A review of in situ observation of defect production with energetic heavy ions

In situ transmission electron microscopy (TEM) observation of radiation damage with energetic heavy ions has been a powerful tool for the study of radiation effects since it provides means to observe evolution of cascade damage. The objective of the present paper is to summarize the status of this experimental technique, its major achievement and current problems and to suggest the future directions. Defect accumulation by irradiation with energetic heavy particles is quite different from that with electron irradiation. Spatial and temporal fluctuations occur in defect production and annihilation. These observations will be summarized together with the dependence of damage evolution on irradiation temperature, target materials, incident ions and specimen geometry. Self ion irradiation is particularly useful for the study of cascade damage. Successful results of self ion irradiation for ion-neutron correlation will be presented. The experimental issues in such in situ heavy ion radiation damage studies are that the samples have to be thin enough to be transparent to the TEM electrons and that the range of self ions to simulate a primary knock-on atom (PKA) is generally short. Moreover, damage distribution is strongly depth-dependent. We have been purposely utilizing 'thin foils', taking advantage of the strong sink effect of surfaces for mobile point defects. The issues will be discussed in terms of the potential use of this technique to derive cascade damage characteristics in the bulk. Additional techniques such as computer simulation of cascade should be incorporated in conjunction with the experiment in order to develop models of defect production, annihilation and evolution. Prospect of the experimental technique will be discussed. (C) 1997 Elsevier Science B.V.