Abstract
Structure and growth mechanism of ultra-thin Al 2O 3 films on NiAl(001) have been investigated with 180°-neutral impact collision ion scattering spectroscopy, high resolution spot profile analysis of low energy electron diffraction, and scanning tunnelling microscopy (STM). Ordered Al 2O 3 films have been prepared by oxygen exposure at room temperature and subsequent annealing at T = 1200 K. The formation of epitaxial oxide films is unaffected by the initial composition or reconstruction of the substrate. The oxidized surface being covered by Al 2O 3 appears to be microscopically rough, reversible stepped with step heights of about 3 Å and consists of a network of elongated equally distributed oxide stripes along 〈100〉 and 〈010〉 directions of the NiAl(001) surface. The lateral anisotropy of the oxide is probably caused by the build up of internal stress in the growth process. After oxygen saturation exposure at room temperature and subsequent annealing, regions with rather regular arranged parallel oxide stripes show up in the STM images (mean width ≈ 27 A ̊ , period ≈ 54 A ̊ ). The corresponding low energy electron diffraction pattern shows the existence of orthogonal (2 × 1) antiphase domains with a (9 × 1) superstructure (period 26.02 Å) close to the mean width of oxide stripes. Next to the oxide stripes, regrowing NiAl terraces and thin layers of amorphous Al 2O 3 have been found.
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