Dynamics of Reactive Metal Adsorption on Organic Thin Films

We have studied the interaction of vapor-deposited Mg and Ca on −CH 3, −COOH, −OH, −OCH 3, and −CO 2 CH 3 terminated self-assembled monolayers (SAMs) on polycrystalline Au{111} using time-of-flight secondary ion mass spectrometry and density functional theory calculations. Magnesium has a very low initial sticking probability on all of the SAMs studied. It inserts into the C−O bonds of oxygen-containing terminal groups and penetrates through methyl-terminated SAMs. In contrast, vapor-deposited calcium vigorously reacts with all of the SAMs studied to form inorganic products. Ca has a high sticking probability on all of the SAMs studied except for methyl-terminated SAMs. The reaction of these metals with SAMs can be explained by a single, general scheme. In the first stages of deposition at low coverages, metal atoms are only adsorbed if they can form a weak complex at the SAM/vacuum interface; otherwise, they are scattered from the surface. The adsorbed metal atoms then either react with the terminal group or penetrate through the monolayer. For metals that do not form weak complexes, only impinging atoms with sufficient energy to react with the terminal group or the methylene chain will adsorb. For all metals, adsorbed atoms provide nucleation sites for the formation of metallic islands and/or overlayers. These findings contribute to a systematic understanding of the interactions of metals with organic surfaces.