Fe203 , surface terminations

Fig. 4 Surface energies of different Fe203(0001) surface terminations, o(g ) the chemical potential per oxygen atom of molecular O2. The allowed range of /z — no ) is indicated by the vertical dotted lines. Solid lines show results for relaxed geometries, and daished lines give, for comparison, results for unreleixed surfaces (from Ref. 122).

All Fe oxide films on Pt have strongly relaxed, unreconstructed bulk-terminated surfaces, but while the Fe304 and Fe203 oxide layers are similar to their respective bulk compounds, the ultrathin FeO layers are true 2D oxide phases that are different from the FeO bulk and stabilized by the metal-oxide interface. 

Figure 7.18. Plot of surface energy vs. oxygen chemical potential for different terminations of the a-Fe203 (0001) from ab initio thermodynamic calculations, (from [85]).

Fig. 1 Fe-terminated (a) and 0-terminated (b) a-Fe203(0001) surface structures. The interlayer relaxations shown in (a) were measured by XPD and predicted by two independent theoretical methods. Those shown in (b) are predicted by spin-DFT theory, but have not been confirmed experimentally.

Fig. 3 Shallow take-off angle (0 - relative to the surface) XPD 01s azimuthal scans for epitaxial a-Fe203(0001) on a-AbOsCOOOl) grown by OPA-MBE. The surface was prepared two different ways to maximize the likelihood of achieving an O termination (a), and an Fe termination (b). Also shown are single scattering simulations for the two terminations. Qualitatively, agreement is superior for the Fe termination for both methods of preparation.

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. 

Fig. 15 shows the results of structural determinations for the three related systems Al203(0001) [8], Cr203(0001) [94, 95] and Fe203(0001) [96]. In all cases a stable structure in UHV is the metal ion terminated surface retaining only half of the number of metal ions in the surface as discussed above [92]. The interlayer distances are very strongly relaxed down to several layers below the surface [10]. The perturbation of the structure of oxides due to the presence of the surface is considerably more pronounced than in metals, where the interlayer relaxations are typically of the order of a few percent. The absence of the screening charge in a dielectric material such as an oxide contributes to this ef-... 

Hong et al. (1987a) have mathematically analyzed the reaction system involving the generation of radicals on the surface of either Fe203 or Ti02, diffusion of SO5 to the bulk phase, and a free-radical chain reaction according to Eqs. 89-96. An additional free-radical termination step involves the surficial reaction of SO as follows ... 

Preliminary CTR scattering data on the hydrated a-Fe203 (0001) surface suggest two distinct types of structure, one that is oxygen terminated and one that is iron terminated (Trainor et al. 2002d). Similar conclusions have been reached by Shaikhutdinov and... 

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