Self-Assembly of Upright, Partially Dehydrogenated Melamine on Pd(111)

The adsorption of melamine (1,3,5-triazine-2,4,6-triamine) on Pd(111) under ultrahigh-vacuum conditions was investigated using scanning tunneling microscopy and reflection–absorption infrared spectroscopy. At all coverages in the submonolayer regime, melamine was found to adsorb with its molecular plane perpendicular, or close to perpendicular, to the (111) surface. Following adsorption at 300 K, at low coverage, 1-D chains of partially dehydrogenated melamine are formed on the Pd surface aligned along the ⟨1̅1̅2⟩ crystallographic directions. At higher coverage, pairing of melamine species is observed, and chain growth directions become less well-defined. The surface chemistry of melamine and the influence of the surface, coadsorbed hydrogen, and intermolecular interactions on the formation of ordered molecular arrangements are discussed.