Dark field imaging microscopy

FIGURE 8.22 Photomicrographs of Cu multilayer cross sections using dark field imaging microscopy. (A) No diffusion of Cu into dielectric (B) excessive Cu diffusion into dielectric, termed blushing. 

In dark-field electron microscopy it is not the transmitted beam which is used to construct an image but, rather, a beam diffracted from one facet of the object under investigation. One method for doing this is to shift the aperture of the microscope so that most of the beam is blocked and only those electrons... 

Dark-field electron microscopy (in which the image is formed from the scattered beam), when combined with improved techniques of sample handling and preparation and minimal radiation exposure, can lead to images of sufficiently undamaged DNA at a resolution of 10 A (116). Figure 45 shows such an image in which the two-dimensional projection of the helix is clearly visible on the undamaged part of the molecule. 

Additional information comes fixim a high-resolution transmission electron microscopy study of crystal morphology by Masse et al. [272]. From dark-field imaging crystallinity is estimated to be 50% in a film drawn to a ratio of 8-9. The aspect ratio of the crystallites is near 1.0 and their diameter is approximately 50 A. This value is considerably lower than the x-ray based value of 120 A, quoted above. The morphology is characterized as micellar , a network of oriented fibrils. 

Fig. 7.1 7 Transmission electron microscopy (a) bright-field image and (b) dark-field image indicating acicular secondary alpha " within large beta grains in the thermomechanically affected zone of the mill-annealed material, (c) Selected area diffraction pattern indicating the Burgers orientation relation between the beta and alpha phases...

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