Imaging of the Al Structure of an Ultrathin Alumina Film Grown on Cu-9 at.%Al(111) by STM

An ultrathin alumina film grown on a Cu-9 at.%Al(111) substrate is investigated using low-temperature scanning tunneling microscopy and spectroscopy. The topographic images show a zigzagged corrugation characterized by the heptagonal and pentagonal organization of interfacial aluminum atoms and by a dependence on the bias voltage. Furthermore, the dI/dV maps and the spectrum reveal an unoccupied state locating at about +0.26 eV, which most likely originates from the aluminum-oxygen hybridization and is possibly responsible for the heptagonal and pentagonal arrangements of Al atoms.