Amorphization of crystalline Auln 2 films by low-temperature ion irradiation

Abstract

The intermetallic compound Auln 2 (CaF 2 type) can be forced into an amorphous (a-) phase by vapour quenching onto a liquid-nitrogen-cooled substrate. Thus, according to a previously stated empirical rule, the a-phase should be obtainable also by suitable ion irradiation experiments. To test this prediction, crystalline Auln 2 films were irradiated at T s < 10 K and T s = 125 K with He + and Ar + ions (350 keV) and the corresponding changes of the electrical resistances and the superconducting transition temperatures were monitored. It is found that at T s < 10 K both types of projectiles lead to complete amorphization, while at 125 K heavy ions are necessary to obtain the a-phase. These results, which confirm the above empirical rule, are discussed within a qualitative model taking into account the role of spikes as well as the process of defect accumulation to obtain an amorphous phase.