Microscopic examination of the silicon surface subjected to high-dose silver implantation

Low-energy ($E$ = 30 keV) Ag$^+$ ions have been implanted into single-crystalline Si wafers ($c$-Si) with an implantation dose varying from 1.25 $\times$ 10$^{15}$ to 1.5 $\times$ 10$^{17}$ ions cm$^{-2}$ and an ion beam current density varying from 2 to 15 $\mu$A/cm$^2$. The surface morphology of implanted wafers has been examined using scanning electron microscopy, transmission electron microscopy, and atomic force microscopy, and their structure has been studied by means of reflection high-energy electron diffraction and elemental microanalysis. It has been shown that for minimal irradiation doses used in experiments, the surface layer of $c$-Si experiences amorphization. It has been found that when the implantation dose is in excess of the threshold value ($\sim$3.1 $\times$ 10$^{15}$ ions cm$^{-2}$), Ag nanoparticles uniformly distributed over the Si surface arise in the irradiated Si layer. At a dose exceeding 10$^{17}$ ions cm$^{-2}$, a porous Si structure is observed. In this case, the Ag nanoparticle size distribution becomes bimodal with coarse particles localized at the walls of Si pores.