Surface Potential of 1,10-Decanedithiol Molecules Inserted into Octanethiol Self-Assembled Monolayers on Au(111)

Abstract

We measured the surface potential of 1,10-decanedithiol (C10S2) molecules inserted into 1-octanethiol (C8S) self-assembled monolayers (SAMs) using Kelvin-probe force microscopy (KFM) with noncontact atomic force microscopy (NC-AFM) under ultrahigh-vacuum (UHV) conditions. C8S SAMs on Au(111) were used as host matrices for C10S2 molecular insertion. Molecular insertion was used to orient the inserted C10S2 molecules to form a Au(111) surface−thiol bond at one end, whereas the thiol termini at the other end protruded from the C8S SAMs. The histograms of the surface potential images of the mixed C10S2:C8S SAMs exhibited two Gaussian peaks; however, the histograms of the surface potential images of the C8S SAMs exhibited only one peak. The surface fractions of C10S2 molecules in the mixed C10S2:C8S SAMs were evaluated from the Gaussian peaks. The surface potential of the inserted C10S2 molecules was 11 mV higher than that of the host C8S SAMs. The dipole moment difference between C10S2 molecules and C8S molecules was evaluated as 16 mD.