Residual stress relaxation mechanism at low homologous temperature in nanocrystalline iron thin film deposited on Si (100) substrate

The effect of thermal stress and the role of defects in residual stress relaxation have been investigated in a nanocrystalline iron thin film coated on Si (1 0 0) substrate using glancing incidence x-ray diffraction (GIXRD) and depth resolved positron beam studies. The film has been annealed isothermally at a low homologous temperature of 400 K (similar to 0.2T(m)) for different time intervals. The change in residual stress, micro-strain and grain size as a function of annealing time has been deduced using GIXRD. The change in vacancy defects as a function of the annealing time has been investigated using defect-sensitive line shape S-parameter from depth-resolved positron beam studies. It is observed that the residual stress relaxes by the creation of defects at the film surface. A physical model has been proposed based on the atomic diffusion through the grain boundaries, which explains the observed results well. The proposed model confirms the residual stress relaxation by the transport of atoms and corresponding point defects between the free surface of the film and the grain boundaries indicating the stress relaxation is mediated by atomic diffusion.