In this study, the XPS characterization of different binary aromatic SAMs on copper is presented. The mixed layers, constituted by benzenethiol (BT) and alternatively 4-fluorobenzenethiol (FBT) or 4-acetamidothiophenol (AA), were prepared by two different methods, namely coadsorption from solution and partial substitution of a preformed BT layer. The overall quality and the surface composition of the different SAMs have been assessed as a function of the solution concentration for the former preparation and of the substitution time for the latter. In addition, the parameters contributing to determine the surface composition of the aromatic mixed layers on copper have been identified. (C) 2014 Elsevier B.V. All rights reserved.