Dependence of heavy-ion-induced adhesion on energy loss and time

The ability of heavy-ion beams to enhance the adhesion of thin metallic films to substrates has been studied as a function of projectile species. Measurements of the adhesion enhancement of a thin gold film to substrates of tantalum and silicon (with native oxides) have been made for beams of 12C, 16O, 28Si, 35Cl, and 58Ni at 2.85 MeV/nucleon. The threshold dose required to pass the Scotch tape peel test was found for the Au-Ta system to be Dth (cm-2) = 1017 (dE/dx)/sup -3.0 plus-or-minus 0.2/ where dE/dx is the electronic stopping power (MeV mg-1 cm2) of the ion in Au. For the Au--Si system, Dth = 6 x 1018 (dE/dx)/sup -4.1 plus-or-minus 0.3/. The steep dependence of Dth on dE/dx found here is in contrast with an earlier measurement for the Au--Ta system by Tombrello et al. The adhesion enhancement was observed to decrease with time after the bombardment in a manner suggesting that diffusion of atoms through the gold film is important. The possible importance of small concentrations of extraneous atoms at the interface is discussed