The reactivity of nucleophiles at H-terminated Si surfaces has been widely exploited to tailor the electronic and mechanical properties of Si interfaces for targeted applications. In select cases, the addition of nucleophiles to Si surfaces has no analogous reaction in molecular silane chemistry. To investigate this phenomenon, H–Si(111) surfaces were reacted with liquid methanol (CH3OH) in the absence or presence of a series of one-electron oxidants and/or illumination. Oxidant-activated methoxylation of H–Si(111) surfaces was observed in the dark after exposure to CH3OH solutions containing the oxidants acetylferrocenium, ferrocenium, or 1,1′-dimethylferrocenium. The oxidant-activated reactivity of intrinsic and n-type H–Si(111) surfaces toward CH3OH increased upon exposure to ambient light. The results suggest that oxidant-activated methoxylation requires that two conditions be met: (1) the position of the quasi-Fermi levels must energetically favor oxidation of the H–Si(111) surface and (2) the position of the quasi-Fermi levels must energetically favor reduction of an oxidant in solution. The results are described by a mechanistic framework that analyzes the positions of the quasi-Fermi levels relative to the applicable energy levels for each system. Thus, the reactions of nucleophiles at H-terminated Si surfaces implicates the bulk charge carriers, allowing for reactions to occur at Si surfaces that are not accessible to molecular silanes.

Mechanistic insights into the oxidative reaction of hydrogen-terminated Si(111) surfaces with liquid methanol

254th National Meeting (2017)

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