Self-assembled monolayers containing biphenyl derivatives as challenge fornc-AFM

Mixed self-assembled monolayers (SAMs) of biphenylmethanethiol derivatives with -CH3 and -COOH terminal groups and those of 1-decanethiol and a biphen ylmethanethiol derivative with a -CH3 or a -COOH terminal group were prepar ed on Au(lll) surfaces. The resulting mixed SAMs were imaged by scanning tu nneling microscopy (STM), These mixed SAMs can be used to study chemical fo rce microscopy (CFM) by noncontact atomic force microscopy (nc-AFM), Namely , the -CH3 and -COOH terminal groups of the SAMs can be recognized by diffe rent surface interactions with a surface functional group on a gold-coated AFM tip derivatized with the same thiol compound with a -CH3 or a -COOH ter minal group. The present result also suggests that these SAMs can be used t o study CFM using nc-AFM with simultaneous tunneling current measurement. B y this method, for example, a molecular location of a biphenylmethanethiol derivative with a -COOH terminal group in an alkanethiol matrix observed by nc-AFM can be confirmed by the tunneling current measurement due to lower tunneling barrier height of the biphenylmethanethiol than that of the alkan ethiol derivative. (C) 2000 Elsevier Science B.V. All rights reserved.