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 RB(k = 1) is lower than the theoretical one (68%) but increases slightly from 18 to 25% after the carburation of the interfaces.
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Farnoux et al. (1993) studied this question.