Dynamic behavior of helium bubbles at high temperature in Si studied by in situ TEM, STEM-EELS, and TDS

Abstract

We demonstrated, using in situ transmission electron microscopy (TEM), the random motion of helium bubbles formed by irradiation with helium ions in an FZ (011)Si specimen at high temperatures. Analysis of the random motion yielded the bubble diffusivity, which was dependent on the bubble size and the annealing temperature. The helium density in individual bubbles, measured using scanning transmission electron microscopy-electron energy loss spectroscopy, was as high as 70 ± 14 He/nm3. It was dependent on the irradiation temperature, beam flux, and annealing temperature but was independent of the bubble size. The bubbles retained a high density of helium atoms at around 800 K, but a significant reduction of the helium density within individual bubbles took place after annealing above about 970 K. Thermal desorption of helium from the specimen, measured using thermal desorption spectroscopy, occurred at temperatures between 650 K and 1100 K, centering at around 890 K. TEM revealed the corresponding microstructure. On the basis of these results, the thermal desorption profile was discussed in terms of the release of helium at lower temperatures from migrating and coalescing overpressurized bubbles and bubbles migrating to the specimen surface, and at higher temperatures from stationary large bubbles.