Cluster effects in collisional processes in a Si crystal bombarded with 10-540-keV C ions

Narumi, Kazumasa; Naramoto, Hiroshi*; Yamada, Keisuke; Chiba, Atsuya; Saito, Yuichi; Morita, Yosuke*; Nakajima, Kaoru*; Kimura, Kenji*; Maeda, Yoshihito

We have investigated cluster effects on damage accumulation and sputtering yield in bombardment of a Si crystal with 10-540-keV C ions. Fluence dependence of the areal density of displaced Si atoms can be well described by assuming a cylindrical volume affected by single-C-ion bombardment, which means an ion-track-like picture in damage accumulation in Si bombarded with keV C ions. The energy dependence of the number of displaced Si atoms by single-C-ion bombardment, N, is different from that of N by monatomic-C-ion bombardment calculated with SRIM2008. The number ratio of displaced Si atoms per C atom N/(60N) which demonstrates the magnitude of the nonlinear effect on damage in Si has shown that the effect is huge and has the maximum around 100 keV. The energy dependence of the ratio can be explained qualitatively by nuclear stopping powers and increase of internuclear distances between C atoms in Si. The sputtering yield has the maximum, ca. 600 per C ion, around 100 keV. Comparing with the monatomic-ion-induced sputtering yield predicted by the linear-cascade theory by Sigmund, nonlinear effect on sputtering yield has been found. It depends on the ion energy: It is more pronounced around the energy where the sputtering yield has the maximum and hardly observed at 10 keV. No n dependence is found, where n is the number of atoms consisting of the projectile cluster.