Orientation Analysis of omega-Substituted Long-Chain Alkanethiols Self-Assembled on Au Substrate

Monolayers from para-substituted benzyl esters of 16-mercaptohexadecanoic acid (R = -Cl; -OCH3) self-assembled on (111)-textured gold films have been studied in detail with infrared and visible spectroscopic ellipsometry and contact angles measurements. The experimental data testify that these monolayers on gold tend to adopt tilt angles smaller than typical for n-alkanethiols, while the orientation of the phenyl rings is almost perpendicular to the surface. The same precursor molecules self-assembled on silver showed arrangement of the aliphatic chains characteristic for long-chain alkanethiols but differently tilted orientation of the terminal phenyl rings. An attempt was made to explain that different behavior with the different surface energetics of gold and silver substrates.