Growth of iron oxide on Cu(001) at elevated temperature
Abstract
The morphology of ultrathin Fe oxide films grown on Cu(001) was studied by STM and LEED. The oxide was grown in situ by high-temperature oxidation of Fe films deposited on a Cu(001) substrate at room temperature. The Fe films were observed to grow in a layer-by-layer manner as observed previously. Oxidation was accomplished by annealing the sample to 810 K in ambient oxygen. Two distinct oxide structures were observed depending on the initial Fe coverage. For Fe films with a thickness of less than 2 ML, Fe1-xO(111) forms with preferential island growth along the {110} directions. These narrow strips of oxide exhibit antiphase domain boundaries producing dark stripes running along the island, as well as a hexagonal superstructure. For initial Fe coverage exceeding 2 ML, a new oxide phase forms, consisting of uniformly thick patches of oxide with large, atomically flat terraces. This oxide also grows in strips, but these are oriented 15° from the [010] azimuth, and the hexagonal superstructure is rotated by 30° from the Fe1-xO. The second phase is identified as Fe3O4(111), consistent with STM, LEED, and thermodynamic data.