A Dynamic Ion Beam Method for Measuring Deuterium Diffusion in Films

Abstract

A new technique is described for the measurement of deuterium diffusion in metal films. Deuterium is ion-beam implanted in the film and simultaneously observed to diffuse to the film's surface by means of the D(d,p)T nuclear reaction. The buildup of deuterium in the near-surface area is modeled and shown to be controlled by migration to depths deeper than the deuteron range (the undamaged region) as well as by migration in the ion-damaged region. Diffusion normal to the film may be measured selectively in each region by choosing appropriate combinations of implant flux, ion energy, film thickness, and target temperature. An advantage to the technique over permeation-type measurements is that surface effects are easily eliminated. The diffusion of deuterium in scandium and scandium deuteride was measured between 12°C and 250°C. Time-dependent D(d,p)T yields were obtained for 0.5 to 5.5 4331538m thick films using 40 keV bombardment (deuteron range ~ 0.4 4331538m) with fluxes to 1.5 mA/cm2. Diffusion was first observed in α-phase scandium. As the deuterium concentration increased, transition to the hydride phase was clearly visible. Subsequent data gave diffusivities for the mixed phase region, which agree well with previous nmr measurements in bulk ScH1.7. The α-phase measurements appear more than an order-of-magnitude greater than the mixed-hydride phase but described by the same activation energy for diffusion. No damage-dependent effects are observed for these bombardment conditions.