Monolayer formation of octyltrimethoxysilane and 7-octenyltrimethoxysilane on silicon (1 0 0) covered with native oxide

Modification has been carried out of silicon (1 0 0) covered with native oxides with monolayers of octyltrimethoxsilane (C8TMS) and octenyltrimethoxysilane (C8enTMS). Different conditions of adsorption from the organic solvents chloroform, toluene and n-hexane with subsequent exposure to ammonia vapour under ambient atmosphere have been tested for monolayer formation without exclusion of moisture. Thickness of resulting adsorbates has been measured using spectroscopic ellipsometry (SE), water contact angles were measured, and the surface roughness was determined by atomic force microscopy (AFM). If all three results are consistent with the presence of monolayers on the surface, further characterisation has been carried out by angle dependent X-ray photoelectron spectroscopy (XPS). For monolayers, surface roughnesses about <0.3 nm were measured, which were mainly determined by the substrate. Thicknesses obtained from SE and XPS agree. Conformational and orientational order of the monolayers determined by attenuated total reflection infrared (ATR-IR) spectroscopy show disordered chains in both cases with nearly isotropic orientation. C8enTMS was found to be partly hydroxylated when treated under alkaline conditions.