Spatial characteristics of displacement cascades in metals

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Abstract
The binary-collision simulation code marlowe has been applied to study spatial characteristics of displacement cascades in fcc metals, particularly Cu. Mean densities of vacancies and interstitials 〈Cv〉 and 〈Ci〉 expressed in terms of radii of gyration of the defect configurations, have been determined as functions of cascade energy. In Cu, 〈Cv〉 decreases from ∼6×10−2 to ∼4×10−4 for energies between 1 and 150 keV, whereas 〈Ci〉∼3×10−3 is roughly constant at energies below 20 keV and approaches 〈Cv〉 asymptotically at higher energies. Although 〈Cv〉/〈Ci〉 decreases with energy, the mean vacancy-interstitial separation Riv is relatively constant. This result supports the classical picture of depleted zones in which increasing numbers of vacancy clusters surrounded by clouds of interstitials are formed as the energy is increased. Perspective plots of the defect configurations in individual cascades presented here also support this picture. Channeling is concluded to have a small effect on 〈Cv〉, but strongly influences the skewness of damage depth profiles. Results are presented for the cascade contraction factor δ. The tendency to form defect clusters and subcascades is discussed.