Atomic structure analysis of ultra thin iron silicide films by stereo atomscope

Three-dimensional atomic arrangements of ultra thin Fe silicide films were directly revealed. By using circularly polarized light with opposite helicities, forward focusing peaks with their positions shifted in photoelectron angular distribution (PEAD) patterns can be obtained. We successfully observed the PEAD patterns of ultra thin Fe silicide films from different core levels of Fe and Si atoms by display-type spherical mirror analyzer (DIANA). The element selective stereo photographs indicate similar hexagonal atomic arrangement with three-fold symmetry for Si and Fe atoms, which is consistent with a model based on a CsCl-type structure with B-type stacking. This is the first observation of stereoscopic atomic arrangements for ultra thin compound films, which implies that the stereo atomscope is very powerful structure analysis tool also for complex structures on surface.