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

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≥0.11×10^-3 mbar showed low interface roughness and embrittlement. Electrical resistance measurements were carried out on the mirrors, multilayers and single films. The sheet resistance of [Ni(50 Å)/Ti(50 Å)]₂₀ multilayers as a function of p_air showed a change of slope, whereas the sheet resistance of Ni(1000 Å) films showed a step-like behaviour in the range 0.1×10^-3 mbar<p_air<0.25×10^-3 mbar. Stress in the samples displayed either compressive to tensile transition or tensile to compressive transition around p_air=0.1×10^-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.