Sauerstoffadsorption und Orientierung dünner Oxidschichten auf (100)-Oberflächen von α-Eisen, untersucht mit Hilfe der Beugung langsamer Elektronen

Abstract

AbstractThe (110) faces of needle shaped monocrystals of α-iron were cleaned by argon bombardment and annealing. The surface was stepwise oxidized then at various temperatures between 20 °C and 220 °C and investigated by LEED. The well-known c (2 × 2) and c(3 × 1) patterns were obtained with 0.5 - 1.0 and 1.5 -2.0 × 10-6 Torr·sec oxygen. Further oxidation at roomtemperature produced a splitting of the fractional order spots of the c (3 × 1) pattern in the two directions [33̅2] and [33̅2̅]. At elevated temperatures (100° - 220 °C) a change of intensity distribution occurred on lines parallel to [11̅0]. In both cases the position of extra spots is a continuous function of the amount of oxygen given to the surface. Two kinds of well ordered epitaxial overgrowth of FeO could be observed after oxidizing with 10-4 Torr·sec at 20 °C and subsequent annealing at 150 - 270 °C and above 300 °C respectively. The epitaxial law is (111)FeO ║ (110)Fe and [101̅]FeO ║ [001]Fe in the former case and [1̅10]FeO ║ [11̅1̅]Fe in the latter case. By an analysis of weak extra spots due to multiple reflections a partial adaption of the lattice constant of the first FeO layers to the substrate could be detected (pseudomorphism). Very strong oxidation produced an overgrowth of spinel crystals with (111) parallel to the surface which were transformed to FeO again by annealing above 360 °C.