Topological insulators (TI) represent an unusual state of matter. While they are insulators in
the bulk they are metals at the surface. Tremendous interest has emerged in the recent past
primarily focused on the study of the electronic and transport properties of uncovered and
adsorbate covered TI?s. The latter is motivated by the question whether the topological
state is robust against adsorption of magnetic and non-magnetic adsorbates. By contrast,
atomically resolved structure studies relating electronic properties to the geometric
structure are hardly available. This talk gives an overview over recent progress in the
structure analysis of the clean [1] and adsorbate covered Bi2Se3 (0001) surface using
surface x-ray diffraction (SXRD) and x-ray absorption spectroscopy. Results are discussed
in the context of theoretical predictions and angular resolved photoemission experiments.

Support by DFG through SPP1666 is acknowledged.

[1] Roy, S., Meyerheim, H. L., Ernst, A, Mohseni, K., Tusche, C., Vergniory, M. G., Menshchikova,
T. V., Otrokov, M. M., Ryabishchenkova, A. G., Aliev, Z. S., Babanly, M. B., Kokh, K. A.,
Tereshchenko, O. E., Chulkov, E.V., Schneider, J., Kirschner, J.
Physical Review Letters 113, 116802 (2014)