Incorporation of tungsten and molybdenum into anodic alumina films

Abstract

The incorporation of tungsten and molybdenum into barrier films on aluminium, formed to 5–350V at 5 mA cm⁻² in 0·1 M tungstate and molybdate electrolytes at 298 K, has been studied by Rutherford backscattering spectroscopy (RBS) and transmission electron microscopy (TEM). RBS indicated that tungsten and molybdenum were incorporated at similar constant rates (2·9 × 10¹³ W atoms cm⁻² V⁻¹ and 2·7 · 10¹³ Mo atoms cm ⁻² V⁻¹), with the surface layers of all films being enriched with either ∼5 × 10¹⁴ W atoms cm⁻² or ∼9 × 10¹⁴ Mo atoms cm⁻². The enrichment was a consequence of immersion in the electrolyte, since similar concentrations of tungsten were picked up by merely dipping electropolished aluminium or anodic alumina films into the tungstate electrolyte. TEM of film sections, assisted by the atomic-number contrast effect associated with incorporated species, revealed that tungsten incorporated into a 50 V film was distributed uniformly in the outer 0·3 of the thickness.