Ion beam induced collisional mixing of interfaces

We have studied collisional mixing of bilayer sample interfaces bombarded with high energy projectiles. Our model is based on the use of mass balance equation to calculate concentration changes and on the Monte Carlo simulations to calculate the relocation cross sections describing the recoils leaving and arriving at certain depth element. Monte Carlo simulations were done for static concentration profiles described by complementary error function. Differential cross sections corresponding to the dynamically changing concentration were obtained from static results by interpolation and the total cross sections were scaled according to only concentration dependent recoil density ratio. The model is used to calculate the mixing rate of Au-Ti, Pt-Pd and W-Mo interfaces located at a depth of 50 nm and mixed with 600 keV Xe, and Cu-Bi interface (depth 120 nm) mixed with 1 MeV Kr-ions. Mixing is calculated up to fluence (1.0-0.6)x1016 at./cm2. In all cases evolution of the profiles can be described with complementary error function. Calculated mixing rates are in the range (1.3-2.1) nm4 and the corresponding mixing efficiencies are (0.32-0.65) nm5/keV. The calculated examples indicate that collisional mixing is adequate in explaining the mixing rates of low or zero heat of mixing systems mixed at low temperatures. (orig.)