Ion irradiation-induced localized stress relaxation in W thin film revealed by cross-sectional X-ray nanodiffraction

The influence of ion irradiation on residual stress and microstructure of thin films is not fully understood. Here, 5 MeV Si2+ ions were used to irradiate a 7 µm thick tungsten film prepared by magnetron sputtering. Cross-sectional X-ray nanodiffraction and electron microscopy analyses revealed a depth-localized relaxation of in-plane compressive residual stresses from to GPa after the irradiation, which is correlated with the calculated displacements per atom within a ~2 µm thick film region. The relaxation can be explained by the irradiation-induced removal of point defects from the crystal lattice, resulting in a reduction of strains of the 3rd order, manifested by a decrease of X-ray diffraction peak broadening, an increase of peak intensities and a decrease of lattice parameter. The results indicate that ion irradiation enables control over the residual stress state at distinct depths in the material.