AES and LEED investigation of Al segregation and oxidation of the (100) face of Fe85Al15 single crystals

The surface segregation and oxidation behavior of Fe85Al15(100) were investigated by means of AES and LEED. Sputter cleaning of the surface causes preferential Al removal and leads to an Al depleted surface layer. The segregation of Al to the Fe85Al15(100) surface was studied in the temperature range from 300 to 800 degrees C. At 375 to 400 degrees C a weak c(2 x 2) LEED pattern is found. At temperatures in excess of 600 degrees C thermodynamic equilibrium is approached very rapidly. At such temperatures Al segregation leads to a well-ordered (1 x 1) LEED structure with bright and sharp spots at a low background intensity. Oxidation at room temperature leads to disordered oxygen adsorption, whereas at 700 degrees C a (6 x 6) superstructure is observed in addition to the matrix spots. This superstructure is attributed to the formation of a thin Al2O3 over-layer on the Fe85Al15(100) surface.