Enhancement in Energy Loss of MeV Silicon Clusters in C Films

Energy losses of 0.63-1.03MeV/atom Si_n (n ≤ 3) clusters in thin carbon films (2-12μg/cm²) have been measured by using a special experimental setup with Rutherford backscattering (RBS) technique. The experimental results show that for a given energy per atom, the energy loss of Si⁺₂ ions, as well as Si⁺₃ ions, is significantly larger than that of Si⁺ ions. This is the first observation of energy loss enhancement in the measurements with RBS technique. The enhancement in energy loss (i.e. the cluster effect) is evident when the effective thickness of the carbon target is thin enough, but not evident when it is thick. The effect will not be obvious until the energy of the projectile is over a certain limit for a special target. This suggests that the cluster effect only occurs in the first layers of the target film, and that the energy of the projectile must be large enough for the effect to be seen.