Mechanisms of defect creation in solids

Irradiation of all kinds of solids (metals, semiconductors, insulators) is known to produce pairs of the point Frenkel defects - vacancies, v, and interstitial atoms, i, which are most often spatially well-correlated [1-9]. In many ionic crystals these Frenkel defects form the so-called F and H centres (anion vacancy with trapped electron and interstitial halide atom X forming the chemical bonding in a form of quasimolecule Xf with some of the nearest regular anions, X ) - Fig. 3.1. In metals the analog of the latter is called the dumbbell interstitial. 

Under moderate energies, the primary event of incident particle interaction with crystals of any nature is very simple it is an elastic pair collision resulting in displacement of atoms (ions) into an interstitial position [1, 7, 10] provided they received energy exceeding a threshold value [11] which is typically 10-20 eV. 

However, in the last two decades it has been shown experimentally [1, 7, 8,12-14] and theoretically [15-18] that in many wide-gap insulators including alkali halides the primary mechanism of the Frenkel defect formation is subthreshold, i.e., lattice defects arise from the non-radiative decay of excitons whose formation energy is less than the forbidden gap of solids, typically 10 eV. These excitons are created easily by X-rays and UV light. Under ionic or electron beam irradiations the main portion of the incident particle 

From pair kinetics toward the many-reactant problem 

---