Reduction of the interfacial diffusion in Ni-Ti neutron-optics multilayers by carburation of the Ni-Ti interfaces

It is shown that it is possible to reduce both interfacial diffusion and interfacial roughness in neutron-optics Ni-Ti multilayered monochromators. This is achieved by the deposition of an ultrathin layer of carbon at the Ni-Ti interfaces. A comparison between treated Ni-Ti multilayers and an untreated one was performed by grazing-angle neutron reflectometry and completed by grazing-angle X-ray reflectometry, Auger electron spectroscopy and secondary-ion mass spectrometry. More specifically, the experimental data show that nickel diffuses into the titanium layers in the untreated multilayers. This diffusion decreases when the Ni-Ti interfaces are separated by 10 Å of carbon. Moreover, the results show that this Ni-Ti multilayer quality is better if the glass substrate is also treated with 30 Å amorphous carbon. The reflectivity of the first Bragg peak R_B(k = 1) is lower than the theoretical one (68%) but increases slightly from 18 to 25% after the carburation of the interfaces.