Crystal structure and band gap of nanoscale phases of Si formed at various depths of the near-surface region of SiO$_{2}$

Si nanophases and nanolayers were obtained by bombardment with Ar$^+$ ions followed by annealing at various depths of silicon oxide. As ion energy $E_0$ varies from 10 to 25 keV, the average depth of Si nanophase formation varies from 15 to 25 nm. It is shown that, as the sizes of Si nanophases vary from $\sim$10 to 25 nm, band gap $E_g$ decreases from 1.9 to 1.5 eV. For Si nanolayers, $E_g$ is $\sim$1.1–1.2 eV.