Amorphisation of ge precipitates in an al-ge alloy by electron bombardment

The results of a TEM study of the effects of electron irradiation on the structure of crystalline Ge precipitates in an Al-Ge alloy are reported. The electron irradiations were performed at−130°C in a HVEM, and dynamic observations on the stability of Ge precipitates were made. A gradual decrease in Ge diffraction spot intensity was observed which recovered on warming at about−30°C provided a dose of 1 × 1023 e/cm2 was not exceeded. The precipitates were crystalline at room temperature. After higher doses, no recovery was seen during warming and the precipitates were amorphous at room temperature. This behaviour is the first reported example of amorphisation of Ge during electron irradiation and shows that amorphisation is possible without the occurrence of collision cascades. It is proposed that amorphisation is the result of a build-up in vacancy concentration within the precipitates which is promoted by the presence of the precipitate-matrix interface acting as a sink for mobile interstitials.