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Complex nanotwin substructure of an asymmetric Σ9 tilt grain boundary in a silicon polycrystal

: Stoffers, A.; Ziebarth, B.; Barthel, J.; Cojocaru-Mirédin, O.; Elsässer, C.; Raabe, D.


Physical review letters 115 (2015), Art.235502
ISSN: 0031-9007
ISSN: 1079-7114
Bundesministerium für Bildung und Forschung BMBF
Deutsche Forschungsgemeinschaft DFG
MA 1280/40-1
Fraunhofer IWM ()
grain and twin boundaries ; scanning transmission; electron microscopy; silicon solar cells

Grain boundaries in materials have substantial influences on device properties, for instance on mechanical stability or electronic minority carrier lifetime in multicrystalline silicon solar cells. This applies especially to asymmetric, less ordered or faceted interface portions. Here, we present the complex atomic interface structure of an asymmetric Σ9 tilt grain boundary in silicon, observed by high resolution scanning transmission electron microscopy (HR-STEM) and explained by atomistic modeling and computer simulation. Structural optimization of interface models for the asymmetric Σ9 and related symmetrical Σ9 and Σ3 tilt grain boundaries, by means of molecular-statics simulations with empirical silicon potentials in combination with first-principles calculations, results in a faceted asymmetric interface structure, whose grain-boundary energy is so low that it is likely to exist. The simulated local atomic structures match the observed HR-STEM images very well.