Compositional distributions in nanoscale metallic multilayers studied using x-ray mapping

At very small layer spacings (< -2 nm) in Cu-Nb and Cu-Cr multilayers the Cu forms a metastable body-centered-cubic (bcc) structure and the films exhibit interesting mechanical properties. No information about the miscibility of bcc Cu in Nb or Cr is available and it is not known whether the films remain compositionally discrete. X-ray mapping in the analytical electron microscope has been used to study the compositional distributions in these films and show that they do remain discrete down to a layer spacing of 1.8 nm. A simple model for the experimentally measured distribution has been used to show that the expected analytical resolution has been achieved and that it should be possible to map layers with a spacing of 0.8 nm.