Unique Mixed Phases and Structures of Self-Assembled Monolayers on Au(111) Derived from Methoxy-terminated Mono(ethylene glycol)ethanethiols

To understand the effect of the ethylene glycol (EG) substituent of alkanethiols on domain formation, surface structure, and adsorption condition of self-assembled monolayers (SAMs) on Au(111), we examined SAMs formed by 1-ethanethiol with methoxy-terminated mono(ethylene glycol) (EG1-OMe SAMs) by scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy and compared the results to those of heptanethiolate SAMs with a normal alkyl chain of similar molecular length. STM imaging clearly revealed that the surface features of EG1-OMe SAMs on Au(111) were noticeably different than those of heptanethiolate SAMs. The adsorption of EG1-OMe molecules on Au(111) in a 1 mM ethanol solution at RT for 1 min led to the formation of SAMs containing mixed phases: a paired-row ordered phase and poorly ordered phase containing molecular spots with an apparent bright contrast. The paired-row ordered domain of EG1-OMe SAMs on Au(111) was assigned to the (2√5 × 5)R11° packing structure, which is comparable to a...