Molecular-dynamics study of compressive stress generation

The relationship between the ion-beam energy and the stress in thin carbon films is studied using two-dimensional molecular-dynamics simulations. In agreement with experiment, a transition is seen from tensile to compressive stress with increasing ion energy. The compressive stress reaches a maximum near 30 eV, after which it slowly decreases. A significant result of the simulations is that the compressive stress does not arise from the implantation of ions beneath the surface layer as has been previously proposed, rather, incident ions are incorporated into growing surface layers. Animation sequences of the impact process also provide detailed insight into the film growth mechanism.