Image Localization: Imaging Conditions

摘要

The study of localized phenomena, defect structures, relaxations, surface impurities, etc., all require the ability to resolve small deviations from equilibrium (average) positions of the atoms. Thus, a useful HREM image must have the property of being a one-to-one mapping of the atomic columns in the image to those in the specimen. This localization of the image depends on the imaging parameters of the microscope and on the spatial frequency of the information (1). Therefore, each microscope should be calibrated for the imaging conditions under which the maximum localisation of the information of any given spatial frequency is obtained. We have done this for the Hitachi H-9000 HREM which is operated typically at 300 kV, with a Cs of 0.9 and a focal spread of approximately 80 A (fwhm).