Precipitation of Cu in Ge. II. Supersaturation Effects

Studies have been made on the precipitation kinetics of Cu from supersaturated solid solution in Ge crystals with dislocation densities 100/cm². We found that the precipitation rates are very strongly dependent upon the degree of supersation. We believe this is evidence for the nucleation of the precipitate particles upon a single type of nucleation site, whose identity has not been established. An attempt is made to fit the experimental data to the simple theory of nucleation in which σ, the surface tension in the phase boundary between precipitate and host lattice, and Eₚ, the structure-sensitive increase in strain energy in the crystal upon formation of the precipitate, are parameters. We find that the data can be fit by σ≈500±50 ergs/cm², and Eₚ≈(1±1)×10^-13 erg/atom, assuming spherical precipitates. No other information about these quantities is available for comparison. An appendix gives a simplified treatment of Ham's derivation of the kinetic law for diffusion-limited precipitation upon spherical precipitate particles, which relates the observed precipitation rate to the number of precipitate particles. Theory and experiment are in reasonable agreement.