A technique that uses field emission of electrons or positive ions from a needle-shaped emitter to produce a magnified image of the emitter surface on a fluorescent screen. In the field electron microscope, the image reveals the variation in work function of the emitter surface. Due to the large lateral velocity of the emitted electrons, a resolution of only about 2.5 nanometers can be achieved. The large lateral velocity arises from a diffraction effect of the de Broglie wave and the large kinetic energy of electrons inside the metal; these effects are intrinsic quantum properties of particles and cannot be eliminated.

The field electron microscope has been used to study adsorption and desorption of gases and vapor-deposited materials, surface migration of adsorption layers and absorbed atoms on single crystal faces, and surface reactions in catalysis. Medium-sized individual molecules such as phthalocyanin have been made visible also.