COMPOSITION AND STRUCTURE OF THE (100)SURFACE AND (110)SURFACE OF FEAL

The structure and composition of the (100) and (110) oriented surfaces of the ordered alloy FeAl were investigated by LEED and AES. Following sputtering and annealing, c(2X2) and (1X1) LEED patterns are observed on the (100) surface. The c(2X2) is attributed to an ordered arrangement of Al atoms on top of a complete Fe layer, while the (1X1) corresponds to the Al terminated surface, as determined previously. On the (110) oriented surface, a (2X1) diffraction pattern, an incommensurate superstructure, and severe streaking are observed with LEED upon annealing. For the (2X1) structure, a missing-row model is compatible with a stoichiometry of Fe2Al. The incommensurate superstructure and streak phase are associated with a nearsurface aluminum concentration >0.5, indicating segregation of Al. In contrast to the NiAl(110) surface, no (1X1), which would indicate the formation of the bulk-like terminated surface, is observed with LEED. Annealing both surfaces over 800 degrees C leads to evaporation of Al.