Benefits and Possibilities of Cc–Correction for TEM / STEM

During the last decade aberration correction became possible for several types of electron optical instruments. Correctors for the spherical aberration of TEM / STEM objective lenses are now commercially available [1,2]. In case of the SEM [3] and the LEEM / PEEM [4] the correction of both the spherical and the chromatic aberration has been demonstrated in experiments. In spite of these great advancements aberration correction for TEM / STEM is still restricted to the spherical aberration. An improvement of the information limit by Cc–correction for the TEM / STEM has not yet been demonstrated. For a Cs–corrected 200kV FEG–TEM equipped with a hexapole corrector an information limit of d = 0.12 nm has been measured. For such an instrument the information limit is determined both by the chromatic aberration of the objective lens and that of the hexapole corrector. In order to reach this limit a very accurate alignment and a sufficient mechanical and electrical stability of the microscope are necessary. For a thin phase object the chromatic information limit can be quantified by a visibility criterion based on the chromatic envelope of the contrast transfer function