Improvement of neutron reflectivity of an Ni-Ti multilayer by hydrogenation of titanium layers

This paper presents the first results confirming the improvement of the neutron reflectivity of Ni-Ti multilayer monochromators by increasing the neutron refractive-index contrast. This operation was performed by hydrogenation of titanium layers during the deposition process in the vacuum chamber. The monochromator, consisting of ten (Ni-TiHx) bilayers and produced by magnetron RF deposition was submitted to heating (to a maximum of 423 K) to study its stability. Variations in both the neutron refractive index of Ni and TiHx layers and the period of the stratified medium were observed. The neutron reflectivity at the first Bragg peak and the refractive-index contrast are better after this heating treatment relative to the Ni-Ti multilayer with the same period. The very strong hydrogen affinity of titanium facilitates the construction of this bilayer monochromator. The monochromator was studied by grazing-angle neutron reflectometry and X-ray diffraction. (orig.)