The effect of the interaction of top metal with the interfacial Si-molecule bond was investigated by altering the direct attachment chemistries. Formation of alkane monolayers from starting alcohol, aldehyde, alkene, and thiol precursors was investigated. Independent of direct attachment chemistry, we report the remarkable observation that deposition of Au results in the displacement of the molecular film from the Si interface. In contrast, the directly attached molecular films are robust toward the deposition of Ag. For both metals, the C18 films formed by hydrosilation reactions on SiO2 remain at the interface. The results of monolayer stability with metal are linked to reactions between the metal and substrate. The displacement of the films by Au is attributed to Au insertion in the Si backbonds, in a reaction analogous to silicide formation. The results demonstrate that one must fully take into account the reactivity of the entire system, including substrates, molecular functional groups, and metal electrodes, when considering the robustness of molecules in metal junctions.
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- J. Phys. Chem. C 2007, 111 (26), 9384-9392
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