THE BRIGHTEST BEAM IN SCIENCE - NEW DIRECTIONS IN ELECTRON-MICROSCOPYAND INTERFEROMETRY

An ultrasharp electron field-emission source, with emission region on the order of atomic size (i.e., fraction of a nanometer), produces a b right, strongly self-focused, highly coherent electron beam-indeed the brightest particle beam currently known to science. Employed in the c onfiguration of a point-production microscope, this ''nanotip'' source facilitates low-energy electron imaging of fragile structures at atom ic-scale resolution. When slightly out of focus, the microscope serves as perhaps the world's simplest electron interferometer providing Fre snel diffraction patterns from which important information like effect ive source size, source brightness, and beam degeneracy can be determi ned. One remarkable feature of point sources is the perfect (i.e., abe rration-free), lensless imaging of periodic structures at a denumerabl e set of focal planes with complete suppression of nonperiodic detail. The high degeneracy and coherent emission of an electron pointlike so urce can be exploited in new. types of quantum interferometry involvin g correlated electrons. (C) 1995 American Association of Physics Teach ers.