Interfacial width and asymmetry evolution in Ni/Ti periodic multilayers with varying Ni thickness and neutron supermirrors with m = 3

Abstract

Slow neutron beams are a powerful tool for scientific exploration. Despite the construction of large-scale neutron beam facilities, the intensity and brilliance of neutron sources remain significantly lower than X-rays produced by synchrotron radiation. High-performance Ni/Ti supermirrors are crucial for efficient neutron beam transport with minimal losses. In this work, the interface widths of [Ni(d nm)/Ti(6 nm)]_N periodic multilayers and an m = 3 Ni/Ti neutron supermirror, fabricated by reactive magnetron sputtering, were systematically investigated as key determinants of reflectivity. All the periodic multilayers were characterized by Grazing Incidence X-ray Reflectivity (GIXRR) and X-ray Diffraction (XRD), the experimental data were fitted by IMD software to estimate the real structure and interface width. The m = 3 neutron supermirrors were characterized by High-Resolution Transmission Electron Microscope (HRTEM), Energy Dispersive X-ray Spectroscopy (EDX), and X-ray Photoelectron Spectroscopy (XPS). Measurement results indicate that interface roughness increases with increasing layer thickness in periodic multilayers and supermirrors. Furthermore, interfacial diffusion exhibits asymmetry, with thicker interlayers forming at Ti-on-Ni interfaces than at Ni-on-Ti interfaces. N, originating from the reactive gas mixture, exhibits preferential segregation at Ti-on-Ni interfaces, resulting in higher N concentrations compared to Ni-on-Ti interfaces.