Interface and crystallization evolution induced by reactive nitrogen and oxygen sputtering in Ni/Ti multilayer

Abstract

Ni/Ti multilayers were reactively deposited with a gas mixture of Ar, N2 and O2 using the magnetron sputtering, while (N2 + O2)/Ar flow ratio during the sputtering process was varied. A detailed study on the microstructure evolution and interfacial properties was performed using grazing incidence X-ray reflectivity, X-ray diffraction, X-ray photoelectron spectroscopy, X-ray diffuse scattering, and transmission electron microscopy. With the increase in (N2 + O2)/Ar flow ratio, the grain size in Ni layers first decreases and then increases at a critical point of 25.0 %, followed with the crystal phase transforming from Ni into NiO. The mechanism of microstructure evolution in Ni layers due to N2 and O2 gas incorporation is discussed in this paper. The interfaces of Ni/Ti multilayer are smoothened due to a decrease in the size of Ni grains. Meanwhile, the interfacial effects including the vertical replication of interfacial roughness and the diffusion between adjacent Ni and Ti layers are suppressed for the N2 and O2 gas incorporation. Furthermore, the lateral correlation length of interfacial roughness varies with (N2 + O2)/Ar flow ratio, which presents the relevance with the grain size.