Initial Stages of Growth of Alumina on NiAl(001) at 1025 K

The initial stages of growth of ordered layers of Al 2 O 3 on NiAl(001) single‐crystal surfaces at 1025 K and 10 −7 mbar (10 −5 Pa) in O 2 have been studied using scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). The STM results evidence the formation of elongated strips (26 Å wide and 11 Å high) of Al 2 O 3 oriented along the [100] and [010] directions of the substrate. With longer oxidation, the substrate is increasingly covered by rectangular and striped islands resulting from the vicinal and parallel growth of the strips. On the ultrathin oxide film formed after 500 L (1 L = 10 −6 torr·s (∼1.33 × 10 −4 Pa·s)) of exposure, STM atomic resolution images have been obtained for the first time. They evidence the [001] orientation of the oxygen sublattice in Bain epitaxy on the substrate. The observation of one‐dimensional atomic trenches together with the strips observed on the nanometer scale is consistent with the growth of θ‐Al 2 O 3 . The STS local measurements evidence the insulating behavior of the oxide layer formed with a gap value ranging from 7 and 8 eV for amorphous and ordered domains, respectively.