Effects of humidity and solution age on growth of organosilane self-assembled monolayers

The effect of humidity on the self-organization and growth mechanism of octadecyltrichlorosilane (OTS) monolayers was investigated using an atomic force microscope (AFM), grazing incidence X-ray diffraction (GIXD), and Fourier transform IR spectroscopy (FT-IR). OTS self-assembled monolayers (SAMs) were prepared under humidity ranging from 5 to 80%. Under humidity ranging from 15 to 80%, OTS molecules produced domain structures early in the growth process that grew twodimensionally on SiO₂ substrates. Also, the crystalline peaks of the obtained from the GIXD measurement indicated that OTSSAMs prepared under high humidity (15-80%) had grown in a crystalline state. Thus, "self-organization" occurred under these conditions. However, OTS-SAMs prepared under 5% humidity were in an amorphous structure. OTS-SAMs prepared at high humidity were denser than those prepared at low humidity. The domain size early in the growth process increased in proportion to the solution age. This shows that the reaction rate is governed by the hydrolysis of organosilane. On the other hand, solution age has no great influence on the density of the OTS-SAMs under conditions of more than 50% humidity.