The dependence of cascade mixing in Pd on the projectile's mass

Abstract

The rate of ion beam mixing of thin (≈5 Å) marker layers of platinum in a palladium matrix at ≈12 K has been measured as a function of projectile mass for ions from neon to samarium. The results are expressed as a mixing efficiency, which is proportional to the rate of increase of the variance of the marker divided by the product of dose and energy deposited per ion at the marker depth. That is, measures the mixing of the marker per unit of energy deposited. For ions from Ni to Sn the mixing efficiency was approximately constant at about 9 Å2/eV. For Ne the efficiency was lower, at 4 Å2/eV, approximately the value expected for ballistic mixing, and for the heavier ions, xenon and samarium, it was higher, at abut 13 Å2/eV. These results are discussed in terms of models of mixing in which atomic motion occurs in the cooling phase of thermal spikes. We identify the thermal spikes with subcascades, rather than with the primary ion cascade and we tentatively attribute the enhanced mixing caused by Xe and Sm ions to overlapping of the subcascades in the primary cascade formed by these ions. © 1986 Elsevier Science Publishers B. V. (North-Holland Physics Publishing Division).