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Torrelles, Xavier; Wendler, Frank; Bikondoa, Oier; Isern, H.; Moritz, Wolfgang; Castro, Germán R. (2001): Structure of the clean NiAl(1 1 0) surface and the Al2O3/NiAl(1 1 0) interface by measurements of crystal truncation rods. In: Surface Science, Vol. 487, No. 1-3: pp. 97-106
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The clean NiAl(1 1 0) surface and the Al2O3/NiAl(1 1 0) interface have been investigated by synchrotron X-ray diffraction experiments. In the case of the oxide surface the analysis of the NiAl(1 1 0) crystal truncation rods (CTR) provide information about the interface between the Al2O3 film and the NiAl substrate. The analysis of the CTR-data shows clearly a rippled Ni-Al topmost surface with an amplitude value of RNi/Al = 0.16 ± 0.01 Å for the clean surface and RNi/Al = 0.18 ± 0.02 Å for the oxide covered surface. On the clean surface the Al sites are expanded by +3.8\% (outwards) and the Ni sites are contracted by -3.2\% (inwards) respect to the unrelaxed interlayer separation. For the oxide covered surface an increase of the expansion of the outermost Al atoms (+7.3\%) relative to their bulk positions has been found, while the Ni atoms remain (-0.9\%) at the bulk position. On both cases, an ideal surface stoichiometry (1:1) was obtained. However, some intermixing (chemical disorder) of one specimen in the sites of the other and vice versa was present (less than 4\%). This chemical disorder was not enhanced by the presence of the Al2O3 overlayer. Neither rippling nor oscillatory relaxation in deeper layers was detectable.