Microstructural characterization of sulfur-doped Bi2Te3 crystals

In this study, the detailed microstructure of sulfur-doped Bi2Te3 and the distribution of sulfur dopants were investigated using X-ray diffraction (XRD) and transmission electron microscopy (TEM). XRD result indicates that the interplanar distances of Bi2Te3 are shortened after introducing sulfur dopants. HRTEM reveals that the unit cell lengths along [001, 100] are decreased as a result of the substitution of Te by smaller S atoms on the anion lattice. XRD and HRTEM analysis suggest that the distortion of the crystal lattice in Bi2Te3 is induced by doping sulfur. High annular angler dark field scanning electron microscopy (HAADF-STEM) image shows obvious contrast variations in the Te atomic columns, indicating that Te sites were unevenly substituted by S dopants. Te columns with least contrast intensity correspond to the preferential occupation sites of S atoms. The replacement of Te atoms by S can be attributed to the evaporated sulfur powder in the gas reaction procedure. The present work is not only contributed to obtain a better understanding of the distribution of sulfur dopants introduced by gas reaction, but also can help explore the structural-property relationship of sulfur-doped Bi2Te3.