Date of Award

2001

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Physics and Astronomy

First Advisor

Richard L. Kurtz

Abstract

In this investigation, I have focused on understanding the structure and morphology of ultrathin iron oxide films and characterizing them by using LEED, photoemission (both angle-resolved and angle-integrated) and photoabsorption measurements. Fe films were deposited on a Cu(100) substrate at room temperature growing in a layer by layer fashion. The sample was then annealed to 810K in oxygen ambient. This oxidation process led to dramatic changes of the sample surface and electronic structure depending on initial Fe coverage. Half-metallic oxides such as CrO2 and Fe3O4 may provide opportunities for new magnetic devices since their single spin orientation at the Fermi level gives rise to spin-dependent transport. However, these films are most often grown on oxide substrates that are not currently incorporated in GMR devices. We report a study of the electronic and geometric structures of Fe3O4 films grown on copper, which is currently used in commercial heterostructures. An array of techniques including ARUPS, NEXAFS, LEED and STM were used to characterize these films. They were grown by depositing Fe on Cu(001) at room temperature and oxidizing at 810K in 10-6 Torr O 2 ambient. The particular oxide phase that forms depends on the initial Fe thickness. For Fe films less than 2 ML thick, LEED and STM measurements show that oxidation produces an FeO(111) bilayer. The oxide forms long, narrow strips with two mutually-perpendicular orientations aligned along Cu[110] and [11¯0]. Oxidation of thicker Fe layers give crystallites of Fe 3O4(111) of micron dimensions, which are oriented 15° from the [010] directions and highly lattice-matched to the Cu substrate. Both core level and valence band photoemission data provide spectroscopic confirmation for the classification of the Fe oxides. Near-edge X-ray absorption fine-structure (NEXAFS) taken at the oxygen K-edge, shows the existence of two distinct valence states for Fe3O4 (Fe2+ and Fe3+) while spectra for FeO shows a single valence state (Fe2+).

ISBN

9780493213842

Pages

136

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