The results of investigations of the Cu/Ru (10 (1) over bar0) adsorption system obtained by using directional elastic peak electron spectroscopy (DEPES), Auger electron spectroscopy and low energy electron diffraction are presented. The measurements were performed for the clean and Cu covered ruthenium surface at a coverage of 7 bilayers at room temperature. At early stages of growth the formation of two flat Cu bilayers was observed. Further adsorption leads to the nucleation of Cu(111) islands of the face centered cubic (fcc) structure. However, the experimental results reveal the formation of two fcc(111) domains which are mutually rotated by 180 degrees arranged in the [2 (11) over bar](111)Cu parallel to[0001](10 (1) over bar0) Ru and [(2) over bar 211](111)Cu parallel to[0001](10 (1) over bar0) Ru orientations with respect to the substrate. Moreover, the quantitative analysis of DEPES data reveals nonequivalent (45%/33%) concentrations of these domains. (C) 2013 Elsevier B.V. All rights reserved.