Structure of the (0001) basal twin boundary in Bi2Te3

We investigate the structure of the (0001) basal twin boundary in Bi2Te3. Electron diffraction measurements show that this interface corresponds to a 180° rotation of the crystal about the [0001] axis, an alignment that reverses the stacking of the basal planes. The basal planes in the perfect Bi2Te3 structure are arranged in a repeating sequence of five-layer wide Te(1)–Bi–Te(2)–Bi–Te(1) packets. Thus, it is possible for the twin interface to be located at one of three distinct locations: at the Te(2) layer, the Bi layer, or the Te(1) layer. Using aberration-corrected high-angle annular dark field scanning transmission electron microscopy, we show that the twin boundary is terminated at the Te(1) layer, where the stacking forms a double-layer of Te. Our observations are consistent with ab initio calculations, which predict this twin termination to have the lowest interfacial energy of the three configurations we considered. Our calculations and observations also find a small expansion in the interplanar spacing at the interface.