Damage creation in silicon single crystals irradiated with 200 keV/atom Au-n(+) clusters

Silicon wafers of (1 0 0) orientation were irradiated with Au, cluster beam s (1 less than or equal to n less than or equal to 7) produced by the 3.5 M V Van de Graaff accelerator of the Institut de Physique Nucleaire de Lyon e quipped with a liquid metal source. The incident energy was of 200 keV per gold atom, which corresponds to a slowing-down mainly governed by elastic p rocesses (nuclear energy loss of Au+ ions: 3 keV nm(-1)). All the irradiati ons were performed at room temperature with fluences up to 5 x 10(14) Au (a t. cm(-2)). The typical beam currents varied from 1.5 nA for Au' down to 20 pA for Au-7(+). The radiation-induced disorder was measured by means of Ru therford backscattering spectrometry in channeling geometry (RBS-C), using a He-4(+) beam accelerated at 2 MV. From the fluence evolution of the latti ce disorder at the target surface, we evidence that polyatomic projectiles produce more defects per incident atom than single Au' ions. As an example we measured damage cross-sections per incident Au atom of 12.5 and 2.7 nm(2 ) for Au; and Au' projectiles, respectively. This cluster effect was ascrib ed to the high density of nuclear energy deposited within the cascade. Tran smission electron microscopy (TEM) was performed on samples irradiated at l ow fluences (10(9) at. cm(=2)) in order to visualize each projectile impact . (C) 2000 Elsevier Science B.V. All rights reserved.