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    Surface Science Tuesday Sessions
       Session SS-TuA

Paper SS-TuA8
A Study of the Surface Reconstruction of Fe@sub 3@O@sub 4@ (100) Using Antiferromagnetic Tips

Tuesday, October 30, 2001, 4:20 pm, Room 121

Session: Metal Oxides: Structure and Photocatalysis
Presenter: G. Mariotto, Trinity College Dublin, Ireland
Authors: G. Mariotto, Trinity College Dublin, Ireland
S. Murphy, Trinity College Dublin, Ireland
I. Shvets, Trinity College Dublin, Ireland
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We have studied the surface structure and chemical composition of an artificially grown single crystal of Fe@sub 3@O@sub 4@ (100) using scanning tunnelling microscopy (STM), low energy electron diffraction (LEED) and Auger electron spectroscopy (AES). The crystal has been also characterized by electrical resistivity measurements as a function of temperature. Two different preparation procedures are discussed. The first one consists of mechanically polishing the sample with diamond paste and then annealing it in situ at a temperature of 990 ± 50 K. It has been found that this procedure gives rise to a surface characterized by the presence of square terraces with the edges aligned along the [110] and [1-10] directions. A p(1x1) LEED pattern has been associated with this type of images and sample preparation. The steps separating adjacent terraces are 2 ± 0.2 Å high, which corresponds to the distance between like sites of iron atoms. A longer annealing induced the onset of a different type of structure: the square terraces split into rows that become sharper and narrower as the annealing time is increased. The separation between these rows ranges from 24 to 40 Å. This type of surface structures manifests itself in the LEED pattern with the presence of satellite spots around the primary spots. Surface contamination by impurities segregating from the bulk are discussed. The second preparation procedure consists of argon ion etching followed by annealing. This method produces a c(2x2) reconstruction that is clearly visible in the LEED pattern. AES spectra indicate a clean surface of magnetite. Terraces separated by 2 ± 0.2 Å are routinely observed. Atomically resolved pictures have been obtained on a sample prepared according to this procedure using an antiferromagnetic MnNi tip. The differences between the two preparation procedures are discussed.