Two-dimensional Structural Control of Alicyclic Thiol Self-Assembled Monolayers on Au(111)

Abstract

Self-assembled monolayers (SAMs) have have an attractive features that enable to control the surface state at molecular level over the practical application in biosensing, nanopatterning, corrosion inhibition, and molecular electronic devices. We examined the odd-even effect of methylene unit between the alicyclic ring and the sulfur headgroup as well as solution temperature effects on 2-D SAM formation (C6H11(CH2)nSH, n=0-3). It was found that the molecular packing structures and adsorption conditions of cyclohexanethiol (CHT) SAMs1,2 on Au(111) was influenced by solution concentration, unlike the case of alkanethiol. On the other hand, the adsorption of alicyclic ring terminated SAMs containing methylene groups between the sulfur headgroups and aliphatic ring exhibit totally different SAMs structure compared to cyclohexanethiol (CHT) SAMs without any methylene groups. It is obtained the first molecular-scale STM image of well-ordered cyclohexylmethanethiol (CHMTs) SAMs formed at solution temperature of -20 °C, and the two-dimensional (2D) ordered SAMs can be described as a (√3 × 2)R57° structure. STM measurement of cyclohexylethanethiol (CHET) and cyclohexylpropanethiol (CHPT) SAMs revealed that the surface condition of alicyclic ring system-SAMs was greatly influenced by the odd - even number of methylene spacer between the endgroup and headgroup.