Stress evolution in platinum thin films during low-energy ion irradiation

Stress evolution of Pt thin films during low-energy ion irradiation is investigated by using wafer bending measurements and molecular dynamics simulations. Noble gas ions ranging in mass from He to Xe and energy from 0.5 to 5 keV are used. Depending on the type and energy of the ion, the change in stress can either be tensile or compressive. Heavier or higher-energy ions tend to create tensile stress, while lighter ions such as He always induce compressive stress. The stress evolution also depends on the initial state of stress in the thin films. The results are explained by a competition between the tensile stress induced by local melting along the ion track and the compressive stress induced by the accumulation of ion-induced interstitials in defect clusters or grain boundaries, often beyond the calculated ion penetration depth. Anisotropic diffusion of interstitials under an external stress field also plays an important role in the stress evolution. Molecular dynamics simulation is employed to evaluate the importance of each of these microscopic mechanisms.