RESONANT X-RAY REFLECTIVITY MEASUREMENTS OF A NI/FE ALLOY THIN-FILM - A COMPOSITION PROFILE

We have measured the composition profile of a Ni/Fe permalloy (0.8 Ni/0.2 Fe) thin film using glancing incidence X-ray reflectivity. Resonant reflectivity measurements were carried out by tuning the X-ray energy below and above, close and away from the respective K-edges of Fe and Ni. The information obtained using this method allows a determination of not only the electron density but also the composition profiles of the Ni/Fe alloy thin film. This non-destructive technique is a promising tool for the determination of the chemical composition of thin film. We used a matrix formalism to describe the wave propagation in a continuous medium. In our calculations, we used linear segments to approach the local electron density profile at the interfaces and Gaussian factors to account for the rms(root mean squre) roughness due to irregularities in the boundary position. We were able to obtain excellent fits to the data and get consistent geometry and composition parameters from the reflectivity measurements at five different X-ray energies. We detected oxidation layers on the top surface and between the alloy thin film and the substrate. We observed also that the Ni/Fe composition at the interfaces deviate from that of the bulk of the thin film sample.