METASTABLE IRON SILICIDE PHASE STABILIZED BY SURFACE SEGREGATION ON FE3SI(100)

The surface properties of single crystalline Fe3Si(100) have been char acterized by AES, UPS, LEED, ISS and XPS measurements. The ideal Fe3Si (100) surface may exhibit two possible terminations: pure Fe or mixed Fe/Si (1:1). XPS shows that the thermally equilibrated surface has a l arger concentration of Si in the top layers than in the bulk. The thic kness of the Si-enriched region is of the order of 2 ML. The segregate d overlayer is ordered according to LEED. It corresponds to a metastab le phase with the structure of the CsCl and an FeSi composition, stabi lized by epitaxy on top of the substrate. The corresponding surface el ectronic structure, as revealed by UPS, is in good agreement with theo retical calculations. ISS and CO titration experiments support the pre sence of both Si and Fe at the external surface, the former giving ris e to a c(2 x 2) surface reconstruction composed of Si adatoms. (C) 199 7 Elsevier Science B.V.