n-Dodecanethiol (RSH) and n-dodecaneselenol (RSeH) molecules have been self-assembled on electrochemically reduced copper sheets. To assess the stability of the resulting monolayers, immersion, during different times varying from minutes to hours, of the modified copper in a solution which contains the competitor molecule has been performed. PM-IRRAS shows a good organisation for all monolayers without any divergence. Based on XPS analysis, we have proved an intercalation process of RSeH molecules followed by adsorption on the free sites of copper modified with the RSH and in similar way the insertion and adsorption of RSH molecules in the RSeH modified copper. The only difference between the two directions is in the kinetics which seems to be faster for thiol compared to selenol. (C) 2009 Elsevier B. V. All rights reserved.