ANOMALOUS ELASTIC BEHAVIOR IN SUPERLATTICES OF TWIST GRAIN-BOUNDARIES IN SILICON

The elastic constants and moduli of superlattices of high-angle twist grain boundaries on the two densest crystallographic planes of silicon are calculated using Stillinger and Weber's three-body potential. While in both cases the Young's and shear moduli are found to be softened, the Poisson ratios and some elastic constants, in particular C33 (in the direction of the interface-plane normal), are found to be hardened. It is shown that the elastic behavior is determined by the structural disorder at the interfaces, and that it cannot be understood in terms of the dimensional changes of the system alone. A comparison with similar calculations for metallic superlattices elucidates the role of the covalent nature of bonding of silicon on its elastic behavior.