Self-assembled monolayers containing biphenyl derivatives as challenge for nc-AFM

Abstract

Mixed self-assembled monolayers (SAMs) of biphenylmethanethiol derivatives with CH 3 and COOH terminal groups and those of 1-decanethiol and a biphenylmethanethiol derivative with a CH 3 or a COOH terminal group were prepared on Au(111) surfaces. The resulting mixed SAMs were imaged by scanning tunneling microscopy (STM). These mixed SAMs can be used to study chemical force microscopy (CFM) by noncontact atomic force microscopy (nc-AFM). Namely, the CH 3 and COOH terminal groups of the SAMs can be recognized by different surface interactions with a surface functional group on a gold-coated AFM tip derivatized with the same thiol compound with a CH 3 or a COOH terminal group. The present result also suggests that these SAMs can be used to study CFM using nc-AFM with simultaneous tunneling current measurement. By 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 alkanethiol derivative.