The Role of Buried Hydrogen Bonds in Self-Assembled Mixed Composition Thiols on Au{111}

We have investigated the role of internal functionality in self-assembled monolayers of a family of amide-containing alkanethiol molecules on Au{111} using scanning tunneling microscopy. In addition to van der Waals interactions that are present within n -alkanethiol self-assembled monolayers, hydrogen bonding between adjacent buried amide groups contributes to the stability of the amide-containing molecules on the surface and causes spontaneous phase separation upon coadsorption with an n -alkanethiol. A deposition solution concentration dependence study reveals that this is an observed trend across a range of examined solution compositions. Additionally, hydrogen bonding affects the packing structure of the amide-containing alkanethiol self-assembled monolayers. Although they adopt the same (√3×√3) R 30° base lattice as n -alkanethiolate self-assembled monolayers, the amide-containing molecules form superlattice structures that are more linear than n -alkanethiol monolayers due to the hydrogen bonds they form. The internal functionality of monolayers can be used to control their formation and stability.