Strain Concentration at the Boundaries in 5-Fold Twins of Diamond and Silicon.

Widely found in metals, semiconductors, oxides, and even organic materials, multiple twinning has important implications in engineering applications of materials. In this work, the intrinsic strain in 5-fold twins of diamond and silicon has been studied combining aberration-corrected electron microscopy and first-principles calculations. In contrast to metallic 5-fold twins, where the strain distribution is relatively smooth, the semiconductor systems show significant strain concentration at the twin boundaries, which is shear modulus dependent. In silicon with moderate strain concentration, the electronic frontier orbitals are located at the center of the 5-fold twins. Accompanying the increased strain concentration in diamond, however, the frontier orbitals are pushed to the surface. The modification of strain state and surface electronic structure by materials elasticity suggest possible routes to tune catalytic, electronic, and mechanical properties of materials.