Tailoring of multilayer interfaces by pulsed laser irradiation

Multilayers (MLs) consisting of a few nm thick alternating layers of two different materials are broadly used in soft X-ray optics and in giant magnetoresistance (GMR) sensors. The efficiency of ML-based devices depends on the quality and thermal stability of the interfaces, which must be sharp at the nm scale. It is shown that, using heating with excimer laser pulses of 30 ns and fluence of approximately 0.1 J cm−2, the diffusion length for one laser pulse in the above mentioned MLs is in the region of nanometers, i.e. it closely matches the thickness of the ML sublayers. Therefore, pulsed laser induced diffusion can be used for controlled manipulation and tailoring of ML interface properties. Depending on the miscibility or immiscibility of the ML material combinations, the interfaces could be intermixed or even sharpened, which is attributed to the backdiffusion process. These phenomena are demonstrated for various combinations of ML building layers, like W/Si, Co/Ag, Fe/W and Co/W. The experimental samples were analyzed by X-ray reflectivity and X-ray diffuse scattering, combined with TEM.