Direct Growth of Highly Ordered Crystalline Zirconia Nanowire Arrays with High Aspect Ratios on Glass by a Tailored Anodization

Abstract

We report a facile approach to fabricate highly ordered zirconia nanowire arrays with controllable dimensions of φ25–40 nm in diameter, 100–550 nm in length, and 3–20 in aspect ratio by a tailored two-step anodization from superimposed Al/Zr layers sputter-deposited on glass substrates. A porous-type Al anodization in a constant potential mode was performed on the Al layer on Zr/glass in strong acidic electrolytes to form highly ordered porous alumina films with different pore sizes and intervals. Successively, a barrier-type Zr anodization in a constant current mode, at a low-critical-current density of 2 A m−2 with open potentials up to 70–500 V in different acidic electrolytes, was carried out on the underlying Zr film via the overlying PAA films, thereby allowing direct growth of the zirconia nanowires within the alumina nanopores on glass. The as-anodized zirconia nanowires were crystalline, comprising a mixture of monoclinic and orthorhombic ZrO2. In particular, the orthorhombic phase in the zirconia nanowires becomes more predominant with increasing terminal anodizing potentials and exhibits a preferential crystalline orientation in the (002) facet. The formation of anodic zirconia nanowires could be ascribed to the enhancement of the transport number of Zr cations in crystalline zirconia affected by the low-critical-current density and the impurities in the initial Zr film.