Study of reactively sputtered nickel nitride thin films

Nickel nitride (Ni–N) thin film samples were deposited using reactive magnetron sputtering process utilizing the different partial flow of N2 (RN2). They were characterized using x-ray reflectivity (XRR), x-ray diffraction (XRD) and x-ray absorption near-edge spectroscopy (XANES) taken at N K-edge and Ni L-edges. From XRR measurements, we find that the deposition rate and the density of Ni–N films decrease due to successively progression in RN2, signifying that Ni–N alloys and compounds are forming both at Ni target surface and also within the thin film samples. The crystal structure obtained from XRD measurements suggest an evolution of different Ni–N compounds given by: Ni, Ni(N), Ni4N, Ni3N, and Ni2N with a gradual rise in RN2. XANES measurements further confirm these phases, in agreement with XRD results. Polarized neutron reflectivity measurements were performed to probe the magnetization, and it was found Ni–N thin films become non-magnetic even when N incorporation increases beyond few at.%. Overall growth behavior of Ni–N samples has been compared with that of rather well-known Fe–N and Co–N systems, yielding similarities and differences among them.