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We have investigated the interaction of vapor-deposited copper with -CH3, -OH, -OCH3, -COOH, and -CO2CH3 terminated alkanethiolate self-assembled monolayers (SAMs) adsorbed on polycrystalline Au using time-of-flight secondary ion mass spectrometry and density functional theory calculations. For -OH, -COOH, and -CO2CH3 terminated SAMs measurements indicate that for all copper coverages there is a competition between Cu atom bond insertion into C-O bonds, stabilization at the SAM/vacuum interface, and penetration to the Au/S interface. In contrast, on a -OCH3 terminated SAM Cu only weakly interacts with the methoxy group and penetrates to the Au substrate, while for a -CH3 terminated SAM deposited copper only penetrates to the Au/S interface. The insertion of copper into C-O terminal group bonds is an activated process. We estimate that the barriers for Cu insertion are 55 +/- 5 kJ mol(-1) for the ester, 50 +/- 5 kJ mol(-1) for the acid, and 55 +/- 5 kJ mol(-1) for the hydroxyl terminated SAMs. The activation barrier for the copper insertion is much higher for the -OCH3 SAM. Copper atoms with energies lower than the activation barrier partition between complexation (weak interaction) with the terminal groups and penetration through the monolayer to the Au/S interface. Weakly stabilized copper atoms at the SAM/vacuum interface slowly penetrate through the monolayer. In contrast to the case of Al deposition, C-O bond insertion is favored over C=O, C-H, and C-C bond insertion.

We have developed a simple, robust method by which to construct complex two-dimensional structures based on controlling interfacial chemistry. Our approach is to employ UV-photopatterning and the reaction of vapor-deposited metals with self-assembled monolayers. To demonstrate the method, we have selectively vapor-deposited Mg on a patterned -CH3/-COOH-terminated alkanethiolate surface. The deposited metal penetrates through the -CH3 SAM to the Au/S interface while reacting with and accumulating on top of the -COOH SAM. This work has important applications in molecular/organic electronics, sensing, and other technologies. Our method has many advantages: it is extensible to many different materials, easily parallelized, affords precise nanoscale placement, and is fully compatible with photolithography.

We have studied the interaction of vapor-deposited Mg and Ca on −CH3, −COOH, −OH, −OCH3, and −CO2CH3 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.

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