Nanoscale characterization of bismuth telluride epitaxial layers by advanced X-ray analysis

The surface properties of topological insulators are strongly correlated with their structural properties, requiring high-resolution techniques capable of probing both surface and bulk structures at once. In this work, the high flux of a synchrotron source, a set of recursive equations for fast X-ray dynamical diffraction simulation and a genetic algorithm for data fitting are combined to reveal the detailed structure of bismuth telluride epitaxial films with thicknesses ranging from 8 to 168 nm. This includes stacking sequences, thickness and composition of layers in model structures, interface coherence, surface termination, and morphology. The results are in agreement with the surface morphology determined by atomic force microscopy. Moreover, by using X-ray data from a zero-noise area detector to construct three-dimensional reciprocal-space maps, insights into the nano­structure of the domains and stacking faults in Bi₂Te₃ films are given.