Raman spectroscopy is used as a probe of the state of amorphous Si (a‐Si) and damaged crystalline Si. MeV ion beams have been used to irradiate structurally relaxeda‐Si. When the density of Si atoms displaced by nuclear collisions exceeds 5%, thea‐Si is ‘‘de‐relaxed’’, and thus returns to its as‐implanted state. This behavior is an indication that point defect complexes exist ina‐Si and play an important role in the process of structural relaxation.