An ultrasharp electron field-emission source, with emission region on the order of atomic size (i.e., fraction of a nanometer), produces a bright, strongly self-focused, highly coherent electron beam—indeed the brightest particle beam currently known to science. Employed in the configuration of a point-production microscope, this ‘‘nanotip’’ source facilitates low-energy electron imaging of fragile structures at atomic-scale resolution. When slightly out of focus, the microscope serves as perhaps the world’s simplest electron interferometer providing Fresnel diffraction patterns from which important information like effective source size, source brightness, and beam degeneracy can be determined. One remarkable feature of point sources is the perfect (i.e., aberration-free), lensless imaging of periodic structures at a denumerable set of focal planes with complete suppression of nonperiodic detail. The high degeneracy and coherent emission of an electron pointlike source can be exploited in new types of quantum interferometry involving correlated electrons.
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Silverman et al. (1995) studied this question.