Scanning tunneling microscopy (STM) was used to investigate the oxide structures underlying the surface of alumina thin-film grown on NiAl(100). At a bias voltage (on the sample) below 2.0 V, STM topography images of the alumina layer beneath the surface were obtained. A probe with depth of 2-8 angstrom was readily attained. The under-surface observation shows that the film consists of stacked layers of alumina whereas the layered alumina unnecessarily comprises entire theta-Al2O3 unit cells. The lattice orientation of the upper alumina layer differs from that of the lower one by 90 degrees - the newly grown oxide structurally matching the horizontal oxide rather than the lower oxide. The results indicate a growth process competing with the typical mode of epitaxial growth for the growth of alumina film. (c) 2012 Elsevier B.V. All rights reserved.