A survey of exo-electron emission phenomena

Abstract

"Exo-electron" emission phenomena are reviewed. Kramer's original hypothesis that exothermal processes are the cause of the effect is no longer considered valid and it is now widely accepted that particularities of the crystal lattice, such as crystal imperfections are present in surfaces showing electron emission after mechanical deformation, X- or ultra-violet irradiation, electron bombardment, etc. Apparently spontaneous emission during phase changes of metals requires the presence of surface films. Oxygen must be present for emission to occur after the mechanical deformation of metals and photo-electric emission measurements suggest that certain surface oxides then contain negative-ion vacancies (F́-centres). The emission from ionic materials, such as alkali halides, depends on the presence of colour centres. The importance of crystal imperfections is brought out by the parallelism between luminescence and exo-electron emission. The latter depends only on the presence of donor-centres, but not on the activator centres necessary for the former to occur. Various applications of exo-electron phenomena and the question of nomenclature are discussed.