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Abstract:
n-Alkyltrichlorosilane films with different alkyl chain length (n-propyltrichlorosilane [PTS, CH3(CH2)29-SiCl3]; n-octadecyltrichlorosilane [OTS, CH3(CH2)17SiCL3]; n-triacontyltrichlorosilane [TCTS, CH3(CH2)29-SiCl3]) and trimethoxysilane films with amino- and methyl-terminated alkyl chains (n-octadecyltrimethoxysilane
[OTMS, CH3(CH3(CH2)17Si(OCH3)3]; (3-aminopropyl)trimethoxysilane [APTMS, NH2(CH2)3Si(OCH3)-
(OCHa)a]; (17-aminoheptadecyl)trimethoxy silane [AHTMS, NH2(CH2)17SI(OCH3)3]) of different chain length have been characterized using near edge X-ray absorption fine structure (NEXAFS) spectroscopy and X-ray photoelectron spectroscopy (XPS) to probe the molecular order and orientation in self-assembled
films. Furthermore, the influence of the different headgroups (trichlorosilanes vs trimethoxysilanes), chain lengths, and chain terminal functions (methyl vs amino) on the resulting film structures was investigated. It was found that methyl-terminated silanes with an alkyl chain of intermediate length like OTS and OTMS tend to form self-assembled monolayers which are oriented almost perpendicular to the surface. The different chemistries of these two compounds during adsorption seems to result in slightly different film structures. Aminosilane (AHTMS) films of the same chain length as OTS and OTMS, however,
are completely disordered. XPS indicates, that this is probably due to the interaction of the amino group with the surface. Short alkyl chain silanes with a terminating methyl or amino group (APTMS, PTS) result in films with no defined orientation of the molecules. Also long chain methyl-terminated alkylsilane films (TCTS) are less well oriented than OTS films, which gives evidence that there is an optimal chain
length for ordering in self-assembled organosilane films.
