Porosity Effects on the Ordering and Stability of Self-Assembled Monolayers on Nanoporous Gold

We investigated the stability, ordering, and composition of mixed self-assembled monolayers (SAMs) on nanoporous gold surfaces formed by dealloying silver–gold leaf. We characterized surface features of the nanoporous gold using fast Fourier transform image analysis and lead underpotential deposition to quantify the surface changes associated with increased dealloying time. SAMs were prepared with ferrocenyl alkylthiols and alkanethiols. We used cyclic voltammetry to investigate the stability of the SAMs and found no stability differences with changes in pore size. Cyclic voltammetry investigations of ferrocenylalkylthiolate SAMs showed differing intermolecular interactions with increased porosity, indicating that changes in pore size can produce or disrupt intermolecular attractions between the attached ferrocene groups. We also found that the porosity of the nanoporous gold decreases the ferrocenylalkylthiolate coverage in mixed ferrocenylalkylthiolate/alkanethiolate molecular layers compared to the solution composition. We used infrared reflection absorption spectroscopy as an additional probe of molecular ordering. Our results show that the nanoporous structure significantly changes the ordering and intermolecular interactions within the ferrocenylalkylthiolate SAMs compared to planar surfaces.