Effect of cohesive energy on atomic transport in ion beam mixed Co/Pt bilayer film

A Co/Pt bilayer was chosen to study the effect of cohesive energy on atomic transport induced by ion beam mixing in a radiation enhanced diffusion reg ime without a thermochemical driving force. because of the large difference in mass and cohesive energy between Co and Pt, and the nearly zero heat of mixing. Pt(29 nm)/Co(40 nmn) bilayer films were deposited onto an SiO2 sub strate at 30-80 degrees C in a high vacuum by alternating electron-beam eva poration. Two Pd layers of a thickiness 1 nm were embedded as marker layers by thermal evaporation during the preparation of the bilayer film. The pre pared film was irradiated by 80 keV Ar+ with a dose of 1.5 x 10(16) ions/cm (2) in the substrate temperature range 77-570 K. The amount of atomic trans port of the constituent elements and the shifts in position of the Pd marke rs were evaluated by Rutherford backscattering spectroscopy. The atomic flu x ratio (J(Co)/J(Pt)) was found to be similar to 1 and similar to 5 at 77 K and 570 K, respectively. The measured atomic flux ratio is compared with t he theoretical value based on our proposed model which describes the atomic transport in terms of the difference in cohesive energies. (C) 1999 Elsevi er Science S.A. All rights reserved.