Effect of reaction temperature on growth of organosilane self-assembled monolayers

The effect of reaction temperature on the self-organization and growth mechanism of octadecyltrichlorosilane (OTS) self-assembled monolayers (SAM) was investigated by atomic force microscopy (AFM), grazing incidence X-ray diffraction (GIXD) measurement, Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS). OTS SAM was prepared by a liquid phase method and chemical vapor deposition. In the liquid phase method, OTS SAM was prepared in the temperature range from 5 to 40 °C. In the reaction temperature range from 5 to 30 °C, OTS molecules formed domain structures early in the growth process and grew two-dimensionally on SiO₂ substrates. In addition, the crystalline peaks of GIXD measurements indicated that OTS SAM prepared at lower temperatures (5-30 °C) grew in the crystalline state. Thus, "self-organization" occurred under these conditions. However, OTS SAM prepared at 40 °C showed an amorphous structure. XPS and FT-IR spectra showed that the SiO₂ peak increased while reaction temperature decreased. These results indicated that the formation of a siloxane bond between OTS molecules was important for the self-organization of the OTS monolayer. In addition, FT-IR measurement indicated that the packing density of the OTS monolayer prepared at lower temperatures was higher than that prepared at higher temperatures by chemical vapor deposition.