Two-dimensional Phase Transitions of Dioctyl Diselenide Self-Assembled Monolayers on Au(111)

Abstract

Phase Transitions and surface structures of dioctyl diselenide (DODSe) self-assembled monolayers (SAMs) on Au(111) were investigated by means of scanning tunneling microscopy, cyclic voltammetry, and contact angle measurements. Compare to the formation of well ordered alkanethiol SAMs on Au(111), DODSe SAMs are composed of disordered phase and a number of vacancy island (VIs) with a higher VIs fraction. We found the phase transitions of DODSe SAMs from molecular aggregations to disordered dense phases via less dense missing-row phases as a function of immersion time. It was also found that the fraction of VIs to the total surface area in DODSe SAMs increases with increasing solution concentration, which is different from alkanethiol SAMs. Compared to alkanethiol SAMs on Au(111), unique SAM characteristics for DODSe SAMs are attributed to the strong chemical interaction of Se headgroups to gold surfaces.