Illumination systems transmission electron

The objective lens is the most important lens for a transmission electron microscope. The condenser lenses are the next most important, the combination of these condenser lenses forms different electron beam to illuminate TEM specimens. The first lens of the projector system (also called the intermediate or diffraction lens) is the third most important one. All the other lenses can be ignored, even though they magnify images. Since the objective lens is the most important, the center of the objective is acmally the optical axis, every other lenses must be aligned with it. TEM alignment starts from top to the bottom. 

Fljring-spot instruments permit point-by-point analysis of surface properties. At first, it would appear that transmission electron microscopes, which illuminate an entire sample, would not be suitable for such an application, and in general, this is so. However, a new transmission electron microscope named EMMA 4 has been developed with combined transmission electron microscope and probe capability by introducing a minilens into the illumination system (Cook etal, 1969 Jacobs, 1971). The EMMA 4 has demonstrated eonsiderable power in a number of applications and could easily be applied to surfaees, but it will not be further considered here because our primary emphasis is on the topography of paint. 

A recent H-NMR study of imidazole bonding in synthetic hemichromes led La Mar to the conclusion that 7r-bonding is important for these systems, and that imidazole acts primarily as a 7r-acceptor (158). However, our evidence on the osmochrome/ osmichrome system lends support to the idea that the jr-donor function of Him should not be overlooked, and more experiments are needed to understand the hemichrome systems. The difficulty encountered in their theoretical treatment is due to the fact that their optical spectra are of the mixed hyper/hypso type (50). Thus there will be a variety of transmission paths for electronic effects which remain to be illuminated. The present article may serve as an intuitive guide and a challenge to further research. 

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