A Tungsten Interlayer Process for Fabrication of Through-Pore AAO Scaffolds on Gold Substrates

Abstract

A W interlayer process is demonstrated for fabrication of a through-pore nanoporous anodic aluminum oxide (AAO) scaffold on gold substrates. The W interlayer process comprises anodization of an Al/W/Au trilayer for the formation of an AAO scaffold with a WO(3) extrusion at the pore bottom and selective removal of the WO(3) to expose the surface of the substrate, without modifying the nanostructure of the scaffold. Structural and kinetic studies of the WO(3) extrusion formation revealed that the anodization of W consumes a fixed thickness of the W layer in acidic electrolytes and that the thickness depends strongly on the anodic voltage. Based on this study, the optimum thickness of a W interlayer in the Al/W/Au trilayer was determined for various anodization conditions. Through-pore AAOs were fabricated on Au substrates using optimum W thicknesses (10 and 20 nm) in 0.3 M sulfuric acid at 25 V, 0.3 M oxalic acid at 40 V, and 5 wt % phosphoric acid at 86 V, without a violent O(2) evolution reaction and without changing the pore diameter. With the resulting AAO scaffolds, vertically aligned freestanding Au and Pt nanowires with diameters ranging from about 12 nm to about 120 nm were grown by electrodeposition on a Au substrate. The methodology demonstrated here should be generally applicable to other inert metallic substrates/underlayers. (c) 2010 The Electrochemical Society.