Aromatic self-assembled monolayers to surface metal complexes: electrochemistry and XPS insights of interfacial structure.

A series of bipyridine-based self-assembled monolayers (BPD SAMs) were fabricated on Au substrates and modified through electron-beam-induced crosslinking and transition-metal (Ni, Co, and Cu) intercalation. Electrochemical reductive desorption revealed enhanced stability after modification, with the desorption potential shifting from -1.278 V vs. SCE for pristine BPD to -1.325 V vs. SCE for crosslinked BPD and -1.336 V vs. SCE for BPD-Ni. X-ray photoelectron spectroscopy (XPS) confirmed the standing-up orientation of BPD molecules on Au, successful intermolecular crosslinking after irradiation, and metal-nitrogen coordination following metal intercalation. Despite reductions in surface coverage and packing density, XPS depth profiling showed significantly improved resistance to Ar+ sputtering, with the C 1s depletion time increasing from 95 s for pristine BPD to 245 s for crosslinked BPD and 195 s for BPD-Ni, corresponding to 2.6-fold and 2.1-fold enhancements, respectively. The combined electrochemical and XPS results demonstrate that crosslinking and metal coordination improve SAM's robustness through the formation of interconnected molecular networks rather than increased molecular packing. These findings provide an effective strategy for developing robust bipyridine-based SAMs for molecular electronics, electrocatalysis, and sensing applications.