A study of uranium-based multilayers: I. Fabrication and structural characterization

This paper addresses the structural characterization of a series of U/Fe, U/Co and U/Gd multilayers. X-ray reflectivity has been employed to investigate the layer thickness and roughness parameters along the growth direction and high angle diffraction measurements have been used to determine the crystal structure and orientation of the layers. For the case of uranium/transition metal systems, the interfaces are diffuse (similar to 17 angstrom) and the transition metals are present in a polycrystalline form of their common bulk phases with a preferred orientation along the closest packed planes; Fe, bcc (110) and Co, hcp (00.1), respectively. The uranium is present in a poorly crystalline orthorhombic, alpha-U state. In contrast, the U/Gd multilayers have sharp interfaces with negligible intermixing of atomic species, and have a roughness, which is strongly dependent on the gadolinium layer thickness. Diffraction spectra indicate a high degree of crystallinity in both U and Gd layers with intensities consistent with the growth of a novel hcp U phase, stabilized by the hcp gadolinium layers.