Scanning Tunneling Spectroscopy of Insulating Self-Assembled Monolayers on Au(111)

Abstract

Self-assembled monolayers (SAMs) of dodecanethiol (DDT), octadecanethiol (ODT), and resorcinarene C10 tetrasulfide (RC10TS) on Au(111) were characterized by scanning tunneling spectroscopy (STS) under ultrahigh vacuum conditions and evaluated as ultrathin resists. A voltage division factor η was used to parametrize the equilibrium Fermi energy level Ef in terms of an applied voltage bias. Nominally symmetric tunneling (η ∼ 0.5) conditions were established by acquiring conductance spectra over a range of set point voltages. The electrical conductivity of the monolayers was observed to be dependent on both the monolayer thickness and the nature of the Au/S bonding. Leakage current densities across DDT and RC10TS SAMs on Au were estimated, with the latter comparing favorably with a 1.5-nm layer of SiO2 on Si.