Inelastic Scattering and Beam Damage of Biological Molecules
There are two kinds of interactions which an incident electron can experience in traversing a thin specimen. It can be elastically scattered from the atomic nuclei without losing energy. Or it can be inelastically scattered from the atomic electrons and impart energy to the specimen. Elastic interactions are useful for high resolution imaging and produce negligible damage. Inelastic interactions, however, can result in molecular or chemical damage. This is important in biological electron microscopy, since experiments have shown that for 30 KeV electrons in carbon one gets 1.6 inelastic events for every elastic event. Moreover, this ratio increases slightly with voltage.The energy loss spectrum of electrons which have traversed thin specimens is directly related to the probability of exciting a particular electronic level.