Improved Strain Relief of Self-Assembled Monolayers from Organohydridochlorosilanes Grafted onto Oxidized (1,0,0) Silicon Wafers

Silylation reactions of oxidized silicon(1,0,0) wafers with octadecylchlorosilanes were performed to determine the influence of the number of hydrolyzable functions on the quality of the film deposited on the surface. Octadecylchlorosilane (C18H37SiH2Cl) and octadecyldichlorosilane (C18H37SiHC12) were synthesized and compared to the well-studied octadecyltrichlorosilane (C18H37SiCl3). The grafting reactions in CCl4 solutions were monitored by in situ internal reflection FTIR spectroscopy. The surfaces were also analyzed by wettability, ellipsometry, and atomic force microscopy (topography and friction). As expected, the Si-H bonds are unreactive under these reaction conditions, indicating that the monochlorosilane and the dichlorosilane behave as mono- and difunctional species, respectively. The surfaces obtained after grafting of octadecyltrichlorosilane and octadecyldichlorosilane-that is, in cases where cross-linking is possible-are similar with a very dense film of organized alkyl chains in the all-trans configuration. On the other hand, in the case of octadecylchlorosilane where no cross-linking is possible, a less organized film of monografted species is obtained.