ИСТИНА

Understanding how topologically protected surface states behave at surfaces and interfaces requires knowledge of the atomic structure. Here we have studied comprehensively the clean (111) surfaces of the prototypical topological insulators Bi2Se3 and Bi2Te3, magnetic and non-magnetic impurities in the bulk, as well as Fe and Co atoms at interfaces Fe,Co/Bi2Te3. To define surface termination and impurity positions we used model-independent photoelectron holography (XPH) to reconstruct three-dimensional (3D) images of the atomic structure around the emitter atom from the measured whole-hemisphere XPD patterns using the scattering pattern extraction algorithm with the maximum entropy method (SPA-MEM). For clean surfaces we confirmed chalcogen termination. In the case of Fe,Co/Bi2Te3 we considered chemical-state selective photoelectron diffraction. Our XPD results reveal that despite of the disordered STM images at room temperature impurity atoms are ordered at the interface and occupy simultaneously hollow adatom positions and interstitial position between third and fourth atomic layer.