Polarization Modulation Fourier Transform Infrared Studies of the Effects of Self-Assembly Time on the Order and Orientation of 11-Ferrocenyl-1-undecanethiol Monolayers on Gold

The effects of self-assembly time on the order and orientation of 11-ferrocenyl-1-undecanethiol (FcC11SH) molecular layers on gold were studied with polarization modulation Fourier transform infrared spectroscopy. A comparison between the intensity of the asymmetric methylene stretching mode of a 1-octadecanethiol monolayer and that of the FcC11SH molecular layer confirmed that the FcC11SH molecules formed a self-assembled monolayer on the gold surface. The conformational order of the monolayer increased with longer self-assembly time as evidenced by a decrease in the vibrational frequencies of the methylene stretching modes and a decrease in the full width at half maximum of these bands. The peak area of the asymmetric methylene stretch also decreased with longer self-assembly time, implying that the FcC11SH molecules stood more erect with respect to the gold surface as the monolayer self-assembled.