Growth and image potential states of the alumina monolayer on Cu-9 at.% Al( 111) were investigated by low temperature scanning tunneling microscopy. The alumina monolayer showed a zigzagged corrugation with the rectangular unit cell that possessed a root 3 ratio between lengths of the two sides. Furthermore, the distance-voltage characteristics revealed that the energy of the n = 1 image potential state on the alumina film shifted by about 024 eV towards the vacuum level compared with that on pristine Cu-9 at.% Al(111). This shift was explained in terms of the joint modification of the surface potential by the repulsion between electrons and the alumina layer as well as by the depression of the electric field in the Stark effects. Probing the energies of image potential states provided a way to investigate how the alumina film influenced interfacial electronic structure, which showed practical applications for the development of electronic devices. (C) 2011 Elsevier B.V. All rights reserved.