The evolution of radiation defects after the thermalization of collision cascades often plays the dominant role in the formation of stable radiation disorder in crystalline solids of interest to electronics and nuclear materials applications. Here, we explore a pulsed-ion-beam method to study defect interaction dynamics in Si crystals bombarded at room temperature with 500 keV Ne, Ar, Kr, and Xe ions. The effective time constant of defect interaction is measured directly by studying the dependence of lattice disorder, monitored by ion channeling, on the passive part of the beam duty cycle. The effective defect diffusion length is revealed by the dependence of damage on the active part of the beam duty cycle. Results show that the defect relaxation behavior obeys a second order kinetic process for all the cases studied, with a time constant in the range of ∼4–13 ms and a diffusion length of ∼15–50 nm. Both radiation dynamics parameters (the time constant and diffusion length) are essentially independent of the maximum instantaneous dose rate, total ion dose, and dopant concentration within the ranges studied. However, both the time constant and diffusion length increase with increasing ion mass. This demonstrates that the density of collision cascades influences not only defect production and annealing efficiencies but also the defect interaction dynamics.

Above room temperature, the accumulation of radiation damage in 3C-SiC is strongly influenced by dynamic defect interaction processes and remains poorly understood. Here, we use a combination of ion channeling and transmission electron microscopy to study lattice disorder in 3C-SiC irradiated with 500 keV Ar ions in the temperature range of 25–250 °C. Results reveal sigmoidal damage buildup for all the temperatures studied. For 150 °C and below, the damage level monotonically increases with ion dose up to amorphization. Starting at 200 °C, the shape of damage–depth profiles becomes anomalous, with the damage peak narrowing and moving to larger depths and an additional shoulder forming close to the ion end of range. As a result, damage buildup curves for 200 and 250 °C exhibit an anomalous two-step shape, with a damage saturation stage followed by rapid amorphization above a critical ion dose, suggesting a nucleation-limited amorphization behavior. Despite their complexity, all damage buildup curves are well described by a phenomenological model based on an assumption of a linear dependence of the effective amorphization cross section on ion dose. In contrast to the results of previous studies, 3C-SiC can be amorphized by bombardment with 500 keV Ar ions even at 250 °C with a relatively large dose rate of ∼2×1013 cm−2 s−1, revealing a dominant role of defect interaction dynamics at elevated temperatures.

Carbon nanoscrolls (CNSs), a graphitic structure formed by rolling of a graphene plane, must overcome an energy barrier in order to form. This energy barrier is the result of competing interactions between the van der Waals force, which wants to cause overlap of the graphene and the torsional or bending force which resists bending of the graphene plane. In this study we used molecular dynamics simulation to examine the effect of vacancies on the CNS formation dynamics. We found that the energy barrier, which must be overcome to obtain a stable scroll structure, can be lowered or completely eliminated by introducing vacancies. Individual vacancy and divacancy configurations are studied and found to reduce the torsional bending energy by allowing local stress relaxation around the defect site. A structural transition diagram is created in which we show the energy barrier height for a range of vacancy concentrations and CNS rolling widths. These results provide the theoretical backing for a new method of fabricating CNSs using a focused ion beam and shed new light on the self-rolling phenomenon in graphene.