Barrier layer non-uniformity effects in anodized aluminum oxide nanopores on ITOsubstrates

Abstract

Nanoporous anodic aluminum oxide (AAO) has been used widely as a template fordevice fabrication. In many nanostructured electro-optical device designs, AAOgrown on an ITO substrate is the desired configuration. However, a residual thinaluminum oxide barrier layer between ITO and the AAO pores remains and processnon-uniformities during the template fabrication can cause serious problems in thequality of nanowires deposited later in these pores. It was observed that in manytemplates, even the pores closest to each other could have their barrier layerthicknesses differ by as much as 10–20 nm. In this paper, causes and remedies forthis non-uniformity are investigated, including the effects of a thin Ti interlayerinserted between the ITO and AAO. Templates with different Ti layer thickness andannealing conditions were compared. Mechanisms for the formation of voids beneaththe barrier layer were analyzed and studied experimentally. Reactive ion etch(RIE) was found to be the preferred method to mitigate process non-uniformities.Using the above methods, barrier-free AAO templates on ITO substrates wereobtained; their thicknesses ranged from 200 to 1000 nm. The characteristics of CdSnanowires electrodeposited into the initial templates with non-uniform barrierlayer thicknesses and into the processed, barrier-free templates were compared.