This book (Practical Electron Microscopy and Database) is a reference for TEM and SEM students, operators, engineers, technicians, managers, and researchers.
The most promising coherent electron sources for electron microscopes (EMs) have been found in ultrasharp nanotips [1–3] in field emission electron guns due to the very high coherence and significant brightness. The important, common structural feature of their brightest field emitters is that they end with a single atom at the apex of a nanoprotrusion. The resulting characteristics are high coherence, strong focusing, sharp energy spectra, and high degeneracy  that significantly improve the spatial and temporal coherence properties. The use of ultrasharp nanotips in the EMs significantly improves the resolution and magnification, and allows for the simultaneous imaging of a larger area.
The phases of two electron beams can be correlated if they originate from a small electron source. The electron beams are coherent or partially coherent, respectively, depending on whether the correlation is complete or partial.
Note that the envelope function is affected by the angular spread α of the electrons incident at any specific point in the object plane because of the limited spatial coherence originated from the finite source size.
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