Variation of Surface Potential of Alkanethiol Self-Assembled Monolayers with Different Chain Lengths on a Gold Substrate

Abstract

A theoretical study on the surface potential of alkanethiol self-assembled monolayers (SAMs) with different alkyl chain lengths on a gold substrate was carried out in terms of the Helmholtz model. The influences of molecular dipole moment, relative permittivity of the SAMs, and angle between the molecular chain and the substrate normal on the surface potential were systematically investigated using quantum chemical softwares Gaussian 03 and MOPAC. We found that the variation of surface potentials for the alkanethiol SAMs with different alkyl chain lengths mainly resulted from regular changes in the angles between the molecular chains and the substrate normal. We propose a new explanation for the variation in surface potentials of the alkanethiol SAMs with different alkyl chain lengths by considering the SAM formation mechanism.