Ion-beam analysis and ion implantation in the study of diffusion

High-energy ion-beam analysis has several desirable features for depth profiling of diffusion couples. The technique is nondestructive, it offers depth resolutions in the range 0.01 to 1 micron, and absolute measurements of both concentration and depth are achieved without the use of reference standards. Ion implantation provides a means for the initial formation of diffusion couples; through the athermal injection of solutes directly into hosts, this approach circumvents several difficulties associated with surface deposition. The application of ion beams to diffusion measurements are first discussed in general terms and then illustrated by two examples. In one case study the diffusion of ion-implanted Sn in Fe was observed by elastic backscattering analysis, thereby extending the range of measured diffusivities downward by 10(5) times. In the other investigation, nuclear reaction analysis was used to depth profile the decay product (3)He in stainless steels exposed to tritium; this permitted a determination of the tritium diffusivity at 273 K, where the migration rate is 10(3) times smaller than that detected previously through gas permeation methods.