in solid-state physics, the directionally selective penetration of crystalline solids by a beam of atoms. The effect was predicted in 1912 by the German physicist Johannes Stark (Stark, Johannes) but was not confirmed until 1960. The directions in which penetration is greatest characteristically are parallel to crystallographic axes, or planes, and the paths followed by the particles are called channels. For example, heavy atoms pass almost unobstructed through suitably oriented aluminum crystals, traversing distances thousands of times those achieved in nonchanneling directions. The phenomenon is useful in studies of crystal structure and in atomic, nuclear, and solid-state physics and holds promise with regard to the fabrication of semiconductors.