Abstract
Vacancy loop formation in cascades formed during heavy-ion irradiation of the h.c.p. metal ruthenium at room temperature has been investigated by transmission electron microscopy. The ion energy and the ion mass were varied between 10 and 100 keV and 84 (Kr+) to 184 (W+) respectively to produce a wide variety of cascade morphologies. Information about the cascade collapse process has been obtained from the measurement of defect yield and cascade efficiency values. The former defines the probability that an incident ion forms a visible loop, and the latter the proportion of vacancies per cascade that remain in the form of a dislocation loop. The defect yield increases with increasing ion energy and has a complex dependence on ion mass, first increasing and then decreasing with increasing mass at low and high energies respectively. Cascade efficiency is not as complex and increases with increasing ion mass and decreasing ion energy. These effects have been interpreted in terms of current cascade collapse models and, in particular, the importance of subcascade formation is highlighted. Finally, a comparison of these data with those from similar self-ion irradiations in other crystal structures has been made.