ARPES study of the surface states from Au/Ag(1 1 1): evolution with coverage and photon energy F.J. Palomares a , M. Serrano a , A. Ruiz a , F. Soria a , K. Horn b , M. Alonso a, * a Instituto de Ciencia de Materiales de Madrid (CSIC), Cantoblanco E-28049 Madrid, Spain b Fritz-Haber-Institut der MPG, Faradayweg 4-6, 14195 Berlin, Germany Received 23 July 2001; accepted for publication 8 April 2002 Abstract The Shockley surface states formed on the (1 1 1) surfaces of noble metals have been extensively studied, but few reports exist on layered thin film systems. We present angle-resolved photoemission (ARPES) results, recorded at normal emission in the photon energy range from 21 to 49 eV, which describe the behavior of these sp-derived surface states for Au layers epitaxially grown on Ag(1 1 1). Growth was performed at room and low temperatures. In both cases, the ARPES spectra are found to evolve from Ag(1 1 1)-like to Au(1 1 1)-like features as the thickness of the Au film increases. In particular, the surface-state binding energy shifts from the Ag(1 1 1) to the bulk Au(1 1 1) position, the shift being already evident at coverages lower than one monolayer. The origin of the changes observed in the surface- state peak as a function of Au coverage and photon energy will be discussed. Ó 2002 Published by Elsevier Science B.V. Keywords: Angle resolved photoemission; Synchrotron radiation photoelectron spectroscopy; Surface electronic phenomena (work function, surface potential, surface states, etc.); Gold; Silver; Low index single crystal surfaces; Metal–metal interfaces 1. Introduction Since the initial report by Gartland and Sla- gsvold in 1975 [1], the L-gap Shockley-type surface states observed on the (1 1 1) surfaces of noble metals have been extensively investigated. Interest continues until today, and for instance, the lifetime and line width of these states have attracted con- siderable attention in the last five years [2–6]. These electronic states have served as prototypes for the study of several phenomena, being partic- ularly interesting as models for the investigation of two-dimensional (2D) electron systems [3,7]. Moreover, lateral confinement of such 2D elec- trons has recently offered the possibility to use the surface as a quantum laboratory, in order to study electronic properties of nanosized structures or even to probe structural properties [8–10]. Most of the studies performed on the surface states of noble metals correspond to single crystal surfaces, while relatively few reports exist on the behaviour in layered thin film structures [11–23]. The Shockley-type states arise mainly from the special boundary conditions introduced by the metal/vacuum interface, such that any modifica- tion of the surface barrier potential or of the substrate band gap will vary the surface-state en- ergy, which can be thus used as a sensitive probe Surface Science 513 (2002) 283–294 www.elsevier.com/locate/susc * Corresponding author. Tel.: +34-91-3349094; fax: +34-91- 3720623. E-mail address: malonso@icmm.csic.es (M. Alonso). 0039-6028/02/$ - see front matter Ó 2002 Published by Elsevier Science B.V. PII:S0039-6028(02)01727-2