X-ray-diffraction studies of Co/Re superlattices

Abstract

The structural properties of sputtered Co/Re equal-thickness superlattices and several Co/Re bilayer films have been investigated using x-ray diffraction. Low-angle x-ray-reflectvity data have been analyzed using an optical model which includes both interfacial mixing and discrete layer-thickness fluctuations. The fits to the bilayer reflectivity data indicate that interfacial mixing is limited to ∼2–3 monolayers for Re deposited on Co, and that a very sharp interface is found for Co deposited on Re. Such an asymmetric interfacial configuration has been confirmed by the fitted results from the superlattice reflectivity data. Somewhat larger average intermixing widths (∼3–5 monolayers) are found in the superlattices and are attributed to the cumulatively increased layer roughness with increasing layer distance from the substrate. High-angle x-ray-diffraction data show that superlattice films have coherent interfaces and a highly textured structure with hcp [002] orientations normal to the plane for periods 41≤Λ≤220 Å. Detailed structures have been determined by fitting the x-ray-diffraction spectra to calculated spectra using a trapezoidal model which considers crystalline multilayer films having extended interfaces with linear composition profiles. The fitted results of the high-angle diffraction spectra are in good agreement with the results obtained from the reflectivity data. In addition, an out-of-plane expansion of the Co(002) layer is observed in all samples and is interpreted to be a consequence of structural disorder which leads to a slightly reduced atomic density.