Lattice strain in sputter-deposited Fe-N-Si films: effects of interstitial mobility

Fe-N-Si films have been sputter-deposited in flowing nitrogen (0.3 sccm). Asymmetric X-ray diffraction from the as-deposited films reveals interplanar spacings d_hkl that are strong functions of diffracting plane orientation θ relative to the film surface and follow d_hkl^obs(θ)=⟨d_hkl^obs ⟩+Δd_hkl^obs cos 2θ. The sign of Δd_hkl^obs suggests a strong biaxial compressive stress in the film plane. The θ-dependent part of d ₂₀₀ is observed to be twice what it should be compared to that of d₁₁₀ based on a simple elastic analysis. By taking account of the mobility of the nitrogen interstitials, the d₂₀₀ and d₁₁₀ data become consistent, provided 10% of the nitrogen concentration in the films (10.1 atomic %) is mobile