Characterization of the low magnification performance of a Philips CM300-FEG

The low magnification performance of a Philips CM300-FEG transmission electron microscope was characterized in three different configurations: CM30-FEG SuperTwin, CM30-FEG Twin and CM300-FEG CryoTwin. Micrographs of gold single crystal, polycrystalline gold, graphitized carbon and copper chloropthalocyanine were recorded in the magnification range 2050× – 100 000× using film as the recording medium and optical diffraction to assay image resolution. Lattice images of gold single crystals could be recorded on film with a resolution of 2.04 Å at 10 500×; copper chloropthalocyanine lattice images could be recorded with a resolution of 6 Å at 4500× and 12 Å at 2050×. This indicates that the film has a line resolution as low as 2.1 μm or 470 lines/mm. The fact that lattice images from different specimens can be recorded at this line spacing regardless of magnification suggests that film rather than the microscope is the major limitation to image resolution at low magnification. The image resolution delivered by the microscope is also ∼4× smaller than the capability of densitometers to digitize it. This suggests that there would be some benefit to digitization of micrographs at finer pixel sizes than currently possible. These observations indicate that tomography of radiation sensitive specimens, where the film is the recording medium, can be recorded at the lowest magnification consistent with digitizing capabilities and desired resolution with confidence in the microscope performance. The potential benefit lies in the possibility of obtaining more images for the same accumulated dose at low magnification and the possibility that more unit cells can be imaged both of which can contribute to the potential success of applying tomographic methods to radiation sensitive specimens.