Early recrystallization of Ni/Ti multilayer due to disorder in the Ni layer

Abstract

Disorders present at the interfaces drive solid state amorphization (SSA) and recrystallization in Ni/Ti multilayers. In this communication, the effect of disorders present in the bulk Ni layers is studied on SSA and recrystallization. The disorder in the Ni layers is created by sputtering Ni layers of the Ni/Ti multilayers under the mixed ambience of argon and nitrogen. It has been observed recently that the neutron optical performances of Ni/Ti graded multilayers or supermirrors can be improved by sputtering of Ni layers under the mixed ambience of argon and nitrogen. In this work, Ni/Ti periodic multilayers deposited under pure argon ambience and under mixed ambience of argon and nitrogen have been annealed under vacuum at 200 °C, 400 °C, and 600 °C for 2 h. All the annealed multilayer samples along with as-deposited multilayers are characterized by x-ray diffraction and grazing incidence x-ray reflectivity measurements in specular and non-specular modes. Atomic diffusion within the layers and across interfaces has been studied as a function of annealing temperature for both sets of multilayers. It is found that the interstitial nitrogen atoms present in the Ni layers play a crucial role in the diffusivity at room temperature as well as high temperature and thus influence the SSA and recrystallization phenomena.