Precipitate strain relief via point defect interaction: models for SiO2
Precipitation in the solid state is often accompanied by a volume mismatch, creating strain which inhibits precipitation. For the SiO2 Si system, this strain, if unrelieved, is large enough to prevent precipitation altogether. The strain is usually assumed to be relieved via emission or absorption of point defects. Here, we suggest a model in which only one species of point defect is involved and the emission/absorption relieves the strain only partially. We generate a Gibbs free energy equation in two variables and by monitoring the atom movements during precipitation, are able to derive two relationships: an expression for the critical radius and, more importantly, a direct correlation between strain and point defect supersaturations. We use this approach to study three systems: SiO2 strain relief via interstitial emission, vacancy absorption and carbon absorption. Finally, the importance of the strain/supersaturation relationship is emphasized by noting its impact upon nucleation rates. Even small point defect supersaturations can eliminate nucleation and must therefore be considered carefully in studies of precipitation. © 1993.
Taylor, WJ; Gösele, UM; Tan, TY
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