| Abstract |
Amorphous anodic oxide films have been formed at high efficiency on aluminium implanted with 3.0 x 10(20) W ions m(-2) in order to study the behaviour of tungsten during film growth. The initial film is composed mainly of alumina because the outer layer of aluminium above the main implanted region of the substrate is oxidized. During this period, tungsten atoms, present in low concentrations in the aluminium, accumulate in a thin metal layer just beneath the anodic film. Subsequently, the main tungsten-implanted region is oxidized, with incorporation of tungsten and aluminium species into the anodic film at the metal-film interface in proportion to their concentrations in the metal. The incorporated tungsten species migrate outwards in the anodic film at about 0.34 times the rate of Al3+ ions. After oxidation of the main tungsten-containing region, more dilute regions of metal containing about 1 at\% W are consumed, with oxidation of aluminium and tungsten in the presence of a highly tungsten-enriched metal layer. The enrichment is initially equivalent to 15 +/- 4 at\% W, assuming that the enriched layer is 2 nm thick. However, rater, as the metal-film interface reaches regions of metal containing about 0.1 at\% VV, the enriched layer contains significantly more tungsten than is usual for such dilute metal regions, indicating that tungsten is transported with the metal-film interface from metal regions of higher prior tungsten concentration as the film thickens. |
