Structural Determination as Function of Film Thickness

The growth of the GdFc2 structure could be continued to the second ML by evaporating approximately 0.5 ML of Gd and 1 ML Fe and subsequent annealing to 500 K [38—40]. The resulting sample topography is shown in Fig. 3.20. The substrate is 

3 Structural and Electronic Properties of Rare Earth Metal Systems 

In the area marked by a box, atomic resolution could be achieved on top of the first and the second ML simultaneously. This image is presented in Fig. 3.21. 

The same periodicity as in the LEED pattern can be found in the atomically resolved STM images. Based on these data a strucmre model for the alloy is deduced and shown in Fig. 3.22. This structure was the only stoichiometry to fit the data. All atoms are drawn to scale of their atomic radius. 

The resulting model in top as well as in side view is presented in Fig. 3.22. The step is only shown in order to compare directly the different step heights. Assuming that this structure model is correct, one should observe a distinctly larger step height from the W(110) substrate to the first ML than from the first ML to the second one being about 2 A (see line sections in Fig. 3.22). 

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