| In order to better understand the initial steps leading to the formation of He-filled cavities in covalent materials, we have performed DFT calculations of systems including several He atoms in interaction with mono and divacancies in silicon. In the case of a single He atom, the mobility of the formed complexes has been investigated, suggesting that an He atom always migrates as an interstitial. For several He atoms, we found that a large number of He atoms can be accommodated in vacancies. The permeation mechanism of a single He atom through a silicon surface has also been investigated, indicating that the surface of a bubble in silicon is porous. Using these results and a simple model for describing He in a highly pressurized fluid state, we were able to determine a range for pressure inside a He-filled bubbles. Finally, a semi-empirical potential has been developed from first-principles results, and preliminary results of finite temperature simulations will be presented. |
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