Dresden 2003 – wissenschaftliches Programm
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O: Oberflächenphysik
O 24: Postersitzung (Epitaxie und Wachstum, Oxide und Isolatoren, Elektronische Struktur, Oberfl
ächenreaktionen, Adsorption an Oberfl
ächen, Organische Dünnschichten)
O 24.19: Poster
Mittwoch, 26. März 2003, 14:30–17:30, P1
Surface Electronic Properties and Phase Transition in Fe3O4 — •D. Schrupp, J. Schäfer, M. Sing, and R. Claessen — Universität Augsburg
Magnetite (Fe3O4) displays a first order phase transition (Verwey transition) at TV≈120 K, which changes the electronic properties dramatically and has traditionally been attributed to the occurence of charge order in the low-temperature phase.
Very recently, this interpretation has become highly controversial. Moreover, based on conflicting results from photoemission spectroscopy (PES), it is also debated whether the Verwey transition is of the insulator-insulator type or one from insulator to metal. While PES provides a direct probe of the electronic excitation spectrum, it suffers from an extreme surface sensitivity. We have therefore systematically studied the evolution of the experimental spectra as function of surface preparation and quality. For this purpose, magnetite single crystal surfaces (particularly the (111) orientation) have been prepared by ion bombardment, annealing and post-oxidation. Surface characterization measurements by LEED, STM, and core level XPS reveal a pronounced sensitivity to details of the preparation process. We are able to correlate the valence band PES data with the nature of the surface, and observe for some surfaces temperature-dependent changes in the electronic structure which reflect the Verwey transition in the bulk and support its interpretation as insulator-insulator transition.