Immobilization mechanisms for ion-implanted deuterium in aluminum

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Abstract
Aluminum was ion implanted with deuterium (D) and then subjected to linear temperature ramping, and the resulting D redistributions were monitored using the ion‐induced nuclear reaction D(3He, p)4He. Data from such experiments were analyzed in terms of various immobilization processes, utilizing numerical solutions of the appropriate diffusion formalism. The identification of mechanisms was augmented by transmission electron microscopy. Irradiation defects believed to be of vacancy type were shown to trap the D with a binding enthalpy of 0.52±0.10 eV relative to solution sites, in excellent agreement with calculations based on effective medium theory. Stronger binding at the surface oxide was quantitatively described by assuming the formation of D2 molecules at the metal‐oxide interface. At higher implanted concentrations the immobilization of D by precipitation of D2 bubbles was observed, and the subsequent release from these bubbles at more elevated temperatures was described by diffusion theory. Small, high‐pressure He bubbles formed by ion implantation of He did not trap the D more strongly than the irradiation defects, in contrast to observations in a number of other metals, but consistent with predictions of effective medium theory for Al.

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