We report on the scanning tunneling microscopy (STM) study of self assembled monolayers (SAMs) on Au(1 1 1). SAMs consist of mono and bi-component alkylthiol of various chemical functionnalizations. Such systems give the opportunity to elaborate surfaces with tuned chemical properties. We will show our first results concerning the selective grafting of conjugated organic groups on a bi-component SAM composed of methyl and alcohol terminated molecules. (C) 2003 Elsevier Science B.V. All rights reserved.