Scanning tunneling spectroscopic images of Bi2Se3, doped with excess Bi, revealed electronic defect states having a striking shape which resembled clover leaves. Using a simple tight-binding model, it was shown that the geometry of the defect states could be directly related to the position of the originating impurities. Only Bi defects at Se sites which were 5 atomic layers below the surface were experimentally observed. It was shown that this effect could be explained by the interplay of defect and surface electronic structures.

Scanning Tunnelling Microscopy of Defect States in the Semiconductor Bi2Se3. S.Urazhdin, D.Bilc, S.H.Tessmer, S.D.Mahanti, T.Kyratsi, M.G.Kanatzidis: Physical Review B, 2002, 66[16], 161306 (4pp)