Sr adatoms on As bridge positions on SrFe2As2 observed by scanning tunneling microscopy at 4.2 K

We used a scanning tunneling microscope to image the surface of SrFe(2)As(2) single crystals at 4.2 K. We found, besides the commonly reported row structures and some disordered areas, also maze-like regions. Atomically resolved images of the maze show that the atoms on the surface sit on As bridge positions of the underlying Fe(2)As(2) layer. Examination of the corner positions within the maze-like reconstruction reveals the presence of adatoms rather than As dimers. Hence, the surface atoms on these samples are most likely to be Sr atoms.