EVALUATION OF THE ANALYTICAL AND IMAGING PERFORMANCES OF A NON-DEDICATED TEM EQUIPPED WITH A PARALLEL ELECTRON-ENERGY-LOSS SPECTROMETER (PEELS) AND IMAGE FILTER (IF)

We have measured the energy resolution and the spatial resolution usin g energy filtering in a non-dedicated cryo-TEM (JEOL 1200EX II), equip ped with a PEELS (Gatan 666-9000) and IF (GIF-100). The energy resolut ion was 0.8 eV and 1.3 eV at emission current of 2 mu A and 8 mu A res pectively. For measuring the spatial resolution, the samples under stu dy have been ferritin molecules spread over mica and thin sections of molecular ferritin crystals embedded in plastic. Each ferritin molecul e contains 4000-5000 atoms of Fe in his inorganic core of 6 to 7 nm of diameter, thus being an ideal standard for sensitivity and spatial re solution in analytical electron microscopy. The theoretical spatial re solution calculated using the Krivanek expression (Krivanek et al., 19 95b) was 2 nm for an optimal collecting angle of 3 mrad in the region of M-2,M-3 ionization edge of Fe. For computing the Fe elemental maps, we have used the three-windows method for background removal. In spre ad ferritin molecules, micro crystals 2 to 4 nm in diameter were visib le in the ferric core in the Fe M-2,M-3 post-edge filtered image and i n the Fe map. In the sections of molecular ferritin crystals the spati al image resolution can be more objective computed across the Fourier analysis of the crystals. We have measured a resolution of 3.35 nm in both post-edge and Fe map. We conclude that our non-dedicated TEM can be used for PEELS micro analytical studies with performances near to t he theoretical ones.