【Other Papers】Crystallographic Orientation Dependence of Nanohole Ordering in Porous Gallium Oxide Formed by Two-Step Anodization of Single-Crystal Gallium

      Researchers from Aichi University of Technology have published a dissertation titled " Crystallographic Orientation Dependence of Nanohole Ordering in Porous Gallium Oxide Formed by Two-Step Anodization of Single-Crystal Gallium " in Electrochimica Acta.

Abstract

      Ordered porous gallium oxide was fabricated by applying two-step anodization to crystal-orientation-controlled single-crystal gallium. Single-crystal gallium substrates with different crystallographic orientations, in which the a-, b-, or c-axis was approximately aligned with the surface normal, were used. The first anodization step produced a porous gallium oxide layer, and subsequent selective dissolution of this layer generated an ordered nanoscale dimple array on the gallium surface. During the second anodization step, these dimples were considered to act as initiation sites for nanohole formation, resulting in the formation of ordered porous gallium oxide. The regularity of the nanohole arrangement was quantitatively evaluated using the relative standard deviation of the interpore-distance distribution. The two-step anodization process significantly improved nanohole ordering compared with direct anodization, and the regularity increased with increasing duration of the first anodization step. The crystallographic orientation of the gallium substrate also strongly influenced pore ordering. Among the examined substrates, the a-axis-oriented sample exhibited the highest regularity, whereas the b- and c-axis-oriented samples showed lower regularity. Under appropriate conditions, porous gallium oxide with nanohole-array regularity comparable to that of anodic porous alumina was obtained. These results demonstrate that the nanohole ordering achieved through the two-step anodization of gallium is strongly governed not only by the first anodization duration but also by the crystallographic orientation of single-crystal gallium. This pronounced orientation dependence of nanohole ordering may be associated with the strong crystal-lattice anisotropy of orthorhombic gallium.

DOI：

https://doi.org/10.1016/j.electacta.2026.149659