On the Experimental Investigation of Ion Beam Mixing in Thin Film Bilayers, Study of the Fe-Al Case

Abstract

The overwhelming majority of experimental research in ion beam mixing starts from the implicit assumption of a particular model description of the mixing process to define effective quantities whose functional dependences on parameters characterizing the target properties and bombardment conditions are studied. In the present work some difficulties inherent to this approach are discussed. Of particular interest here are the uncertainties in the evaluation of the energy deposited to nuclear collisions per unit path length at the interface, FD. Experimental results appearing in the literature and a own study on the ion beam mixing in Fe/Al bilayers are discussed in the scope of the limitations imposed by the uncertainties of model parameters. In conclusion it is suggested that the differences in the geometry of collision cascades may account for the observed deviations of the experimental results from the theoretically predicted dependences of ion mixing on temperature and FD.

Ion Beam Mixing of Ag/Si Bilayer

“…Even though a zero dose necessarily corresponds to no induced mixing, deviation from the linear behavior for the low dose ion mixing has been observed, see e.g. [10]. This implies that the value of the mixing rate, determined by least square fitting of a straight line, is rather a mean quantity in a given dose range.…”

“…The inclusion of the origin in the fitting, however, insignificantly affects our results, to within 3%. It should be mentioned that depending on the portion of the 4Dt versus F curves spanned by the measurements, a straight line representing the mean value in that range may intersect below or above the origin of the plot when extrapolated to zero dose [10]. This is so, since collision cascades cover only a limited region near the surface of the solid.…”

“…A number of facts based on cascade theories and the chemical nature of the system or thermodynamic factors, including the heat of mixing and intrinsic diffusion coefficient has been established. In addition, a correlation between IM and steady state thermal annealing was sought for and attributed to defect migration upon irradiation [10]. In summary, the extent of mixing due to each model is characterized by a mixing rate parameter, 4DtaF, as well as the dependence on the mixing enthalpies and cohesive energies [20].…”