| Abstract
| - The interaction of deposited metals with monolayer films is critical to the understanding of, and ultimateutility of, the emerging arena of molecular electronics. We present the results of a thorough study of theinteraction of vapor-deposited Au and Ag on alkane films attached to Si substrates. Two distinct categoriesof films are studied: C18 films formed from the hydrosilation reaction of octadecyl trichlorosilane with thinSiO2 layers and C18 films formed from the direct attachment of functionalized alkanes with hydrogen-terminatedSi. Two direct attachment chemistries were studied: (Si)3−Si−O−C linkages of 1-octadecanol and octadecanalon H-terminated Si(111) and (Si)3−Si−C linkages of 1-octadecene on H-terminated Si(111). The reactivityof the films was studied with p-polarized backside reflection absorption spectroscopy (pb-RAIRS), sputterdepth profiling X-ray photoelectron spectroscopy (XPS), spectroscopic ellipsometry (SE), atomic forcemicroscopy (AFM), and device electrical tests. Independent of direct attachment chemistry, we report theremarkable observation that deposition of Au results in the displacement of the molecular film from the Siinterface. In contrast, the directly attached molecular films are robust toward the deposition of Ag. For bothmetals, the C18 films formed by hydrosilation reactions on SiO2 remain at the interface. The results ofmonolayer stability with metal are linked to reactions between the metal and substrate. The displacement ofthe 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, includingsubstrates, molecular functional groups, and metal electrodes, when considering the robustness of moleculesin metal junctions.
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