Oxygen LEED analysis

Figure 1 A Model of the surface crystallography of iron oxide (Fe20s) as determined from LEED analysis of a thin fdm grown at Imbar oxygen pressure. The numbers indicate the positional changes of the atomic layers in percent with respect to the position in the bulk structure. B LEED image of a film before and after use as catalyst of dehydrogenation of ethylbenzene (EB) to styrene reaction temperature 873 K, reactant pressure Ibar, composition steam to EB 10 1, LHSV 0.5 h. The unit cell reflections for (001) Fe20s are indicated by circles. C Evolution of the conversion to styrene as function of time on stream under the conditions given in (B)...

The c(6x2) reconstruction, which is obtained by a combination of annealing under oxygen and UHV, has been shown remarkably long-range ordered and stable in O2 or in ambient air [128]. It has been characterised by LEED and STM] and very recently by GIXS [129]. Measurements of in-plane reconstraction rods from this surface have been recorded, but are still under analysis. 

It is expected that addition of this terminal layer of oxygen will modify the surface structure. The Cr-terminated surface has been investigated by LEED I-V analysis and found to be strongly inwardly relaxed, as is the Fe-terminated a-Fe203(0001) surface. Rohr et al. [41, 42] measured inward relaxations of-38%, -21%, -25%, and +11% of the associated bulk values. The structure of the chromyl-terminated surface has not been determined. 

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