Figure 1: Topographic and spectroscopic identification of Bi_Se defects.

(a) Topography showing Se vacancies and corresponding dI/dV image (b) showing Bi_Se defects in Bi₂Se₃ at −380 meV, I=500 pA. (c) 2.9 × 3.5 nm atomic resolution imaging of a Bi_Se defect at −500 meV and ab initio STM simulations for a Bi_Se defect in the 5th (d) and 6th (e) layer at the same scale. (f) Contours from d overlaid on c. (g) Atomic structure of Bi₂Se₃, where hexagons separate the quintuple layers. (h) dI/dV spectroscopy on two defect types, taken on their lobes: the dim defect type, labelled with a circle in b, and a bright defect type, labelled with a square in b, as well as spectroscopy taken away from any defects. The bright and dim defects show a significant difference in their energy position on undoped Bi₂Se₃. To physically distinguish the defects, the lobes on the dim defects are slightly further from the centre, more likely corresponding to a deeper defect as per the simulation in e, whereas the bright defect is more compact, better corresponding to d. The scale bar in a and b is 30 nm.