Amorphization of Ge/Al or Si/Al bilayer specimens induced by 1 MeV electron irradiation at 10 K

The effects of 1 MeV electron irradiation on crystalline Ge/Al or Si/Al bilayer specimens at 10 K have been studied in situ by high-voltage electron microscopy. It is demonstrated that a crystalline-to-amorphous (c-to-a) transition takes place at the interface of a Ge/Al bilayer specimen only if the Ge layer faces the incident beam, while amorphization occurs in a Si/Al bilayer specimen regardless of the incident beam's direction with respect to the bilayer specimen. Diffuse rings in selected-area diffraction patterns first appear at a fluence of about 3 × 1023 cm−2 (about 30, 19 or 18 displacements per atom in Ge, Si or Al respectively), and the amorphous volume fraction increases with increasing fluence. These results can be understood in terms of a simple recoil-implantation mechanism.