Analysis of irradiated Ag and Si by molecular dynamics and simulated HREM images

In order to clarify the limits of HREM observations of defects due to radiation damage, a simulation method has been designed which combines molecular dynamics and HREM simulation. Disorder due to ion irradiation in Si and Ag is simulated by using a molecular dynamics technique and HREM images are computed by a multislice dynamic procedure. The conditions to achieve a good HREM visibility of such defective structures have been investigated by analyzing the effects of the physical inputs of molecular dynamics as well as the ones of the instrumental parameters of TEM observations. This analysis indicates that the structure of the damaged region is not critical. On the contrary, the fractional disorder is of paramount importance and determines the conditions leading to an appreciable contrast of the disordered region against the crystalline background.