Quantification of irradiation damage generated during HRTEM with 1250 keV electrons

We introduce a method to quantify the extend to which HRTEM imaging with high-energy electrons damages the specimen. The method rests on digital comparison of images recorded at increasing beam exposure times but otherwise constant conditions. Difference images we calculate from these original images reveal whether damaging preferentially occurs at extended defects like internal interfaces. Further image analysis allows us to estimate how long one may image the specimen before irradiation damage interferes with solving the specimen structure at a given level of confidence. We demonstrate the usefulness of the method by applying it to HRTEM images of two types of interfaces: the interface between Cu and sapphire, and the Σ3 (111) twin boundary in NiAl, both imaged in a high voltage high resolution microscope operating with 1250 keV electrons. From our results we conclude that under these conditions HRTEM images of the two interfaces should be recorded during the first 10 min of observation in order to avoid irradiation-related artifacts in structure analysis.