Investigation of 3-mercaptopropyltrimethoxysilane self-assembled monolayers on Au(111) surface

In this paper, preparation method of two-dimensional (2D) silica-like surface from self-assembled monolayers (SAMs) of 3-mercaptopropyltrimethoxysilane (MPTMS) on Au(111) surface is presented. The surface structure and morphology were characterized by scanning tunneling microscopy (STM) and secondary ion mass spectrometry (SIMS). In a first step, gold surface was imaged in order to find the topography. Then investigations were focused on MPTMS deposited on Au(111). Further steps like hydrolysis and condensation of MPTMS end-groups were performed and monitored by STM and SIMS methods. Hydrolysis and condensation reactions lead to 2D SiO2 network called glass monolayer. It can be also described as 2D sol-gel processes. All procedures were performed in monolayer. When the state of end groups of MPTMS changes, i.e. when methoxy (Si-OCH3) groups undergo hydrolysis to silanols (Si-OH) groups, the surface topography changes. The similar phenomena may be observed when silanols undergo condensation and siloxy (Si-O-Si) bonds are created.