The fabrication of mono-domain highly ordered nanoporous alumina on a wafer scale by a guided electric field (original) (raw)
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Photonics and Nanostructures-fundamentals and Applications, 2007
A pre-patterning method of aluminium surface, in order to obtain highly ordered nanoporous anodized alumina on large areas is presented. Aluminium single crystals have been used as a substrate and a 2D hexagonally closed-packed lattice of shallow pits, with diameter of about 200 nm and period of 350 nm, has been successfully achieved by direct writing laser lithography (DWL) and wet etching. Finally, anodic oxidation of the single crystal at high cell voltage in phosphoric solution results in oxide growth with pore ordering superimposed by the pre-patterning procedure. #
Alumina nanotemplate fabrication on silicon substrate
Nanotechnology, 2004
ABSTRACT Alumina nanotemplates integrated on silicon substrate with pore diameters of 12–100 nm were prepared by galvanostatic (constant current) anodization. High current density (e.g. 100 mA cm−2) promoted a highly ordered hexagonal pore structure with fast formation rate independent of anodizing solution. Alumina formation rates of 2000 and 1000 nm min−1 were achieved at current densities of 100 and 50 mA cm−2, respectively. These rates were approximately two orders of magnitude greater than other reports in the literature. Different electrolytes of sulfuric acid (1.8–7.2 M), oxalic acid (0.3 M) and mixed solutions of sulfuric and oxalic acids were evaluated as anodizing solutions. At fixed current density, sulfuric acid promoted smaller pore diameter with lower porosity than mixed acids and oxalic acid. The I–V characteristics of aluminium anodization show the measured voltages at given current densities strongly depend on solution composition, operating temperature, and bath agitation. The pore diameter of the silicon-integrated alumina nanotemplate varied linearly with measured voltage with a slope of 2.1 nm V−1, which is slightly smaller than reported data.
Fabrication of Commercial Nanoporous Alumina by Low Voltage Anodizing
Egyptian Journal of Chemistry, 2018
T HE PRESENT work is considered as an introductory study on the procurement of membranes from nanoporous alumina through one-step anodization. The nonporous alumina was obtained by anodizing the specimens at low voltage 5V for 20 minutes in phosphoric acid. The self-ordered porous arrangements can be acquired by using this process. The variables of space between pores, high pore density on the alumina surface are subjected to comparison with membranes which obtained by other methods. The mixture of phosphoric acid and chromium trioxide is used for removing the formed aluminum oxide after the first anodization. The self-ordered porous configuration is obtained at the second anodization step at the same conditions of the first anodization process. The nonporous alumina membrane was subjected to characterization of its surface morphology by scanning electron microscopy SEM and the electric properties were examined by using the electrochemical impedance test EIS. The formed nanoporous structures can be used for fabrication of sensor elements.
Nanotechnology, 2008
A combined process of electrochemical formation of self-assembled porous anodic alumina thin films on a Si substrate and Si etching through the pores was used to fabricate ideally ordered nanostructures on the silicon surface with a long-range, two-dimensional arrangement in a hexagonal close-packed lattice. Pore arrangement in the alumina film was achieved without any pre-patterning of the film surface before anodization. Perfect pattern transfer was achieved by an initial dry etching step, followed by wet or electrochemical etching of Si at the pore bottoms. Anisotropic wet etching using tetramethyl ammonium hydroxide (TMAH) solution resulted in pits in the form of inverted pyramids, while electrochemical etching using a hydrofluoric acid (HF) solution resulted in concave nanopits in the form of semi-spheres. Nanopatterns with lateral size in the range 12-200 nm, depth in the range 50-300 nm and periodicity in the range 30-200 nm were achieved either on large Si areas or on pre-selected confined areas on the Si substrate. The pore size and periodicity were tuned by changing the electrolyte for porous anodic alumina formation and the alumina pore widening time. This parallel large-area nanopatterning technique shows significant potential for use in Si technology and devices.
Highly ordered anodic alumina nanotemplate with about 14 nm diameter
Korean Journal of Chemical Engineering, 2008
A novel method for the fabrication of highly ordered nanopore arrays with very small diameter of 14 nm was demonstrated by using low-temperature anodization. Two-step anodization was carried out at 25 V, sulfuric acid concentration of 0.3 M, and electrolyte temperature of −15 o C. After anodization, a regular pore array with mean diameter of 14 nm and interpore distance of 65 nm was formed. The pore diameter and regular arrangement were confirmed by scanning electron microscopy (SEM) and fast Fourier transformation (FFT), respectively. The present results strongly suggest that the diameter of pores in a highly ordered alumina template can be reduced by lowering the anodization temperature.