with well defined morphologies to adapt spatial constraints and self-organizeinto desired geometries.

Fabrication and Optical Properties of Mesoporous SnO2 Nanowire Arrays

Large-scale SnO2 mesoporous nanowires have been successfully synthesized by an improved sol-gel method within the nanochannels of porous anodic alumina templates. In this method, chloride of stannic and urea are used as precursors, chloride of stannic is acting as source of tin ions, and urea offers a basic medium through its hydrolysis. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and selected-area electron diffraction are used to characterize the SnO2 mesoporous nanowires. It is found that the as-prepared nanowires consist of SnO2 nanoparticles and pores. They can be indexed as rutile structures and diameters are about 50-70 nm. The growth mechanism of the mesoporous nanowires is also been discussed. The band gap of the as-prepared mesoporous nanowires is 3.735 eV, determined by UV/visible absorption spectral results. The SnO2 mesoporous nanowires show strong and stable photoluminescence with emission peak centered at 3.730 eV, which has never been reported in nanowires. It could be attributed to the exciton recombination.

High-Sensitivity and Stable Cellular Fluorescence Imaging by Patterned Silver Nanocap Arrays

Patterned silver nanocap arrays (PSNAs) prepared on porous anodic alumina templates by a simple coating technique yield enhanced sensitivity and stability in cellular fluorescence imaging. Microstructural analysis, surface-enhanced Raman scattering mapping, and finite difference time domain simulation indicate that the hot spots are evenly distributed on the substrate. Ag1522 or Chinese Hamster Ovary cells are labeled by phalloidin-fluorscein isothiocyanate (P-FITC) on the cytoskeletons and the fluorescence signals from the fluorophores bound on the cell cytoskeletons on the PSNAs are enhanced 8-fold compared to those on glass used in conventional imaging. In addition to the intensity enhancement, the photostability is improved dramatically. Spectral analysis suggests that the PSNAs can create more excitons in the light-emitting P-FITC because of plasmon resonance energy transfer from the silver nanocaps to the nearby P-FITC. They can also act as plasmonic antennae by converting a part of the nonradiative near-field emission from the fluorophores to the far field consequently enhancing the emission.

Synthesis and Characteristics of Electrodeposited CoxZn1−x Nanorods

CoxZn1−x nanorod arrays were fabricated by electrodeposition in porous anodic aluminum oxide templates at different electric potentials. X-ray diffraction and transmission electron microscopy indicate that highly-ordered and uniform nanorods have been fabricated. The amounts of Co and Zn contents are investigated using energy dispersive spectroscopy, which demonstrates that the atom ratio of the alloy nanorods changes with the deposition potential. In addition, magnetic measurements show that the magnetic isotropy Co-rich CoZn nanorods will change to magnetic anisotropy nanorods with the easy axis parallel to the rod long axis with decreasing Co content.

Nanowire-based nanogap electrodes by annealing of multisegmented Pt/Au/Pt nanowires in air

A simple thermally lithographic method for fabricating nanowire-based metallic nanogap electrodes is presented, in which the multisegmented Pt/Au/Pt nanowires were electrodeposited in the pores of porous anodic aluminum oxide (AAO) templates first and then thermally annealed to form a nanoscale gap at the interface of Au/Pt. We proposed that the breaking of the multisegmented Pt/Au/Pt nanowires is due to the chemical and physical transformations of the Au segment with O 2. These electrodes are ideally suited for electron-transport studies of chemically synthesized nanostructures, and their utility is demonstrated here by measuring the electronic conduction of short (54-base-pairs) double-stranded (ds) DNA molecules in a dry state.

Size-dependent field-emission characteristics of ZnO nanowires grown by porous anodic aluminum oxide templates assistance

The field-emission electrical properties of hydrothermally synthesized zinc-oxide nanowires grown on SiO 2–Si substrate are reported. Vertically aligned single-crystalline emitters with distinct length L and diameter D are realized by controlling the assisted growth of porous anodic aluminum oxide (AAO) templates. Field-emission measurement revealed that these field emitters exhibited controllable turn-on field E to and the field enhancement factor β. Sample with feature size of L = 500 nm and D = 80 nm was prepared and then used as a basis for examining the size effect. Lower E to and higher β were observed consistently for increasing the aspect ratio L/ D. The enhanced properties of E to = 1.48 V/μm and β up to 6100 are achieved for L/ D = 53 ( L = 1600 nm and D = 30 nm). Optimal characterizing parameters of E to and β will be reached while pursuing extreme L/D practically. Factors such as the geometric limit of AAO template manufacture and the filling efficiency of ZnO into AAO pores will exert influence on the size-dependent effect.

Strong Surface Plasmon Resonance of Ordered Gold Nanorod Array Fabricated in Porous Anodic Alumina Template

High-density, uniform-sized and vertically aligned gold nanorods were grown on aluminum substrate by DC electrodeposition into modified porous anodic alumina (PAA) template. Optical reflection measurements using s- and p-polarized light showed strong surface plasmon resonances (SPRs), for both Au/PAA composites and freestanding Au nanorod arrays. By changing the aspect ratio of the Au nanorods, the angle of incidence of the polarized light, and the dielectric environment, it was possible to vary the position and the intensity of the SPR reflection minima in a reproducible and predictable manner. We successfully measured higher order transverse SPR, which proves the formation of highly uniform Au nanorods.

Uniform and Reproducible Barrier Layer Removal of Porous Anodic Alumina Membrane

A method for the fabrication of porous anodic alumina (PAA) membrane without bottom barrier layer on Al substrate is described. In this method, two-step anodizing followed by a barrier thinning process at the end of the second anodization was used to prepare wide range highly-ordered PAA membrane with a thin barrier layer. Finally, cathodic polarization and pore widening processes were combined to remove the barrier layer completely between the oxide film and Al substrate. Scanning electron microscope (SEM) was used to characterize the morphology and structure of the PAA membrane. From the SEM images, the PAA membrane prepared with the assistance of cathodic polarization showed more homogeneous pore diameters and pore wall quality than that made by pore widening only. In addition, the barrier layer was removed completely with 7.5 min of cathodic polarization and 70 min of pore widening without corrosion in the Al substrate. It was possible to control the pore diameter without any damage to the PAA template from 70 to 90 nm. The fabricated PAA template can be applied to the growth of ordered nanowires, nanorods, nanotubes, and similar structures.