Synthesis of octadecyltrichlorosilane self-assembled monolayer films by vapor deposition on plasma activated silicon substrates

Molecular films of octadecyltrichlorosilane (OTS) silanized on silicon substrates were obtained by a succession of fabrication steps consisting in plasma hydroxylation of silicon surface, formation of a water layer adsorbed on hydroxylated surface by substrate exposure to water vapor and OTS vapor deposition. All fabrication steps were realized in the same vacuum chamber to avoid surface contamination and to control the amount of water adsorbed on the hydroxylated surface. It is proved that the amount of water on the substrate surface plays a key role in fabrication of smooth OTS molecular films, large amounts of water on substrates resulting in formation of 3D OTS aggregates. The atomic force microscopy (AFM) investigations of the film surface revealed formation of liquid-expanded and liquid-condensed domains in OTS molecular films. Annealing of the OTS films promotes film dehydration, increases the film hydrophobicity and reduces nanoscopic adhesion and friction forces between silicon AFM tips and film surface.

Automated summary

The fabrication of smooth OTS molecular films on silicon substrates relies on the crucial role played by the amount of water on the substrate surface, with excessive water leading to the formation of 3D OTS aggregates. AFM investigations indicate the presence of liquid-expanded and liquid-condensed domains within the OTS molecular films. Annealing of the OTS films promotes film dehydration, enhances hydrophobicity, and diminishes nanoscopic adhesion and friction forces between silicon AFM tips and film surface.