Relationship between neutron reflectivity, electrical resistance, stress, and embrittlement in reactively sputtered Ni/Ti multilayers and supermirrors

Abstract

Ni/Ti supermirrors, multilayers and single films of Ni were investigated to enhance neutron reflectivity of the mirrors while retaining their mechanical stability. The neutron reflectivity of the Ni/Ti mirrors was enhanced by reactively sputtering the Ni layers in synthetic air. The mirrors sputtered at partial pressures of air p(air) >= 0.11 X 10(-3) mbar showed low interface roughness and embrittlernent. Electrical resistance measurements were carried out on the mirrors, multilayers and single films. The sheet resistance of [Ni(50 angstrom)/Ti(50 angstrom)](20) multilayers as a function of p(air) showed a change of slope, whereas the sheet resistance of Ni(1000 angstrom) films showed a step-like behaviour in the range 0.1 X 10(-3) mbar < p(air) < 0.25 x 10(-3) mbar. Stress in the samples displayed either compressive to tensile transition or tensile to compressive transition around p(air) = 0.1 x 10(-3) mbar. All the behaviours mentioned above are due to the interstitial occupancy of the reactive gas atoms used for the sputtering of the Ni layers. (c) 2006 Elsevier B.V. All rights reserved.