The Role of Ion Irradiation Induced Viscous Flow in Thin Film Structuring: Hard Matter Going Soft

Abstract

Ion beams provide unique opportunities for modifying thin film structural and mechanical properties on length scales ranging from several nanometers to macroscopic dimensions. In a variety of materials, including polycrystalline and amorphous metals and semiconductors, plastic effects can dominate, which originates from processes in the small volumes of materials affected by a single ion impact. The underlying atomic-scale kinetics as well as its applications for self-organized structuring are investigated using a combination of experiments and molecular–dynamics (MD) computer simulations: We report experiments, that illustrate the impact of radiation induced viscous flow on morphology and stresses, such as interface smoothing, stress relaxation, radiation induced sintering or self–organized pattern formation. Using MD simulations we study the underlying atomic–scale mechanisms for the two energy regimes, where local melting along the ion track is either dominant or not. We show, that macroscopic plastic flow does not require melting, indicating, that defect–like entities are sufficient to mediate plastic flow.