An in situ surface X-ray diffraction study of the clean, oxidized and subsequently annealed surfaces of regularly stepped NiAl(671) was presented. The results showed that the UHV stable, clean surface was not faceted, and consisted of a regular array of (110) terraces and (011) steps. The top-most Al and Ni atoms on the terraces exhibited a rippled relaxation while the step atoms were relaxed towards the bulk. Preferential Al oxidation at 540K and 6 x 10−6 mbar O2 led to the formation of a 5Å disordered alumina layer and induces Al vacancies and Ni anti-sites in the Al-depleted interfacial region. The terrace-step structure of the clean surface was maintained, but strong inward relaxations of the interfacial atoms change the strain field around the steps. Massive (110) faceting with facets up to 50 times larger than the original terraces occurs after high-temperature annealing, during which the surface oxide develops a complex long-range ordering. These results could be understood by the change of interfacial strain, which removes the energy barrier for mass transport. In addition, unlike the case for low-index (110) surfaces, step-induced suppression of twin domain formation was found in the alumina film grown on NiAl(671). The results showed that the interplay between oxidation and strain could have dramatic effects on the morphology of vicinal surfaces.

In situ X-ray Study of the Oxidation of a Vicinal NiAl(671) Surface. C.Ellinger, V.Vonk, N.Khorshidi, A.Vlad, A.Stierle, H.Dosch: New Journal of Physics, 2009, 11[11], 113004