Imaging Dislocations in Topologically-Insulating Bi_1-xSb_x Alloys

Line defects (dislocations) in electronic materials have long been considered detrimental due to their tendency to impede the flow of electricity. However, in topological insulators, certain dislocations are predicted to act as nano-pipelines for confinement of carriers and preservation of their spin states. For Bi_1-xSb_x (0.07 < x < 0.22), dislocations in the {011}<100> slip system are predicted to host 1D topological states. In this work, we explore the formation, propagation, and transport properties of dislocations in Bi_1-xSb_x single crystals with x = 0.12. We use electron channeling (EC) in the scanning electron microscope (SEM) to align single crystals of rhombohedral Bi_1-xSb_x. Following cleavage to expose (111) surfaces, we search for dislocations in the vicinity of the cleaved surfaces using secondary electron (SE) and backscattered electron (BSE) imaging in the SEM. For individual dislocations, BSE images are collected after aligning the sample to various {1-10} and {-211} EC directions; those directions for which dislocations disappear from the BSE images correspond to the Burgers vectors. In-situ straining of the Bi1-xSbx crystals to generate dislocations via plastic deformation and measurement of their transport properties will also be discussed.