[en] The effect of alloying element Ca (0, 1, and 2 wt%) on corrosion resistance and bioactivity of the as-received and anodized surface of rolled plate AM60 alloys was investigated. A plasma electrolytic oxidation (PEO) was carried out to form anodic oxide film in 0.5 mol dm"-"3 Na_3PO_4 solution. The corrosion behavior was studied by polarization measurements while the in vitro bioactivity was tested by soaking the specimens in Simulated Body Fluid (1.5xSBF). Optical micrograph and elemental analysis of the substrate surfaces indicated that the number of intermetallic particles increased with Ca content in the alloys owing to the formation of a new phase Al2Ca. The corrosion resistance of AM60 specimens improved only slightly by alloying with 2 wt% Ca which was attributed to the reticular distribution of Al2Ca phase existed in the alloy that might became barrier for corrosion propagation across grain boundaries. Corrosion resistance of the three alloys was significantly improved by coating the substrates with anodic oxide film formed by PEO. The film mainly composed of magnesium phosphate with thickness in the range 30 - 40 μm. The heat resistant phase of Al_2Ca was believed to retard the plasma discharge during anodization and, hence, decreased the film thickness of Ca-containing alloys. The highest apatite forming ability in 1.5xSBF was observed for AM60-1Ca specimens (both substrate and anodized) that exhibited more degradation than the other two alloys as indicated by surface observation. The increase of surface roughness and the degree of supersaturation of 1.5xSBF due to dissolution of Mg ions from the substrate surface or the release of film compounds from the anodized surface are important factors to enhance deposition of Ca-P compound on the specimen surfaces.

[en] Periodic inverted pyramid arrays in silicon were fabricated using a nonlithographic technique combining the localized anodization of the substrate and the subsequent anisotropic chemical etching in an alkali solution. A silicon oxide layer with a honeycomb pattern, which was produced by the anodization of a silicon substrate coated with self-assembled microspheres, served as a passivation layer for alkaline etching. After the removal of microspheres, the unoxidized silicon region was etched selectively by chemical etching in tetramethyl ammonium hydroxide, resulting in the formation of ordered inverted pyramid arrays in silicon. The interval between inverted pyramid holes could be controlled by changing the diameter of the spheres used as an initial mask for silicon anodization. (fast track communication)

[en] Large-scale self-aligned GaAs nanowire arrays were successfully fabricated by the anodic etching of an n-type GaAs (111)B substrate. Although pore generation occurred randomly at the early stage of anodic etching, homogeneous pore growth with a high pore density was accomplished spontaneously on the entire surface of the substrate by prolonged anodic etching under optimized conditions. The GaAs pore walls gradually dissolved during anodic etching and finally three adjacent pores were interconnected to yield a GaAs nanowire with a diameter of approximately 200 nm, a length of approximately 110 μm, and a high aspect ratio of over 500. Aggregates of GaAs nanowires exhibited a good electron emission property, a low turn-on electric field (2.5 V μm"−"1), and a stable field emission current. The field-emission characteristics were enhanced by increasing the spacing between emission sites through post-chemical etching. (paper)

[en] To fabricate a freestanding through-hole Au membrane using an anodic porous alumina template, Au was deposited on the outermost surface of an anodic film followed by the removal of the template. Alumina templates with different dimensions (e.g. diameters and number of pores) were prepared by two-step anodization in the range of 40–80 V and pore-widening. The Au thin films were deposited onto alumina templates with well-controlled surface morphologies by sputter deposition using a commercially available ion sputter coater. After the removal of the alumina template, a variety of Au membranes with nanoholes, nanotubes, or branched pores were obtained, which reflect the morphology of the alumina template. When the sputtered Au penetrates the pores of the alumina film, Au nanotube arrays with an aspect ratio of ∼3 can be fabricated. The present method is much simpler than the traditional template process involving multi-step replication because there is no need to separate the alumina template from the aluminum substrate before Au deposition. (paper)

[en] Highlights: • Sealing process of anodic alumina films was studied by advanced SEM, TEM and XPS. • In boiling water, boehmite precipitates as small flakes due to (100)-oriented growth. • As pore walls dissolve, boehmite flakes increase, forming an intertwined structure. • A three-layered sealing film with different densities of flaky boehmite is formed. • Neither preferential pore mouth closure nor uniform pore narrowing was identified. The mechanism of the hot water sealing of anodic alumina films was studied using electron microscopy and compositional analysis. The films dissolve in boiling water and boehmite precipitates as small flakes due to (100)-oriented growth with 3-nm average thickness and evenly dispersing in the pores and the surface. The quantity and size of flakes increase with increasing sealing time forming a densely intertwined boehmite structure. Eventually, a three-layered structure is formed, which is composed of an outer vertically grown coarse flaky layer, an intermediate dense flaky layer with 2:1 thickness ratio, and a porous layer filled with dense flaky boehmite.

[en] To fabricate ordered geometric patterns consisting of InP nanoporous structures, a photoresist mask with periodic opening arrays was prepared by sphere photolithography. The diameter and interval of the openings of the photoresist mask could be controlled independently by adjusting the diameter of silica spheres used as a lens and the exposure time. Through this resist mask with a two-dimensional (2D) hexagonal array of openings, the pore growth of InP during anodic etching was investigated. The isolated openings could act as initiation sites for the radial growth of pores, resulting in the formation of hexagonal geometric patterns based on Voronoi tessellation in 2D space. With further anodic etching, inside the substrate, the growth direction of the pores changed from radial to perpendicular relative to the substrate. Moreover, by removing domains consisting of nanopores by anisotropic chemical etching, the fabrication of InP microhole arrays with circular and triangular cross sections was also achieved. (paper)

[en] The structural features of anodic oxide films formed on an aluminum substrate coated with self-assembled microspheres were investigated by scanning electron microscopy and atomic force microscopy. In the first anodization in neutral solution, the growth of a barrier-type film was partially suppressed in the contact area between the spheres and the underlying aluminum substrate, resulting in the formation of ordered dimple arrays in an anodic oxide film. After the subsequent second anodization in acid solution at a voltage lower than that of the first anodization, nanopores were generated only within each dimple. The nanoporous region could be removed selectively by post-chemical etching using the difference in structural dimensions between the porous region and the surrounding barrier region. The mechanism of anodic oxide growth on the aluminum substrate coated with microspheres through multistep anodization is discussed.

[en] The effects of electrolyte pH and temperature on the structure and properties of anodic oxide films formed on niobium in phosphoric acid solution with the addition of NH₄OH for pH adjustment have been investigated. The film thickness formed at the same voltage slightly increased with increasing pH and significantly increased with increasing electrolyte temperature. The capacitance of the film was independent of electrolyte pH in an acid region, while it notably increased with increasing pH in an alkaline region. The relative permittivity of the film changed 43.7-80.5 when the electrolyte pH was increased from 1.6 to 10. The incorporation depth and content of phosphorus in the film were markedly suppressed at pH 10, and nitrogen was found to penetrate into a depth of 70%. Furthermore, the apparent transport number of Nb⁵⁺ ion decreased from 0.26 to 0.02 by a pH increase from 1.6 to 10. The notable changes in structure and dielectric properties of the anodic niobia film formed in the alkaline region would primarily be caused by the different incorporation behavior of electrolyte species such as phosphorous and nitrogen.

[en] The structure and properties of anodic films formed in a relatively low voltage range in ammonium adipate solution have been investigated focusing on the effect of formation voltage. When anodization voltage was identical, the linear relationship of film thickness with the log of the final current density during film growth could be ascertained for all the films formed even at low voltages such as 5 V. The anodization ratio determined from the transmission electron microscopy (TEM) cross section of the film formed at 5 mA cm^-2 until voltage increased to 5 V was 1.8 nm/V suggesting a lower electric field strength during anodization than that for the film formed at the voltage higher than 20 V. Furthermore, the transport number of Al³⁺ ions and amount of incorporated anions decreased with decreasing formation voltage, particularly at the voltage lower than 10 V. Changes in chemical dissolution rate in the depth of the films in an acid solution indicated that the films formed in the voltage range from 20 to 80 V were composed of one layer and the films formed at voltages lower than 10 V were composed of two layers with different dissolution rates. However, when applied voltage was kept constant following current decay, the film formed one layer, implying the inward migration of the incorporated anions to the film/metal interface. It was suggested that the outer layer with the higher dissolution rate contains electrolyte anions and the inner layer with the lower dissolution rate consists of pure alumina. Thus, it is clarified that the structure and properties of anodic film change with increasing anodization voltage because of the change in electric field strength, even if anodization is conducted at a constant current density

[en] An oxide system Sc_2−xFe_xO₃ prepared by a conventional solid-state reaction method was found to change its color from the well-known reddish color at x = 2.0 to a yellowish color at x ≈ 0.6 and to a greenish-yellow color at 0.2 ≤ x ≤ 0.4. According to the structural characterization results for this system, the monophasic corundum phase region persists for 1.6 ≤ x ≤ 2.0, whereas the bixbyite-type phase is monophasic for 0 ≤ x ≤ 1.0. The intermediate region of 1.2 ≤ x ≤ 1.4 is a mixed region. Because green is a rare color for iron oxides, powder of the most typical composition, x = 0.4, with (L^*, a^*, b^*) coordinates of (77.3, −0.5, 51.0) was tested as a pigment for a Japanese-style painting and also as an overglaze enamel on porcelain; reasonably good results were obtained.