Understanding the relationship between surface coverage and molecular orientation in polar self-assembled monolayers

We report here a study of surface coverage and molecular orientation in polar self-assembled monolayers (SAMs). The ordering in these SAMs arises from the competition of bonding to the surface and mutual steric effects that force alignment of the dipolar chromophores. The optimized molecular orientation was found to be 32 +/- 3 degrees, and the maximum surface coverage was approximately 2-4 molecules per nm(2) depending on the molecular cross section. Second harmonic generation (SHG) measurements were performed to verify the polar alignment; transmission electron microscopy (TEM) was employed to determine the monolayer thin-film thickness (4.3 nm) in a selected SAM.