Factors Affecting Fresnel Fringes
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In TEM measurements, the Fresnel fringes are mainly affected by the specimen edge cross section and are also partially affected by other factors, such as the angular dispersion of the incident beam (determined by the size of electron source and condenser aperture), the lens aberrations, and the elastic and inelastic scattering, the penetration power, and phase shift of the specimen.

For instance, the number of Fresnel fringes formed in the TEM image of a holey carbon (C) film is much higher for a microscope with a field-emission filament than for a tungsten (W) thermionic filament due to the difference of the sizes of the electron sources. The effective size of the field-emission source is only ~5 nm so that the emitted electrons are in-phase, and thus the source is coherent (see page1409).

 

 

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