Comparative study of the molecular aggregation state of alkyl organic monolayers prepared on Si and hydrogen-terminated Si substrates

A comparative study of the molecular aggregation states of n-octadecyltrichlorosilane (OTS) and octadecene monolayers was carried out based on water contact angle, x-ray reflectivity (XR), grazing incidence x-ray diffraction (GIXD), and Fourier transform infrared spectroscopy (FT-IR) measurements. Water contact angle, XR, and FT-IR measurements revealed that the packing density and orientational order of the OTS were higher than those of octadecene. The OTS monolayer was in a hexagonal crystalline state with (10) spacing of 0.417 nm, whereas the octadecene monolayer was in an amorphous state. The growth mechanisms of the OTS and octadecene monolayers are also proposed. The alkyl molecular aggregation states strongly depended on the chemical bonding state at the interface between the alkyl organic molecule and the substrate surface.