Effect of carbon on microstructure and interfaces of NiC/Ti multilayers for neutron applications

NiC/Ti and Ni/Ti multilayer samples were fabricated by direct-current (DC) magnetron sputtering technique for investigating the effects of C atoms on their microstructure, interfaces and composition. Both multilayers consist of 10-nm-thickness Ti layers and 8.5-nm-thickness Ni or NiC layers, respectively. Grazing incidence X-ray reflectivity (GIXR) was performed to characterize the layer thicknesses and interfaces of multilayers. X-ray diffraction (XRD) was utilized to characterize their crystallizations. The layer morphology of these multilayers was investigated by transmission electron microscopy (TEM), and the depth distributions of Ni, Ti and C in both multilayers were studied through energy dispersive X-ray (EDX). Finally, depth profile X-ray photoelectron spectroscopy (XPS) was used to study the chemical state of Ni, Ti, and C. The experimental results present that crystallizations of the NiC/Ti multilayer were suppressed for not only Ni layers but also for Ti layers so that its interfaces were smoother than those of the Ni/Ti multilayer. In the NiC/Ti multilayer, a high concentration of carbon at the interfaces and the existence of carbon in the Ti layers were found. These phenomena could be explained by the compound formation and resputtering effect.