The microstructure of 5 MeV ion implanted silicon at room temperature has been investigated in detail by means of cross-sectional transmission electron microscopy. Buried amorphous layers were observed in the specimens obtained by ion doses of 1×1017and 2×1017/cm2with abrupt amorphous-to-crystal interfaces. Damaged layers adjacent to the amorphous layers included many dislocation loops and the concentration increased toward the amorphous region. Microdiffraction patterns and high-resolution images showed that this damaged region is defective crystalline silicon, suggesting that homogeneous amorphization occurs due to an accumulation of defects. The atomistic structure of the damaged regions was analyzed by comparing high-resolution electron microscopy images with those calculated on the basis of a model for amorphization processes proposed previously [T. Motooka, Phys. Rev. B49, 16 367 (1994)]. ©1997 American Institute of Physics.