Electronic structure of alkali halide–metal interface: LiCl(001)/Cu(001) M. Kiguchi a, * , H. Inoue b , K. Saiki a,b , T. Sasaki a , Y. Iwasawa b , A. Koma b a Department of Complexity Science and Engineering, Graduate School of Frontier Sciences, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan b Department of Chemistry, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan Received 18 January 2002; accepted for publication 13 September 2002 Abstract Electronic structure of the heteroepitaxial LiCl thin film grown on Cu(0 0 1) was studied using electron energy loss spectroscopy (EELS) and ultraviolet photoelectron spectroscopy (UPS), as a model system of the insulator/metal in- terface. The EELS results did not show any change in the band gap of the LiCl film, though the AndersonÕs prediction indicated that the band gap of an insulator decreased at the insulator/metal interface. The change in the band gap of the LiCl film is discussed by considering Madelung potential and many body effects. The UPS results, on the other hand, showed an upward shift of the Cl 3p with an increasing film thickness. Ó 2002 Elsevier Science B.V. All rights reserved. Keywords: Metal–insulator interfaces; Electron energy loss spectroscopy (EELS); Photoelectron spectroscopy; Alkali halides; Copper 1. Introduction Thin films of insulating materials have attracted wide attention not only for fundamental science but also for technological applications in micro- electronic, nonlinear optical devices and ferro- electronic devices. If well-ordered single-crystalline insulating thin films can be prepared on metal substrates, various properties can be expected for insulating films and the metal/insulator interface; furthermore these are expected to open a novel field in surface and interface sciences. For exam- ple, the band gap narrowing and the metal–insu- lator transition are predicted at and in the vicinity of the interface [1–6]. The Madelung potential should decrease in the film state, and the electron– electron interaction may change at the metal/ insulator interface because of electron spill over from a metal to an insulator, and appearance of image potential in the metal. However, the large difference in chemical bond between metals and insulators makes it difficult to form a well-ordered interface. In many studies, three-dimensional island growth has been ob- served. Otherwise only the initial stage of growth has been studied by low energy electron diffraction (LEED)andscanningtunnelingmicroscope(STM), which can not be distinguished from the adsorp- tion of isolated molecules on metals [7]. Thus, the electronic structure has not been explored * Corresponding author. Tel./fax: +81-3-58418867. E-mail address: kiguchi@k.u-tokyo.ac.jp (M. Kiguchi). 0039-6028/02/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved. PII:S0039-6028(02)02329-4 Surface Science 522 (2003) 84–89 www.elsevier.com/locate/susc