... series of post-specimen lenses. The objective lens produces the first image of the object and is, therefore, required to be the most perfect of the lenses. Depending on how the beams reaching the ... discussion of the analysis of diffraction effects is well beyond the scope of this book. Some notion of the correlation between structure and diffraction patterns can be gained from the model of thin ... time one of the diffracted beams is chosen by means of an aperture that blocks the central beam and the other diffracted beams. The micrograph of alternating 40 A-wide films in the GaAs-Al,,,Ga,~,As...