Filtered electron image contrast in amorphous objects. I. Elastic scattering

A general expression of the intensity available in CTEM for each point of the image of amorphous specimens has been calculated from the point of view of the influence of the thickness of the sample, of the value of the objective aperture and of the energy loss window selected for filtered image formation. From this expression, the signal change due to a small mass-thickness variation is deduced and the practical contrast available can be calculated. This is made in the case of elastic scattering. Contrast enhancement possibilities are considered in the case of bright and dark field images of unstained and stained specimens. A contrast enhancement is demonstrated by calculation and also on images in the case of bright field images of thin foils.