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 morethan half a micrometre is described in terms of delaying the chemical dissolution of theformed oxide in fluorinated electrolytes either by controlling the anodization temperatureor by making a protective oxide. It was revealed that both the growth rate and thedissolution rate in the formation of porous niobium oxide films increase as the anodizationtemperature increases. X-ray diffraction (XRD) and x-ray photoelectron spectroscopy(XPS) analyses show that the anodically prepared niobium oxide consists of amorphousNb2O5.For the strategy to make protective oxide, self-ordered nanoporous niobium oxide withdouble layers consisting of an outer layer of around 90–130 nm and an inner layer of around300–400 nm is prepared by anodization–annealing–anodization. We believe that the outeroxide, which undergoes annealing, plays the role of a protective layer for theformation of the inner oxide film grown underneath the outer layer, leading to anodicniobium oxide with a thickness greater than that obtained by single anodization.