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Published online by Cambridge University Press: 25 February 2011
High resolution electron microscopy and high spatial resolution analytical electron microscopy were used to analyze the structure and chemistry of a Σ3 {111} twin boundary in cast polysilicon and a Σ13 (510), [001] tilt boundary in a Si bicrystal. Twin boundaries in cast polysilicon were associated with lattice defects and discrete second phase precipitates. The precipitate was single phase amorphous and faceted on the Si {111} planes. Nanospectroscopy showed mem to be substoichiometric oxide. Similar oxide precipitates, but with different morphology, were also observed on the Σ13 tilt boundary in Si bicrystal, indicating that tilt grain boundaries and steps on twin boundaries were effective heterogeneous sites for nucleation of oxygen containing precipitates. The observed Σ13 tilt boundary exhibited a coincident site lattice periodicity but had an aperiodic interface dislocation core structure. Oxygen that diffused into the boundary in regions where precipitation did not occur may have played a role in modifying the GB core structures, resulting in aperiodicity. For both cases, a detailed analysis of grain boundary atomic structure and precipitate morphology is presented.