AVS 46th International Symposium
    Surface Science Division Tuesday Sessions
       Session SS1+EM-TuA

Paper SS1+EM-TuA2
Ultrathin Iron Oxide Films

Tuesday, October 26, 1999, 2:20 pm, Room 606

Session: Oxides: Growth and Structure
Presenter: R.L. Stockbauer, Louisiana State University
Authors: R.L. Stockbauer, Louisiana State University
J. Karunamuni, Louisiana State University
A. Koveshnikov, Louisiana State University
R. Madjoe, Louisiana State University
R.L. Kurtz, Louisiana State University
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Thin films of spin polarized conductors are receiving increased attention as potential contacts for devices such as spin-valves and high-sensitivity disk sensors. We have succeeded in producing ultra thin films of FeO and Fe@sub 3@O@sub 4@ and characterized their morphology using STM and LEED. The oxides are grown by depositing thin films of Fe on a Cu(100) surface at room temperature. The Cu substrate has terraces ca. 100Å wide with steps perpendicular to the [010] direction. The Fe grows layer-by-layer in islands uniformly distributed on the Cu terraces. The oxides are formed by heating to 840K in 10@super -6@ Torr O@sub 2@. The change in the morphology of the surface after oxidation is truly striking. At low Fe coverage (<2ML), FeO completely rearranges the Cu substrate. Large terraces up to 1µm wide are now observed. The FeO itself forms long stripes typically 0.2µm wide and up to 10µm long parallel to the [011] direction. Shorter stripes are observed in the perpendicular direction. The FeO stripes display two superstructures. A coarse structure consists of a series of dark bands parallel to the stripe direction and spaced at 360Å intervals. The fine structure is a 20.5Å hexagonal pattern. A comparison of LEED data and simulations indicates that the overlayer is FeO(111) with stripes aligned along the [110] directions. Oxidizing Fe films thicker than 2ML results in the oxide phase of device interest, Fe@sub 3@O@sub 4@. These patches show a 170Å banded structure and the same size hexagonal superstructure but rotated 30° from that observed for the FeO . LEED data, simulations, and thermochemistry are consistent with the overlayer being Fe@sub 3@O@sub 4@(111) rotated 15° from the [001] azimuth. Surprisingly, these highly oriented oxide films do not show strong angular dependence in photoemission. MOKE, circular dichroism, and spin polarized measurements are underway to determine the magnetic properties of the oxide films.