Benzene bilayer islands were observed by STM to be structurally similar on both Cu(111) and Cu(110) surfaces. The local electronic structure of the bilayers was studied using tunneling spectroscopy of Stark-shifted image potential states. On both Cu substrates, the n = 1 bilayer state was locally shifted away from the Fermi level when compared to the n = 1 monolayer state. The Stark-shift due to the electric field of the STM tip was observed to be greater for the n = 1 bilayer state than the n = 1 monolayer state on Cu(111). (c) 2006 Elsevier B.V. All rights reserved.