Hydroxyl ions react with diazonium salts to give transient diazohydroxides, which are deprotonated to diazoates. The latter react spontaneously with Fe and Au to give surfaces modified with aryl groups. These surfaces are characterized by XPS and IR spectroscopies. The mechanism involves the homolytic reduction of the diazoate to give a radical that binds to the substrate. (C) 2008 Elsevier Ltd. All rights reserved.