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

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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 σ rms-interface width for Fe deposition on Cr ( σ Cr=0.70±0.1 nm) is not very different from that of Cr deposition on Fe ( σ Fe=0.85±0.1 nm), in Co–Cu double layers, in contrast, for Cu deposition on Co, the width ( σ Co=0.65±0.1 nm) is much smaller than for Co deposition on Cu ( σ 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, ξ and the roughness exponent, h, were determined. For both types of double layers extremely high ξ-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.