Spin–orbit splitting in ultra thin Ag films on Cu(1 0 0) V. Mik  si  c Trontl a,b , M. Kralj a,1 , M. Milun a , P. Pervan a, * a Institute of Physics, P.O. Box 304, Bijenicka c. 46, HR 10000 Zagreb, Croatia b Faculty of Electrical Engineering and Computing, Unska 2, HR 10000 Zagreb, Croatia Received 24 October 2003; accepted for publication 2 January 2004 Abstract Ultra thin silver films deposited on Cu(1 0 0) have been studied by high energy and angle resolved photoemission spectroscopy (ARPES), scanning tunnelling microscopy (STM) and low electron energy diffraction (LEED). An effective spin–orbit splitting in the Ag 4d was measured as the morphology of deposited silver was changing from the silver–copper alloy to separated silver–copper systems. It is found that in the limit of small silver concentration the spin–orbit splitting is equal to the atomic value, i.e., 0.22 eV. With the increasing silver concentration the splitting continuously increases reaching the value of 0.28 eV at the saturation coverage (0.9 ML). Possible effects that induce increase of the effective spin–orbit splitting are discussed. Ó 2004 Elsevier B.V. All rights reserved. Keywords: Angle resolved photoemission; Metallic films; Silver; Copper 1. Introduction The case of ultra thin silver films on Cu(1 0 0) falls into the category of heteroepitaxial systems that exhibit a change from surface alloying to a complete separation of the elements with increas- ing concentration of adlayer metal. Despite the positive heat of mixing that inhibits solubility of silver in copper it has been established that the alloying can take place for a small concentration of Ag deposited on Cu(1 0 0) [1]. For coverages lower than 0.13 silver atoms substitute the Cu surface atoms of Cu(1 0 0), as demonstrated by the low temperature scanning tunnelling microscopy (STM) [1] and X-ray photoelectron diffraction (XPD) [2]. A recent molecular dynamic simulation support these experimental findings and, in addi- tion, suggests that even at moderately elevated temperatures, conditions for silver–copper alloy- ing can be achieved well above the concentration equilibrium in the solids [3]. However, as the concentration of silver on Cu(1 0 0) increases the driving force for the formation of Ag islands in- creases. At room temperature and below, the sat- urated silver layer appears to be structurally completely separated from copper topmost layer, i.e., all Ag atoms are contained within the layer and none within the Cu topmost layer. The satu- rated Ag monolayer has a well known c(10 · 2) structure [4]. This structure is a slightly deformed hexagonal structure of Ag(1 1 1) surface that is introduced by 13% mismatch between the Cu(1 0 0) and Ag(1 1 1) lattices. * Corresponding author. Tel.: +385-1-4698888; fax: +385-1- 4698889. E-mail address: pervan@ifs.hr (P. Pervan). 1 Present address: Institute for Physical Chemistry, Bonn University, Germany. 0039-6028/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.susc.2004.01.001 Surface Science 551 (2004) 125–131 www.elsevier.com/locate/susc