Atomic, molecular and chemical physics LEED analysis
American Physical Society
Mariotto, G.; Murphy, S.; Shvets, I. V., Charge ordering on the surface of Fe3O4(001), Physical Review B (Condensed Matter and Materials Physics), 66, 24, 2002, 245426
Physical Review B (Condensed Matter and Materials Physics); 66; 24;
We have studied the (001) surface of a Fe3O4 single crystal using scanning tunneling microscopy (STM), low-energy electron diffraction (LEED), and Auger electron spectroscopy. A clean surface was obtained by a combination of Ar+ ion sputtering, in situ annealing in O2 atmosphere, and further annealing in ultra high vacuum conditions. A sharp (√2×√2)R45° reconstruction was observed by LEED and STM analysis at room temperature. The STM measurements were performed using a tip of antiferromagnetic MnNi alloy. Atomically resolved STM images provide evidence of a surface terminated at the octahedral plane, with rows of Fe cations running along the  and [11¯0] crystallographic axes. The 3 Å periodicity of the Fe rows expected for a bulk-terminated B plane is not observed. Instead, two different kinds of Fe cations with a separation of 6 Å are imaged. The periodicity between Fe cations of the same kind is about 12 Å. We propose a model to explain the observed symmetry in terms of charge ordering of the Fe cations on the octahedral sites of the inverse spinel lattice. We also explain the (√2×√2)R45° LEED pattern in terms of charge ordering, as opposed to a structural rearrangement of the atoms on the surface. We further suggest the possibility of a spin polarized effect, in view of the anomalous corrugation observed along the  Fe rows on the octahedral plane, in agreement with the different spin configuration of Fe2+ and Fe3+ ions.
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