Deformation during surface modification of silicon carbide using rare-gas ion-beam irradiation

Surface shape modification of silicon carbide (SiC) as induced by swelling resulting from irradiation has been studied using helium (He) ion irradiation (similar to2x10(21) He/m(2)) at room temperature. Using a mask (TEM-mesh) containing an array of microscopic holes, an array of bumps, resulting from near-surface swelling, was produced on the surface of SiC. The exterior appearance of these bumps is smooth with no evidence of blistering or cracking, even when calculated swelling values are greater than 10%(1.2). The fact that these bumps are free of cracks and blistering phenomenon is welcome but surprising because the irradiated regions are confined in their deformation by the surrounding unirradiated regions. The aim of the present study is to consider some possible deformation mechanisms that could allow these bumps to form without cracking or blistering and also to investigate the dependence of swelling on mask hole-size and the projected-range of He-ions. In this study, accommodation deformation of SiC during He-ion irradiation was simulated using finite element modeling (FEM). Elastic deformation and irradiation induced creep provided the accommodation deformation. When using only elasticity to provide the accommodation deformation, the calculated stresses at the vicinity of the boundary between the irradiated and the unirradiated region were much higher than the fracture stress of SiC. However, when elasticity and irradiation creep provided the accommodation deformation, the stresses were below the fracture stress. Swelling increased with increasing the mask hole-size, and the effect of the projected range was varied with the mask hole-size when irradiation enhanced creep was introduced into the FEM model.