Radiation defect dynamics studied by pulsed ion beams

The formation of stable radiation damage in solids often proceeds via complex dynamic annealing processes, involving migration and interaction of ballistically-generated point defects. Our current understanding of the underlying physics is still not sufficient for predicting radiation damage even for Si, which is arguably the simplest and most extensively studied material. The complexity of radiation damage is closely related to radiation defect dynamics. Here, we demonstrate how defect interaction dynamics can be studied by pulsed beam irradiation when the total ion fluence is split into a train of equal square pulses. By varying the passive portion of the beam duty cycle, we measure a characteristic time constant of dynamic annealing and, hence, the defect relaxation rate. Measurements of stable lattice disorder as a function of the active portion of the beam duty cycle give an effective defect diffusion length. We illustrate the pulsed beam method with examples for Si bombarded at 100 °C with 500 keV Ar ions.