Unprecedented Severe Atomic Redistribution in Germanium Induced by MeV Self-Irradiation

We present a pronounced unprecedented surface modification of a crystalline Ge layer under heavy ion irradiation with a Ge ion beam at high energy of 2.5 MeV. Under the irradiation conditions, the Ge layer did not become porous as observed for other projectiles and lower energies but develops into an uneven ripple morphology in which the roughness monotonically increases with the irradiation doses. We show that this phenomenon is caused neither by surface erosion effect nor by a non-uniform volumetric expansion. Rather, atomic redistribution in the bulk of the material is the only drive for the ripple surface. Furthermore, the deformation of the Ge layer likely occurs to largest extend after irradiation, as indicated by the very flat interface around the end-of-range region. The observed morphology modification is discussed based on irradiation-induced plastic flow, coupled with a larger contribution of the electronic component in the ion-solid interactions.