In-situ observation of the microstructural evolution in germanium under the low-energy helium ion irradiation

Effects of helium aroma on the defect clustering in germanium are examined by irradiation with low-energy helium ions, using a specially designed transmission electron microscope which is connected with an ion accelerator. Dynamic microstructure evolution under low-energy (10 keV) helium ion irradiation with a beam flux of 7.0x10(16) ions m(-2) s(-1) is observed at various temperatures between 85 and 870 It. Under around 290 K, a number of small defects (<6 nm in the diameter) are formed, which are probably of vacancy-helium complex and the precursor of {001} lenticular helium bubbles. At about 290-670 It, interstitial-type defects lying on {113} planes are mainly produced which grow to form perfect dislocation loops under the irradiation. The features of the {113} defects introduced under the low-energy helium ion irradiation are compared with those formed by electron irradiation. The enhanced formation of {113} interstitial-type defects and the extensive width of the defects under the irradiation of helium ions above 290 K imply the mechanism of helium cutting saturated bonds between germanium atoms.