Features of Defect Formation in Nanostructured Silicon under Ion Irradiation

Nanostructured silicon is irradiated by Si⁺ and He⁺ ions with energies of 200 and 150 keV, respectively. Destruction of the structure of irradiated samples and the accumulation of defects at different irradiation fluences are investigated by Raman scattering. It is shown that single-crystal silicon films are amorphized under irradiation at 0.7 displacements per atom. However, at 0.5 displacements per atom, porous silicon does not completely amorphize and the Raman spectra contain a weak signal of the amorphous silicon phase along with a pronounced signal of the crystalline silicon phase. The size of nanocrystals in the structure of porous silicon at different irradiation fluences is estimated.