In situ transmission electron microscopy has been used to observe the production and annealing of individual amorphous zones in silicon resulting from impacts of 200-keV Xe ions at room temperature. As has been observed previously, the total amorphous volume fraction decreases over a temperature range from room temperature to approximately 500 °C. When individual amorphous zones were monitored, however, there appeared to be no correlation of the annealing temperature with initial size: zones with similar starting sizes disappeared (crystallized) at temperatures anywhere from 70 °C to more than 400 °C. Frame-by-frame analysis of video recordings revealed that the recovery of individual zones is a two-step process that occurred in a stepwise manner with changes taking place over seconds, separated by longer periods of stability.
Theoretical models are presented to explain how thermal spike processes can induce the development of preferred orientation of polycrystalline grains during ion-assisted atomic deposition and thin film growth. Two ion energy regimes are investigated. In the first, higher-energy regime, ions penetrate growing grains and generate defects at rates dependent upon the probability of ion channeling in individual grains. The volume free-energy density of different grains is, therefore, different and the thermal spike arising from each ion impact results in preferential growth of grains with the lowest volume free-energy density. In the second, lower-energy regime, ions do not penetrate nor create defects in grains but the ion-induced thermal spikes centered on the surface can enhance surface atomic migration and lead to preferential growth of grains with the lowest surface free-energy density. The results in these two regimes are compared with the predictions of a model for preferred grain orientation evolution in the absence of ion assistance and where minimization of surface free-energy density is the driving process. Ion energy, ion flux density, depositing atom flux density, and system temperature conditions are established where ion-assisted and non-ion-assisted rates of preferred grain orientation become comparable. It is shown that, in general, the tendency toward preferred orientation is not a simple function of the energy per deposited atom.
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