Defect Production


Fig. 2 A schematic illustration of the physical processes occurring during the impact of an energetic ion with a solid.

the lattice atoms which produce electronic excitation and by elastic collisions which scatter the incoming ion and may displace lattice atoms from their position and produce defects (4). The resulting collision cascade affects thousands of atoms for a medium mass, 10 keV incident ion. Cascades near the surface give rise to sputtering or removal of atoms from the surface or "hot" atoms if they do not have sufficient energy to escape the binding energy of the surface.

The ion impact can interact with the film nucleation processes ¡n a number of ways such as production of nucleation sites on the surface, break-up of nuclei by sputtering or enhancement of diffusion processes by "hot" atoms, thermal spikes or increased defect populations. Film growth may be altered by break-up of columnar grain nuclei in the collision cascade, by cascade mixing which alters the growth mode (e.g., disrupts island growth), by enhanced diffusion in the defect flux etc. A number of mechanisms of interaction have been proposed but few definitive experiments have been conducted to identify the operative mechanisms.

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