Two-step Anodization Process Research Articles

Electrogenerated chemiluminescence of chosen terbium complexes deposited into Al 2O 3 layer at the aluminium cathode

Cathodic electrogenerated luminescence of terbium(III)-(acetylacetonate) 3-1,10-phenanthroline, terbium(III)-(salicylate) 3 and terbium(III)-(salicylate) 3-1,10-phenanthroline complexes were studied. In this experiment terbium complexes were coated upon aluminium porous oxide layer by physical adsorption from methanolic or acetonate solution. The hexagonally ordered porous aluminium oxide has been prepared in a two-step anodization process in sulphuric acid solution. The primary step of cathodic ECL in this method is tunnel emission of hot electrons through barrier oxide layer. Electrochemiluminescence was achieved by recombination of the radical species, such as reduced ligand's aromatic moiety and strong oxidizing agent, i.e. sulphate radicals. This study was conducted to investigate ECL spectra, kinetic and integral ECL intensity relative to the porous aluminium oxide layer thickness.

A novel ammonia sensor based on high density, small diameter polypyrrole nanowire arrays

A novel sensor based on the PPy nanowire arrays with high density, small diameter (about 50 nm) presented a significantly high surface-to-volume ratio. Conducting polypyrrole (PPy) nanowire arrays were synthesized by electropolymerization in the anodic aluminum oxide (AAO) template which was fabricated by two-step anodizing process. Then, two sides of the PPys/AAO were pasted by Si substrates and the AAO template was etched by HF acid. At last, the gold wires were attached on Si substrates, and the sensor came into being. The sensor was sensitive to ammonia at room temperature and showed relatively high response in low concentration and comparatively short response and recovery time.

Controlled growth of anodic aluminium oxide films with hexagonal array of nanometer-sized pores filled with textured copper nanowires

Anodic aluminium oxide (AAO) films exhibiting a homogeneous morphology of parallel pores perpendicular to the surface were prepared in a two-step anodization process and filled with copper by electrochemical deposition. The optimum growth conditions for the formation of free-standing AAO films with hexagonal compact array of cylindrical pores were studied by field emission scanning electron microscopy and small angle X-ray scattering. The results show well-defined periodic structures with uniform pores size distribution for films with pore diameters between 40 and 70 nm prepared using different voltages and temperatures during the second anodization step. X-ray photoelectron spectroscopy and X-ray diffraction analysis of AAO films filled with copper show the formation of nanowires with high structural order, exhibiting a preferential crystalline orientation along the (2 2 0) axis and only small fraction of copper oxides. The best results for textured Cu nanowires were obtained at a reduction potential of −300 mV.

Polymer nanopillars using self‐ordered nanoporous alumina templates

AbstractThe fabrication of polymer nanostructures by replication process using self‐ordered nanoporous alumina with different pore depth and pore diameter as template is reported here. The method entails vacuum infiltration of a Poly(methyl methacrylate) (PMMA) solution into the pores of the template, which was fabricated by using a two‐step anodization process in 0.3 M oxalic acid at 50 V and 15 °C. We have studied how the aspect ratio of the nanopores influence the PMMA nanopillars fabrication. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

How structure changes in fabrication of large size ordered anodic alumina film?

Large size anodic alumina film has not been used in the industry due to that the fabrication parameters are very difficult to control, but the fabrication of large size anodic alumina is exigent as a template in the fabrication of diverse nano-devices oriented to the industrialization. In this paper, large size (width length = 80 mm × 80 mm) porous ordered anodic alumina film was fabricated by using two-step anodization process as compared to the small size (diameter = 40 mm) anodic alumina film in the structures. Pore size and film thickness of anodic alumina film are strongly related to the size of the anodization film. The large size anodic alumina film has an ideally ordered pattern by applying low voltage. However, with the increase of voltage, the ordered pattern of the PAA films was gradually disrupted, especially in the 70 V due to the local thermal imbalance.

A Novel Protocol Toward Perfect Alignment of Anodized TiO2 Nanotubes

Perfectly aligned high-aspect-ratio TiO2 nanotubes that are perpendicularly oriented to a substrate are obtained using a two-step anodization process in ethylene glycol containing 0.5 wt% NH4F and 1 vol% HF, overcoming the bundling issue of TiO2 NTs commonly observed in conventional approaches. They are then used as a template for the electrodeposition of Pt nanowires.

Study the effect of striping in two-step anodizing process on pore arrangement of nano-porous alumina

Two-step anodic oxidation of aluminum is generally employed to produce the ordered porous anodized alumina (PAA). Dissolving away (striping) the oxide film after the first anodizing step plays a key role in the final arrangement of nano-pores. In this work, different striping durations between 1 and 6 h were applied to the sample that was initially anodized at a constant voltage of 40 V at 17 °C for 15 h. The striping duration of 3 h was realized as the optimum time for achieving the best ordering degree for the pores. Scanning electron microscopy (SEM) was used during and at the end of the process to examine the cross section and finishing surface of the specimens. Linear-angular fast Fourier transform (LA-FFT), an in-house technique based on MATLAB software, was employed to assess the ordering degree of the anodized samples.

Nanostructure of the nanopores in anodic aluminum oxide films used as template to fabricate Ag nanowires

Well-ordered nanoporous anodic aluminum oxide (AAO) templates have been prepared on aluminum substrates by a two-step anodization process. A voltage-controlled branching method was successfully used to thin the barrier layer of the AAO template. The nanostructures of the pores, the branched subpores, and the barrier layer in the AAO template were studied in association with the anodization process and barrier layer thinning methods. Results demonstrate the voltage-controlled branching method is a facile and effective way to thin the barrier layer. Uniform silver nanowires can be easily fabricated using alternating current (ac) electrodeposition into the pores of AAO after redressing the barrier layer.

Large-Scale, Noncurling, and Free-Standing Crystallized TiO2 Nanotube Arrays for Dye-Sensitized Solar Cells

Large-area noncurling crystallized free-standing TiO2 nanotube (TNT) arrays have been fabricated by a two-step anodization process. These free-standing crystallized TNT arrays can be easily transferred to fluorine-doped tin oxide glass substrates without any crack. Furthermore, the investigation of these crystallized free-standing TNT arrays in dye-sensitized solar cells (DSSCs) was carried out and showed a roughly 100% enhanced conversion efficiency compared with that of the TNT array on a Ti substrate.

Microfluidic chip with porous anodic alumina integrated with PDMS/glass substrate for immuno-diagnosis

An efficient system for diagnosis of disease marker molecules in microfluidic devices was developed by employing anodic aluminum oxide (AAO) which has highly ordered, uniform, and straight nanopore arrays by a two-step anodization process. AAO on glass substrate was integrated within poly(dimethylsiloxane) (PDMS) microchannel structure. Vacuum-deposited aluminum thin film was anodized by variation of electrolyte composition, applied voltage and anodizing time, for specific pore sizes and depth. The pore was tunable to achieve a size corresponding to target proteins. For enhancement of antibody immobilization and adhesiveness with a PDMS micro-pattern, surface activation of AAO was performed by TMOS–sol spin-coating and calcinations to form a SiO 2 layer. The demonstration of diagnosis of bio-marker protein was performed by employing conventional sandwich-type immuno-assay for hepatitis B virus (HBV). The anti-hepatitis B surface antigen (anti-HBsAg) was immobilized by bridges using γ-aminopropyltriethoxysilane and glutaraldehyde. The hepatitis B surface antigen (HBsAg) was coupled with anti-HBsAg and sheep anti-HBs/horseradish peroxidase conjugate. The result was analyzed by colorimetric assay for comparison with the result using conventional immuno-assay and it showed higher efficiency using microfluidic channels. The AAO inside the PDMS microfluidic channel allows specific immobilization of proteins by controlling the size for access. This study can be extended for a high-throughput system for bio-marker proteins.

Extremely high aspect ratio alumina transmission nanomasks: their fabrication andcharacterization using electron microscopy

Free standing, nanoporous alumina templates were fabricated as transmissionmasks from aluminium using a two-step anodization process followed by acidetching. The resulting membrane comprises self-ordered, periodic arrays ofnon-connecting circular channels which can be prepared with pore diameters<100 nm and with minimal occlusion. Aspect ratios greater than 300:1 were measured directlyusing electron transmission and the channels were shown to be highly aligned(angular) over membrane thicknesses of tens of microns. Also evident is some localorder associated with both azimuthal and angular domain structure giving rise tolocal channel tilt which has not previously been reported. Transmission electronmicroscopy has been shown to be an important characterization tool for thesenanomasks as the channels are transparent to electrons, providing a means of directlymeasuring their thickness and aspect ratio. Expressions for determining theirthickness and aspect ratio are also presented and evaluated in this work. Thesemembranes are well suited for use as nanotemplates in transmission lithographyapplications including ion implantation and ion or electron beam collimation.

Novel Magnetoresistive Structures Using Self-Assembly and Nanowires on Si

AbstractAnodic Aluminum Oxide (AAO) was grown both as free-standing membranes and as integrated layers on Si as templates for arrays of magnetoresistive nanowires. These structures will be useful for applications such as current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) sensors, magnetic random access memory (MRAM) and microwave oscillator arrays. As the AAO was formed, using a two-step anodization process, columnar nanopores self-assembled inside the oxide to form a close-packed array. The pore diameters could be varied from 10-60nm by changing the anodization conditions. As the diameter of the AAO nanopores decreased, the distance between the nanopores also decreased. The free-standing membranes had pores with lengths of 17um. The pores that were grown directly onto Si with an adhesion layer of Ti were 600nm in length. In addition to growing these latter pores directly onto Si, they were also grown onto Co/Cu/Co thin films that were evaporated onto the Si. Au nanocontacts were electroplated into these nanopores to study point-contact magnetoresistance and microwave response. For the magnetoresistive nanostructures, multilayered Co/Cu nanowires were fabricated via electrochemical deposition. The samples were measured with vibrating sample magnetometry (VSM) and also using ac and dc magnetotransport systems. The highest magnetoresistance was found in nanowires that had hysteresis loops that were identical as measured in plane and perpendicular to the plane. The highest measured MR (Delta R/R = 11%) of the multilayers was calculated as 33% by subtracting the resistance of the Cu leads on either side of the multilayers from the denominator. Shorter wires are currently under construction to avoid this effect. Spin transfer torque (STT) was also measured in the samples. For 10-60nm diameter nanowires, the change in resistance due to STT was around 6% which represents the full magnetoresistance of the larger wires, but only half that of the smaller nanowires. It is therefore concluded that the 10-nm Co layers do not align antiparallel to parallel as fully at the switching current density of JAP-P = 2.7 × 108 A/cm2 compared to the larger wires which switch at JAP-P = 3.2 × 107 A/cm2. With diameters in the 10-60 nm range and integration with Si, these nanostructures have great potential for future nanosensors, MRAM and microwave oscillator arrays.

Technique for Self-Assembly of Tin Nano-Particles on Anodic Aluminum Oxide (AAO) Templates

Various pore sizes of anodic aluminum oxide (AAO) were fabricated using a two-step anodization process. AAO pores with diameters ranging from 5 to 500 nm were formed in diluted electrolyte solutions of sulfuric acid, oxalic acid, and phosphoric acid. Irregularly shaped tin particles in nano sizes were formed on the AAO using a thermo-vaporizing process. Tin spheres with diameters ranging from 3 to 500nm were then obtained by reflowing vaporized AAO in silicate oil. A transmission electron microscope (TEM JEOL 2000) was employed to characterize the crystalline structure of a tin sphere with 18 nm diameter.

Silicon nanopore array structure using porous anodic alumina

A free-standing, bidirectionally permeable and ultra-thin （500—1000 nm） porous anodic alumina membrane was fabricated using a two-step aluminium anodization process, which was then placed on top of a silicon film as an etching mask. The pattern was transferred to silicon using dry-etching technology, and the silicon nanopore array structure was formed. The factors which affict the pattern transfer process are discussed. Observation of the nanopatterned sample under a scanning electron microscope shows that the structure obtained by this method is made up of uniform and highly ordered holes, which attains to 125 nm depth. The photoluminescence spectrum from the nanopatterned sample，the surface of which has been thermal-oxidized, shows that the the luminesce is evidently enhanced, the mechanism of which is based on the normally weak TO phonon assisted bandgap light-emission process, and the physical reasons that underlic the enhancement have been analyzed. The PL results do show an attractive optical characteristic, which provides a promising pathway to achieve efficient light emission from silicon.

Characterization of electrodeposited Ni and Ni80Fe20 nanowires

In this work we use nanoporous alumina substrates as templates for the growth of Ni and Ni 80 Fe 20 nanowires. Our membranes were obtained by a two-step anodization process of high-purity aluminum foils: first anodizations were performed at 40 V for 15 h in 0.3 M oxalic acid, at 2–6 °C; the second anodization was carried out using the same conditions for 30 min, resulting in pore lengths of ∼1.3 μm. After the second anodization, the pore bottom barrier-layer was thinned, to allow the current to flow through electron tunneling. A pulsed electrodeposition method was then used to grow Ni and Ni 80 Fe 20 nanowires. Transport characterization and isothermal magnetization measurements performed on the produced arrays are presented.

Application of highly ordered carbon nanotubes templates to field-emission organic light-emitting diodes

An anodic aluminum oxide (AAO) template was formed by a two-step anodization process. Carbon nanotubes (CNTs) were successfully synthesized along with AAO pores and the diameters of CNTs equaled those of AAO pores. The lengths of CNTs during a chemical vapor deposition synthesized process on the AAO template were effectively controlled. These AAO–CNTs exhibit excellent field emission with a low turn-on field (0.7 V/μm) and a low threshold field (1.4 V/μm). The field enhancement factor, calculated from the non-saturated region of the Fowler–Nordheim (F–N) plot, is about 8237. A novel field-emission organic light-emitting diode (FEOLED) combining AAO–CNTs cathodes as electron source with organic electroluminescent (EL) light-emitting layers coated on indium-tin-oxide (ITO) is produced. The uniform and dense luminescence image is obtained in the FEOLEDs. Organic EL light-emitting materials have lower working voltage than inorganic phosphor-coated fluorescent screens.

Fabrication of Thin Film Titania with Nanopores, Nanopoles, and Nanopipes by Nanoporous Alumina Template

We demonstrate the formation of thin film titania (TiO2) with a dense array of nanopores, nanopoles, and nanopipes. The heights of pores, poles, and pipes were approximately 130 nm, 180 nm, and 200 nm, respectively. The aspect ratios of these three structures were approximated between 2 and 3. In order to obtain titania thin films, a nanoporous alumina (Al2O3) template was fabricated by performing a two-step anodization process. The spin-coated titania films were uniformly patterned by a nanoimprinting lithography technique with a textured poly(methyl methacrylate) (PMMA) mold or nanoporous alumina template. The titania films are very useful for solar cells, photocatalytic and sensing applications, in which nano-structuring of surfaces with controlled dimensions is vital.

Structural and luminescence characterization of porous anodic oxide films on aluminum formed in sulfamic acid solution

Atomic force microscopy (AFM) and luminescence methods (galvanoluminescence and photoluminescence) were used to characterize porous oxide films obtained by aluminum anodization in sulfamic acid solution. For the first time we measured weak galvanoluminescence during aluminum anodization in sulfamic acid and found strong influence of sample's surface pretreatment as well as anodic conditions on luminescence intensity. AFM analysis showed that the pore arrangement of porous oxide films formed in sulfamic acid by two-step anodization process at a constant voltage of 15–30 V is relatively irregular.

Influence of the microstructure of the aluminum substrate on the regularity of the nanopore arrangement in an alumina layer formed by anodic oxidation

We investigated the microstructure of aluminum sheets with different purities (Al 99.999%, Al 99.95%, Al 99.5% and AlMg1) before and after different treatments (polishing and annealing) by X-ray diffraction (phase analysis and pole figures) and high-resolution scanning electron microscopy. In a two-step anodisation process within sulfuric acid a nanoporous alumina layer (with mean diameters of 25 nm and mean distances of 30 nm) was formed on the aluminum sheets. We found that the regularity of the nanopore arrangement correlates with the fraction of aluminum grains with (100) orientation in the aluminum substrate. A correlation with the grain boundary and dislocation densities within the aluminum could not be determined.

High Density Silver Nanowire Arrays using Self-ordered Anodic Aluminum Oxide(AAO) Membrane

Highly ordered silver nanowire with a diameter of 10 ㎚ was arrayed by electroless deposition in a porous anodic aluminum oxide (AAO) membrane. The AAO membrane was fabricated electrochemically in an oxalic acid solution via a two-step anodization process, while growth of the silver nanowire was initiated by using electroless deposition at the long-range-ordered nanochannels of the AAO membrane followed by thermal reduction of a silver nitrate aqueous solution by increasing the temperature up to 350℃ for an hour. An additional electro-chemical procedure was applied after the two-step anodization to control the pore size and channel density of AAO, which enabled us to fabricate highly-ordered silver nanowire on a large scale. Electroless deposition of silver nitrate aqueous solution into the AAO membrane and thermal reduction of silver nanowires was performed by increasing the temperature up to 350℃ for 1 h. The morphologies of silver nanowires arrayed in the AAO membrane were investigated using SEM. The chemical composition and crystalline structure were confirmed by XRD and EDX. The electrolessdeposited silver nanowires in AAO revealed a well-crystallized self-ordered array with a width of 10 ㎚.