Defects on a topological insulator Bi2Se3 surface studied using scanning tunneling microscope

The native defects of Bi₂Se₃ were investigated using scanning tunneling microscopy (STM). STM images revealed both atomic-scale and nanometer-scale features. The most frequently observed defects appeared as depressions at the atomic scale and were identified as Se vacancies in the top Se layer. Nanometer-scale defects, including triangular, cloverleaf-shaped, and rounded features, were also observed and attributed to subsurface defects due to their extended size. While the triangular and cloverleaf-shaped defects are associated with interstitial Se atoms and substitutional Bi atoms at subsurface Se sites, respectively, the exact nature of the rounded defects remains undetermined. In addition to these point defects, previously unreported linear defects were identified. These linear defects, appearing as stripe-like features across the images, are attributed to wrinkles in the top Se layer of the Bi₂Se₃ surface, likely formed during sample growth and subsequently exposed by cleavage.