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Polymer nanofibers prepared via continuous spinning using anodic porous alumina are reported.

Anodic porous oxides with ordered nanohole array structures were prepared by the formation of concave arrays on the surface of Cu, Zn, and Ni substrates and the subsequent anodization of the prepatterned substrates. The concave arrays on the surface of the substrate were formed by Ar ion milling using an alumina mask. Although the anodization of Cu, Zn, and Ni substrates without prepatterning generates spongelike porous structures, ordered arrays of cylindrical nanoholes were obtained by the anodization of prepatterned substrates. The interpore distance of the obtained nanohole arrays was controlled by changing the period of the concave arrays. Crystallized ordered nanohole arrays of Cu

Ordered alumina through-hole membrane with an interhole distance of 1 μm.

Self-ordered anodic porous alumina with a long-range ordered hole arrangement having an inter-hole spacing of over 1.5 μm was prepared by anodization in a citric acid electrolyte containing a small amount of phosphoric acid. The inter-hole spacing of the ordered anodic porous alumina could be controlled within a range of 700 nm to 1.8 μm by adjusting the anodization conditions. The use of an electrolyte with a mixture of water and ethylene glycols, especially tetraethylene glycol, was effective for preparing ordered anodic porous alumina with large inter-hole spacings. The obtained anodic porous alumina is suitable for various applications that require highly ordered hole array structures with large inter-hole spacings.

Ideally ordered TiO2 through-hole membranes were obtained by a combination of Ti substrate pre-patterning and two-layer anodization. The Ti substrate was pre-patterned by Ar ion milling using ideally ordered porous alumina as an etching mask. Each concave pit formed by dry etching acted as an initiation site for hole development during anodization, and ideally ordered anodic porous TiO2 was produced by anodization using an electrolyte containing fluoride ions. Two-layered anodic porous TiO2 samples with different solubilities were formed by heat treatment for the crystallization of the first anodized oxide layer and a subsequent second anodization. The selective dissolution of the lower part of the two-layered porous TiO2 produced an ideally ordered TiO2 through-hole membrane. Using the present process, the repeated preparation of ideally ordered TiO2 membranes can be conducted because the ideally ordered concave array, which corresponds to the hole arrangement at the bottom of the detached TiO2 membrane, is maintained even after detaching the membrane. The obtained samples can be applied to various functional devices, such as photonic crystals and filtration membranes with photocatalytic properties.

Anodic porous alumina membranes with site controlled through-holes were prepared by the formation of a masking layer on the surface of anodic porous alumina and subsequent selective second anodization in concentrated sulfuric acid to form a readily soluble layer. After the anodization, the residual Al substrate was removed, and the highly soluble alumina layer formed in concentrated sulfuric acid was dissolved selectively by wet etching. An advantageous point of this process is the controllability of the pattern of through-holes, and the preparation of large samples with selective through-holes is possible. The pattern of through-holes was controlled by changing the mask pattern formed on the surface of anodic porous alumina. The alumina membranes obtained by this process are expected to be used for various applications that require porous alumina membranes with site controlled through-holes.

Polymer micro/nano hierarchical structures were successfully formed by photo-nanoimprinting using anodic porous alumina molds. Anodic porous alumina molds with hierarchical structures were prepared by the anodization of an Al substrate with a micro-concave array. The obtained surfaces with hierarchical structures exhibited superhydrophobicity. The hydrophobic properties of the obtained samples were dependent on the surface structures and could be optimized by changing the micro- and nanopatterns in the hierarchical structure.

Nanoporous alumina spheres with an ordered hole arrangement were prepared through a two-step anodization of small Al particles. The hole periodicity in the ordered anodic porous alumina could be controlled by adjusting the anodizing conditions. Nanoporous hollow spheres were also obtained by removal of residual Al in an etchant. Additionally, nanoporous spheres loaded with Au nanoparticles on their surfaces were obtained through electrochemical or chemical deposition of Au nanoparticles. The obtained Au/alumina composite hollow spheres were used as a substrate for surface-enhanced Raman scattering measurements.

A new type of process for the fabrication of ideally ordered anodic porous alumina with the desired hole interval based on the deformation of a polymer template and the subsequent formation of a metal mold is described. In this process, a pattern composed of an ordered array of concave structures is first prepared on a polymer sheet by imprinting using a starting metal (Ni) mold, and the interval in the pattern is tuned through the deformation of the polymer sheet. The Ni mold with the pattern having the tuned interval is formed by the electroplating of Ni using the polymer sheet as a template. Finally, the pretexturing of Al by imprinting using the obtained Ni mold and subsequent anodization generate ideally ordered anodic porous alumina with the desired hole interval.

TiO2 hollow spheres with nanoporous structures on their surfaces were prepared by the anodization of small Ti particles and the subsequent leaching of the residual metal. The geometrical structures of the TiO2 porous layers could be controlled by changing the anodization conditions. Au-loaded TiO2 hollow spheres were also obtained by depositing Au nanoparticles on the surface of the TiO2 spheres. The obtained porous hollow spheres and metal loaded TiO2 composite hollow spheres can be applied to various types of functional devices.

Uniform-sized nanoparticles of metal oxides were fabricated by membrane emulsification using ordered anodic porous alumina as a membrane and subsequent solidification. The size of the nanoparticles could be controlled by adjusting the pore size of the anodic porous alumina membrane. This process allows the high throughput preparation of monodisperse nanoparticles of various types of metal oxide with controlled size due to the capability of continuous formation of monodisperse emulsion droplets through the porous membrane.

Correction for ‘Preparation of superhydrophobic surfaces with micro/nano alumina molds’ by Takashi Yanagishita et al., RSC Adv., 2018, 8, 36697–36704.

Well-defined one-dimensional arrays of gold nanoparticles dispersed in triphenylphosphine nanowires were obtained by annealing of chloro(triphenylphosphine) gold(I) complexes in a porous alumina template. The obtained nanocomposite wires exhibit strong surface plasmon coupling due to the close proximity of adjacent gold nanoparticles.

Creating sublithographic scale uniform nanowires for large area is an important issue for nanowire-based various device applications. Although anodic aluminium oxide (AAO) membrane is a promising technique, existing attached AAO membrane mask methods have not been able to fabricate such small nanowires for large areas due to difficulties on transferring a thin membrane. Here we demonstrate a facile and scalable methodology to fabricate sublithographic scale uniform-sized nanowires by introducing ultra-thin AAO free-standing membrane with a rigid Al frame and a hydrophilic contacting method. The present method allows us to fabricate sub 20 nm nanowires with the standard deviations of 1.1 nm via defining the size and spacing of metal catalysts for nanowire growth. We also show the scalability of the present attached AAO membrane mask method for a 4-inch scale wafer.