A freestanding membrane of highly ordered anodic ZrO2 nanotube arrays

This paper demonstrates the formation of self-organized and highly ordered zirconium oxide (ZrO2) nanotubes via an electrochemical anodization with an electropolished zirconium (Zr) substrate in nonaqueous electrolytes (i.e. an ethylene glycol solution containing a small amount of ammonium fluoride (0.38 wt% NH4F) and 1.79 wt% H2O). Compared with aqueous electrolytes, nanotubes with much smoother wall surfaces were grown in nonaqueous electrolytes. In addition, highly regular arrays of anodic ZrO2 nanotubes were achieved with an electropolished Zr substrate which guaranteed the uniform growth rate of oxide nanotubes on the underlying flat metal surface. A freestanding ZrO2 membrane was produced through the detachment of the existing self-organized ZrO2 nanotubular layer from the underlying remaining-Zr metal by applying a reverse-bias voltage to it.