Electron-irradiation-induced crystalline to amorphous transition in α-Sic single crystals

Abstract

An electron-irradiation induced crystalline-to-amorphous (C-A) transition in α-Sic single crystals of the 6H polytype has been studied as a function of irradiation temperature, incident electron energy and orientation of the incident beam, by means of ultra-high voltage electron microscopy. The C-A transition can be induced at temperatures below 290 K. The minimum energy of incident electrons to cause the C-A transition is 725 ± 25 keV. The electron dosage required for the C-A transition is essentially constant at temperatures below 220 K, while at temperatures above 220 K, the dosage increases quickly with temperature until no amorphization can be induced any more at the critical temperature of 290 K. At fixed temperatures below the critical temperature, the required dosage decreases with increasing incident electron energy. The temperature and incident energy dependence of the required dosage indicate that a knock-on mechanism rather than an ionization mechanism is responsible for the C-A transition. The amorphization dosage of the irradiation along the ⟨1120⟩ and ⟨1100⟩ directions (i.e. parallel to the basal plane) is smaller than that of the irradiation along the ⟨0001⟩ direction (i.e. perpendicular to the basal plane). The crystallization temperature of the irradiation-produced amorphous Sic is 1148 ± 25 K.