Exoelectron emission (EE) is a weak electron emission phenomenon observed in solids that have been pre‑treated by processes such as irradiation, mechanical deformation, or other forms of excitation. The pretreatment places the material in a non‑equilibrium (unequilibrial) state that stores excess energy in electron traps or defect sites within the crystal lattice. When the excited material subsequently undergoes a relaxation process—often induced by slight heating or long‑wave illumination—electrons are released from these traps and emitted from the surface.
Characteristics
- Weak emission – The number of emitted electrons is typically several orders of magnitude lower than in more common electron‑emission processes such as thermionic or field emission.
- Requirement for pretreatment – Untreated, pristine samples generally do not exhibit exoelectron emission under the same relaxation conditions.
- Stimulus‑dependent – The relaxation can be triggered thermally (thermo‑stimulated exoelectron emission, TSEE) or optically (photo‑stimulated exoelectron emission, PSEE).
Mechanism
The prevailing model attributes EE to the release of electrons that have been captured in deep traps associated with lattice defects, impurity states, or radiation‑induced color centers. When the material is heated or illuminated with photons of sufficient energy, these trapped electrons acquire enough energy to overcome the trapping potential and escape to the vacuum, producing a measurable electron current. The process is analogous to phosphorescence or thermally stimulated luminescence, where stored excitation energy is released as light rather than as electrons.
Historical Context
The term “exoelectron emission” was introduced in the mid‑20th century to describe electron emission that occurs after an external excitation, distinguishing it from primary electron emission caused directly by incident particles or fields. Early investigations focused on insulating crystals and oxides, where radiation‑induced defects generate sizable trap populations.
Applications and Research Areas
- Material characterization – The energy spectrum and intensity of exoelectron emission provide information about the nature and distribution of defect states in solids, complementing techniques such as thermoluminescence.
- Radiation dosimetry – Because EE intensity correlates with the dose of ionizing radiation received by a material, it has been explored as a dosimetric method for monitoring exposure.
- Surface science – Studies of EE contribute to understanding surface charge dynamics, electron‑phonon coupling, and the role of adsorbates in modifying emission yields.
References
- Oster, L.; Yaskolko, V.; Haddad, J. (1999). “Classification of Exoelectron Emission Mechanisms”. Physica Status Solidi A 174 (2): 431. doi:10.1002/(SICI)1521‑396X(199908)174:2<431::AID‑PSSA431>3.0.CO;2‑Z.
- Gerasimov, A. B.; Dolidze, G. M.; Mizandari, L. A.; Tsertsvadze, A. A. (1976). “On the physical mechanism of exoelectron emission”. Physica Status Solidi A 35 (2): K131. doi:10.1002/pssa.2210350256.
This entry summarizes the current understanding of exoelectron emission as reported in peer‑reviewed literature and standard reference works.