Study of low energy Si$_5^-$ and Cs$^-$ implantation induced   amorphization effects in Si(100)
  The damage growth and surface modifications in Si(100), induced by 25 keV Si$_5^-$ cluster ions, as a function of fluence, $\phi$, has been studied using atomic force microscopy (AFM) and channeling Rutherford backscattering spectrometry (CRBS). CRBS results indicate a nonlinear growth in damage from which it has been possible to get a threshold fluence, $\phi_0$, for amorphization as $2.5\times 10^{13}$ ions-cm$^{-2}$. For $\phi$ below $\phi_0$, a growth in damage as well as surface roughness has been observed. At a $\phi$ of $1\times 10^{14}$ ions-cm$^{-2}$, damage saturation coupled with a much reduced surface roughness has been found. In this case a power spectrum analysis of AFM data showed a significant drop, in spectral density, as compared to the same obtained for a fluence, $\phi < \phi_0$. This drop, together with damage saturation, can be correlated with a transition to a stress relaxed amorphous phase. Irradiation with similar mass Cs$^-$ ions, at the same energy and fluence, has been found to result in a reduced accumulation of defects in the near surface region leading to reduced surface features. 
H. P. Lenka, B. Joseph, P. K. Kuiri, G. Sahu, P. Mishra, D. Ghose, and   D. P. Mahapatra