Compositional distributions in nanoscale metallic multilayers studied using x-ray mapping
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A. Misra, H. Kung, and T.E. Mitchell Materials Science and Technology Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (Received 25 August 2000; accepted 1 May 2001)
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.
I. INTRODUCTION
Metallic multilayer systems have been the focus of a number of investigations in recent years due to their interesting mechanical, electrical, and magnetic properties.1 For example, metallic multilayer systems show increasing strength as the layer periodicity decreases. At small layer dimensions, the Hall–Petch relationship is no longer obeyed, suggesting that different deformation mechanisms occur in these nanoscale thin films than in bulk systems.2,3 Applications for these materials are as high-strength/high-conductivity materials in high-field magnets, in load-bearing components, and in energyabsorbing applications such as body armor. Other applications of multilayered materials include wear-resistant coatings and in magnetic heads and recording media, etc. Structural investigations of systems such as Cu–Nb and Cu–Cr, where Cu is layered with a body-centeredcubic (bcc) metal, have shown that at very small layer spacings (
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