Characterization of magnetron-sputtered ε iron-nitride films

Abstract

Iron nitride films of 250–450 nm thickness were produced over a wide range of compositions by reactive magnetron sputtering. These films were analyzed by a combination of conversion electron Mössbauer spectroscopy (CEMS), Rutherford backscattering spectrometry (RBS), resonant nuclear reaction analysis (RNRA) and X-ray diffraction. The iron and nitrogen concentration profiles and thus the compositions of the samples were determined by RBS and RNRA. With the known dependence of the lattice constant on the nitrogen content for the ε-Fe 2N 1− z nitride it was also possible to determine the composition via the analysis of the X-ray diffraction pattern. For ε-Fe 2N 1− z (0 ⩽ z ⩽ 0.33) the CEMS spectra could be well resolved in terms of different iron sites (environments), enabling an accurate determination of the nitrogen content in the 150 nm sampling range near the surface. It has been confirmed experimentally that the paramagnetic ε-Fe 2N 1− z phase with z ⩽ 0.13 also has two different iron sites. Thus it was possible to compare the compositions obtained by the four different methods. For the hexagonal ε iron-nitride phase, Mössbauer spectroscopy proves that it experiences an ordering of the nitrogen atoms on the interstitial sites.