Si implanted with 1014, 1015, and 5×1015 ions/cm2 of 80 KeV Xe ions was examined by electron microscopy and nuclear backscattering. Implantation created amorphous Si, which, after annealing at 700°C, transformed into single crystal material for doses ?1015/cm2 and into a heavily twinned material for the higher dose. Under suitable conditions, such implants can be used as diffusion markers in the study of surface reactions.