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

Abstract

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 regime 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 nm) bilayer films were deposited onto an SiO 2 substrate at 30–80°C in a high vacuum by alternating electron-beam evaporation. Two Pd layers of a thickness 1 nm were embedded as marker layers by thermal evaporation during the preparation of the bilayer film. The prepared film was irradiated by 80 keV Ar + with a dose of 1.5×10 16 ions/cm 2 in the substrate temperature range 77–570 K. The amount of atomic transport of the constituent elements and the shifts in position of the Pd markers were evaluated by Rutherford backscattering spectroscopy. The atomic flux ratio ( J Co/ J Pt) was found to be ∼1 and ∼5 at 77 K and 570 K, respectively. The measured atomic flux ratio is compared with the theoretical value based on our proposed model which describes the atomic transport in terms of the difference in cohesive energies.