Porous niobium oxide films prepared by anodization-annealing-anodization

Abstract

In this paper, a method to prepare anodic porous niobium oxide with a thickness of more than half a micrometre is described in terms of delaying the chemical dissolution of the formed oxide in fluorinated electrolytes either by controlling the anodization temperature or by making a protective oxide. It was revealed that both the growth rate and the dissolution rate in the formation of porous niobium oxide films increase as the anodization temperature increases. X-ray diffraction ( XRD) and x-ray photoelectron spectroscopy ( XPS) analyses show that the anodically prepared niobium oxide consists of amorphous Nb(2)O(5). For the strategy to make protective oxide, self-ordered nanoporous niobium oxide with double layers consisting of an outer layer of around 90 - 130 nm and an inner layer of around 300 - 400 nm is prepared by anodization - annealing - anodization. We believe that the outer oxide, which undergoes annealing, plays the role of a protective layer for the formation of the inner oxide film grown underneath the outer layer, leading to anodic niobium oxide with a thickness greater than that obtained by single anodization.