Diffusion in multilayers

An overview on the laser induced diffusion in metallic multilayers (MLs) is given. The method of measurement is illustrated on the studies of Co/Agg bilayers, trilayers and Fe/w and Co/W multilayers for magnetoresistance sensors and of W/Si MLs for X-ray mirrors. Pulsed excimer XeCl and KrF lasers with 30 nm pulses were used. The main advantage of pulsed laser heating is low inertia of the process because the heating is restricted to the certain area of the sample. Moreover, heat is delivered reproducibly in certain quanta. Therefore, as it will be shown, the characteristic diffusion distances in MLs of only a few nm per pulse could be recorded. The laser heating was performed at flounces of 0.05 - 0.6 J/cm(2) and number of pulses up to 100. They were directed to the same site. In this paper, basic diffusion parameters for the above mentioned structures are summarized. Due to the rapid laser heating and subsequent rapid cooling, some interesting phenomena in layered structures could be observed e.g. the grain boundary diffusion with low activation energy was recorded in Co/Ag system up to the melting point of Ag. This is because the crystallization does not proceed enough fast. Moreover, for mutually immiscible combination of materials the sharpening of interfaces in MLs due to the backdiffusion effect was found.