Size dependence of interfacial intermixing in Fe/Si multilayer

Abstract

Size effect on interface structure in Fe/Si multilayers and interfacial phase formation as a result of thermal annealing and irradiation with high energy heavy ions has been studied, using a combination of x-ray reflectivity and depth-resolved x-ray diffraction measurements. Study using a single sample with two multilayer structures with different bilayer periods allows us to elucidate the size effects keeping the process parameters identical. In conformity with some earlier studies, in the as-deposited multilayer Fe-on-Si interface is more diffused as compared to Si-on-Fe interface. This interfacial asymmetry is found to diminish with increasing layer thicknesses. Furthermore, β-FeSi2 is formed preferentially at Fe-on-Si interface, which again is more pronounced in the low bilayer period structure as compared to the high bilayer period structure. Thermal annealing results in formation of ε-FeSi, which also preferentially forms at the Fe-on-Si interface. Difference in the structure of the interfaces in terms of concentration gradient, interfacial stresses and disorder may contribute to the observed behavior. In contrast, irradiation with heavy ions results in formation of bcc Fe(Si) alloy and β-FeSi2 phase. Intermixing is significantly stronger in the low bilayer period as compared to the high bilayer period structure. The results can be understood in terms of thermal spike model for irradiation induced modifications.