Thermodynamic effects in depth profiling and ion-beam mixing without invoking thermal spikes

Abstract

Various studies on ion-beam mixing suggest that the extent of mixing is sensitive to the sign and magnitude of the heat of mixing, ΔHm. This implies a role, not only for random motion, but also for chemical driving forces of the type where the total diffusion flux is modified by the factor [1−αi(1−αi) 2hmp/RT(1+p)]. Here α1 is the atomic fraction of component i, αi(1−αi)hm is the heat of mixing of a regular solution, and p is the ratio of the diffusivities for chemically guided defect motion to those for random motion of all types. The parameter p has never been evaluated for any system and we wish to evaluate it first by analyzing the profiling experiments of Marton, Fine, and Chambers on multilayers of Ni-Ag. We then obtain further values of p from ion-beam mixing experiments on bilayers and multilayers. It is shown that it is possible to understand a variety of experimental results relating to profiling and to ion-beam mixing in terms of chemical driving forces and, moreover, to do so without invoking thermal spikes.