Direct observations of ion-implanted xenon marker layers in anodic barrier films on aluminium

Abstract

Transmission electron microscopy of ultramicrotomed sections of an aluminium substrate and the attached anodic film has been employed to reveal clearly an implanted xenon marker layer within the film. The position of the marker layer can be determined directly and relatively precisely, without the need for any indirect analytical techniques. However, depending on whether the xenon atoms are initially implanted into the metal or into a preformed thin anodic film, variation in the resultant anodic behaviour is observed. A normal and relatively uniform barrier- type film formation is observed when xenon atoms are implanted into a preformed film. However, in the case of implantation into the metal, a more heavily flawed and less current-efficient film growth is observed over the implanted area, accompanied by a copious gas evolution. In the latter case, transmission electron microscopy of the stripped film reveals the flaws as lighter and finely textured spots with diameters of up to about 0.2 μm and a population density of about 1.5 × 10 13 m -2. Anomalous behaviour is also observed in the distribution of the implanted xenon atoms within the anodic film in the case of implantation into the metal. Thus, for future work concerned with the relative mobilities of migrating species contributing to anodic film growth, implantation into a preformed anodic film is necessary.