Use of anomalous scattering for synchrotron X-ray reflectivity studies of Fe-Cr and Co-Cu double layers

Double layers of Fe-Cr and Co-Cu, respectively, were prepared on oxidized Si substrates by pulsed laser deposition (PLD). The interfacial roughness structure was studied by synchrotron X-ray reflectivity measurements at the absorption K-edges using the contrast enhancement due to resonant scattering. The results are determined from simulations of the measured specular and diffuse scans. Whereas in Fe-Cr double layers the rms-interface width for Fe deposition on Cr (sigma_Cr = 0.70 ± 0.1 nm) is not very different from that of Cr deposition on Fe (sigma_Fe = 0.85 ± 0.1 nm), in Co-Cu double layers, in contrast, for Cu deposition on Co, the width (sigma_Co = 0.65 ± 0.1 nm) is much smaller than for Co deposition on Cu (sigma_Cu = 1.5 ± 0.15 nm). On the basis of the fractal model to describe the interface roughness morphology, from the off-specular scans the lateral roughness correlation length, xi, and the roughness exponent, h, were determined. For both types of double layers extremely high xi-values (larger than 2 µm) were found. However, the flatness is accompanied by a high short-scale roughness (jaggedness), expressed by a small h-parameter (h = 0.25 ± 0.05). Both facts were found to be characteristic for the 'as-deposited' state of such metal/metal layers prepared by PLD.