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A Fourier approach to optical shadowing with a transmission electron microscope
Author(s) -
Scales Donald J.
Publication year - 1974
Publication title -
journal of microscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.569
H-Index - 111
eISSN - 1365-2818
pISSN - 0022-2720
DOI - 10.1111/j.1365-2818.1974.tb03965.x
Subject(s) - optics , image formation , fourier transform , physics , diffraction , microscope , aperture (computer memory) , ptychography , computer science , image (mathematics) , computer vision , acoustics , quantum mechanics
SUMMARY Optical shadowing offers the possibility of combining the high resolution of the transmission electron microscope with the study of surface detail, commonly investigated with the scanning electron microscope. Image formation in this mode of operation is treated according to the formalism of Fourier optics, where we consider the objective aperture to be a spatial filter in a coherent imaging system. For a simple specimen it is shown theoretically as well as experimentally that the image appears to be a shadowed representation of the object, when the objective aperture is moved off centre so that half of the zero‐order diffraction spot is blocked. A computer model is presented that gives a faithful description of the theoretical and experimental image intensity profile for the simple test specimen. The computer model is then used to predict image profiles for more complicated (or more realistic) specimen profiles. The calculations show that a certain ambiguity arises when one attempts to interpret the optically‐shadowed image profiles: it would be difficult to distinguish the three different edge contours based only on their appearance in this mode of operation. As with any other EM technique, then, results obtained with optical shadowing must be compared with the results obtained using the others.