Structural Effects on the Formation of Self-assembled Monolayers by Aromatic Thiols on Au(111)

Abstract

Self-assembled monolayers (SAMs) of aromatic thiols have drawn much attention due to their interesting electrical and optical properties that may be applicable in molecular electronics. It has been demonstrated that the electrical properties of SAM-based molecular devices are markedly influenced by changes in both functionality and orientation of adsorbed molecules. Therefore it is essential to tune the two-dimensional (2D) SAM structures of aromatic thiols on metal surfaces. In this study, we examined using scanning tunneling microscopy the odd-even effects of methylene unit between the aromatic ring and the sulfur headgroup as well as solution temperature effects for 2D SAM formation (C6H5(CH2)nS-Au, n=0-3). We found that benzenethiol and benzeneethanethiol with an even unit have ordered SAMs showing the lower density line structures, whereas benzenemetanethiol and benzenepropanethiol with an odd unit have ordered SAMs with the higher packing density domains.