Mechanical and structural properties of Ni/Ti multilayers and films: An application to neutron supermirrors

Multilayers containing Ni and Ti have been investigated for their applicati ons in neutron-optical devices. These multilayers exhibit low neutron refle ctivity when sputtered in Ar owing to large interface roughness and interdi ffusion. While attempting to improve the interface smoothness by reactive s puttering of Ni in partial pressures of Ar and air, stress and embrittlemen t develops. Stress and x-ray diffraction measurements on Ni films and multi layers reveal a transition that is attributed to the occupancy of the inter stitial sites by nitrogen and oxygen atoms. After identifying appropriate s puttering conditions so as to keep both macroscopic and local stresses with in a tolerable limit, we have successfully prepared several supermirrors ha ving 600-1200 layers yielding critical angles of reflection from 3.65 to 4. 15 times that of bulk Ni. (C) 1998 American Institute of Physics. [S0021-89 79(98)00824-X].