The structures of nickel decorated cavities and Ni precipitates epitaxially grown in the nanocavity band in separation by implantation of oxygen (SIMOX) are studied. The nanocavities are generated in the silicon substrate of the SIMOX wafer by proton implantation followed by Ni implantation into the Si overlayer. Channeling Rutherford backscattering spectrometry results indicate that Ni implantation changes the crystalline Si overlayer into amorphous Si. After annealing at 1000 degrees C for 2 h, the amorphous Si evolves into a polycrystalline structure composed of NiSi2 and polycrystalline silicon. In the meantime, most of the nickel atoms diffuse through the buried oxide layer and are gettered by the nanocavity band. NiSi2 precipitates are observed both in the nanocavities and at the residual defects created by H implantation. The microstructure of the Ni precipitate depends on whether there are cavities nearby. Without cavities in the vicinity, dislocations are observed in the neighborhood of the precipitate, whereas no dislocation is detected around the precipitate when there are nanocavities in the neighborhood. The precipitation and gettering behavior can be explained by the gettering of Si interstitials to the microcavities and lowering of the nucleation barrier.