Influence of irradiation with swift heavy ions on multilayer Si/SiO$_2$ heterostructures

The influence of Xe ions with an energy of 167 MeV and a dose in the range 10$^{12}$–3 $\cdot$ 10$^{13}$ cm$^{-2}$ on heterostructures consisting of six pairs of Si/SiO$_2$ layers with the thicknesses $\sim$ 8 and $\sim$ 10 nm, correspondingly, is studied. As follows from electron microscopy data, the irradiation breaks down the integrity of the layers. At the same time, Raman studies give evidence for the enhancement of scattering in amorphous silicon. In addition, a yellow-orange band inherent to small-size Si clusters released from SiO$_2$ appears in the photoluminescence spectra. Annealing at 800$^\circ$C recovers the SiO$_2$ network, whereas annealing at 1100$^\circ$C brings about the appearance of a more intense photoluminescence peak at $\sim$ 780 nm typical of Si nanocrystals. The 780-nm-peak intensity increases, as the irradiation dose is increased. It is thought that irradiation produces nuclei, which promote Si-nanocrystal formation upon subsequent annealing. The processes occur within the tracks due to strong heating because of ionization losses of the ions.