Abstract
According to the theorem of reciprocity, as related to STEM and CTEM images, identical images should be formed under equivalent operating conditions in the two modes of microscopy. Experimental results have shown this to be generally true for diffraction contrast images. The electron optical parameters are such that higher resolution is usually achieved in CTEM, and the advantages of image processing and increased sample penetration are realized in STEM. Electron diffraction patterns can be obtained by both, with better angular resolution in CTEM and very small selected areas (< 25 Å) attainable in STEM. The equivalence of phase contrast images has been demonstrated by means of Fresnel diffraction and lattice plane images. All the STEM results reported have been obtained using high brightness field emission or LaB6 guns. Incident probe coherence and poor signal/noise have effectively excluded the use of conventional tungsten hair-pin sources.
Published Version
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